All-vanadium redox flow battery ACDC type equalization system and electric energy equalization method thereof

Abstract

The invention relates to an all-vanadium redox flow battery ACDC type equalization system and an electric energy equalization method thereof. The system comprises an ACDC equalizer, a PDU power distribution unit and a PCS energy storage converter. Each battery subsystem of the all-vanadium redox flow battery is connected with an AC power grid through a PCS energy storage converter to form a general charging and discharging loop; the AC power grid is respectively connected with the positive and negative electrodes of each battery subsystem in the all-vanadium redox flow battery through the ACDC equalizer and the PDU power distribution unit in sequence to form a balanced charging and discharging loop, and the PDU power distribution unit sequentially comprises two front-stage buses connected with the positive and negative electrodes of the ACDC equalizer and a plurality of rear-stage buses connected with the positive and negative electrodes of each battery subsystem; and the front-stage bus is connected with the rear-stage bus through the change-over switches KpN and KnN after being shunted. According to the invention, a high-efficiency charging and discharging loop for each battery subsystem is formed, and the intelligent master control system is matched to realize the energy balance between the battery units and realize the automatic and high-efficiency electric quantity balance of the all-vanadium redox flow battery subsystem.

Description

Technical Field

[0001] The present invention relates to the field of electric energy storage technology and system equipment, and in particular to an all-vanadium liquid flow battery ACDC type balancing system and an electric energy balancing method thereof. Background Art

[0002] At present, in the field of power energy storage technology, all-vanadium liquid flow batteries have attracted much attention due to their advantages such as long life, large energy storage, high energy efficiency and good environmental adaptability. With the continuous improvement of the scale and complexity of all-vanadium liquid flow battery systems, the imbalance problem between battery subsystems has gradually emerged, and this problem directly affects the performance and service life of the overall system. The battery balancing problem of all-vanadium liquid flow batteries is mainly reflected in the concentration difference of the electrolyte and the voltage difference of the battery cells. During long-term operation, the charge and discharge state of each battery cell cannot be kept consistent, which leads to uneven distribution of vanadium ion concentration in the electrolyte, which in turn causes a decline in battery performance and loss of capacity. In addition, the voltage difference between battery cells will cause some battery subsystems to be overcharged or over-discharged, further exacerbating the risk of battery aging and damage. Summary of the invention

[0003] The technical problem to be solved by the present invention is: to provide an all-vanadium liquid flow battery ACDC type balancing system and an electric energy balancing method thereof, which constitutes an efficient charging and discharging circuit for each battery subsystem through an ACDC equalizer and a PDU power distribution unit, cooperates with an intelligent main control system, monitors the voltage and power parameters of the battery unit in real time, and performs feedback control on the ACDC equalizer and the PDU power distribution unit to achieve energy balance between battery units and realize automatic and efficient power balancing of the all-vanadium liquid flow battery subsystem, thereby improving the overall performance and life of the all-vanadium liquid flow battery system.

[0004] The ACDC type balancing system of the all-vanadium liquid flow battery includes an ACDC equalizer, a PDU power distribution unit, and a PCS energy storage converter; each battery subsystem of the all-vanadium liquid flow battery is connected to the AC power grid via the PCS energy storage converter to form a general charging and discharging circuit; the AC power grid is sequentially connected to the positive and negative electrodes of each battery subsystem in the all-vanadium liquid flow battery via the ACDC equalizer and the PDU power distribution unit to form a balanced charging and discharging circuit, wherein the PDU power distribution unit sequentially includes two front-stage busbars connected to the positive and negative electrodes of the ACDC equalizer, and several rear-stage busbars connected to the positive and negative electrodes of each battery subsystem; in the case of the N In the balancing charge and discharge circuit of each battery subsystem, the front-stage busbar of the positive terminal of the ACDC equalizer is divided into N branches, and a switching switch KpN is provided on the corresponding branch; the front-stage busbar of the negative terminal of the ACDC equalizer is divided into N branches, and a switching switch KnN is provided on the corresponding branch; the branch where the switching switch Kp1 is located is connected to the rear-stage busbar on the positive side of the first battery subsystem, the branch where the switching switch KnN is located is connected to the rear-stage busbar on the negative side of the Nth battery subsystem, and the branch where the switching switch KpN is located is connected to the rear-stage busbar on the positive side of the Nth battery subsystem after merging with the branch where the switching switch Kn-1N is located.

[0005] Optimally, the front-stage bus is provided with equalizer main switches Q1 and Q2 for disconnecting the PDU power distribution unit and the ACDC equalizer, and the front-stage bus is provided with a battery cluster switch Qn+2 for switching the battery subsystem connected to the equalization loop.

[0006] Furthermore, in a balanced charge and discharge circuit including N battery subsystems, the positive bus at the output end of the ACDC equalizer is divided into N branches after the equalizer main switch Q1, and the switching switches KpN are respectively set on the corresponding branches; the negative electrode at the output end of the ACDC equalizer is divided into N branches after the equalizer main switch Q2, and the switching switches KnN are respectively set on the corresponding branches; the branch where the switching switch Kp1 is located is connected to the positive side of the first battery subsystem after the battery cluster switch Q3, the branch where the switching switch KnN is located is connected to the negative side of the Nth battery subsystem after the battery cluster switch Qn+3, and the branch where the switching switch KpN is located is connected to the positive side of the Nth battery subsystem after merging with the branch where the switching switch Kn-1N is located through the battery cluster switch Qn+2.

[0007] Optimized, the ACDC equalizer is provided with a power transmission circuit for forming a power mode charging and discharging channel, the power transmission circuit includes a main power circuit, a rectifier bridge circuit and an inverter circuit, the rectifier bridge circuit and the inverter circuit are respectively connected in parallel with the charging and discharging switches, and then connected in series with the rear stage and the front stage of the main power circuit.

[0008] Optimally, an isolation transformer is provided between the AC power grid and the ACDC equalizer and the PCS energy storage converter.

[0009] The all-vanadium liquid flow battery ACDC type equalization system also includes a main control device, the input end of the main control device is connected to the PCS energy storage converter and each battery subsystem, and the output end of the main control device is connected to the ACDC equalizer and the PDU power distribution unit; the main control device includes a microprocessor, a multi-channel signal channel module, a relay module, a 485 interface module, a DO / AO interface module, a display module, and a wireless data transmission module.

[0010] Furthermore, the PCS energy storage inverter, the voltage transformers and SOC sensors integrated on each battery subsystem are connected to the microprocessor input via a multi-channel signal channel module, the microprocessor output is connected to the DO / AO interface module via a relay module, and the 485 interface module, wireless data transmission module and display module are serially connected to the microprocessor. The microprocessor is connected to the PCS energy storage converter and the ACDC equalizer through the 485 interface module. The former is used to receive signals and judge the charging and discharging condition signals, and the latter is used to control the ACDC equalizer to switch the voltage to control the voltage / power mode. The microprocessor determines the sub-battery system to be charged and discharged through calculation. After the charging and discharging is completed, the output signal is converted into a switch signal or an analog signal executed by the common switch through the signal relay module, and the equalizer main switch, battery cluster switch, and switching switch are connected through the DO / AO interface module to transmit the execution signal to realize automatic control. The display module is integrated with a liquid crystal display screen, which is used to display the PCS charging and discharging condition determined by the microprocessor, the charging and discharging voltage and SOC value of each sub-battery system received, the number of the battery subsystem to be charged and discharged determined, and the charging and discharging time and progress calculated. The wireless data transmission module is used to upload the above parameter data to the remote host computer synchronously, and download and execute the instructions or programs sent by the remote host computer for parameter adjustment or system upgrade.

[0011] The electric energy balancing method of the all-vanadium liquid flow battery ACDC type balancing system realizes the electric energy balancing of each sub-battery system during the charging and discharging process through the above-mentioned all-vanadium liquid flow battery ACDC type balancing system. The method for realizing electric energy balancing of the system includes the following steps: S1: The system closes the equalizer main switches Q1 and Q2 of the PDU power distribution unit and all battery cluster switches Qn+2; S2: The system starts the ACDC equalizer to run and establish voltage; S3: The system determines the charge and discharge direction of the battery subsystem; S4: The system determines the battery subsystem that needs to be charged or discharged; S5: The system controls the ACDC equalizer to change the mode, controls the switch of the PDU power distribution unit, and charges or discharges the battery subsystem that needs to be charged or discharged.

[0012] Further, the method for determining the battery subsystem that needs to be charged or discharged described in step S4 is as follows: S41: When the system in step S3 determines that the PCS energy storage converter is in the forward charging mode, collect the SOC values of each battery subsystem and sort them. The highest SOC value of the battery subsystem is denoted as SOC_max, and the lowest SOC value of the battery subsystem is denoted as SOC_min, and the serial number is denoted as A. When SOC_max - SOC_min > X%, it is determined that the battery subsystem A needs to be charged; S42: When the system in step S3 determines that the PCS energy storage converter is in the reverse discharging mode, collect the SOC values of each battery subsystem and sort them. The lowest SOC value of the battery subsystem is denoted as SOC_min, and the highest SOC value of the battery subsystem is denoted as SOC_max, and the serial number is denoted as B. When SOC_max - SOC_min > X%, it is determined that the battery subsystem B needs to be discharged.

[0013] Further, the method for charging the battery subsystem that needs to be charged described in step S5 is as follows: S4151: The system controls the ACDC equalizer to output a voltage equal to the current voltage value of the battery subsystem A, and then controls the PDU power distribution unit to close its corresponding switching switches KpA and KnA; S4152: The ACDC equalizer switches to the power mode to charge the battery subsystem A. When SOC_max - SOC_min < Y% of the battery subsystem, the charging is completed, and the positive and negative switching switches KpA and KnA are disconnected. Then the ACDC equalizer switches to the control voltage mode and returns to step S4.

[0014] Further, the method for discharging the battery subsystem that needs to be discharged described in step S5 is as follows: S4251: The system controls the PDU power distribution unit to close its corresponding switching switches KpB and KnB; S4252: The ACDC equalizer switches to the power mode to discharge from the battery subsystem B to the AC grid. When SOC_max - SOC_min < Y% of the flow battery subsystem, the discharging is completed, and the positive and negative switching switches KpB and KnB are disconnected. Then the ACDC equalizer switches to the control voltage mode and returns to step S4.

[0015] The beneficial effects of the all-vanadium redox flow battery ACDC type equalization system and its electric energy equalization method of the present invention are as follows: (1) An efficient charging and discharging circuit for each battery subsystem is formed by the ACDC equalizer and the PDU power distribution unit; (2) The intelligent main control system monitors the voltage and power parameters of the battery unit in real time and displays them on site and transmits the data remotely, ensuring that the operating status of the battery subsystem and the power balancing process are clearly known; (3) Through the intelligent main control system, the ACDC equalizer and PDU power distribution unit are feedback controlled to achieve energy balance between battery cells and realize automatic and efficient power balancing of the all-vanadium liquid flow battery subsystem. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following is a further description of an all-vanadium liquid flow battery ACDC type equalization system and an electric energy equalization method thereof according to the present invention in conjunction with the accompanying drawings: Figure 1 This is a wireframe diagram of the logic structure and connection principle of the ACDC type equalization system embodiment 1 of the all-vanadium liquid flow battery; Figure 2 It is a circuit diagram of the PDU power distribution unit described in Example 2 of the all-vanadium liquid flow battery ACDC type balancing system; Figure 3 It is a logic structure connection wireframe diagram of the power transmission circuit described in Example 3 of the all-vanadium liquid flow battery ACDC type equalization system; Figure 4 This is a wireframe diagram of the logic structure and connection principle of the ACDC type equalization system embodiment 5 of the all-vanadium liquid flow battery; Figure 5 It is a logic structure connection wireframe diagram of the main control device described in Example 5 of the all-vanadium liquid flow battery ACDC type equalization system; Figure 6 This is a step diagram of the implementation method of the electric energy balancing method of the all-vanadium liquid flow battery ACDC type balancing system; Figure 7 This is the operation flow chart of the electric energy balancing method of the all-vanadium liquid flow battery ACDC type balancing system; Figure 8 This is a switching action timing diagram of the power balancing method of the all-vanadium liquid flow battery ACDC type balancing system.

[0017] In the figure: 1-ACDC equalizer, 2-PDU power distribution unit, 3-PCS energy storage converter, 4-battery subsystem, 5-AC grid, 6-isolation transformer; 11-power transmission circuit; 111-main power circuit, 112-rectifier bridge circuit, 113-inverter circuit 10-main control device; 101-microprocessor, 102-multi-channel signal channel module, 103-relay module, 104-485 interface module, 105-DO / AO interface module, 106-display module, 107-wireless data transmission module. DETAILED DESCRIPTION

[0018] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] In the description of the present invention, it should be understood that the terms "left", "right", "front", "back", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0020] The technical solution of the present invention is further described below with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0021] Example 1: Figure 1 As shown, the ACDC type balancing system of the all-vanadium liquid flow battery includes an ACDC balancer 1, a PDU power distribution unit 2, and a PCS energy storage converter 3; each battery subsystem 4 of the all-vanadium liquid flow battery is connected to the AC power grid 5 via the PCS energy storage converter 3 to form a general charging and discharging circuit; the AC power grid 5 is sequentially connected to the positive and negative electrodes of each battery subsystem 4 in the all-vanadium liquid flow battery via the ACDC balancer 1 and the PDU power distribution unit 2 to form a balanced charging and discharging circuit, wherein the PDU power distribution unit 2 sequentially includes two front-stage busbars connected to the positive and negative electrodes of the ACDC balancer 1, and several rear-stage busbars connected to the positive and negative electrodes of each battery subsystem 4. line; in a balancing charge and discharge circuit including N battery subsystems 4, the front-stage busbar of the positive terminal of the ACDC equalizer 1 is divided into N branches, and a switching switch KpN is provided on the corresponding branches; the front-stage busbar of the negative terminal of the ACDC equalizer 1 is divided into N branches, and a switching switch KnN is provided on the corresponding branches; the branch where the switching switch Kp1 is located is connected to the rear-stage busbar on the positive side of the first battery subsystem, the branch where the switching switch KnN is located is connected to the rear-stage busbar on the negative side of the Nth battery subsystem, and the branch where the switching switch KpN is located is connected to the rear-stage busbar on the positive side of the Nth battery subsystem after merging with the branch where the switching switch Kn-1N is located.

[0022] Example 2: Figure 2As shown, the front-stage busbar of the ACDC type balancing system of the all-vanadium liquid flow battery is provided with balancer main switches Q1 and Q2 for disconnecting the PDU power distribution unit 2 and the ACDC balancer 1, and the front-stage busbar is provided with a battery cluster switch Qn+2 for switching the battery subsystem connected in the balancing loop. In the balancing charge and discharge loop containing N battery subsystems, the positive busbar at the output end of the ACDC balancer 1 is divided into N branches after the balancer main switch Q1, and the switching switches KpN are respectively arranged on the corresponding branches; the negative pole at the output end of the ACDC balancer 1 is divided into N branches after the balancer main switch Q2, and the switching switches KnN are respectively arranged on the corresponding branches; the branch where the switching switch Kp1 is located is connected to the positive side of the first battery subsystem after the battery cluster switch Q3, the branch where the switching switch KnN is located is connected to the negative side of the Nth battery subsystem after the battery cluster switch Qn+3, and the branch where the switching switch KpN is located is connected to the positive side of the Nth battery subsystem after the battery cluster switch Qn+2 after merging with the branch where the switching switch Kn-1N is located. In this embodiment, N is set to 3 (ie, it includes three sub-battery system balanced charge and discharge circuits). The remaining structures and components are as described in Embodiment 1 and will not be described again.

[0023] Example 3: Figure 3 As shown, the ACDC equalizer 1 of the all-vanadium liquid flow battery ACDC type equalization system is provided with a power transmission circuit 11 for forming a power mode charging and discharging channel. The power transmission circuit 11 includes a main power circuit 111, a rectifier bridge circuit 112 and an inverter circuit 113. The rectifier bridge circuit 112 and the inverter circuit 113 are connected in parallel with the charging and discharging switches respectively, and then connected in series with the rear stage and the front stage of the main power circuit 11.

[0024] Embodiment 4: The ACDC type equalization system of the all-vanadium liquid flow battery is provided with an isolation transformer 6 between the AC grid 5 and the ACDC equalizer 1 and the PCS energy storage converter 3. The remaining structures and components are as described in Embodiment 1 and will not be described again.

[0025] Example 5: Figure 4 , 5As shown, the ACDC type balancing system of the all-vanadium liquid flow battery The ACDC type balancing system of the all-vanadium liquid flow battery also includes a main control device 10, the input end of the main control device 10 is connected to the PCS energy storage converter 3 and each battery subsystem 4, and the output end of the main control device 10 is connected to the ACDC equalizer 1 and the PDU power distribution unit 2; the main control device includes a microprocessor 101, a multi-channel signal channel module 102, a relay module 103, a 485 interface module 104, a DO / AO interface module 105, a display module 106, and a wireless data transmission module 107. The voltage transformer and SOC sensor integrated on the PCS energy storage converter 3 and each battery subsystem 4 are connected to the input end of the microprocessor 101 through the multi-channel signal channel module 102, and the output end of the microprocessor 101 is connected to the DO / AO interface module 105 through the relay module 103. The 485 interface module 104, the wireless data transmission module 106, and the display module 107 are serially connected to the microprocessor. The microprocessor is connected to the PCS energy storage converter and the ACDC equalizer through the 485 interface module. The former is used to receive signals and judge the charging and discharging condition signal, and the latter is used to control the ACDC equalizer to switch the voltage to control the voltage / power mode; the microprocessor determines the sub-battery system to be charged and discharged through calculation, and after the charging and discharging is completed, the output signal is converted into a switch signal or analog signal executed by the common switch through the signal relay module, and the equalizer main switch, battery cluster switch, and switching switch are connected through the DO / AO interface module and the execution signal is transmitted to realize automatic control; the display module is integrated with a liquid crystal display screen, which is used to display the PCS charging and discharging condition determined by the microprocessor, the charging and discharging voltage and SOC value of each sub-battery system received, the number of the battery subsystem to be charged and discharged, and the charging and discharging time and progress calculated. The wireless data transmission module is used to upload the above parameter data to the remote host computer synchronously, and download and execute the instructions or programs sent by the remote host computer for parameter adjustment or system upgrade. The remaining structures and components are as described in Implementation 1 and will not be described again.

[0026] Implementation method: Figure 6 , 7 As shown, the energy balancing method of the all-vanadium liquid flow battery ACDC type balancing system realizes the energy balancing of each sub-battery system during the charging and discharging process through the above-mentioned all-vanadium liquid flow battery ACDC type balancing system. The method for realizing energy balancing in the system includes the following steps: S1: The system closes the equalizer main switches Q1 and Q2 of the PDU power distribution unit 2 and all battery cluster switches Qn+2; S2: The system starts ACDC equalizer 1 to run and establish voltage; S3: The system determines the charging and discharging direction of the battery subsystem 4; S4: The system determines the battery subsystem 4 that needs to be charged or discharged; S5: The system controls the ACDC equalizer 1 to change the mode, controls the switching switch of the PDU power distribution unit 2, and charges or discharges the battery subsystem to be charged or discharged.

[0027] Among them, as described in step S4, the method for determining the battery subsystem to be charged or discharged is: When the system in step S3 determines that the PCS energy storage converter 3 is in the forward charging condition, collect the SOC values of each battery subsystem 4 and sort them. The highest battery subsystem SOC value is recorded as SOC_max, and the lowest battery subsystem SOC value SOC_min and the serial number are recorded as A; when SOC_max - SOC_min > X%, it is determined that the battery subsystem A needs to be charged; When the system in step S3 determines that the PCS energy storage converter 3 is in the reverse discharging condition, collect the SOC values of each battery subsystem 4 and sort them. The lowest battery subsystem SOC value is SOC_min, and the highest battery subsystem SOC value is recorded as SOC_max, and the serial number is recorded as B; when SOC_max - SOC_min > X%, it is determined that the battery subsystem B needs to be discharged.

[0028] Among them, as described in step S5, the method for charging the battery subsystem to be charged is: The system controls the ACDC equalizer 1 to output a voltage equal to the current voltage value of the battery subsystem A, and then controls the PDU power distribution unit 2 to close its corresponding switching switches KpA and KnA; the ACDC equalizer 1 switches to the power mode to charge the battery subsystem A. When SOC_max - SOC_min < Y% in the battery subsystem, the charging is completed, and the positive and negative switching switches KpA and KnA are disconnected. Then the ACDC equalizer 1 switches to the control voltage mode and returns to step S4.

[0029] The method for discharging the battery subsystem to be discharged is: The system controls the PDU power distribution unit 2 to close its corresponding switching switches KpB and KnB; the ACDC equalizer 1 switches to the power mode to discharge from the battery subsystem B to the AC grid. When SOC_max - SOC_min < Y% in the flow battery subsystem, the discharging is completed, and the positive and negative switching switches KpB and KnB are disconnected. Then the ACDC equalizer 1 switches to the control voltage mode and returns to step S4.

[0030] During the above charging and discharging process, the system (master control device) controls the action timing of each switch as Figure 8 shown.

[0031] The all-vanadium liquid flow battery ACDC type balancing system and its electric energy balancing method form a high-efficiency charging and discharging circuit for each battery subsystem through an ACDC equalizer and a PDU power distribution unit, cooperate with an intelligent main control system, monitor the voltage and power parameters of the battery unit in real time, and feedback control the ACDC equalizer and the PDU power distribution unit to achieve energy balance between battery units and realize automatic and efficient power balancing of the all-vanadium liquid flow battery subsystem, thereby improving the overall performance and life of the all-vanadium liquid flow battery system.

[0032] The above description shows the main features, basic principles, and advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments or embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the above embodiments or embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An all-vanadium liquid flow battery ACDC type equalization system, characterized by: It includes an ACDC equalizer (1), a PDU power distribution unit (2), and a PCS energy storage converter (3); each battery subsystem (4) of the all-vanadium liquid flow battery is connected to an AC power grid (5) via the PCS energy storage converter (3) to form a general charging and discharging circuit; the AC power grid (5) is connected to the positive and negative electrodes of each battery subsystem (4) in the all-vanadium liquid flow battery in turn via the ACDC equalizer (1) and the PDU power distribution unit (2) to form a balanced charging and discharging circuit, wherein: The PDU power distribution unit (2) comprises, in sequence, two front-stage busbars connected to the positive and negative poles of the ACDC equalizer (1), and a plurality of rear-stage busbars connected to the positive and negative poles of each battery subsystem (4); in a balanced charge and discharge circuit comprising N battery subsystems (4), the front-stage busbar at the positive end of the ACDC equalizer (1) is divided into N branches, and a switching switch KpN is provided on the corresponding branches; the front-stage busbar at the negative pole of the ACDC equalizer (1) is divided into N branches, and a switching switch KnN is provided on the corresponding branches; the branch where the switching switch Kp1 is located is connected to the rear-stage busbar on the positive pole side of the first battery subsystem, the branch where the switching switch KnN is located is connected to the rear-stage busbar on the negative pole side of the Nth battery subsystem, and the branch where the switching switch KpN is located is connected to the rear-stage busbar on the positive pole side of the Nth battery subsystem after merging with the branch where the switching switch Kn-1N is located.

2. The ACDC type equalization system of all-vanadium liquid flow battery according to claim 1 is characterized in that: The front-stage bus is provided with equalizer main switches Q1 and Q2 for disconnecting the PDU power distribution unit (2) and the ACDC equalizer (1), and the front-stage bus is provided with a battery cluster switch Qn+2 for switching the battery subsystem connected to the equalization loop.

3. The ACDC type equalization system of all-vanadium liquid flow battery according to claim 2 is characterized in that: In a balanced charge and discharge circuit including N battery subsystems, the positive busbar at the output end of an ACDC balancer (1) is divided into N branches after passing through a balancer main switch Q1, and the switching switches KpN are respectively arranged on the corresponding branches; the negative electrode at the output end of the ACDC balancer (1) is divided into N branches after passing through a balancer main switch Q2, and the switching switches KnN are respectively arranged on the corresponding branches; the branch where the switching switch Kp1 is located is connected to the positive electrode side of the first battery subsystem after passing through a battery cluster switch Q3, the branch where the switching switch KnN is located is connected to the negative electrode side of the Nth battery subsystem after passing through a battery cluster switch Qn+3, and the branch where the switching switch KpN is located is connected to the positive electrode side of the Nth battery subsystem after merging with the branch where the switching switch Kn-1N is located through a battery cluster switch Qn+2.

4. The ACDC type equalization system of all-vanadium liquid flow battery according to claim 2 is characterized in that: An isolation transformer (6) is provided between the AC power grid (5), the ACDC equalizer (1), and the PCS energy storage converter (3).

5. An energy balancing method for an all-vanadium liquid flow battery ACDC type balancing system, characterized by: The all-vanadium liquid flow battery ACDC type balancing system is the all-vanadium liquid flow battery ACDC type balancing system according to any one of claims 2 to 4. The method for realizing electric energy balancing in the system comprises the following steps: S1: The system closes the equalizer main switches Q1, Q2 and all battery cluster switches Qn+2 of the PDU power distribution unit (2); S2: The system starts the ACDC equalizer (1) to run and establish the voltage; S3: the system determines the charging and discharging direction of the battery subsystem (4); S4: The system determines the battery subsystem that needs to be charged or discharged (4); S5: The system controls the ACDC equalizer (1) to change the mode, controls the switching switch of the PDU power distribution unit (2), and charges or discharges the battery subsystem to be charged or discharged.

6. The method for equalizing electric energy of the all-vanadium redox flow battery ACDC type equalization system according to claim 5, characterized in that: The method for determining the battery subsystem to be charged or discharged as described in step S4 is: S41: When the system in step S3 determines that the PCS energy storage converter (3) is in the forward charging condition, collect the SOC values of each battery subsystem (4) and sort them. Among them, the highest battery subsystem SOC value is recorded as SOC_max, the lowest battery subsystem SOC value SOC_min, and the serial number is recorded as A; when SOC_max - SOC_min > X%, it is determined that the battery subsystem A needs to be charged; S42: When the system in step S3 determines that the PCS energy storage converter (3) is in the reverse discharging condition, collect the SOC values of each battery subsystem (4) and sort them. Among them, the lowest battery subsystem SOC value is SOC_min, the highest battery subsystem SOC value is recorded as SOC_max, and the serial number is recorded as B; when SOC_max - SOC_min > X%, it is determined that the battery subsystem B needs to be discharged.

7. The method for equalizing electric energy of the all-vanadium redox flow battery ACDC type equalization system according to claim 6, characterized in that: The method for charging the battery subsystem to be charged as described in step S5 is S4151: The system controls the ACDC equalizer (1) to output a voltage equal to the current voltage value of the battery subsystem A, and then controls the PDU power distribution unit (2) to close its corresponding switching switches KpA and KnA; S4152: The ACDC equalizer (1) switches to the power mode to charge the battery subsystem A. When SOC_max - SOC_min < Y% in the battery subsystem, the charging is completed, the positive and negative switching switches KpA and KnA are disconnected, and then the ACDC equalizer (1) switches to the control voltage mode and returns to step S4.

8. The method for equalizing electric energy of the all-vanadium redox flow battery ACDC type equalization system according to claim 6, characterized in that: The method for discharging the battery subsystem to be discharged as described in step S5 is S4251: The system controls the PDU power distribution unit (2) to close its corresponding switching switches KpB and KnB; S4252: The ACDC equalizer (1) switches to the power mode to discharge from the battery subsystem B to the AC power grid. When SOC_max - SOC_min < Y% in the redox flow battery subsystem, the discharging is completed, the positive and negative switching switches KpB and KnB are disconnected, and then the ACDC equalizer (1) switches to the control voltage mode and returns to step S4.

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