Split-phase independent control method and system for three-phase energy storage converter

Abstract

The invention 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. Each phase of energy storage converter is independently controlled by the AC / DC bridge arm corresponding to the energy storage converter in a split-phase manner, a grid-connected loop and an off-grid loop of each AC / DC bridge arm are in the same control loop, identification and switching are only performed on control quantity, switching is not performed on the loops, the control method of each control loop is the same, and the control method of each control loop is the same as that of each AC / DC bridge arm. And seamless switching between a grid-connected mode and an off-grid mode is realized by adopting the same set of control loop. Flexible operation under a three-phase or single-phase power grid is supported, the requirements of single-phase grid-connected charging and discharging and other two-phase off-grid loading are met, the applicability of the system in single-phase power grid scenes such as remote areas or islands is improved, meanwhile, the control structure is simplified, and the reliability and compatibility of the system are enhanced.

Description

Technical Field

[0001] The present invention relates to the fields of energy storage systems and new energy power generation, and in particular to a method and system for independent phase-split control of a three-phase energy storage converter. Background Art

[0002] Typical three-phase energy storage systems PCS in existing technologies are as follows: Figure 1 As shown, the system is mainly divided into a DC end and an AC end. The DC end includes a battery BATT (101) and a DC bus capacitor BUSCAP (102). The AC end includes a three-phase grid GRID (103), a three-phase load LOAD (104), and a three-phase AC contactor KM (105). The core of the system is a three-phase energy storage converter AC / DC (106) that converts DC voltage into three-phase AC voltage. When the grid is normal, the three-phase AC contactor KM (105) is closed, and the three-phase grid GRID (103) supplies power to the three-phase load LOAD (104). At the same time, the battery BATT (101) is charged through the three-phase energy storage converter AC / DC (106). The three-phase energy storage system PCS operates in a grid-connected working 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 an off-grid operation mode.

[0003] When the three-phase grid is normal, the three-phase energy storage converter AC / DC (106) is in the grid-connected working mode. When the PCS detects an abnormality in any phase of the grid, the three-phase energy storage converter AC / DC (106) switches to the off-grid working mode to ensure the continuous operation of the load. However, in some application scenarios on islands or remote areas, there is only a single-phase grid and a three-phase load. At this time, the user cannot use the three-phase energy storage system to meet the use of the load in both grid-connected and off-grid conditions. Only three or more single-phase energy storage systems can be used to meet the needs of the use scenario. The user is forced to use multiple single-phase systems, which increases cost and complexity.

[0004] In view of the above problems, the existing technology is in urgent need of improvement. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and to propose a method and system for independent phase control of a three-phase energy storage converter.

[0006] The present invention adopts the following technical solutions: 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 identification and switching are performed on the control quantity, and no switching is performed on the loop. The control method of each control loop is the same.

[0007] A three-phase energy storage converter phase-split independent control system, characterized in that the three-phase energy storage converter phase-split independent control method is applied, the system includes a three-phase energy storage system PCS, the three-phase energy storage system PCS includes independently operating phase A power grid, phase B power grid and phase C power grid, the phase A power grid, phase B power grid and phase C power grid all include grid-connected operation circuit and off-grid operation circuit, for each phase power grid, the grid-connected operation circuit and off-grid operation circuit use the same set of control loops, only identification and switching are performed on the control quantity, and no switching is performed on the control loop, and the operation detection logic is: when the three-phase energy storage system PCS detects that the phase power grid voltage is normal, the phase is switched to the grid-connected operation circuit; otherwise, the phase is switched 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 the A-phase power grid includes: the effective value of the A-phase voltage given VaRmsref and the effective value of the A-phase voltage feedback VaRmsfb are differentiated and sent to the second PI controller, the reference target value of the A-phase reactive power Qaref and the actual value of the A-phase reactive power Qafb are differentiated and sent to the first PI controller, the effective value of the A-phase 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 the A-phase voltage given Varef; wherein θa is the phase angle of the A-phase power grid, Varef is differentiated from the instantaneous value feedback of the A-phase voltage Vafb and sent to the third PI controller; the output of the third PI controller is differentiated from the A-phase output current Iafb and sent to the fourth PI controller; the output of the fourth PI controller and the instantaneous value feedback of the A-phase voltage Vafb are added and sent to the PWM CALC, and output PWM to AC / DC; the control principles of the voltage control loop of phase B grid and the voltage control loop of phase C grid are the same as those of phase A grid, and the required parameters are the grid values ​​of their corresponding phases.

[0010] Optionally, when the first switch K1 is closed and the second switch K2 is disconnected, the grid is connected to the controller, the effective value of the phase A voltage given VaRmsref is equal to the effective value feedback of the phase A voltage grid VgaRmsfb, Qaref is the system reactive scheduling power, the proportional coefficient and the integral coefficient of the first PI controller are not equal to 0; the proportional coefficient and the 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 disconnected and the second switch K2 is closed for off-grid operation, the effective value of the phase A voltage given VaRmsref is equal to the system rated operating voltage Vrated, the reference target value Qaref of the phase A reactive power 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 the 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 the A-phase power grid includes: the difference between the A-phase active power reference Paref and the A-phase active power feedback Pafb is sent to the fifth PI controller, the difference between the A-phase desired phase angle θaref and the A-phase phase feedback θafb is sent to the sixth PI controller, the output of the fifth PI controller and the output of the sixth PI controller and the system angular velocity W0 are added and sent to the integrator 1 / s, and the phase angle θa of the A-phase power grid is obtained after integration by the integrator; the control principles of the frequency control loop of the B-phase power grid and the frequency control loop of the C-phase power grid are the same as those of the frequency control loop of the A-phase 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 disconnected, the grid is connected to the grid, the A-phase active power given Paref is the system active dispatching power, the A-phase expected phase angle θaref is the A grid phase θgaref, W0 is the angular velocity Wg of the grid, 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 disconnected and the second switch K2 is closed, the system operates off-grid, the active power reference Paref of phase A is equal to 0, the expected phase angle θaref of phase A is the natural oscillation phase θarated of phase A, W0 is the rated angular velocity Wrated of 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 the integral coefficient of the sixth PI controller are not equal to 0.

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

[0016] The beneficial effects achieved by the present invention are: Through independent phase control, it supports multiple operating modes such as three-phase grid-connected, three-phase off-grid, and single-phase grid-connected (the remaining two phases are off-grid), meeting the needs of mixed scenarios of single-phase grid and three-phase load in remote areas or islands, and flexibly adapting to various 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, and the other two phases can continue to operate on or off the grid, avoiding overall system shutdown. Independent phase control improves system reliability.

[0018] By using the same control loop in both on-grid and off-grid modes, switching is achieved only through parameter adjustment (such as the PI controller coefficient), eliminating transient impacts caused by loop switching in traditional solutions, improving stability, and achieving seamless switching and dynamic response optimization. At the same time, the single-machine system and the parallel system share the same control architecture, reducing development complexity; the modular design facilitates expansion and maintenance, simplifies system design and enhances compatibility, replacing traditional solutions with multiple single-phase PCSs, 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 the single-phase grid-connected scenario, the grid-connected phase can prioritize the scheduling of charging and discharging power, while the off-grid phase can autonomously stabilize the voltage and frequency, optimize energy utilization, and achieve efficient energy management.

[0020] By adopting the same control method for each phase, standardizing the control logic, and unifying the algorithm to achieve three-phase coordination (such as a fixed 120° phase difference), phase desynchronization caused by phase-splitting control can be avoided, ensuring the output power quality.

[0021] To further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the drawings provided are only for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a typical three-phase energy storage system PCS structure diagram; Figure 2 This is a schematic diagram of the three AC / DC bridge arms of the three-phase energy storage converter working simultaneously in off-grid / grid-connected mode; Figure 3 Schematic diagram of the phase-separated independent control method of the three-phase energy storage converter of the present invention; Figure 4 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: Phase A voltage RMS feedback, Qaref: Phase A reactive power reference target, Qafb: Phase A reactive power actual value, VaRmsref: Phase A voltage RMS reference, Varef: Phase A voltage instantaneous reference; θa: Phase A grid phase angle, Vafb: Phase A voltage instantaneous feedback; Iafb: Phase A output current, PWM CALC: Pulse width modulation calculation module, RMS CALC: effective value calculation module, PLL CALC: phase-locked loop calculation module, PQCALC: active-reactive power calculation module, Vrated: system rated operating voltage, θaref: expected phase angle of phase A, θarated: natural oscillation phase of phase A; θgaref: grid phase A, Wg: grid angular velocity, Wrated: system rated angular velocity, W0: system angular velocity, L2: second inductor, L1: first inductor, C: capacitor, Ugafb: instantaneous value sampling of phase A grid voltage, Uafb: instantaneous value sampling of phase A output voltage. DETAILED DESCRIPTION

[0024] The following is an explanation of the embodiments of the present invention through specific embodiments. Those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and the 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. In addition, the drawings of the present invention are only for simple schematic illustrations and are not depicted according to actual dimensions. It is stated in advance. The following embodiments will further explain the relevant technical contents of the present invention in detail, but the disclosed contents are not intended to limit the scope of protection of the present invention.

[0025] Embodiment 1: A method for independent phase control of 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, 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 (grid voltage or output voltage) is composed of three elements: amplitude, frequency, and phase. The voltage control loop controls the amplitude, and the frequency control loop controls the phase. The amplitude and phase are controlled in parallel.

[0027] like Figure 2 As shown in the figure, the three AC / DC bridge legs of a traditional three-phase energy storage converter operate simultaneously in grid-connected mode or off-grid mode. When all three grid phases are normal, the three AC / DC bridge legs of the three-phase energy storage converter operate in grid-connected mode. If the three-phase energy storage system (PCS) detects an anomaly in any grid phase, the three AC / DC bridge legs of the three-phase energy storage converter simultaneously switch to off-grid mode. Because the three bridge legs cannot operate independently, traditional three-phase energy storage converters cannot meet the operating conditions where one bridge leg is grid-connected while the other bridge legs operate 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. The grid voltage and frequency are tracked when connected to the grid, and the rated voltage and frequency are maintained when off-grid. This embodiment supports flexible operation under three-phase or single-phase grids, meeting the needs of single-phase grid-connected charging and discharging and the other two-phase off-grid load requirements. This improves the system's applicability in single-phase grid scenarios such as remote areas or islands, while simplifying the control structure and enhancing the system's reliability and compatibility. It also enables the use of the same control method for both stand-alone and parallel systems.

[0029] Embodiment 2: This embodiment should be understood as including all the features of any of the foregoing embodiments, and is further improved on the basis of the foregoing embodiments, and also provides a three-phase energy storage converter phase-independent control system, characterized in that the three-phase energy storage converter phase-independent control method is applied, the system includes a three-phase energy storage system PCS, the three-phase energy storage system PCS includes an A-phase power grid, a B-phase power grid and a C-phase power grid that operate independently of each other, the A-phase power grid, the B-phase power grid and the C-phase power grid all include a grid-connected operation circuit and an off-grid operation circuit, for each phase power grid, the grid-connected operation circuit and the off-grid operation circuit use the same set of control loops, only identify and switch on the control quantity but not on the control loop, and the operation detection logic is: when the three-phase energy storage system PCS detects that the voltage of the phase power grid is normal, the phase is switched to the grid-connected operation circuit, otherwise, the phase is switched to the off-grid operation circuit.

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

[0031] Optionally, the voltage control loop of the A-phase power grid comprises: the A-phase voltage effective value given value VaRmsref and the A-phase voltage effective value feedback VaRmsfb are subtracted and sent to a second PI controller, the reference target value Qaref of the A-phase reactive power and the actual value Qafb of the A-phase reactive power are subtracted and sent to a first PI controller, the A-phase voltage effective value given value VaRmsref and the output of the first PI controller and the output of the second PI controller are added and multiplied by 1.414*cosθa to obtain the A-phase voltage instantaneous value given value Varef; wherein θa is the phase angle of the A-phase power grid, Varef and the A-phase voltage instantaneous value feedback Vafb are subtracted and sent to a third PI controller; the output of the third PI controller and the A-phase output current Iafb are subtracted and sent to a fourth PI controller; the output of the fourth PI controller and the A-phase voltage instantaneous value feedback Vafb are added and sent to a PWM CALC, and the output PWM is sent to AC / DC; the control principles of the voltage control loop of the B-phase power grid and the voltage control loop of the C-phase power grid are the same as those of the voltage control loop of the A-phase power grid, and the required parameters are the grid values of the corresponding phases.

[0032] Optionally, the transfer function of each PI controller is OUT=(Kp+Ki*1 / s)*Err, 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 opened, the grid-connected operation is performed, the A-phase voltage effective value given value VaRmsref is equal to the A-phase voltage grid effective value feedback VgaRmsfb, Qaref is the system reactive power scheduling, the proportional coefficient and the integral coefficient of the first PI controller are not equal to 0; the proportional coefficient and the 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 opened and the second switch K2 is closed, the off-grid operation is performed, the A-phase voltage effective value given value VaRmsref is equal to the system rated operating voltage Vrated, the reference target value Qaref of the A-phase reactive power 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 the 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 rated operating voltage Vrated is generally 220V or 230V in China.

[0036] Optionally, the frequency control loop of the A-phase power grid comprises: the A-phase active power given value Paref and the A-phase active power feedback value Pafb are subtracted to input into the fifth PI controller, the A-phase expected phase angle θaref and the A-phase phase feedback value θafb are subtracted to input into the sixth PI controller, the output of the fifth PI controller and the output of the sixth PI controller are added to input into the integrator 1 / s, and the phase angle θa of the A-phase power grid is obtained after integration by the integrator; the control principles of the frequency control loop of the B-phase power grid and the frequency control loop of the C-phase power grid are the same as that of the A-phase power grid, and the required parameters are the grid values of the corresponding phases.

[0037] Optionally, when the first switch K1 is closed and the second switch K2 is opened, the grid-connected operation is performed, the A-phase active power given value Paref is the system active scheduling power, the A-phase expected phase angle θaref is the A-phase grid phase θgaref, W0 is the angular velocity Wg of the power grid, 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 the integral coefficient of the sixth PI controller are not equal to 0.

[0038] Optionally, when the first switch K1 is opened and the second switch K2 is closed, the off-grid operation is performed, the A-phase active power given value Paref is equal to 0, the A-phase expected phase angle θaref is the A-phase self-oscillation phase θarated, W0 is the system rated angular velocity 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 the integral coefficient of the sixth PI controller are not equal to 0.

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

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

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

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

[0043] This embodiment supports multiple operating modes such as three-phase grid-connected, three-phase off-grid, and single-phase grid-connected (the remaining two phases are off-grid) through independent phase control. This meets the needs of mixed scenarios of single-phase grids and three-phase loads in remote areas or islands, and can flexibly adapt to various grid operating conditions. Each phase 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, and the remaining two phases can continue to operate on-grid or off-grid, avoiding overall system shutdown. Independent phase control improves system reliability. By utilizing the same control loop for both on-grid and off-grid modes, switching is achieved solely through parameter adjustments (such as PI controller coefficients). This eliminates transient shocks caused by loop switching in traditional solutions, improves stability, and enables seamless switching and optimized dynamic response. Both stand-alone and parallel systems share the same control architecture, reducing development complexity. The modular design facilitates expansion and maintenance, simplifies system design, and enhances compatibility. It replaces traditional solutions with multiple single-phase PCSs, reducing equipment count and installation costs. This solution is particularly suitable for scenarios where three-phase loads coexist with single-phase power grids, thereby lowering user costs. In single-phase on-grid scenarios, the on-grid phase prioritizes charge and discharge power scheduling, while the off-grid phase maintains independent voltage and frequency regulation, optimizing energy utilization and achieving efficient energy management. A unified algorithm achieves three-phase coordination (e.g., a fixed 120° phase difference), preventing phase desynchronization caused by split-phase control and ensuring output power quality.

[0044] The contents disclosed above are only preferred feasible embodiments of the present invention and do not limit the scope of protection of the present invention. Therefore, all equivalent technical changes made using the contents of the present invention description and drawings are included in the scope of protection of the present invention. In addition, the elements therein can be updated as technology develops.

Claims

1. A three-phase energy storage converter phase-independent control method, 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 identification and switching are performed on the control quantity, and no switching is performed on the loop. The control method of each control loop is the same.

2. A three-phase energy storage converter phase-independent control system, characterized in that: The three-phase energy storage converter phase-independent control method as described in claim 1 is applied, and the system includes a three-phase energy storage system PCS, and the three-phase energy storage system PCS includes independently operated phase A, phase B and phase C power grids, and the phase A, phase B and phase C power grids all include grid-connected operation circuits and off-grid operation circuits. For each phase of the power grid, the grid-connected operation circuit and the off-grid operation circuit use the same set of control loops, and only identify and switch on the control quantity, and do not switch on the control loop. The operation detection logic is: when the three-phase energy storage system PCS detects that the voltage of the phase power grid is normal, the phase is switched to the grid-connected operation circuit; otherwise, the phase is switched to the off-grid operation circuit.

3. A three-phase energy storage converter phase-independent control system according to claim 2, characterized in that: The control loop includes a voltage control loop and a frequency control loop.

4. A three-phase energy storage converter phase-independent control system according to claim 3, characterized in that: The voltage control loop of the phase A power grid includes: the effective value of the phase A voltage given VaRmsref and the effective value of the phase A voltage feedback VaRmsfb are subtracted and sent to the second PI controller, the reference target value of the phase A reactive power Qaref and the actual value of the phase A reactive power Qafb are subtracted and sent to the first PI controller, the effective value of the 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 the phase A voltage given Varef; wherein θa is the phase angle of the phase A power grid, Varef is subtracted from the instantaneous value feedback of the phase A voltage Vafb and sent to the third PI controller; the output of the third PI controller is subtracted from the output current of the phase A Iafb and sent to the fourth PI controller; the output of the fourth PI controller and the instantaneous value feedback of the phase A voltage Vafb are added and sent to the PWM CALC, and output PWM to AC / DC; the control principles of the voltage control loop of phase B grid and the voltage control loop of phase C grid are the same as those of phase A grid, and the required parameters are the grid values ​​of their corresponding phases.

5. A three-phase energy storage converter phase-independent control system according to claim 4, characterized in that: When the first switch K1 is closed and the second switch K2 is open, the grid is connected and the phase A voltage effective value given VaRmsref is equal to the phase A voltage grid effective value feedback VgaRmsfb, Qaref is the system reactive power, 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.

6. A three-phase energy storage converter phase-independent control system according to claim 4, characterized in that: 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 system operating voltage 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.

7. A three-phase energy storage converter phase-independent control system according to claim 3, characterized in that: The frequency control loop of the A-phase power grid includes: the difference between the A-phase active power reference Paref and the A-phase active power feedback Pafb is sent to the fifth PI controller, the difference between the A-phase desired phase angle θaref and the A-phase phase feedback θafb is sent to the sixth PI controller, the output of the fifth PI controller, the output of the sixth PI controller and the system angular velocity W0 are added and sent to the integrator 1 / s, and the phase angle θa of the A-phase power grid is obtained after integration by the integrator; the control principles of the frequency control loops of the B-phase power grid and the C-phase power grid are the same as those of the A-phase power grid, and the required parameters are the power grid values ​​of their corresponding phases.

8. A three-phase energy storage converter phase-independent control system according to claim 7, characterized in that: When the first switch K1 is closed and the second switch K2 is disconnected, the system is connected to the grid. The A-phase active power reference Paref is the system active dispatching power, the A-phase desired phase angle θaref is the A grid phase θgaref, W0 is the grid angular velocity 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 the integral coefficient of the sixth PI controller are not equal to 0.

9. A three-phase energy storage converter phase-independent control system according to claim 7, characterized in that: When the first switch K1 is disconnected and the second switch K2 is closed, the system operates off-grid. The active power reference Paref of phase A is equal to 0. The expected phase angle θaref of phase A is equal to the natural oscillation phase θarated of phase A. W0 is the rated angular velocity Wrated of 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 the integral coefficient of the sixth PI controller are not equal to 0.

10. The three-phase energy storage converter phase-independent control system according to claim 3, characterized in that: 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.

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