Inverter parallel system and zero-sequence current control method thereof

Abstract

The present invention discloses an inverter parallel system and a zero-sequence current control method thereof. The inverter parallel system comprises a plurality of inverters which are connected in parallel and connected to a load; the inverter parallel system also comprises a first current acquisition unit, a first voltage acquisition unit, and a drive control unit. The inverter comprises a main control unit, and the drive control unit comprises a reference value acquisition unit, a first controller, a second controller, and a coordinate conversion unit. Communication transmission is performed between the inverters, and the average output current DC component of each inverter is used as a reference quantity of the zero-sequence current loop of the current inverter to effectively suppress the zero-sequence circulating current and realize current sharing control under different load conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of zero-sequence current control of inverters, and in particular to an inverter parallel system and a zero-sequence current control method thereof. Background Art

[0002] Energy storage systems are an important part of the power production process. With the continuous advancement of power conversion technology, the use of inverters is of great significance to the construction of smart grids.

[0003] When the energy storage system is charging and discharging, it is necessary to ensure that the inverter is in the current sharing control state. When a single inverter performs current sharing control, the following is generally used: Figure 1 The control method shown in the figure directly applies the output of the zero-sequence current loop to the modulation wave, or superimposes the output of the zero-sequence current loop on the output of the voltage loop, and then adjusts the modulation wave through the current loop. In some complex application scenarios, multiple inverters need to be connected in parallel. When supplying power to the load, it is necessary to ensure that all inverters are in a current-sharing control state to ensure the stability and reliability of the load power supply. However, due to the differences in the output parameters of each inverter and the influence of the output voltage of other parallel inverters, it is easy to generate zero-sequence circulating current in the parallel system, affecting the stable operation of the inverter parallel system. Since the zero-sequence circulating current is reflected in the rectifier of each inverter in the form of zero-sequence current, the control of zero-sequence current is the key to suppressing the zero-sequence circulating current.

[0004] If the above single-machine current sharing control method is adopted, the control effect is poor. If there is no zero-sequence current loop but only a zero-sequence voltage loop, a small zero-sequence voltage may cause a large zero-sequence current (related to the size of the inverter internal resistance and the line impedance). Therefore, the conventional practice is to set the reference of the zero-sequence current loop to 0, which can be used for current sharing control of symmetrical loads. However, for half-wave loads or asymmetrical loads, directly setting it to 0 will cause zero-crossing distortion of the current, affecting the smooth operation of the inverter parallel system. Summary of the invention

[0005] In order to overcome at least one defect existing in the inverter current sharing control method in the prior art, the present invention proposes an inverter parallel system and a zero-sequence current control method thereof which can realize current sharing control under different load conditions.

[0006] The present invention is mainly achieved through the following technical solutions:

[0007] The inverter parallel system provided by the present invention comprises a plurality of inverters connected in parallel and connected to a load; the inverter parallel system further comprises a first current acquisition unit, a first voltage acquisition unit, and a drive control unit; the inverter comprises a main control unit, the drive control unit comprises a reference value acquisition unit, a first controller, a second controller, and a coordinate conversion unit, and the main control units of the plurality of inverters are connected via a signal transmission unit;

[0008] The first current acquisition unit is used to acquire the instantaneous value Io of the output current of the current inverter in real time within a sampling period;

[0009] The first voltage acquisition unit is used to acquire the instantaneous value Vo of the output voltage of the current inverter in real time within a sampling period;

[0010] The main control unit is used to obtain the output current DC component Ia' of other inverters, and obtain the output current DC component Ia and output voltage DC component Va of the current inverter according to the output current instantaneous value Io and output voltage instantaneous value Vo collected by the current inverter, and calculate the average output current DC component of each inverter. ;

[0011] A signal transmission unit, used for sending the output current DC component Ia of the current inverter to other inverters, and receiving the output current DC component Ia′ of other inverters;

[0012] A reference value acquisition unit, used to acquire the instantaneous reference value Iref of the current of the inverter under multi-loop control;

[0013] The first controller is used to convert the average output current DC component The difference is made with the obtained DC component Ia of the output current of the current inverter, and the zero-sequence current compensation △I output by the zero-sequence current loop is obtained through PI adjustment;

[0014] The second controller is used to make a difference between the zero-sequence voltage target value Vb stored in the main control unit of the current inverter and the obtained output voltage DC component Va of the corresponding inverter, obtain the zero-sequence voltage compensation amount △U output by the zero-sequence voltage loop through PI adjustment, and superimpose it with the zero-sequence current compensation amount △I output by the zero-sequence current loop, and output the superimposed amount;

[0015] The coordinate conversion unit is used to transform the acquired instantaneous current reference value Iref and the superposition amount through the dq / abc coordinate system to obtain the modulation wave driving signal of the power unit of the current inverter.

[0016] The multi-loop control includes: control based on a power loop, an effective value voltage loop, a voltage loop, and a current loop.

[0017] Furthermore, the inverter includes a single-phase inverter module, a first inductor, a second inductor and a first capacitor, the single-phase inverter module includes at least one power unit, the single-phase inverter module, the first inductor, the first capacitor and the second inductor are connected in sequence to form a loop, the first capacitor is connected in parallel at both ends of the load, and the two ends of the first capacitor in several of the inverters are connected in parallel to connect to the same load.

[0018] Furthermore, the inverter parallel system further includes a second current acquisition unit, and the reference value acquisition unit includes a third controller, a fourth controller, a fifth controller and a given acquisition unit;

[0019] The second current acquisition unit is used to acquire the instantaneous current value IL1 of the first inductor of the current inverter in real time within a sampling period;

[0020] The given acquisition unit is used to acquire the given effective value Vref of the current inverter voltage;

[0021] The main control unit is further used to obtain the current effective value Vrms of the output voltage of the inverter, the current instantaneous value Vo of the output voltage of the inverter, and the current instantaneous value IL1 of the current of the first inductor of the inverter;

[0022] The third controller takes the difference between the given effective value Vref of the inverter voltage and the effective value Vrms of the current inverter output voltage as the voltage adjustment amount of the voltage reference value Vg stored in the main control unit of the inverter, and obtains the voltage amplitude output by the effective value voltage loop by PI adjustment of the adjusted voltage reference value;

[0023] The fourth controller makes a difference between the voltage amplitude and the instantaneous value Vo of the output voltage of the current inverter, and obtains the voltage outer loop output of the voltage loop through PI regulation;

[0024] The fifth controller combines the voltage outer loop output with the current instantaneous value The instantaneous reference value Iref of the current loop output is obtained by making a difference and adjusting it through PI.

[0025] Further, the given acquisition unit includes a sixth controller;

[0026] The signal transmission unit is also used to send the output power Po of the current inverter to other inverters, and transmit the output power Po´ of other inverters;

[0027] The main control unit is also used to obtain the output power Po of the current inverter, receive the output power Po' of other inverters, and calculate the average output power of each inverter. ;

[0028] The sixth controller is used to convert the average output power The voltage Vref output by the power loop is obtained by subtracting the obtained current inverter output power Po and adjusting it through PI.

[0029] Furthermore, the signal transmission unit is a CAN bus.

[0030] The present invention also provides a zero-sequence current control method for an inverter parallel system, which is applicable to the inverter parallel system, wherein the inverter parallel system comprises a plurality of inverters connected in communication, wherein the inverter comprises a single-phase inverter module, a first inductor, a second inductor and a first capacitor, wherein the single-phase inverter module comprises at least one power unit, wherein the single-phase inverter module, the first inductor, the first capacitor and the second inductor are sequentially connected to form a loop, wherein the first capacitor is connected in parallel at both ends of a load, and both ends of the first capacitors in the plurality of inverters are connected in parallel to access the same load;

[0031] The zero-sequence current control method comprises performing the following operations on each inverter:

[0032] A multi-loop control method is adopted to obtain the instantaneous reference value Iref of the current of the inverter to be controlled;

[0033] According to the sampling period, the instantaneous value of the output current Io and the instantaneous value of the output voltage Vo of the current inverter are collected in real time;

[0034] According to the instantaneous value of the output current Io and the instantaneous value of the output voltage Vo of the current inverter, the output current DC component Ia and the output voltage DC component Va of the current inverter are respectively obtained;

[0035] Receive the DC component Ia´ of the output current of other inverters transmitted;

[0036] Calculate the average DC component of the output current of each inverter ;

[0037] The average output current DC component The difference is made with the obtained DC component Ia of the output current of the current inverter, and the zero-sequence current compensation △I output by the zero-sequence current loop is obtained through PI adjustment;

[0038] The zero-sequence voltage target value Vb stored in the main control unit of the current inverter is subtracted from the DC component Va of the output voltage of the corresponding inverter, and the zero-sequence voltage compensation △U output by the zero-sequence voltage loop is obtained through PI adjustment, and superimposed with the zero-sequence current compensation △I output by the zero-sequence current loop;

[0039] The above superposition amount and the obtained instantaneous reference value of current Iref are transformed through the dq / abc coordinate system to obtain the modulation wave driving signal of the power unit of the current inverter, so as to realize the current equalization output to the load.

[0040] Furthermore, obtaining the instantaneous current reference value Iref includes the following steps:

[0041] The instantaneous current value IL1 of the first inductor of the current inverter is collected in real time during the sampling period;

[0042] Obtain the current effective value of the inverter voltage Vref and the current effective value of the inverter output voltage Vrms;

[0043] The voltage effective value given Vref of the inverter is subtracted from the current output voltage effective value Vrms of the inverter as the voltage adjustment amount of the voltage reference value Vg stored in the main control unit of the inverter, and the adjusted voltage reference value is adjusted by PI to obtain the voltage amplitude output by the effective value voltage loop;

[0044] The voltage amplitude is subtracted from the instantaneous value Vo of the output voltage of the current inverter, and the voltage outer loop output of the voltage loop is obtained through PI regulation;

[0045] The voltage outer loop output and the instantaneous current value The instantaneous reference value Iref of the current loop output is obtained by making a difference and adjusting it through PI.

[0046] Furthermore, obtaining the instantaneous voltage reference value includes the following steps:

[0047] Get the output power Po of the current inverter and receive the output power Po´ of other inverters;

[0048] Calculate the average output power of each inverter ;

[0049] The average output power The voltage Vref output by the power loop is obtained by subtracting the obtained current inverter output power Po and adjusting it through PI.

[0050] Furthermore, the zero-sequence voltage target value Vb is set to 0.

[0051] Furthermore, the modulation wave is SPWM or SVPWM.

[0052] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0053] The inverter parallel system and zero-sequence current control method provided by the present invention use the average output current DC component of each inverter as the reference amount of the zero-sequence current loop, superimpose the zero-sequence voltage compensation amount and the zero-sequence current compensation amount, and transform the superimposed amount and the current instantaneous reference value Iref through the dq0 / abc coordinate system, and adjust the modulation wave drive signal of the power unit of the inverter so that the output current of the inverter is adjusted to the required value. Since the busbars of each inverter are independent of each other, there is no high-frequency circulating current, which can offset the low-frequency circulating current. When the load is unknown, it can adapt to the current sharing control in various situations such as symmetrical load, half-wave load or asymmetrical load, so that the inverter parallel system can run smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 It is a block diagram of zero-sequence current control of an existing single inverter;

[0056] Figure 2 It is a structural principle block diagram of a single inverter of the inverter parallel system provided by an embodiment of the present invention;

[0057] Figure 3 is a circuit schematic diagram of the inverters connected to each other provided by an embodiment of the present invention;

[0058] Figure 4 is a flow chart of a zero-sequence current control method of an inverter parallel system provided by an embodiment of the present invention;

[0059] Figure 5 It is a control block diagram of a zero-sequence current control method of an inverter parallel system provided by an embodiment of the present invention.

[0060] The reference numerals are as follows:

[0061] 1. Inverter, 2. First current acquisition unit, 3. First voltage acquisition unit, 4. Drive control unit, 5. Main control unit, 6. Reference value acquisition unit, 7. First controller, 8. Second controller, 9. Coordinate conversion unit, 10. Signal transmission unit, 11. Single-phase inverter module, 12. Second current acquisition unit, 13. Third controller, 14. Fourth controller, 15. Fifth controller, 16. Given acquisition unit, 20. Load. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the present invention, and thus to more clearly define the scope of the present invention, the present invention is described in detail with respect to some specific embodiments of the present invention. It should be noted that the following are only some specific implementation methods of the present invention, which are only part of the embodiments of the present invention, wherein the specific and direct description of the relevant structure is only for the convenience of understanding the present invention, and each specific feature does not naturally and directly limit the scope of implementation of the present invention. The conventional selection and replacement made by those skilled in the art under the guidance of the present invention should be regarded as within the scope of the present invention.

[0063] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0064] Example 1

[0065] like Figure 2 As shown, the present invention provides an inverter parallel system, the inverter parallel system includes a plurality of inverters 1 connected in parallel and connected to a load 20, wherein the number of inverters 1 is set to A, A≥2, and when paralleling, one of the inverters 1 needs to be set as the master. The inverter parallel system also includes a first current acquisition unit 2, a first voltage acquisition unit 3, a second current acquisition unit 12 and a drive control unit 4, the drive control unit 4 includes a reference value acquisition unit 6 for acquiring a current instantaneous reference value Iref of the inverter 1 under multi-loop control, a first controller 7, a second controller 8 and a coordinate conversion unit 9, the reference value acquisition unit 6 includes a third controller 13, a fourth controller 14, a fifth controller 15 and a given acquisition unit 16 for acquiring a given voltage effective value Vref of the current inverter 1, and the given acquisition unit 16 includes a sixth controller.

[0066] like Figure 3 As shown, the inverter 1 includes a main control unit 5, a single-phase inverter module 11, a first inductor L1, a second inductor L2 and a first capacitor C1. The single-phase inverter module 11 includes at least one power unit. The single-phase inverter module 11, the first inductor L1, the first capacitor C1 and the second inductor L2 are connected in sequence to form a loop. The first capacitor C1 is connected in parallel at both ends of the load 20. The two ends of the first capacitor C1 in several inverters 1 are connected in parallel to access the same load 20.

[0067] The connection relationship between the inverter parallel systems is described by taking one of the inverters 1 as an example.

[0068] The first current acquisition unit 2, the first voltage acquisition unit 3, the second current acquisition unit 12, the first controller 7, the second controller 8, the third controller 13, the fourth controller 14, the fifth controller 15, and the sixth controller are respectively connected to the main control unit 5, the sixth controller, the third controller 13, the fourth controller 14, the fifth controller 15, the coordinate conversion unit 9 and the single-phase inverter module 11 are connected in sequence, the first controller 7 is connected to the second controller 8, and the second controller 8 is connected to the coordinate conversion unit 9.

[0069] The main control units 5 of several inverters 1 are connected through a signal transmission unit 10. The signal transmission unit 10 is a CAN bus. In addition to the CAN communication method, serial communication and optical fiber communication can also be used, but the transmission rate is slow or the cost is high. It is necessary to determine the best method of the signal transmission unit 10 according to the application scenario. In wired short-distance transmission, the CAN communication method is the best. The signal transmission unit 10 is used to send the output current DC component Ia and output power Po of the current inverter 1 to other inverters 1, and transmit the output current DC component Ia' and output power Po' of other inverters 1.

[0070] The first current acquisition unit 2 is used to collect the instantaneous value of the output current Io of the current inverter 1 in real time within the sampling period T. The second current acquisition unit 12 is used to collect the instantaneous value of the current of the first inductor L1 of the current inverter 1 in real time within the sampling period T. .

[0071] The first voltage acquisition unit 3 is used to acquire the instantaneous value Vo of the output voltage of the current inverter 1 in real time within the sampling period T.

[0072] The main control unit 5 is used to obtain the output power Po of the current inverter 1, receive the output power Po' of other inverters 1, and calculate the average output power of each inverter 1 ; It is also used to obtain the current output voltage effective value Vrms of the inverter 1, the current output voltage instantaneous value Vo of the inverter 1, and the current instantaneous current value of the first inductor L1 of the inverter 1 It is also used to obtain the output current DC component Ia' of other inverters 1, and obtain the output current DC component Ia and output voltage DC component Va of the current inverter 1 according to the output current instantaneous value Io and output voltage instantaneous value Vo collected by the current inverter 1, and obtain the average output current DC component of each inverter 1 .

[0073] In this embodiment, the output power Po of the inverter 1 is calculated based on the instantaneous value of the output current Io and the instantaneous value of the output voltage Vo. The average output power The total output power of all inverters 1 is divided by the number of inverters A. The output voltage effective value Vrms is calculated based on the instantaneous value of the output voltage Vo. The average output current DC component The total DC component of the output current of all inverters 1 is divided by the number of inverters A. The calculation method adopts the existing conventional technology and will not be repeated here.

[0074] For a three-phase system, the zero-sequence current includes the zero-sequence current DC component and the zero-sequence current higher harmonic component, and the zero-sequence voltage includes the zero-sequence voltage DC component and the zero-sequence voltage higher harmonic component. For a single-phase system, the zero-sequence current is the zero-sequence current DC component, and the zero-sequence voltage is the zero-sequence voltage DC component. Therefore, the output current DC component Ia is the output current instantaneous value Io, and the output voltage DC component Va is the output voltage instantaneous value Vo.

[0075] Due to the inconsistency of device parameters in the inverter (such as inconsistent voltage drops of power tubes, inconsistent characteristics of internal series bus capacitors, etc.), zero-sequence voltage DC components will be generated, and zero-sequence voltage DC components will damage electrical equipment, especially transformer loads, which will easily cause transformer saturation, so it is necessary to control the zero-sequence voltage DC component. Although the zero-sequence voltage in the system is very small after zero-sequence voltage control, there will still be a certain zero-sequence voltage DC component (mainly determined by the size of the system internal resistance), so it is also necessary to control the zero-sequence current DC component, and treat the inherent zero-sequence current DC component of the system load (for example, a sinusoidal voltage with a half-wave load will have an inherent zero-sequence DC component) and the zero-sequence current DC component generated by the zero-sequence voltage differently. Only the zero-sequence current DC component generated by the zero-sequence voltage will be controlled, while the inherent zero-sequence current DC component of the load will have little effect, avoiding a large DC component in the output voltage.

[0076] The sixth controller is used to convert the average output power The voltage is subtracted from the output power Po of the current inverter 1, and the voltage effective value Vref output by the power loop is obtained through PI adjustment. The third controller 13, subtracts the voltage effective value Vref of the inverter 1 from the current output voltage effective value Vrms of the inverter 1, as the voltage adjustment amount of the voltage reference value Vg stored in the main control unit 5 of the inverter 1, and the adjusted voltage reference value is subjected to PI adjustment to obtain the voltage amplitude output by the effective value voltage loop. The fourth controller 14, subtracts the voltage amplitude from the instantaneous value Vo of the output voltage of the current inverter 1, and obtains the voltage outer loop output of the voltage loop through PI adjustment. The fifth controller 15, compares the voltage outer loop output with the instantaneous value Vo of the current The instantaneous reference value Iref of the current loop output is obtained by making a difference and adjusting it through PI.

[0077] The first controller 7 is used to convert the average output current DC component The zero-sequence current compensation value △I output by the zero-sequence current loop is obtained by subtracting the zero-sequence voltage target value Vb stored in the main control unit 5 of the current inverter 1 from the obtained output voltage DC component Va of the current inverter 1, and obtaining the zero-sequence voltage compensation value △U output by the zero-sequence voltage loop through PI adjustment, and superimposing it with the zero-sequence current compensation value △I output by the zero-sequence current loop, and outputting the superimposed amount, wherein the zero-sequence reference voltage is set to 0. The coordinate conversion unit 9 is used to transform the obtained current instantaneous reference value Iref and the above-mentioned superimposed amount through the dq0 / abc coordinate system to obtain the modulation wave drive signal of the power unit of the current inverter 1.

[0078] like Figure 4-5 As shown, the present invention also provides a zero-sequence current control method for an inverter parallel system, which is applicable to the above-mentioned inverter parallel system, wherein the inverter parallel system includes a plurality of inverters 1 connected in communication, wherein the inverter 1 includes a single-phase inverter module, a first inductor, a second inductor and a first capacitor, wherein the single-phase inverter module, the first inductor, the first capacitor and the second inductor are sequentially connected to form a loop, wherein the first capacitor is connected in parallel at both ends of a load 20, and both ends of the first capacitors in a plurality of inverters 1 are connected in parallel to access the same load 20. The zero-sequence current control method includes performing the following operations on each inverter 1:

[0079] The instantaneous current value IL1 of the first inductor L1 of the current inverter 1, the instantaneous output current value Io and the instantaneous output voltage value Vo are collected in real time within the sampling period T. According to the current Io and Vo, the output current DC component Ia and the output voltage DC component Va of the current inverter 1 are calculated respectively, and the output power Po and the output voltage effective value Vrms of the current inverter 1 are obtained. The output power Po´ and the output current DC component Ia´ of other inverters 1 are received and transmitted, and the average output power of each inverter 1 is obtained according to Po and Po´. , according to Ia and Ia´, calculate the average output current DC component of each inverter 1 ;

[0080] A multi-loop control method is adopted to obtain the instantaneous current reference value Iref of the inverter 1 to be controlled; the multi-loop control includes: control based on a power loop, an effective value voltage loop, a voltage loop, and a current loop, including the following steps:

[0081] The average output power Subtract the obtained output power Po of the current inverter 1, and obtain the voltage effective value Vref output by the power loop through PI regulation;

[0082] The voltage effective value Vref is subtracted from the current output voltage effective value Vrms of the inverter 1 to be used as the voltage adjustment amount of the voltage reference value Vg stored in the main control unit 5 of the inverter 1, and the adjusted voltage reference value is PI-regulated to obtain the voltage amplitude output by the effective value voltage loop;

[0083] The voltage amplitude is subtracted from the instantaneous value Vo of the output voltage of the current inverter 1, and the voltage outer loop output of the voltage loop is obtained through PI regulation;

[0084] The voltage outer loop output and the instantaneous current value Make a difference, and obtain the instantaneous reference value Iref of the current loop output through PI regulation;

[0085] The average output current DC component The obtained DC component Ia of the output current of the current inverter 1 is subtracted, and the zero-sequence current compensation amount △I output by the zero-sequence current loop is obtained through PI adjustment;

[0086] The zero-sequence voltage target value Vb stored in the main control unit 5 of the current inverter 1 is subtracted from the DC component Va of the output voltage of the corresponding inverter 1, and the zero-sequence voltage compensation amount △U output by the zero-sequence voltage loop is obtained through PI adjustment, and is superimposed with the zero-sequence current compensation amount △I output by the zero-sequence current loop. The above-mentioned superposition amount and the obtained current instantaneous reference value Iref are transformed through the dq0 / abc coordinate system to obtain the modulation wave drive signal of the power unit of the current inverter 1, so as to achieve current sharing output to the load 20.

[0087] In this embodiment, the zero-sequence voltage target value Vb is set to 0, and the modulation wave is SPWM or SVPWM. Among them, the output power Po, average output power, output voltage effective value Vrms and average output current DC component of the inverter 1 are The calculation method of has been explained in the parallel system and will not be repeated here.

[0088] A multi-loop control method is adopted, a power loop is added before the effective value voltage loop, the zero-sequence current loop is superimposed on the zero-sequence voltage loop, and the zero-sequence current loop and the instantaneous current reference value Iref output by the current loop act together on the power unit of inverter 1 to control the zero-sequence current and zero-sequence voltage of the inverter, so that the zero-sequence voltage DC component of the current inverter is close to 0, and the zero-sequence voltage DC component of the current inverter is close to the average value of the zero-sequence voltage DC components of each inverter.

[0089] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. An inverter parallel system, It is characterized in that The inverter parallel system comprises a plurality of inverters (1) connected in parallel and connected to a load (20); the inverter parallel system further comprises a first current acquisition unit (2), a first voltage acquisition unit (3), and a drive control unit (4); the inverter (1) comprises a main control unit (5); the drive control unit (4) comprises a reference value acquisition unit (6), a first controller (7), a second controller (8), and a coordinate conversion unit (9); the main control units (5) of the plurality of inverters (1) are connected via a signal transmission unit (10); A first current acquisition unit (2) is used to acquire the instantaneous value Io of the output current of the current inverter (1) in real time within a sampling period; A first voltage acquisition unit (3) is used to acquire the instantaneous value Vo of the output voltage of the current inverter (1) in real time within a sampling period; The main control unit (5) is used to obtain the output current DC component Ia' of other inverters (1), and obtain the output current DC component Ia and the output voltage DC component Va of the current inverter (1) according to the output current instantaneous value Io and the output voltage instantaneous value Vo collected by the current inverter (1), and calculate the average output current DC component of each inverter (1). A signal transmission unit (10) is used to send the output current DC component Ia of the current inverter (1) to other inverters (1), and receive the output current DC component Ia′ of other inverters (1); A reference value acquisition unit (6), used for acquiring an instantaneous current reference value Iref of the inverter (1) under multi-loop control; The first controller (7) is used to convert the average output current DC component The obtained DC component Ia of the output current of the current inverter (1) is subtracted, and the zero-sequence current compensation amount △I output by the zero-sequence current loop is obtained through PI adjustment; The second controller (8) is used to make a difference between the zero-sequence voltage target value Vb stored and set in the main control unit (5) of the current inverter (1) and the obtained output voltage DC component Va of the corresponding inverter (1), obtain a zero-sequence voltage compensation amount △U output by the zero-sequence voltage loop through PI regulation, and superimpose it with the zero-sequence current compensation amount △I output by the zero-sequence current loop, and output the superimposed amount; The coordinate conversion unit (9) is used to transform the acquired instantaneous current reference value Iref and the superposition amount through the dq0 / abc coordinate system to obtain the modulation wave driving signal of the power unit of the current inverter (1).

2. The inverter parallel system according to claim 1, Features: The inverter (1) comprises a single-phase inverter module (11), a first inductor, a second inductor and a first capacitor; the single-phase inverter module (11) comprises at least one power unit; the single-phase inverter module (11), the first inductor, the first capacitor and the second inductor are connected in sequence to form a loop; the first capacitor is connected in parallel at both ends of a load (20); and the two ends of the first capacitors in a plurality of the inverters (1) are connected in parallel to access the same load (20).

3. The inverter parallel system according to claim 2, Features: The inverter parallel system further comprises a second current acquisition unit (12), and the reference value acquisition unit (6) comprises a third controller (13), a fourth controller (14), a fifth controller (15) and a given acquisition unit (16); The second current acquisition unit (12) is used to acquire the instantaneous current value I of the first inductor of the current inverter (1) in real time within a sampling period. L1 ; The given acquisition unit (16) is used to acquire the given effective value Vref of the current voltage of the inverter (1); The main control unit (5) is also used to obtain the current effective value Vrms of the output voltage of the inverter (1), the current instantaneous value Vo of the output voltage of the inverter (1), and the current instantaneous value I of the current of the first inductor of the inverter (1). L1 ; The third controller (13) calculates the difference between the given effective value Vref of the voltage of the inverter (1) and the effective value Vrms of the output voltage of the current inverter (1), and uses the difference as the voltage adjustment amount of the voltage reference value Vg stored and set in the main control unit (5) of the inverter (1), and obtains the voltage amplitude output by the effective value voltage loop by subjecting the adjusted voltage reference value to PI adjustment; The fourth controller (14) performs a PI adjustment to obtain a voltage outer loop output of the voltage loop by subtracting the voltage amplitude from the instantaneous value Vo of the output voltage of the current inverter (1); The fifth controller (15) combines the voltage outer loop output with the current instantaneous value I L1 The instantaneous reference value Iref of the current loop output is obtained by making a difference and adjusting it through PI.

4. The inverter parallel system according to claim 3, Features: The given acquisition unit (16) includes a sixth controller; The signal transmission unit (10) is also used to send the output power Po of the current inverter (1) to other inverters (1), and transmit the output power Po′ of other inverters (1); The main control unit (5) is also used to obtain the output power Po of the current inverter (1), receive the output power Po' of other inverters (1), and calculate the average output power of each inverter (1). The sixth controller is used to convert the average output power The obtained current output power Po of the inverter (1) is subtracted and the effective voltage value Vref output by the power loop is obtained through PI regulation.

5. The inverter parallel system according to claim 1, Features: The signal transmission unit (10) is a CAN bus.

6. A zero-sequence current control method for an inverter parallel system, applicable to the inverter parallel system according to any one of claims 1 to 5, It is characterized in that The inverter parallel system comprises a plurality of inverters (1) connected in communication, the inverter (1) comprising a single-phase inverter module (11), a first inductor, a second inductor and a first capacitor, the single-phase inverter module (11) comprising at least one power unit, the single-phase inverter module (11), the first inductor, the first capacitor and the second inductor are sequentially connected to form a loop, the first capacitor is connected in parallel to both ends of a load (20), and both ends of the first capacitors in the plurality of inverters (1) are connected in parallel to access the same load (20); The zero-sequence current control method comprises performing the following operations on each inverter (1): A multi-loop control method is used to obtain an instantaneous current reference value Iref of the inverter (1) to be controlled; According to the sampling period, the instantaneous value of the output current Io and the instantaneous value of the output voltage Vo of the current inverter (1) are collected in real time; According to the instantaneous value of the output current Io and the instantaneous value of the output voltage Vo of the current inverter (1), the output current DC component Ia and the output voltage DC component Va of the current inverter (1) are respectively obtained; receiving the output current DC component Ia′ of the other inverter (1) transmitted; Calculate the average DC component of the output current of each inverter (1) The average output current DC component The obtained DC component Ia of the output current of the current inverter (1) is subtracted, and the zero-sequence current compensation amount △I output by the zero-sequence current loop is obtained through PI adjustment; The zero-sequence voltage target value Vb stored in the main control unit (5) of the current inverter (1) is subtracted from the DC component Va of the output voltage of the corresponding inverter (1), and a zero-sequence voltage compensation amount △U output by the zero-sequence voltage loop is obtained through PI regulation, and the zero-sequence current compensation amount △I output by the zero-sequence current loop is superimposed; The above-mentioned superposition amount and the obtained instantaneous current reference value Iref are transformed through the dq0 / abc coordinate system to obtain the modulation wave drive signal of the power unit of the current inverter (1), so as to realize the current equalization output to the load (20).

7. The zero-sequence current control method of the inverter parallel system according to claim 6, Features: Obtaining the instantaneous current reference value Iref includes the following steps: The instantaneous current value I of the first inductor of the current inverter (1) is collected in real time during the sampling period. L1 ; Obtaining a current effective value Vref of the voltage of the inverter (1) and a current effective value Vrms of the output voltage of the inverter (1); The voltage effective value Vref of the inverter (1) is subtracted from the current output voltage effective value Vrms of the inverter (1) to be used as the voltage adjustment amount of the voltage reference value Vg stored and set in the main control unit (5) of the inverter (1), and the adjusted voltage reference value is subjected to PI adjustment to obtain the voltage amplitude output by the effective value voltage loop; The voltage amplitude is subtracted from the instantaneous value Vo of the output voltage of the current inverter (1), and the voltage outer loop output of the voltage loop is obtained through PI regulation; The voltage outer loop output and the instantaneous current value I L1 The instantaneous reference value Iref of the current loop output is obtained by making a difference and adjusting it through PI.

8. The zero-sequence current control method of the inverter parallel system according to claim 7, Features: Obtaining the instantaneous voltage reference value includes the following steps: Obtain the output power Po of the current inverter (1), and receive the output power Po′ of other inverters (1) transmitted; Calculate the average output power of each inverter (1) The average output power The obtained current output power Po of the inverter (1) is subtracted and the effective voltage value Vref output by the power loop is obtained through PI regulation.

9. The zero-sequence current control method of the inverter parallel system according to claim 6, Features: The zero-sequence voltage target value Vb is set to 0.

10. The zero-sequence current control method of the inverter parallel system according to claim 6, Features: The modulation wave is SPWM or SVPWM.

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