Harmonic suppression method of energy storage grid-connected system and energy storage grid-connected system

Abstract

The invention provides a harmonic suppression method of an energy storage grid-connected system and the energy storage grid-connected system, and belongs to the technical field of harmonic suppression. Acquiring three-phase electric energy information of a grid-connected point of the energy storage grid-connected system in real time, and determining harmonic current content according to the three-phase electric energy information; if the harmonic current content of the grid-connected point of the energy storage grid-connected system does not meet the preset power grid harmonic standard, acquiring three-phase current output by each energy storage converter in the energy storage grid-connected system in real time, and determining nth harmonic current corresponding to each energy storage converter based on the three-phase current output by each energy storage converter; and generating a target driving signal based on the nth harmonic current corresponding to each energy storage converter, and sending the target driving signal to each energy storage converter to control each energy storage converter to cooperatively execute harmonic suppression. According to the invention, the harmonic suppression strategy can be dynamically adjusted based on the real-time total harmonic distortion rate of the energy storage grid-connected system and the harmonic difference state of the plurality of energy storage converters, so that the harmonic suppression capability of the energy storage grid-connected system is improved.

Description

Technical Field

[0001] This application relates to the field of harmonic suppression technology, and more specifically, to a harmonic suppression method and an energy storage grid-connected system. Background Technology

[0002] With the large-scale grid connection of renewable energy and the increasing demand for flexible regulation capabilities in power systems, electrochemical energy storage systems have been widely used on the generation, grid, and user sides due to their advantages of rapid response and flexible configuration. As the core power conversion and control device of electrochemical energy storage systems, the energy storage converter's power quality, especially its harmonic characteristics, directly affects the safe and stable operation of the power grid and the lifespan and efficiency of connected equipment. However, when multiple energy storage converters are connected in parallel to the same point of common coupling (PCC), factors such as the discreteness of power device parameters, differences in battery charge, and environmental variations cause non-uniform superposition of amplitude and phase harmonics in the output current of each converter. This increases the total harmonic distortion rate at the grid connection point, threatening power quality and the safety of power electronic equipment.

[0003] In related technologies, current harmonics in parallel energy storage converters are often suppressed in three ways: the first is to add hardware devices such as passive filters, active filters, or hybrid filters to filter out or compensate for harmonics of a specific order; the second is to suppress current harmonics through software control methods such as virtual impedance method and droop control; and the third is to suppress high-order harmonics generated during the inverter process of multi-circuit topology circulating current devices by injecting harmonic current of a specific frequency into the circuit.

[0004] However, while various methods disclosed in related technologies are used for harmonic suppression in parallel energy storage converters, these methods primarily focus on harmonic optimization of a single energy storage converter, lacking coordinated observation and global control of the overall harmonic state of the grid-connected system. This results in poor suppression performance in scenarios with multiple energy storage converters operating in parallel. Furthermore, due to differences in manufacturing processes, varying degrees of device aging, and differences in battery state of charge, the harmonic suppression requirements of multiple converters operating in parallel are not entirely the same, making it difficult for related technologies to achieve differentiated harmonic suppression. Moreover, these technologies cannot dynamically adjust the control strategy based on the actual total harmonic distortion rate at the grid connection point, leading to poor harmonic suppression performance. Summary of the Invention

[0005] The purpose of this application is to provide a harmonic suppression method and a grid-connected energy storage system, which can achieve the effect of dynamically adjusting the harmonic suppression strategy based on the real-time total harmonic distortion rate of the grid-connected energy storage system and the harmonic difference state of multiple energy storage converters, so as to improve the harmonic suppression capability of the grid-connected energy storage system.

[0006] The embodiments of this application are implemented as follows: A first aspect of this application provides a harmonic suppression method for an energy storage grid-connected system. The method is applied to a control module within the energy storage grid-connected system and includes: The system collects three-phase power information at the grid connection point of the energy storage grid-connected system in real time, and determines the harmonic current content at the grid connection point of the energy storage grid-connected system based on the three-phase power information. The three-phase power information includes three-phase current and three-phase voltage. If the harmonic current content at the grid connection point of the energy storage grid connection system does not meet the preset grid harmonic standard, the three-phase current output of each energy storage converter in the energy storage grid connection system is collected in real time, and the nth harmonic current corresponding to each energy storage converter is determined based on the three-phase current output of each energy storage converter, where n is a positive integer greater than zero. The target drive signal is generated based on the nth harmonic current corresponding to each energy storage converter, and the target drive signal is sent to each energy storage converter to control each energy storage converter to perform harmonic suppression in a coordinated manner.

[0007] As one possible implementation, the aforementioned harmonic current content includes: total harmonic current content and nth harmonic current content. Real-time acquisition of three-phase power information at the grid connection point of the energy storage grid-connected system is performed, and the harmonic current content at the grid connection point of the energy storage grid-connected system is determined based on the three-phase power information, including: Harmonic analysis is performed on the three-phase current and three-phase voltage to determine the total harmonic current content and the nth harmonic current content at the grid connection point of the energy storage grid-connected system.

[0008] As one possible implementation, the nth harmonic current corresponding to each energy storage converter is determined based on the three-phase current of each energy storage converter, including: The three-phase currents of each energy storage converter are subjected to fundamental frequency filtering to obtain the total harmonic current components corresponding to each energy storage converter. The three-phase current of each energy storage converter is subjected to fundamental frequency phase-locked loop processing to obtain the baseband current phase corresponding to each energy storage converter; Based on the baseband current phase corresponding to each energy storage converter, the coordinate transformation is performed on the total harmonic current component corresponding to each energy storage converter to obtain the coordinate transformed total harmonic current component corresponding to each energy storage converter. Harmonic extraction is performed on the total harmonic current components after coordinate transformation to obtain the nth harmonic current corresponding to each energy storage converter.

[0009] As one possible implementation, a target drive signal is sent to each energy storage converter based on the nth harmonic current corresponding to each energy storage converter, including: Based on the nth harmonic current corresponding to each energy storage converter, determine the reference harmonic current corresponding to each energy storage converter. Based on the nth harmonic current and reference harmonic current corresponding to each energy storage converter, the harmonic compensation voltage corresponding to each energy storage converter is generated, and the harmonic compensation voltage is subjected to inverse coordinate transformation to obtain the three-phase compensation voltage corresponding to each energy storage converter. Based on the three-phase current output by each energy storage converter, determine the corresponding three-phase reference voltage for each energy storage converter. Based on the three-phase reference voltage and three-phase compensation voltage corresponding to each energy storage converter, a target drive signal corresponding to each energy storage converter is generated, and each target drive signal is sent to the corresponding energy storage converter.

[0010] As one possible implementation, the aforementioned nth harmonic current includes: active harmonic current and reactive harmonic current; the aforementioned reference harmonic current includes: active reference harmonic current and reactive reference harmonic current; the aforementioned harmonic compensation voltage includes: active harmonic compensation voltage and reactive harmonic compensation voltage; and based on the nth harmonic current and reference harmonic current corresponding to each energy storage converter, the harmonic compensation voltage corresponding to each energy storage converter is generated, including: Based on the active harmonic current and active reference harmonic current corresponding to each energy storage converter, the active harmonic current difference corresponding to each energy storage converter is determined, and based on the active harmonic current difference, the active harmonic compensation voltage corresponding to each energy storage converter is generated. Based on the reactive harmonic current and reactive reference harmonic current corresponding to each energy storage converter, the reactive harmonic current difference corresponding to each energy storage converter is determined, and based on the reactive harmonic current difference, the reactive harmonic compensation voltage corresponding to each energy storage converter is generated.

[0011] As one possible implementation, based on the three-phase reference voltage and three-phase compensation voltage corresponding to each energy storage converter, a target drive signal corresponding to each energy storage converter is generated, including: The reference voltages of each phase in the three-phase reference voltage corresponding to the energy storage converter are added to the compensation voltages of each phase in the three-phase compensation voltage corresponding to the energy storage converter to obtain the target voltages of each phase corresponding to the energy storage converter. The target voltages of each phase corresponding to the energy storage converter are input into the pulse width modulator to obtain the target drive signal corresponding to each energy storage converter.

[0012] As one possible implementation, the harmonic suppression method for the above-mentioned energy storage grid-connected system also includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the first preset threshold, then the reference harmonic current of at least one energy storage converter other than the target energy storage converter is reduced according to the preset adjustment strategy.

[0013] As one possible implementation, the harmonic suppression method for the above-mentioned energy storage grid-connected system also includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the second preset threshold, a shutdown drive signal is generated and sent to the switch corresponding to the target energy storage converter so that the target energy storage converter is forcibly shut down. The second preset threshold is greater than the first preset threshold.

[0014] A second aspect of the present application provides an energy storage grid-connected system, which includes: multiple energy storage converters, a control module, and multiple switches and multiple energy storage batteries corresponding to each energy storage converter. One end of each energy storage converter is connected to the external AC power grid via a switch, and the other end of each energy storage converter is connected to an energy storage battery. The control module is connected to the grid connection point of each energy storage converter, the output terminal of each energy storage converter, the control terminal of each energy storage converter, and the control terminal of each switch. The control module is used to execute the steps of the harmonic suppression method for the energy storage grid-connected system described in the first aspect above.

[0015] As one possible implementation, the above control module includes: a centralized controller, a judgment unit, a band-stop filter, a coordinate transformer, a subtractor, an integral controller, an inverse coordinate transformer, an adder, a pulse width modulator, a power control unit, and a phase-locked loop; The first input terminal of the centralized controller is connected to the grid connection point where all energy storage converters are connected. The second input terminal of the centralized controller, the input terminal of the phase-locked loop, and the input terminal of the power control unit are all connected to the output terminal of each energy storage converter. The first output terminal of the centralized controller is connected to the input terminal of the judgment unit, and the second output terminal of the centralized controller is connected to the control terminal of each switch. The output of the judgment unit is connected to the input of the band-stop filter, the output of the band-stop filter is connected to the first input of the coordinate transformer, and the second input of the coordinate transformer and the second input of the inverse coordinate transformer are both connected to the output of the phase-locked loop. The first output of the coordinate transformer and the third output of the centralized controller are both connected to the input of a subtractor. The second output of the coordinate transformer and the fourth output of the centralized controller are both connected to the input of another subtractor. The output of each subtractor is connected to the input of an integral controller. The output of each integral controller is connected to the first input of the inverse coordinate transformer. The output of the inverse coordinate transformer is connected via the first input of an adder. The output of the power control unit is connected to the second input of the adder. The output of the adder is connected to the input of the pulse width modulator. The output of the pulse width modulator is connected to the control terminal of each energy storage converter.

[0016] The beneficial effects of the embodiments of this application include: This application provides a harmonic suppression method for an energy storage grid-connected system. The method involves real-time acquisition of the three-phase voltage and current at the grid connection point of the energy storage grid-connected system, determining the harmonic current content at the grid connection point based on these values, and determining whether the harmonic current content meets a preset current harmonic standard. If so, the method real-time acquisition of the three-phase current on the output side of each parallel energy storage converter in the energy storage grid-connected system, and determining the nth harmonic current corresponding to each energy storage converter based on the three-phase current on the output side of each energy storage converter. A target driving signal is generated based on the nth harmonic current corresponding to each energy storage converter, and the target driving signal is sent to each corresponding energy storage converter to control the energy storage converters to collaboratively perform harmonic suppression, thereby achieving global harmonic suppression of the energy storage grid-connected system. The control module determines whether harmonic suppression is needed for the energy storage grid-connected system based on real-time three-phase power information at the grid connection point. It also determines the reference harmonic current value for each energy storage converter based on the actual nth harmonic current of each converter, thus achieving differentiated harmonic collaborative suppression. This allows for dynamic adjustment of the harmonic suppression strategy based on the real-time total harmonic distortion rate of the energy storage grid-connected system and the harmonic differences among multiple energy storage converters, thereby improving the harmonic suppression capability of the energy storage grid-connected system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of the first type of energy storage grid-connected system provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of a second type of energy storage grid-connected system provided in an embodiment of this application; Figure 3 A flowchart illustrating a first harmonic suppression method for an energy storage grid-connected system provided in this application embodiment; Figure 4 A flowchart illustrating a second harmonic suppression method for an energy storage grid-connected system provided in this application embodiment; Figure 5 A flowchart illustrating the harmonic suppression method for a third energy storage grid-connected system provided in this application embodiment; Figure 6 A flowchart illustrating the fourth harmonic suppression method for an energy storage grid-connected system provided in this application embodiment; Figure 7A flowchart of a fifth harmonic suppression method for an energy storage grid-connected system provided in this application embodiment.

[0019] Reference numerals: 10: Energy storage grid-connected system; 101: Energy storage converter; 102: Control module; 1021: Central controller; 1022: Judgment unit; 1023: Band-stop filter; 1024: Coordinate transformer; 1025: Subtractor; 1026: Integrator controller; 1027: Inverse coordinate transformer; 1028: Adder; 1029: Pulse width modulator; 10210: Power control unit; 10211: Phase-locked loop; 103: Switch; 104: Energy storage battery. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] In the description of this application, it should be noted that the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] Currently, current harmonics in parallel energy storage converters are typically suppressed using three methods: first, by adding (active, passive, or hybrid) filters to filter out or compensate for harmonics of specific orders; second, by using software control methods such as virtual impedance and droop control to suppress current harmonics; and third, by injecting harmonic currents of specific frequencies into the circuit to suppress high-order harmonics generated during the inverter process of multi-circuit topology circulating current devices. However, these methods mainly focus on harmonic optimization of a single energy storage converter, lacking coordinated observation and global control of the overall harmonic state of the grid-connected system, resulting in poor harmonic suppression performance. Furthermore, due to differences in manufacturing processes, device aging, and battery state of charge among multiple parallel energy storage converters in a grid-connected system, their harmonic suppression requirements also vary. Existing technologies cannot effectively manage the different states of each energy storage converter. Furthermore, the control strategies of existing technical solutions are fixed and singular, and cannot be dynamically adjusted according to the total harmonic distortion rate of the grid-connected system, which also leads to poor harmonic suppression effect of the grid-connected system.

[0025] To address this, this application provides a resonance suppression method for energy storage grid-connected systems. This method involves real-time acquisition of the three-phase voltage and current at the grid connection point of the energy storage grid-connected system, and determining the harmonic current content at the grid connection point based on these parameters. It then determines whether the harmonic current content at the grid connection point meets a preset current harmonic standard. If so, it acquires the three-phase current at the output side of each parallel energy storage converter in the energy storage grid-connected system in real-time, and determines the nth harmonic current corresponding to each energy storage converter based on the three-phase current at the output side of each energy storage converter. A target driving signal is generated based on the nth harmonic current corresponding to each energy storage converter, and this target driving signal is sent to the corresponding energy storage converter to control the energy storage converters to collaboratively perform harmonic suppression, thereby achieving global harmonic suppression of the energy storage grid-connected system. This achieves the effect of dynamically adjusting the harmonic suppression strategy based on the real-time total harmonic distortion rate of the energy storage grid-connected system and the harmonic difference state of multiple energy storage converters, thereby improving the harmonic suppression capability of the energy storage grid-connected system.

[0026] The following description, in conjunction with the accompanying drawings, provides a detailed explanation of the energy storage grid-connected system and the resonance suppression method for the energy storage grid-connected system provided in the embodiments of this application.

[0027] Figure 1 See the schematic diagram of an energy storage grid-connected system provided in this application. Figure 1 The energy storage grid-connected system 10 provided in this application embodiment includes: multiple energy storage converters 101, a control module 102, and multiple switches 103 and multiple energy storage batteries 104 corresponding to each energy storage converter 101.

[0028] One end of each energy storage converter 101 is connected to the external AC power grid via a switch 103, and the other end of each energy storage converter 101 is connected to an energy storage battery 104. The control module 102 is connected to the grid connection point common to each energy storage converter 101, the output terminal of each energy storage converter 101, the control terminal of each energy storage converter 101, and the control terminal of each switch 103. The control module 102 is used to perform the steps of the harmonic suppression method for the energy storage grid-connected system described below.

[0029] Specifically, the AC output terminal of each energy storage converter 101 is connected to the AC bus of the external AC power grid via a switch 103, so that each energy storage converter 101 can be independently connected to or disconnected from the AC power grid; the DC input terminal of each energy storage converter 101 is connected to an independent energy storage battery 104 to form a one-to-one power supply relationship, ensuring that each energy storage converter 101 has an independent energy source, which facilitates refined management and maintenance.

[0030] Furthermore, the control module 102, as the core control element of the entire energy storage grid-connected system 10, is connected to the grid connection point shared by each energy storage converter 101, the output terminal of each energy storage converter 101, the control terminal of each energy storage converter 101, and the control terminal of each switch 103. Specifically, the control module 102 samples the three-phase voltage and three-phase current of the entire energy storage grid-connected system 10 via the grid connection point; it samples the three-phase current output from the AC output terminal of each energy storage converter 101 via the output terminal of each energy storage converter 101; based on its internal processing logic, the control module 102 issues control commands to the local controller of each energy storage converter 101; and based on its internal processing logic, it sends closing or opening commands to the corresponding switch 103 of each energy storage converter 101.

[0031] Optionally, each energy storage converter 101 serves as the core power conversion device of the energy storage grid-connected system 10, used to realize bidirectional conversion between the DC power of the energy storage battery 104 and the AC power of the external AC grid. Each energy storage converter 101 can complete basic charging or discharging functions under the control of the control module 102 down to zero. Under the action of the differentiated harmonic current reference command issued by the control module 102, it can also generate and output harmonic compensation current of a specific number to offset its own or assist in offsetting the harmonic current of the energy storage grid-connected system 10.

[0032] Optionally, each energy storage battery 104 serves as an energy storage element in the energy storage grid-connected system 10, providing active power support for the entire energy storage grid-connected system 10. Specifically, each energy storage battery 104 can provide the necessary energy support for its corresponding energy storage inverter 101 to perform harmonic compensation functions, and provide active power for its corresponding energy storage inverter 101 to generate harmonic compensation current of a specific order.

[0033] It should be noted that each energy storage converter 101 has its corresponding energy storage battery 104. Even if one of the energy storage batteries 104 or energy storage converters 101 in the energy storage grid-connected system 10 malfunctions, the other energy storage converters 101 that are not malfunctioning can still continue to perform harmonic suppression tasks under the control of the control module 102, thereby improving the reliability of harmonic suppression in the energy storage grid-connected system 10.

[0034] Optionally, each switch 103 can typically be implemented by a circuit breaker or contactor, serving as a physical switching device connecting each energy storage converter 101 to the external AC power grid. When the control module 102 determines that a certain energy storage converter 101 in the energy storage grid-connected system 10 has severely excessive harmonic content that cannot be corrected, the control module 102 can send a shutdown command to the switch 103 corresponding to that energy storage converter 101, so that the faulty energy storage converter 101 can be quickly disconnected from the energy storage grid-connected system 10, preventing the faulty energy storage converter 101 from affecting the power quality of the entire energy storage grid-connected system 10.

[0035] In this way, a single energy storage converter 101 can be switched on and maintained in a targeted manner without affecting the normal operation of other energy storage converters 101.

[0036] Optionally, the control module 102, as the core control element of the energy storage grid-connected system 10, can not only monitor the total harmonic level of the common grid connection point of the energy storage grid-connected system 10 in real time, but also monitor the individual harmonic content of each energy storage converter 101 in real time, thereby grasping the global harmonic distribution status of the energy storage grid-connected system 10. Furthermore, based on the global harmonic distribution status of the energy storage grid-connected system 10, the control module 102 determines whether to initiate coordinated control. If initiated, it issues differentiated harmonic current reference commands to each energy storage converter 101 according to the harmonic contribution of each energy storage converter 101, achieving coordinated optimization. In addition, the control module 102 can also execute a hierarchical control strategy. That is, when there is a harmonic anomaly in an energy storage converter 101, it first adjusts the harmonic reference command. If this is ineffective, it then sends a shutdown command to the switch 103 corresponding to the energy storage converter 101, so that the faulty energy storage converter 101 is quickly disconnected, ensuring the normal operation of other healthy energy storage converters 101.

[0037] Optionally, the energy storage grid-connected system 10, through centralized intelligent scheduling by the control module 102, organizes multiple independent energy storage converters 101 and their corresponding energy storage batteries 104 into a collaborative whole. This not only enables basic charging and discharging functions but also, through real-time communication and closed-loop control, allows each energy storage converter 101 to dynamically output the required harmonic compensation current while outputting fundamental power. Furthermore, the switches 103 corresponding to each energy storage converter 101 provide necessary physical isolation and safety guarantees for the energy storage grid-connected system 10. In this way, the global optimization capabilities of centralized control and the reliability advantages of distributed execution are fully utilized, effectively solving the harmonic superposition and conflict problems when multiple energy storage converters are connected in parallel, and significantly improving the power quality at the grid connection point of a large-scale energy storage power station.

[0038] In one alternative implementation, see [link to implementation details]. Figure 2 The control module 102 in the energy storage grid-connected system 10 provided in this application embodiment includes: a centralized controller 1021, a judgment unit 1022, a band-stop filter 1023, a coordinate transformer 1024, a subtractor 1025, an integral controller 1026, an inverse coordinate transformer 1027, an adder 1028, a pulse width modulator 1029, a power control unit 10210, and a phase-locked loop 10211.

[0039] The first input terminal of the centralized controller 1021 is connected to the grid connection point where each energy storage converter 101 is connected. The second input terminal of the centralized controller 1021, the input terminal of the phase-locked loop 10211, and the input terminal of the power control unit 10210 are all connected to the output terminal of each energy storage converter 101. The first output terminal of the centralized controller 1021 is connected to the input terminal of the judgment unit 1022. The second output terminal of the centralized controller 1021 is connected to the control terminal of each switch 103.

[0040] Optionally, the centralized controller 1021 serves as the information aggregation and decision-making center of the control module 102. Its first input terminal is connected to the grid connection point of the energy storage grid-connected system 10 to collect the three-phase voltage and three-phase current of the grid connection point of the energy storage grid-connected system 10. Its second input terminal is connected to the output terminal of each energy storage converter 101 to collect the three-phase current of each energy storage converter 101. Its first output terminal is connected to the input terminal of the judgment unit 1022 to issue a command to start harmonic suppression. Its second output terminal is connected to the control terminal of each switch 103 to execute the switching control of the faulty energy storage converter 101. Its third and fourth output terminals output the active reference harmonic current (Idref) and reactive reference harmonic current (Iqref), respectively.

[0041] Optionally, the input terminals of the phase-locked loop 10211 and the power control unit 10210 are both connected to the output terminals of each energy storage converter. The phase-locked loop 10211 is used to obtain the grid synchronization phase, and the power control unit 10210 is used to receive power commands and execute fundamental power control.

[0042] The output of the judgment unit 1022 is connected to the input of the band-stop filter 1023. The output of the band-stop filter 1023 is connected to the first input of the coordinate transformer 1024. The second input of the coordinate transformer 1024 and the second input of the inverse coordinate transformer 1027 are both connected to the output of the phase-locked loop 10211.

[0043] Optionally, the output of the judgment unit 1022 is connected to the input of the band-stop filter 1023 to form a trigger switch for the harmonic extraction channel.

[0044] Optionally, the total harmonic current or three-phase harmonic current output by the band-stop filter 1023 and the grid synchronization phase (ωt) output by the phase-locked loop 10211 are input together to the coordinate transformer 1024. The active harmonic current output by the coordinate transformer 1024 and the active reference harmonic current output by the centralized controller 1021 are input together to a subtractor 1025 for subtraction. The reactive harmonic current output by the coordinate transformer 1024 and the reactive reference harmonic current output by the centralized controller 1021 are input together to another subtractor 1025 for subtraction.

[0045] The first output terminal of coordinate transformer 1024 and the third output terminal of centralized controller 1021 are both connected to the input terminal of subtractor 1025. The second output terminal of coordinate transformer 1024 and the fourth output terminal of centralized controller 1021 are both connected to the input terminal of another subtractor 1025. The output terminal of each subtractor 1025 is connected to the input terminal of an integral controller 1026. The output terminal of each integral controller 1026 is connected to the first input terminal of coordinate inverse transformer 1027. The output terminal of coordinate inverse transformer 1027 is connected via the first input terminal of adder. The output terminal of power control unit 10210 is connected to the second input terminal of adder 1028. The output terminal of adder 1028 is connected to the input terminal of pulse width modulator 1029. The output terminal of pulse width modulator 1029 is connected to the control terminal of each energy storage converter 101.

[0046] Optionally, the error signals output by each subtractor 1025 are adjusted by the corresponding integral controller 1026 to obtain the harmonic compensation voltage corresponding to each energy storage converter 101. The harmonic compensation voltage is converted by the coordinate inverse transformer 1027 to obtain the three-phase compensation voltage corresponding to each energy storage converter 101.

[0047] Optionally, the three-phase compensation voltage output by the coordinate inverse transformer 1027 and the three-phase reference voltage output by the power control unit 10210 are vector-superimposed in the adder 1028 to form the final total voltage reference command, and the total voltage reference command is sent to the pulse width modulator 1029 to generate the pulse width modulation signal driving the switching circuits in each energy storage converter 101.

[0048] The centralized controller 1021 is mainly responsible for collecting the power information of the grid connection point of the energy storage grid-connected system 10 and the output terminals of each energy storage converter 101, and performing harmonic analysis on the power information. Based on the harmonic analysis results, it formulates a collaborative suppression strategy and then distributes differentiated harmonic current reference commands or sends disconnection commands to the switches corresponding to the faulty energy storage converter 101 in extreme cases. The judgment unit 1022 is mainly used to receive commands from the centralized controller 1021. When it detects that the harmonic current content of the grid connection point exceeds the standard, it outputs an enable signal to activate the subsequent harmonic extraction and control channel. If the harmonic content meets the standard, it keeps the channel closed to save resources.

[0049] Optionally, the band-stop filter 1023 is used as a hardware pre-filter, with its center frequency set to the fundamental frequency of the AC power grid (such as 50Hz). It is used to quickly and effectively filter out the strong fundamental component from the three-phase current output by the energy storage converter 101, thereby separating the total harmonic current containing harmonic currents of each frequency, and preparing for the accurate extraction of the subsequent nth harmonic current.

[0050] Optionally, the coordinate transformer 1024 is mainly used to accurately extract harmonic components. Based on the grid synchronization phase (ωt) provided by the phase-locked loop 10211, the total harmonic current is transformed into a negative-sequence dq coordinate system rotating at n times the fundamental frequency, thereby quickly obtaining the active and reactive components corresponding to the specific nth harmonic current.

[0051] In addition, the subtractor 1025 and the integrator 1026 together form a tracking control loop for harmonic current. The subtractor 1025 is used to calculate the error between the actual harmonic component and the reference harmonic command. The integrator 1026 (usually a PI controller) is used to calculate the error and generate the required harmonic compensation voltage command. The goal is to make the actual harmonic current track the reference value issued by the central controller without steady-state error.

[0052] Furthermore, the coordinate inverse transformer 1027 uses the grid synchronization phase output by the phase-locked loop 10211 to inversely transform the harmonic compensation voltage calculated in the dq rotating coordinate system back to the instantaneous voltage value in the three-phase stationary coordinate system, so as to synthesize it with the grid fundamental voltage.

[0053] Optionally, the phase-locked loop 10211 tracks the phase and frequency of the grid voltage in real time, providing a unified synchronization angle for the entire energy storage grid-connected system 10, ensuring that all control operations are strictly synchronized with the grid; the power control unit 10210 receives active or reactive power commands issued by the centralized controller 1021, and generates a three-phase reference voltage to achieve the required power flow through its internal current inner loop control and other algorithms; the adder 1028 is used to vector-add the three-phase reference voltage generated by the power control unit 10210 with the harmonic compensation voltage output by the coordinate inverse transformer 1027 to form a composite voltage reference command that simultaneously contains fundamental power control information and harmonic compensation information.

[0054] Optionally, the pulse width modulator 1029 serves as the "final actuator" of the control module 102, converting the continuous voltage reference signal output by the adder 1028 into a high-frequency pulse width modulated signal that can be executed by the power electronic switch, thereby actually generating the desired voltage waveform at the output of the energy storage converter 101.

[0055] Figure 3 A flowchart of a harmonic suppression method for an energy storage grid-connected system provided in this application is provided. This method is applied to the above-mentioned... Figure 2 The control module 102 in the grid-connected energy storage system 10 shown. See also... Figure 3 This application provides a harmonic suppression method for an energy storage grid-connected system, comprising: S301. Real-time acquisition of three-phase power information at the grid connection point of the energy storage grid-connected system, and determination of harmonic current content at the grid connection point of the energy storage grid-connected system based on the three-phase power information. The three-phase power information includes three-phase current and three-phase voltage.

[0056] Optionally, the centralized controller 1021 in the control module 102 collects the three-phase power information of the grid connection point of the energy storage grid-connected system 10 in real time. The three-phase power information includes three-phase voltage and three-phase current. Both the three-phase voltage and three-phase current are instantaneous values. The instantaneous values ​​of the three-phase current include Ia, Ib, and Ic, and the instantaneous values ​​of the three-phase voltage include Ua, Ub, and Uc.

[0057] Optionally, the centralized controller 1021 performs harmonic analysis on the three-phase power information collected at the grid connection point to determine the total harmonic current content and the content of each harmonic current at the grid connection point. Specifically, harmonic analysis can be achieved through fast Fourier transform, and this application does not impose specific limitations on this.

[0058] Optionally, the centralized controller 1021 inputs the calculated total harmonic current content and the harmonic current content of each order into the judgment unit 1022. The judgment unit 1022 compares the total harmonic current content and the harmonic current content of each order at the grid connection point of the energy storage grid-connected system 10 with the preset grid harmonic standard to determine whether the harmonic current content at the grid connection point of the energy storage grid-connected system 10 meets the preset grid harmonic standard. The preset grid harmonic standard is a power quality standard pre-set by the national grid or local grid, and this application does not specifically limit it.

[0059] S302. If the harmonic current content at the grid connection point of the energy storage grid connection system does not meet the preset grid harmonic standard, the three-phase current output of each energy storage converter in the energy storage grid connection system is collected in real time, and the nth harmonic current corresponding to each energy storage converter is determined based on the three-phase current output of each energy storage converter, where n is a positive integer greater than zero.

[0060] Optionally, if the judgment result obtained by the judgment unit 1022 is that the harmonic current content at the grid connection point of the energy storage grid-connected system 10 does not meet the preset grid harmonic standard, then the coordinated harmonic suppression process is initiated. The centralized controller 1021 then collects the three-phase current output from the output terminal of each energy storage converter 101 in the energy storage grid-connected system 10 in real time, and performs n harmonic current extraction operations for each energy storage converter 101.

[0061] For example, if it is necessary to extract the third harmonic current from the three-phase current output by each energy storage converter in the grid-connected energy storage system, the fundamental (50Hz) component in the three-phase current output by each energy storage converter is first filtered out by a hardware band-stop filter to obtain the total harmonic current containing each harmonic. At the same time, the phase-locked loop obtains the accurate grid fundamental phase ωt based on the three-phase current or three-phase voltage output by each energy storage converter. Then, the coordinate transformer transforms the total harmonic current to the negative sequence dq coordinate system that rotates synchronously with 3 times the fundamental phase, and in this coordinate system, the third harmonic current of the energy storage converter is separated and extracted from the total harmonic current.

[0062] It should be noted that the nth harmonic current can be the 3rd harmonic current, the 5th harmonic current, the 7th harmonic current, etc., and this application does not make a specific limitation on it.

[0063] S303. Generate a target drive signal based on the nth harmonic current corresponding to each energy storage converter, and send the target drive signal to each energy storage converter to control each energy storage converter to perform harmonic suppression in a coordinated manner.

[0064] Optionally, after acquiring the nth harmonic current of all energy storage converters 101, the centralized controller 1021 makes a collaborative decision based on the global optimization principle, generates a target drive signal corresponding to each energy storage converter 101, and sends each target drive signal to the control terminal of the switching circuit in each energy storage converter 101, so that each energy storage converter 101 can collaboratively perform harmonic suppression.

[0065] Optionally, the centralized controller 1021 analyzes the differences in harmonic pollution levels among the energy storage converters 101, assigning smaller harmonic compensation tasks to the energy storage converters 101 with higher harmonic content, thereby achieving a synergistic suppression effect of suppressing strong harmonics and supporting weak harmonics. Based on this, it calculates the reference harmonic current corresponding to the nth harmonic current of each energy storage converter 101. After acquiring new harmonic data in the next control cycle, it dynamically adjusts the reference harmonic current sent to each energy storage converter 101, forming a closed-loop optimization.

[0066] Optionally, after receiving the target drive signal sent by the control module 102, each energy storage converter 101 starts local tracking control to effectively suppress the harmonics at the grid connection point of the entire energy storage grid-connected system 10, and ensure that the grid-connected current quality meets the requirements.

[0067] In this embodiment, the three-phase voltage and three-phase current of the grid connection point of the energy storage grid-connected system are collected in real time, and the harmonic current content of the grid connection point of the energy storage grid-connected system is determined based on the three-phase voltage and three-phase current of the grid connection point. It is then determined whether the harmonic current content of the grid connection point of the energy storage grid-connected system meets the preset current harmonic standard. If so, the three-phase current of the output side of each energy storage converter connected in parallel in the energy storage grid-connected system is collected in real time, and the nth harmonic current corresponding to each energy storage converter is determined based on the three-phase current of the output side of each energy storage converter. A target driving signal is generated based on the nth harmonic current corresponding to each energy storage converter, and the target driving signal is sent to each corresponding energy storage converter to control each energy storage converter to perform harmonic suppression in a coordinated manner, thereby realizing global harmonic suppression of the energy storage grid-connected system. The control module determines whether harmonic suppression is needed for the energy storage grid-connected system based on real-time three-phase power information at the grid connection point. It also determines the reference harmonic current value for each energy storage converter based on the actual nth harmonic current of each converter, thus achieving differentiated harmonic collaborative suppression. This allows for dynamic adjustment of the harmonic suppression strategy based on the real-time total harmonic distortion rate of the energy storage grid-connected system and the harmonic differences among multiple energy storage converters, thereby improving the harmonic suppression capability of the energy storage grid-connected system.

[0068] In an optional implementation, the harmonic current content includes: total harmonic current content and nth harmonic current content, and the operation of step S301 can specifically be as follows: Harmonic analysis is performed on the three-phase current and three-phase voltage to determine the total harmonic current content and the nth harmonic current content at the grid connection point of the energy storage grid-connected system.

[0069] Optionally, the centralized controller 1021 performs digital harmonic analysis on the collected three-phase voltage and three-phase current at the grid connection point to obtain the total harmonic current content and the nth harmonic current content at the grid connection point of the energy storage grid-connected system. Specifically, the centralized controller 1021 performs spectrum analysis on the collected three-phase current at the grid connection point to obtain the total harmonic current content characterizing the overall distortion level (usually expressed as total harmonic distortion rate THD). i (represented); simultaneously, the centralized controller 1021 performs frequency decomposition on the three-phase voltage of the grid connection point, identifies and quantifies the nth harmonic current content of each specific order (such as the 5th, 7th, 11th, etc.) (usually expressed as the harmonic content rate HR of each harmonic). in express).

[0070] Digital harmonic analysis can be achieved through fast Fourier transform, instantaneous power theory decomposition, or other applicable spectrum calculation methods, and this application does not impose specific limitations on this.

[0071] In this embodiment, the control module can comprehensively and accurately assess the harmonic pollution status of the grid connection point by synchronously monitoring the total harmonic content and the content of each harmonic at the grid connection point, providing accurate data for subsequent judgment on whether synergistic suppression is triggered and for formulating targeted suppression strategies.

[0072] In one alternative implementation, see [link to implementation details]. Figure 4 The operation of "determining the nth harmonic current corresponding to each energy storage converter based on the three-phase current of each energy storage converter" in step S302 above can be specifically as follows: S401. Perform fundamental frequency filtering on the three-phase current of each energy storage converter to obtain the total harmonic current component corresponding to each energy storage converter.

[0073] Optionally, the band-stop filter 1023 performs fundamental frequency filtering on the phase currents covered by the three-phase currents output by each energy storage converter 101 to obtain the total harmonic current components corresponding to each energy storage converter 101.

[0074] Specifically, the dominant grid fundamental frequency component (e.g., 50Hz) in the three-phase current output by each energy storage converter 101 is filtered out by the band-stop filter 1023 to obtain the total harmonic current component after removing the fundamental frequency. This component contains all harmonic components from the second to higher orders, providing a signal basis for the subsequent accurate extraction of the nth harmonic.

[0075] S402. Perform fundamental frequency phase-locked loop processing on the three-phase current of each energy storage converter to obtain the baseband current phase corresponding to each energy storage converter.

[0076] Optionally, the three-phase current output by each energy storage converter 101 is subjected to fundamental frequency phase-locked processing via a phase-locked loop 10211 to obtain the baseband current phase corresponding to each energy storage converter, so as to track the phase and frequency of the grid voltage or current fundamental wave in real time and accurately. Here, the fundamental wave current phase refers to the current phase that is strictly synchronized with the grid fundamental wave.

[0077] S403. Based on the baseband current phase corresponding to each energy storage converter, perform coordinate transformation on the total harmonic current component corresponding to each energy storage converter to obtain the coordinate transformed total harmonic current component corresponding to each energy storage converter.

[0078] Optionally, the coordinate transformer 1024 transforms the total harmonic current components corresponding to each energy storage converter 101 from a three-phase stationary coordinate system (abc coordinate system) to a two-phase rotating coordinate system (dq coordinate system) that rotates synchronously with the grid fundamental wave, based on the baseband current phase of each energy storage converter 101 provided by the phase-locked loop 10211, to obtain the coordinate-transformed total harmonic current components corresponding to each energy storage converter 101. Specifically, the coordinate-transformed total harmonic current components are harmonic signals represented in the dq coordinate system at a specific rotation speed.

[0079] S404. Harmonic extraction is performed on the total harmonic current components after coordinate transformation to obtain the nth harmonic current corresponding to each energy storage converter.

[0080] Optionally, the total harmonic current components of each energy storage converter 101 are transformed to a negative-sequence dq coordinate system rotating at n times the fundamental angular frequency using a coordinate transformer 1024. In this coordinate system, the nth harmonic component will be represented as a DC quantity, while other harmonics will remain as AC quantities. By using a simple low-pass filter or directly reading the DC component, the nth harmonic current corresponding to each energy storage converter 101 can be efficiently and accurately separated.

[0081] In one alternative implementation, see [link to implementation details]. Figure 5 The specific operation of step S303 above can be as follows: S501. Determine the reference harmonic current for each energy storage converter based on the nth harmonic current corresponding to each energy storage converter.

[0082] Optionally, the centralized controller 1021 performs system-level analysis and optimization decisions based on the nth harmonic current corresponding to each energy storage converter 101 to determine the reference harmonic current to be issued to each energy storage converter 101.

[0083] Specifically, the centralized controller 1021 does not issue a uniform reference harmonic current to all energy storage converters 101. Instead, based on a global optimization objective (such as minimizing the total harmonic distortion rate at the grid connection point) and combined with the harmonic output characteristics of each energy storage converter 101 (i.e., the amplitude and phase of the nth harmonic current of each energy storage converter 101), it sends different reference harmonic currents to each energy storage converter 101. For example, for an energy storage converter with a high nth harmonic content, a smaller reference harmonic current may be assigned, reducing its suppression workload; for an energy storage converter with a low harmonic content, a relatively larger reference harmonic current may be assigned, allowing it to undertake more active suppression, thereby achieving the optimal harmonic cancellation effect.

[0084] S502. Based on the nth harmonic current and reference harmonic current corresponding to each energy storage converter, generate the harmonic compensation voltage corresponding to each energy storage converter, and perform inverse coordinate transformation on the harmonic compensation voltage to obtain the three-phase compensation voltage corresponding to each energy storage converter.

[0085] Optionally, the subtractor 1025 compares the actual nth harmonic current of each energy storage converter 101 with the reference harmonic current generated by the centralized controller 1021 for each energy storage converter 101 to obtain the harmonic current error, and inputs the harmonic current error into the integrator controller 1026; the integrator controller 1026 adjusts the harmonic current error of each energy storage converter 101 to obtain the harmonic compensation voltage corresponding to each energy storage converter. The harmonic compensation voltage is the harmonic compensation voltage required to force the actual nth harmonic current to track the reference harmonic current in the dq rotating coordinate system.

[0086] Optionally, the integral controller 1026 inputs the harmonic compensation voltage corresponding to each energy storage converter 101 into the coordinate inverter 1027. The coordinate inverter 1027 converts the harmonic compensation voltage in the dq coordinate system corresponding to each energy storage converter 101 back to the three-phase compensation voltage in the three-phase stationary coordinate system based on the baseband current phase corresponding to each energy storage converter 101 provided by the phase-locked loop 10211.

[0087] The frequency and phase of the three-phase compensation voltage correspond in the time domain to the nth harmonic current of the energy storage converter 101.

[0088] S503. Determine the three-phase reference voltage corresponding to each energy storage converter based on the three-phase current output by each energy storage converter.

[0089] Optionally, the power control unit 10210 performs closed-loop calculations based on the three-phase current output by each energy storage converter 101 and the active power command or reactive power command issued by the centralized controller 1021 to obtain the three-phase reference voltage corresponding to each energy storage converter. The three-phase reference voltage is a pure fundamental voltage signal used to control the charging and discharging functions of each energy storage converter 101.

[0090] S504. Based on the three-phase reference voltage and three-phase compensation voltage corresponding to each energy storage converter, generate the target drive signal corresponding to each energy storage converter, and send each target drive signal to the corresponding energy storage converter.

[0091] Optionally, the adder 1028 vector-superimposes the phase reference voltages included in the three-phase reference voltages provided by the power control unit 10210 for each energy storage converter 101 and the phase compensation voltages included in the three-phase compensation voltages generated by the harmonic suppression loop for each energy storage converter 101, respectively, to obtain a total voltage reference signal that simultaneously contains fundamental power control information and harmonic compensation information.

[0092] Optionally, the adder 1028 inputs the total voltage reference signal corresponding to each energy storage converter 101 into the pulse width modulator 1029. The pulse width modulator 1029 generates a high-frequency target drive signal based on the total voltage reference signal. The pulse width modulator 1029 sends the target drive signal to the control terminal of the switching circuit of the corresponding energy storage converter 101 to realize the power exchange control and harmonic compensation injection of the energy storage converter 101.

[0093] In one optional implementation, the nth harmonic current includes: active harmonic current and reactive harmonic current; the reference harmonic current includes: active reference harmonic current and reactive reference harmonic current; and the harmonic compensation voltage includes: active harmonic compensation voltage and reactive harmonic compensation voltage. (See also...) Figure 6 The operation of "generating the harmonic compensation voltage corresponding to each energy storage converter based on the nth harmonic current and the reference harmonic current corresponding to each energy storage converter" in step S502 above can be specifically as follows: S601. Based on the active harmonic current and active reference harmonic current corresponding to each energy storage converter, determine the active harmonic current difference corresponding to each energy storage converter, and generate the active harmonic compensation voltage corresponding to each energy storage converter based on the active harmonic current difference.

[0094] Optionally, a subtractor 1025 is used to subtract the active harmonic current in the nth harmonic current of each energy storage converter 101 output by the harmonic suppression loop from the active reference harmonic current in the reference harmonic current generated by the centralized controller 1021 for each energy storage converter 101, so as to obtain the active harmonic current difference corresponding to each energy storage converter 101.

[0095] Optionally, the subtractor 1025 inputs the active harmonic current difference value into the corresponding integrator 1026. The integrator 1026 calculates the active harmonic current difference value according to preset control parameters to obtain the active harmonic compensation voltage corresponding to each energy storage converter 101. The active harmonic compensation voltage is used to adjust the active harmonic current of each energy storage converter 101, enabling it to accurately track the active reference harmonic current.

[0096] S602. Based on the reactive harmonic current and reactive reference harmonic current corresponding to each energy storage converter, determine the reactive harmonic current difference corresponding to each energy storage converter, and generate the reactive harmonic compensation voltage corresponding to each energy storage converter based on the reactive harmonic current difference.

[0097] Optionally, another subtractor 1025 is used to subtract the reactive harmonic current in the nth harmonic current of each energy storage converter 101 output by the harmonic suppression loop from the reactive reference harmonic current in the reference harmonic current generated by the centralized controller 1021 for each energy storage converter 101, so as to obtain the reactive harmonic current difference corresponding to each energy storage converter 101.

[0098] Optionally, the subtractor 1025 inputs the reactive harmonic current difference value into the corresponding integrator 1026. The integrator 1026 calculates the reactive harmonic current difference value according to preset control parameters to obtain the reactive harmonic compensation voltage corresponding to each energy storage converter 101. The reactive harmonic compensation voltage is used to adjust the reactive harmonic current of each energy storage converter 101, enabling it to accurately track the reactive reference harmonic current.

[0099] In one alternative implementation, see [link to implementation details]. Figure 7 The operation of "generating the target drive signal corresponding to each energy storage converter based on the three-phase reference voltage and three-phase compensation voltage corresponding to each energy storage converter" in step S504 above can be specifically as follows: S701. Add the reference voltage of each phase included in the three-phase reference voltage corresponding to the energy storage converter to the compensation voltage of each phase included in the three-phase compensation voltage corresponding to the energy storage converter to obtain the target voltage of each phase corresponding to the energy storage converter.

[0100] Optionally, the multiple adders 1028 in the control module 102 perform phase-by-phase synthesis of the phase reference voltage in the three-phase reference voltage corresponding to each energy storage converter 101 and the phase compensation voltage included in the three-phase compensation voltage to obtain the phase target voltage corresponding to each energy storage converter 101.

[0101] Specifically, each adder adds the phase reference voltages included in the three-phase reference voltages generated by the power control unit 10210 for each energy storage converter 101 to the phase compensation voltages included in the three-phase compensation voltages generated by the harmonic suppression loop (composed of a band-stop filter 1023, a coordinate transformer 1024, a subtractor 1025, an integrator controller 1026, and a coordinate inverse transformer 1027) for each energy storage converter 101 at instantaneous values ​​to obtain the target phase voltages corresponding to each energy storage converter 101.

[0102] S702. Input the target voltage of each phase corresponding to the energy storage converter into the pulse width modulator to obtain the target drive signal corresponding to each energy storage converter.

[0103] Optionally, multiple adders 1028 input the target voltage of each phase corresponding to each energy storage converter as the modulation wave into the pulse width modulator 1029. The pulse width modulator 1029 converts the continuous voltage reference signal into a series of discrete, duty cycle controllable high-frequency pulse signals, i.e., target drive signals, according to a predetermined carrier frequency and modulation strategy (such as space vector pulse width modulation SVPWM or sinusoidal pulse width modulation SPWM).

[0104] Optionally, the pulse width modulator 1029 sends each target drive signal to the control terminal of the corresponding energy storage converter 101's switching circuit to precisely control the on / off timing of the switching circuit, so that the AC output terminal of the energy storage converter 101 can reproduce the actual voltage waveform consistent with the voltage reference command, thereby realizing the coordinated control of the fundamental and harmonic components of the energy storage grid-connected system 10.

[0105] In an optional implementation, the harmonic suppression method for the above-mentioned energy storage grid-connected system further includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the first preset threshold, then the reference harmonic current of at least one energy storage converter other than the target energy storage converter is reduced according to the preset adjustment strategy.

[0106] Optionally, the centralized controller 1021 continuously monitors the nth harmonic current of each energy storage converter. When it determines that the amplitude of the nth harmonic current of the target energy storage converter in the energy storage grid-connected system 10 is greater than or equal to the first preset threshold, it indicates that the harmonic output of the energy storage converter 101 may be significantly higher than the average level due to device characteristics, operating conditions or minor abnormalities. In order to avoid the excessively high harmonic content of this single energy storage converter 101 from raising the total harmonic level of the grid connection point, the centralized controller 1021 will activate the preset adjustment strategy by utilizing the harmonic compensation capability of other normal energy storage converters 101 in the energy storage grid-connected system 10.

[0107] This adjustment strategy does not simply adjust the reference harmonic current of the target energy storage converter 101 itself, but rather reduces the reference harmonic current of at least one other normal energy storage converter 101. For example, the reference harmonic current of all other normal energy storage converters can be reduced proportionally and uniformly, or the reference harmonic current of other energy storage converters with harmonics in phase with the output of the target converter can be selectively reduced.

[0108] It should be noted that by reducing the active compensation output of these normal energy storage converters, the vector relationship of the total harmonic current synthesized at the grid connection point of the energy storage grid-connected system 10 can be changed, thereby partially offsetting or balancing the excess harmonic components generated by the target energy storage converter 101 as a whole, so that the total harmonic content at the grid connection point returns to an acceptable range.

[0109] Optionally, the first preset threshold can be set according to power grid standards, historical operating data or system tolerances, and this application does not specifically limit it.

[0110] It should also be noted that the target energy storage converter 101 can be any energy storage converter in the energy storage grid-connected system 10 with excessive harmonic current, and this application does not make specific limitations on this.

[0111] In an optional implementation, the harmonic suppression method for the above-mentioned energy storage grid-connected system further includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the second preset threshold, a shutdown drive signal is generated and sent to the switch corresponding to the target energy storage converter so that the target energy storage converter is forcibly shut down. The second preset threshold is greater than the first preset threshold.

[0112] Optionally, the setting of the second preset threshold is usually based on the safety limits of the equipment, the power grid protection requirements, and the maximum single point of failure that the system can tolerate. The second preset threshold is greater than the first preset threshold used to trigger the coordinated adjustment mechanism, representing a more severe level of failure or performance degradation.

[0113] Optionally, when the centralized controller 1021 determines that the amplitude of the nth harmonic current of the target energy storage converter 101 in the energy storage grid-connected system 10 is greater than or equal to a second preset threshold, it indicates that the target energy storage converter 101 has experienced a serious abnormality (such as power device failure, control instability, or internal filter failure), and the harmonic pollution it generates has exceeded the range that can be compensated for through the internal coordinated adjustment of the energy storage grid-connected system 10. Therefore, if the target energy storage converter 101 continues to be connected to the energy storage grid-connected system 10, it will not only seriously affect the power quality at the grid connection point, but may also endanger the safe operation of other normal energy storage converters 101.

[0114] In this case, the centralized controller 1021 generates a shutdown drive signal (such as a low level or trip command) and sends it to the control terminal of the switch 103 corresponding to the target energy storage converter. After receiving the shutdown drive signal, the switch 103 performs a tripping action, thereby forcibly shutting down the target energy storage converter 101 from the AC parallel bus.

[0115] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0116] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A harmonic suppression method for an energy storage grid-connected system, characterized in that, The method is applied to the control module of an energy storage grid-connected system, and the method includes: The three-phase power information of the grid connection point of the energy storage grid-connected system is collected in real time, and the harmonic current content of the grid connection point of the energy storage grid-connected system is determined based on the three-phase power information. The three-phase power information includes three-phase current and three-phase voltage. If the harmonic current content at the grid connection point of the energy storage grid-connected system does not meet the preset grid harmonic standard, the three-phase current output of each energy storage converter in the energy storage grid-connected system is collected in real time, and the nth harmonic current corresponding to each energy storage converter is determined based on the three-phase current output of each energy storage converter, where n is a positive integer greater than zero. A target drive signal is generated based on the nth harmonic current corresponding to each energy storage converter, and the target drive signal is sent to each energy storage converter to control each energy storage converter to perform harmonic suppression in a coordinated manner.

2. The harmonic suppression method for an energy storage grid-connected system according to claim 1, characterized in that, The harmonic current content includes: total harmonic current content and nth harmonic current content. The real-time acquisition of three-phase power information at the grid connection point of the energy storage grid-connected system, and the determination of the harmonic current content at the grid connection point of the energy storage grid-connected system based on the three-phase power information, includes: Harmonic analysis is performed on the three-phase current and the three-phase voltage to determine the total harmonic current content and the nth harmonic current content at the grid connection point of the energy storage grid-connected system.

3. The harmonic suppression method for an energy storage grid-connected system according to claim 1, characterized in that, The determination of the nth harmonic current corresponding to each energy storage converter based on the three-phase current of each energy storage converter includes: The three-phase currents of each energy storage converter are subjected to fundamental frequency filtering to obtain the total harmonic current components corresponding to each energy storage converter. The three-phase current of each energy storage converter is subjected to fundamental frequency phase-locked loop processing to obtain the baseband current phase corresponding to each energy storage converter; Based on the baseband current phase corresponding to each energy storage converter, the coordinate transformation is performed on the total harmonic current component corresponding to each energy storage converter to obtain the coordinate transformed total harmonic current component corresponding to each energy storage converter. Harmonic extraction is performed on the total harmonic current components after coordinate transformation to obtain the nth harmonic current corresponding to each energy storage converter.

4. The harmonic suppression method for an energy storage grid-connected system according to claim 1, characterized in that, The step of sending target drive signals to each energy storage converter based on the nth harmonic current corresponding to each energy storage converter includes: Based on the nth harmonic current corresponding to each energy storage converter, determine the reference harmonic current corresponding to each energy storage converter. Based on the nth harmonic current and reference harmonic current corresponding to each energy storage converter, the harmonic compensation voltage corresponding to each energy storage converter is generated, and the harmonic compensation voltage is subjected to coordinate inverse transformation to obtain the three-phase compensation voltage corresponding to each energy storage converter. Based on the three-phase current output by each energy storage converter, determine the corresponding three-phase reference voltage for each energy storage converter. Based on the three-phase reference voltage and three-phase compensation voltage corresponding to each energy storage converter, a target drive signal corresponding to each energy storage converter is generated, and each target drive signal is sent to the corresponding energy storage converter.

5. The harmonic suppression method for an energy storage grid-connected system according to claim 4, characterized in that, The nth harmonic current includes: active harmonic current and reactive harmonic current; the reference harmonic current includes: active reference harmonic current and reactive reference harmonic current; the harmonic compensation voltage includes: active harmonic compensation voltage and reactive harmonic compensation voltage; generating the harmonic compensation voltage corresponding to each energy storage converter based on the nth harmonic current and reference harmonic current corresponding to each energy storage converter includes: Based on the active harmonic current and active reference harmonic current corresponding to each energy storage converter, the active harmonic current difference corresponding to each energy storage converter is determined, and based on the active harmonic current difference, the active harmonic compensation voltage corresponding to each energy storage converter is generated. Based on the reactive harmonic current and reactive reference harmonic current corresponding to each energy storage converter, the reactive harmonic current difference corresponding to each energy storage converter is determined, and based on the reactive harmonic current difference, the reactive harmonic compensation voltage corresponding to each energy storage converter is generated.

6. The harmonic suppression method for an energy storage grid-connected system according to claim 4, characterized in that, The step of generating target drive signals for each energy storage converter based on the three-phase reference voltage and three-phase compensation voltage of each energy storage converter includes: The reference voltages of each phase in the three-phase reference voltage corresponding to the energy storage converter are added to the compensation voltages of each phase in the three-phase compensation voltage corresponding to the energy storage converter to obtain the target voltages of each phase corresponding to the energy storage converter. The target voltages of each phase corresponding to the energy storage converter are input into the pulse width modulator to obtain the target drive signal corresponding to each energy storage converter.

7. The harmonic suppression method for an energy storage grid-connected system according to claim 1, characterized in that, The method further includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the first preset threshold, then the reference harmonic current of at least one energy storage converter other than the target energy storage converter is reduced according to the preset adjustment strategy.

8. The harmonic suppression method for an energy storage grid-connected system according to claim 7, characterized in that, The method further includes: If the nth harmonic current of the target energy storage converter is greater than or equal to the second preset threshold, a shutdown drive signal is generated and sent to the switch corresponding to the target energy storage converter so that the target energy storage converter is forcibly shut down. The second preset threshold is greater than the first preset threshold.

9. An energy storage grid-connected system, characterized in that, The energy storage grid-connected system includes: multiple energy storage converters, a control module, and multiple switches and multiple energy storage batteries corresponding to each energy storage converter. One end of each energy storage converter is connected to the external AC power grid via a switch, and the other end of each energy storage converter is connected to an energy storage battery. The control module is connected to the grid connection point common to each energy storage converter, the output terminal of each energy storage converter, the control terminal of each energy storage converter, and the control terminal of each switch. The control module is used to perform the steps of the harmonic suppression method for the energy storage grid-connected system according to any one of claims 1-8.

10. The energy storage grid-connected system according to claim 9, characterized in that, The control module includes: a centralized controller, a judgment unit, a band-stop filter, a coordinate transformer, a subtractor, an integral controller, an inverse coordinate transformer, an adder, a pulse width modulator, a power control unit, and a phase-locked loop; The first input terminal of the centralized controller is connected to the grid connection point common to all energy storage converters. The second input terminal of the centralized controller, the input terminal of the phase-locked loop, and the input terminal of the power control unit are all connected to the output terminals of each energy storage converter. The first output terminal of the centralized controller is connected to the input terminal of the judgment unit, and the second output terminal of the centralized controller is connected to the control terminal of each switch. The output of the judgment unit is connected to the input of the band-stop filter, the output of the band-stop filter is connected to the first input of the coordinate transformer, and the second input of the coordinate transformer and the second input of the inverse coordinate transformer are both connected to the output of the phase-locked loop. The first output of the coordinate transformer and the third output of the centralized controller are both connected to the input of a subtractor. The second output of the coordinate transformer and the fourth output of the centralized controller are both connected to the input of another subtractor. The output of each subtractor is connected to the input of an integral controller. The output of each integral controller is connected to the first input of the inverse coordinate transformer. The output of the inverse coordinate transformer is connected via the first input of the adder. The output of the power control unit is connected to the second input of the adder. The output of the adder is connected to the input of the pulse width modulator. The output of the pulse width modulator is connected to the control terminal of each energy storage converter.

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