Off-grid inverter parallel control method and system and inverter off-grid parallel operation system

Abstract

The invention discloses an off-grid inverter parallel control method, an off-grid inverter parallel control system and an inverter off-grid parallel operation system, relates to the technical field of photovoltaic inverter parallel operation, is used for realizing parallel control of off-grid inverters, and provides the off-grid inverter parallel control method aiming at a series of problems existing in a traditional control scheme. The host sends the integral component of the given value of the current loop to the slave through communication, namely, a semi-master-slave control scheme is provided, the integral component of the voltage loop of the host is filled with the integral component of the voltage loop of the slave, it can be ensured that output of a control system is consistent when the host and the slave are in a steady state, and control parameters of the host and the slave do not need to be additionally adjusted. Besides, in the method, the slave machine reserves the proportional controller of the slave machine, so that when the communication quality between the host machine and the slave machine is poor or even is disconnected, the slave machine can adjust the output of the system through the proportional controller, and the continuous operation of the system is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic inverter parallel connection, and in particular to an off-grid inverter parallel connection control method and system and an inverter off-grid parallel connection system. Background Art

[0002] The inverter off-grid parallel system is an inverter system that converts the DC power generated by the distributed power source into AC power, selects the maximum power point through a low-voltage DC switch, and finally outputs it to the grid or load. This system combines the functions of off-grid and grid-connected, and can operate independently or in conjunction with a large grid. It has high flexibility and adaptability and is widely used in various power usage scenarios.

[0003] At present, the control of the inverter off-grid parallel system mainly adopts the master-slave communication scheme or the droop control scheme. Among them, the master-slave communication scheme is that the master transmits control information to the slave through communication, and the slave receives the control information and controls it. This scheme has high requirements on the quality of parallel communication. When there is a problem with the parallel communication, it seriously affects the operation of the system. The droop control scheme is that the master and slave adjust the frequency and value of the off-grid output voltage according to the active and reactive power of the system, so as to finally realize the off-grid parallel output power equalization of the off-grid parallel system. The disadvantages of this scheme are mainly the poor universal performance of the droop control parameters and the poor dynamic performance of the off-grid parallel system controlled thereby.

[0004] Therefore, technicians in this field now urgently need an off-grid inverter parallel control method to solve the problems of high requirements on parallel communication quality or poor parameter universal performance in the current common inverter off-grid parallel system control schemes. Summary of the invention

[0005] The purpose of this application is to provide an off-grid inverter parallel control method, system and inverter off-grid parallel system to solve the problems of high requirements on parallel communication quality or poor parameter universal performance in the current common inverter off-grid parallel system control scheme.

[0006] In order to solve the above technical problems, the present application provides an off-grid inverter parallel control method, which is applied to the host side, including:

[0007] Determine the phase of the host output voltage according to the given frequency;

[0008] Determine a host current loop given value through a host voltage loop according to a reference voltage and a phase of the host output voltage;

[0009] The integral component of the master current loop given value is sent to each slave; wherein the integral component is used as the integral part of the slave voltage loop to determine the slave current loop given value;

[0010] Determine the driving signal through the host current loop and the forward stack modulation function according to the reference voltage and the given value;

[0011] The driving signal is output to the corresponding inverter.

[0012] In a possible embodiment, the host voltage loop is a proportional resonant controller;

[0013] Then, determining the host current loop given value through the host voltage loop according to the reference voltage and the phase of the host output voltage includes:

[0014] According to the vectors of the output voltage and the output current on the abc axis and the phase of the host output voltage, the vectors of the output voltage and the output current on the dq0 axis are determined by coordinate transformation;

[0015] The host current loop set value is determined by the proportional resonant controller according to the reference voltage and the vector of the output voltage on the dq0 axis.

[0016] In order to solve the above technical problems, the present application also provides an off-grid inverter parallel control method, which is applied to the slave side, including:

[0017] Get the phase of the host output voltage;

[0018] Receiving an integral component sent by a host; wherein the integral component is an integral component of a given value of a host current loop; the given value of the host current loop is determined by the host through a host voltage loop according to a reference voltage and a phase of the host output voltage;

[0019] Using the integral component sent by the host as the integral part of the slave voltage loop, and determining the slave current loop given value through the slave voltage loop according to the phase of the reference voltage and the host output voltage;

[0020] Determine a drive signal according to the reference voltage and the given value through a slave current loop and a forward stack modulation function;

[0021] The driving signal is output to the corresponding inverter.

[0022] In a possible embodiment, the slave voltage loop is a proportional integrator, including the integral part and the proportional part;

[0023] Then, the step of using the integral component sent by the host as the integral part of the slave voltage loop and determining the slave current loop given value through the slave voltage loop according to the phase of the reference voltage and the host output voltage includes:

[0024] The proportional part is obtained through a proportional device according to the phase of the reference voltage and the host output voltage, and the slave current loop given value is obtained by combining with the integral part.

[0025] In a possible embodiment, obtaining the phase of the host output voltage includes:

[0026] The load bus voltage is locked by a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage.

[0027] In order to solve the above technical problems, the present application also provides an off-grid inverter parallel control method, comprising:

[0028] Determine its own master and slave flags;

[0029] If it is a host, the phase of the host output voltage is determined according to the given frequency; if it is a slave, the load bus voltage is locked through a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage;

[0030] If it is a host, the host current loop given value is determined through the host voltage loop according to the reference voltage and the phase of the host output voltage, and the integral component of the host current loop given value is sent to each slave; if it is a slave, the integral component sent by the host is received, and the integral component is used as the integral part of the slave voltage loop, and the slave current loop given value is determined through the slave voltage loop according to the reference voltage and the phase of the host output voltage;

[0031] Determine the driving signal through the current loop and the forward stack modulation function according to the reference voltage and the given value;

[0032] The driving signal is output to the corresponding inverter.

[0033] In order to solve the above technical problems, the present application also provides an off-grid inverter parallel control system, comprising: a plurality of inverters;

[0034] The load ends of the inverters are connected in common; one inverter is used as a master, and the other inverters are used as slaves;

[0035] The host is used to implement the steps of the off-grid inverter parallel control method as described above;

[0036] The slave machine is used to implement the steps of the off-grid inverter parallel control method as described above.

[0037] In a possible embodiment, the inverter includes: a voltage loop, a current loop and a forward stack modulation module; when the inverter serves as the host, it also includes: a phase generation module and a coordinate transformation module;

[0038] When the inverter is used as the slave, it also includes: a phase-locked loop module and the coordinate transformation module;

[0039] Wherein, the phase generation module is used to determine the phase of the host output voltage according to a given frequency;

[0040] The coordinate transformation module is used to determine the vectors of the output voltage and the output current on the dq0 axis through coordinate transformation according to the vectors of the output voltage and the output current on the abc axis and the phase of the host output voltage;

[0041] The phase-locked loop module is used to lock the load bus voltage to obtain the phase of the load bus voltage as the phase of the host output voltage.

[0042] In a possible embodiment, the host and the slave are connected via a CAN bus communication.

[0043] In order to solve the above technical problems, the present application also provides an inverter off-grid parallel system, comprising: the off-grid inverter parallel control system as described above, as well as a photovoltaic power generation system and an off-grid output terminal;

[0044] Wherein, the photovoltaic power generation system is connected one-to-one with the host or slave in the off-grid inverter parallel control system;

[0045] The load ends of the inverters in the off-grid inverter parallel control system are connected together to form the off-grid output end.

[0046] The present application provides a parallel control method for off-grid inverters, which uses communication to send the integral component of the host current loop given value to the slave after the host determines the given value of the host current loop, so that the slave directly uses the integral component sent by the host as the integral part of the slave voltage loop to determine the given value of the slave current loop. That is, the present application provides a semi-master-slave control scheme, which fills the integral component of the slave voltage loop with the integral component of the host voltage loop, and can ensure that the output of the control system of the master and slave is consistent in steady state, without additionally adjusting the control parameters of the master and slave, and solves the problem of poor universal performance of the parameters of the droop control scheme, and the scheme is theoretically unlimited in the number of parallel machines. In addition, in the semi-master-slave control scheme provided by the present application, since the slave retains its own control part, when the communication quality between the host and the slave is poor or even disconnected, the slave can also adjust the output of the system through the control part to ensure that the system can continue to operate, thereby improving stability, and can effectively solve the problem of strict communication quality requirements of the master-slave communication scheme.

[0047] The off-grid inverter parallel control system and the inverter off-grid parallel system provided in the present application correspond to the above method and have the same effect as above. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 A flow chart of a parallel control method for off-grid inverters applied to a host side provided by the present invention;

[0050] Figure 2 A flow chart of a parallel control method for off-grid inverters applied to a slave side provided by the present invention;

[0051] Figure 3 A structural diagram of an off-grid parallel inverter system provided by the present invention;

[0052] Figure 4 A control principle diagram of a slave voltage loop provided by the present invention;

[0053] Figure 5 A control principle diagram of an off-grid inverter parallel control system provided by the present invention. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0055] The core of this application is to provide an off-grid inverter parallel control method and system and an inverter off-grid parallel system.

[0056] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0057] In the related technologies, there are two main solutions for realizing off-grid parallel control of inverters:

[0058] 1. Master-slave communication solution.

[0059] The master-slave communication scheme mainly involves the host transmitting control information to the slave through communication, and the slave receives the control information and performs corresponding control.

[0060] The advantage of this mode is that the master-slave control has a high degree of synchronization, and there is no need to adjust parameters for each slave. The slave can complete the control drive task by responding to the control information sent by the host.

[0061] However, this mode has high requirements on the quality of parallel communication, that is, the communication between the master and slaves must be stable and reliable. When there is a problem with the parallel communication, the slave cannot receive the control information sent by the master or receives wrong control information, which will cause the drive control of the inverter to stop or errors to occur, thus seriously affecting the operation of the system.

[0062] 2. Droop control scheme.

[0063] The droop control scheme mainly involves the master and slave machines adjusting the frequency and value of the off-grid output voltage according to the active and reactive power of the system, so as to ultimately achieve equal distribution of the off-grid parallel output power of the off-grid parallel system.

[0064] The advantage of this solution is that the slave machine's drive control of the inverter does not rely on the master machine, and the control effect is not limited by the parallel communication quality.

[0065] However, the main disadvantage of this solution is that the droop control parameter universality is weak, and each parallel machine (i.e., the master and slave) needs to be debugged separately. In addition, the droop control solution also has the problem of poor system dynamic performance.

[0066] It can be seen that the above two inverter off-grid parallel control schemes have their own problems and cannot meet the actual needs well. Therefore, in order to solve the above problems, this application provides an off-grid inverter parallel control method, which is applied to the host side and the slave side respectively. The method will also be described from the host side and the slave side respectively. It should be noted that the host and slave here both refer to inverters, but based on the different functions, the inverters are divided into hosts and slaves.

[0067] First, applied to the host side, the embodiment of the present application provides a parallel control method for off-grid inverters, such as Figure 1 As shown, including:

[0068] S11: Determine the phase of the host output voltage according to the given frequency.

[0069] S12: According to the phase between the reference voltage and the host output voltage, the host current loop set value is determined through the host voltage loop.

[0070] S13: Send the integral component of the master current loop given value to each slave.

[0071] The integral component is used as the integral part of the slave voltage loop to determine the given value of the slave current loop.

[0072] S14: Determine the driving signal through the host current loop and the forward stack modulation function according to the reference voltage and the given value.

[0073] S15: Output the driving signal to the corresponding inverter.

[0074] First, step S11 is a step of determining the phase of the host output voltage according to the pre-provided given frequency Freq. Since this step is a common step in the current inverter off-grid parallel control, the phase ωt of the host output voltage is determined for the subsequent determination of the given value of the current loop through the voltage loop, so the specific calculation principle and calculation process are not repeated in this embodiment.

[0075] For step S12, the voltage loop and current loop mentioned therein together constitute a dual closed-loop control system to achieve the stability of the inverter drive control. This dual closed-loop control system is integrated inside the inverter and is used to control the core part of the drive inverter - the insulated gate bipolar transistor (IGBT) module. Among them, the voltage loop is the outer loop in the dual closed-loop control system, and the output of the voltage loop is also the given Idq0_ref of the current loop (Idq0_ref is a vector on the dq0 coordinate axis). The voltage loop controls the DC bus voltage of the photovoltaic system by adjusting the output active power of the inverter to ensure the safe operation of the system. The current loop is the inner loop in the dual closed-loop control system, which is mainly responsible for quickly responding to changes in the load and power grid and maintaining the stability of the current. Both the host and the slave include a voltage loop and a current loop, wherein the voltage loop in the host is the above-mentioned host voltage loop, and the current loop in the host is the above-mentioned host current loop. Similarly, the voltage loop in the slave is the slave voltage loop, and the current loop in the slave is the slave current loop.

[0076] Furthermore, for the specific implementation of step S12, this embodiment also provides a possible implementation scheme:

[0077] The host voltage loop is specifically a proportional-resonant (PR) controller. The transfer function G(s) of the PR controller is:

[0078] ;

[0079] In the formula, K i and K p are integral gain and proportional gain respectively. s is a complex variable. and are the resonant frequency and cutoff frequency of the PR controller respectively.

[0080] It should be noted that the value output by the PR controller is the component Id_ref of the vector Idq0_ref in the d-axis direction. The components Iq_ref and I0_ref of Idq0_ref in the q-axis and 0-axis directions are both 0. Therefore, the vector Idq0_ref can be obtained based on the PR controller as the given value of the current loop.

[0081] Then step S12 is specifically as follows:

[0082] S121: According to the vectors of the output voltage and the output current on the abc axis (Uabc and Iabc) and the phase of the host output voltage, the vectors of the output voltage and the output current on the dq0 axis (Udq0 and Idq0) are determined by coordinate transformation.

[0083] S122: Determine the host current loop set value through the proportional resonant controller according to the reference voltage and the vector of the output voltage on the dq0 axis.

[0084] This embodiment provides a specific solution for determining a current loop set value, which is simple to calculate and easy to implement, and can improve the efficiency of inverter parallel and off-grid control.

[0085] For step S13, which is also the core step of this method, a semi-master-slave communication control scheme is implemented. Compared with the droop control scheme, this method allows the host to transmit the integral component of the host current loop given value to each slave to fill the integral component of the slave voltage loop, ensuring that the output of the control system of the master and slave is consistent in steady state, without adjusting the corresponding control parameters for each slave and with better dynamic performance. Compared with the master-slave communication scheme, this method only transmits the integral component of the host current loop given value to each slave, and the slave also needs to determine the current loop given in combination with the proportional part of its own current loop, reducing dependence on the host. Even if the communication quality is poor or disconnected, the slave can adjust the output of the system through the proportional controller to ensure that the system can continue to operate and improve the stability of the system.

[0086] Step S14 and step S15 are steps of determining the drive signal (CMPA signal) of the inverter based on the host current loop and the forward stack modulation function after determining the host current loop given value, and controlling the inverter operation according to the drive signal. Similar to the above step S11, step S14 and step S15 are common steps in the current inverter off-grid parallel control, so they are not repeated in this embodiment.

[0087] On the other hand, for the method applied to the slave side, this embodiment also provides an off-grid inverter parallel control method, such as Figure 2 As shown, including:

[0088] S21: Get the phase of the host output voltage.

[0089] S22: Receive the integral component sent by the host.

[0090] The integral component is the integral component of the host current loop given value. The host current loop given value is determined by the host through the host voltage loop according to the phase of the reference voltage and the host output voltage.

[0091] S23: The integral component sent by the host is used as the integral part of the slave voltage loop, and the slave current loop given value is determined through the slave voltage loop according to the phase of the reference voltage and the host output voltage.

[0092] S24: Determine the driving signal according to the reference voltage and the given value through the slave current loop and the forward stack modulation function.

[0093] S25: Output the driving signal to the corresponding inverter.

[0094] For step S21, the present application does not limit the specific scheme of the slave obtaining the output voltage phase of the host. The slave may request the host to obtain the phase, or request other devices to obtain the phase, or the slave may calculate the phase according to certain parameters, which is not limited in the present embodiment.

[0095] However, if the slave obtains the phase of the host output voltage through communication with the host, the amount of information communicated between the master and the slave will increase, which increases the requirements for the master-slave communication quality. Although even if the master output voltage phase is additionally transmitted by master-slave communication, it still has the advantage of low requirements for the master-slave communication quality compared to the above master-slave communication scheme, but this is contrary to the original intention of this application to reduce the requirements for the master-slave communication quality.

[0096] Based on this, this embodiment provides a scheme for obtaining the output voltage phase of the host without the slave communicating with the host. Step S22 is specifically as follows:

[0097] The load bus voltage is locked through a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage.

[0098] The load bus voltage is the voltage at the load bus, which is the off-grid output terminal to which the load terminals of each inverter are connected in the off-grid parallel inverter system.

[0099] Specifically, Figure 3 As shown in Figure 1, the load ends of the inverter off-grid parallel system are connected together. Figure 3 In the application scenario shown, the load (LOAD) of the inverter off-grid parallel system is the off-grid output load Backup LOAD. That is, the output current of both the master and slave is converged to the off-grid output terminal. Therefore, the slave can lock the voltage at the load convergence point through a phase-locked loop to determine the phase of the master output voltage.

[0100] It can be seen that the solution provided by this embodiment for the slave to obtain the output voltage phase of the host does not need to be obtained through communication with the host, reducing the dependence on master-slave communication, which is beneficial to reducing the impact of the master-slave communication quality on the inverter parallel and off-grid control.

[0101] Then, step S23 is the core step of the method on the slave side. By filling the integral component of the host voltage loop into the slave voltage loop, the output of the control system of the master and slave is ensured to be consistent in steady state.

[0102] Similarly, regarding how to determine the given value of the slave current loop in step S23, this embodiment also provides a corresponding implementation scheme:

[0103] The slave voltage loop is a proportional integrator, which includes an integral part and a proportional part.

[0104] Then step S23 is specifically:

[0105] The proportional part is obtained by the proportional device according to the phase of the reference voltage and the host output voltage, and the slave current loop given value is obtained by combining with the integral part.

[0106] Further, in combination with the specific implementation scheme of the host determining the host current loop given value through the host voltage loop in the above embodiment, this embodiment provides a method as follows: Figure 4 The slave voltage loop control diagram is shown in Figure 1. Figure 4 It can be seen that the host voltage loop is a PR controller. After obtaining the host current loop given value Idq0_ref, it transmits the integral component of Idq0_ref to each slave. Each slave fills the integral component of Idq0_ref as the integral part of the slave voltage loop, and combines the proportional part of the slave voltage loop to obtain the final output as the given value of the slave current loop. The slave voltage loop control scheme provided by this solution is easy to implement, which is conducive to more efficient parallel and off-grid control of the inverter.

[0107] On the other hand, the above is an explanation of a parallel control method for off-grid inverters provided by the present application based on both the host and the slave. The host is used to implement the above steps S11 to S15, and the slave is used to implement the above steps S21 to S25. The steps performed by the host and the slave are not completely consistent. This requires that the host and the slave write different control program codes (i.e., program codes for implementing steps S11 to S15 or steps S21 to S25) when compiling and writing codes.

[0108] However, in actual inverter parallel and off-grid control, the master and slave are usually relative concepts. The master and slave are generally implemented by exactly the same inverter. The user can arbitrarily select any inverter as the master, and the remaining inverters are slaves. Therefore, if different control program codes are compiled and entered in advance, the master and slave are predetermined. And when the master fails, it is necessary to replace it with a new one, or re-enter the control program code corresponding to the master into a slave to take over the work of the master, which is not easy to implement and not flexible enough.

[0109] Based on this, this embodiment also provides a comprehensive off-grid inverter parallel control method, which is no longer limited to whether the parallel machine is a master or a slave, and the method includes:

[0110] S31: Determine its own master-slave flag.

[0111] S32-A: If it is a host, the phase of the host output voltage is determined according to the given frequency.

[0112] S32-B: If it is a slave, the load bus voltage is locked through a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage.

[0113] S33-A: If it is a master, the master current loop set value is determined through the master voltage loop according to the reference voltage and the phase of the master output voltage, and the integral component of the master current loop set value is sent to each slave.

[0114] S33-B: If it is a slave, it receives the integral component sent by the host and uses the integral component as the integral part of the slave voltage loop. According to the phase of the reference voltage and the host output voltage, the slave current loop given value is determined through the slave voltage loop.

[0115] S34: Determine the driving signal through the current loop and the forward stack modulation function according to the reference voltage and the given value.

[0116] It should be noted that this step does not distinguish between the master and the slave, so if the current loop is in the master, it is the master current loop, and if it is in the slave, it is the slave current loop.

[0117] S35: Output the driving signal to the corresponding inverter.

[0118] That is, the method provided in this embodiment does not need to distinguish between the host and the slave in advance, but during the execution of the method, it is determined whether the self-machine is the host or the slave according to the master-slave flag, and then the method on the host side or the method on the slave side is executed. It is not difficult to understand that step S31 only needs to be executed once when the master-slave flag has not changed, and the subsequent steps S32~S35 are real-time control of the inverter, which needs to be performed continuously (periodically). The advantage of this embodiment is that there is no need to distinguish between the host and the slave. Each parallel machine in the system can adjust its own task arbitrarily according to the master-slave flag. When the host fails, the master-slave flag can be adjusted by other slaves to take over the control task of the host, making the inverter off-grid control more flexible and improving stability and reliability.

[0119] On the other hand, this embodiment also provides an off-grid inverter parallel control system, such as Figure 3 As shown, it includes: multiple inverters.

[0120] The load ends of the inverters are connected together; one inverter serves as a master, and the rest of the inverters serve as slaves.

[0121] The host is used to implement the steps of the off-grid inverter parallel control method applied to the host side as described in the above embodiment, namely steps S11 to S15 and the steps defined or extended in further embodiments thereof.

[0122] The slave machine is used to implement the steps of the off-grid inverter parallel control method applied to the slave machine side as described in the above embodiment, namely steps S21 to S25 and the steps defined or extended in further embodiments thereof.

[0123] It is not difficult to understand that the off-grid inverter parallel control system provided in this embodiment corresponds to the embodiment of the off-grid inverter parallel control method provided in the above embodiment. Therefore, for the embodiment of the system part, please refer to the description of the embodiment of the method part, which will not be repeated here.

[0124] However, the present application also provides several other embodiments of off-grid inverter parallel control systems that are different from the above method embodiments. Specifically, this embodiment provides a possible implementation scheme of an off-grid inverter parallel control system, such as Figure 5 As shown:

[0125] The inverter includes: a voltage loop, a current loop and a forward stack modulation module.

[0126] When the inverter serves as the host, it also includes: a phase generation module and a coordinate transformation module.

[0127] When the inverter is used as a slave, it also includes: a phase-locked loop module and a coordinate transformation module.

[0128] The phase generation module is used to determine the phase of the host output voltage according to a given frequency.

[0129] The coordinate transformation module is used to determine the vectors of the output voltage and the output current on the dq0 axis through coordinate transformation according to the vectors of the output voltage and the output current on the abc axis and the phase of the host output voltage.

[0130] The phase-locked loop module is used to lock the load bus voltage to obtain the phase of the load bus voltage as the phase of the host output voltage.

[0131] It should be noted that since the structures of the slaves are exactly the same and they all have a communication relationship with the master, Figure 5 It only shows the structure and communication connection relationship of the master and one slave. Figure 5 Limitation: The off-grid inverter parallel control system provided in the present application only includes one host and one slave. In practical applications, according to different actual needs, the off-grid inverter parallel control system may include one host and any number of slaves. Theoretically, the off-grid parallel control of the inverter implemented by an off-grid inverter parallel control method provided in the present application has no restriction on the number of parallel machines, that is, there is no restriction on the number of slaves in the system. In addition, it can be seen from the above embodiments that the control part composed of functional modules such as the voltage loop, the current loop, and the forward stack modulation module is used to drive and control the IGBT module in the inverter. As the core part of the inverter to realize the function, the IGBT module is used to generate a pulse width modulation (PWM) signal with a specific duty cycle according to the CMPA signal output by the parallel machine, so that the IGBT module outputs a specific waveform signal such as a sine wave to the load.

[0132] This embodiment provides a possible implementation scheme composed of a host and a slave functional module, which is an embodiment adapted to the different steps and functions performed by the host and the slave in some embodiments of the above method. And the implementation scheme provided by this embodiment is a relatively simple hardware implementation scheme to support the implementation of the above method embodiment, which has a simple, reliable and easy-to-implement structure, and is conducive to the implementation and deployment of the off-grid inverter parallel control method and system provided by this application.

[0133] In addition, this embodiment also provides another implementation scheme for the off-grid inverter parallel control system: the above-mentioned host and slave are connected via a controller area network (CAN) bus.

[0134] The CAN bus uses differential transmission and error detection and correction mechanisms, which can effectively reduce the error rate during data transmission and automatically correct errors when they occur. This effectively reduces the reliance on communication quality. When the communication quality is poor, the error detection and correction mechanism can be used to reduce the possibility of transmission errors, thereby improving the stability and reliability of the inverter parallel and off-grid control. In addition, the CAN bus also has good electromagnetic compatibility and can work normally in harsh electromagnetic environments. It is very suitable for working in an environment with strong electromagnetic interference such as the inverter parallel and off-grid control, which is conducive to improving the reliability of communication. In addition, the CAN bus also has the advantages of high real-time performance, which are conducive to improving the control effect of the parallel off-grid inverter.

[0135] Finally, this embodiment also provides an inverter off-grid parallel system, such as Figure 3 As shown, the inverter off-grid parallel system includes: the off-grid inverter parallel control system as described in the above embodiment, as well as a photovoltaic power generation system (PV1~PVn) and an off-grid output terminal (Backup LOAD).

[0136] The photovoltaic power generation system is connected to the host or slave in the off-grid inverter parallel control system in a one-to-one correspondence. The load ends of the inverters in the off-grid inverter parallel control system are connected together to form an off-grid output end.

[0137] Since the inverter off-grid parallel system provided in this embodiment corresponds to the embodiment of the off-grid inverter parallel control system part provided in the above embodiment, the embodiment of the inverter off-grid parallel system part refers to the description of the embodiment of the off-grid inverter parallel control system part above, which will not be repeated here.

[0138] The above is a detailed introduction to an off-grid inverter parallel control method, system and inverter off-grid parallel system provided by the present application. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can refer to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the present application.

[0139] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Claims

1. A parallel control method for off-grid inverters, characterized in that: Applied to the host side, including: Determine the phase of the host output voltage according to the given frequency; Determine a host current loop given value through a host voltage loop according to a reference voltage and a phase of the host output voltage; The integral component of the master current loop given value is sent to each slave; wherein the integral component is used as the integral part of the slave voltage loop to determine the slave current loop given value; Determine the driving signal through the host current loop and the forward stack modulation function according to the reference voltage and the given value; The driving signal is output to the corresponding inverter.

2. The off-grid inverter parallel control method according to claim 1, characterized in that: The host voltage loop is a proportional resonant controller; Then, determining the host current loop given value through the host voltage loop according to the reference voltage and the phase of the host output voltage includes: According to the vectors of the output voltage and the output current on the abc axis and the phase of the host output voltage, the vectors of the output voltage and the output current on the dq0 axis are determined by coordinate transformation; The host current loop set value is determined by the proportional resonant controller according to the reference voltage and the vector of the output voltage on the dq0 axis.

3. A parallel control method for off-grid inverters, characterized in that: Applied to the slave side, including: Get the phase of the host output voltage; Receiving an integral component sent by a host; wherein the integral component is an integral component of a given value of a host current loop; the given value of the host current loop is determined by the host through a host voltage loop according to a reference voltage and a phase of the host output voltage; Using the integral component sent by the host as the integral part of the slave voltage loop, and determining the slave current loop given value through the slave voltage loop according to the phase of the reference voltage and the host output voltage; Determine a drive signal according to the reference voltage and the given value through a slave current loop and a forward stack modulation function; The driving signal is output to the corresponding inverter.

4. The off-grid inverter parallel control method according to claim 3, characterized in that: The slave voltage loop is a proportional integrator, including the integral part and the proportional part; Then, the step of using the integral component sent by the host as the integral part of the slave voltage loop and determining the slave current loop given value through the slave voltage loop according to the phase of the reference voltage and the host output voltage includes: The proportional part is obtained through a proportional device according to the phase of the reference voltage and the host output voltage, and the slave current loop given value is obtained by combining with the integral part.

5. The off-grid inverter parallel control method according to claim 3, characterized in that: The step of obtaining the phase of the host output voltage comprises: The load bus voltage is locked by a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage.

6. A parallel control method for off-grid inverters, characterized in that: include: Determine its own master and slave flags; If it is a host, the phase of the host output voltage is determined according to the given frequency; If it is a slave, the load bus voltage is locked through a phase-locked loop, and the phase of the load bus voltage is obtained as the phase of the host output voltage; If it is a master, the master current loop given value is determined through the master voltage loop according to the reference voltage and the phase of the master output voltage, and the integral component of the master current loop given value is sent to each slave; If it is a slave, receiving the integral component sent by the host, and using the integral component as the integral part of the slave voltage loop, and determining the slave current loop given value through the slave voltage loop according to the phase of the reference voltage and the host output voltage; Determine the driving signal through the current loop and the forward stack modulation function according to the reference voltage and the given value; The driving signal is output to the corresponding inverter.

7. An off-grid inverter parallel control system, characterized in that: include: Multiple inverters; The load ends of the inverters are connected in common; one inverter is used as a master, and the other inverters are used as slaves; The host is used to implement the steps of the off-grid inverter parallel control method according to claim 1 or 2; The slave machine is used to implement the steps of the off-grid inverter parallel control method as described in any one of claims 3 to 5.

8. The off-grid inverter parallel control system according to claim 7, wherein the inverter comprises: Voltage loop, current loop and forward stack modulation module; characterized in that, when the inverter is used as the host, it also includes: a phase generation module and a coordinate transformation module; When the inverter is used as the slave, it also includes: a phase-locked loop module and the coordinate transformation module; Wherein, the phase generation module is used to determine the phase of the host output voltage according to a given frequency; The coordinate transformation module is used to determine the vectors of the output voltage and the output current on the dq0 axis through coordinate transformation according to the vectors of the output voltage and the output current on the abc axis and the phase of the host output voltage; The phase-locked loop module is used to lock the load bus voltage to obtain the phase of the load bus voltage as the phase of the host output voltage.

9. The off-grid inverter parallel control system according to claim 7, characterized in that: The host and the slave are connected via a CAN bus communication.

10. An inverter off-grid parallel system, characterized in that: include: An off-grid inverter parallel control system as claimed in any one of claims 7 to 9, as well as a photovoltaic power generation system and an off-grid output terminal; Wherein, the photovoltaic power generation system is connected one-to-one with the host or slave in the off-grid inverter parallel control system; The load ends of the inverters in the off-grid inverter parallel control system are connected together to form the off-grid output end.

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