Current control method and apparatus for grid-connected system, and energy storage valve controller

Abstract

The present application is applicable to the technical field of power systems. Provided are a current control method and apparatus for a grid-connected system, and an energy storage valve controller. The method comprises: on the basis of the current operating situation, determining an integral term limit value of a current loop controller; on the basis of a current instruction value, a current measurement value, and the integral term limit value, determining an input reference voltage of a grid-connected system; and determining a switching strategy on the basis of the input reference voltage, and executing the switching strategy, such that the operating stability of the grid-connected system can be improved.

Description

Current control method, device and energy storage valve controller of grid-connected system

[0001] The present application claims priority from the Chinese patent application No. 202410865761.7 filed on June 28, 2024, and entitled "Current control method, device and energy storage valve controller of grid-connected system", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the technical field of power systems, and in particular relates to a current control method, device and energy storage valve controller of a grid-connected system. BACKGROUND

[0003] At present, with the rapid development of renewable energy and the transformation of power systems, energy storage systems are increasingly applied in power systems. Energy storage systems can be used to balance the volatility of renewable energy, improve the utilization rate of renewable energy, and improve the reliability and stability of power systems. Energy storage systems can be used for peak shaving, backup power, power trading, etc.

[0004] Among them, the energy storage system can be composed of a grid-connected system with a converter, which is connected to the AC power grid and the power generation system through the converter. The converter can convert the DC voltage on the DC side into an AC voltage with the required amplitude, frequency or phase of the AC power grid, thereby adjusting the reactive power of the AC power grid and maintaining the stability of the grid voltage. When the load of the AC power grid changes, the number of energy storage sub-modules in the energy storage system of the grid-connected system can be controlled to inject or absorb power from the AC power grid, thereby maintaining the stability of the grid.

[0005] Therefore, the stable operation of the grid-connected system is very important for the power system. However, at present, various working conditions may affect the operation stability of the grid-connected system, i.e., the current grid-connected system has poor stability. TECHNICAL PROBLEM

[0006] Therefore, the present application provides a current control method, device and energy storage valve controller of a grid-connected system to solve the technical problem that the operation stability of the current grid-connected system is easily affected by various working conditions, resulting in poor operation stability of the grid-connected system. TECHNICAL SOLUTION

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a current control method of a grid-connected system, applied to an energy storage valve controller, comprising:

[0009] determine the integral term limit value of the current loop controller according to the current operating condition;

[0010] determine the input reference voltage of the grid-connected system according to the current command value, the current measurement value and the integral term limit value;

[0011] determine the switching strategy according to the input reference voltage, and execute the switching strategy.

[0012] In the embodiments of the present application, the integral term limit value of the current loop controller corresponding to different operating conditions is different, that is, the integral term can be limited at different integral term limit values under different operating conditions, so that the current control is closer to the actual operating condition, and the operating stability of the system can be better improved.

[0013] In an optional implementation of the first aspect, the integral term limit value of the current loop controller is determined according to the current operating condition, comprising:

[0014] In the case that the energy storage valve controller is in the locked state, the integral term limit value of the current loop controller is set to 0;

[0015] In the case that the energy storage valve controller is in the unlocked state and the operating period of the energy storage valve controller is within the first n1 periods, the upper limit value of the integral term of the current loop controller is set to the minimum value of the allowable charging current of each input sub-module, and the lower limit value of the integral term of the current loop controller is set to the minimum value of the allowable discharging current of each input sub-module;

[0016] In the case that the energy storage valve controller is in the unlocked state and the operating period of the energy storage valve controller is after the first n1 periods, the upper limit value of the integral term of the current loop controller is set to the minimum value of the allowable charging current of each available sub-module, and the lower limit value of the integral term of the current loop controller is set to the minimum value of the allowable discharging current of each available sub-module; wherein n1 is a positive integer greater than 0.

[0017] In the embodiment of the application, in the case that the energy storage valve controller is in the locked state, the integral term limit value of the current loop controller is set to 0, that is, in the case that the current has not reached the constant current control stage, the current loop controller is cut out by setting the integral term limit value of the current loop controller to 0, so that the current loop controller does not affect the system. In the first n1 cycles of the operation cycle of the energy storage valve controller, the minimum allowable charge and discharge current of the available sub-modules is used to limit the integral term of the current loop controller, which can make the current regulation process more stable, thereby reducing the influence of the current fluctuation generated when the energy storage valve controller is just unlocked on the system, and improving the stability of the system. After the operation cycle is in the first n1 cycles, the minimum allowable charge and discharge current of the put-in sub-module is used to limit the integral term of the current loop controller, which can make the constant current control more accurate and further improve the reliability of the system.

[0018] In an optional implementation of the first aspect, before determining the put-in reference voltage of the grid-connected system according to the current instruction value and the integral term limit value, the method further includes:

[0019] Limiting the current instruction value according to the current operation condition.

[0020] In the embodiment of the application, the current instruction value is limited according to different operation conditions, which can adapt the current instruction value to the operation condition and reduce the variation range of the current instruction value, thereby reducing the influence of the current instruction value fluctuation on the system stability.

[0021] In an optional implementation of the first aspect, limiting the current instruction value according to the current operation condition includes:

[0022] In the case of occurrence of an AC grid fault, an AC fault limit value is obtained;

[0023] The current instruction value is limited according to the AC fault limit value.

[0024] In an optional implementation of the first aspect, limiting the current instruction value according to the current operation condition includes:

[0025] In the case of no occurrence of an AC grid fault, the minimum allowable charge and discharge current of the available sub-module is obtained, the upper limit value of the current instruction limit value is set to the value corresponding to the smaller one of the minimum allowable charge and discharge current of the available sub-module and the current instruction value, and the lower limit value of the current instruction limit value is set to the value corresponding to the smaller one of the minimum allowable charge and discharge current of the available sub-module and the opposite of the current instruction value, to determine the current instruction limit value;

[0026] The current command value is limited according to an upper limit value of the current command limit value and a lower limit value of the current command limit value.

[0027] In the embodiments of the present application, by limiting the current command value, the fault current of the AC side can effectively pass through, thereby reducing the current fluctuation of the grid-connected system caused by single-phase fault or multi-phase fault of the AC side, and improving the operation stability of the grid-connected system.

[0028] In an optional implementation of the first aspect, after limiting the current command value according to the current operation condition, the method further comprises:

[0029] In the case of detecting that the AC power grid is in fault ride-through, the integral term of the current loop controller before the fault is latched.

[0030] In the embodiments of the present application, in the case of fault ride-through of the AC power grid, latching the integral term can further reduce the influence of the fault current generated by the fault ride-through on the grid stability, and can effectively realize the fault ride-through.

[0031] In an optional implementation of the first aspect, the determining the input reference voltage of the grid-connected system according to the current command value, the current measurement value and the integral term limit value comprises:

[0032] The current loop controller is limited based on the integral term limit value, and an output value of the current loop controller is determined according to the current command value and the current measurement value;

[0033] The input reference voltage of the grid-connected system is determined according to the output value of the current loop controller.

[0034] In the embodiments of the present application, different input reference voltages can be selected according to the operation condition of the converter controller, so that the current fluctuation caused by unlocking of the voltage source converter (VSC) can be reduced in the process of current control, and the stability of the system is improved.

[0035] In an optional implementation of the first aspect, the determining the input reference voltage of the grid-connected system according to the output value of the current loop controller comprises:

[0036] In the case that the operation period of the converter controller is after the first n2 periods, the input reference voltage is determined according to the voltage measurement value and the output value of the current loop controller;

[0037] The input reference voltage is determined according to the voltage instruction value and the output value of the current loop controller when the operation cycle of the converter valve controller is within the first n2 cycles, where n2 is a positive integer greater than 0.

[0038] In the embodiment, the input reference voltage determined by the voltage instruction value and the output value of the current loop controller when the VSC is unlocked can make the voltage of the system reach the voltage instruction value faster, so that the system tends to be stable faster. After n2 control cycles, the input reference voltage is determined by the voltage measurement value and the output value of the current loop controller, so that the voltage of the grid-connected system can be adjusted more accurately, thereby further improving the reliability of the system.

[0039] In an optional implementation of the first aspect, the method further includes:

[0040] The number of energy storage submodules to be input is calculated according to the input reference voltage and the average capacitor voltage of available submodules when the operation cycle of the energy storage valve controller is within the first n1 cycles.

[0041] The number of energy storage submodules to be input is calculated according to the input reference voltage and the average capacitor voltage of input submodules when the operation cycle of the energy storage valve controller is after the first n1 cycles.

[0042] In the embodiment, the number of energy storage submodules to be input is calculated by using the average capacitor voltage of available submodules in the first several control cycles when the VBC is unlocked, which can reduce the disturbance of the system current caused by the change of the number of input submodules at the moment when the VBC is unlocked, thereby effectively improving the stability of the system.

[0043] In an optional implementation of the first aspect, the current control method further includes limiting the output value of the current loop controller.

[0044] In the embodiment, by limiting the output value of the current loop controller, the stable state of the grid-connected system caused by the too large output value of the current loop controller can be reduced, thereby further improving the operation stability of the grid-connected system.

[0045] In a second aspect, the embodiment provides a current control device of a grid-connected system, including:

[0046] The limiting module is configured to determine the integral term limiting value of the current loop controller according to the current operating condition.

[0047] The determining module is configured to determine the input reference voltage of the grid-connected system according to the current instruction value, the current measurement value, and the integral term limiting value.

[0048] The execution module is configured to determine a switching strategy according to the input reference voltage, and execute the switching strategy.

[0049] In a third aspect, an embodiment of the present application provides another current control device of a grid-connected system, including a memory and a computer program stored in the memory and executable on a processor, and the processor implements the current control method according to any of the optional implementation manners of the first aspect.

[0050] In a fourth aspect, an embodiment of the present application provides a computer readable storage medium, which stores a computer program, and the computer program is executable on a processor to implement the current control method according to any of the optional implementation manners of the first aspect.

[0051] In a fifth aspect, an embodiment of the present application provides an energy storage valve controller, including the current control device of the grid-connected system according to the second aspect or the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0053] FIG. 1 is a schematic structural diagram of a power system according to an embodiment of the present application;

[0054] FIG. 2 is a schematic architecture diagram of a grid-connected system to which a current control method according to an embodiment of the present application is applicable;

[0055] FIG. 3 is a schematic flowchart of a current control method of a grid-connected system according to an embodiment of the present application;

[0056] FIG. 4 is a schematic flowchart of S301 of a current control method of a grid-connected system according to an embodiment of the present application;

[0057] FIG. 5 is a schematic diagram of an adjustment process of a current loop controller according to an embodiment of the present application;

[0058] FIG. 6 is a schematic flowchart of a current control method of a grid-connected system according to another embodiment of the present application;

[0059] FIG. 7 is a schematic flowchart of S601 of a current control method of a grid-connected system according to an embodiment of the present application;

[0060] Fig. 8 is a schematic flow chart of a current control method of a grid-connected system according to another embodiment of the present application;

[0061] Fig. 9 is a schematic flow chart of a current control method of a grid-connected system according to another embodiment of the present application;

[0062] Fig. 10 is a schematic diagram of a regulation process of a current loop controller according to another embodiment of the present application;

[0063] Fig. 11 is a schematic flow chart of a current control method of a grid-connected system according to another embodiment of the present application;

[0064] Fig. 12 is a schematic flow chart of a current control method of a grid-connected system according to another embodiment of the present application;

[0065] Fig. 13 is a schematic diagram of a current control device of a grid-connected system according to an embodiment of the present application;

[0066] Fig. 14 is a schematic diagram of a current control device of a grid-connected system according to another embodiment of the present application. Embodiments of the present application

[0067] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore should not be used to limit the protection scope of the present application.

[0068] It should be noted that, unless otherwise specified, all technical terms used in the embodiments of the present application have the same meanings as those commonly understood by those skilled in the art to which the present application belongs. The technical terms used in the embodiments of the present application are only used to explain the specific embodiments of the present application, and are not intended to limit the present application.

[0069] In the description of the embodiments of the present application, the technical terms "comprise", "contain", "have" and any variants thereof all mean "comprise but are not limited to", unless otherwise specified.

[0070] In the description of the embodiments of the present application, unless otherwise specified, the technical term "multiple" means two or more than two, and the technical terms "at least one" and "one or more" mean one, two or more than two.

[0071] The technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0072] The technical term "and / or" is merely a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing simultaneously, and B existing alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after it.

[0073] "Embodiments" mentioned in the description of the embodiments of the present application mean that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0074] At present, with the rapid development of renewable energy and the transformation of power systems, energy storage systems are increasingly applied in power systems. Energy storage systems can be used to balance the volatility of renewable energy, improve the utilization rate of renewable energy, and improve the reliability and stability of power systems. Energy storage systems can be used for peak shaving, backup power, power trading, etc.

[0075] Among them, the energy storage system can be composed with the converter to form a grid-connected system, and the converter is connected with the AC power grid and the power generation system. The converter can convert the DC voltage on the DC side into an AC voltage with an amplitude, frequency or phase required by the AC power grid, so as to adjust the reactive power of the AC power grid and maintain the stability of the grid voltage. When the load of the AC power grid changes, the number of energy storage sub-modules put into the energy storage system of the grid-connected system can be controlled to inject power into the AC power grid or absorb power from the AC power grid, thereby maintaining the stability of the grid.

[0076] In the application process, the unlocking logic of the grid-connected system can be to unlock the converter valve controller VSC for voltage control first, and then unlock the energy storage valve controller for current control. This is to enable the system to prioritize establishing a stable voltage control loop during startup to improve voltage stability and improve the safety of equipment operation.

[0077] It should be noted that the above unlocking refers to the conversion of the system from a non-working state to a working state.

[0078] The constant current control is one of the most basic control modes of the grid-connected system, and the control task of the control mode is to maintain the DC current output by the grid-connected system at a certain constant value, which can be achieved by a current loop controller. In the energy storage system, the control of the DC current of the system is mainly realized by the energy storage valve controller (VBC) and the voltage source converter (VSC). Among them, the voltage source converter VSC can output a current instruction value to the current loop controller according to the grid demand, the current loop controller can determine the voltage reference value of the grid-connected system according to the current instruction value and the real-time current value of the grid-connected system, and the energy storage valve controller VBC can determine the number of energy storage submodules to be put in or cut out according to the voltage reference value and the capacitor voltage of the energy storage submodule, thereby realizing the control of the DC current of the grid-connected system.

[0079] However, in the above VBC unlocking and VSC unlocking process, the system voltage and current may fluctuate, which will affect the operation stability of the grid-connected system, and when the AC power grid fails, it will also affect the operation stability of the grid-connected system.

[0080] In summary, the current operating conditions may affect the operation stability of the grid-connected system, that is, the current grid-connected system has the problem of poor stability.

[0081] In order to improve the operation stability of the grid-connected system, the current control method of the grid-connected system provided by the embodiments of the present application can determine the integral term limit value of the current loop controller suitable for the current operating condition according to the current operating condition, and determine the input reference voltage of the grid-connected system based on the integral term limit value, so that the energy storage valve controller can control the switching of the energy storage submodule based on the current operating condition when executing the switching strategy, thereby reducing the current fluctuation of the system and improving the operation stability of the grid-connected system.

[0082] The current control method of the grid-connected system and the energy storage valve controller provided by the embodiments of the present application will be described in detail below with reference to the accompanying drawings:

[0083] Please refer to FIG. 1, which is a schematic architecture diagram of a grid-connected system to which a current control method provided by an embodiment of the present application is applicable. The grid-connected system 10 can include a commutation valve controller 101 and an energy storage valve controller 102. The commutation valve controller 101 can be connected to an AC power grid 20 through a commutation module. The energy storage valve controller 102 can be connected to an energy storage system 30, which can include a plurality of energy storage submodules 301. The energy storage valve controller 102 can control the switching in or out of the energy storage submodules 301, i.e., the energy storage valve controller 102 can control the connection or disconnection of the energy storage submodules 301 to the grid-connected system (specifically, the energy storage valve controller 102 can control the number of energy storage submodules 301 connected to the grid-connected system).

[0084] Here, the energy storage submodule 301 connected to the grid-connected system is referred to as a switched-in submodule, and the energy storage submodule 301 disconnected from the grid-connected system, not bypassed, and not equal to 0 is referred to as an available submodule.

[0085] In a specific application, the above-mentioned preset SOC threshold value can be set according to actual application requirements.

[0086] In a specific application, the above-mentioned energy storage valve controller 102 can further include a current loop controller 102a. As shown in FIG. 2, an input end of the current loop controller 102a can be connected to the commutation valve controller 101. The current loop controller 102a can output a switched-in reference voltage according to a current specification value given by the commutation valve controller 101 and a current sample value collected.

[0087] The above-mentioned energy storage valve controller 102 can calculate the number of energy storage submodules needed to be switched in to the grid-connected system according to the switched-in reference voltage determined by the current loop controller 102a, thereby determining a switching strategy to be executed and executing the switching strategy so that the DC current of the grid-connected system can be maintained at a required level.

[0088] It can be understood that the above-mentioned switching strategy can be to control how many energy storage submodules 301 to switch in or how many energy storage submodules 301 to switch out. Switching in energy storage submodules 301 means connecting available submodules to the grid-connected system, and switching out energy storage submodules 301 means disconnecting switched-in submodules from the grid-connected system.

[0089] Specifically, the above-mentioned converter valve controller 101 can be located in a converter, an AC end of the converter can be connected with the above-mentioned AC power grid 20, a DC end of the converter can be connected with the power generation system 40 through a DC bus, and the energy storage system 30 can be connected to the DC bus. The above-mentioned connecting the energy storage sub-module 301 in the energy storage system 30 to the grid system can be specifically connecting the energy storage sub-module to the DC bus, and the above-mentioned disconnecting the energy storage sub-module 301 in the energy storage system 30 from the grid system can be specifically disconnecting the energy storage sub-module from the DC bus.

[0090] Specifically, the converter can include a converter module and the converter valve controller 101.

[0091] The converter module can be configured to realize mutual conversion between AC power and DC power.

[0092] For example, for a three-phase three-wire AC power grid, the converter module can include three bridge arms corresponding to three different phases of AC power, and the three bridge arms can be connected in parallel to the DC bus. Optionally, each bridge arm can include an upper bridge arm and a lower bridge arm connected in series, and the common connection points of the upper bridge arm and the lower bridge arm of each bridge arm can be connected to the corresponding phase line of AC power.

[0093] Each upper bridge arm or lower bridge arm can include a bridge arm resistor R, a bridge arm inductor L and at least one power module connected in series, and the power module can include a switching device such as an insulated gate bipolar transistor (IGBT) and / or a diode.

[0094] For example, for a three-phase four-wire AC power grid, the converter module can include three bridge arms corresponding to three different phases of AC power, and a bridge arm connected to the zero line, and the four bridge arms can be connected in parallel to the DC bus.

[0095] In some implementations, the above-mentioned converter valve controller 101 can be, but is not limited to, a controller device such as a programmable logic controller (PLC) or a micro controller unit (MCU).

[0096] It should be noted that the converter valve controller 101 can give corresponding voltage command values and current command values according to the required voltage and current of the power grid specification, for example, for a power grid that needs to provide a power supply voltage of 35kV and a current of 2000A, the voltage command value can be set to ±70kV, and the current command value can be set to 2000A.

[0097] The output of the above-mentioned converter valve controller 101 can be connected with each power module in the converter. Based on this, the converter valve controller 101 can realize operation control (such as control of the output power of the converter) of the converter by switching control of each power module.

[0098] In some embodiments, since when a single-phase fault or a multi-phase fault occurs in the alternating current power grid, the fault current of the power grid can pass through to the direct current side, thereby generating oscillation, therefore, in order to reduce the current generated during the fault, the current instruction value is limited.

[0099] In specific applications, the above-mentioned energy storage valve controller 102 can realize control of putting in and cutting out of the energy storage sub-module by controlling the switching of the power module in the energy storage sub-module.

[0100] In specific applications, the energy storage system can include a plurality of cascaded energy storage sub-modules, each energy storage sub-module can include a power module and a battery module, the power module can adopt a half-bridge power module, or can adopt a full-bridge power module, and the above-mentioned battery module can be a single-branch series battery module, or can be a multi-branch series-parallel sub-module.

[0101] Specifically, the energy storage valve controller 201 can realize regulation of the system direct current by executing the current control method provided by the embodiments of the present application. It should be noted that the specific content of the current control method will be described below, which will not be described here in detail.

[0102] Please refer to FIG. 3, which is a schematic flow chart of a current control method of a grid-connected system provided by the embodiments of the present application. The execution subject of the current control method can be the above-mentioned energy storage valve controller. The current control method can include S301 to S303, which are described in detail as follows:

[0103] S301, determining the integral term limiting value of the current loop controller according to the current operating condition.

[0104] Specifically, the above-mentioned current operating condition can refer to the operating condition of the energy storage valve controller and the operating condition of the converter valve controller, the operating condition of the energy storage valve controller can include the operating state and the operating period of the energy storage valve controller, and the operating condition of the converter valve controller can include the operating state and the operating period of the converter valve controller. The operating state of the energy storage valve controller can be an unlocked state or a locked state, and the operating period of the energy storage valve controller refers to the control period after unlocking. The operating state of the converter valve controller can be an unlocked state or a locked state, and the operating period of the converter valve controller refers to the control period after unlocking.

[0105] In some embodiments, the current operating condition can specifically include, but is not limited to, the energy storage valve controller being in a lockout state, the energy storage valve controller being in an unlock state and the operating period being within the first n1 periods, the energy storage valve controller being in an unlock state and the operating period being after the first n1 periods, the converter valve controller being in a lockout state, the converter valve controller being in an unlock state and the operating period being within the first n2 periods, the converter valve controller being in an unlock state and the operating period being after the first n2 periods, and the like.

[0106] It should be noted that in each control period, the energy storage valve controller determines the number of energy storage submodules to be put into the grid-connected system according to the input reference voltage of the energy storage system and the capacitor voltage of each energy storage submodule, that is, the switching strategy of the current control period can be determined, and the switching strategy is executed to realize the current control of the system.

[0107] Since the current stability of the grid-connected system is inconsistent under different operating conditions, in order to make the current change of the grid-connected system more smooth, the integral term limit value of the current loop controller is determined according to the current operating condition, so as to reduce the change range of the input reference voltage output by the current loop controller, and thus the current of the grid-connected system can be better stabilized, and the stability and reliability of the system are improved.

[0108] It should be noted that the integral term limit value is set to limit the integral term, so as to effectively control the growth rate of the integral term. In the current loop controller, the integral term generally represents the cumulative error of the system, and the integral term limit value can control the cumulative error of the system, so as to reduce the problem of system instability caused by excessive cumulative error.

[0109] In specific applications, the integral term limit value can include an upper limit value of the integral term and a lower limit value of the integral term.

[0110] In the embodiments of the present application, the integral term limit value of the current loop controller corresponding to different operating conditions is different, that is, the integral term can be limited under different integral term limit values under different operating conditions, so that the current control is closer to the actual operating condition, and the operating stability of the system can be better improved.

[0111] In some embodiments, as shown in FIG. 4, S301 can specifically include the following steps:

[0112] 301-1: Detect whether the energy storage valve controller is in a lockout state.

[0113] In specific applications, the operating state of the energy storage valve controller can be obtained through a monitoring module of the system, that is, the grid-connected system can further include a monitoring module, and the monitoring module can monitor the operating state of each controller.

[0114] 301-2: In the case that the energy storage valve controller is in the locked state, set the integral term limit value of the current loop controller to 0.

[0115] In a specific application, the energy storage valve controller is in the locked state, which means that the energy storage valve controller is not currently working at this time. At this time, the integral term limit value of the current loop controller is set to 0, that is, the current loop controller is not allowed to participate in control. That is, in the case that the current has not yet reached the constant current control stage, by setting the integral term limit value of the current loop controller to 0, the current loop controller can be cut out, so that the current loop controller will not affect the system.

[0116] 301-3, in the case that the energy storage valve controller is in the unlocked state, determine whether the running period of the energy storage valve controller is after the first n1 period.

[0117] 301-4, in the case that the running period of the energy storage valve controller is after the first n1 period, set the upper limit value of the integral term of the current loop controller to the minimum value of the allowable charging current of each input sub-module, and set the lower limit value of the integral term of the current loop controller to the minimum value of the allowable discharging current of each input sub-module.

[0118] 301-5, in the case that the running period of the energy storage valve controller is within the first n1 period, set the upper limit value of the integral term of the current loop controller to the minimum value of the allowable charging current of each available sub-module, and set the lower limit value of the integral term of the current loop controller to the minimum value of the allowable discharging current of each available sub-module.

[0119] In a specific application, since the running period of the energy storage valve controller is within the first n1 period, it means that the constant current control has just started. At this time, the difference between the current control and the current command value of the system is large, and the current change is relatively unstable. Using the minimum value of the allowable charging and discharging current of the available sub-module to limit the integral term of the current loop controller can make the current regulation process more stable, thereby reducing the influence of the current fluctuation generated when the energy storage valve controller is unlocked on the system, and improving the stability of the system.

[0120] After the running period is after the first n1 period, since the influence of the unlocking of the energy storage valve controller has gradually disappeared, using the minimum value of the allowable charging and discharging current of the input sub-module to limit the integral term of the current loop controller can make the constant current control more accurate, and can further improve the reliability of the system.

[0121] It should be noted that the above n1 is a positive integer greater than 0, and the first n1 period can be set according to actual application requirements, for example, set to 3 periods, 2 periods, etc.

[0122] In this embodiment, the integral term limit value corresponding to the operating condition of the energy storage valve controller can be selected, so as to reduce the influence of the current fluctuation generated by the energy storage valve controller unlocking on the system, and effectively improve the stability of the system.

[0123] S302, determine the input reference voltage of the grid-connected system according to the current instruction value, the current measurement value, and the integral term limit value.

[0124] In specific applications, the current instruction value is determined by the converter valve controller according to the power supply demand of the grid-connected system, and the current measurement value refers to the measured current value, that is, in each control period, the current loop controller can obtain the direct current value of the system in this control period, which is the current measurement value. The integral term limit value can be determined according to S301.

[0125] In each control period, the current loop controller determines the input reference voltage according to the current instruction value given by the converter valve controller and the actual collected direct current based on the PI regulation algorithm, wherein the integral term limit value used in the process of determining the input reference voltage by the PI regulation algorithm is the integral term limit value determined by S301.

[0126] S302 can specifically be: limiting the current loop controller based on the integral term limit value, and determining the output value of the current loop controller according to the current instruction value and the current measurement value, and then determining the input reference voltage according to the output value of the current loop controller.

[0127] In some embodiments, referring to FIG. 5, the input value of the current loop controller can be the current instruction value Itarget and the current measurement value Imea, which are processed by the integral proportional controller (IP controller) and the I value limiting module, and then the corresponding regulation reference voltage ΔNdc_ref can be output.

[0128] The input reference voltage determined according to the output value of the current loop controller can be set as the sum of the voltage instruction value and the output value of the current loop controller, or can be set as the sum of the voltage measurement value and the output value of the current loop controller.

[0129] It should be noted that the current measurement value can be obtained by a current sampling module, a current sampling circuit, etc.

[0130] S303: determine the switching strategy according to the input reference voltage, and execute the switching strategy.

[0131] In a specific application, after the input reference voltage is determined, the number of energy storage sub-modules that need to be input is calculated according to the average capacitor voltage of the energy storage sub-modules, and then a control strategy such as a phase-shifted pulse width modulation (PSPWM) strategy, a nearest level modulation (NLM) strategy, etc. is used to determine which energy storage sub-modules need to be cut out or input, that is, to determine the switching strategy corresponding to the number of energy storage sub-modules that need to be input, so that the switching strategy can be executed by the energy storage valve controller to control the direct current of the system.

[0132] As can be seen from the above, the current control method provided by the embodiments of the present application can determine the integral term limit value of the current loop controller suitable for the current operating condition according to the current operating condition, and use the integral term limit value to participate in the calculation of the input reference voltage, so as to reduce the variation range of the input reference voltage output by the current loop controller, and further to better stabilize the current of the grid-connected system and improve the stability and reliability of the system.

[0133] In the application process, the converter valve controller VSC is a controller for constant voltage control. In the case of single-phase fault or multi-phase fault of the alternating current grid, a fault ride-through current is generated, which further causes the direct current on the direct current side to fluctuate. In order to reduce the current fluctuation caused by the fault of the alternating current side, the current instruction value input to the above-mentioned current loop controller can be limited, and the current instruction value can also be limited when no fault of the alternating current side occurs, so as to reduce the influence of the fluctuation of the current instruction value on the stability of the system.

[0134] Referring to FIG. 6, in another embodiment, an embodiment of the present application provides a current control method different from the above-mentioned embodiments. As shown in FIG. 6, in the embodiment of the present application, the above-mentioned current control method further includes the following steps:

[0135] S601: limiting the current instruction value according to the current operating condition.

[0136] The above-mentioned current operating condition can also be a fault of the alternating current grid. In some embodiments, as shown in FIG. 7, the above-mentioned S601 can specifically include the following steps:

[0137] 601-1: detecting whether a fault of the alternating current grid occurs.

[0138] 601-2: obtaining an alternating current fault limit value in the case of a fault of the alternating current grid.

[0139] In a specific application, the above-mentioned alternating current fault limit value can be calculated by the converter valve controller according to the actual fault condition.

[0140] 601-3: limit the current command value according to the above-mentioned AC fault limiting value.

[0141] In a specific application, the limiting of the current command value according to the AC fault limiting value is specifically setting the upper limit value of the current command value as the absolute value of the AC fault limiting value, and setting the lower limit of the current command value as the opposite number of the absolute value of the AC fault limiting value.

[0142] 601-4: in the case where no AC grid fault occurs, obtaining the minimum allowable charge-discharge current of each available sub-module, and determining the current command limiting value according to the minimum allowable charge-discharge current of the available sub-module and the current command value.

[0143] In a specific application, the minimum allowable charge-discharge current of each available sub-module can include the minimum allowable charge current of each available sub-module and the minimum allowable discharge current of each available sub-module, and the determination of the current command limiting value according to the minimum allowable charge-discharge current of the available sub-module and the current command value includes:

[0144] setting the upper limit value of the current command limiting value as the smaller value between the minimum allowable charge current of the available sub-module and the current command value, i.e., taking the minimum of the minimum allowable charge current of the available sub-module and the current command value, and setting the value obtained by taking the minimum as the upper limit value of the current command limiting value.

[0145] setting the lower limit value of the current command limiting value as the smaller value between the minimum allowable discharge current of the available sub-module and the opposite number of the current command value, i.e., taking the minimum of the minimum allowable discharge current of the available sub-module and the opposite number of the current command value, and setting the value obtained by taking the minimum as the lower limit value of the current command limiting value.

[0146] In some implementations, the current command value can be 1 times the reference current (i.e., 1 pu).

[0147] It should be noted that in the embodiments of the present application, a positive current value represents a charge current, and a negative current value represents a discharge current.

[0148] 601-5: limiting the current command value according to the upper limit value of the current command limiting value and the lower limit value of the current command limiting value.

[0149] The limiting of the current command according to the current command limiting value can be specifically setting the upper limit value of the current command value as the upper limit value of the current command limiting value, and setting the lower limit of the current command value as the lower limit value of the current command limiting value.

[0150] In the embodiment of the present application, by limiting the current instruction value, the fault current of the AC side can effectively pass through, thereby reducing the current fluctuation of the grid-connected system caused by single-phase fault or multi-phase fault of the AC side, and improving the operation stability of the grid-connected system.

[0151] In an embodiment of the present application, as shown in FIG. 8, the current control method provided by the embodiment of the present application can further include the following steps:

[0152] S801: In the case of detecting that the AC power grid is in fault ride-through, latch the integral term of the current loop controller before the fault.

[0153] In a specific application, the integral term of the current loop controller before the fault specifically refers to setting the integral term of the current loop controller to the integral term before the fault, and keeping it unchanged.

[0154] In the embodiment, in the case of fault ride-through of the AC power grid, latching the integral term can further reduce the influence of the fault current generated by the fault ride-through on the grid stability, and effectively realize the fault ride-through.

[0155] In an embodiment of the present application, as shown in FIG. 9, the current control method provided by the embodiment of the present application can further include the following steps:

[0156] S901: Limit the output value of the current loop controller.

[0157] It should be noted that limiting the output value of the current loop controller refers to controlling the output value of the current loop controller between the upper limit value and the lower limit value of the output limit value.

[0158] It should be noted that the upper limit value and the lower limit value of the output limit value can be set according to actual application requirements.

[0159] In some embodiments, as shown in FIG. 10, limiting the output value of the current loop controller can be performed by a PI limiting module, that is, the input value of the current loop controller can be the current instruction value Itarget and the current measurement value Imea, which are processed by the integral proportional controller (IP controller) and the I value limiting module and the PI value limiting module, and then the corresponding adjustment reference voltage ΔNdc_ref can be output.

[0160] By limiting the output value of the current loop controller, the stable condition of the grid-connected system caused by the too large output value of the current loop controller can be reduced, and the operation stability of the grid-connected system is further improved.

[0161] In an embodiment of the present application, the system stability is also affected when the converter controller VSC is unlocked, therefore, in order to reduce the influence of the VSC unlocking process on the system stability and improve the system stability, an embodiment of the present application provides another current control method, which is different from the above-mentioned current control method, as shown in FIG. 11, in an embodiment of the present application, the above-mentioned current control method further includes the following steps:

[0162] S1101: determining whether the running period of the converter controller is after the first n2 periods.

[0163] S1102: in the case where the running period of the converter controller is after the first n2 periods, determining the input reference voltage according to the voltage measurement value and the output value of the current loop controller.

[0164] S1103: in the case where the running period of the converter controller is within the first n2 periods, determining the input reference voltage according to the voltage instruction value and the output value of the current loop controller.

[0165] In a specific application, different parameters are selected according to the running period of the converter controller to determine the input reference voltage, that is, in the first several control periods after unlocking, the input reference voltage is determined by using the voltage instruction value and the output value of the current loop controller. Specifically, the input reference voltage can be the sum of the voltage instruction value and the output value of the current loop controller, that is, Nde_ref=Nord+I_pi.

[0166] Wherein, Nde_ref represents the input reference voltage, Nord represents the voltage instruction value, and I_pi represents the output value of the current loop controller.

[0167] Since the VSC is just unlocked, the voltage of the system is not stable, therefore, the input reference voltage determined by using the voltage instruction value and the output value of the current loop controller together can make the voltage of the system reach the voltage instruction value more quickly, so that the system tends to be in a stable state more quickly.

[0168] It should be noted that the above-mentioned voltage instruction value is determined by the VSC based on the power supply demand of the alternating current power grid.

[0169] After n2 control periods are run, the input reference voltage determined by using the voltage measurement value and the output value of the current loop controller can more accurately adjust the voltage of the grid-connected system, thereby further improving the reliability of the system.

[0170] Specifically, the above-mentioned input reference voltage can be the sum of the voltage measurement value and the output value of the current loop controller, that is, Nde_ref=Nmea+I_pi.

[0171] Wherein, Nde_ref represents the input reference voltage, Nmea represents the voltage measurement value, and I_pi represents the output value of the current loop controller.

[0172] It should be noted that n2 is a positive integer greater than 0, and the first n2 periods can be set according to actual application requirements, for example, 3 periods, 2 periods, 4 periods, etc.

[0173] As can be seen from the above, the embodiment of the application can select different input reference voltages according to the operating conditions of the converter controller, so as to reduce the current fluctuation caused by VSC unlocking during the current control process, thereby improving the stability of the system.

[0174] In an embodiment of the application, as shown in FIG. 12, the current control method provided by the embodiment of the application can perform the following steps when determining the number of input energy storage submodules:

[0175] S1201: In the case where the operating period of the energy storage valve controller is within the first n1 periods, the number of input energy storage submodules is calculated according to the input reference voltage and the average capacitor voltage of the available submodules.

[0176] In specific applications, calculating the number of input energy storage submodules according to the input reference voltage and the average capacitor voltage of the available submodules is specifically: Ninput=Ndc_ref / Uav_ava;

[0177] Wherein, Ninput represents the number of input energy storage submodules, which can only be an integer at this point, so the calculation result of the formula will be rounded up to obtain the corresponding number, Ndc_ref represents the input reference voltage, and Uav_ava represents the average capacitor voltage of the available submodules.

[0178] S1202: In the case where the operating period of the energy storage valve controller is after the first n1 periods, the number of input energy storage submodules is calculated according to the input reference voltage and the average capacitor voltage of the input submodules.

[0179] In specific applications, calculating the number of input energy storage submodules according to the input reference voltage and the average capacitor voltage of the input submodules is specifically: Ninput=Ndc_ref / Uav_input;

[0180] Wherein, Ninput represents the number of input energy storage submodules, which can only be an integer at this point, so the calculation result of the formula will be rounded up to obtain the corresponding number, Ndc_ref represents the input reference, and Uav_input represents the average capacitor voltage of the input submodules.

[0181] In the first several control cycles of the VBC unlocking, the number of the energy storage sub-modules to be put in is calculated by using the average capacitor voltage of the available sub-modules, which can reduce the disturbance of the grid-connected system caused by the change of the number of the sub-modules to be put in at the moment of the VBC unlocking, thereby effectively improving the stability of the system.

[0182] It can be understood that the size of the serial number of each step in the above embodiments does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0183] Based on the current control method provided in the above embodiments, the present embodiment further provides an embodiment of an operation control device of a converter for implementing the above method embodiments. Please refer to FIG. 13, which is a structural schematic diagram of a control device provided in the present embodiment. For the convenience of description, only the parts related to the present embodiment are shown. As shown in FIG. 13, the operation control device 130 of the converter can include an amplitude limiting module 1301, a determination module 1302, and an execution module 1303. Among them:

[0184] The amplitude limiting module 1301 is configured to determine the integral term amplitude limit value of the current loop controller according to the current operating condition.

[0185] The determination module 1302 is configured to determine the put-in reference voltage of the grid-connected system according to the current instruction value, the current measurement value, and the integral term amplitude limit value.

[0186] The execution module 1303 is configured to determine the switching strategy according to the put-in reference voltage, and execute the switching strategy.

[0187] In some implementations, the above amplitude limiting module 1301 is specifically configured to, in the case that the energy storage valve controller is in the locked state, set the integral term amplitude limit value of the current loop controller to 0; in the case that the energy storage valve controller is in the unlocked state and the operating cycle of the energy storage valve controller is within the first n1 cycles, set the upper limit value of the integral term of the current loop controller to the minimum value of the allowable charging current of each put-in sub-module, and set the lower limit value of the integral term of the current loop controller to the minimum value of the allowable discharging current of each put-in sub-module; in the case that the energy storage valve controller is in the unlocked state and the operating cycle of the energy storage valve controller is after the first n1 cycles, set the upper limit value of the integral term of the current loop controller to the minimum value of the allowable charging current of each available sub-module, and set the lower limit value of the integral term of the current loop controller to the minimum value of the allowable discharging current of each available sub-module; wherein n1 is a positive integer greater than 0.

[0188] In some implementations, the current control device of the grid-connected system further includes a second current limiting module configured to limit the amplitude of the current instruction value according to the current operating condition.

[0189] In some implementations, the second current limiting module is specifically configured to, in the case where the AC power grid fault occurs, obtain an AC fault limiting value; and limit the current instruction value according to the AC fault limiting value.

[0190] In some implementations, the second current limiting module is further configured to, in the case where the AC power grid fault does not occur, obtain a minimum allowable charge-discharge current of the available sub-modules, set an upper limit value of the current instruction limiting value as a value corresponding to the minimum allowable charge current of the available sub-modules and the current instruction value being smaller, and set a lower limit value of the current instruction limiting value as a value corresponding to the minimum allowable discharge current of the available sub-modules and the opposite of the current instruction value being smaller, to determine the current instruction limiting value; and limit the current instruction value according to the upper limit value of the current instruction limiting value and the lower limit value of the current instruction limiting value.

[0191] In some implementations, the current control device of the grid-connected system can further include a latch module configured to latch an integral term of the current loop controller before the fault in the case where the AC power grid fault is detected.

[0192] In some implementations, the determination module 1302 is specifically configured to limit the current loop controller based on the integral term limiting value, and determine an output value of the current loop controller according to the current instruction value and a current measurement value; and determine the input reference voltage of the grid-connected system according to the output value of the current loop controller.

[0193] In some implementations, the determination module 1302 is specifically configured to, in the case where the operation period of the converter valve controller is after the first n2 periods, determine the input reference voltage according to the voltage measurement value and the output value of the current loop controller; and in the case where the operation period of the converter valve controller is within the first n2 periods, determine the input reference voltage according to the voltage instruction value and the output value of the current loop controller, where n2 is a positive integer greater than 0.

[0194] In some implementations, the execution module 1303 can further include a calculation unit configured to, in the case where the operation period of the energy storage valve controller is within the first n1 periods, calculate the number of input energy storage sub-modules according to the input reference voltage and the average capacitor voltage of the available sub-modules; and in the case where the operation period of the energy storage valve controller is after the first n1 periods, calculate the number of input energy storage sub-modules according to the input reference voltage and the average capacitor voltage of the input sub-modules.

[0195] In some implementations, the current control device of the grid-connected system can further include a third limiting module configured to limit the output value of the current loop controller.

[0196] It should be noted that the information interaction and execution process between the above units are based on the same concept as the method embodiments of the present application, and the specific functions and technical effects brought by them can be referred to the method embodiments part. Here, no longer be described.

[0197] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above division of each functional module / unit is exemplified, and in actual application, the above functions can be completed by different functional modules / units according to needs, that is, the internal structure of the control device is divided into different functional modules / units to complete all or part of the above described functions. Each functional module / unit in the embodiment can be integrated in one processing unit, or each unit can be physically independent, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or software functional module / unit. In addition, the specific name of each functional module / unit is only for easy distinction, and does not limit the protection scope of the present application. The specific working process of each unit in the control device can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0198] Please refer to FIG. 14, which is a structural schematic diagram of a running control device of a converter according to another embodiment of the present application. As shown in FIG. 14, the running control device 14 of the converter according to the embodiment can include a processor 140, a memory 141, and a computer program 142 stored in the memory 141 and executable on the processor 140, such as a program corresponding to the current control method. The processor 140 implements the steps in the current control method embodiments described above, such as S301-S303 shown in FIG. 3, when executing the computer program 142. Alternatively, the processor 140 implements the functions of each module / unit in the control device embodiments described above, such as the functions of the units 1301-1303 shown in FIG. 13, when executing the computer program 142.

[0199] For example, the computer program 142 can be divided into one or more modules / units, which are stored in the memory 141 and executed by the processor 140 to complete the present application. One or more modules / units can be a series of computer program instruction segments that can complete a specific function, which are used to describe the execution process of the computer program 142 in the control device 14. For example, the computer program 142 can be divided into an acquisition module and a setting module. The specific functions of each module can refer to the related description in the corresponding embodiment of FIG. 14, which will not be described here.

[0200] Those skilled in the art can understand that FIG. 14 is only an example of the control device 14, and does not constitute a limitation on the control device 14, and can include more or fewer components than those shown, or combine certain components, or different components.

[0201] The processor 140 can be a central processing unit (CPU), and can also be other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0202] The memory 141 can be an internal storage unit of the control device 14, such as a hard disk or a memory of the control device 14. The memory 141 can also be an external storage device of the control device 14, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card or a flash card, etc. equipped on the control device 14. Further, the memory 141 can include both the internal storage unit and the external storage device of the control device 14. The memory 141 is used to store computer programs and other programs and data required by the control device. The memory 141 can also be used to temporarily store data that has been output or will be output.

[0203] The embodiment of the present application also provides a computer readable storage medium, which stores a computer program. The computer program is executed by a processor to implement each step of the current control method in the current method embodiment.

[0204] The embodiment of the present application provides a computer program product. When the computer program product is run on a control device, the control device implements the steps in each method embodiment.

[0205] The embodiment of the present application also provides an energy storage valve controller, which includes the current control device of the grid-connected system in the above embodiment.

[0206] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0207] Those skilled in the art can understand that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software manner depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0208] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent replacements; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A current control method for a grid-connected system, applied to an energy storage valve controller, the current control method comprising: Determine the integral term limit value of the current loop controller based on the current operating conditions; The reference voltage for grid connection is determined based on the current command value, the current measurement value, and the integral term limit value. The switching strategy is determined based on the input reference voltage, and the switching strategy is executed.

2. The current control method according to claim 1, wherein, The determination of the integral term limit value of the current loop controller based on the current operating conditions includes: When the energy storage valve controller is in the locked state, the integral term limit value of the current loop controller is set to 0; When the energy storage valve controller is in the unlocked state and the operating cycle of the energy storage valve controller is within the first n1 cycles, the upper limit of the integral term of the current loop controller is set to the minimum allowable charging current of each input sub-module, and the lower limit of the integral term of the current loop controller is set to the minimum allowable discharge current of each input sub-module. When the energy storage valve controller is in the unlocked state and the operating cycle of the energy storage valve controller is after the previous n1 cycles, the upper limit of the integral term of the current loop controller is set to the minimum allowable charging current of each available submodule, and the lower limit of the integral term of the current loop controller is set to the minimum allowable discharge current of each available submodule; where n1 is a positive integer greater than 0.

3. The current control method according to claim 1 or 2, wherein, Before determining the grid-connected system's input reference voltage based on the current command value and the integral term limiting value, the method further includes: The current command value is limited based on the current operating conditions.

4. The current control method according to claim 3, wherein, Limiting the current command value based on the current operating conditions includes: In the event of an AC power grid fault, obtain the AC fault limit value; The current command value is limited according to the AC fault limit value.

5. The current control method according to claim 3, wherein, Limiting the current command value based on the current operating conditions includes: In the absence of an AC power grid fault, the minimum allowable charging and discharging current of the available submodule is obtained. The upper limit of the current command limit is set to the smaller value of the minimum allowable charging current of the available submodule and the current command value. The lower limit of the current command limit is set to the smaller value of the minimum allowable discharging current of the available submodule and the opposite of the current command value. The current command value is limited according to the upper limit value and the lower limit value of the current command limit value.

6. The current control method according to claim 3, wherein, After limiting the current command value according to the current operating conditions, the method further includes: In the event of a detected fault ride-through in the AC power grid, the integral term of the current loop controller prior to the fault is latched.

7. The current control method according to any one of claims 1 to 6, wherein, The step of determining the grid-connected system's input reference voltage based on the current command value, the current measurement value, and the integral term limiting value includes: The current loop controller is limited based on the integral term limiting value, and the output value of the current loop controller is determined according to the current command value and the current measurement value. The input reference voltage of the grid-connected system is determined based on the output value of the current loop controller.

8. The current control method according to claim 7, wherein, Determining the grid-connected system's input reference voltage based on the output value of the current loop controller includes: When the operating cycle of the converter valve controller is after the first n2 cycles, the input reference voltage is determined based on the voltage measurement value and the output value of the current loop controller; If the operating cycle of the converter valve controller is within the first n2 cycles, the input reference voltage is determined based on the voltage command value and the output value of the current loop controller, where n2 is a positive integer greater than 0.

9. The current control method according to claim 7, wherein, Also includes: When the operating cycle of the energy storage valve controller is within the first n1 cycles, the number of energy storage sub-modules to be put into operation is calculated based on the input reference voltage and the average capacitor voltage of the available sub-modules. When the operating cycle of the energy storage valve controller is after the first n1 cycles, the number of energy storage sub-modules to be put into operation is calculated based on the input reference voltage and the average capacitor voltage of the input sub-module.

10. The current control method according to any one of claims 7 to 9, wherein, Also includes: The output value of the current loop controller is limited.

11. A current control device in a grid-connected system, comprising: The limiting module is used to determine the limiting value of the integral term of the current loop controller based on the current operating conditions; The determination module is used to determine the input reference voltage of the grid-connected system based on the current command value, the current measurement value, and the integral term limit value. An execution module is used to determine a switching strategy based on the input reference voltage and execute the switching strategy.

12. A current control device in a grid-connected system, wherein, It includes a memory and a computer program stored in the memory and executable on a processor, wherein the processor, when executing the computer program, implements the current control method as described in any one of claims 1-10.

13. An energy storage valve controller, characterized in that, The energy storage valve controller includes the current control device as described in claim 11 or claim 12.

14. A computer-readable storage medium storing a computer program, wherein, When the computer program is executed by the processor, it implements the current control method as described in any one of claims 1-10.

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