Three-phase energy storage inverter, control method and controller thereof, and three-phase energy storage system

Abstract

The application discloses a three-phase energy storage inverter, a control method and a controller thereof, and a three-phase energy storage system, and relates to the technical field of energy storage. In the control method of the three-phase energy storage inverter, the output current of a first-level bus voltage control loop and the output current of a second-level bus voltage control loop are acquired first; the size relationship between a first bus voltage reference value and a second bus voltage reference value is determined according to the output current; then, three-phase current inner loops are controlled respectively, the power instruction of each phase is determined, and the power instruction is converted into a current instruction; and the current instruction corresponding to the three-phase current inner loop is subjected to amplitude limiting control according to the size relationship, the output current of the first-level bus voltage control loop and the output current of the second-level bus voltage control loop, so as to limit the amplitude of the current of each phase. The application aims to improve the operation safety and control flexibility of the three-phase energy storage system under complex working conditions.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and in particular to a three-phase energy storage inverter and its control method, controller and three-phase energy storage system. Background Technology

[0002] Three-phase energy storage inverters typically employ a three-phase four-wire topology to enable independent load control for each of the three phases in off-grid mode. However, traditional three-phase energy storage inverters generally use a three-phase balance control strategy based on the DQ coordinate system, maintaining voltage stability solely through a single bus voltage outer loop. This forces the three-phase power flow to be bound together, meaning all three phases can only simultaneously feed energy to or absorb energy from the grid, failing to achieve independent bidirectional power control for each phase. Consequently, traditional three-phase energy storage inverters cannot simultaneously absorb excess energy in one phase and feed energy to other phases, preventing the transfer of excess energy across phases. This not only wastes energy but may also cause voltage rise issues, affecting the operational stability of the three-phase energy storage system. Summary of the Invention

[0003] The main objective of this invention is to propose a three-phase energy storage inverter and its control method, controller, and three-phase energy storage system, aiming to improve the operational safety and control flexibility of the three-phase energy storage system under complex operating conditions.

[0004] To achieve the above objectives, this invention proposes a control method for a three-phase energy storage inverter, applicable to a three-phase energy storage inverter. The three-phase energy storage inverter includes a DC bus capacitor, a three-phase inverter bridge, and a controller. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor. The AC output terminal of the three-phase inverter bridge is used to connect to three-phase AC power. The control loop of the controller includes a first-stage bus voltage control loop, a second-stage bus voltage control loop, and three independent current inner loops for each phase. The first-stage bus voltage control loop has a first bus voltage reference value, and the second-stage bus voltage control loop has a second bus voltage reference value. The control method for the three-phase energy storage inverter includes: Obtain the output current of the first-stage bus voltage control loop and the output current of the second-stage bus voltage control loop; The magnitude relationship between the first bus voltage reference value and the second bus voltage reference value is determined based on the output current; The three phases are controlled to operate in their respective current inner loops, and the power command for each phase is determined, and the power command is converted into a current command. Based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop, the current command corresponding to the three-phase current inner loop is subjected to amplitude limiting control to limit the amplitude of the current in each phase.

[0005] In one embodiment, determining the magnitude relationship between the first bus voltage reference value and the second bus voltage reference value based on the output current includes: When the output current of the first-stage bus voltage control loop is positive, the reference value of the second bus voltage is determined to be greater than the reference value of the first bus voltage. When the output current of the first-stage bus voltage control loop is negative, the reference value of the second bus voltage is determined to be less than the reference value of the first bus voltage.

[0006] In one embodiment, the step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is positive, the output current of the first-stage bus voltage control loop is determined as the upper limit value of the current. When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is reversed, the phase corresponding to the current command is controlled to absorb energy from the DC bus capacitor. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

[0007] In one embodiment, the control method for the three-phase energy storage inverter further includes: Determine the voltage across the DC bus capacitor to obtain the bus voltage; When the bus voltage rises to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the lower limit value of the current.

[0008] In one embodiment, the step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is reversed, the output current of the first-stage bus voltage control loop is determined as the lower limit value of the current. When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is positive, the energy is controlled to be output to the DC bus capacitor corresponding to the current command. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

[0009] In one embodiment, the control method for the three-phase energy storage inverter further includes: Determine the voltage across the DC bus capacitor to obtain the bus voltage; When the bus voltage drops to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the upper limit value of the current.

[0010] In one embodiment, the first bus voltage reference value is used to determine the operating state of the three-phase energy storage inverter, and the second bus voltage reference value is used to control the magnitude of the bus voltage.

[0011] This application also proposes a controller comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the control method for the three-phase energy storage inverter described above.

[0012] This application also proposes a three-phase energy storage inverter, which includes a DC bus capacitor, a three-phase inverter bridge, and the controller described above. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC side input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor, and the AC side output terminal of the three-phase inverter bridge is used to connect to three-phase AC power.

[0013] This application also proposes a three-phase energy storage system, which includes the three-phase energy storage inverter described above and a single-phase grid-connected inverter, wherein the AC output terminal of the single-phase grid-connected inverter is electrically connected to the AC output terminal of any one phase of the three-phase energy storage inverter. In practical applications, by constructing a two-stage bus voltage control architecture comprising a first-stage bus voltage control loop and a second-stage bus voltage control loop, coupled with independent three-phase current inner-loop control, independent regulation of three-phase power can be achieved. Simultaneously, by acquiring the output current of both loops in real time and determining the relative magnitudes of the first and second bus voltage reference values, and by applying amplitude limiting control to the three-phase current commands based on this relationship, the risk of voltage runaway caused by excessive extraction or injection of energy from the bus capacitor in a specific phase is effectively reduced. Furthermore, the charging and discharging characteristics of the DC bus capacitor can be utilized to maintain relative stability of the bus voltage, improving the operational safety and control flexibility of the three-phase energy storage system under complex operating conditions. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0015] Figure 1 This is a flowchart of the first embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 2 This is a flowchart of the second embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 3 This is a flowchart of the third embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 4 This is a flowchart of the fourth embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 5 This is a flowchart of the fifth embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 6 This is a flowchart of the sixth embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 7 This is a schematic diagram of the modules in the first embodiment of a three-phase energy storage system in a traditional scheme; Figure 8 This is a flowchart of the seventh embodiment of the control method for the three-phase energy storage inverter of the present invention; Figure 9 This is a control logic block diagram of the first embodiment of the three-phase energy storage inverter of the present invention; Figure 10 This is a control logic block diagram of the second embodiment of the three-phase energy storage inverter of the present invention. The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that step designations such as S100 and S200 are used in this document for the purpose of more clearly and concisely describing the corresponding content, and do not constitute a substantial limitation on the order. In specific implementation, those skilled in the art may execute S200 first and then S100, etc., but these should all be within the protection scope of this application. Three-phase energy storage inverters typically employ a three-phase four-wire topology to enable independent load control for each of the three phases in off-grid mode. However, traditional three-phase energy storage inverters generally use a three-phase balance control strategy based on the DQ coordinate system, maintaining voltage stability solely through a single bus voltage outer loop. This forces the three-phase power flow to be bound together, meaning all three phases can only simultaneously feed energy to or absorb energy from the grid, failing to achieve independent bidirectional power control for each phase. Consequently, traditional three-phase energy storage inverters cannot simultaneously absorb excess energy in one phase and feed energy to other phases, preventing the transfer of excess energy across phases. This not only wastes energy but may also cause voltage rise issues, affecting the operational stability of the three-phase energy storage system.

[0018] refer to Figure 7 In a three-phase AC coupled system, the three-phase outputs are connected to different loads, with one phase also connected in parallel to a single-phase grid-connected inverter. Ideally, when the energy of the single-phase grid-connected inverter exceeds the load on that phase, the energy of the single-phase inverter should be absorbed by that phase of the three-phase inverter and transferred to other phases for output. However, in traditional control methods, all three phases are either fed to the grid or absorb grid energy. When the single-phase grid-connected inverter has sufficient energy, it cannot indirectly provide energy to other phase loads through the three-phase inverter, wasting its excess energy. To ensure stable bus voltage, the output of each phase needs to be limited by the bus voltage loop output. This means that the three-phase current is either entirely fed to the grid or entirely absorbs grid energy, making it impossible to simultaneously achieve independent bidirectional energy flow between each phase.

[0019] Therefore, refer to Figure 1 This invention proposes a control method for a three-phase energy storage inverter, applicable to a three-phase energy storage inverter. The three-phase energy storage inverter includes a DC bus capacitor, a three-phase inverter bridge, and a controller. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC side input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor, and the AC side output terminal of the three-phase inverter bridge is used to connect to three-phase AC power. The control loop of the controller includes a first-stage bus voltage control loop, a second-stage bus voltage control loop, and three independent current inner loops for each phase. The first-stage bus voltage control loop has a first bus voltage reference value, and the second-stage bus voltage control loop has a second bus voltage reference value. The control method for the three-phase energy storage inverter includes: Step S100: Obtain the output current of the first-stage bus voltage control loop and the output current of the second-stage bus voltage control loop; Step S200: Determine the relationship between the first bus voltage reference value and the second bus voltage reference value based on the output current; Step S300: Control the operation of the three-phase current inner loop respectively, determine the power command of each phase, and convert the power command into a current command. Step S400: Based on the magnitude relationship, the output current of the first-stage bus voltage control loop and the output current of the second-stage bus voltage control loop, the current command corresponding to the three-phase current inner loop is subjected to amplitude limiting control to limit the amplitude of the current in each phase.

[0020] In this embodiment, the control method for the three-phase energy storage inverter of the present invention can be applied to the controller of a three-phase energy storage inverter or a three-phase energy storage system. The controller includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The computer program is configured to implement the steps of the control method for the three-phase energy storage inverter described above. The controller can be implemented using a main controller, such as an MCU (Micro Controller Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), PLC (Programmable Logic Controller), or SOC (System on Chip).

[0021] In this embodiment, the DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The charging and discharging of the DC bus capacitor itself can maintain the relative stability of the bus voltage. The DC input terminal of the three-phase inverter bridge is connected to the DC bus capacitor, while the AC output terminal is used to connect to the three-phase AC power grid or local load. The three-phase inverter bridge converts DC power into AC power or rectifies AC power into DC power by switching its internal transistors on and off, thereby realizing bidirectional flow of electrical energy.

[0022] In this embodiment, the controller's internal loop includes a first-stage bus voltage control loop, a second-stage bus voltage control loop, and three-phase independent current inner loops. The first-stage bus voltage control loop is the main control loop of the three-phase energy storage system, responsible for maintaining the stability of the bus voltage. Developers can pre-set a first bus voltage reference value as a baseline. The second-stage bus voltage control loop serves as a safety protection and dynamic buffer loop. Developers can pre-set a second bus voltage reference value. When the bus voltage approaches the safety boundary, the second-stage bus voltage control loop is used to prevent the bus voltage from running out of control. The three-phase independent current inner loops allow for independent adjustment of the currents in phases A, B, and C.

[0023] In this embodiment, obtaining the output currents of the first-stage bus voltage control loop and the second-stage bus voltage control loop is to provide reference data for subsequent dynamic and asymmetrical limiting of the three-phase current inner loop. The output currents of the first-stage bus voltage control loop are denoted as Id_bus1 and the second-stage bus voltage control loop is denoted as Id_bus2.

[0024] In this embodiment, the controller can read the sign of the output current (Id_bus1) of the first-stage bus voltage control loop through its internal logic judgment module. For example, when Id_bus1 is determined to be positive (representing that the system as a whole is feeding energy to the grid), the controller assigns the second bus voltage reference value (BusRef2) to be greater than the first bus voltage reference value (BusRef1); conversely, when Id_bus1 is determined to be negative (representing that the system as a whole is absorbing energy from the grid), the controller assigns BusRef2 to be less than BusRef1. It is understood that both the first and second bus voltage reference values ​​can be pre-set and stored in the controller's memory by the developers, and the difference between them can be adaptively adjusted according to the bus capacitance size and transient energy requirements. In this way, by judging the positive and negative states of the output current of the first-stage bus voltage control loop, the rising and falling trend of the bus voltage can be determined in advance, thereby dynamically setting the relative magnitudes of the two voltage reference values ​​(BusRef1 and BusRef2) (for example, when the system as a whole releases energy to the outside, set BusRef2 > BusRef1).

[0025] In this embodiment, the controller can independently calculate the active power command and reactive power command for phases A, B, and C based on the local load demand and power generation output of each phase. Then, using a preset power-current conversion model, the power command for each phase is converted into the corresponding three-phase current command. Furthermore, it can combine grid phase information obtained from a software phase-locked loop (PLL) to perform coordinate transformation, thereby generating precise current commands for each phase. This breaks free from the constraints of traditional three-phase balance control methods, enabling independent control of the three-phase power.

[0026] In this embodiment, the controller is equipped with a configurable limiting module. When the controller determines that the entire system is in a power-feeding state (Id_bus1 > 0) and the current command direction of a certain phase is positive, the limiting module uses the value of Id_bus1 as the upper limit of the current in that phase to prevent that phase from excessively drawing energy from the bus capacitor. Conversely, when the entire system is in a power-absorbing state (Id_bus1 < 0) and the current command of a certain phase is negative, Id_bus1 is used as the lower limit of the current. Through this dynamic limiting, the current amplitude of each phase is restricted within a safe range.

[0027] In practical applications, by constructing a two-stage bus voltage control architecture comprising a first-stage bus voltage control loop and a second-stage bus voltage control loop, coupled with independent three-phase current inner-loop control, independent regulation of three-phase power can be achieved. Simultaneously, by acquiring the output current of both loops in real time and determining the relative magnitudes of the first and second bus voltage reference values, and by applying amplitude limiting control to the three-phase current commands based on this relationship, the risk of voltage runaway caused by excessive extraction or injection of energy from the bus capacitor in a specific phase is effectively reduced. Furthermore, the charging and discharging characteristics of the DC bus capacitor can be utilized to maintain relative stability of the bus voltage, improving the operational safety and control flexibility of the three-phase energy storage system under complex operating conditions. In another embodiment, reference Figure 2 The step of determining the relationship between the first bus voltage reference value and the second bus voltage reference value based on the output current includes: Step S410: When the output current of the first-stage bus voltage control loop is positive, determine that the reference value of the second bus voltage is greater than the reference value of the first bus voltage. Step S420: When the output current of the first-stage bus voltage control loop is negative, determine that the reference value of the second bus voltage is less than the reference value of the first bus voltage.

[0028] It should be noted that the traditional control method only has one bus voltage control loop and one fixed voltage reference point. Once the energy imbalance occurs, the bus voltage is very easy to become uncontrollable. In order to ensure the stability of the bus voltage, the only possible control methods are to have all three phases simultaneously in grid-feed mode or to have all three phases simultaneously absorb energy from the grid.

[0029] In this embodiment, when the first-stage loop output current (Id_bus1) is positive, it means that the system as a whole is in a state of feeding energy to the grid (discharging). At this time, the DC bus capacitor is accumulating energy, and the bus voltage tends to rise. To prevent the bus voltage from rising indefinitely and causing hardware damage, a higher safety threshold (i.e., BusRef2) can be set above the normal operating point (BusRef1). That is, the controller can set BusRef2 to be greater than BusRef1. Here, BusRef2 = BusRef1 + Vadjust, and the difference Vadjust can be adaptively adjusted according to the size of the bus capacitor and the transient absorbable energy when the bus input and output power are mismatched.

[0030] Understandably, if the bus voltage continues to rise and reaches BusRef2, the controller can trigger the second-stage loop protection mechanism (such as forced energy discharge) to prevent the bus from overvoltage and running out of control.

[0031] In this embodiment, when the first-stage loop output current (Id_bus1) is negative, it means that the system as a whole is in a state of absorbing energy from the grid (charging). At this time, the energy of the DC bus capacitor is continuously drawn away, and the bus voltage tends to decrease. To prevent the system from losing power or the inverter from failing to work properly due to excessively low bus voltage, a lower safety warning line (BusRef2) can be set below the normal operating point (BusRef1). That is, the controller can set BusRef2 to be less than BusRef1, BusRef2 = BusRef1 - Vadjust; Vadjust can be adjusted according to the bus capacitor size and the transient energy that can be released when the bus input and output power are mismatched. If the bus voltage continues to drop and touches BusRef2, the controller will trigger the protection mechanism of the second-stage loop (such as limiting the energy absorption power or forcing the system to enter the grid feed state), thereby avoiding bus undervoltage runaway.

[0032] In this way, the first-stage bus voltage control loop can be responsible for energy balance, and the second-stage bus voltage control loop is responsible for protection under extreme conditions, enabling the three-phase energy storage system to dynamically define safety boundaries based on the current charging and discharging state.

[0033] In one embodiment, reference Figure 3The step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: Step S410: When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is positive, the output current of the first-stage bus voltage control loop is determined as the upper limit value of the current. Step S420: When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is reversed, control the phase corresponding to the current command to absorb energy from the DC bus capacitor. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

[0034] Optionally, refer to Figure 4 The control method for the three-phase energy storage inverter further includes: Step S500: Determine the voltage across the DC bus capacitor to obtain the bus voltage; Step S600: When the bus voltage rises to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the lower limit value of the current.

[0035] In this embodiment, the controller's control loop also includes a three-phase power control loop. This outer loop is responsible for independently calculating the active and reactive power commands for each phase based on the actual load demand and power generation output of each phase. The three-phase independent current inner loop receives the corresponding power commands, converts them into corresponding current commands, and executes them. Because the three-phase power control loop can independently calculate the power demand of each phase, the lower-level three-phase independent current inner loop can achieve independent adjustment of the current amplitude and direction of each phase. When the power control loop of one phase calculates that the phase needs to absorb energy (i.e., the power command is negative), while the power control loops of other phases calculate that energy needs to be fed (i.e., the power command is positive), the three-phase independent current inner loop will execute the reverse and forward current commands respectively, thereby achieving inter-phase energy transfer at the physical level.

[0036] To ensure that this independent control method does not lead to DC bus voltage runaway, the power control loop of each phase must be subject to "upper and lower limit limiting" by the two-stage bus control loop. In this embodiment, the controller can asymmetrically clamp the current command based on the energy flow direction. (See reference...) Figure 8 and Figure 9When the output current (Id_bus1) of the first-stage bus control loop is positive and the current command direction of a certain phase is positive (i.e., the output of the three-phase power control loop is also positive, such as flowing from the DC bus capacitor to the three-phase inverter bridge, i.e. feeding power to the grid), Id_bus1 is determined as the upper limit value of the current of that phase.

[0037] It should be noted that a positive value for Id_bus1 indicates that the system as a whole is releasing energy to the grid, and the bus capacitor is storing energy. If a phase continues to draw a large amount of energy from the bus at this time, it will cause drastic fluctuations in the bus voltage. Setting Id_bus1 as an upper limit is to limit excessive energy extraction from the bus capacitor by that phase, ensuring that the bus voltage remains near the normal operating point set by BusRef1.

[0038] In this embodiment, when Id_bus1 is positive, but the current command direction of a certain phase is reversed (i.e., the output of the three-phase power control loop is negative, such as flowing from the three-phase inverter bridge to the DC bus capacitor, i.e. absorbing energy from the grid), the controller controls that phase to absorb energy from the DC bus capacitor.

[0039] It should be noted that when the system as a whole releases energy (Id_bus1 > 0), a certain phase may need to absorb energy. This indicates that the local load demand of that phase is relatively large, or that other phases are feeding a large amount of power. In this case, the energy absorbed by that phase is actually provided by the DC bus capacitor, and then supplemented by the power supply from other phases.

[0040] In this embodiment, the controller can detect the voltage across the DC bus capacitor in real time through an internal voltage detection circuit to obtain the current actual bus voltage value. When the bus voltage rises to the second bus voltage reference value (BusRef2), the output current (Id_bus2) of the second-stage bus voltage control loop is determined as the lower limit of the current. That is, when the system is in a power feeding state, BusRef2 is set to be greater than BusRef1. If the bus voltage is raised to BusRef2, it means that the energy generated by the system has exceeded the normal regulation capability and faces the risk of overvoltage. At this time, forcibly setting Id_bus2 as the lower limit of the current means that the system must forcibly release the excess energy, thereby avoiding the bus voltage from continuing to rise and causing hardware damage or system malfunction.

[0041] The three-phase power control loop can independently calculate power commands based on the local load and power generation demand of each phase. Combined with the inner current loop, this allows each phase to independently adjust the current amplitude and direction. Simultaneously, the output current of the first-stage bus voltage control loop clamps the forward current, effectively preventing drastic fluctuations in bus voltage caused by excessive energy extraction from a single phase during overall energy release, ensuring the bus voltage remains at its normal operating point. Furthermore, the introduction of a second-stage bus voltage control loop forces a lower current limit when the bus voltage rises abnormally, allowing the system to quickly release excess energy and reducing the risk of hardware overvoltage damage. Thus, while ensuring efficient energy transfer between phases, the response speed and operational safety of the three-phase energy storage system are improved. In another embodiment, reference Figure 5 The step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: Step S430: When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is reversed, the output current of the first-stage bus voltage control loop is determined as the lower limit value of the current. Step S440: When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is positive, control the DC bus capacitor corresponding to the current command to output energy. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

[0042] refer to Figure 6 The control method for the three-phase energy storage inverter further includes: Step S700: Determine the voltage across the DC bus capacitor to obtain the bus voltage; Step S800: When the bus voltage drops to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the upper limit value of the current.

[0043] In this embodiment, reference Figure 8 and Figure 10 When the output current (Id_bus1) of the first-level bus control loop is negative, and the current command direction of a certain phase (such as phase A) is reversed (i.e., the output of the three-phase power control loop is also negative, such as flowing from the three-phase inverter bridge to the DC bus capacitor, i.e. absorbing energy from the grid), the controller can determine Id_bus1 as the lower limit value of the current of that phase.

[0044] It should be noted that a negative value for Id_bus1 indicates that the three-phase energy storage system is in a state of absorbing energy from the grid. If a phase (phase A) continues to draw energy from the grid at this time, it will cause the bus voltage to drop sharply. Therefore, setting Id_bus1 as a lower limit is to limit excessive energy absorption by that phase, ensure that the bus voltage is maintained near the normal operating point set by BusRef1, and prevent the system from shutting down abnormally due to undervoltage.

[0045] In this embodiment, when Id_bus1 is negative, but the current command direction of a certain phase (such as phase A) is positive (i.e., the power control loop is positive, flowing from the DC bus capacitor to the three-phase inverter bridge, i.e., outputting energy to the grid or local load), the controller controls that phase to output energy to the DC bus capacitor (actually, the energy absorbed by other phases is transferred through the bus).

[0046] It is understandable that if a phase needs to output energy while the entire system is absorbing energy from the grid (Id_bus1 < 0), it indicates that the phase has a large local load demand or power generation capacity, while other phases (such as phases B and C) are absorbing a large amount of electricity from the grid. Therefore, the energy output by that phase is actually absorbed and transferred from the grid by other phases.

[0047] In this embodiment, the controller can detect the voltage across the DC bus capacitor in real time through its internal voltage detection circuit. When the bus voltage drops to the second bus voltage reference value (BusRef2), the output current (Id_bus2) of the second-stage bus voltage control loop is set as the upper limit of the current. Under the overall energy absorption state of the system, BusRef2 is set to be less than BusRef1. If the bus voltage is pulled down to BusRef2, it indicates that the energy consumed by the system has exceeded its normal regulation capacity, facing the risk of undervoltage. At this time, forcing Id_bus2 as the upper limit of the current means that the system must limit its ability to absorb energy from the grid, and may even force some phases to reduce power absorption or switch to a power feeding state, thereby reducing the risk of hardware damage or system failure due to a continued drop in bus voltage.

[0048] It should be noted that the first bus voltage reference value is used to determine the operating state of the three-phase energy storage inverter, and the second bus voltage reference value is used to control the magnitude of the bus voltage.

[0049] In this embodiment, the first bus voltage reference value (BusRef1) is used to determine the operating state of the three-phase energy storage inverter, thus determining the inverter's current overall operating mode. When Id_bus1 is positive, it indicates that the system is in a state of feeding energy to the grid; when Id_bus1 is negative, it indicates that the system is in a state of absorbing energy from the grid.

[0050] In this embodiment, the second bus voltage reference value (BusRef2) is used to control the magnitude of the bus voltage. BusRef2 is used to control the magnitude of the bus voltage under extreme operating conditions to prevent voltage runaway. For example, when feeding energy, BusRef2 > BusRef1, and when absorbing energy, BusRef2 < BusRef1. When the actual bus voltage exceeds the reference due to energy imbalance and touches this safety boundary, the second-stage bus voltage control loop will immediately intervene. When the bus voltage is raised to BusRef2, a lower current limit is forcibly set; when the voltage is pulled down to BusRef2, an upper current limit is forcibly set to limit the system from absorbing more energy. In this way, the magnitude of the bus voltage is controlled within a safe range by limiting the current.

[0051] By implementing a two-stage bus control loop to limit the three-phase power loop, each phase can be either fed into the grid or absorb energy from the grid, maintaining stable bus voltage. This gives each phase output independent bidirectional energy control capabilities, enabling flexible energy dispatch management and enhancing the competitiveness of the inverter product. This application also proposes a controller comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the control method for the three-phase energy storage inverter described above.

[0052] In this embodiment, the controller can be the controller of a three-phase energy storage inverter or a three-phase energy storage system. The controller can be implemented using a main controller, such as an MCU (Micro Controller Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), or a SOC (System-on-Chip).

[0053] It is worth noting that since the controller of the present invention is based on the control method of the three-phase energy storage inverter described above, the embodiments of the controller of the present invention include all the technical solutions of all embodiments of the control method of the three-phase energy storage inverter described above, and the technical effects achieved are exactly the same, so they will not be repeated here. This application also proposes a three-phase energy storage inverter, which includes a DC bus capacitor, a three-phase inverter bridge, and the controller described above. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC side input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor, and the AC side output terminal of the three-phase inverter bridge is used to connect to three-phase AC power.

[0054] In this embodiment, the DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The charging and discharging of the DC bus capacitor itself maintains the relative stability of the bus voltage. The DC input terminal of the three-phase inverter bridge is connected to the DC bus capacitor, while the AC output terminal is used to connect to a three-phase AC power grid or a local load to receive three-phase AC power. The three-phase inverter bridge converts DC power to AC power or rectifies AC power to DC power by switching its internal transistors on and off, thus achieving bidirectional flow of electrical energy.

[0055] It is worth noting that since the three-phase energy storage inverter of the present invention is based on the controller described above, the embodiments of the three-phase energy storage inverter of the present invention include all the technical solutions of all embodiments of the controller described above, and the technical effects achieved are exactly the same, so they will not be repeated here. This application also proposes a three-phase energy storage system, which includes the three-phase energy storage inverter described above and a single-phase grid-connected inverter, wherein the AC output terminal of the single-phase grid-connected inverter is electrically connected to the AC output terminal of any one phase of the three-phase energy storage inverter.

[0056] Based on the above embodiments, when a single-phase grid-connected inverter has sufficient energy, it can indirectly provide energy to other phase loads through a three-phase inverter to consume the excess energy of the single-phase grid-connected inverter and realize the transfer of energy between phases.

[0057] It is worth noting that since the three-phase energy storage system of the present invention is based on the three-phase energy storage inverter described above, the embodiments of the three-phase energy storage system of the present invention include all the technical solutions of all the embodiments of the three-phase energy storage inverter described above, and the technical effects achieved are exactly the same, so they will not be repeated here.

[0058] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A control method for a three-phase energy storage inverter, characterized in that, This invention relates to a three-phase energy storage inverter, which includes a DC bus capacitor, a three-phase inverter bridge, and a controller. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor, and the AC output terminal of the three-phase inverter bridge is used to connect to three-phase AC power. The controller's control loop includes a first-stage bus voltage control loop, a second-stage bus voltage control loop, and three independent current inner loops for each phase. The first-stage bus voltage control loop has a first bus voltage reference value, and the second-stage bus voltage control loop has a second bus voltage reference value. The control method for the three-phase energy storage inverter includes: Obtain the output current of the first-stage bus voltage control loop and the output current of the second-stage bus voltage control loop; The magnitude relationship between the first bus voltage reference value and the second bus voltage reference value is determined based on the output current; The three phases are controlled to operate in their respective current inner loops, and the power command for each phase is determined, and the power command is converted into a current command. Based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop, the current command corresponding to the three-phase current inner loop is subjected to amplitude limiting control to limit the amplitude of the current in each phase.

2. The control method for a three-phase energy storage inverter as described in claim 1, characterized in that, Determining the relationship between the first bus voltage reference value and the second bus voltage reference value based on the output current includes: When the output current of the first-stage bus voltage control loop is positive, the reference value of the second bus voltage is determined to be greater than the reference value of the first bus voltage. When the output current of the first-stage bus voltage control loop is negative, the reference value of the second bus voltage is determined to be less than the reference value of the first bus voltage.

3. The control method for a three-phase energy storage inverter as described in claim 1, characterized in that, The step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is positive, the output current of the first-stage bus voltage control loop is determined as the upper limit value of the current. When the output current of the first-stage bus voltage control loop is positive and the direction of the current command is reversed, the phase corresponding to the current command is controlled to absorb energy from the DC bus capacitor. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

4. The control method for a three-phase energy storage inverter as described in claim 3, characterized in that, The control method for the three-phase energy storage inverter also includes: Determine the voltage across the DC bus capacitor to obtain the bus voltage; When the bus voltage rises to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the lower limit value of the current.

5. The control method for a three-phase energy storage inverter as described in claim 1, characterized in that, The step of limiting the current command corresponding to the three-phase current inner loop based on the magnitude relationship, the output current of the first-stage bus voltage control loop, and the output current of the second-stage bus voltage control loop includes: When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is reversed, the output current of the first-stage bus voltage control loop is determined as the lower limit value of the current. When the output current of the first-stage bus voltage control loop is negative and the direction of the current command is positive, the energy is controlled to be output to the DC bus capacitor corresponding to the current command. The positive characterization current flows from the DC bus capacitor to the three-phase inverter bridge, and the reverse characterization current flows from the three-phase inverter bridge to the DC bus capacitor.

6. The control method for a three-phase energy storage inverter as described in claim 5, characterized in that, The control method for the three-phase energy storage inverter also includes: Determine the voltage across the DC bus capacitor to obtain the bus voltage; When the bus voltage drops to the reference value of the second bus voltage, the output current of the second-stage bus voltage control loop is determined as the upper limit value of the current.

7. The control method for a three-phase energy storage inverter as described in any one of claims 1 to 6, characterized in that, The first bus voltage reference value is used to determine the operating state of the three-phase energy storage inverter, and the second bus voltage reference value is used to control the magnitude of the bus voltage.

8. A controller, characterized in that, The controller includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the control method for a three-phase energy storage inverter as described in any one of claims 1 to 7.

9. A three-phase energy storage inverter, characterized in that, The three-phase energy storage inverter includes a DC bus capacitor, a three-phase inverter bridge, and a controller as described in claim 8. The DC bus capacitor is connected in parallel between the positive and negative terminals of the DC bus. The DC input terminal of the three-phase inverter bridge is electrically connected to the DC bus capacitor. The AC output terminal of the three-phase inverter bridge is used to connect to three-phase AC power.

10. A three-phase energy storage system, characterized in that, The three-phase energy storage system includes a three-phase energy storage inverter as described in claim 9, and a single-phase grid-connected inverter, wherein the AC output terminal of the single-phase grid-connected inverter is electrically connected to the AC output terminal of any one phase of the three-phase energy storage inverter.

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