CN111404406A - PWM rectifier internal model control system and method based on virtual flux linkage orientation - Google Patents

Abstract

The application provides a PWM rectifier internal model control system based on virtual flux linkage is directional, includes: the input filter is used for filtering the input current; a voltage regulator for providing input voltage ranges of different magnitudes; the drive board is used for realizing conversion from a digital signal to a power signal and carrying out PWM (pulse-width modulation) drive control on the insulated gate bipolar transistor IGBT; the sampling plate is used for conditioning current and voltage signals respectively acquired by the current Hall and the voltage Hall; an adjustable load resistance box; a switching power supply; the direct-current bus capacitor is used for carrying out voltage stabilization and energy storage on the direct-current bus capacitor after receiving alternating current of a three-phase full-bridge rectification power grid; and the core development board is used for responding to the signals and the instructions.

Description

A PWM rectifier internal model control system and method based on virtual flux linkage orientation

technical field

The invention relates to the field of circuit control, in particular to an internal model control system and method based on virtual flux linkage orientation of a three-phase voltage-type PWM rectifier.

Background technique

Since the 1980s, with the maturity of power electronic devices that can be turned off, power electronic technology has developed by leaps and bounds. Among them, rectification technology has been widely used in HVDC transmission, static reactive power compensation, electric locomotive traction. , AC and DC power drives, high-performance AC and DC power supply and other power systems and electrical engineering. With the continuous improvement of the performance of power semiconductor switching devices and the needs of practical applications, the development of rectifier circuits has experienced successively from the traditional rectification method to the current mainstream pulse width modulation (PWM) rectification method. At present, PWM rectification technology has become one of the important development directions in the field of solving harmonic pollution and reactive power loss of power grid and saving energy.

The PWM rectifier is based on PWM technology, which has a decisive influence on improving the power factor of the grid, reducing the harmonic content of the grid current, stabilizing the bus voltage and ensuring the normal operation of the grid-side inverter. The main idea of PWM rectification is to modulate the AC voltage into a DC voltage by controlling the on-off of the switching device to achieve a stable DC voltage output, and at the same time control the voltage and current on the grid side, so that the phase current on the grid side is sinusoidal and is the same as the phase voltage on the grid side. phase so that the rectifier operates at unity power factor. Since the switch tube needs to withstand the DC bus voltage, in high-voltage applications, the two-level topology has higher requirements on the power tube. With the increasing number of high-voltage and large-capacity power electronic devices, the research on high-performance control technology of PWM rectifiers is gradually becoming a research focus in PWM rectifier technology.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of traditional rectifiers such as low power factor, large harmonic pollution, and overcurrent in the starting process, this paper proposes a virtual flux orientation based algorithm that combines the flux orientation algorithm and internal model control algorithm in the field of motor control with rectifier control. PWM rectifier internal model control system.

The present application provides an internal model control system for a PWM rectifier based on virtual flux linkage orientation, including: an input filter for filtering input current; a voltage regulator for providing input voltage ranges of different sizes; a driver board , used to realize the conversion of digital signal to power signal, PWM drive control of insulated gate bipolar transistor IGBT; sampling board, used to adjust the current and voltage signals collected by current Hall and voltage Hall respectively; A load regulating resistance box; a switching power supply; a three-phase full bridge and a DC bus capacitor, the DC bus capacitor is used for the DC bus capacitor to receive the AC power from the three-phase full-bridge rectified power grid for voltage stabilization and energy storage; A core development board that responds to signals and commands.

In a possible implementation manner, the system further includes an input unit, and the communication between the input unit and the DSP can be realized through SPI, and parameters can be set and modified.

In a possible implementation manner, the adjustable load resistance box adopts an adjustable range of 0-180Ω; the DC bus capacitor adopts two parallel high-voltage 1200V-1100μF large electrolytic capacitors; the core development board adopts DSP2812 core development board; the driver board adopts HCPL-316J optocoupler driver chip as the core IGBT driver board, the switching power supply can realize the conversion of single-phase 220V to obtain the ±15V required by the driver board and the sampling board ±12V and sampling ±5V required by the conditioning circuit.

In a possible implementation, the system includes a main power circuit, and the main power circuit includes:

DC bus capacitors and a three-phase bridge rectifier consisting of six SKM7512 type IGBTs.

In a possible implementation manner, the system includes a sampling circuit design, including an AC side current detection circuit, an AC side voltage detection circuit, and a DC bus voltage detection circuit.

In a possible implementation manner, the AC side current detection circuit adopts a current Hall sensor, and its output current is converted into a voltage signal by resistance sampling, and the AC signal is raised into a DC signal through an inverting summation circuit, and then proportional The amplifier adjusts the amplitude and phase of the output voltage signal, and sends the obtained signal to the AD sampling port of the microcontroller;

The AC side voltage detection circuit adopts a voltage Hall sensor, and the sensor sampling signal is subjected to signal conditioning through a differential amplifier circuit, and the obtained signal is sent to the AD sampling port of the single-chip microcomputer;

The DC bus voltage detection circuit adopts a resistive voltage divider circuit, and implements low-voltage protection for the H-bridge cascaded multi-level inverter by feeding back the DC voltage.

In a possible implementation manner, the switching power supply includes: designing a single-ended flyback quasi-resonant switching power supply using the UCC28740 chip.

In a possible implementation, the core development board runs a main program and an interrupt service subroutine;

The main program is used to initialize the system and execute the SVM algorithm;

The interrupt service subroutine includes timer interrupt, ADC interrupt subroutine and capture interrupt subroutine, and the interrupt service subroutine is also used for nested execution of different control algorithms.

In a possible implementation manner, the initialization of the system includes the configuration of the system clock, the general-purpose input and output interface, the PWM module, the capture module, the AD module control register, and the initialization of the control state variables in the system;

Described interrupt service subroutine, including algorithm and controller calculation and fault protection, output PWM pulse, sampling processing of voltage and current signal;

The ADC interrupt service subroutine includes sampling of the DC bus voltage and output current and average filtering calculation;

The timer interrupt service subroutine includes optimizing the SVM control algorithm, and updating the duty cycle to output the PWM pulse for controlling the switch tube.

According to another aspect of the present application, a method for controlling the internal model of a PWM rectifier based on virtual flux linkage orientation is provided, and the method includes at least the following steps:

Step 1, collecting symmetrical three-phase currents i _a , _{ib , ic , symmetrical three-phase voltages U a , U b , U c , and DC} bus voltage U _dc of the three-phase voltage-type PWM rectifier;

Step 2, the three-phase currents i _a , i _b , _ic and the three-phase voltages U _a , U _b , U _c are Clark transformed to output the two-phase currents i _α , i in the two-phase static rectangular coordinate system α-β _β two-phase voltage U _α , U _β ;

Step 3, the two-phase voltages U _α and U _β obtain the phase angle θ _e through the virtual flux linkage orientation as the conversion angle from the three-phase stationary coordinate system to the two-phase rotating coordinate system;

Step 4, the two-phase currents i _α and i _β undergo Clark transformation to output the two-phase currents _id and i _q in the two-phase synchronous rotating coordinate system dq;

Step 5, make a difference between the d-axis reference voltage U ^* _dc and the DC bus voltage U _dc obtained in step 1, and after the difference is adjusted by PI, the grid active reference current I ^* _d is estimated according to the principle of power equivalence;

Step 6, make a difference between the reference current I ^* _d obtained in step 5 and the two-phase current id obtained in step 4, and output the difference value (i ^* _d - _{id )} ;

Step 7, make a difference between the q-axis reference current i ^* _q and the two-phase current i _q obtained in step 4, and output the difference value (i ^* _q -i _q );

Step 8: Adjust the difference values (i ^* _d - _id ) and (i ^* _q - _iq ) obtained in step 6 and step 7 through internal model control (IMC) to obtain d-axis reference voltages U ^* _d and q axis reference voltage U ^* _q ;

Step 9: The d-axis reference voltage U ^* _d and the q-axis reference voltage U ^* _q are subjected to Clark transformation to output the two-phase control voltages U ^* _α and U ^* _β under the two-phase static rectangular coordinate system;

Step 10: Perform space vector modulation on the two-phase control voltages U ^* _α and U ^* _β , and output a switch signal.

The beneficial effects brought by the technical solutions provided in the embodiments of the present application include at least:

The present invention provides a novel PWM rectifier internal model control system based on virtual flux linkage orientation. Compared with the prior art, the virtual flux linkage orientation vector control does not need to directly sample the grid voltage, and only needs to control the output current according to the system. The power grid synchronization signal can be estimated by using the DC voltage; the internal model control technology is introduced into the current control of the voltage-type PWM rectifier, and the internal model control principle is used to design the current inner loop parameters. This method does not rely too much on the accurate mathematical model of the controlled object. The accuracy requirements of system parameters are not high, and the controller design is simple, the direction of parameter debugging is simple, and a large number of repeated test losses are avoided.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the drawings that are used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

Fig. 1 is the overall control block diagram of the system provided by an exemplary embodiment of the present invention;

FIG. 2 is an overall scheme design of a PWM rectifier hardware system provided by an exemplary embodiment of the present invention;

3 is a schematic diagram of a main power circuit provided by an exemplary embodiment of the present invention;

FIG. 4 is an optocoupler isolation drive circuit provided by an exemplary embodiment of the present invention;

5 is a schematic diagram of a flyback switching power supply provided by an exemplary embodiment of the present invention;

6 is a flow chart of a main program provided by an exemplary embodiment of the present invention;

7 is a flowchart of an ADC interrupt service provided by an exemplary embodiment of the present invention;

8 is a flowchart of a timer interrupt service subroutine provided by an exemplary embodiment of the present invention;

FIG. 9 is a simulated current and voltage waveform diagram provided by an exemplary embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the inventive concept. These all belong to the protection scope of the present invention.

A PWM rectifier internal model control system based on virtual flux linkage orientation provided by this embodiment includes: an input filter, which is used to filter the input current; a voltage regulator, which is used to provide input voltage ranges of different sizes; a driver board , used to realize the conversion of digital signal to power signal, PWM drive control of insulated gate bipolar transistor IGBT; sampling board, used to adjust the current and voltage signals collected by current Hall and voltage Hall respectively; A load regulating resistance box; a switching power supply; a three-phase full bridge and a DC bus capacitor, the DC bus capacitor is used for the DC bus capacitor to receive the AC power from the three-phase full-bridge rectified power grid for voltage stabilization and energy storage; A core development board that responds to signals and commands.

The present invention will be described in further detail below with reference to FIGS. 1 to 9 . The control steps of the system mainly include:

Step 1, collect symmetrical three-phase currents i _a , _{ib , ic , symmetrical three-phase voltages U a , U b , U c , and DC} bus voltage U _dc of the three-phase voltage-type PWM rectifier.

Step 2, the three-phase currents i _a , i _b , _ic and the three-phase voltages U _a , U _b , U _c are Clark transformed to output the two-phase currents i _α , i in the two-phase stationary rectangular coordinate system α-β _β two-phase voltage U _α , U _β ;

The components of the symmetrical three-phase currents i _a , _ib , and _ic in the α-β coordinate system are obtained by Clark transformation:

(22) The components of the symmetrical three-phase currents u _a , u _b , and u _c in the α-β coordinate system are obtained by Clark transformation:

(23) The states of the six IGBT switches of the three-phase voltage-type PWM rectifier are expressed as follows:

(24) The relationship between the DC side voltage and the duty cycle of the switching function:

_Wherein , da , _db , and dc are the duty ratios of the corresponding bridge arm switching function Sk, respectively, and the PWM duty cycle _dk is the average value of the switching function Sk in one switching cycle;

Step 3, the two-phase voltages U _α and U _β obtain the phase angle θ _e through the virtual flux linkage orientation as the conversion angle from the three-phase stationary coordinate system to the two-phase rotating coordinate system.

在α-β坐标系下的分量可由以下公式得到，其中：L为三相电压型PWM整流器交流侧的滤波电感(31) Virtual magnetic link

The components in the α-β coordinate system can be obtained by the following formula, where: L is the filter inductance on the AC side of the three-phase voltage-type PWM rectifier

(32) Active power P and reactive power Q can be obtained by the following formula, where ω is the grid voltage angular velocity;

Step 4, the two-phase currents i _α and i _β are Clark transformed to output the two-phase currents _id and i _q in the two-phase synchronous rotating coordinate system dq.

(41) The components of the two-phase voltage u _α and u _β in the dq coordinate system are obtained by using Park transformation:

(42) Mathematical model of three-phase PWM rectifier in d-q coordinate system:

Step 5, make a difference between the d-axis reference voltage U ^* _dc and the DC bus voltage U _dc obtained in step 1, and after the difference is adjusted by PI, the grid active reference current I ^* _d is estimated according to the power equivalence principle.

Step 6, make a difference between the reference current I ^* _d obtained in step 5 and the two-phase current id obtained in step 4, and output the difference value (i ^* _d - _{id )} ;

Step 7, make a difference between the q-axis reference current i ^* _q and the two-phase current i _q obtained in step 4, and output the difference value (i ^* _q -i _q );

Step 8: Adjust the difference values (i ^* _d - _id ) and (i ^* _q - _iq ) obtained in step 6 and step 7 through internal model control (IMC) to obtain d-axis reference voltages U ^* _d and q Shaft reference voltage U ^* _q .

(81) The mathematical model of PWM rectifier is:

Let u' _d = _ed - u _dc s _d , u' _d = e _q - u _dc s _q , we can get:

(82) After the three-phase voltage-type PWM rectifier adopts the current internal model control, the transfer function of the current is:

and

thus:

则根据上式可得：①If the model estimation is accurate, that is:

Then according to the above formula we can get:

估计有偏差，在d轴上，来自q轴的耦合电压为ω_eLi_q，而内模控制解耦电压为

稳态时i^*-i_d＝0，

基本不影响解耦效果，只要选择合适的带宽λ，可以使得电流分量得到有效解耦。②If the parameter

The estimate is biased, on the d-axis, the coupling voltage from the q-axis is ω _e Li _q , while the internal-mode control decoupling voltage is

i ^* _-id = 0 in steady state,

It basically does not affect the decoupling effect, as long as an appropriate bandwidth λ is selected, the current component can be effectively decoupled.

Step 9: The d-axis reference voltage U ^* _d and the q-axis reference voltage U ^* _q are Clark transformed to output the two-phase control voltages U ^* _α and U ^* _β in the two-phase static rectangular coordinate system.

(91) The components of the two-phase rotating voltage ud and uq in the α-β coordinate system are obtained by using the inverse Park transformation:

Step 10: Perform space vector modulation on the two-phase control voltages U ^* _α and U ^* _β , and output a switch signal.

Figure 3 shows the schematic diagram of the main power circuit. The J1 port is the power grid input port. After the AC input is rectified by a three-phase full bridge, the DC bus capacitor C1 stabilizes the energy storage, and the J2 port is the tributary output port. The maximum DC bus voltage is designed to be 1200V, and a 450uf/1000V electrolytic capacitor is selected as the DC bus capacitor. In the inverter part, six SKM7512 IGBTs are selected to form a three-phase bridge rectifier with a withstand voltage of 1200V, a withstand current of 75A, and an on-resistance of 400mW.

Figure 4 is a diagram of the optocoupler isolation drive circuit. The optocoupler tube LED1 and the like form an input control circuit, and VIN+ and VIN- are the positive/negative logic signal input terminals respectively. When a negative logic signal is input, VIN+ is required to be set to a high level, and VIN- is connected to the input signal; on the contrary, when a positive logic signal is input, VIN- is required to be set to a low level, and VIN+ is connected to the input signal. The input signal is transmitted from LED1 to the internal drive circuit through the gate circuit and converted into IGBT gate drive signal. The optocoupler tube LED2 etc. constitute the fault signal control circuit. Terminal 7 of the driver is left floating (users can use it by themselves, such as bypassing the input signal in case of failure, etc.), terminal 8 is grounded, VCC1 and GND1 are the power supply of the input side, VCC2 and VEE are the power supply of the output side, and VC is a push-pull type The power supply of the collector of the output transistor can be directly connected to VCC2 or a resistor RC can be connected in series to limit the output conduction current. VOUT is the gate drive voltage output terminal.

Figure 5 is the schematic diagram of the flyback switching power supply. Each power unit in the PWM rectifier needs a low-voltage DC power supply. Using TI's UCC28740 chip, a single-ended flyback quasi-resonant switching power supply is designed, which can realize six channels (3 channels +15V, 1-way +12V, 1-way -12V, 1-way +5V) output isolation and voltage regulation, providing stable and reliable DC power supply for the main circuit and control circuit.

Figure 6 is the main program flow chart, the main program mainly completes the initialization of variables and interrupt waiting. In the main program, the initialization of the system should be carried out first, including the system clock, general input and output interface (GPIO), PWM module, capture module, AD module control register configuration and initialization of control state variables in the system. After completing the system initialization and the configuration of the relevant registers, the main program enters an infinite loop until an interrupt request occurs, and then jumps out of the loop to execute the corresponding interrupt service subroutine.

Figure 7 is the flow chart of ADC interrupt service. The first start of ADC is completed in the main program, and subsequent starts are completed in the timer interrupt service subroutine to ensure that the ADC works in a continuous state.

Figure 8 is a flowchart of the timer interrupt service subroutine, the timer interrupt service subroutine mainly completes the calculation of the optimized SVM algorithm. In each timer cycle, a new duty ratio is obtained by calculation, and the output PWM pulse controls the on-off of the switch tube.

Figure 9 is a simulation current and voltage waveform diagram, Figure a is the A-phase voltage Ua, current Ia and DC bus voltage Vdc waveform; Figure b is a partial enlarged view during the loading process; Figure c is the DC bus voltage Vdc steady-state voltage waveform; Figure d is the DC bus voltage Vdc dynamic waveform; Figure e is the d-axis current waveform; Figure g is the q-axis current waveform; Figure f is the d-axis current dynamic waveform; Figure h is the power factor. 0~0.1s is the light load state, 0.1~0.2s is the heavy load state, the load is doubled at 0.1s, it can be seen that the input voltage and current waveform realizes the power factor control of 1, the steady-state current waveform is sinusoidal and the ripple is small, reaching Expect standards. At the same time, the d-axis current achieves fast tracking in the dynamic process of loading, which verifies the rapidity of the control strategy. The steady-state fluctuation of the DC bus voltage is as small as 3-5V, the voltage drop during dynamic loading is less than 5V, and it can quickly recover to a given value. The simulation results verify the effectiveness of our proposed virtual flux linkage orientation + internal model control strategy.

Specific examples are used herein to describe the inventive concept in detail, and the descriptions of the above embodiments are only used to help understand the core idea of the present invention. It should be pointed out that for those skilled in the art, any obvious modifications, equivalent replacements or other improvements made without departing from the inventive concept should be included within the protection scope of the present invention.

Other embodiments of the present application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of this application that follow the general principles of this application and include common knowledge or conventional techniques in the technical field not disclosed in this application . The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the application being indicated by the foregoing claims.

It is to be understood that the present application is not limited to the precise structures described above and illustrated in the accompanying drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

It should be understood that references herein to "a plurality" means two or more. "And/or", which describes the association relationship of the associated objects, means that there can be three kinds of relationships, for example, A and/or B, which can mean that A exists alone, A and B exist at the same time, and B exists alone. The character "/" generally indicates that the associated objects are an "or" relationship.

Those of ordinary skill in the art can understand that all or part of the steps of implementing the above embodiments can be completed by hardware, or can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium. The storage medium mentioned may be a read-only memory, a magnetic disk or an optical disk, etc.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims (10)

1. A PWM rectifier internal model control system based on virtual flux linkage orientation is characterized by comprising: the input filter is used for filtering the input current;

a voltage regulator for providing input voltage ranges of different magnitudes;

the drive board is used for realizing conversion from a digital signal to a power signal and carrying out PWM (pulse-width modulation) drive control on the insulated gate bipolar transistor IGBT;

the sampling plate is used for conditioning current and voltage signals respectively acquired by the current Hall and the voltage Hall;

an adjustable load resistance box;

a switching power supply;

the direct-current bus capacitor is used for carrying out voltage stabilization and energy storage on the direct-current bus capacitor after receiving alternating current of a three-phase full-bridge rectification power grid;

and the core development board is used for responding to the signals and the instructions.

2. The internal model control system of the PWM rectifier based on the virtual flux linkage orientation as claimed in claim 1, wherein the system further comprises an input unit, the input unit and the DSP can be communicated through SPI, and parameters can be set and modified.

3. The internal model control system of the PWM rectifier based on the virtual flux linkage orientation is characterized in that the adjustable range of the adjustable load resistor box is 0-180 omega, the direct-current bus capacitor adopts two parallel-connected large electrolytic capacitors with the withstand voltage of 1200V-1100 muF, the core development board adopts a DSP2812 core development board, the drive board adopts an HCP L-316J optocoupler drive chip as a core IGBT drive board, and the switching power supply can achieve +/-15V required by the drive board, +/-12V required by a sampling board and +/-5V required by a sampling conditioning circuit for single-phase 220V conversion.

4. The internal model control system of the virtual flux linkage orientation based PWM rectifier of claim 1, wherein the system comprises a main power circuit, the main power circuit comprising:

and the direct-current bus capacitor and the six SKM7512 type IGBTs form a three-phase bridge rectifier.

5. The internal model control system of the PWM rectifier based on the virtual flux linkage orientation as claimed in claim 1, wherein the system comprises a sampling circuit design including an AC side current detection circuit, an AC side voltage detection circuit, and a DC bus voltage detection circuit.

6. The internal model control system of the PWM rectifier based on virtual flux linkage orientation according to claim 5,

the alternating current side current detection circuit adopts a current Hall sensor, the output current of the current Hall sensor is converted into a voltage signal by adopting resistance sampling, the alternating current signal is raised into a direct current signal through an inverted summation circuit, then the amplitude and the phase of the output voltage signal are regulated by a proportional amplifier, and the obtained signal is transmitted to an AD sampling port of the singlechip;

the alternating current side voltage detection circuit adopts a voltage Hall sensor, a sensor sampling signal is subjected to signal conditioning through a differential amplification circuit, and the obtained signal is transmitted to an AD sampling port of the single chip microcomputer;

the direct current bus voltage detection circuit adopts a resistance voltage division circuit, and realizes low voltage protection on the H-bridge cascade multi-level inverter by feeding back direct current voltage.

7. The internal model control system of the PWM rectifier based on virtual flux linkage orientation according to claim 1, wherein the switching power supply comprises: a single-ended flyback quasi-resonant switching power supply is designed by adopting a UCC28740 chip.

8. The internal model control system of the PWM rectifier based on the virtual flux linkage orientation as claimed in claim 1, wherein a main program and an interrupt service subprogram are run in the core development board;

the main program is used for initializing the system and executing an SVM algorithm;

the interrupt service subprogram comprises a timer interrupt, an ADC interrupt subprogram and a capture interrupt subprogram, and the interrupt service subprogram is also used for executing different control algorithms in a nested mode.

9. The internal model control system of the PWM rectifier based on virtual flux linkage orientation according to claim 8,

the initialization of the system comprises the configuration of a clock, a general input/output interface, a PWM module, a capture module and an AD module control register of the system and the initialization of control state variables in the system;

the interrupt service subprogram comprises the calculation of an algorithm and a controller and the protection during the fault, outputs PWM pulses and samples and processes voltage and current signals;

the ADC interrupt service subprogram comprises sampling of the direct current bus voltage and the output current and average filtering calculation;

the timer interrupt service subroutine comprises an optimization SVM control algorithm, and the duty ratio is updated to output PWM pulses for controlling the switching tube.

10. A PWM rectifier internal model control method based on virtual flux linkage orientation is characterized by at least comprising the following steps:

step 1, collecting symmetrical three-phase current i of a three-phase voltage type PWM rectifier_a、i_b、i_cSymmetric three-phase voltage U_a、U_b、U_cDC bus voltage U_dc；

Step 2, three-phase current i_a、i_b、i_cAnd three phase voltage U_a、U_b、U_cThe two-phase current i under a two-phase static rectangular coordinate system α - β is output through Clark transformation_α、i_βTwo-phase voltage U_α、U_β；

Step 3, two-phase voltage U_α、U_βObtaining phase angle theta through virtual flux linkage orientation_eAs three-phase stationary coordinate system to two-phase rotating coordinate systemConverting the angle;

step 4, two-phase current i_α、i_βThrough Clark conversion, two-phase current i under a two-phase synchronous rotating coordinate system dq is output_d、i_q；

Step 5, reference voltage U of d axis^* _dcAnd the DC bus voltage U obtained in the step 1_dcAfter the difference value is adjusted through PI, the active reference current I of the power grid is estimated according to the power equivalence principle^* _d；

Step 6, the reference current I obtained in the step 5 is used^* _dWith the two-phase current i obtained in step 4_dMaking a difference and outputting a difference value (i)^* _d-i_d)；

Step 7, reference current i of q axis^* _qWith the two-phase current i obtained in step 4_qMaking a difference and outputting a difference value (i)^* _q-i_q)；

Step 8, the difference values (i) obtained in the step 6 and the step 7 are respectively^* _d-i_d) And (i)^* _q-i_q) Obtaining d-axis reference voltage U through Internal Model Control (IMC) regulation^* _dAnd q-axis reference voltage U^* _q；

Step 9, reference voltage U of d axis^* _dAnd q-axis reference voltage U^* _qThe two-phase control voltage U under the two-phase static rectangular coordinate system is output through Clark transformation^* _α、U^* _β；

Step 10, controlling the two phases of the voltage U^* _α、U^* _βAnd carrying out space vector modulation and outputting a switching signal.

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