CN114696630B - Bootstrap-type compensated three-port converter and control method and system thereof - Google Patents

Abstract

The invention provides a three-port converter with bootstrap compensation and a control method and system thereof, belonging to the technical field of power electronic converters. The converter includes: a grid-side rectifier circuit, a series-compensation-side inverter circuit and a transformer; The first winding is the primary winding, the second winding and the third winding are the secondary windings; the same name end of each phase winding of the first winding is connected to each phase line of the power grid, and the different name end of each phase winding is used as the primary side. Each phase port of the winding; the same name terminal of the second winding is connected as the neutral point of the secondary side of the transformer, as the terminal connecting the DC low voltage port; the same name terminal of each phase winding of the third winding is used as each phase port of the secondary winding of the transformer; the second winding and The zigzag connection method is used between the third windings. The invention improves the operation stability of the converter.

Description

A bootstrap compensation three-port converter and its control method and system

technical field

The invention belongs to the technical field of power electronic converters, and more particularly, relates to a three-port converter with bootstrap compensation and a control method and system thereof.

Background technique

With the development of economy and society, people's demand for energy is constantly increasing, and the development and extensive use of new energy has become a hotspot in the development of power grid energy. New energy power generation is usually affected by the environment and has intermittent and fluctuating effects, and the power regulation role of energy storage systems has become particularly prominent. At the same time, the large-scale distributed energy construction network results in small short-circuit capacity and low short-circuit ratio of the power grid, and the node voltage is easily affected by the line current, which in turn reduces the stability of the distributed energy inverter. In order to solve the problem of line voltage stability and power fluctuation caused by large-scale distributed energy grid connection, the development of energy storage system provides an efficient and reliable solution for the above problems, so that new energy power generation can provide high-quality electric energy, Maintain the system voltage stability, provide active and reactive power support for the power grid, etc., realize power peak regulation, and make it possible for large-scale grid-connected applications of new energy power generation. The key part of the energy storage system is the converter that provides a bridge for the grid and the energy storage battery. The existing energy storage converter consists of a three-phase AC/DC converter that provides a grid interface and a DC/DC that isolates charge and discharge. Converter composition.

In the prior art, the three-port converter often combines two types of topologies into one topology, which makes the structure simple, the control difficulty is low, and has high research value; the bidirectional DC-DC-AC converter based on the three-port H-bridge, The topology is simple, the device usage is small, and it can be input to the AC power grid of a higher voltage level through low voltage and high power density, and does not generate low-frequency harmonics to damage the device, but the two inductors connected to the low-voltage port on the DC side pass through. The AC current with the opposite phase is large, which leads to the power loss of the inductor, the heat is large, and the safety is not high; at the same time, most of the grid-connected inverters use the direct-voltage control method based on the phase-locked loop, which has high requirements for the stability of the sampling voltage. , the existing converter topology control is difficult to deal with the weak grid with low short-circuit ratio, so it is necessary to propose a converter topology with higher stability.

SUMMARY OF THE INVENTION

In view of the defects of the prior art, the purpose of the present invention is to provide a bootstrap compensation three-port converter and its control method and system, aiming at solving the bidirectional DC-DC-AC conversion of the existing three-port H-bridge The two inductors connected to the low-voltage port of the DC side of the inverter pass through alternating currents with opposite phases, resulting in extra power loss in the switch tube, high heat generation, and low safety. The direct voltage control method has high requirements on the stability of the sampling voltage, and the existing converter topology control is difficult to deal with the problem of a weak grid with a low short-circuit ratio.

In order to achieve the above object, on the one hand, the present invention provides a three-port converter with bootstrap compensation, including: a grid-side rectifier circuit, a series-compensated side inverter circuit and a transformer; wherein, the grid-side rectifier circuit and The inverter circuit on the series compensation side is a three-phase H-bridge circuit; the transformer is a three-phase three-winding transformer;

The first winding in the transformer is the primary winding, the second winding and the third winding are the secondary windings; the same name end of each phase winding of the first winding is connected to each phase line of the power grid, and the different name end of each phase winding is used as the original winding. Each phase port of the side winding; the same name terminal of the second winding is connected as the neutral point of the secondary side of the transformer, which is used to connect the terminal of the DC low voltage port in the inverter circuit of the series compensation side; the same name terminal of each phase winding of the third winding is used as the secondary side of the transformer Each phase port of the winding; the zigzag connection method is adopted between the second winding and the third winding; the grid-side rectifier circuit is connected in parallel with the series-compensation-side inverter circuit;

The series-compensation side inverter circuit is used to output three-phase voltage to the transformer, suppressing the influence of the grid-side rectifier circuit output voltage by the bus voltage fluctuation; the grid-side rectifier current is used to stabilize the voltage of the series-compensation side inverter circuit DC high-voltage port, and at the same time The DC power input by the DC low voltage port of the inverter circuit on the series compensation side is converted into AC active power, and energy is transmitted to the grid.

Further preferably, the series compensation side inverter circuit includes: a series compensation side three-phase H bridge, a series compensation side filter unit, a DC filter inductor, a third filter capacitor and a DC voltage source;

The three-phase H bridge on the series compensation side is connected with the first end of the filter unit on the series compensation side; the second end of the filter unit on the series compensation side is used as an AC port and is connected with the synonymous end of the third winding of the transformer; the port connected with the DC filter inductor is DC low voltage port, one side of the DC filter inductor is connected to the positive pole of the DC voltage source, and the other side is connected to the neutral point port of the transformer, which is used to suppress the high frequency ripple of the DC current output from the DC low voltage port; the DC voltage source The negative pole is connected to the third filter capacitor for outputting DC power; the port connected to the third filter capacitor is used as a high-voltage port, and the third filter capacitor is connected in parallel between the first three-phase H bridge and the grid-side rectifier circuit, and the third The filter capacitor is used to suppress the voltage ripple on the DC high voltage side.

Further preferably, the grid-side rectified current includes: a grid-side three-phase H bridge and a grid-side filter unit;

The grid-side three-phase H-bridge and the series-compensation-side three-phase H-bridge are connected in parallel through a third filter capacitor; the grid-side filter unit is connected between the grid-side three-phase H-bridge and the grid.

Further preferably, the grid-side three-phase H-bridge and the series-compensation-side three-phase H-bridge are fully controlled power electronic devices, including transistors and diodes connected in anti-parallel with them;

The series compensation side filter unit includes a first grid-connected resistor, a first grid-connected inductor and a first filter capacitor; the first port of the first grid-connected inductor is connected to the first port of the first grid-connected resistor, and the first grid-connected resistor The two ports are used as the first port of the filter unit on the series compensation side, and the first filter capacitor is connected to the second port of the first grid-connected inductor, and is used as the second port of the filter unit on the series compensation side, and is connected with the opposite end of the third winding;

The grid-side filter unit includes a second grid-connected resistor, a second grid-connected inductor, and a second filter capacitor; the first port of the first grid-connected inductor is connected to the first port of the second grid-connected resistor, and the second grid-connected resistor The port is used as the first port of the grid-side filter unit, and the second filter capacitor is connected to the second port of the second grid-connected inductor, and is used as the second port of the grid-side filter unit, and is connected to the synonymous end of the first winding;

The first grid-connected inductance and the second grid-connected inductance are used to suppress high-frequency current ripple; the first grid-connected resistor is used as a parasitic resistance of the first grid-connected inductor to suppress the first grid-connected inductance and the first filter capacitor. Generated harmonic currents;

The second grid-connected resistance is used as a parasitic resistance of the second grid-connected inductance to suppress the harmonic current generated by the second grid-connected inductance and the second filter capacitor.

In another aspect, the present invention provides a grid-connected operation control method for a series-compensated inverter circuit, comprising the following steps:

Perform PARK transformation on the three-phase voltage of the secondary side port of the transformer and the input three-phase current of the AC port in the series-side inverter circuit, and obtain the voltage of the secondary side port of the transformer and the input current of the AC port under the two-phase synchronous rotation coordinates respectively;

Transform the grid-side current reference value through PARK to obtain the complex form of the grid-side current reference value and transmit it to the proportional link Z;

Multiply the output result of the proportional link Z and the reference value of the rotation angle to obtain the reference value of the output AC voltage of the inverter circuit on the series compensation side;

Subtract the d-axis reference value of the output AC voltage of the inverter circuit on the series compensation side and the d-axis voltage of the secondary port of the transformer, and the difference is input to the voltage loop proportional-integral controller to output the first integral value; The capacitance value of the filter capacitor is multiplied by the output AC voltage q-axis reference value of the series-compensation side inverter circuit to obtain the first multiplication result; the negative value of the first integral value is added with the first multiplication result to obtain the value As the d-axis current reference value of the inverter circuit on the series compensation side;

Subtract the q-axis reference value of the output AC voltage of the inverter circuit on the series compensation side and the q-axis voltage of the secondary side port of the transformer, and the difference is input to the voltage loop proportional-integral controller to output the second integral value; The product of the capacitance value of the filter capacitor and the output AC voltage d-axis voltage of the series-compensation side inverter circuit is used to obtain the second multiplication result; the negative value of the second integral value is subtracted from the second multiplication result, and the obtained value is used as The q-axis current reference value of the inverter circuit on the series compensation side;

Subtract the d-axis current reference value of the series compensation side inverter circuit and the d-axis current of the AC port in the series compensation side inverter circuit, the difference is input to the current loop proportional integral controller, and the third integral value is output; The product of the d-axis voltage of the port, the grid angular velocity and the q-axis current of the AC port in the series-compensated side inverter circuit is used to obtain the third multiplication result; the negative value of the third integral value is added to the third multiplication result to obtain The value is used as the reference value of the d-axis voltage at the midpoint of the bridge arm of the AC port of the inverter circuit on the series compensation side;

Subtract the output AC current q-axis reference value of the series-compensation side inverter circuit with the q-axis current of the AC port in the series-compensation side inverter circuit, the difference is input to the current loop proportional-integral controller, and the fourth integral value is output; Obtain the fourth multiplication result by multiplying the q-axis voltage of the secondary side port, the grid angular velocity and the d-axis current of the AC port in the series-compensation side inverter circuit; subtract the negative value of the fourth integral value from the fourth multiplication result, The obtained value is used as the reference value of the q-axis voltage at the midpoint of the bridge arm of the AC port of the inverter circuit on the series compensation side;

与串补侧逆变电路交流端口桥臂中点q轴电压参考值

反PARK变换，经过标幺化，输出串补侧逆变电路交流端口桥臂中点三相电压标幺化参考值；The reference value of the d-axis voltage at the middle point of the bridge arm of the AC port of the inverter circuit on the series compensation side

The reference value of the q-axis voltage at the midpoint of the bridge arm of the AC port of the inverter circuit on the series compensation side

Inverse PARK transformation, after per-unitization, output the reference value of the three-phase voltage at the midpoint of the bridge arm of the AC port of the series-compensated side inverter circuit;

The per-unit reference value of the three-phase voltage at the middle point of the bridge arm of the AC port of the series-compensated side inverter circuit is added to the per-unitized reference value of the three-phase voltage offset at the middle point of the bridge arm of the series-compensated side inverter circuit. A modulated voltage generates a first PWM signal to control the transistors in the series-complement side inverter circuit.

Further preferably, the method for obtaining the per-unit reference value of the three-phase voltage offset at the midpoint of the bridge arm of the series-compensated side inverter circuit is:

，将输出电流指定值

与直流低压端口输出直流电流I_dc相减，其差值输入直流电流环比例积分控制器，控制输出串补侧逆变电路桥臂中点三相电压偏移量标幺化参考值U_abc；Set the specified value of the output current of the DC low voltage port to

, set the output current to the specified value

It is subtracted from the output DC current I _dc of the DC low-voltage port, and the difference is input to the DC current loop proportional-integral controller to control the per-unit reference value U _abc of the three-phase voltage offset at the midpoint of the bridge arm of the output series-compensated side inverter circuit;

On the other hand, the present invention provides a grid-connected operation control method of a grid-side rectifier circuit, comprising the following steps:

Perform PARK transformation on the output three-phase voltage of the grid-side rectifier circuit and the output three-phase current of the grid-side rectifier circuit, and obtain the output voltage of the grid-side rectifier circuit and the output current of the grid-side rectifier circuit under the two-phase synchronous rotating coordinate system respectively;

Set the reference value of the DC high voltage port voltage of the inverter circuit on the series compensation side, subtract it from the DC high voltage port voltage, and input the difference value into the voltage loop proportional-integral controller to output the reference value of the d-axis current of the grid side rectifier circuit; set the grid side The q-axis current reference value of the rectifier circuit is 0;

Subtract the d-axis current reference value of the grid-side rectifier circuit and the d-axis current in the two-phase synchronous rotation coordinate system output by the grid-side rectifier circuit, and input the difference into the current loop proportional-integral controller to output the fifth integral value; The product of the d-axis voltage and grid angular velocity in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit and the q-axis current in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit is obtained to obtain the fifth multiplication result; The negative value of the fifth integral value is subtracted from the fifth multiplication result, and the obtained value is used as the reference value of the d-axis voltage at the midpoint of the bridge arm of the grid-side rectifier circuit;

Subtract the q-axis current reference value of the grid-side rectifier circuit and the q-axis current in the two-phase synchronous rotation coordinate system output by the grid-side rectifier circuit, and input the difference into the current loop proportional-integral controller to output the sixth integral value; Obtain the sixth multiplication result by multiplying the product of the q-axis voltage in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit, the grid angular velocity and the d-axis current in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit; The negative value of the sixth integral value and the sixth multiplication result are added together, and the obtained value is used as the reference value of the q-axis voltage at the midpoint of the bridge arm of the grid-side rectifier circuit;

Inverse PARK transformation of the d-axis voltage reference value at the midpoint of the bridge arm of the grid-side rectifier circuit and the q-axis voltage reference value at the midpoint of the bridge arm of the grid-side rectifier circuit. The voltage reference value is used to generate a second modulation voltage and input it to the PWM generator to form a second PWM signal to control the 6 transistors in the grid-side rectifier circuit.

Correspondingly, the present invention provides a control system for a series compensation side inverter circuit in a three-port converter, including:

The first PARK converter is used to convert the grid-side current reference value through PARK to obtain the complex form of the grid-side current reference value, and transmit it to the proportional link Z;

The calculation unit for outputting the AC voltage reference value is used to multiply the result of the Z operation output of the proportional link with the rotation angle reference value to obtain the output AC voltage reference value of the series-complement side inverter circuit;

The first subtractor is used to subtract the d-axis reference value of the output AC voltage of the inverter circuit on the series compensation side from the d-axis voltage of the secondary port of the transformer; the first voltage loop proportional-integral controller is used to invert the series compensation side. The difference between the output AC voltage d-axis reference value of the transformer circuit and the d-axis voltage of the secondary port of the transformer is subjected to proportional integral operation to obtain the first integral value; the first multiplier is used to calculate the grid angular velocity, the first filter capacitor The capacitance value of 1 is multiplied by the q-axis reference value of the output AC voltage of the series-compensation side inverter circuit to obtain the first multiplication result; the first adder is used to add the negative value of the first integral value to the first multiplication result. Add to obtain the reference value of the d-axis current of the inverter circuit on the series compensation side;

The second subtractor is used to subtract the q-axis reference value of the output AC voltage of the inverter circuit on the series compensation side from the q-axis voltage of the secondary port of the transformer; the second voltage loop proportional-integral controller is used to invert the series compensation side The difference between the output AC voltage q-axis reference value of the transformer circuit and the q-axis voltage of the secondary port of the transformer is subjected to proportional integral operation, and the second integral value is output; the second multiplier is used to calculate the grid angular velocity, the first filter capacitor The product of the capacitance value of , and the output AC voltage d-axis voltage of the series-compensation side inverter circuit can obtain the second multiplication result; the third subtractor is used to subtract the negative value of the second integral value from the second multiplication result. , obtain the reference value of the q-axis current of the inverter circuit on the series compensation side;

The fourth subtractor is used to subtract the d-axis current reference value of the inverter circuit at the series compensation side from the d-axis current of the AC port; the first current loop proportional-integral controller is used to subtract the d-axis current of the inverter circuit at the series compensation side The difference between the current reference value and the d-axis current of the AC port is calculated by proportional and integral, and the third integral value is output; the third multiplier is used to invert the d-axis voltage of the secondary port of the transformer, the angular velocity of the grid and the series compensation side. The product of the q-axis current of the AC port in the circuit is used to obtain the third multiplication result; the second adder is used to add the negative value of the third integral value and the third multiplication result to obtain the AC port of the series-complement side inverter circuit The reference value of the d-axis voltage at the midpoint of the bridge arm;

The fifth subtractor is used to subtract the q-axis reference value of the output AC current of the inverter circuit on the series compensation side and the q-axis current of the AC port; The difference between the q-axis reference value of the output AC current and the q-axis current of the AC port is calculated by proportional and integral, and the fourth integral value is output; The product of the d-axis current of the AC port in the inverter circuit is used to obtain the fourth multiplication result; the sixth subtractor is used to subtract the negative value of the fourth integral value from the fourth multiplication result to obtain the series-complement side inverter circuit The reference value of the q-axis voltage at the midpoint of the bridge arm of the AC port;

The inverse PARK converter is used for inverse PARK transformation of the reference value of the d-axis voltage at the middle point of the AC port bridge arm of the series-compensation side inverter circuit and the reference value of the q-axis voltage. The reference value of the three-phase voltage at the midpoint of the arm is per unitized reference value; the third adder is used to use the series compensation side inverter circuit AC port of the bridge arm between the reference value of the three-phase voltage at the midpoint and the perunitized reference value of the three-phase voltage offset. plus, to generate a first modulation voltage; a first SPWM inverter is used to generate a first PWM signal by using the first modulation voltage; the first PWM signal is used to control the transistors in the series-complement side inverter circuit.

Further preferably, the method for obtaining the per-unit reference value of the three-phase voltage offset at the midpoint of the bridge arm of the series-compensated side inverter circuit is:

Set the specified value of the output current of the DC low-voltage port, subtract the specified value of the output current from the output DC current of the DC low-voltage port, and input the difference to the proportional-integral controller of the DC current loop to control the middle point 3 of the bridge arm of the inverter circuit on the output series compensation side. The per-unitized reference value for the phase voltage offset.

Correspondingly, the present invention provides a control system for a grid-side rectifier circuit in a three-port converter, including:

The second PARK converter is used to PARK transform the output three-phase voltage of the grid-side rectifier circuit and the output three-phase current of the grid-side rectifier circuit to obtain the grid-side rectifier circuit output voltage and grid-side rectifier respectively in the two-phase synchronous rotating coordinate system circuit output current;

The seventh subtractor is used to set the reference value of the DC high voltage port voltage of the series compensation side inverter circuit, which is subtracted from the DC high voltage port voltage; the third voltage loop proportional-integral controller is used for the series compensation side inverter circuit. The difference between the DC high voltage port voltage reference value and the DC high voltage port voltage is calculated by proportional integral operation, and the d-axis current reference value of the grid-side rectifier circuit is output; the q-axis current reference value of the grid-side rectifier circuit is set to 0;

The eighth subtractor is used to subtract the d-axis current reference value of the grid-side rectifier circuit from the d-axis output current of the grid-side rectifier circuit; the third current loop proportional-integral controller is used for the d-axis of the grid-side rectifier circuit. The difference between the current reference value and the d-axis output current of the grid-side rectifier circuit is proportional and integral to obtain the fifth integral value; the fifth multiplier is used to calculate the d-axis output voltage of the grid-side rectifier circuit, the grid angular velocity and the The product of the q-axis output current of the grid-side rectifier circuit is used to obtain the fifth multiplication result; the ninth subtractor is used to subtract the negative value of the fifth integral value from the fifth multiplication result, and the obtained value is used as the grid-side rectifier The reference value of the d-axis voltage at the midpoint of the circuit bridge arm;

The tenth subtractor is used to subtract the q-axis current reference value of the grid-side rectifier circuit from the q-axis output current of the grid-side rectifier circuit; the fourth current loop proportional-integral controller is used for the q-axis of the grid-side rectifier circuit. The difference between the current reference value and the q-axis output current of the grid-side rectifier circuit is proportional and integral to output the sixth integral value; the sixth multiplier is used to calculate the q-axis output voltage of the grid-side rectifier circuit, grid angular velocity and The product of the d-axis output current of the grid-side rectifier circuit is used to obtain the sixth multiplication result; the fourth adder is used to add the negative value of the sixth integral value and the sixth multiplication result, and the obtained value is used as the grid-side rectification The reference value of the q-axis voltage at the midpoint of the circuit arm;

The second inverse PARK converter is used to inverse PARK transform the d-axis voltage reference value at the midpoint of the bridge arm of the grid-side rectifier circuit and the reference value of the q-axis voltage. The voltage reference value is used as the second modulation voltage; the second SPWM inverter is used to generate a second PWM signal through the second modulation voltage; the second PWM signal is used for the transistors in the series-complement side inverter circuit Take control.

In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

The present invention provides a topology structure of a three-port converter with bootstrap compensation, wherein a meander transformer replaces an inductor to connect a DC low-voltage port and an AC port of an inverter circuit, and the neutral point of the meander transformer secondary winding is used as the topological structure. The connection port of the DC low voltage port, the AC port of the secondary winding of the zigzag transformer is used as the connection port of the AC side of the inverter circuit, and the DC voltage source of the low voltage DC port is connected to the neutral point of the secondary side of the transformer through the DC filter inductor, which not only realizes the stable output power of the DC voltage source, but also It also suppresses the AC circulating current induced by the inductance; the zigzag connection of the transformer makes the DC magnetic flux generated by the DC current on the same iron core offset, reducing the saturation degree of the iron core.

In order to offset the influence of the equivalent impedance of the weak grid in the prior art, the method of generating the opposite phase voltage by the grid current is _feedback is often used, and a negative impedance similar to the equivalent impedance of the weak grid is equivalently formed on the line, thereby reducing the low short-circuit of the weak grid. On the basis of the existing voltage compensation control technology, the present invention uses the grid-side rectifier circuit input current reference value _{i ^* abc2} instead of the grid current is as the current reference value for generating the given voltage of the series-compensation side inverter circuit. Bootstrap excitation of the secondary winding of the transformer can predict the change of grid current caused by the change of the DC power of the low-voltage DC port in advance, quickly suppress the fluctuation of the sampling voltage, stabilize the frequency and reference phase of the sampling voltage output through the phase-locked loop, and finally improve the The operational stability of the converter.

The invention provides a topological structure of a three-port converter with bootstrap compensation, wherein the primary winding of the transformer is connected in series between the power grid and the three-phase H-bridge circuit, and the inverse winding connected to the secondary winding of the transformer is connected in series. The transformer circuit performs bootstrap excitation, and the primary winding induces a given compensation voltage; when the grid voltage fluctuates due to the grid current, the primary winding will induce the corresponding reverse voltage according to the current size, thereby inhibiting the grid-side rectification. Circuit sampling voltage fluctuations.

According to the topology structure of the three-port converter, the present invention provides a control method for rapidly generating a compensation voltage by a series compensation side ^inverter circuit. The side winding compensation voltage u _cq can predictably offset the bus voltage deviation caused by the grid current, thereby ensuring the stability of the sampling voltage point u _gabc .

On the basis of the technology used in the existing meander transformer and back-to-back converter, the present invention leads out the DC low-voltage port through the neutral point of the transformer, and alternately operates three Boost topologies and one inverter circuit to complete the AC and DC of the inverter circuit on this side. , DC and DC conversion; compared with the function of the existing unified power quality regulator (UPQC), in the present invention, the series compensation side inverter circuit is connected to the grid line in parallel by a meandering transformer, and the grid side rectifier circuit is connected in series to the grid line. The power grid line reduces the number of transformers structurally, and at the same time functionally increases the role of the grid-side rectifier circuit and the DC low-voltage port to jointly support the power grid.

Description of drawings

1 is a block diagram of a system structure provided by an embodiment of the present invention;

FIG. 2 is a control block diagram of a series-compensation side inverter circuit for grid-connected operation provided by an embodiment of the present invention;

3 is a control block diagram of a grid-side rectifier circuit for grid-connected operation provided by an embodiment of the present invention;

FIG. 4( a ) is a schematic diagram of an AC side voltage waveform in a grid-side rectifier circuit output under grid-connected operation provided by an embodiment of the present invention;

Figure 4(b) is a schematic diagram of a three-phase current waveform of a power grid under grid-connected operation provided by an embodiment of the present invention;

FIG. 5 is the RMS waveform of the sampled voltage before and after series compensation under grid-connected operation according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

1 is a topology structure of a three-port converter with bootstrap compensation provided by an embodiment of the present invention, including two three-phase H-bridge circuits and a three-phase three-winding transformer with meander connection;

The three-phase three-winding transformer includes a first winding, a second winding and a third winding, wherein the first winding is the primary winding, and the second winding and the third winding are the secondary windings; the first winding includes A, B, and C phases Three windings; the second winding includes a1, b1, c1 phase three windings; the third winding includes a2, b2, c2 groups of three windings; the leakage inductance of each winding in the first winding is L _σ1 , in the second winding The leakage inductance of each winding is L _σ2 , and the leakage inductance of each winding in the third winding is L _σ3 ; end) as the port of each phase of the primary winding; the same name end of each phase winding of the second winding is connected together to form the neutral point N of the secondary side of the transformer, the synonym end of the a1 winding is connected to the synonym end of the b2 winding, the synonym of the b1 winding is connected The end is connected to the synonym end of the c2 winding, the synonym end of the c1 winding is connected to the synonym end of the a2 winding; the synonym end of each phase winding of the third winding is used as each phase port of the secondary winding of the transformer; the leakage inductance L _σ1 of the first winding The function is to appropriately increase the line inductance and suppress the high-frequency ripple of the grid current; the leakage inductance L _σ2 of the second winding and the leakage inductance L _σ3 of the third winding function to appropriately increase the inductance of the inverter circuit on the series compensation side, and input the inverter circuit on the series compensation side. The current filters out high-frequency ripples;

Two three-phase H-bridge circuits form a three-port converter, which are the grid-side rectifier circuit and the series-compensation-side inverter circuit;

The series compensation side inverter circuit includes one AC port and two DC ports;

The AC port of the inverter circuit on the series compensation side is connected to the synonymous end of the third winding on the secondary side of the zigzag transformer, which is connected through the first grid-connected resistance r ₁ , the first grid-connected inductance L ₁ and the first filter capacitor C ₁ ; The grid-connected inductance L ₁ is used to suppress the high-frequency ripple of the current, the filter capacitor C ₁ is used to filter out the high-frequency harmonics of the voltage, and the grid-connected resistance r ₁ is used as the parasitic resistance of the grid-connected inductance, which can be used to suppress the grid-connected inductance and the parallel connection. The resonant current generated by the existence of the grid capacitance;

The DC port of the series compensation side inverter circuit includes a high voltage port and a low voltage port; a third filter capacitor C is connected between the two ports of the high voltage port; a DC filter inductor L _d is connected between the two ports of the low voltage port, and the DC voltage source The positive pole of U _d2 is connected; the negative pole of the DC voltage source U _d2 is connected to the negative pole of the third filter capacitor C; the DC filter inductor is connected to the neutral point port N of the three-phase transformer (ie, the left port of L _σ2 ) _; It is used to output DC power and support the power grid; the DC filter capacitor C of the high-voltage port is used to suppress the voltage ripple of the DC high-voltage side voltage U _d1 ; the DC filter inductor L _d is used to suppress the high-frequency ripple of the output DC current of the DC low-voltage port Wave;

The grid-side rectifier circuit includes an AC port and a DC port; the AC port is connected to the different end of the primary winding of the three-phase three-winding transformer, the second grid-connected resistance is r ₂ , the second grid-connected inductance is L ₂ , and the second grid-connected inductance is L 2 . The second filter capacitor is C ₂ ;

The DC high voltage port of the inverter circuit on the series compensation side is connected to the DC high voltage port of the grid side rectifier circuit; each three-phase H-bridge includes 6 IGBT switch tubes (Q ₁ ~Q ₆ ) and 6 diodes (D ₁ ~D ) ₆ ); switch tubes Q1 and _Q2 form _a phase _- a bridge arm, the source of Q1 is connected to the drain of _Q2 , and is connected to the grid-connected inductor of phase _a , the anode of diode D1 and the cathode of diode D2 _{; The} drain of Q1 is connected to the cathode of the diode D1 and the anode _of the DC high voltage port _; the source of _Q2 is connected to the anode of the diode D2 and the cathode of the DC high voltage port; the switch tubes _Q3 and _Q4 form the b-phase bridge arm , the source of _Q3 is connected to the drain of _Q4 , and is connected to the b-phase grid-connected inductor, the anode of diode _D3 and the cathode of diode D4 _; the drain of _Q3 is connected to the cathode of _D3 , the anode of the DC high voltage port The positive electrode is connected to the positive electrode _; the source electrode of _Q4 is connected to the positive electrode of D4 and the negative electrode of the DC high voltage port; the switch tube _Q5 and _Q6 form a c-phase bridge arm, and the source electrode of _Q5 is connected to the drain electrode of _Q6 , and is connected with c Phase grid inductance, the anode of diode D5 is connected to the cathode of diode D6 _; the drain of _Q5 is connected to the cathode of _D5 and the anode of the DC high voltage port, and the source of _Q6 is connected to the _anode of _D6 and the DC high voltage port connected to the negative pole;

The functions of the six switch tubes Q ₁ to Q ₆ are to perform high-frequency switching operations by receiving PWM signals, so that the midpoint voltage of the circuit bridge arm outputs the SPWM voltage waveform, and at the same time, during the power conversion process from the DC low voltage port to the DC high voltage port , the conduction can provide reverse voltage drop for the diodes connected in parallel; the function of the 6 diodes D ₁ ~ D ₆ is to realize the freewheeling function of the current flowing into the midpoint of the bridge arm, and at the same time, the switch tubes connected in parallel are turned off. Provides a soft-switching environment with zero-voltage turn-off;

The primary winding of the zigzag transformer is connected in series between the power grid and the grid-side rectifier circuit to provide a certain three-phase voltage u _cq to compensate for the voltage change caused by the influence of the large current in the weak power grid; the secondary winding of the secondary winding is used for A neutral point N is formed, which provides a port for connecting the power grid for the low-voltage DC side; the third winding of the secondary winding is used to provide a port for connecting the power grid for the inverter circuit of the series compensation side; the zigzag connection method between the second winding and the third winding It is used to suppress the DC magnetic flux in the magnetic core to reduce the saturation degree of the iron core;

Weak power grid is defined as a power grid in which the combined effect of nonlinear load and line impedance cannot be ignored in practical applications, and the short-circuit ratio is used to describe the magnitude of the effect of weak power grid impedance; The ratio of rated power, the larger the short-circuit ratio, the greater the short-circuit capacity of the power grid, and the smaller the effect of the power grid impedance. On the contrary, the smaller the short-circuit ratio, the greater the effect of the power grid impedance. Large inductance, the change of the grid current will easily lead to the fluctuation of the bus voltage.

The series compensation side inverter circuit is used to output the three-phase voltage u _tabc to the secondary winding, and induce the given three-phase voltage u _cq in the primary winding through the transformer, so as to suppress the influence of the bus voltage fluctuation caused by the grid current on the output voltage of the grid-side rectifier circuit , the effective value of the output line voltage of the control grid-side rectifier circuit is about 380V; the grid-side rectifier current i _abc2 is used to stabilize the voltage of the filter capacitor C of the DC high-voltage port, and at the same time, it will convert the DC power input from the DC low-voltage port into AC active power. The grid transmits energy.

The invention provides a three-port converter topology with bootstrap compensation when grid-connected operation, realizes voltage compensation of sampling voltage under weak grid through series transformer, and can realize power flow of low-voltage DC side power supply.

Below in conjunction with Fig. 1 to Fig. 5, introduce the specific embodiment of the present invention:

Fig. 1 is a kind of bootstrap compensation three-port converter provided by the embodiment of the present invention, when the grid-connected operation:

In the series-compensated side inverter circuit, the three-phase voltage output from the AC port is: u _{ca1 , u cb1 ,} and u _cc1 ;

In the series-compensated side inverter circuit, the input three-phase currents at the AC port are: i _a1 , i _b1 , and i _c1 ;

In the series-compensated inverter circuit, the three-phase voltages at the secondary port of the transformer are: u _ta , u _tb , and u _tc ;

In the inverter circuit of the series compensation side, the output voltage of the DC low-voltage port is: U _d2 ;

In the inverter circuit of the series compensation side, the output current of the DC low-voltage port is: I _dc ;

In the series compensation side inverter circuit, the DC bias current flowing through each winding from the DC low voltage port is: I _La , I _Lb , and I _Lc ;

In the grid-side rectifier circuit, the output three-phase voltage of the AC port is: u _ca2 , u _cb2 , u _cc2 ;

In the grid-side rectifier circuit, the input three-phase current of the AC port is: i _a2 , i _b2 , i _c2 ;

In the grid-side rectifier circuit, the grid output three-phase voltage is: u _ga , u _gb , u _gc ;

In the grid-side rectifier circuit, the output voltage of the DC high-voltage port is: U _d1 ;

2 is a block diagram of grid-connected operation control of a series-compensated side inverter circuit provided by an embodiment of the present invention, including the following steps:

(1) Carry out the three-phase voltage u _tabc (u _ta , u _tb , u _tc ) at the secondary side port of the transformer and the input three-phase current i _abc1 (i _a1 , i _b1 , i _c1 ) at the AC port in the series-compensated side inverter circuit PARK transformation, respectively obtain the voltage _utd , u _tq and current _id1 , i _q1 in the two-phase synchronous rotating coordinate system;

(2) Transform the grid-side current reference value i ^* ₂ through PARK, obtain i ^* _d2 and i ^* _q2 to construct a complex number, and transmit the constructed complex number to the proportional link Z;

(3) Multiply the complex number output by the proportional link with the rotation angle reference value e ^jθ , and extract the output AC voltage reference values _ud ^* and u _q ^* of the inverter circuit on the series compensation side;

(4) Subtract the output AC voltage d-axis reference value u _d ^* of the inverter circuit on the series compensation side with the d-axis voltage u _td of the transformer secondary side port, the difference is input to the voltage loop proportional-integral controller, and the first integral is output. value;

(5) Multiply the grid angular velocity, the capacitance value of the first filter capacitor C ₁ and the output AC voltage q-axis reference value u _q ^* of the series compensation side inverter circuit to obtain the first multiplication result;

(6) Add the negative value of the first integral value to the first multiplication result, and the obtained value is used as the _d -axis current reference value id ^* ₁ of the inverter circuit at the series compensation side;

(7) Subtract the output AC voltage q-axis reference value u _q ^* of the inverter circuit on the series compensation side with the q-axis voltage u _tq of the secondary port of the transformer, the difference is input to the voltage loop proportional-integral controller, and the second integral is output value;

(8) Multiply the grid angular velocity, the capacitance value of the first filter capacitor C ₁ and the output AC voltage d-axis voltage u _td of the series-complement side inverter circuit to obtain the second multiplication result;

(9) Subtract the negative value of the second integral value from the second multiplication result, and the obtained value is used as the q-axis current reference value i _q ^* ₁ of the inverter circuit at the series compensation side;

(10) Subtract the d-axis current reference value i _d ^* ₁ of the inverter circuit on the series compensation side and the d-axis current i _d1 of the AC port in the inverter circuit on the series compensation side, and the difference is input to the current loop proportional-integral controller, and the output the third integral value;

(11) Multiply the d-axis voltage u _td of the secondary side port of the transformer, the grid angular velocity and the q-axis current i _q1 of the AC port in the series-compensated side inverter circuit to obtain the third multiplication result;

；(12) Add the negative value of the third integral value and the third multiplication result, and the obtained value is used as the reference value of the d-axis voltage at the middle point of the bridge arm of the AC port of the series compensation side inverter circuit

;

(13) Subtract the output AC current q-axis reference value i _q ^* ₁ of the series-compensation side inverter circuit with the AC port q-axis current i _q1 in the series-compensation side inverter circuit, and the difference is input to the current loop proportional-integral controller , output the fourth integral value;

(14) Multiply the q-axis voltage u _tq of the secondary side port of the transformer, the grid angular velocity and the d-axis current i _d1 of the AC port in the series-compensated side inverter circuit to obtain the fourth multiplication result;

；(15) Subtract the negative value of the fourth integral value from the fourth multiplication result, and the obtained value is used as the reference value of the q-axis voltage at the middle point of the bridge arm of the AC port of the series compensation side inverter circuit

;

与串补侧逆变电路交流端口桥臂中点q轴电压参考值

反PARK变换，经过标幺化，输出串补侧逆变电路交流端口桥臂中点三相电压标幺化参考值e_a ^* ₁、e_b ^* ₁、e_c ^* ₁；(16) Reference value of the d-axis voltage at the midpoint of the bridge arm of the AC port of the inverter circuit on the series compensation side

The reference value of the q-axis voltage at the midpoint of the bridge arm of the AC port of the inverter circuit on the series compensation side

Inverse PARK transformation, after per-unit conversion, output the reference values e _a ^* ₁ , e _b ^* ₁ , and e _c ^* ₁ of the three-phase voltage at the midpoint of the bridge arm of the AC port of the series-complement side inverter circuit;

(17) The Boost topology IGBT switch tube is used to control its duty cycle N to output DC power, and the three-phase voltage reference value of the middle point of the bridge arm of the AC port of the series compensation side inverter circuit and the three-phase voltage of the middle point of the bridge arm of the series compensation side inverter circuit are used. The per-unit reference value U _abc of the voltage offset is added, and the first PWM signal is generated by the generated modulation voltage to control the six IGBTs in the series-complement side inverter circuit.

A more specific description of step (17) is as follows:

In the series compensation side inverter circuit, the power conversion form of the DC low voltage port to the high voltage port adopts the Boost topology;

The Boost topology includes three independent Boost circuits; the i-th Boost circuit includes the winding inductance L _σ2i and the IGBT switch of the i-th lower bridge arm; or the winding inductance L _σ2i and the diode of the upper bridge arm; i=a, b, c ; Wherein, when the Boost circuit includes the diode of the upper bridge arm, the IGBT switch of the lower bridge arm is in an off state;

In the Boost topology, the IGBT switch tube of the Boost circuit controls its duty cycle M to output DC power, including the following steps:

，将输出电流指定值

与直流低压端口输出直流电流I_dc相减，其差值输入直流电流环比例积分控制器，控制输出串补侧逆变电路桥臂中点三相电压偏移量标幺化参考值U_abc，进而控制了IGBT的占空比M=(U_abc+1)/2；(1) Set the specified value of the output current of the DC low voltage port as

, set the output current to the specified value

It is subtracted from the output DC current I _dc of the DC low-voltage port, and the difference is input to the DC current loop proportional-integral controller to control the output series compensation side inverter _circuit . Then the duty cycle of the IGBT is controlled M=(U _abc +1)/2;

(2) The per-unitized reference value of the three-phase voltage at the midpoint of the bridge arm of the AC port of the series-compensated side inverter circuit and the per-unitized reference value U of the offset of the three-phase voltage at the midpoint of the bridge arm of the AC port of the series-compensated side inverter circuit respectively Add _abc to generate a modulation voltage e _sabc1 and input it to the first PWM generator to form a first PWM signal to control the 6 IGBTs in the series-complement side inverter circuit.

Figure 3 is a grid-connected operation control block diagram of the grid-side rectifier circuit, including the following steps:

(1) Perform PARK transformation on the output three-phase voltage u _gabc of the grid-side rectifier circuit and the output three-phase current i _2abc of the grid-side rectifier circuit, and obtain the voltage _ugd , _ugq and current i _d2 , i _q2 ;

(2) Set the reference value U _d1 ^* of the DC high voltage port voltage of the inverter circuit on the series compensation side, subtract it from the DC high voltage port voltage U _d1 , and input the difference into the d-axis of the output grid side rectifier circuit of the voltage loop proportional-integral controller. Current reference value i _d ^* ₂ ; set the q-axis current reference value i _q ^* ₂ of the grid-side rectifier circuit to 0;

(3) Subtract the d-axis current reference value i _d ^* ₂ of the grid-side rectifier circuit and the d-axis current i _d2 in the two-phase synchronous rotation coordinate system output by the grid-side rectifier circuit, and the difference is input into the current loop proportional-integral control , output the fifth integral value;

(4) Multiply the d-axis voltage _ugd and grid angular velocity in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit and the q-axis current i _q2 in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit to obtain The fifth multiplication result;

(5) The negative value of the fifth integral value is subtracted from the fifth multiplication result, and the obtained value is used as the d-axis voltage reference value E _d ^* ₂ at the midpoint of the bridge arm of the grid-side rectifier circuit;

(6) Subtract the q-axis current reference value i _q ^* ₂ of the grid-side rectifier circuit and the q-axis current i _q2 in the two-phase synchronous rotation coordinate system output by the grid-side rectifier circuit, and the difference is input into the current loop proportional-integral control , output the sixth integral value;

(7) Multiply the q-axis voltage u _gq , the grid angular velocity in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit, and the d-axis current i _d2 in the two-phase synchronous rotating coordinate system output by the grid-side rectifier circuit to obtain The sixth multiplication result;

(8) Add the negative value of the sixth integral value and the sixth multiplication result, and the obtained value is used as the q-axis voltage reference value E _q ^* ₂ at the midpoint of the bridge arm of the grid-side rectifier circuit;

(9) Inverse PARK transformation between the d-axis voltage reference value E _d ^* ₂ at the midpoint of the bridge arm of the grid-side rectifier circuit and the q-axis voltage reference value E _q ^* ₂ at the midpoint of the bridge arm of the grid-side rectifier circuit, after per-unitization, Output the three-phase voltage reference values e _a ^* ₂ , e _b ^* ₂ , and e _c ^* ₂ at the midpoint of the bridge arm of the grid-side rectifier circuit, as the modulation voltage; generate the modulation voltage e _sabc2 and input it into the PWM generator to form a PWM signal, which is connected to the grid. The 6 IGBTs in the side rectifier circuit are controlled.

Correspondingly, the present invention provides a control system for a series-compensated inverter circuit in a three-port converter, including:

The first PARK converter is used to convert the grid-side current reference value through PARK to obtain the complex form of the grid-side current reference value, and transmit it to the proportional link Z;

The calculation unit for outputting the AC voltage reference value is used to multiply the result of the Z operation output of the proportional link with the rotation angle reference value to obtain the output AC voltage reference value of the series-complement side inverter circuit;

The first subtractor is used to subtract the d-axis reference value of the output AC voltage of the inverter circuit on the series compensation side from the d-axis voltage of the secondary port of the transformer; the first voltage loop proportional-integral controller is used to invert the series compensation side. The difference between the output AC voltage d-axis reference value of the transformer circuit and the d-axis voltage of the secondary port of the transformer is subjected to proportional integral operation to obtain the first integral value; the first multiplier is used to calculate the grid angular velocity, the first filter capacitor The capacitance value of 1 is multiplied by the q-axis reference value of the output AC voltage of the series-compensation side inverter circuit to obtain the first multiplication result; the first adder is used to add the negative value of the first integral value to the first multiplication result. Add to obtain the reference value of the d-axis current of the inverter circuit on the series compensation side;

The second subtractor is used to subtract the q-axis reference value of the output AC voltage of the inverter circuit on the series compensation side from the q-axis voltage of the secondary port of the transformer; the second voltage loop proportional-integral controller is used to invert the series compensation side The difference between the output AC voltage q-axis reference value of the transformer circuit and the q-axis voltage of the secondary port of the transformer is subjected to proportional integral operation, and the second integral value is output; the second multiplier is used to calculate the grid angular velocity, the first filter capacitor The product of the capacitance value of , and the output AC voltage d-axis voltage of the series-compensation side inverter circuit can obtain the second multiplication result; the third subtractor is used to subtract the negative value of the second integral value from the second multiplication result. , obtain the reference value of the q-axis current of the inverter circuit on the series compensation side;

The fourth subtractor is used to subtract the d-axis current reference value of the inverter circuit at the series compensation side from the d-axis current of the AC port; the first current loop proportional-integral controller is used to subtract the d-axis current of the inverter circuit at the series compensation side The difference between the current reference value and the d-axis current of the AC port is calculated by proportional and integral, and the third integral value is output; the third multiplier is used to invert the d-axis voltage of the secondary port of the transformer, the angular velocity of the grid and the series compensation side. The product of the q-axis current of the AC port in the circuit is used to obtain the third multiplication result; the second adder is used to add the negative value of the third integral value and the third multiplication result to obtain the AC port of the series-complement side inverter circuit The reference value of the d-axis voltage at the midpoint of the bridge arm;

The fifth subtractor is used to subtract the q-axis reference value of the output AC current of the inverter circuit on the series compensation side and the q-axis current of the AC port; The difference between the q-axis reference value of the output AC current and the q-axis current of the AC port is calculated by proportional and integral, and the fourth integral value is output; The product of the d-axis current of the AC port in the inverter circuit is used to obtain the fourth multiplication result; the sixth subtractor is used to subtract the negative value of the fourth integral value from the fourth multiplication result to obtain the series-complement side inverter circuit The reference value of the q-axis voltage at the midpoint of the bridge arm of the AC port;

The inverse PARK converter is used for inverse PARK transformation of the reference value of the d-axis voltage at the middle point of the AC port bridge arm of the series-compensation side inverter circuit and the reference value of the q-axis voltage. The reference value of the three-phase voltage at the midpoint of the arm is per unitized reference value; the third adder is used to use the series compensation side inverter circuit AC port of the bridge arm between the reference value of the three-phase voltage at the midpoint and the perunitized reference value of the three-phase voltage offset. plus, to generate a first modulation voltage; a first SPWM inverter is used to generate a first PWM signal by using the first modulation voltage; the first PWM signal is used to control the transistors in the series-complement side inverter circuit.

Further preferably, the method for obtaining the per-unit reference value of the three-phase voltage offset at the midpoint of the bridge arm of the series-compensated side inverter circuit is:

Set the specified value of the output current of the DC low-voltage port, subtract the specified value of the output current from the output DC current of the DC low-voltage port, and input the difference to the proportional-integral controller of the DC current loop to control the middle point 3 of the bridge arm of the inverter circuit on the output series compensation side. The per-unitized reference value for the phase voltage offset.

Correspondingly, the present invention provides a control system for a grid-side rectifier circuit in a three-port converter, including:

The second PARK converter is used to PARK transform the output three-phase voltage of the grid-side rectifier circuit and the output three-phase current of the grid-side rectifier circuit to obtain the grid-side rectifier circuit output voltage and grid-side rectifier respectively in the two-phase synchronous rotating coordinate system circuit output current;

The seventh subtractor is used to set the reference value of the DC high voltage port voltage of the series compensation side inverter circuit, which is subtracted from the DC high voltage port voltage; the third voltage loop proportional-integral controller is used for the series compensation side inverter circuit. The difference between the DC high voltage port voltage reference value and the DC high voltage port voltage is calculated by proportional integral operation, and the d-axis current reference value of the grid-side rectifier circuit is output; the q-axis current reference value of the grid-side rectifier circuit is set to 0;

The eighth subtractor is used to subtract the d-axis current reference value of the grid-side rectifier circuit from the d-axis output current of the grid-side rectifier circuit; the third current loop proportional-integral controller is used for the d-axis of the grid-side rectifier circuit. The difference between the current reference value and the d-axis output current of the grid-side rectifier circuit is proportional and integral to obtain the fifth integral value; the fifth multiplier is used to calculate the d-axis output voltage of the grid-side rectifier circuit, the grid angular velocity and the The product of the q-axis output current of the grid-side rectifier circuit is used to obtain the fifth multiplication result; the ninth subtractor is used to subtract the negative value of the fifth integral value from the fifth multiplication result, and the obtained value is used as the grid-side rectifier The reference value of the d-axis voltage at the midpoint of the circuit bridge arm;

The tenth subtractor is used to subtract the q-axis current reference value of the grid-side rectifier circuit from the q-axis output current of the grid-side rectifier circuit; the fourth current loop proportional-integral controller is used for the q-axis of the grid-side rectifier circuit. The difference between the current reference value and the q-axis output current of the grid-side rectifier circuit is proportional and integral to output the sixth integral value; the sixth multiplier is used to calculate the q-axis output voltage of the grid-side rectifier circuit, grid angular velocity and The product of the d-axis output current of the grid-side rectifier circuit is used to obtain the sixth multiplication result; the fourth adder is used to add the negative value of the sixth integral value and the sixth multiplication result, and the obtained value is used as the grid-side rectification The reference value of the q-axis voltage at the midpoint of the circuit arm;

The second inverse PARK converter is used to inverse PARK transform the d-axis voltage reference value at the midpoint of the bridge arm of the grid-side rectifier circuit and the reference value of the q-axis voltage. The voltage reference value is used as the second modulation voltage; the second SPWM inverter is used to generate a second PWM signal through the second modulation voltage; the second PWM signal is used for the transistors in the series-complement side inverter circuit Take control.

The MATLAB/Simulink simulation experiment platform is used to verify that the corresponding control methods of Fig. 2 and Fig. 3 provided by the present invention act on the three-port converter with bootstrap compensation. Capacitor C, the low-voltage side energy storage device is the battery U _d2 . The simulation results of grid-connected operation are shown in Figure 4(a), Figure 4(b) and Figure 5. In grid-connected operation, the AC port of the grid-side rectifier circuit is connected to the 220V AC grid through the primary winding of the zigzag transformer. The voltage of the DC high-voltage port is 700V, and the voltage of the low-voltage port is 350V. The low-voltage DC side is set to output 15kW of active power. Set the reference value of the three-phase voltage at the midpoint of the bridge arm of the AC port of the series compensation side inverter circuit in the control of the series compensation side inverter circuit before the series compensation is always 0. The AC side voltage waveform and the grid three-phase current waveform in the grid-side rectifier circuit are shown in Figure 4(a) and Figure 4(b) respectively, and the RMS waveform of the sampling line voltage before and after series compensation is shown in Figure 5.

In Figure 4(a) and Figure 4(b), under grid-connected operation, the three-phase voltage amplitude is stable at 314V, the three-phase current amplitude is stable at 36A, and the waveform is a standard sine wave, which indicates that the output and input current harmonics of the device are The wave content is extremely low and the power quality is high. In Figure 5, the RMS value of the sampling voltage before series compensation rises to 400V, which means that the current input to the weak grid increases the amplitude of the voltage at the sampling point, and the higher AC voltage will cause the voltage reference value of the grid-side rectifier circuit to be greater than Ud1/2. The phenomenon of modulation saturation is formed, and then the output voltage and current harmonics of the grid-side rectifier circuit are generated. At the same time, the high AC voltage will passively increase the capacitor voltage of the DC high-voltage port, threatening the safety of the capacitor; Compared with the voltage, under the action of the primary winding of the transformer with the bootstrap compensation, the voltage stability of the device under weak grid operation can be achieved, which largely solves the problem of grid-side rectifier circuit stability and lock-up caused by bus voltage fluctuations. The problem of phase loop stability, thereby improving the stability and reliability of the device.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (8)

1. A bootstrap compensated three-port converter, comprising: a network side rectifying circuit, a series compensation side inverter circuit and a transformer; the grid side rectifying circuit and the series compensation side inverter circuit are three-phase H-bridge circuits; the transformer is a three-phase three-winding transformer;

a first winding in the transformer is a primary winding, and a second winding and a third winding are secondary windings; the homonymous end of each phase winding of the first winding is connected with each phase line of the power grid, and the heteronymous end of each phase winding is used as each phase port of the primary winding; the dotted end of the second winding is connected as a transformer secondary neutral point and is used for connecting a terminal of a direct-current low-voltage port in the series compensation side inverter circuit; the homonymous end of each phase of winding of the third winding is used as an port of each phase of secondary winding of the transformer and is used for connecting a series compensation side inverter circuit with a port of a power grid; the second winding and the third winding adopt a zigzag connection method; the network side rectifying circuit is connected with the series compensation side inverter circuit in parallel;

the series compensation side inverter circuit is used for outputting three-phase voltage to the transformer and inhibiting the output voltage of the network side rectifier circuit from being influenced by the voltage fluctuation of a bus; the network side rectification current is used for stabilizing the voltage of the direct-current high-voltage port of the series compensation side inverter circuit, and simultaneously converting direct-current power input by the direct-current low-voltage port of the series compensation side inverter circuit into alternating-current active power to transmit energy to a power grid;

the series compensation side inverter circuit includes: the series compensation side three-phase H bridge, the series compensation side filter unit, the direct current filter inductor, the third filter capacitor and the direct current voltage source are connected in series;

the series compensation side three-phase H bridge is connected with a first end of the series compensation side filtering unit; the second end of the series compensation side filtering unit is used as an alternating current port and is connected with a third winding different name end of the transformer; the port connected with the direct current filter inductor is a direct current low-voltage port, one side of the direct current filter inductor is connected with the positive electrode of the direct current voltage source, and the other side of the direct current filter inductor is connected with the neutral point port of the transformer and used for inhibiting high-frequency ripples of direct current output by the direct current low-voltage port; the negative electrode of the direct current voltage source is connected with the third filter capacitor and used for outputting direct current power; a port connected with the third filter capacitor is used as a high-voltage port, the third filter capacitor is connected in parallel between the first three-phase H bridge and the network side rectifying circuit, and the third filter capacitor is used for inhibiting voltage ripples at the direct-current high-voltage side;

the net side rectified current comprises: a network side three-phase H bridge and a network side filtering unit;

the grid side three-phase H bridge and the series compensation side three-phase H bridge are connected in parallel through a third filter capacitor; and the grid side filtering unit is connected between the grid side three-phase H bridge and a power grid.

2. The three-port converter according to claim 1, wherein the grid-side three-phase H-bridge and the series compensation-side three-phase H-bridge are fully-controlled power electronic devices comprising transistors and diodes connected in anti-parallel therewith;

the series compensation side filtering unit comprises a first grid-connected resistor, a first grid-connected inductor and a first filtering capacitor; a first port of the first grid-connected inductor is connected with a first port of the first grid-connected resistor, a second port of the first grid-connected resistor is used as a first port of the series compensation side filter unit, and the first filter capacitor is connected with a second port of the first grid-connected inductor, is used as a second port of the series compensation side filter unit and is connected with a different name end of the third winding;

the network side filtering unit comprises a second grid-connected resistor, a second grid-connected inductor and a second filtering capacitor; a first port of the first grid-connected inductor is connected with a first port of a second grid-connected resistor, a second port of the second grid-connected resistor is used as a first port of a grid-side filtering unit, and a second filtering capacitor is connected with a second port of the second grid-connected inductor, is used as a second port of the grid-side filtering unit and is connected with a first winding synonym terminal;

the first grid-connected inductor and the second grid-connected inductor are used for suppressing current high-frequency ripples; the first grid-connected resistor is used as a first grid-connected inductor parasitic resistor and is used for suppressing harmonic current generated by a first grid-connected inductor and a first filter capacitor;

the second grid-connected resistor is used as a second grid-connected inductor parasitic resistor and is used for suppressing harmonic current generated by the second grid-connected inductor and the second filter capacitor.

3. The method for controlling the series compensation side inverter circuit in the three-port converter according to claim 2, comprising the steps of:

the grid side current reference value is subjected to PARK conversion to obtain a complex form of the grid side current reference value and the complex form is transmitted to a proportion link Z; multiplying the result output by the Z operation of the comparison example link by the reference value of the rotation angle to obtain the reference value of the output alternating voltage of the series compensation side inverter circuit;

subtracting a d-axis reference value of output alternating voltage of the inverter circuit on the series compensation side from d-axis voltage of a secondary side port of the transformer, inputting a difference value into a voltage loop proportional integral controller, and outputting a first integral value; multiplying the angular speed of the power grid, the capacitance value of the first filter capacitor and the output alternating voltage q-axis reference value of the series compensation side inverter circuit to obtain a first multiplication result; adding the negative value of the first integral value and the first multiplication result to obtain a d-axis current reference value of the series compensation side inverter circuit;

subtracting the q-axis reference value of the output alternating voltage of the series compensation side inverter circuit from the q-axis voltage of the secondary side port of the transformer, inputting the difference value into a voltage loop proportional integral controller, and outputting a second integral value; multiplying the angular speed of the power grid, the capacitance value of the first filter capacitor and the output alternating-current voltage d-axis voltage of the series compensation side inverter circuit to obtain a second multiplication result; subtracting the negative value of the second integral value from the second multiplication result to obtain a q-axis current reference value of the series compensation side inverter circuit;

subtracting a d-axis current reference value of the inverter circuit on the series compensation side from a d-axis current of the alternating current port, inputting a difference value into a current loop proportional-integral controller, and outputting a third integral value; multiplying the d-axis voltage of the secondary side port of the transformer, the angular speed of the power grid and the q-axis current of the alternating current port in the series compensation side inverter circuit to obtain a third phase multiplication result; adding the negative value of the third integral value and the third phase multiplication result to obtain a d-axis voltage reference value of the midpoint of the bridge arm of the alternating current port of the series compensation side inverter circuit;

subtracting the q-axis reference value of the output alternating current of the series compensation side inverter circuit from the q-axis current of the alternating current port, inputting the difference value into a current loop proportional-integral controller, and outputting a fourth integral value; obtaining a fourth multiplication result by multiplying the q-axis voltage of the secondary side port of the transformer, the angular speed of the power grid and the d-axis current of the alternating current port in the series compensation side inverter circuit; subtracting the negative value of the fourth integral value from the fourth multiplication result to obtain a q-axis voltage reference value of the midpoint of the bridge arm of the alternating current port of the series compensation side inverter circuit;

inverse PARK conversion is carried out on the point d-axis voltage reference value and the point q-axis voltage reference value in the bridge arm of the alternating current port of the inverter circuit at the serial compensation side, and the point three-phase voltage per unit reference value in the bridge arm of the alternating current port of the inverter circuit at the serial compensation side is output after per unit conversion; and adding the per-unit reference value of the midpoint three-phase voltage and the per-unit reference value of the three-phase voltage offset in the bridge arm of the alternating current port of the series compensation side inverter circuit, and generating a first PWM signal through the generated first modulation voltage to control a transistor in the series compensation side inverter circuit.

4. The control method according to claim 3, wherein the method for obtaining the per-unit reference value of the three-phase voltage offset in the bridge arm of the series compensation side inverter circuit comprises the following steps:

and setting a specified value of the output current of the direct-current low-voltage port, subtracting the specified value of the output current from the direct-current low-voltage port output direct current, inputting the difference value into a direct-current loop proportional-integral controller, and controlling the per-unit reference value of the point three-phase voltage offset in the bridge arm of the output series compensation side inverter circuit.

5. The method for controlling the grid-side rectifying circuit of the three-port converter according to claim 2, comprising the steps of:

carrying out PARK conversion on three-phase voltage output by the network side rectifying circuit and three-phase current output by the network side rectifying circuit, and respectively obtaining network side rectifying circuit output voltage and network side rectifying circuit output current under a two-phase synchronous rotating coordinate system;

setting a direct-current high-voltage port voltage reference value of the series compensation side inverter circuit, subtracting the direct-current high-voltage port voltage, inputting a difference value into a voltage loop proportional integral controller, and outputting a d-axis current reference value of the network side rectifier circuit; setting a q-axis current reference value of a network side rectifying circuit to be 0;

subtracting the d-axis current reference value of the network side rectifying circuit from the d-axis output current of the network side rectifying circuit, inputting the difference value into a current loop proportional-integral controller, and outputting a fifth integral value; multiplying the d-axis output voltage of the network-side rectifying circuit, the grid angular velocity and the q-axis output current of the network-side rectifying circuit to obtain a fifth multiplication result; subtracting the fifth multiplication result from the negative value of the fifth integral value to obtain a value serving as a d-axis voltage reference value of the middle point of the bridge arm of the network-side rectifying circuit;

subtracting a q-axis current reference value of the network side rectifying circuit from a q-axis output current of the network side rectifying circuit, inputting a difference value into a current loop proportional-integral controller, and outputting a sixth integral value; multiplying the q-axis output voltage of the grid-side rectifying circuit, the grid angular velocity and the d-axis output current of the grid-side rectifying circuit to obtain a sixth multiplication result; adding the negative value of the sixth integral value and the sixth multiplication result to obtain a value serving as a q-axis voltage reference value of the middle point of the bridge arm of the network-side rectifying circuit;

and performing inverse PARK conversion on the d-axis voltage reference value and the q-axis voltage reference value of the midpoint of the bridge arm of the network side rectifying circuit, outputting the three-phase voltage reference value of the midpoint of the bridge arm of the network side rectifying circuit after per unit conversion, taking the three-phase voltage reference value as a second modulation voltage, forming a second PWM signal through the generated second modulation voltage, and controlling 6 transistors in the network side rectifying circuit.

6. A control system for a series compensation side inverter circuit in a three-port converter according to claim 2, comprising:

the first PARK converter is used for converting the network side current reference value through PARK to obtain a complex form of the network side current reference value and transmitting the complex form to the proportion link Z;

the calculation unit is used for multiplying the result output by the Z operation of the comparison link by the reference value of the rotation angle to obtain the output alternating voltage reference value of the series compensation side inverter circuit;

the first subtracter is used for subtracting the d-axis voltage of the secondary side port of the transformer from the d-axis reference value of the output alternating voltage of the series compensation side inverter circuit; the first voltage loop proportional integral controller is used for carrying out proportional integral operation on a difference value between an output alternating voltage d-axis reference value of the series compensation side inverter circuit and a d-axis voltage of a secondary side port of the transformer to obtain a first integral value; the first multiplier is used for multiplying the angular speed of a power grid, the capacitance value of the first filter capacitor and the output alternating voltage q-axis reference value of the series compensation side inverter circuit to obtain a first multiplication result; the first adder is used for adding the negative value of the first integral value and the first multiplication result to obtain a d-axis current reference value of the series compensation side inverter circuit;

the second subtracter is used for subtracting the q-axis voltage of the secondary side port of the transformer from the q-axis reference value of the output alternating voltage of the series compensation side inverter circuit; the second voltage loop proportional integral controller is used for carrying out proportional integral operation on a difference value between an output alternating voltage q-axis reference value of the series compensation side inverter circuit and a q-axis voltage of a secondary side port of the transformer and outputting a second integral value; the second multiplier is used for multiplying the angular speed of the power grid, the capacitance value of the first filter capacitor and the output alternating-current voltage d-axis voltage of the series compensation side inverter circuit to obtain a second multiplication result; the third subtracter is used for subtracting the negative value of the second integral value from the second multiplication result to obtain a q-axis current reference value of the series compensation side inverter circuit;

the fourth subtracter is used for subtracting the d-axis current reference value of the inverter circuit on the series compensation side from the d-axis current of the alternating current port; the first current loop proportional-integral controller is used for carrying out proportional-integral operation on a difference value between a d-axis current reference value of the series compensation side inverter circuit and d-axis current of the alternating current port and outputting a third integral value; the third multiplier is used for multiplying the d-axis voltage of the secondary side port of the transformer, the angular speed of the power grid and the q-axis current of the alternating current port in the series compensation side inverter circuit to obtain a third phase multiplication result; the second adder is used for adding a negative value of the third integral value and a third phase multiplication result to obtain a d-axis voltage reference value of a midpoint of a bridge arm of an alternating current port of the series compensation side inverter circuit;

the fifth subtracter is used for subtracting the q-axis current of the alternating current port from the q-axis reference value of the output alternating current of the series compensation side inverter circuit; the second current loop proportional-integral controller is used for carrying out proportional-integral operation on a difference value between an output alternating current q-axis reference value of the series compensation side inverter circuit and an alternating current port q-axis current and outputting a fourth integral value; the fourth multiplier is used for multiplying the q-axis voltage of the secondary side port of the transformer, the angular speed of the power grid and the d-axis current of the alternating current port in the series compensation side inverter circuit to obtain a fourth multiplication result; the sixth subtracter is used for subtracting the negative value of the fourth integral value from the fourth multiplication result to obtain a q-axis voltage reference value of the midpoint of the bridge arm of the alternating current port of the series compensation side inverter circuit;

the inverse PARK converter is used for carrying out inverse PARK conversion on a point d-axis voltage reference value and a point q-axis voltage reference value in an alternating current port bridge arm of the inverter circuit on the serial compensation side, and outputting a point three-phase voltage per-unit reference value in the alternating current port bridge arm of the inverter circuit on the serial compensation side after per-unit conversion; the third adder is used for adding the three-phase voltage reference value in the bridge arm of the alternating current port of the series compensation side inverter circuit and the three-phase voltage offset per-unit reference value to generate a first modulation voltage; the first SPWM inverter is used for generating a first PWM signal through a first modulation voltage; the first PWM signal is used for controlling a transistor in the series compensation side inverter circuit.

7. The control system according to claim 6, wherein the method for obtaining the per-unit reference value of the three-phase voltage offset in the bridge arm of the series compensation side inverter circuit comprises the following steps:

and setting a specified value of the output current of the direct-current low-voltage port, subtracting the specified value of the output current from the direct-current low-voltage port output direct current, inputting the difference value into a direct-current loop proportional-integral controller, and controlling the per-unit reference value of the point three-phase voltage offset in the bridge arm of the output series compensation side inverter circuit.

8. The control system of a grid-side rectifier circuit in a three-port converter according to claim 2, comprising:

the second PARK converter is used for carrying out PARK conversion on the three-phase voltage output by the network side rectifying circuit and the three-phase current output by the network side rectifying circuit, and respectively acquiring the output voltage of the network side rectifying circuit and the output current of the network side rectifying circuit under the two-phase synchronous rotating coordinate system;

the seventh subtracter is used for setting a direct-current high-voltage port voltage reference value of the series compensation side inverter circuit, and subtracting the direct-current high-voltage port voltage from the direct-current high-voltage port voltage reference value; the third voltage loop proportional integral controller is used for carrying out proportional integral operation on a difference value between a direct-current high-voltage port voltage reference value of the series compensation side inverter circuit and a direct-current high-voltage port voltage and outputting a d-axis current reference value of the network side rectifying circuit; setting a q-axis current reference value of a network side rectifying circuit to be 0;

an eighth subtractor for subtracting the d-axis current reference value of the network-side rectifying circuit from the d-axis output current of the network-side rectifying circuit; the third current loop proportional-integral controller is used for carrying out proportional-integral operation on a difference value between a d-axis current reference value of the network side rectifying circuit and d-axis output current of the network side rectifying circuit to obtain a fifth integral value; the fifth multiplier is used for multiplying the d-axis output voltage of the grid-side rectifying circuit, the grid angular velocity and the q-axis output current of the grid-side rectifying circuit to obtain a fifth multiplication result; the ninth subtracter is used for subtracting the fifth multiplication result from the negative value of the fifth integral value to obtain a value which is used as a d-axis voltage reference value of the middle point of the bridge arm of the network-side rectifying circuit;

a tenth subtractor for subtracting the q-axis output current of the network-side rectifying circuit from the q-axis current reference value of the network-side rectifying circuit; the fourth current loop proportional-integral controller is used for carrying out proportional-integral operation on a difference value between a q-axis current reference value of the network side rectifying circuit and a q-axis output current of the network side rectifying circuit and outputting a sixth integral value; the sixth multiplier is used for multiplying the q-axis output voltage of the grid-side rectifying circuit, the grid angular velocity and the d-axis output current of the grid-side rectifying circuit to obtain a sixth multiplication result; a fourth adder, configured to add a negative value of the sixth integral value and the sixth multiplication result, and use the obtained value as a q-axis voltage reference value of the midpoint of the bridge arm of the network-side rectifier circuit;

the second inverse PARK converter is used for inverse PARK conversion of the d-axis voltage reference value and the q-axis voltage reference value at the midpoint of the bridge arm of the network side rectifying circuit, outputting the three-phase voltage reference value at the midpoint of the bridge arm of the network side rectifying circuit after per-unit conversion, and taking the three-phase voltage reference value as a second modulation voltage; the second SPWM inverter is used for generating a second PWM signal through a second modulation voltage; and the second PWM signal is used for controlling a transistor in the series compensation side inverter circuit.

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