A flow battery equalization, charging, discharging device and system control method

Abstract

The present invention discloses a balancing, charging, and discharging device and a system control method for a liquid flow battery, and relates to the field of chemical technology. The present invention includes a balancing cabinet, a DC contactor, a DC fuse, a DC Hall sensor, a DC / DC bidirectional converter, a DC copper busbar, an AC / DC bidirectional converter, an isolation transformer, an AC current transformer, an AC contactor, an AC circuit breaker, and a touch screen for a balancer, all of which are integrated in the balancing cabinet. The present invention configures the balancing cabinet through a liquid flow energy storage system, which can effectively reduce the barrel effect of the series branch, significantly increase the system charging and discharging amount, and improve economic benefits; at the same time, it avoids over-capacity of the system to achieve the rated charging and discharging amount, and reduces the system cost; by configuring the multifunctional balancing cabinet through a liquid flow energy storage system, there is no need to require the PCS manufacturer to customize and develop a PCS with a 0V charging function, and directly selects a high-power conventional PCS with a DC side voltage of 800-1500V, thereby reducing the cost of PCS equipment and doubling the optional range of PCS.

Description

Technical Field

[0001] The present invention belongs to the field of chemical technology, and in particular relates to an equalization, charging, discharging device and a system control method for a liquid flow battery. Background Art

[0002] First, liquid flow batteries are different from lithium batteries, lead-acid batteries, sodium batteries, etc. The power unit and capacity unit are separated, and the battery system does not store any electricity before delivery; the electrolyte of the liquid flow battery is filled at the project site, and the filled electrolyte needs to be charged and activated on site. However, there is currently no dedicated converter for liquid flow batteries on the market, and converters suitable for other batteries cannot meet the on-site activation needs of liquid flow batteries. At present, the on-site activation method is designed and completed by the liquid flow manufacturer itself, and the on-site workload is very large; second, the liquid flow battery stack is a whole formed by tightly stacking and connecting multiple single cells in series. Usually, the number of cells connected in series inside the stack can reach dozens, and then n stacks are connected in series and in parallel to form a high-power battery module. Due to the huge number of single cells and the different voltage consistency caused by the production process and material differences of the single cells, the voltage of the stack inside the high-power battery module is prone to voltage inconsistency. In addition, the electrolyte distribution inside each stack is uneven, and the voltage inconsistency of the stack is increasing. The more the number of battery stacks connected in series, the greater the inconsistency, resulting in a reduction in the system's charge and discharge range, causing system capacity loss; 3. There are common pipelines and liquid circuits in parallel between flow battery stacks and battery stacks. In the presence of a potential difference, single-chip batteries at different points can form a discharge circuit through parallel pipelines. After multiple discharge circuits are superimposed, the discharge current in specific pipelines and battery stack areas is very large, which will reduce the working current during normal charging and discharging operations. The heat caused by the leakage current of the electrolyte, pipelines, and battery components will be carried away by the flowing electrolyte. However, in the case of high SOC of the system, the electrolyte cannot flow, causing this part of the heat to accumulate. When the temperature rises to a certain level, it will damage the battery stack materials and pipelines, causing damage to the battery stack and pipelines and leakage. At present, the practice of various manufacturers is to reduce the number of single batteries in series in a single battery stack, thereby reducing the leakage current. This practice makes it difficult to increase the power of the battery stack after it reaches a certain level.

[0003] In view of the above problems, a device and a control method are proposed which can simultaneously solve the problem of on-site activation 0, the problem of balancing between battery modules and the problem of leakage current in the shutdown state. Summary of the invention

[0004] The object of the present invention is to provide a flow battery balancing, charging, discharging device and system control method to solve the existing problems.

[0005] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0006] The present invention is a balancing, charging and discharging device for a liquid flow battery, comprising a balancing cabinet, wherein the balancing cabinet is provided with the following components:

[0007] DC contactor, the battery modules that need to be balanced are connected to the lower end of the DC contactor through cables, and the battery pack is connected to the balancer;

[0008] The DC fuse is connected in series with a copper bar at the upper end of the DC contactor. The DC fuse is connected in series between the copper bars of the DC positive and negative poles of the equalizer, and mainly plays a role in DC short-circuit protection;

[0009] The DC Hall sensor is installed on the busbar in a perforated manner. It is mainly used to measure the equalizing current and bus current and provide reference current for the equalizer output.

[0010] DC / DC bidirectional converter, two DC / DC bidirectional converters are configured as needed, and the DC / DC bidirectional converter plays a role in DC boost and voltage reduction, raising the low voltage of the battery to the bus voltage, or reducing the bus voltage to the voltage required by the battery; the low-voltage input end of the DC / DC bidirectional converter is connected to the DC fuse through a copper bus;

[0011] AC / DC bidirectional converter, the DC end and AC end are all connected by copper bars, which play the role of rectification and inversion; the electric energy on the AC side is rectified into DC and then transmitted to the battery pack that needs to replenish electric energy;

[0012] A DC copper busbar, which serves to connect a DC / DC bidirectional converter and an AC / DC bidirectional converter, and a plurality of DC / DC bidirectional converters are connected in parallel on the DC copper busbar;

[0013] The isolation transformer is connected in series at the output end of the AC / DC bidirectional converter to isolate the power grid and the equalizer;

[0014] AC current transformer, installed through holes on the AC copper busbar, measures the charging or discharging current at the AC end of the equalizer;

[0015] An AC contactor, which is used to control the equalizer to be connected to or disconnected from the power grid;

[0016] AC circuit breaker, which is the AC output end of the equalizer. The power grid is connected to the AC circuit breaker through a cable to provide AC short-circuit protection.

[0017] The touch operation screen of the equalizer is installed on the door of the equalizer cabinet. The operation and alarm status of the equalizer can be viewed through the screen. It has the functions of inputting and modifying the operation parameters and starting and stopping the equalizer.

[0018] The DC contactor, DC fuse, DC Hall sensor, DC / DC bidirectional converter, DC copper busbar, AC / DC bidirectional converter, isolation transformer, AC current transformer, AC contactor, AC circuit breaker and equalizer touch operation screen are all integrated in the balancing cabinet.

[0019] The balancing cabinet has an IP54 protection grade and is suitable for outdoor installation.

[0020] A system control method for equalization, charging and discharging devices for a flow battery, the system control method comprising the following steps:

[0021] Step 1: Input the SOC value of the battery module; the equalizer receives data from the battery management system BMS, which mainly includes the actual SOC value of each battery module and the charging, discharging, shutdown and fault status of the battery system; the equalizer control system sorts the input SOC values ​​according to size, such as SOC1<SOC2<SOC3;

[0022] Step 2: Determine the module that needs to be balanced; when the battery system is in a fault state or shutdown state, the balancing module automatically enters the shutdown state; when the battery system is in a discharging state, the module represented by SOC1 is the module that needs to be balanced, and the module needs to be charged and supplemented with power through the equalizer; when the battery system is in a charging state, the module represented by SOC3 is the module that needs to be balanced, and the module needs to be discharged through the equalizer; the judgment conditions are: during the discharge process, the SOC value of any battery module is less than the SOC average value * 95%; during the charging process, the SOC value of any battery module is greater than the SOC average value * 105%; when the SOC values ​​of multiple modules meet the balancing requirements, they are sorted and enter the waiting balancing queue;

[0023] Step 3: The DC contactor corresponding to the module that needs to be balanced is closed, and the positive and negative electrodes of the corresponding battery modules are connected to the DC output terminal of the balancer;

[0024] Step 4: The AC contactor is closed to introduce the mains power into the balancer;

[0025] Step 5: Set the balancing current on the balancer control screen and click the start button. The balancer will start running according to the established charging and discharging logic. During the balancing process, the balancer transfers the electric energy of the battery modules under different DC / DC bidirectional converters to the required battery modules, and outputs the electric energy to the grid when there is no charging load on the DC bus.

[0026] Step 5: During the balancing process, the module SOC value is collected in real time. When the battery system is in the discharge process and the SOC1 value of the battery module in the balancing process = (SOC2+SOC3) / 2*1.1, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues;

[0027] Step 6: During the balancing process, the module SOC value is collected in real time. When the battery system is in the charging process and the SOC3 value of the battery module being balanced = (SOC1+SOC2) / 2*0.9, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues;

[0028] Step 7: When there is no module that needs to be balanced in the waiting queue, the equalizer stops running and simultaneously disconnects the AC contactor and the DC contactor;

[0029] Step 8: After the balancing module exits operation, it maintains communication with the battery management system BMS and calculates and compares the SOC value in real time;

[0030] Step 9: Repeat steps 1 to 8 above.

[0031] The present invention has the following beneficial effects:

[0032] The present invention configures the multifunctional balancing cabinet through the liquid flow energy storage system, which can effectively reduce the barrel effect of the series branch, significantly increase the system charging and discharging capacity, and improve economic benefits; at the same time, it avoids over-capacity of the system to achieve the rated charging and discharging capacity, and reduces system costs.

[0033] The present invention configures the multifunctional balancing cabinet through a liquid flow energy storage system, and does not require a PCS manufacturer to customize and develop a PCS with a 0V charging function. A high-power conventional PCS with a DC side voltage of 800-1500V is directly selected, thereby reducing the cost of PCS equipment and doubling the optional range of PCS.

[0034] The present invention reduces the complexity of the design of the liquid flow battery pipeline system, and parts such as shutdown drainage and startup exhaust can be appropriately cancelled or reduced.

[0035] The present invention has a wide range of applications. The system can be applied not only to all-vanadium liquid flow battery systems, but also to other liquid flow batteries facing the same problem. At the same time, it can be applied not only between multiple series-connected battery modules, but also inside battery modules with multiple batteries connected in series and parallel, and can even be configured inside battery modules and between series-connected battery modules at the same time to achieve a better balancing effect.

[0036] The present invention organically combines the 0V charging, battery system balancing, and shutdown discharge functions that are urgently needed by liquid flow batteries. A large energy storage unit equipped with a balancing cabinet can complete the functions required for operations such as PCS 0V charging modules, various separate charging modules, capacitor balancing, liquid and gas drainage, etc.; and the present invention has clear principles and is easy to operate, and can be automatically executed by simply communicating with the BMS system.

[0037] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0039] Figure 1 It is a schematic diagram of the structure of an equalization, charging and discharging device for a liquid flow battery;

[0040] Figure 2 The application of the present invention to a series-connected battery module;

[0041] Figure 3 The application of the present invention to a series-parallel battery stack group;

[0042] Figure 4 The present invention is applied to a battery stack in a series battery module.

[0043] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0044] 1. DC contactor; 2. DC fuse; 3. 6. DC Hall sensor; 4. DC / DC bidirectional converter; 5. DC copper busbar; 7. AC / DC bidirectional converter; 8. Isolation transformer; 9. AC current transformer; 10. AC contactor; 11. AC circuit breaker; 12. Equalizer touch screen; 13. Equalization cabinet. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be understood that the terms "upper", "middle", "outer", "inner" and the like indicating directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0047] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] See also Figure 1-Figure 4 As shown, the present invention is a balancing, charging and discharging device for a liquid flow battery, including a balancing cabinet 13, in which the following components are arranged:

[0049] DC contactor 1, the battery modules that need to be balanced are connected to the lower end of the DC contactor 1 through cables. There are multiple DC contactors 1 at this location. By selectively controlling the corresponding DC contactors 1, different battery groups can be connected to the balancer;

[0050] The DC fuse 2 is connected in series with the upper end of the DC contactor 1 using a copper busbar. The DC fuse 2 is connected in series between the copper busbars of the DC total positive and negative poles of the equalizer, and mainly plays a role in DC short-circuit protection;

[0051] The DC Hall sensor 3 is mounted on the busbar in a perforated manner, and is mainly used to measure the equalizing current and busbar current, and provide a reference current for the equalizer output;

[0052] DC / DC direct current bidirectional converter 4, the DC / DC direct current bidirectional converter 4 can be configured n as needed, and this embodiment takes two DC / DC modules as an example for explanation, the DC / DC direct current bidirectional converter 4 plays the role of DC boost and voltage reduction, and can increase the low voltage of the battery to the bus voltage, or reduce the bus voltage to the voltage required by the battery; the low voltage input end of the DC / DC direct current bidirectional converter 4 is connected to the DC fuse 2 through a copper bus;

[0053] AC / DC bidirectional converter 7, the DC end and the AC end are all connected by copper bars, which play a role of rectification and inversion; the electric energy on the AC side can be rectified into DC and then transmitted to the battery pack that needs to be supplemented with electric energy, or the module with over-high voltage of the battery pack can be discharged to the power grid;

[0054] A DC copper busbar 5, which is used to connect the DC / DC bidirectional converter 4 and the AC / DC bidirectional converter 7. At the same time, multiple DC / DC bidirectional converters 4 can be connected in parallel to the DC copper busbar 5;

[0055] An isolation transformer 8 is connected in series to the output end of the AC / DC bidirectional converter 7 to isolate the power grid from the equalizer;

[0056] AC current transformer 9, installed through a hole on the AC copper busbar, measures the charging or discharging current at the AC end of the equalizer;

[0057] The AC contactor 10 is used to control the AC contactor 10 to put the equalizer into or out of the power grid;

[0058] AC circuit breaker 11, which is the AC output terminal of the equalizer. The power of the power grid is connected to the AC circuit breaker 11 through a cable to play an AC short-circuit protection role;

[0059] The touch operation screen 12 of the equalizer is installed on the door of the equalizer cabinet 13. The operation and alarm status of the equalizer can be viewed through the screen. It has the functions of inputting and modifying the operation parameters and starting and stopping the equalizer.

[0060] The DC contactor 1, the DC fuse 2, the DC Hall sensor 3, the DC / DC bidirectional converter 4, the DC copper busbar 5, the AC / DC bidirectional converter 7, the isolation transformer 8, the AC current transformer 9, the AC contactor 10, the AC circuit breaker 11 and the equalizer touch operation screen 12 are all integrated in the equalization cabinet 13.

[0061] In the embodiment, the balancing cabinet 13 has an IP54 protection grade and is capable of outdoor installation.

[0062] A system control method for equalization, charging and discharging devices for a flow battery, the system control method comprising the following steps:

[0063] Step 1: Input the SOC value of the battery module; the equalizer receives data from the battery management system BMS, which mainly includes the actual SOC value of each battery module and the charging, discharging, shutdown and fault status of the battery system; the equalizer control system sorts the input SOC values ​​according to size, such as SOC1<SOC2<SOC3;

[0064] Step 2: Determine the module that needs to be balanced; when the battery system is in a fault state or shutdown state, the balancing module automatically enters the shutdown state; when the battery system is in a discharging state, the module represented by SOC1 is the module that needs to be balanced, and the module needs to be charged and supplemented with power through the equalizer; when the battery system is in a charging state, the module represented by SOC3 is the module that needs to be balanced, and the module needs to be discharged through the equalizer; the judgment conditions are: during the discharge process, the SOC value of any battery module is less than the SOC average value * 95%; during the charging process, the SOC value of any battery module is greater than the SOC average value * 105%; when the SOC values ​​of multiple modules meet the balancing requirements, they are sorted and enter the waiting balancing queue;

[0065] Step 3: The DC contactor 1 corresponding to the module to be balanced is closed, and the positive and negative electrodes of the corresponding battery module are connected to the DC output terminal of the balancer;

[0066] Step 4: The AC contactor 10 is closed to introduce the mains power into the equalizer;

[0067] Step 5: Set the balancing current on the balancer control screen, click the start button, and the balancer will be put into operation according to the established charging and discharging logic; during the balancing process, the balancer transfers the electric energy of the battery modules under different DC / DC bidirectional converters 4 to the required battery modules, and outputs the electric energy to the grid when there is no charging load on the DC bus;

[0068] Step 5: During the balancing process, the module SOC value is collected in real time. When the battery system is in the discharge process and the SOC1 value of the battery module in the balancing process = (SOC2+SOC3) / 2*1.1, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues;

[0069] Step 6: During the balancing process, the module SOC value is collected in real time. When the battery system is in the charging process and the SOC3 value of the battery module being balanced = (SOC1+SOC2) / 2*0.9, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues;

[0070] Step 7: When there is no module that needs to be balanced in the waiting queue, the equalizer stops running and simultaneously disconnects the AC contactor 10 and the DC contactor 1;

[0071] Step 8: After the balancing module exits operation, it maintains communication with the battery management system BMS and calculates and compares the SOC value in real time;

[0072] Step 9: Repeat steps 1 to 8 above.

[0073] See also Figure 1-Figure 4 As shown, this embodiment is a description of the working principle of a flow battery equalization, charging and discharging device:

[0074] 1) n single cells X-kW (X represents the battery stack power such as 25, 32, 45, 50, 65, etc., kW represents the power unit) are connected in series and parallel to form a battery module, and the power of the module is NX-kW; the open circuit voltage of the battery module U1≤500V; the center of the battery module and the battery outlets at both ends of the module are equipped with DC contactors, which can be controlled by BMS; the module can have a single or multiple circulation systems;

[0075] 2) m modules with a power of NX-kW are connected in series to form a series battery module group with an output power of MNX-kW; the voltage of the module group is ≤1500V and the capacity is ≤1.725MW PCS; the PCS is conventional, with a DC voltage range of 800-1500V and an AC voltage of 0.5kV-0.69kV;

[0076] 3) After each of the k MNX-kW series modules is configured with one PCS, the PCS is connected in parallel to a 2MVA-6.3MVA step-up transformer T1, and the output voltage on the AC side of T1 is 6kV~35kV.

[0077] 4) The power distribution of the auxiliary electrical equipment (circulation pump, heat exchanger, air conditioner, heater, sensor, etc.) inside the above battery modules is all powered by an isolation transformer, and the power supply of the transformer can be taken from the AC side of the PCS or the AC side of the T1 transformer;

[0078] 5) Based on the above configuration, the multifunctional 0V charging, balancing, and shutdown discharge module of the invention is configured. This module can be configured at multiple levels, such as being configured between multiple modules to perform 0V charging, shutdown discharge, and balancing on the entire module. In this case, a single module or multiple modules can be used simultaneously; it can also be used between modules in an internal group, with a higher degree of balancing refinement; it can also be configured in a single module to balance the parallel battery stack group inside the module, which can achieve battery stack-level balancing and has the best balancing effect.

[0079] 6) 0V charging function realization:

[0080] Take the all-vanadium liquid flow battery as an example: after the 3.5-valent alum sulfate electrolyte is filled into the positive and negative storage tanks, the positive and negative electrode circulation pumps of the battery system are turned on to transport the electrolyte to the n battery stacks inside the module; at this time, since the electrolyte is not activated, the positive and negative open circuit voltages at both ends of the battery stack and the battery module are 0V;

[0081] The multifunctional balancing module closes the AC side contactor under the control of BMS;

[0082] The AC / DC module uses a constant DC side power mode to rectify and output DC750V to the DC bus, and n DC balancing modules are connected in parallel under the DC bus;

[0083] The number of DC balancing modules can be adjusted according to the number of battery modules that need to be balanced. The DC input voltage range of each DC balancing module is 0-500v, and the maximum input and output current is 300A; the output of each DC / DC balancing module is connected to the positive and negative poles of the corresponding battery module;

[0084] The BMS sends a command to the corresponding BMU to disconnect the contactor connecting each module;

[0085] The DC balancing module uses the DC side constant current mode to charge the battery module. The constant current can be given according to the battery characteristics. The output current can be adjusted arbitrarily from 0 to 300V. The charging process is cut off under voltage conditions. When the voltage reaches the battery set stop voltage, the DC balancing module stops and the module activation is completed. This process can activate and charge n battery modules at the same time.

[0086] After the DC balancing module is charged, it exits operation, and the BMS sends a command to close the contactor for connecting the battery module. After the contactor is closed, multiple battery modules form a series circuit. After n battery modules are connected in series, the output voltage meets the conventional large-capacity PCS DC side voltage range (800-1500V).

[0087] The PCS charges and discharges the series-connected battery modules in a constant power mode on the DC side.

[0088] 7) Balance function realization:

[0089] A. Balance between modules:

[0090] Balanced charging process: Here we take three modules in series as an example. During the charging process, the real-time voltages of module 1, module 2 and module 3 are u1, u2 and u3 respectively; the ideal charging cutoff condition is u1+u2+u3≤1500V, but due to the consistency differences between single-chip batteries and battery stacks, the differences in the electrolyte distribution inside the battery stacks, the differences in the temperature field inside the battery stacks, etc., the open circuit voltage of each battery stack will be different under the same charging current. The overall manifestation is that the voltage of the battery stack with a large internal resistance is higher, and the internal resistance of the battery stack with a small internal resistance is small. At this time, in order to prevent the battery system from overcharging, additional restrictions will be added: the voltage of each of the n battery stacks inside u1 must be ≤ the rated voltage of the battery stack; at this time, when the voltage of one battery stack reaches the charging voltage cutoff condition, the charging of the entire system must be stopped. Similarly, when the voltage of a single module reaches the cutoff condition, the entire branch must also stop charging; in this case, the battery stack and module with a lower internal resistance have not yet When fully charged, charging will be terminated in advance or the actual charging capacity and charging time of the system may be less than the nominal design capacity. At this time, the balancing module is put into operation, and the BMS controls the AC side contactor of the multi-function balancer to close, and an internal DC750V bus is established. The DC balancing module corresponding to module 1 adopts a small current discharge mode to discharge to the DC750V bus. Other balancing modules can charge the modules with lower voltages in the process. For example, when the voltage of module 2 is low, power can be taken from the DC750V bus, and then charged to module 2 through balancing module 2. At the same time, when the series branch or the battery module connected to the balancer does not have a low voltage required by the voltage load, the multi-function balancer can be output to the AC auxiliary system power supply bus in a discharge mode. This part of the power is consumed by the auxiliary system (circulating pump, heat exchanger, etc.). At the same time, the direction of the total incoming current is detected. When it is detected that the current direction points to the grid, the balancer reduces the discharge power or shuts down.

[0091] Balance during discharge process: The discharge process requires balanced battery stacks and battery stack modules, which is the opposite of the above-mentioned charging process. It is necessary to charge the battery stacks and battery modules with lower voltages to slow down the voltage drop trend. In this process, the balancing module adopts the charging mode to draw power from other modules with higher voltages or the AC side of the balancing module to charge the modules with lower voltages or the battery stack group.

[0092] B. When a smaller level of balancing is required, such as balancing multiple parallel-connected battery stacks inside a battery module, it is only necessary to configure the above-mentioned balancing system inside the battery stack module and adjust the wiring to the two sides of the battery stack that needs to be balanced; the function implementation process is the same as A above.

[0093] 8) Shutdown discharge function realization:

[0094] Due to the unique stack structure of the flow battery, multiple single cells share a common flow channel and multiple stacks share an electrolyte delivery pipeline. When there is charged electrolyte in the stack, there will be self-discharge current between the stack and the pipeline in the stack system. In order to reduce the damage to the stack structure and the pipeline structure caused by the self-discharge of the electrolyte retained in the stack when the charging and discharging is stopped, the electrolyte in the stack needs to be discharged after the battery system is shut down. However, it is currently difficult to discharge the electrolyte. Even after the discharge, the air gap remaining inside will cause difficulties for the next electrolyte to enter. In view of the above difficulties, the present invention adopts the following scheme to complete the discharge of the amount of electricity in the electrolyte after the battery system PCS is shut down by using a balancing module:

[0095] Take three battery modules connected in series as an example:

[0096] The BMS controls the battery module 1 circulation system to shut down and disconnects the contactors between the modules;

[0097] The circulation systems of battery modules 2 and 3 remain in operation, and the AC side contactor of the multifunctional balancing module is closed; the balancing module 1 corresponding to the battery module 1 draws power from the battery and boosts the voltage to the internal DC750v bus, and the AC / DC module adopts the constant DC side power mode to transmit the electric energy inside the module to the AC bus of the auxiliary system power distribution, and this part of the energy is consumed by the auxiliary system; the above process monitors the direction of the AC side current and reduces the discharge power when reverse power occurs; when module 1 completes the discharge, it rotates to module 2 and module 3 for discharge; the above can also discharge modules 1, 2 and 3 at the same time, and the principle is the same as above.

[0098] It needs to be further explained that during the shutdown and discharge process, the auxiliary system must be guaranteed to have a certain load, and non-dispatched discharge of the energy storage power station must not occur (that is, the balancing module discharges the electricity in the battery stack, but the auxiliary system cannot consume it and returns it to the grid); user-side projects are not subject to this restriction.

[0099] Example:

[0100] 1. Between multiple series battery modules:

[0101] like Figure 2 As shown, the charging process is balanced: here, three modules are connected in series as an example. The real-time voltages of module 1, module 2 and module 3 in the charging process are u1, u2 and u3 respectively; the ideal charging cut-off condition is u1+u2+u3≤1500V, but due to the consistency differences between single-chip batteries and battery stacks, the differences in the electrolyte distribution inside the battery stack, the differences in the temperature field inside the battery stack, etc., the open circuit voltage of each battery stack will be different under the same charging current. The overall manifestation is that the voltage of the battery stack with a large internal resistance is higher, and the internal resistance of the battery stack with a small internal resistance is small. At this time, in order to prevent the battery system from overcharging, additional restrictions will be added: the voltage of each of the n battery stacks inside u1 must be ≤ the rated voltage of the battery stack; at this time, when the voltage of one battery stack reaches the charging voltage cut-off condition, the charging of the entire system must be stopped. Similarly, when the voltage of a single module reaches the cut-off condition, the charging of the entire branch must also be stopped; in this case, the battery stack and module with a lower internal resistance are also If the battery is not fully charged, charging may be terminated in advance, or the actual charging capacity and charging time of the system may be less than the nominal design capacity. At this time, the balancing module is put into operation, and the BMS controls the AC side contactor of the multi-function balancer to close, and an internal DC750V bus is established. The DC balancing module corresponding to module 1 adopts a small current discharge mode to discharge to the DC750V bus. Other balancing modules can charge the modules with lower voltages in the process. For example, when the voltage of module 2 is low, power can be drawn from the DC750V bus, and then charged to module 2 through balancing module 2. At the same time, when the series branch or the battery module connected to the balancer does not have a low voltage required by the voltage load, the multi-function balancer can be output to the AC auxiliary system power supply bus in a discharge mode. This part of the power is consumed by the auxiliary system (circulating pump, heat exchanger, etc.). At the same time, the direction of the total incoming current is detected. When it is detected that the current direction is pointing to the grid, the balancer reduces the discharge power or shuts down.

[0102] Balance during discharge process: The discharge process requires balanced battery stacks and battery stack modules, which is the opposite of the above-mentioned charging process. It is necessary to charge the battery stacks and battery modules with lower voltages to slow down the voltage drop trend. In this process, the balancing module adopts the charging mode to draw power from other modules with higher voltages or the AC side of the balancing module to charge the modules with lower voltages or the battery stack group.

[0103] 2. Between multiple series-parallel battery stacks:

[0104] like Figure 3As shown, when a single battery module is internally grouped, take 3 battery modules connected in series and the battery module is further divided into 2 groups as an example: at this time, a DC positive and negative busbar and a controllable AC contactor can be set at the output port of each DC balancing module, and the original 1 output is adjusted to 2 selectable outputs, and the two outputs are respectively connected to the two ends of the two groups of batteries in the grouped battery module; balancing can be done at the group level, pre-charging can be completed according to the overall module, and shutdown discharge can be performed according to the group or a single module. The execution process is more complicated than that of a single module, mainly because there is more control over the DC output circuit selection of the DC balancing module.

[0105] 3. Stack-level balancing

[0106] like Figure 4 As shown, when module-level and module group-level balancing cannot meet the balancing requirements, stack-level balancing can be added, and the equalizer can be configured inside a single module; the stack inside the module can be single-series connected, series-parallel connected, etc. This section explains the series connection of three parallel multi-stacks inside a single module.

[0107] The positive and negative ends of each parallel battery pack are connected to a balancer. The BMS turns on the balancer according to the voltage of the battery stack to balance the battery stack inside the battery module. The principle is the same as before.

[0108] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0109] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A balancing, charging and discharging device for a liquid flow battery, comprising a balancing cabinet (13), characterized in that: The balancing cabinet (13) is provided with the following components: A DC contactor (1), the battery module to be balanced is connected to the lower end of the DC contactor (1) through a cable, and the battery group is connected to the balancer; A DC fuse (2) is connected in series with a copper bar at the upper end of the DC contactor (1). The DC fuse (2) is connected in series between the copper bars of the DC total positive and negative electrodes of the equalizer, and mainly plays a role in DC short-circuit protection; The DC Hall sensor (3) is mounted on the busbar in a perforated manner, and is mainly used to measure the equalizing current and busbar current, and to provide a reference current for the equalizer output; A DC / DC direct current bidirectional converter (4), wherein two DC / DC direct current bidirectional converters (4) are configured as required, and the DC / DC direct current bidirectional converter (4) plays a role in DC voltage step-up and voltage step-down, raising the low voltage of the battery to the bus voltage, or lowering the bus voltage to the voltage required by the battery; the low voltage input end of the DC / DC direct current bidirectional converter (4) is connected to the DC fuse (2) via a copper busbar; The AC / DC bidirectional converter (7), the DC end and the AC end are all connected by copper bars, which plays a role of rectification and inversion; the electric energy on the AC side is rectified into DC and then transmitted to the battery pack that needs to be supplemented with electric energy; A direct current copper busbar (5), wherein the direct current copper busbar (5) serves to connect a DC / DC direct current bidirectional converter (4) and an AC / DC bidirectional converter (7), and a plurality of DC / DC direct current bidirectional converters (4) are connected in parallel to the direct current copper busbar (5); An isolation transformer (8) is connected in series to the output end of the AC / DC bidirectional converter (7) to isolate the power grid from the equalizer; An AC current transformer (9) is installed through a hole on the AC copper busbar to measure the charging or discharging current at the AC end of the equalizer; An AC contactor (10), which is used to connect or disconnect the equalizer from the power grid by controlling the AC contactor (10); An AC circuit breaker (11), the AC circuit breaker (11) being the AC output end of the equalizer, the power grid is connected to the AC circuit breaker (11) via a cable, and plays a role in AC short-circuit protection; The equalizer touch operation screen (12) is installed on the cabinet door of the equalizer cabinet (13), and the operation and alarm status of the equalizer can be viewed through the screen. It has the functions of inputting and modifying operation parameters and starting and stopping the equalizer; The DC contactor (1), DC fuse (2), DC Hall sensor (3), DC / DC bidirectional converter (4), DC copper busbar (5), AC / DC bidirectional converter (7), isolation transformer (8), AC current transformer (9), AC contactor (10), AC circuit breaker (11) and equalizer touch operation screen (12) are all integrated in the equalization cabinet (13).

2. A flow battery equalization, charging and discharging device according to claim 1, characterized in that: The balancing cabinet (13) has an IP54 protection grade and is capable of outdoor installation.

3. A system control method for equalization, charging and discharging devices for flow batteries, using the device according to any one of claims 1-2, characterized in that: The system control method comprises the following steps: Step 1: Input the SOC value of the battery module; the equalizer receives data from the battery management system BMS, which mainly includes the actual SOC value of each battery module and the charging, discharging, shutdown and fault status of the battery system; the equalizer control system sorts the input SOC values ​​according to size, such as SOC1<SOC2<SOC3; Step 2: Determine the module that needs to be balanced; when the battery system is in a fault state or shutdown state, the balancing module automatically enters the shutdown state; when the battery system is in a discharging state, the module represented by SOC1 is the module that needs to be balanced, and the module needs to be charged and supplemented with power through the equalizer; when the battery system is in a charging state, the module represented by SOC3 is the module that needs to be balanced, and the module needs to be discharged through the equalizer; the judgment conditions are: during the discharge process, the SOC value of any battery module is less than the SOC average value * 95%; during the charging process, the SOC value of any battery module is greater than the SOC average value * 105%; when the SOC values ​​of multiple modules meet the balancing requirements, they are sorted and enter the waiting balancing queue; Step 3: The DC contactor (1) corresponding to the module to be balanced is closed, and the positive and negative electrodes of the corresponding battery module are connected to the DC output terminal of the balancer; Step 4: The AC contactor (10) is closed to introduce the mains power into the equalizer; Step 5: Set the balancing current on the balancer control screen and click the start button. The balancer will start running according to the established charging and discharging logic. During the balancing process, the balancer transfers the electric energy of the battery modules under different DC / DC bidirectional converters (4) to the required battery modules, and outputs the electric energy to the grid when there is no charging load on the DC bus. Step 5: During the balancing process, the module SOC value is collected in real time. When the battery system is in the discharge process and the SOC1 value of the battery module in the balancing process = (SOC2+SOC3) / 2*1.1, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues; Step 6: During the balancing process, the module SOC value is collected in real time. When the battery system is in the charging process and the SOC3 value of the battery module being balanced = (SOC1+SOC2) / 2*0.9, the balancer disconnects the battery module, and then puts the DC contactor corresponding to the battery module in the waiting queue into operation, and the balancing continues; Step 7: When there is no module in the waiting queue that needs to be balanced, the equalizer stops running and simultaneously disconnects the AC contactor (10) and the DC contactor (1); Step 8: After the balancing module exits operation, it maintains communication with the battery management system BMS and calculates and compares the SOC value in real time; Step 9: Repeat steps 1 to 8 above.

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