Inverter parallel system and control method thereof

Abstract

The present invention discloses an inverter parallel system and a control method thereof. The control method comprises: the inverter host collects the host AC current output by the inverter host, and converts the host AC current into the host DC current in a two-phase rotating coordinate system; the inverter slave collects the slave AC current, and converts the slave AC current into the slave DC current in a two-phase rotating coordinate system; the inverter host sends the host DC current and a query instruction to all inverter slaves; the inverter slave receives the host DC current and the query instruction; the inverter slave determines the current sharing adjustment amount according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction; the inverter host receives the slave DC current, and determines the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC current of all inverter slaves. The present invention can reduce the complexity of the control method and improve the anti-interference performance.

Description

Technical Field

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

[0002] As people's demand for photovoltaic energy storage systems grows, a single household energy storage inverter is difficult to meet the demand. Therefore, the demand for user energy storage systems with multiple inverters in parallel is also increasing. Correspondingly, the control of the inverter parallel system is becoming more and more important.

[0003] In the related technology, the control of the inverter parallel system mainly includes current sharing control, and the current sharing control methods include centralized control, wired current sharing, and droop control. In the centralized control method, signal transmission is easily interfered; in the wired current sharing method, there will be multiple modules occupying the bus, and there will be multiple reference sources on the bus, making the reference source inconsistent. The droop control method has the problem of complex control method and high control difficulty. Summary of the invention

[0004] The present invention provides an inverter parallel system and a control method thereof, so as to reduce the complexity of the control method and improve the anti-interference performance.

[0005] According to one aspect of the present invention, a control method for an inverter parallel system is provided, wherein the method is applied to the inverter parallel system, wherein the inverter parallel system includes an inverter master and a plurality of inverter slaves; the control method for the inverter parallel system includes:

[0006] The inverter host collects the host AC current output by the inverter host, and transforms the host AC current into a host DC current in a two-phase rotating coordinate system; the inverter slave collects the slave AC current output by the inverter slave, and transforms the slave AC current into a slave DC current in a two-phase rotating coordinate system;

[0007] The inverter master sends the master DC current and the query instruction to all the inverter slaves;

[0008] The inverter slave receives the host DC current and the query instruction;

[0009] The inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction;

[0010] The inverter host receives the slave DC current, and determines a current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves.

[0011] Optionally, the inverter master sending the host DC current and the query instruction to the inverter slave comprises:

[0012] The inverter master sends the master DC current and the query instruction to all the inverter slaves at preset intervals; wherein the query instruction includes an instruction to specify one of the inverter slaves to return the slave DC current.

[0013] Optionally, the inverter master and the inverter slave in the inverter parallel system are connected via a controller area network bus, an Ethernet bus, an Ethernet control automation technology bus or a PROFINET bus.

[0014] Optionally, determining the current sharing adjustment amount of the inverter master according to the master DC current and the slave DC currents of all the inverter slaves includes:

[0015] Determine the cumulative value of the DC current of the inverter master within a preset period, and the cumulative value of the slave DC current of each of the inverter slaves within the preset period;

[0016] Determine an average value of the cumulative value of the host DC current and the cumulative value of the slave DC current corresponding to each of the inverter slaves;

[0017] Determine a first difference between the cumulative value of the host DC current and the average value;

[0018] The current sharing adjustment amount of the inverter host is determined according to the first difference.

[0019] Optionally, the inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current, including:

[0020] Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave;

[0021] The current sharing adjustment amount of the inverter slave is determined according to the second difference.

[0022] According to another aspect of the present invention, a control method for an inverter parallel system is provided, which is applied to an inverter master of the inverter parallel system, wherein the inverter parallel system comprises an inverter master and a plurality of inverter slaves; the control method for the inverter parallel system comprises:

[0023] Collecting the host AC current output by the inverter host;

[0024] Converting the host AC current into a host DC current in a two-phase rotating coordinate system;

[0025] Sending the host DC current and query command to all the inverter slaves;

[0026] receiving a slave direct current of the inverter slave returned by the inverter slave;

[0027] The current sharing adjustment amount of the inverter host is determined according to the host DC current and the slave DC currents of all the inverter slaves.

[0028] Optionally, the sending of the host DC current and the query instruction to the inverter slave includes:

[0029] The host DC current and the query instruction are sent to the inverter slave at preset intervals; wherein the query instruction includes an instruction for specifying one of the inverter slaves to return the slave DC current of the inverter slave.

[0030] Optionally, the sending the host DC current and the query instruction to the inverter slave at preset intervals includes:

[0031] The query instructions corresponding to the address information of each inverter slave are sent in sequence at intervals of the preset time, so as to specify each inverter slave to return the slave DC current of the inverter slave in sequence according to the address information of the inverter slave.

[0032] Optionally, determining the current sharing adjustment amount of the inverter master according to the master DC current and the slave DC currents of all the inverter slaves includes:

[0033] Determine the cumulative value of the DC current of the inverter master within a preset period, and the cumulative value of the slave DC current of each of the inverter slaves within the preset period;

[0034] Determine an average value of the cumulative value of the host DC current and the cumulative value of the slave DC current corresponding to each of the inverter slaves;

[0035] Determine a first difference between the cumulative value of the host DC current and the average value;

[0036] The current sharing adjustment amount of the inverter host is determined according to the first difference.

[0037] Optionally, the converting the host AC current into a host DC current in a two-phase rotating coordinate system includes:

[0038] The host AC current is subjected to Clark transformation and Park transformation to obtain the host DC current.

[0039] According to another aspect of the present invention, a control method for an inverter parallel system is provided, which is applied to an inverter slave of the inverter parallel system, wherein the inverter parallel system includes an inverter master and a plurality of inverter slaves; the control method for the inverter parallel system includes:

[0040] Collecting slave AC current of the inverter slave;

[0041] Converting the slave AC current into a slave DC current in a two-phase rotating coordinate system;

[0042] Receiving a host DC current and a query instruction sent by the inverter host;

[0043] The current sharing adjustment amount of the inverter slave is determined according to the host DC current and the slave DC current; and whether to send the slave DC current to the inverter host is determined according to the query instruction.

[0044] Optionally, determining whether to send the slave DC current to the inverter master according to the query instruction includes:

[0045] If the query instruction specifies that the inverter slave machine replies, the slave machine direct current is sent to the inverter master machine.

[0046] Optionally, determining the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current includes:

[0047] Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave;

[0048] The current sharing adjustment amount of the inverter slave is determined according to the second difference.

[0049] According to another aspect of the present invention, there is provided an inverter parallel system, the inverter parallel system comprising an inverter master and a plurality of inverter slaves;

[0050] The inverter host is used to collect the host AC current output by the inverter host, and transform the host AC current into the host DC current in a two-phase rotating coordinate system; send the host DC current and a query instruction to all the inverter slaves; receive the slave DC current, and determine the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves;

[0051] The inverter slave is used to collect the slave AC current output by the inverter slave and convert the slave AC current into a slave DC current in a two-phase rotating coordinate system; receive the host DC current and the query instruction; and determine the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determine whether to send the slave DC current to the inverter host according to the query instruction.

[0052] The technical solution of this embodiment, the control method of the inverter parallel control system adopted includes the following steps: the inverter host collects the host AC current output by the inverter host, and converts the host AC current into the host DC current under the two-phase rotating coordinate system; the inverter slave collects the slave AC current output by the inverter slave, and converts the slave AC current into the slave DC current under the two-phase rotating coordinate system; the inverter host sends the host DC current and query instructions to all inverter slaves; the inverter slave receives the host DC current and query instructions; the inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction; the inverter host receives the slave DC current, and determines the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC current of all inverter slaves. In this embodiment, the current signals transmitted between the inverter host and the inverter slave are all DC, with strong anti-interference ability, and can achieve better current sharing effect. And the algorithm is simple and the complexity is low.

[0054] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0056] Figure 1 A flow chart of a control method for an inverter parallel system provided by an embodiment of the present invention;

[0057] Figure 2 A schematic diagram of the structure of an inverter parallel system provided by an embodiment of the present invention;

[0058] Figure 3 A flow chart of another control method for an inverter parallel system provided by an embodiment of the present invention;

[0059] Figure 4 A calculation block diagram of a current sharing adjustment amount of an inverter host provided by an embodiment of the present invention;

[0060] Figure 5 A block diagram of loop regulation of an inverter provided in an embodiment of the present invention;

[0061] Figure 6 A flow chart of another control method for an inverter parallel system provided by an embodiment of the present invention;

[0062] Figure 7 A calculation block diagram of a current sharing regulation amount of an inverter slave provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0064] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0065] Figure 1 A flow chart of a control method for an inverter parallel system provided by an embodiment of the present invention, Figure 2 A schematic diagram of the structure of an inverter parallel system provided by an embodiment of the present invention. Figure 1 and Figure 2, the inverter parallel system includes a plurality of inverters 11, and in this embodiment, the inverter parallel system includes n inverters 11. The inverter parallel system also includes n photovoltaic strings, each photovoltaic string includes at least one photovoltaic group PV, and the photovoltaic group PV can be electrically connected to the inverter 11 through a photovoltaic switch 12. In addition, the inverter parallel system can also include n energy storage batteries 14 and n DC circuit breakers 13. The energy storage battery 14 is electrically connected to the inverter 11 through the corresponding DC circuit breaker 13. The energy storage battery 14 can also include a battery management system BMS, and the energy storage battery 14 is also communicatively connected to the inverter 11. The grid connection end of each inverter 11 is connected to the grid 27 after being converged through the grid side circuit breaker 21. The load end of the inverter 11 is connected to the first load 28 after being converged through the load side circuit breaker 22. Of course, the load side circuit breaker 22 can be connected to the first load 28 through the DPDT relay 23. The inverter 11 can also be connected to the smart meter 24 for communication, and the smart meter 24 can obtain the corresponding amount of electricity on the grid side through the power supply 26. The grid-side circuit breaker 21 can be connected to the grid 27 through the meter 25. And the side of the grid-side circuit breaker 21 connected to the grid can also be connected to the second load 29. Among the multiple inverters 11 in the inverter parallel system, they are divided into one inverter master and n-1 inverter slaves. n is an integer greater than or equal to 1, and illustratively, n can be 8.

[0066] refer to Figure 1 The control method of the inverter parallel system shown in this embodiment can be applied to the inverter host to perform current sharing control on the inverter host. The control method of the inverter parallel system includes:

[0067] Step S110, the inverter host collects the host AC current output by the inverter host, and transforms the host AC current into the host DC current in a two-phase rotating coordinate system; the inverter slave collects the slave AC current output by the inverter slave, and transforms the slave AC current into the slave DC current in a two-phase rotating coordinate system;

[0068] Specifically, before performing current sharing control, the inverter parallel system first determines one of the multiple inverters 11 as the inverter master, and the other inverters are determined as inverter slaves. The specific determination method is, for example, determined according to the inverter number information. If the inverters are numbered from 1 to n, the inverter numbered 1 can be determined as the inverter master, and the inverters with other numbers can be determined as inverter slaves. When the inverter master fails, a fault-free inverter can also be designated as the inverter master. The inverter master can collect the instantaneous value of the host AC current of the inverter master in real time, that is, (I(a), I(b) and I(c)). It should be noted that the inverter in the inverter parallel system can be a single-phase inverter, a three-phase inverter or an energy storage converter, etc. Similarly, the inverter slave collects the instantaneous value of its own slave AC current in real time. The slave AC current is an AC quantity, for example, a three-phase AC signal, including three phases I(a), I(b) and I(c). The host AC current output by the inverter host is an AC quantity. If the AC host AC current is directly transmitted to the inverter slave, it is more susceptible to interference, thereby making the current sharing control effect of the inverter parallel system poor. In this embodiment, the host AC current is converted into a DC quantity, which can greatly improve the anti-interference ability of the inverter host and the inverter slave communication, and thus can make the current sharing control of the inverter parallel system have a better effect. The slave AC current output by the inverter slave is an AC quantity. If the AC host AC current is directly transmitted to the inverter host, it is more susceptible to interference, thereby making the current sharing control effect of the inverter parallel system poor. In this embodiment, the slave AC current is converted into a DC quantity, which can greatly improve the anti-interference ability of the inverter host and the inverter slave communication, and thus can make the current sharing control of the inverter parallel system have a better effect.

[0069] Step S120, the inverter master sends the master DC current and the query command to all inverter slaves;

[0070] Specifically, the inverter host sends the host DC current to each inverter slave. Among them, the inverter host can send the host DC current and the query instruction to all inverter slaves at the same time, and each inverter slave can perform its own current sharing adjustment according to the received host DC current of the inverter host, and the specific method will be described later. In addition, the inverter host controls the inverter slave through the query instruction to return the slave DC current corresponding to the inverter slave to the inverter host. In some embodiments, the host DC current of the inverter host can be packaged into the query instruction and sent to the inverter slave.

[0071] Step S130, the inverter slave receives the DC current and query instruction from the host;

[0072] Step S140, the inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction;

[0073] Specifically, after the inverter slave receives the host DC current of the inverter master, it can calculate the current sharing adjustment amount of the inverter slave in real time, thereby achieving the effect of rapid current sharing. And according to the query instruction, the slave DC current of the inverter slave can be sent to the inverter master, so that the inverter master can calculate the current sharing adjustment amount of the inverter master.

[0074] Step S150: the inverter master receives the slave DC current, and determines the current sharing adjustment amount of the inverter master according to the master DC current and the slave DC currents of all the inverter slaves.

[0075] Specifically, the inverter host can calculate the DC current of all inverters in the parallel system according to the host DC current of the inverter host and the slave DC current of all inverter slaves for current balancing adjustment. The inverter host needs to obtain the slave DC current of all inverter slaves before it can perform current balancing adjustment, which can be understood as slow adjustment; and the current balancing adjustment of the inverter host refers to the current of all inverters in the inverter parallel system, so that the current output by the inverter host is closer to the average current of the inverter parallel system, and the current output by the inverter slave after current balancing is closer to the current of the inverter host, that is, this embodiment adopts a combination of fast current balancing and slow current balancing, which can achieve current balancing effect in the inverter parallel system with lower complexity and higher anti-interference.

[0076] The technical solution of this embodiment, the control method of the inverter parallel control system adopted includes the following steps: the inverter host collects the host AC current output by the inverter host, and converts the host AC current into the host DC current under the two-phase rotating coordinate system; the inverter slave collects the slave AC current output by the inverter slave, and converts the slave AC current into the slave DC current under the two-phase rotating coordinate system; the inverter host sends the host DC current and query instructions to all inverter slaves; the inverter slave receives the host DC current and query instructions; the inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction; the inverter host receives the slave DC current, and determines the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC current of all inverter slaves. In this embodiment, the current signals transmitted between the inverter host and the inverter slave are all DC, with strong anti-interference ability, and can achieve better current sharing effect. And the algorithm is simple and the complexity is low.

[0077] Optionally, the inverter master sending the host DC current and the query instruction to the inverter slave comprises:

[0078] The inverter master sends the master DC current and the query instruction to all the inverter slaves at preset intervals; wherein the query instruction includes an instruction to specify one of the inverter slaves to return the slave DC current.

[0079] Specifically, the preset time is, for example, 1ms, and the inverter host sends a query instruction to all inverter slaves every 1ms. And the query instruction specifies one of the inverter slaves to return its own slave DC current to the inverter host each time. Therefore, when the inverter slave sends the slave DC current to the inverter host, only one inverter slave sends the slave DC current to the inverter host each time, and there is no problem of multiple inverters sending signals to the inverter host at the same time. The inverter host can send the host DC current and the query instruction to the inverter slave every preset time, including: sending the query instruction corresponding to the address information of each inverter slave in sequence at intervals of the preset time, so as to specify each inverter slave to return the slave DC current of the inverter slave in sequence according to the address information of the inverter slave. The address information is, for example, the number of each inverter slave. In this embodiment, the inverter host specifies each inverter slave to reply the corresponding slave DC current in sequence at intervals of the preset time. Thus, the inverter master can obtain the slave DC currents of all inverter slaves for its own current sharing control, so that the accuracy of the current sharing control is higher.

[0080] Optionally, refer to Figure 2 The inverter master and the inverter slave in the inverter parallel system are connected through a controller area network (CAN) bus, an Ethernet bus, an Ethernet control automation technology (EtherCAT) bus or a PROFINET bus. In this embodiment, only one communication bus is required between the inverter master and the inverter slave, and no additional current sharing signal line, clock bus or synchronization bus is required, so it has the advantage of simple structure and can save the cost of the inverter parallel system.

[0081] Optionally, determining the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all inverter slaves includes:

[0082] Determine the cumulative value of the DC current of the inverter master within a preset period, and the cumulative value of the DC current of each inverter slave within a preset period;

[0083] Specifically, the preset period is, for example, a mains power period, that is, 0.02s. The inverter host can obtain multiple slave DC currents of each inverter slave within each preset period, and the inverter host accumulates the multiple slave DC currents of each inverter slave to obtain the cumulative value of the slave DC current of each inverter slave within a preset period. For the inverter host, the inverter host can collect the same number of host DC currents as the multiple slave DC currents of the inverter slave within a preset period for calculation. Alternatively, within a preset period, the DC current of the inverter changes less, so the host DC current of the inverter host within a preset period can also be averaged, and the slave DC current of each inverter slave obtained can be averaged.

[0084] Determine an average value of the accumulated value of the DC current of the host and the accumulated value of the DC current of the slave corresponding to each inverter slave;

[0085] Specifically, the average DC current of the parallel system can be obtained by taking the average value of the accumulated values ​​of each inverter obtained above.

[0086] Determine a first difference between the cumulative value and the average value of the host DC current;

[0087] Specifically, the first difference Ierr can be obtained by subtracting the accumulated value of the DC current of the inverter host from the average DC current of the parallel system.

[0088] The current sharing adjustment amount of the inverter host is determined according to the first difference.

[0089] Specifically, the first difference Ierr can be obtained through the current sharing loop controller to obtain the current sharing adjustment value Icmd of the inverter host. The current sharing loop controller, for example, filters the first difference Ierr and performs PI control, etc. The specific principle is well known to those skilled in the art and will not be repeated here.

[0090] In this embodiment, the inverter host will calculate the average value of the DC current of all inverters in the inverter parallel system within a preset period, and use the average value as the reference value for the inverter host current equalization regulation. After the inverter host performs current equalization regulation, its output current is closer to the average current of the inverter parallel system. After the inverter host subsequently sends its own host DC current to each inverter slave, since the slave DC current of the inverter host is close to the average current of the inverter parallel system, the reference amount of the current equalization regulation of each inverter slave (i.e., the host DC current of the inverter host) is also close to the average current of the inverter parallel system, thereby making the current of each inverter slave after current equalization control also close to the average current of the inverter parallel system. In other words, the control method of the inverter parallel system of this embodiment can make the output current of each inverter close to the average value of the output current of all inverters, and has the advantages of fast and effective current equalization. In this embodiment, the inverter host does not perform current balancing adjustment in real time, but performs current balancing adjustment once every preset period, which can be understood as slow current balancing, and has the advantages of high accuracy.

[0091] Optionally, the inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current, including:

[0092] Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave;

[0093] Specifically, each time the inverter slave receives the host DC current of the inverter master, the second difference value Ierr2 can be calculated by subtracting the slave DC current of the inverter slave from the host DC current of the inverter master.

[0094] The current sharing adjustment amount of the inverter slave is determined according to the second difference.

[0095] Specifically, the second difference Ierr2 can be obtained by the current sharing controller to obtain the current sharing adjustment amount Icmd2 of the inverter slave. The current sharing controller, for example, filters the second difference Ierr2 and performs PI control. The specific principle is well known to those skilled in the art and will not be repeated here.

[0096] Figure 3 Flow chart of another control method of an inverter parallel system provided by an embodiment of the present invention. The control method of the inverter parallel system of this embodiment is applied to the inverter slave, such as Figure 3 As shown, the control method of the inverter parallel system includes:

[0097] Step S210, collecting the host AC current output by the inverter host;

[0098] Specifically, before performing current sharing control, the inverter parallel system first determines one of the multiple inverters 11 as the inverter master, and the other inverters are determined as inverter slaves. The specific determination method is, for example, determined based on the inverter number information. If the inverters are numbered from 1 to n, the inverter numbered 1 can be determined as the inverter master, and the inverters with other numbers can be determined as inverter slaves. When the inverter master fails, a fault-free inverter can also be designated as the inverter master. The inverter master can collect the instantaneous value of the host AC current of the inverter master in real time, that is, (I(a), I(b) and I(c)). It should be noted that the inverter in the inverter parallel system can be a single-phase inverter, a three-phase inverter or an energy storage converter, etc.

[0099] Step S220, transforming the host AC current into the host DC current in a two-phase rotating coordinate system;

[0100] Specifically, the host AC current output by the inverter host is an AC quantity. If the AC host AC current is directly transmitted to the inverter slave, it is more susceptible to interference, thereby making the current sharing control effect of the inverter parallel system poor. In this embodiment, the host AC current is converted into a DC quantity, which can greatly improve the anti-interference ability of the communication between the inverter host and the inverter slave, and thus make the current sharing control of the inverter parallel system have a better effect.

[0101] Step S230, sending the host DC current and the query command to the inverter slave;

[0102] Specifically, the inverter host sends the host DC current to each inverter slave. Among them, the inverter host can send the host DC current and the query instruction to all inverter slaves at the same time, and each inverter slave can perform its own current sharing adjustment according to the received host DC current of the inverter host, and the specific method will be described later. In addition, the inverter host controls the inverter slave through the query instruction to return the slave DC current corresponding to the inverter slave to the inverter host. In some embodiments, the host DC current of the inverter host can be packaged into the query instruction and sent to the inverter slave.

[0103] Step S240, receiving the slave DC current of the inverter slave returned by the inverter slave;

[0104] Specifically, the inverter slave calculates its own slave DC current in real time, and when receiving a query instruction from the inverter master to return the slave DC current, the inverter slave returns its own slave DC current to the inverter master. The inverter master receives the slave DC current of the inverter slave, which is then used for its own subsequent current sharing regulation.

[0105] Step S250, determining the current sharing adjustment amount of the inverter master according to the master DC current and the slave DC currents of all inverter slaves.

[0106] Specifically, the inverter host can calculate the DC current of all inverters in the parallel system according to the host DC current of the inverter host and the slave DC current of all inverter slaves for current balancing adjustment. The inverter host needs to obtain the slave DC current of all inverter slaves before it can perform current balancing adjustment, which can be understood as slow adjustment; and the current balancing adjustment of the inverter host refers to the current of all inverters in the inverter parallel system, so that the current output by the inverter host is closer to the average current of the inverter parallel system, and the current output by the inverter slave after current balancing is closer to the current of the inverter host, that is, this embodiment adopts a combination of fast current balancing and slow current balancing, which can achieve current balancing effect in the inverter parallel system with lower complexity and higher anti-interference.

[0107] The technical solution of this embodiment adopts a control method of the inverter parallel control system, which includes collecting the host AC current output by the inverter host; converting the host AC current into the host DC current in a two-phase rotating coordinate system; sending the host DC current and query instructions to the inverter slave; receiving the slave DC current of the inverter slave returned by the inverter slave; and determining the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC current of all inverter slaves. In this embodiment, the current signals transmitted between the inverter host and the inverter slave are all DC, with strong anti-interference ability, and can achieve better current sharing effect. And the algorithm is simple and the complexity is low.

[0108] Optionally, sending the host DC current and the query instruction to the inverter slave includes:

[0109] The host DC current and the query instruction are sent to the inverter slave at preset intervals; wherein the query instruction includes an instruction for specifying an inverter slave to return the slave DC current of the inverter slave.

[0110] Specifically, the preset time is, for example, 1 ms, and the inverter master sends a query command to all inverter slaves every 1 ms. And the query command specifies one of the inverter slaves to return its own slave DC current to the inverter master each time. Therefore, when the inverter slave sends the slave DC current to the inverter master, only one inverter slave sends the slave DC current to the inverter master each time, and there is no problem of multiple inverters sending signals to the inverter master at the same time.

[0111] Optionally, sending the host DC current and query instructions to the inverter slave at preset time intervals includes: sending query instructions corresponding to the address information of each inverter slave in sequence at preset time intervals, so as to specify each inverter slave to return the slave DC current of the inverter slave in sequence according to the address information of the inverter slave.

[0112] Specifically, the address information is, for example, the serial number of each inverter slave. In this embodiment, the inverter master sequentially specifies each inverter slave to reply to the corresponding slave DC current at intervals of a preset time. Thus, the inverter master can obtain the slave DC current of all inverter slaves for its own current sharing control, so that the accuracy of the current sharing control is higher.

[0113] Optionally, Figure 4 A calculation block diagram of the current sharing adjustment amount of an inverter host provided in an embodiment of the present invention, referring to Figure 4 The current sharing adjustment amount of the inverter host is determined based on the host DC current and the slave DC currents of all inverter slaves, including:

[0114] Determine the cumulative value of the host DC current of the inverter host within a preset period, and the cumulative value of the slave DC current of each inverter slave within a preset period;

[0115] Specifically, the preset period is, for example, a mains power period, that is, 0.02s. The inverter host can obtain multiple slave DC currents of each inverter slave within each preset period, and the inverter host accumulates the multiple slave DC currents of each inverter slave to obtain the cumulative value of the slave DC current of each inverter slave within a preset period. For the inverter host, the inverter host can collect the same number of host DC currents as the multiple slave DC currents of the inverter slave within a preset period for calculation. Alternatively, within a preset period, the DC current of the inverter changes less, so the host DC current of the inverter host within a preset period can also be averaged, and the slave DC current of each inverter slave obtained can be averaged.

[0116] Determine the average value of the cumulative value of the host DC current and the cumulative value of the slave DC current corresponding to each inverter slave (ie, the parallel system average current). Specifically, the cumulative values ​​of each inverter obtained above are averaged to obtain the parallel system average DC current.

[0117] Determine a first difference between the cumulative value and the average value of the host DC current;

[0118] Specifically, the first difference Ierr can be obtained by subtracting the accumulated value of the DC current of the inverter host from the average DC current of the parallel system.

[0119] The current sharing adjustment amount of the inverter host is determined according to the first difference.

[0120] Specifically, the first difference Ierr can be obtained through the current sharing loop controller to obtain the current sharing adjustment value Icmd of the inverter host. The current sharing loop controller, for example, filters the first difference Ierr and performs PI control, etc. The specific principle is well known to those skilled in the art and will not be repeated here.

[0121] In this embodiment, the inverter host will calculate the average value of the DC current of all inverters in the inverter parallel system within a preset period, and use the average value as the reference value for the inverter host current equalization regulation. After the inverter host performs current equalization regulation, its output current is closer to the average current of the inverter parallel system. After the inverter host subsequently sends its own host DC current to each inverter slave, since the slave DC current of the inverter host is close to the average current of the inverter parallel system, the reference amount of the current equalization regulation of each inverter slave (i.e., the host DC current of the inverter host) is also close to the average current of the inverter parallel system, thereby making the current of each inverter slave after current equalization control also close to the average current of the inverter parallel system. In other words, the control method of the inverter parallel system of this embodiment can make the output current of each inverter close to the average value of the output current of all inverters, and has the advantages of fast and effective current equalization. In this embodiment, the inverter host does not perform current balancing adjustment in real time, but performs current balancing adjustment once every preset period, which can be understood as slow current balancing, and has the advantages of high accuracy.

[0122] Exemplarily, in some embodiments, transforming the host AC current into the host DC current in a two-phase rotating coordinate system includes: performing Clarke transformation and Park transformation on the host AC current to obtain the host DC current.

[0123] Specifically, the three-phase host AC current (I(a), I(b) and I(c)) can first be subjected to Clarke transformation to obtain the host AC current I(α) and I(β) in a two-phase stationary coordinate system, and then I(α) and I(β) can be subjected to Park transformation to obtain the DC current I(d) and I(q). The specific working principles of Clarke transformation and Park transformation are well known to those skilled in the art and will not be described in detail here. Of course, in some other implementations, other transformations can be performed on the host AC current to convert the AC host AC current into a DC current.

[0124] Optionally, Figure 5 A block diagram of a loop regulation of an inverter provided by an embodiment of the present invention, referring to Figure 5The loop of the inverter includes a voltage loop and a current loop. The inverter voltage reference and the inverter voltage sampling value are subtracted and then output through the voltage loop regulator as the reference of the current loop. The reference of the current loop is subtracted from the inverter current sampling value and then output through the current loop regulator. The output of the current loop regulator is added with the grid voltage feedforward and the output current feedforward, and finally the current sharing regulation amount Icmd is added to drive the inverter output, that is, to control the state of each switch in the inverter. In this embodiment, the current sharing regulation amount Icmd is the current sharing regulation amount of the inverter host.

[0125] Figure 6 Flow chart of another control method of an inverter parallel system provided by an embodiment of the present invention. The control method of the inverter parallel system of this embodiment is applied to the inverter slave, such as Figure 6 As shown, the control method of the inverter parallel system includes:

[0126] Step S310, collecting slave AC current of the inverter slave;

[0127] Specifically, the specific structure of the inverter parallel system can be referred to Figure 2 Description. The control method corresponding to the inverter slave can be executed in conjunction with the control method corresponding to the inverter master. The inverter slave collects the instantaneous value of its own slave AC current in real time. The slave AC current is an AC quantity, for example, a three-phase AC signal, including three phases I(a), I(b) and I(c).

[0128] Step S320, converting the slave AC current into the slave DC current in a two-phase rotating coordinate system;

[0129] Specifically, the slave AC current output by the inverter slave is an AC quantity. If the AC host AC current is directly transmitted to the inverter host, it is more susceptible to interference, thereby making the current sharing control effect of the inverter parallel system poor. In this embodiment, the slave AC current is converted into a DC quantity, which can greatly improve the anti-interference ability of the inverter host and the inverter slave communication, and thus can make the current sharing control of the inverter parallel system have a better effect. Exemplarily, the slave AC current is converted into a slave DC current in two rotating coordinate systems, including: Clarke transformation and Park transformation of the slave AC current to obtain the slave DC current. Clarke transformation can be first performed on the three-phase slave AC current (I (a), I (b) and I (c)) to obtain the current I (α) and I (β) of the slave AC current in the two-phase stationary coordinate system, and then, I (α) and I (β) are continuously Park transformed to obtain the slave DC current I (d) and I (q). The specific working principles of Clarke transformation and Park transformation are well known to those skilled in the art and will not be described in detail here. Of course, in some other implementations, other transformations may be performed on the slave AC current to transform the AC slave AC current into a DC current.

[0130] Step S330, receiving the host DC current and query instruction sent by the inverter host;

[0131] Specifically, the inverter master sends a query instruction and the host DC current of the inverter master once every preset time. For each inverter slave, a query instruction and the host DC current of the inverter master can be received once every preset time.

[0132] Step S340, determining the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determining whether to send the slave DC current of the inverter slave to the inverter host according to the query instruction.

[0133] Specifically, after the inverter slave receives the host DC current of the inverter master, it can calculate the current sharing adjustment amount of the inverter slave in real time, thereby achieving the effect of rapid current sharing. And according to the query instruction, the slave DC current of the inverter slave can be sent to the inverter master, so that the inverter master can calculate the current sharing adjustment amount of the inverter master.

[0134] The technical solution of this embodiment adopts a control method for the inverter parallel system, including collecting the slave AC current of the inverter slave; converting the slave AC current into the slave DC current in a two-phase rotating coordinate system; receiving the host DC current and query instructions sent by the inverter host; determining the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determining whether to send the slave DC current of the inverter slave to the inverter host according to the query instruction. In this embodiment, the current signals transmitted between the inverter host and the inverter slave are all DC, with strong anti-interference ability, and can achieve better current sharing effect.

[0135] Optionally, refer to Figure 2 The inverter master and the inverter slave in the inverter parallel system are connected via a CAN bus, an Ethernet bus, an EtherCAT bus, or a PROFINET bus. In this embodiment, only one communication bus is required between the inverter master and the inverter slave, and no additional current sharing signal line, clock bus, or synchronization bus is required, so it has the advantage of a simple structure and can save the cost of the inverter parallel system.

[0136] Optionally, determining whether to send the slave DC current to the inverter host according to the query instruction includes:

[0137] If the query command specifies that the inverter slave responds, the slave DC current will be sent to the inverter master.

[0138] Specifically, the inverter host sends a query instruction and the host DC current of the inverter host once every preset time. All inverter slaves in the inverter parallel system can receive the query instruction and the host DC current. And the query instruction only specifies one inverter slave to reply each time, that is, if the query instruction received by the inverter slave specifies that the inverter slave reply, the corresponding slave DC current will be replied to the inverter host; conversely, if the query instruction received by the inverter slave does not specify that the inverter slave reply, the information will be returned to the inverter host. As a result, only one inverter slave sends the slave DC current to the inverter host at a time, and there is no problem of multiple inverters sending signals to the inverter host at the same time.

[0139] Optionally, Figure 7 A calculation block diagram of the current sharing adjustment amount of the inverter slave provided in an embodiment of the present invention, referring to Figure 7 The current sharing adjustment amount of the inverter slave is determined according to the host DC current of the inverter host and the slave DC current of the inverter slave, including:

[0140] Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave;

[0141] Specifically, each time the inverter slave receives the host DC current of the inverter master, the second difference value Ierr2 can be calculated by subtracting the slave DC current of the inverter slave from the host DC current of the inverter master.

[0142] The current sharing adjustment amount of the inverter slave is determined according to the second difference.

[0143] Specifically, the second difference Ierr2 can be obtained by the current sharing controller to obtain the current sharing adjustment amount Icmd2 of the inverter slave. The current sharing controller, for example, filters the second difference Ierr2 and performs PI control. The specific principle is well known to those skilled in the art and will not be repeated here.

[0144] Optionally, Figure 5 The loop regulation method of the inverter shown can also be applied to the inverter slave. For the inverter slave, the inverter loop includes a voltage loop and a current loop. The inverter voltage reference and the inverter voltage sampling value are subtracted and output through the voltage loop regulator as the reference of the current loop. The reference of the current loop is subtracted from the inverter current sampling value and then output through the current loop regulator. The output of the current loop regulator is added with the grid voltage feedforward and the output current feedforward, and finally the inverter slave current equalization regulation amount Icmd2 is added to drive the inverter output, that is, to control the state of each switch in the inverter.

[0145] This embodiment also provides an inverter parallel system, such as Figure 2 As shown. The inverter parallel system includes an inverter host and multiple inverter slaves. The inverter host is used to collect the host AC current output by the inverter host, and convert the host AC current into the host DC current in a two-phase rotating coordinate system; send the host DC current and query instructions to all inverter slaves; receive the slave DC current, and determine the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all inverter slaves;

[0146] The inverter slave is used to collect the slave AC current output by the inverter slave and convert the slave AC current into a slave DC current in a two-phase rotating coordinate system; receive the host DC current and query instructions; and determine the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determine whether to send the slave DC current to the inverter host according to the query instruction.

[0147] The inverter parallel system of this embodiment can refer to the description of the control method of the inverter parallel system in the present invention, and has the same beneficial effects, which will not be repeated here.

[0148] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0149] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for an inverter parallel system, characterized in that: Applied to an inverter parallel system, the inverter parallel system includes an inverter master and multiple inverter slaves; the control method of the inverter parallel system includes: The inverter host collects the host AC current output by the inverter host, and transforms the host AC current into a host DC current in a two-phase rotating coordinate system; the inverter slave collects the slave AC current output by the inverter slave, and transforms the slave AC current into a slave DC current in a two-phase rotating coordinate system; The inverter master sends the master DC current and the query instruction to all the inverter slaves; The inverter slave receives the host DC current and the query instruction; The inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; and determines whether to send the slave DC current to the inverter host according to the query instruction; The inverter host receives the slave DC current, and determines a current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves.

2. The control method of the inverter parallel system according to claim 1, characterized in that: The inverter host sends the host DC current and the query instruction to the inverter slave, including: The inverter master sends the master DC current and the query instruction to all the inverter slaves at preset intervals; wherein the query instruction includes an instruction to specify one of the inverter slaves to return the slave DC current.

3. The control method of the inverter parallel system according to claim 1, characterized in that: The inverter master and the inverter slave in the inverter parallel system are connected via a controller area network bus, an Ethernet bus, an Ethernet control automation technology bus or a PROFINET bus.

4. The control method of the inverter parallel system according to claim 1, characterized in that: Determining the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves includes: Determine the cumulative value of the DC current of the inverter master within a preset period, and the cumulative value of the slave DC current of each of the inverter slaves within the preset period; Determine an average value of the cumulative value of the host DC current and the cumulative value of the slave DC current corresponding to each of the inverter slaves; Determine a first difference between the cumulative value of the host DC current and the average value; The current sharing adjustment amount of the inverter host is determined according to the first difference.

5. The control method of the inverter parallel system according to claim 1, characterized in that: The inverter slave determines the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current, including: Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave; The current sharing adjustment amount of the inverter slave is determined according to the second difference.

6. A control method for an inverter parallel system, characterized in that: An inverter host applied to the inverter parallel system, wherein the inverter parallel system comprises an inverter host and a plurality of inverter slaves; The control method of the inverter parallel system includes: Collecting the host AC current output by the inverter host; Converting the host AC current into a host DC current in a two-phase rotating coordinate system; Sending the host DC current and query command to all the inverter slaves; receiving a slave direct current of the inverter slave returned by the inverter slave; The current sharing adjustment amount of the inverter host is determined according to the host DC current and the slave DC currents of all the inverter slaves.

7. The control method of the inverter parallel system according to claim 6, characterized in that: The sending of the host DC current and the query instruction to the inverter slave comprises: The host DC current and the query instruction are sent to the inverter slave at preset intervals; wherein the query instruction includes an instruction for specifying one of the inverter slaves to return the slave DC current of the inverter slave.

8. The control method of the inverter parallel system according to claim 7, characterized in that: The sending of the host DC current and the query instruction to the inverter slave at preset intervals includes: The query instructions corresponding to the address information of each inverter slave are sent in sequence at intervals of the preset time, so as to specify each inverter slave to return the slave DC current of the inverter slave in sequence according to the address information of the inverter slave.

9. The control method of the inverter parallel system according to claim 6, characterized in that: Determining the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves includes: Determine the cumulative value of the DC current of the inverter master within a preset period, and the cumulative value of the slave DC current of each of the inverter slaves within the preset period; Determine an average value of the cumulative value of the host DC current and the cumulative value of the slave DC current corresponding to each of the inverter slaves; Determine a first difference between the cumulative value of the host DC current and the average value; The current sharing adjustment amount of the inverter host is determined according to the first difference.

10. The control method of the inverter parallel system according to claim 6, characterized in that: The step of converting the host AC current into a host DC current in a two-phase rotating coordinate system comprises: The host AC current is subjected to Clark transformation and Park transformation to obtain the host DC current.

11. A control method for an inverter parallel system, characterized in that: An inverter slave applied to the inverter parallel system, wherein the inverter parallel system comprises an inverter master and a plurality of inverter slaves; The control method of the inverter parallel system includes: Collecting slave AC current of the inverter slave; Converting the slave AC current into a slave DC current in a two-phase rotating coordinate system; Receiving a host DC current and a query instruction sent by the inverter host; The current sharing adjustment amount of the inverter slave is determined according to the host DC current and the slave DC current; and whether to send the slave DC current to the inverter host is determined according to the query instruction.

12. The control method of the inverter parallel system according to claim 11, characterized in that: The step of determining whether to send the slave DC current to the inverter host according to the query instruction includes: If the query instruction specifies that the inverter slave machine replies, the slave machine direct current is sent to the inverter master machine.

13. The control method of the inverter parallel system according to claim 11, characterized in that: Determining the current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current includes: Determine a second difference between a master DC current of the inverter master and a slave DC current of the inverter slave; The current sharing adjustment amount of the inverter slave is determined according to the second difference.

14. An inverter parallel system, characterized in that: The inverter parallel system includes an inverter master and a plurality of inverter slaves; The inverter host is used to collect the host AC current output by the inverter host, and transform the host AC current into the host DC current in a two-phase rotating coordinate system; send the host DC current and a query instruction to all the inverter slaves; receive the slave DC current, and determine the current sharing adjustment amount of the inverter host according to the host DC current and the slave DC currents of all the inverter slaves; The inverter slave is used to collect the slave AC current output by the inverter slave and transform the slave AC current into a slave DC current in a two-phase rotating coordinate system; receive the host DC current and the query instruction; and determining a current sharing adjustment amount of the inverter slave according to the host DC current and the slave DC current; And determine whether to send the slave DC current to the inverter host according to the query instruction.

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