A three-phase energy storage converter split-phase independent control method and system

Abstract

The present application relates to the field of energy storage systems and new energy power generation, and provides a three-phase energy storage converter split-phase independent control method and system. The energy storage converter of each phase is independently controlled by the corresponding AC / DC bridge arm, and the grid-connected loop and off-grid loop of each AC / DC bridge arm are in the same control loop, only the control quantity is identified and switched, and the loop is not switched, the control method of each control loop is the same, and the same set of control loops is used to realize seamless switching between grid-connected and off-grid modes. The present application supports flexible operation under three-phase or single-phase power grid, meets the demand of single-phase grid-connected charging and discharging and off-grid load of the remaining two phases, improves the applicability of the system in remote areas or island single-phase power grid scenes, simplifies the control structure, and enhances the reliability and compatibility of the system.

Description

Technical Field

[0001] This invention relates to the fields of energy storage systems and new energy power generation, specifically to a three-phase energy storage converter phase-independent control method and system. Background Technology

[0002] Existing technologies typically include three-phase energy storage systems (PCS) such as Figure 1 As shown, the system is mainly divided into a DC end and an AC end. The DC end includes the battery BATT (101) and the DC bus capacitor BUSCAP (102). The AC end includes the three-phase grid GRID (103), the three-phase load LOAD (104), and the three-phase AC contactor KM (105). The core of the system is the three-phase energy storage converter AC / DC (106), which converts DC voltage to three-phase AC voltage. When the grid is normal, the three-phase AC contactor KM (105) closes, and the three-phase grid GRID (103) supplies power to the three-phase load LOAD (104). At the same time, the three-phase energy storage converter AC / DC (106) charges the battery BATT (101). The three-phase energy storage system PCS operates in grid-connected mode. When the power grid is abnormal, the three-phase AC contactor KM (105) is disconnected, and the battery BATT (101) supplies power to the load through the three-phase energy storage converter AC / DC (106). At this time, the three-phase energy storage system PCS operates in off-grid mode.

[0003] When the three-phase power grid is normal, the three-phase energy storage converter AC / DC (106) operates in grid-connected mode. When the PCS detects an anomaly in any phase of the power grid, the three-phase energy storage converter AC / DC (106) switches to off-grid mode to ensure the continuous operation of the load. However, in some application scenarios on islands or in remote areas, where there is only a single-phase power grid and a three-phase load, users cannot use a three-phase energy storage system to simultaneously meet the load's needs in both grid-connected and off-grid conditions. Instead, they must use three or more single-phase energy storage systems to meet the requirements of the application scenario. Users are forced to use multiple single-phase systems, increasing costs and complexity.

[0004] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a phase-independent control method and system for a three-phase energy storage converter.

[0006] The present invention adopts the following technical solution: A method for independent phase control of a three-phase energy storage converter is characterized in that each phase of the energy storage converter is independently controlled by its corresponding AC / DC bridge arm, and the grid-connected loop and off-grid loop of each AC / DC bridge arm are in the same control loop, only the control quantity is identified and switched, and no switching is performed on the loop, and the control method of each control loop is the same.

[0007] A phase-independent control system for a three-phase energy storage converter is characterized by applying the phase-independent control method for the three-phase energy storage converter. The system includes a three-phase energy storage system (PCS), which comprises independently operating A-phase, B-phase, and C-phase power grids. Each of the A-phase, B-phase, and C-phase power grids includes a grid-connected operation circuit and an off-grid operation circuit. For each phase of the power grid, the grid-connected and off-grid operation circuits use the same control loop, performing identification and switching only on the control quantity, without switching on the control loop itself. The operation detection logic is as follows: when the three-phase energy storage system (PCS) detects that the voltage of the corresponding phase of the power grid is normal, it switches the corresponding phase to the grid-connected operation circuit; otherwise, it switches the corresponding phase to the off-grid operation circuit.

[0008] Optionally, the control loop includes a voltage control loop and a frequency control loop.

[0009] Optionally, the voltage control loop of phase A grid includes: the difference between the effective value of phase A voltage given VaRmsref and the effective value feedback of phase A voltage VaRmsfb is sent to the second PI controller; the difference between the reference target value of phase A reactive power Qaref and the actual value of phase A reactive power Qafb is sent to the first PI controller; the effective value of phase A voltage given VaRmsref is added to the output of the first PI controller and the output of the second PI controller, and then multiplied by 1.414*cosθa to obtain the instantaneous value of phase A voltage given Varef; where θa is the phase angle of phase A grid; the difference between Varef and the instantaneous value feedback of phase A voltage Vaafb is sent to the third PI controller; the difference between the output of the third PI controller and the phase A output current Iafb is sent to the fourth PI controller; the output of the fourth PI controller is added to the instantaneous value feedback of phase A voltage Vaafb and then sent to the PWM controller. CALC outputs PWM to AC / DC; the voltage control circuits of phase B and phase C are based on the same principle as those of phase A, and the required parameters are the grid values ​​for their corresponding phases.

[0010] Optionally, when the first switch K1 is closed and the second switch K2 is open, the system operates in grid-connected mode. The effective value of the phase A voltage given VaRmsref is equal to the effective value feedback of the phase A voltage grid VgaRmsfb, and Qaref is the reactive power dispatch power of the system. The proportional coefficient and integral coefficient of the first PI controller are not equal to 0; the proportional coefficient and integral coefficient of the second PI controller are both equal to 0; the proportional coefficient of the third PI controller is not equal to 0, and the integral coefficient is equal to 0; the proportional coefficient of the fourth PI controller is not equal to 0, and the integral coefficient is equal to 0.

[0011] Optionally, when the first switch K1 is open and the second switch K2 is closed, the system operates off-grid. The effective value of the phase A voltage, VaRmsref, is equal to the rated operating voltage of the system, Vrated. The reference target value of the phase A reactive power, Qaref, is equal to 0. The proportional coefficient of the first PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the second PI controller are not equal to 0. The proportional coefficient Kp of the third PI controller is not equal to 0, and the integral coefficient Ki is equal to zero. The proportional coefficient Kp of the fourth PI controller is not equal to 0, and the integral coefficient Ki is equal to 0.

[0012] Optionally, the frequency control loop of phase A power grid includes: the difference between the phase A active power setpoint Paref and the phase A active power feedback Pafb is sent to the fifth PI controller; the difference between the phase A desired phase angle θaref and the phase A feedback θafb is sent to the sixth PI controller; the outputs of the fifth and sixth PI controllers are added to the system angular velocity W0 and sent to the integrator 1 / s; after integration by the integrator, the phase angle θa of phase A power grid is obtained; the frequency control loops of phase B power grid and phase C power grid have the same control principle as the frequency control loop of phase A power grid, and the required parameters are the power grid values ​​of their corresponding phases.

[0013] Optionally, when the first switch K1 is closed and the second switch K2 is open, the grid is connected to the grid. The active power given in phase A, Paref, is the active power dispatched by the system. The expected phase angle of phase A, θaref, is the phase angle of the grid, θgaref, and W0 is the angular velocity of the grid, Wg. The proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

[0014] Optionally, when the first switch K1 is open and the second switch K2 is closed, the system operates off-grid. The active power given Paref for phase A is equal to 0, the desired phase angle θaref for phase A is the natural phase θarated for phase A, W0 is the rated angular velocity Wrated for the system, the proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0; the proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

[0015] Optionally, the phase angle of phase B is θb = θa + 2 * Π / 3, the phase angle of phase C is θc = θa + 1 * Π / 3, the rated angular velocity of the system is Wrated = 2 * Π * F, where F is the rated frequency of the output voltage, and the phase angle of phase A is θa = Wrated * T, where T is time.

[0016] The beneficial effects achieved by this invention are: With independent phase control, it supports multiple operating modes such as three-phase grid connection, three-phase off-grid, and single-phase grid connection (with the other two phases off-grid), meeting the needs of mixed single-phase power grids and three-phase loads in remote areas or islands, and flexibly adapting to various power grid operating conditions.

[0017] Each phase of the energy storage converter is independently controlled by its corresponding AC / DC bridge arm. Each phase bridge arm can independently detect the grid status and switch modes. In the event of a single-phase fault, only the faulty phase needs to be isolated, while the other two phases can continue to operate in grid-connected or off-grid mode, avoiding a complete system shutdown. Independent phase control improves system reliability.

[0018] By using the same control loop in both grid-connected and off-grid modes, switching is achieved solely through parameter adjustments (such as PI controller coefficients), eliminating transient impacts caused by loop switching in traditional solutions, improving stability, and achieving seamless switching and dynamic response optimization. Simultaneously, the single-unit system and the parallel system share the same control architecture, reducing development complexity. Modular design facilitates expansion and maintenance, simplifies system design, and enhances compatibility, replacing traditional solutions with multiple single-phase PCS units, reducing the number of devices and installation costs. It is particularly suitable for special scenarios where three-phase loads and single-phase power grids coexist, reducing user costs.

[0019] In single-phase grid-connected scenarios, the grid-connected phase can prioritize the scheduling of charging and discharging power, while the off-grid phase can autonomously stabilize voltage and frequency, optimizing energy utilization and achieving efficient energy management.

[0020] By using the same control method for each phase, standardizing control logic, and unifying algorithms to achieve three-phase coordination (such as fixing a 120° phase difference), the phase loss problem caused by phase-separated control is avoided, ensuring the quality of output power.

[0021] To further understand the features and technical content of the present invention, please refer to the following detailed description and drawings of the present invention. However, the drawings provided are for reference and illustration only and are not intended to limit the present invention. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a typical three-phase energy storage system (PCS). Figure 2 A schematic diagram of the three AC / DC bridge arms of a three-phase energy storage converter operating simultaneously in off-grid / grid-connected mode. Figure 3 This is a schematic diagram of the phase-independent control method for the three-phase energy storage converter of the present invention; Figure 4 This is a schematic diagram of the control loop of the A-phase energy storage converter of the present invention.

[0023] 101: Battery (BATT), 102: DC bus capacitor (BUSCAP), 103: Three-phase grid (GRID), 104: Three-phase load (LOAD), 105: Three-phase AC contactor (KM), 106: Three-phase AC voltage three-phase energy storage converter (AC / DC), PI_1: First PI controller, PI_2: Second PI controller, PI_3: Third PI controller, PI_4: Fourth PI controller, PI_5: Fifth PI controller, PI_6: Sixth PI controller, K1: First switch, K2: Second switch, VaRmsfb: A-phase voltage RMS feedback, Qaref: A-phase reactive power reference target value, Qafb: A-phase reactive power actual value, VaRmsref: A-phase voltage RMS setpoint, Varef: A-phase voltage instantaneous setpoint; θa: A-phase grid phase angle, Vaafb: A-phase voltage instantaneous feedback; Iafb: A-phase output current, PWM CALC: Pulse Width Modulation Calculation Module, RMS CALC: Effective value calculation module, PLL CALC: Phase-locked loop calculation module, PQ CALC: Active-reactive power calculation module, Vrated: System rated operating voltage, θaref: Desired phase angle of phase A, θarated: Self-oscillating phase of phase A; θgaref: Phase of grid A, Wg: Angular velocity of grid, Wrated: Rated angular velocity of system, W0: Angular velocity of system, L2: Second inductor, L1: First inductor, C: Capacitor, Ugafb: Instantaneous value sampling of grid voltage of phase A, Uafb: Instantaneous value sampling of output voltage of phase A. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention. Furthermore, the accompanying drawings of the present invention are for simple illustrative purposes only and are not depictions of actual dimensions; this is stated in advance. The following embodiments will further describe the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the scope of protection of the present invention.

[0025] Example 1: A phase-by-phase independent control method for a three-phase energy storage converter, characterized in that each phase of the energy storage converter is controlled independently by its corresponding AC / DC bridge arm, and the grid-connected loop and off-grid loop of each AC / DC bridge arm are in the same control loop, only identification and switching are performed on the control quantity, and no switching is performed on the loop, and the control method of each control loop is the same.

[0026] Specifically, each control loop includes a voltage control loop and a frequency control loop. The AC voltage (mains voltage or output voltage) consists of three elements: amplitude, frequency, and phase. The voltage control loop controls the amplitude, and the frequency control loop controls the phase. The control of amplitude and phase are carried out in parallel.

[0027] like Figure 2 As shown, a traditional three-phase energy storage converter operates its three AC / DC arms simultaneously in either grid-connected or off-grid mode. When all three phases of the power grid are normal, the three AC / DC arms of the three-phase energy storage converter operate in grid-connected mode. When the three-phase energy storage system's PCS detects an anomaly in any one phase of the power grid, all three AC / DC arms of the three-phase energy storage converter simultaneously switch to off-grid mode. Because the three arms cannot operate independently, a traditional three-phase energy storage converter cannot meet the requirement of one phase arm being connected to the grid while the other arms are operating off-grid.

[0028] This embodiment achieves seamless switching between grid-connected and off-grid modes by independently controlling the three-phase bridge arms and using the same control loop. When grid-connected, it tracks the grid voltage and frequency; when off-grid, it maintains the rated voltage and frequency. This embodiment supports flexible operation under three-phase or single-phase grids, meeting the needs of single-phase grid-connected charging and discharging as well as the off-grid load-carrying requirements of the other two phases. It improves the system's applicability in single-phase grid scenarios such as remote areas or islands, simplifies the control structure, enhances system reliability and compatibility, and enables the use of the same control method for both stand-alone and parallel systems.

[0029] Example 2: This example should be understood as including all the features of any of the foregoing examples, and further improving upon them. It also provides a three-phase energy storage converter phase-independent control system, characterized in that it applies the three-phase energy storage converter phase-independent control method. The system includes a three-phase energy storage system (PCS), which comprises independently operating A-phase, B-phase, and C-phase power grids. Each of the A-phase, B-phase, and C-phase power grids includes a grid-connected operation circuit and an off-grid operation circuit. For each phase of the power grid, the grid-connected and off-grid operation circuits use the same control loop, performing identification and switching only on the control quantity, but not on the control loop itself. The operation detection logic is as follows: when the three-phase energy storage system (PCS) detects that the voltage of that phase of the power grid is normal, it switches that phase to the grid-connected operation circuit; otherwise, it switches that phase to the off-grid operation circuit.

[0030] Optionally, the control loop includes a voltage control loop and a frequency control loop.

[0031] Optionally, the voltage control loop of phase A grid includes: the difference between the effective value of phase A voltage given VaRmsref and the effective value feedback of phase A voltage VaRmsfb is sent to the second PI controller; the difference between the reference target value of phase A reactive power Qaref and the actual value of phase A reactive power Qafb is sent to the first PI controller; the effective value of phase A voltage given VaRmsref is added to the output of the first PI controller and the output of the second PI controller, and then multiplied by 1.414*cosθa to obtain the instantaneous value of phase A voltage given Varef; where θa is the phase angle of phase A grid; the difference between Varef and the instantaneous value feedback of phase A voltage Vaafb is sent to the third PI controller; the difference between the output of the third PI controller and the phase A output current Iafb is sent to the fourth PI controller; the output of the fourth PI controller is added to the instantaneous value feedback of phase A voltage Vaafb and then sent to the PWM controller. CALC outputs PWM to AC / DC; the voltage control circuits of phase B and phase C are based on the same principle as those of phase A, and the required parameters are the grid values ​​for their corresponding phases.

[0032] Optionally, the transfer function of each PI controller is OUT=(Kp+Ki*1 / s)*Err, where OUT is the output of the PI controller, Kp is the proportional coefficient, Ki is the integral coefficient, 1 / s is the integral operator, and Err is the input of the controller.

[0033] Optionally, when the first switch K1 is closed and the second switch K2 is open, the system operates in grid-connected mode. The effective value of the phase A voltage given VaRmsref is equal to the effective value feedback of the phase A voltage grid VgaRmsfb, and Qaref is the reactive power dispatch power of the system. The proportional coefficient and integral coefficient of the first PI controller are not equal to 0; the proportional coefficient and integral coefficient of the second PI controller are both equal to 0; the proportional coefficient of the third PI controller is not equal to 0, and the integral coefficient is equal to 0; the proportional coefficient of the fourth PI controller is not equal to 0, and the integral coefficient is equal to 0.

[0034] Optionally, when the first switch K1 is open and the second switch K2 is closed, the system operates off-grid. The effective value of the phase A voltage, VaRmsref, is equal to the rated operating voltage of the system, Vrated. The reference target value of the phase A reactive power, Qaref, is equal to 0. The proportional coefficient of the first PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the second PI controller are not equal to 0. The proportional coefficient Kp of the third PI controller is not equal to 0, and the integral coefficient Ki is equal to zero. The proportional coefficient Kp of the fourth PI controller is not equal to 0, and the integral coefficient Ki is equal to 0.

[0035] The system's rated operating voltage Vrated is generally 220V or 230V in China.

[0036] Optionally, the frequency control loop of phase A power grid includes: the difference between the phase A active power setpoint Paref and the phase A active power feedback Pafb is sent to the fifth PI controller; the difference between the phase A desired phase angle θaref and the phase A feedback θafb is sent to the sixth PI controller; the outputs of the fifth and sixth PI controllers are added to the system angular velocity W0 and sent to the integrator 1 / s; after integration by the integrator, the phase angle θa of phase A power grid is obtained; the frequency control loops of phase B power grid and phase C power grid have the same control principle as the frequency control loop of phase A power grid, and the required parameters are the power grid values ​​of their corresponding phases.

[0037] Optionally, when the first switch K1 is closed and the second switch K2 is open, the grid is connected to the grid. The active power given in phase A, Paref, is the active power dispatched by the system. The expected phase angle of phase A, θaref, is the phase angle of the grid, θgaref, and W0 is the angular velocity of the grid, Wg. The proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

[0038] Optionally, when the first switch K1 is open and the second switch K2 is closed, the system operates off-grid. The active power given Paref for phase A is equal to 0, the desired phase angle θaref for phase A is the natural phase θarated for phase A, W0 is the rated angular velocity Wrated for the system, the proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0; the proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

[0039] Optionally, the phase angle of phase B is θb = θa + 2 * Π / 3, the phase angle of phase C is θc = θa + 1 * Π / 3, the rated angular velocity of the system is Wrated = 2 * Π * F, where F is the rated frequency of the output voltage, and the phase angle of phase A is θa = Wrated * T, where T is time.

[0040] The RMS CALC module calculates the effective value of each phase voltage, outputting the effective value VxRmsfb, where x can be a, b, or c. The PLL CALC module calculates the phase-locked loop, outputting the desired phase angle θxfb and grid phase θgxref, where x can be a, b, or c. The PQ CALC module calculates active and reactive power, outputting the active power Pxfb and reactive power Qxfb, where x can be a, b, or c. The PWM CALC module calculates the pulse width modulation, with the transfer function PWM = (1 / 2 + Vin / Vbus) * Ts, where PWM is the output, Vin is the input, Vbus is the voltage across the DC bus capacitor, and Ts is the switching cycle time.

[0041] Specifically, the first switch K1 controls the input of Wg for the system angular velocity W0, and the second switch K2 controls the input of Wrated; the first switch K1 controls the input of θgxref for the grid phase, and the second switch K2 controls the input of θxrated, where x can be a, b, or c; the first switch K1 controls the input of VgxRmsfb for the voltage RMS value setpoint VxRmsfb, and the second switch K2 controls the input of Vrated, where x can be a, b, or c.

[0042] Optionally, the switch can be a logic switch or a mode selection signal to control the switching of grid-connected / off-grid loop parameters.

[0043] This embodiment supports multiple operating modes, including three-phase grid-connected, three-phase off-grid, and single-phase grid-connected (with the other two phases off-grid), through phase-independent control. This meets the needs of mixed single-phase grids and three-phase loads in remote areas or islands, and flexibly adapts to various grid conditions. Each phase energy storage converter is controlled independently by its corresponding AC / DC bridge arm. Each phase bridge arm can independently detect the grid status and switch modes. In the event of a single-phase fault, only the faulty phase needs to be isolated, while the other two phases can continue to operate in grid-connected or off-grid mode, avoiding overall system shutdown. Phase-independent control improves system reliability. By employing the same control loop in both grid-connected and off-grid modes, switching is achieved solely through parameter adjustments (such as PI controller coefficients), eliminating transient impacts caused by loop switching in traditional solutions, improving stability, and achieving seamless switching and dynamic response optimization. Simultaneously, the single-unit and parallel systems share the same control architecture, reducing development complexity. Modular design facilitates expansion and maintenance, simplifies system design, and enhances compatibility, replacing traditional solutions with multiple single-phase PCS units, reducing equipment quantity and installation costs. It is particularly suitable for special scenarios where three-phase loads coexist with single-phase power grids, reducing user costs. In single-phase grid-connected scenarios, the grid-connected phase can prioritize charging and discharging power, while the off-grid phase autonomously stabilizes voltage and frequency, optimizing energy utilization and achieving efficient energy management. A unified algorithm achieves three-phase coordination (e.g., a fixed 120° phase difference), avoiding phase synchronization issues caused by phase-separated control and ensuring output power quality.

[0044] The content disclosed above is only a preferred and feasible embodiment of the present invention, and is not intended to limit the scope of protection of the present invention. Therefore, all equivalent technical changes made based on the content of the present invention specification and drawings are included within the scope of protection of the present invention. Furthermore, the elements therein can be updated as technology develops.

Claims

1. A phase-independent control system for a three-phase energy storage converter, characterized in that, Each phase of the energy storage converter is independently controlled by its corresponding AC / DC bridge arm. The grid-connected and off-grid loops of each AC / DC bridge arm are on the same control loop, with only identification and switching at the control quantity level, not switching within the loop itself. The control method for each control loop is identical. The system includes a three-phase energy storage system (PCS), which comprises independently operating A-phase, B-phase, and C-phase power grids. Each of these grids includes both grid-connected and off-grid operation circuits. For each phase, the grid-connected and off-grid operation circuits use the same control loop, with only identification and switching at the control quantity level, not switching within the control loop itself. The operation detection logic is as follows: when the three-phase energy storage system (PCS) detects a positive voltage in that phase of the grid... Normally, the phase is switched to the grid-connected operation circuit; otherwise, it is switched to the off-grid operation circuit. The control loop includes a voltage control loop and a frequency control loop. The frequency control loop for phase A includes: the difference between the phase A active power setpoint Paref and the phase A active power feedback Pafb is sent to the fifth PI controller; the difference between the phase A desired phase angle θaref and the phase A feedback θafb is sent to the sixth PI controller; the outputs of the fifth and sixth PI controllers are added to the system angular velocity W0 and sent to the integrator 1 / s. After integration, the phase angle θa of the phase A grid is obtained. The frequency control loops for phase B and phase C operate on the same principle as those for phase A, requiring the corresponding grid values ​​for each phase.

2. The three-phase energy storage converter phase-independent control system as described in claim 1, characterized in that, The voltage control loop of phase A power grid includes: the difference between the effective value of phase A voltage (VaRmsref) and the feedback value of phase A voltage (VaRmsfb) is sent to the second PI controller; the difference between the reference target value of phase A reactive power (Qaref) and the actual value of phase A reactive power (Qafb) is sent to the first PI controller; the effective value of phase A voltage (VaRmsref) is added to the outputs of the first and second PI controllers, and then multiplied by 1.414*cosθa to obtain the instantaneous value of phase A voltage (Varef); where θa is the phase angle of phase A power grid; the difference between Varef and the instantaneous value feedback value of phase A voltage (Vafb) is sent to the third PI controller; the difference between the output of the third PI controller and the phase A output current (Iafb) is sent to the fourth PI controller; the output of the fourth PI controller is added to the instantaneous value feedback value of phase A voltage (Vafb) and then sent to the PWM controller. CALC outputs PWM to AC / DC; the voltage control circuits of phase B and phase C are based on the same principle as those of phase A, and the required parameters are the grid values ​​for their corresponding phases.

3. The three-phase energy storage converter phase-independent control system as described in claim 2, characterized in that, When the first switch K1 is closed and the second switch K2 is open, the system is connected to the grid. The effective value of the phase A voltage given VaRmsref is equal to the effective value of the phase A voltage grid feedback VgaRmsfb. Qaref is the reactive power dispatch power of the system. The proportional coefficient and integral coefficient of the first PI controller are not equal to 0; the proportional coefficient and integral coefficient of the second PI controller are both equal to 0; the proportional coefficient of the third PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient of the fourth PI controller is not equal to 0, and the integral coefficient is equal to 0.

4. The three-phase energy storage converter phase-independent control system as described in claim 2, characterized in that, When the first switch K1 is open and the second switch K2 is closed, the system is off-grid. The effective value of the phase A voltage VaRmsref is equal to the rated operating voltage Vrated of the system. The reference target value of the phase A reactive power Qaref is equal to 0. The proportional coefficient of the first PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional and integral coefficients of the second PI controller are not equal to 0; The proportional coefficient Kp of the third PI controller is not equal to 0, and the integral coefficient Ki is equal to zero. The proportional coefficient Kp of the fourth PI controller is not equal to 0, and the integral coefficient Ki is equal to 0.

5. The three-phase energy storage converter phase-independent control system as described in claim 1, characterized in that, When the first switch K1 is closed and the second switch K2 is open, the grid is connected to the grid. The active power given in phase A, Paref, is the active power dispatched by the system. The expected phase angle of phase A, θaref, is the phase angle of the grid, θgaref. W0 is the angular velocity of the grid, Wg. The proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

6. The three-phase energy storage converter phase-independent control system as described in claim 1, characterized in that, When the first switch K1 is open and the second switch K2 is closed, the system operates off-grid. The active power given for phase A, Paref, is equal to 0. The desired phase angle of phase A, θaref, is the natural phase of phase A, θarated. W0 is the rated angular velocity of the system, Wrated. The proportional coefficient of the fifth PI controller is not equal to 0, and the integral coefficient is equal to 0. The proportional coefficient and integral coefficient of the sixth PI controller are not equal to 0.

Images