CN106936148A - A kind of photovoltaic energy storage converter system and its control method - Google Patents

Abstract

The present invention provides a photovoltaic-energy storage conversion system and its control method, wherein the photovoltaic-energy storage conversion system includes a bidirectional DC/DC converter, a grid-connected inverter, and is used to control the bidirectional DC/DC converter. The DC/DC control module of the DC converter and the inverter control module for controlling the grid-connected inverter, the DC/DC control module includes a voltage control module, a current control module electrically connected to the voltage control module, and a comparison module, the output end of the current control module is electrically connected to the comparison module. The present invention provides a photovoltaic-energy storage conversion system and its control method to solve the technical problems of the existing photovoltaic-energy storage conversion system requiring power failure and unstable DC bus voltage when charging and discharging energy storage batteries.

Description

A photovoltaic-energy storage conversion system and its control method

technical field

The present invention relates to the technical field of photovoltaic energy storage, and more specifically, to a photovoltaic-energy storage conversion system and a control method thereof.

Background technique

Solar energy, as the cleanest energy source, has received extensive attention. Solar power generation systems have their own characteristics, that is, they are affected by the natural environment. Compared with traditional fossil energy, photovoltaic power generation system cannot provide stable and continuous energy. Medium and small-capacity photovoltaic power generation systems have power dispersion, large equivalent impedance and violent output power fluctuations. For the local power grid, the photovoltaic power generation system is an impact power source. The larger the installed capacity, the greater the thermal reserve capacity required by the power grid. .

In the case of completely isolated operation, each photovoltaic power source lacks the "support" function of the grid, and requires strong coordinated control. When the photovoltaic power is greater than the load demand, the electric energy should be stored; when the photovoltaic electric energy cannot meet the load demand, the electric energy should be replenished in time to collect and utilize renewable energy with the highest efficiency. Therefore, energy storage is necessary for distributed independent power generation systems based on renewable energy, and it is also the basis for improving the reliability of power supply. It can also maximize the use of photovoltaic energy and reduce the impact and dependence on the grid.

Western China has a vast territory, scattered residents, and the national large power grid still does not fully cover this area. The research shows that the photovoltaic-energy storage power supply system is an economical and reliable solution to the public infrastructure power supply in remote villages, outlying islands and remote areas. Therefore, the research It is necessary and meaningful to develop a photovoltaic-energy storage power supply system.

However, in the existing photovoltaic-energy storage power supply system, when the energy storage battery is switched from the charging operation state to the discharge operation state (or the energy storage battery is switched from the discharge operation state to the charging operation state), the photovoltaic-energy storage power supply system is usually powered off first, The operating state of the system is artificially adjusted and then resumed, which brings inconvenience to actual use; in addition, the existing bidirectional DC/DC converter cannot adjust the voltage of the DC bus, resulting in instability of the DC bus voltage.

Contents of the invention

The present invention provides a photovoltaic-energy storage conversion system and its control method to solve the technical problems of the existing photovoltaic-energy storage conversion system, such as the need for power outages and unstable voltage on the DC bus when the energy storage battery is charged and discharged. .

According to one aspect of the present invention, a photovoltaic-energy storage conversion system is provided, including a bidirectional DC/DC converter and a grid-connected inverter, wherein the system includes: a system for controlling the bidirectional DC/DC A DC/DC control module of the converter and an inverter control module for controlling the grid-connected inverter.

The DC/DC control module includes a voltage control module for obtaining a total command current, a current control module electrically connected to the voltage control module for obtaining three-way duty ratios, and a current control module for obtaining the bidirectional DC/DC A comparison module of the switch control signal of the DC converter, the output terminal of the current control module is electrically connected with the comparison module.

Preferably on the basis of the above solution, the system further includes an energy storage battery pack and a photovoltaic module, and the photovoltaic module is connected to the energy storage battery pack through the bidirectional DC/DC converter; one end of the grid-connected inverter It is connected with the photovoltaic module, and its other end is connected with the grid.

Preferably, on the basis of the above solution, the voltage control module is used to compare the terminal voltage of the energy storage battery pack with the command voltage, obtain the voltage deviation, and obtain the total command current based on the voltage loop control algorithm.

The present invention also provides a control method of a photovoltaic-energy storage conversion system,

Obtain the control signal of the bidirectional DC/DC converter based on the terminal voltage of the energy storage battery pack;

Based on the command voltage of the q-axis and the d-axis, the DC bus voltage and current, the control signal of the grid-connected inverter is obtained.

Preferably on the basis of the above scheme, the control signal acquisition method of the bidirectional DC/DC converter includes:

S1. Obtain the voltage deviation by comparing the terminal voltage of the energy storage battery pack with the command voltage, and obtain the total command current based on the voltage loop control algorithm;

S2. Obtain the sub-instruction currents of the three channels based on the total command current, and obtain the duty ratios of the three channels respectively through the current control algorithm;

S3. Based on the duty ratios of the three channels, the switching control signals of the DC/DC converter are obtained by comparing them with the carrier wave respectively.

Preferably on the basis of the above scheme, the step S1 further includes:

Based on the minimum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage and the given DC bus voltage minimum value, obtaining a voltage deviation value, and obtaining the upper limit value of the total command current through the third PI controller;

Based on the maximum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage with the maximum value of the given DC bus voltage to obtain a voltage deviation value, and obtaining a lower limit value for limiting the total command current through the third PI controller .

Preferably on the basis of the above scheme, the control mathematical model for obtaining the upper limit value of the total command current is:

Among them, k _p3 represents the proportional coefficient of the third PI controller; k _i3 represents the integral coefficient of the third PI controller; Indicates the upper limit value of the charging current, and Limited to [1.5C 0.05C], u _dci represents the DC bus voltage, u _{dci_min} represents the minimum voltage of the DC bus, and C represents the capacity of the energy storage battery.

Preferably on the basis of the above scheme, the control mathematical model for obtaining the minimum current value of the total command current is:

Among them, k _p3 represents the proportional coefficient of the third PI controller; k _i3 represents the integral coefficient of the third PI controller; Indicates the lower limit value of the charging current, and Limited to [-3C-0.05C], u _{dci represents the voltage at both ends of the DC bus, u dci_max represents} the maximum voltage of the DC bus, and C represents the capacity of the energy storage battery.

Preferably on the basis of the above scheme, the voltage loop control algorithm in step S1 includes obtaining the total command current through the fourth PI controller based on the voltage deviation between the terminal voltage of the energy storage battery pack and the command voltage, and the control mathematical model of the voltage loop control algorithm for:

i _{dc_ref} = k _{p_4} (u _{dco_ref} -u _dco )+k _{i_4} ∫(u _{dco_ref} -u _dco )dt;

Wherein, u _{dco_ref} indicates the command voltage; k _{p_4} indicates the proportional coefficient of the fourth PI controller; k _{i_4} indicates the integral coefficient of the fourth PI controller; u _dco indicates the terminal voltage of the energy storage battery.

Preferably on the basis of the above scheme, the current control algorithm in step S2 includes: comparing the command currents of the three circuits with the charging current of the energy storage battery pack to obtain the current deviation, and obtaining the duty ratio of the three circuits through the fifth PI controller, so The control mathematical model of the current control algorithm is:

Among them, d ₁ , d ₂ , d ₃ represent three duty ratios; k _p5 represents the proportional coefficient of the fifth PI controller; k _i5 represents the integral coefficient of the fifth PI controller; current i ₁ , i ₂ , i ₃ Indicates the charging current of the energy storage battery pack.

The invention provides a photovoltaic-energy storage conversion system, which controls the charging and discharging of the energy storage battery pack through a DC/DC control module, prevents the energy storage battery pack from overcharging or over-discharging, and cooperates with the DC bus voltage lower limit control module and The DC bus voltage upper limit control module can stabilize the DC bus voltage within a reasonable range.

Description of drawings

Fig. 1 is the overall circuit structure diagram of the photovoltaic-energy storage conversion system of the present invention;

Fig. 2 is the hardware control block diagram of DC/DC control module and inverter control module of the present invention;

Fig. 3 is a functional block diagram of the DC/DC control module of the present invention;

Fig. 4 is the schematic diagram of the inverter control module of the present invention;

Fig. 5 is the work flowchart of DC/DC control module of the present invention;

Fig. 6 is a working flowchart of the inverter control module of the present invention.

detailed description

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Please refer to Figure 1, the present invention provides a photovoltaic-energy storage conversion system, including energy storage battery packs, photovoltaic modules, bidirectional DC/DC converters and grid-connected inverters, photovoltaic modules through bidirectional DC/DC The converter is connected to the energy storage battery pack, the DC input terminal of the grid-connected inverter is connected in parallel to both ends of the photovoltaic module, and then connected to the grid through an isolation transformer.

Among them, the bidirectional DC/DC converter of the present invention includes six IGBT transistors S' ₁ , S' ₂ , S' ₃ , S' ₄ , S' ₅ , and S' ₆ , and the two ends of the photovoltaic module are respectively connected to a linkage switch The left end of K1 is connected, and a capacitor C _bus is connected in parallel to the right end of the linkage switch K1, and then the right end of the linkage switch K2 is connected with the collector of the IGBT transistor _S'1 and the emitter of the IGBT transistor _S'2 , and the IGBT transistor S' _The emitter of IGBT transistor _S'2 is connected to the emitter of IGBT transistor _S'2 , the emitter of IGBT transistor _S'3 is connected to the collector of IGBT transistor _S'4 , the emitter of IGBT transistor _S'5 is connected to the collector of IGBT transistor S'6 The electrodes are connected together, and the collector of IGBT transistor _S'1 , the collector of IGBT transistor _S'3 and the collector of IGBT transistor _S'5 are connected together, the emitter of IGBT transistor _S'2 , the collector of IGBT transistor _S'4 The emitter and the emitter of the IGBT transistor _S'6 are connected together.

In addition, an LC filter circuit is also connected between the bidirectional DC/DC converter of the present invention and the energy storage battery pack, wherein the LC filter circuit includes three inductors L1, L2 and L3, wherein the left end of the inductor L1 is connected to the IGBT transistor S _The emitter of ' ₁ , the left end of the inductance L2 is connected to the emitter of the IGBT transistor _S'3 , the left end of the inductance L3 is connected to the emitter of the IGBT transistor S'5; The sensor is then connected to one end of the energy storage battery pack. Preferably, the LC filter circuit of the present invention further includes a capacitor C _o , the two ends of the capacitor C _o are respectively connected in parallel with the two ends of the energy storage battery pack.

Preferably, at the moment of charging, since the voltage at both ends of the filter capacitor is different from the terminal voltage of the energy storage battery, resulting in a large inrush current, the present invention also installs a safety control module between the LC filter circuit and the energy storage battery pack . Wherein, the safety control module includes a charging switch and a current-limiting circuit, wherein the right end of the charging switch K3 is connected to one end of the energy storage battery pack, and its left end is connected to one end of the capacitor _CO ; the current-limiting circuit of the present invention includes a current-limiting switch K4 and a current-limiting resistor connected in series with the current-limiting switch K4, and the current-limiting circuit is connected in parallel at both ends of the charging switch K3.

In order to further describe the technical solution of the present invention in detail, please continue to refer to FIG. 1 , and the circuit structure of the grid-connected inverter of the present invention will be introduced in detail below.

The grid-connected inverter of the present invention includes six switching tubes S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , and S ₆ , and the emitter of switching tube S ₁ is connected to the collector of switching tube S ₂ , _The emitter of the switching tube S3 is connected to the collector of _S4 , the emitter of the switching tube S5 is connected to the collector of _{S6 ;} the collector of the switching tube S1, the collector _{of S3} and the collector _of S5 are connected together , the emitter of the switch tube _S2 , the emitter of _S4 and the emitter of _S6 are connected together. Connect the collector _of the switching tube S1 to the upper end of the capacitor C _bus , and the emitter of the switching tube S2 to the lower end of the capacitor C _bus , so that the grid _- connected inverter and the bidirectional branch converter are connected in parallel at both ends of the photovoltaic module; And a capacitor C _Inv is connected between the collector _of the switching tube _S1 and the emitter of the switching tube S2.

Furthermore, in the present invention, an LC filter circuit is connected to the output end of the grid-connected inverter, and the LC filter circuit includes three inductors L _A , L _B , and L _C , wherein the emitter of the switch tube S ₁ is connected to _The left end of the inductor L _A , the emitter of the switch tube S3 is connected to the left end _of the inductor L _B , the emitter of the switch tube S5 is connected to the left end of the inductor L _C ; the left ends of the inductors L _A , L _B , and L _C are respectively connected to the isolation transformer Phase A, phase B and phase C; the upper end of capacitor C _a is connected to phase A of the primary side of the transformer, the upper end of capacitor C _b is connected to phase B of the primary side of the transformer, and the upper end of capacitor C _c is connected to phase C of the primary side of the transformer; capacitor C The lower ends of _a , C _b , and C _c are connected together; the three Hall current sensors are passed between the left ends of the inductors L _A , L _B , and L _C and the contacts of the capacitors C _a , C _b , and C _c and the transformer; the transformer Phase a, phase b and phase c of the secondary side are connected to switch K5, and switch K5 is respectively connected to phase a, phase b and phase c of the grid.

The present invention also includes a DC/DC control module for controlling the bidirectional DC/DC converter and an inverter control module for controlling the grid-connected inverter. Among them, the output terminals of the DC/DC control module controlling the bidirectional DC/DC converter are respectively connected with the six IGBT transistors S′ ₁ , S′ ₂ , S′ ₃ , S′ ₄ , and S′ ₅ of the bidirectional DC/DC converter. , The bases of S' ₆ are connected to control the on-off of the six IGBT transistors. The output terminals of the inverter control module controlling the grid-connected inverter are respectively connected to the bases of the grid-connected inverter including six switch tubes S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , and S ₆ It is used to control the on-off of 6 switch tubes.

Please continue to refer to Figure 3. In order to accurately control the on-off of the bidirectional DC/DC converter and ensure that the energy storage battery pack is continuously powered during the charging and discharging conversion process, the present invention will introduce in detail the control of the bidirectional DC/DC converter. The structure of the DC/DC control module and its control method.

As shown in FIG. 3 , the DC/DC control module of the present invention includes a voltage control module, a current control module and a comparison module electrically connected to the voltage control module, and the output terminal of the current control module is electrically connected to the comparison module. Among them, the voltage control module is used to compare the terminal voltage of the energy storage battery pack with the command voltage to obtain the voltage deviation, and obtain the total command current based on the voltage loop control algorithm, wherein the voltage loop control algorithm is the terminal voltage of the energy storage battery pack and the command voltage The voltage difference between the voltages is obtained by the fourth PI controller to obtain the total command current, and the control model of the voltage loop control algorithm is:

i _{dc_ref} = k _{p_4} (u _{dco_ref} -u _dco )+k _{i_4} ∫(u _{dco_ref} -u _dco )dt;

Wherein, u _{dco_ref} indicates the command voltage; k _{p_4} indicates the proportional coefficient of the fourth PI controller; k _{i_4} indicates the integral coefficient of the fourth PI controller; u _dco indicates the terminal voltage of the energy storage battery.

The current control module of the present invention respectively obtains the three-way sub-command current through the total command current, and respectively obtains the three-way duty cycle based on the current control algorithm, wherein the current control algorithm includes: respectively comparing the three-way sub-command current and the charging current, The current deviation is obtained, and the current deviation is obtained through the fifth PI controller to obtain the three-way duty ratio, and the control model of the current control algorithm is:

Among them, d ₁ , d ₂ , d ₃ represent three duty ratios; k _p5 represents the proportional coefficient of the fifth PI controller; k _i5 represents the integral coefficient of the fifth PI controller; current i ₁ , i ₂ , i ₃ Indicates the charging current of the energy storage battery pack.

However, the comparison module of the present invention compares the three-way duty cycle with the carrier wave with a phase difference of 120°, obtains the switch control signal of the bidirectional DC/DC converter, and sends the switch control signal to six IGBT transistors S' ₁ , The bases of S' ₂ , S' ₃ , S' ₄ , S' ₅ , and S' ₆ control the switching states of the six IGBT transistors.

Further, the DC/DC control module of the present invention also includes a DC bus voltage lower limit control module and a DC bus voltage upper limit control module connected to the output terminal of the voltage control module. By setting the DC bus voltage upper limit control module and the lower limit control module, the The DC bus voltage is limited within a reasonable range to ensure the normal operation of the grid-connected inverter.

Among them, the control algorithm of the DC bus voltage upper limit control module is:

Among them, k _p3 and k _i3 represent the proportional coefficient and integral coefficient of the PI_3 algorithm, respectively; Indicates the upper limit value of the charging current, and Limited to [1.5C 0.05C], u _{dci indicates the voltage at both ends of the DC bus, and u dci_min indicates} the minimum voltage of the DC bus.

And the mathematical model of the DC bus voltage lower limit control module of the present invention is:

Among them, k _p3 and k _i3 represent the proportional coefficient and integral coefficient of the PI_3 algorithm, respectively; Indicates the lower limit value of the charging current, and Limited to [-3C-0.05C], u _{dci indicates the voltage at both ends of the DC bus, and u dci_max indicates} the maximum voltage of the DC bus.

The present invention also provides a control method of a photovoltaic-energy storage conversion system, which includes the following steps;

Obtain the control signal of the bidirectional DC/DC converter based on the terminal voltage of the energy storage battery pack;

Based on the q-axis, the d-axis command voltage, the voltage and current of the DC bus, the control signal of the grid-connected inverter is obtained.

Please refer to Figure 2, in the process of obtaining the control signal of the bidirectional DC/DC converter, firstly, the physical quantities such as current i ₁ , i ₂ and i ₃ , voltage u _dci , u _dco and temperature are detected by the sampling conditioning board, and Send it to the sampling port of the control board, DSP28335 executes the control scheme and control algorithm to generate 6 PWM signals, the driving and protection circuit processes the 6 PWM signals, and then drives the switch tubes S' ₁ , S' ₂ , S' ₃ , S' ₄ , S' ₅ and S'₆; the RS485 serial port on the control board is used to communicate with the photovoltaic inverter and the touch screen.

In the process of obtaining the control signal of the grid-connected inverter, the conditioning board first detects the current ia, ib and ic, the voltages u _{dc_pv} , u _a (e _a ), u _{b (} e _b ), u _{c ( e c} ) and temperature, etc., and then sent to the sampling port of the control board; DSP28335 executes the control scheme and control algorithm, and the control board outputs 6 SVPWM signals. S2, S3, S4, S5 and S6; the RS485 serial port on the control board is used to communicate with the inverter and touch screen, please refer to Figure 3 for details.

By obtaining the control signal of the bidirectional DC/DC converter, the charging and discharging process of the energy storage battery pack is controlled. At the same time, with the control signal of the grid-connected inverter, the power supply of the photovoltaic module to the grid or the energy storage battery pack is realized.

In one embodiment of the present invention, please continue to refer to FIG. 3, the control signal acquisition method of the bidirectional DC/DC converter of the present invention includes:

S1. Obtain the voltage deviation by comparing the terminal voltage of the energy storage battery pack with the command voltage, and obtain the total command current based on the voltage loop control algorithm;

S2. Obtain the sub-instruction currents of the three circuits based on the total instruction current, and respectively obtain the duty ratios of the three output circuits through the current control algorithm;

S3. Based on the duty ratios of the three channels, the switching control signals of the bidirectional DC/DC converter are obtained by comparing them with the carriers with phase differences of 120°.

During the control process, the voltage control module compares the terminal voltage u _dco of the energy storage battery pack with the command voltage u _dco-ref to obtain the voltage deviation, and uses the voltage control algorithm to obtain the total command current, and then divides the total command current by 3 Obtain the input value of the current control module, that is, the command current of each channel of the bidirectional DC/DC converter, and then control i ₁ , i ₂ and i ₃ respectively through the current control algorithm and three PI_5 algorithms, and output the three-way duty Compared with d ₁ , d ₂ and d ₃ , use the three-way duty cycle to compare with the three-way carrier (triangular wave) with a phase difference of 120 degrees to generate switching signals G′ ₁ , G′ ₂ , G′ ₃ G′ _4. G' ₅ and G' ₆ , respectively drive the switch tubes S' ₁ , S' ₂ , S' ₃ , S' ₄ , S' ₅ and S' ₆ with the six switching signals.

In another embodiment of the present invention, on the basis of the above-mentioned embodiments, in order to prevent the battery components from being overcharged or over-discharged and affecting the service life of the battery, step S1 of the present invention further includes:

Based on the minimum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage and the given DC bus voltage minimum value to obtain the voltage deviation, and obtaining the upper limit value of the total command current through the third PI controller;

Based on the maximum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage with the maximum value of the given DC bus voltage to obtain a voltage deviation value, and obtaining a lower limit value for limiting the total command current through the third PI controller .

Among them, the control algorithm for obtaining the upper limit value of the total command current is:

Wherein, k _p3 and k _i3 respectively represent the proportional coefficient and integral coefficient of the third PI controller; Indicates the upper limit value of the charging current, and Limited to [1.5C 0.05C], u _dci represents the DC bus voltage, and u _{dci_min} represents the minimum voltage of the DC bus.

The control algorithm for obtaining the lower limit value of the total command current is:

Wherein, k _p3 and k _i3 respectively represent the proportional coefficient and integral coefficient of the third PI controller; Indicates the charging current lower limit value, and Limited to [-3C-0.05C], u _dci represents the DC bus voltage, and u _{dci_max} represents the maximum voltage of the DC bus.

The present invention can achieve the following purposes by obtaining the upper limit value of the total command current and the lower limit value of the total command current. First, dynamically adjust the upper (lower) limit value of the charging (discharging) current; The command voltage u _{dco_ref} is set to 0.7 times u _{battery_norm} , the voltage control algorithm of the DC/DC control module outputs a negative current command (the voltage loop control algorithm is in a saturated state), that is, the discharge of the energy storage battery is controlled, and the DC bus voltage gradually increases. During the gradual increase of the bus voltage, the upper limit control module gradually exits saturation, and finally controls the DC bus voltage to stabilize the DC bus voltage at the highest voltage. During the discharge process of the energy storage battery, the terminal voltage of the energy storage battery gradually decreases, and the voltage control loop is gradually put into control, which can prevent the energy storage battery from being discharged too low; when the system is connected to the grid, the command voltage u _{dco_ref} is set to 1.05 times u _{battery_norm} , the voltage control algorithm of the DC/DC control module outputs a positive current command (the voltage loop control algorithm is in a saturated state), so that the bidirectional DC/DC converter charges the energy storage battery. As the charging process progresses, the terminal voltage of the energy storage battery Gradually increase, the voltage loop of the DC/DC control module gradually exits saturation, and puts into control to prevent overcharging of the energy storage battery. During the charging process of the energy storage battery, the DC bus voltage gradually decreases, and the lower limit control loop of the DC bus voltage gradually exits Saturation, and put into operation, to prevent excessive discharge of the DC bus terminal, so that the DC bus voltage is finally stabilized at u _dci _ _min

Further, the voltage loop control algorithm in step S1 of the present invention includes the voltage deviation between the terminal voltage of the energy storage battery pack and the command voltage, and the total command current is obtained through the fourth PI controller, wherein the control mathematical model of the voltage loop control algorithm is :

i _{dc_ref} = k _{p_4} (u _{dco_ref} -u _dco )+k _{i_4} ∫(u _{dco_ref} -u _dco )dt;

Wherein, u _{dco_ref} indicates the command voltage; k _{p_4} indicates the proportional coefficient of the fourth PI controller; k _{i_4} indicates the integral coefficient of the fourth PI controller; u _dco indicates the terminal voltage of the energy storage battery.

During the working process, when the grid-connected inverter is connected to the grid, u _{dco_ref} =1.05u _{battery_norm} ; when the grid-connected inverter is running off-grid, u _{dco_ref} =0.7u _{battery_norm} , and u _{battery_norm} is the rated voltage of the energy storage battery.

In addition, the current control algorithm in step S2 of the present invention includes comparing the command currents of the three circuits with the charging current of the energy storage battery pack to obtain the current deviation, and the current deviation is processed by the fifth PI controller to obtain the duty ratio of the three circuits, and the current control algorithm The control mathematical model of is:

Among them, d ₁ , d ₂ , d ₃ represent three duty ratios; k _p5 represents the proportional coefficient of the fifth PI controller; k _i5 represents the integral coefficient of the fifth PI controller; current i ₁ , i ₂ , i ₃ Indicates the charging current of the energy storage battery pack.

In order to facilitate the understanding of the working principle of the DC/DC control module of the present invention, the implementation steps of the control software of the DC/DC control module of the present invention will be introduced in detail below, please refer to FIG. 5 for details.

The first step: configure the function of the microprocessor (DSP28335);

The second step is to initialize the variables in the bidirectional DC/DC converter;

The third step is to enable the interrupt;

Step 4: Wait for the interrupt;

Step 5: If there is no interruption, communicate with the touch screen and the control system of the grid-connected inverter. After the communication is completed, return to step 4; if an interruption occurs, perform sampling and process the sampled data.

Step 6: Determine whether there is an overcurrent, overvoltage or overheating fault. If one of the above faults occurs in the system, the drive signal is blocked and the machine is shut down; if the above fault does not occur, judge whether the DC bus is undervoltage .

Step 7: If the DC bus is undervoltage, block the driving signal, and the bidirectional DC/DC converter enters the standby state; if the DC voltage is normal, execute the eighth step.

Step 8: If the inverter is running off-grid, set the command voltage of the bidirectional DC/DC converter to be 0.7 times u _{battery_norm} ; if the inverter is running in parallel with the grid, set the command voltage of the bidirectional DC/DC converter to be 1.05 times u _{battery_norm} ;

Step 9: Execute the lower limit control loop of the DC bus voltage;

Step 10: Execute the upper limit control loop of the DC bus voltage;

Step 11: Control the charging voltage to obtain the total command current;

Step 12: limit the total command current, and calculate three command currents;

Step 12: Control the charging current;

Step 13: Generate six PWM drive signals according to the duty cycle output by the current loop;

Step Fourteen: Restoring the site;

Step 15: Interrupt return;

The steps 4 to 15 are repeated every 208.3 microseconds.

In order to further describe the technical solution of the present invention in detail, please continue to refer to FIG. 4 , and the control method of the grid-connected inverter of the present invention will be introduced in detail below.

When the grid-connected inverter is connected to the grid, the command current switch is switched to the ① terminal, and the "MPPT-DC side voltage loop-inductance current loop" cascade control scheme is adopted. The specific control process is as follows:

First, the grid voltage [e _a e _b e _c ]′, grid-connected current [i _a i _b i _c ]′ and other physical quantities are subjected to Parker transformation to obtain the voltage column phasor [e _d e _q ]′ and the current column phasor [i _d i _q ]′, the Parker transformation formula is:

Secondly, sample the DC bus voltage and current, use the maximum power point tracking (MPPT) algorithm to track the maximum power of the photovoltaic module, and output the command voltage u _{dci_ref} on the DC side. The DC side voltage is controlled by a nonlinear proportional-integral control algorithm. The control algorithm is as follows:

i _{d_ref} =k _{v_pN} (u _{dci_ref} -u _dci )+k _{v_iN} ∫u _dci (u _{dci_ref} -u _dci )dt;

In the formula: k _{v_pN} and k _{v_iN} are the proportional coefficient and integral coefficient of the control algorithm NPI respectively, and u _dci is the DC side voltage.

Again, control the inductor current. In the synchronous rotating coordinate system, the PI algorithm is used to control i _d and i _q respectively, and the control algorithm is:

m _d =k _p2 (i _{d_ref} -i _d )+k _i2 ∫(i _{d_ref} -i _d )dt-ωLi _q +e _d ;

m _q =k _p2 (i _{q_ref} -i _q )+k _i2 ∫(i _{q_ref} -i _q )dt+ωLi _d +e _q ;

In the formula: k _p2 and k _i2 are the proportional coefficient and integral coefficient of the control algorithm PI_2 respectively.

Fourth, the duty cycle (m _d , m _q ) output by the current loop, the m _d and m _q are subjected to inverse Parker transformation to obtain the duty cycle ma , m _b and m _c in the abc coordinate axis _system , so The Parker inverse transformation is described as:

Finally, use the SVPWM algorithm to generate driving signals (G ₁ , G ₂ , G ₃ , G ₄ , G ₅ , G ₆ ), which are used to drive the switching tubes of the inverter.

⑵When the grid-connected inverter is running off-grid, the command current switch is switched to ②, and the "AC voltage loop-inductance current loop" cascade control scheme is adopted.

First, the output voltage [u _a u _b u _c ]′, the inductor current [i _a i _b i _c ]′ and other physical quantities are subjected to Parker transformation, and the transformation process is as follows:

Secondly, the "AC voltage loop-inductance current loop" cascade control scheme is adopted in the synchronous rotating coordinate system, and the voltage control algorithm is:

i _{d_ref} =k _p1 (u _{d_ref} -u _d )+k _i1 ∫(u _{d_ref} -u _d )dt

i _{q_ref} ＝k _p1 (0-u _q )+k _i1 ∫(0-u _q )dt

In the formula, u _{d_ref} is the command voltage of the d-axis, 0 is the command voltage of the q-axis, k _p1 is the proportional coefficient of the PI_1 algorithm, and k _i1 is the integral coefficient of the PI_1 algorithm.

Fourth, the current control scheme and its control algorithm during off-grid operation are completely consistent with the current control scheme and its control algorithm during grid-connected operation, and the algorithm for generating drive signals is also consistent, so I won’t repeat them here.

In order to facilitate the understanding of the technical solution of the present invention, the following will introduce the implementation steps of the photovoltaic inverter control software of the present invention, specifically:

The first step: configure the function of the microprocessor (DSP28335);

The second step is to initialize the variables in the photovoltaic inverter control system;

The third step is to enable the interrupt;

Step 4: Wait for the interrupt;

Step 5: If no interruption occurs, communicate with the touch screen and the control system of the bidirectional DC/DC converter; if the communication ends, return to step 4; if an interruption occurs, execute step 6;

Step 6: Sampling and processing the sampled data.

Step 7: Determine whether there is an overcurrent, overvoltage or overheating fault. If one of the faults occurs in the system, the drive signal is blocked and the machine is shut down; if the fault does not occur, execute the eighth step.

Step 8: Determine whether the DC bus is undervoltage. If the DC bus is undervoltage, block the drive signal and enter the standby state; if the DC bus is normal, execute the ninth step;

Step 9: Perform Parker transformation on the AC voltage and current to obtain the values of each physical quantity in the synchronous rotating coordinate system;

Step 10: Determine whether the photovoltaic inverter is connected to the grid. If it is connected to the grid, execute the MPPT algorithm to control the DC bus voltage; if it is operated off-grid, control the AC output voltage of the photovoltaic inverter;

Step 11: Control the inductance current of the photovoltaic inverter, output duty cycle m _d , m _q ;

Step 12: Execute the SVPWM algorithm and output 6 drive signals (PWM);

Step 13: Enable the output of six PWM drive signals;

Step 14: Resume the scene and return from the interruption.

The steps 4 to 14 are repeated every 208.3 microseconds, please refer to FIG. 6 for details.

Finally, the method of the present application is only a preferred embodiment, and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A photovoltaic-energy storage conversion system, comprising a bidirectional DC/DC converter and a grid-connected inverter, characterized in that the system comprises: a DC/DC for controlling the bidirectional DC/DC converter a control module and an inverter control module for controlling the grid-connected inverter, The DC/DC control module includes a voltage control module for obtaining a total command current, a current control module electrically connected to the voltage control module for obtaining three-way duty ratios, and a current control module for obtaining the bidirectional DC/DC A comparison module for switching control signals of the DC converter, the output terminal of the current control module is electrically connected to the comparison module. 2. A photovoltaic-energy storage conversion system according to claim 1, characterized in that, the system further includes an energy storage battery pack and a photovoltaic module, and the photovoltaic module communicates with the bidirectional DC/DC converter through the The energy storage battery pack is connected; one end of the grid-connected inverter is connected to the photovoltaic module, and the other end is connected to the grid. 3. A photovoltaic-energy storage conversion system according to claim 2, wherein the voltage control module is used to compare the terminal voltage of the energy storage battery pack with the command voltage to obtain the voltage deviation, and based on The voltage loop control algorithm obtains the total command current. 4. A control method for a photovoltaic-energy storage conversion system, characterized in that: Obtain the control signal of the bidirectional DC/DC converter based on the terminal voltage of the energy storage battery pack; Based on the command voltage of the q-axis and the d-axis, the DC bus voltage and current, the control signal of the grid-connected inverter is obtained. 5. The control method of a photovoltaic-energy storage conversion system according to claim 4, wherein the control signal acquisition method of the bidirectional DC/DC converter comprises: S1. Obtain the voltage deviation by comparing the terminal voltage of the energy storage battery pack with the command voltage, and obtain the total command current based on the voltage loop control algorithm; S2. Obtain the three-way sub-instruction current based on the total instruction current, and obtain the three-way duty cycle respectively through the current control algorithm; S3. Based on the duty ratios of the three channels, the switching control signals of the DC/DC converter are obtained by comparing them with the carrier wave respectively. 6. The control method of a photovoltaic-energy storage conversion system according to claim 5, wherein the step S1 further comprises: Based on the minimum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage and the given DC bus voltage minimum value, obtaining a voltage deviation value, and obtaining the upper limit value of the total command current through the third PI controller; Based on the maximum value of the DC bus voltage and the given DC bus voltage, comparing the DC bus voltage with the maximum value of the given DC bus voltage to obtain a voltage deviation value, and obtaining a lower limit value for limiting the total command current through the third PI controller . 7. The control method of a photovoltaic-energy storage conversion system as claimed in claim 6, wherein the control mathematical model for obtaining the upper limit value of the total command current is: ${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; arg</span>}\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Integral;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ;</span>$ Wherein, k _p3 represents the proportional coefficient of the third PI controller; and k _i3 represents the integral coefficient of the third PI controller; Indicates the upper limit value of the charging current, and Limited to [1.5C 0.05C], u _dci represents the DC bus voltage, u _{dci_min} represents the minimum voltage of the DC bus, and C represents the capacity of the energy storage battery. 8. The control method of a photovoltaic-energy storage conversion system as claimed in claim 6, wherein the control mathematical model for obtaining the minimum current value of the total command current is: ${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; arg</span>}\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Integral;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ;</span>$ Among them, k _p3 represents the proportional coefficient of the third PI controller; k _i3 represents the integral coefficient of the third PI controller; Indicates the lower limit value of the charging current, and Limited to [-3C-0.05C], u _{dci represents the voltage at both ends of the DC bus, u dci_max represents} the maximum voltage of the DC bus, and C represents the capacity of the energy storage battery. 9. The control method of a photovoltaic-energy storage conversion system according to claim 5, wherein the voltage loop control algorithm in step S1 includes passing the first step based on the voltage deviation between the terminal voltage of the energy storage battery pack and the command voltage. The four PI controllers obtain the total command current, and the control mathematical model of the voltage loop control algorithm is: i _{dc_ref} = k _{p_4} (u _{dco_ref} -u _dco )+k _{i_4} ∫(u _{dco_ref} -u _dco )dt; Wherein, u _{dco_ref} indicates the command voltage; k _{p_4} indicates the proportional coefficient of the fourth PI controller; k _{i_4} indicates the integral coefficient of the fourth PI controller; u _dco indicates the terminal voltage of the energy storage battery. 10. The control method of a photovoltaic-energy storage conversion system as claimed in claim 5, wherein the current control algorithm in step S2 includes: comparing the three-way sub-command current with the charging current of the energy storage battery pack, Obtain the current deviation, obtain the three-way duty ratio through the fifth PI controller, and the control mathematical model of the current control algorithm is: ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; \&Integral;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; \&Integral;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; \&Integral;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ;</span>$ Among them, d ₁ , d ₂ , d ₃ represent three duty ratios; k _p5 represents the proportional coefficient of the fifth PI controller; k _i5 represents the integral coefficient of the fifth PI controller; current i ₁ , i ₂ , i ₃ Indicates the charging current of the energy storage battery pack.