A flat layer structure VRFB self-discharge control method and system under high SOC working condition

Abstract

The application relates to a self-discharge control method and system of a flat-layer structure VRFB under a high SOC condition. The method part mainly comprises the following steps: establishing a stack self-circulation path, setting a self-circulation valve and an evaporator on the stack self-circulation path; monitoring the SOC value of the stack in real time, and judging whether the current SOC value meets a preset high SOC condition; if the current SOC value meets the high SOC condition and the system enters an idle mode, closing the inlet and outlet valves of the positive electrolyte storage tank and the negative electrolyte storage tank, opening the self-circulation valve, and reducing the running frequency of an electrolyte circulating pump to a preset low frequency range; monitoring the electrolyte temperature in real time, and if the temperature reaches a preset temperature threshold, starting the evaporator to dissipate heat and controlling the electrolyte temperature in a preset temperature range. The application can reduce invalid electrolyte circulation, reduce the probability of self-discharge reaction, and synchronously control the stack temperature, and overcomes the defects that the existing flat-layer structure all-vanadium redox flow battery system has serious self-discharge heat release and fast SOC drop when being idle under a high SOC condition.

Description

Technical Field

[0001] This application relates to the field of vanadium redox flow battery energy storage technology, and in particular to a self-discharge control method and system for a flat-layer VRFB under high SOC conditions. Background Technology

[0002] Vanadium redox flow batteries (VRFBs), as an important energy storage technology, have been widely used in large-scale energy storage scenarios due to their cyclical electrolyte, long charge-discharge life, and high safety. Flat-layer VRFB systems, with their electrolyte storage units (tanks) and stack on the same plane without significant height differences, offer advantages such as convenient installation and high space utilization, making them suitable for small and medium-sized energy storage sites and providing new application options and development directions for the energy storage field. With the continuous growth of energy storage demand, the application of VRFB technology in various fields is becoming increasingly widespread, playing a crucial role in stabilizing the power grid and improving energy efficiency.

[0003] However, the inherent characteristics of the flat-layer structure mean that during charging and discharging, the electrolyte mainly remains inside the stack (including the stack inlet and outlet pipelines), with only a small amount circulating between the storage tank and the stack. When the system is in a high state of charge (SOC), such as SOC ≥ 80%, and is not in operation, the high-concentration vanadium ion electrolyte inside the stack is prone to self-discharge: on the one hand, vanadium ions at the positive and negative electrodes of the stack permeate through the diaphragm and undergo redox reactions, generating useless heat energy; on the other hand, the self-discharge reaction continuously consumes active vanadium ions, causing the system SOC to drop rapidly (actual measurements show that the average daily SOC decrease rate of a conventional flat-layer system can reach 4%-6% when idle at high SOC). In addition, if the heat generated by self-discharge cannot be dissipated in time, it will cause the internal temperature of the stack to rise, accelerate diaphragm aging, shorten the stack's service life, and even cause electrolyte stability problems.

[0004] In terms of self-discharge control in vanadium redox flow batteries, existing technologies mainly focus on optimizing electrolyte concentration, improving separator performance, or overall system insulation / heat dissipation design. For example, some solutions attempt to reduce self-discharge by optimizing electrolyte concentration and adjusting the proportions of various components in the electrolyte; others focus on improving separator performance to enhance its ability to block vanadium ions, thereby reducing the probability of vanadium ions penetrating through the separator from both the positive and negative electrodes; still others take a holistic approach, implementing insulation or heat dissipation designs to maintain the temperature stability of the battery system. None of these solutions address the core characteristic of "electrolyte retention within the stack" in a flat-structure battery. For instance, some solutions increase the electrolyte storage capacity by increasing the tank volume, but the space limitations of a flat-structure battery prevent significant capacity expansion; other solutions intermittently activate the circulation pump to promote electrolyte mixing between the tank and the stack, but frequent start-stop cycles at high SOC exacerbate vanadium ion penetration, thus increasing the risk of self-discharge. In short, existing technologies cannot effectively suppress the self-discharge defect problem of flat-structure vanadium redox flow battery systems at high SOC.

[0005] Therefore, overcoming the problem of the inability of existing technologies to effectively suppress the self-discharge defect of flat-structure vanadium redox flow battery systems at high SOC is a problem to be solved in this technical field. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, and in order to solve the problem that the existing technology cannot effectively suppress the self-discharge defect of the flat-structure vanadium redox flow battery system under high SOC, this application provides a self-discharge control method and system for flat-structure VRFB under high SOC conditions. It can reduce the ineffective circulation of electrolyte, reduce the probability of self-discharge reaction, and synchronously control the stack temperature, thus overcoming the defects of the existing flat-structure vanadium redox flow battery system with severe self-discharge heat release and rapid SOC drop when idle at high SOC.

[0007] The embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, this application provides a self-discharge control method for a single-story VRFB structure under high SOC conditions, including:

[0009] Establish a self-circulation path for the fuel cell stack, and install self-circulation valves and evaporators on the self-circulation path;

[0010] Real-time monitoring of the SOC value of the fuel cell stack to determine whether the current SOC value meets the preset high SOC condition;

[0011] If the current SOC value meets the high SOC condition and the system enters idle mode, close the inlet and outlet valves of the positive electrolyte tank and the negative electrolyte tank, open the self-circulation valve, and reduce the operating frequency of the electrolyte circulation pump to the preset low frequency range.

[0012] The electrolyte temperature is monitored in real time. If the temperature reaches the preset temperature threshold, the evaporator is started to dissipate heat and control the electrolyte temperature within the preset temperature range.

[0013] By adopting the above technical solutions, establishing a self-circulation path for the battery stack, and setting up self-circulation valves and evaporators, specific circulation control can be achieved under high SOC conditions. Real-time monitoring of the battery stack SOC value and determination of whether high SOC conditions are met allows for timely detection of high SOC states. Closing the inlet and outlet valves of the positive and negative electrolyte storage tanks, opening the self-circulation valves, and reducing the operating frequency of the electrolyte circulation pump can avoid ineffective circulation of high SOC electrolyte between the storage tanks and the battery stack, reduce vanadium ion permeation, maintain low-speed electrolyte flow, and prevent local accumulation of high-concentration vanadium ions. Real-time monitoring of electrolyte temperature and activation of the evaporator for heat dissipation when a preset temperature threshold is reached can control the electrolyte temperature within a preset range, preventing the accumulation of self-discharge heat, reducing self-discharge reactions and high-temperature shocks under high SOC, extending the life of the battery stack diaphragm, and improving electrolyte stability. Ultimately, this effectively overcomes the shortcomings of existing flat-layer vanadium redox flow battery systems, such as severe self-discharge heat release and rapid SOC decline during high SOC idle periods.

[0014] In some embodiments, the method further includes: when SOC ≤ 10% is detected or a system start command is received, shutting down the evaporator function, extending the self-circulation time, and then stopping the operation of the electrolyte circulation pump.

[0015] By adopting the above technical solution, a complete exit mechanism is provided when the SOC drops to a safe range or the system needs to be restarted. First, shutting down the evaporator avoids unnecessary energy consumption, and extending the self-circulation time before stopping the pump ensures thorough mixing and cooling of the electrolyte, preventing localized concentration imbalances or residual temperature, and guaranteeing a smooth transition of the system state.

[0016] In some embodiments, upon receiving a discharge command, the self-circulation valve is closed, the frequency of the electrolyte circulation pump is restored to the rated frequency, and the inlet and outlet valves of the positive and negative electrolyte storage tanks are opened, so that the system enters the normal discharge operation mode.

[0017] By adopting the above technical solution, a rapid response mechanism was designed to meet discharge requirements. Through rapid switching of valve states and pump frequency recovery, the system can switch from energy-saving self-circulation mode to normal operation mode in the shortest possible time, ensuring both energy conservation and system response speed.

[0018] In some embodiments, the idle mode is the idle mode after the system has stopped normally after charging.

[0019] By adopting the above technical solution, the applicable scenario is clearly defined as the idle state after charging is completed. This optimized design under specific working conditions is more targeted.

[0020] In some embodiments, the high SOC condition includes: SOC ≥ 80%.

[0021] By adopting the above technical solution, the judgment criteria for high SOC state are quantified, that is, SOC≥80%. This threshold setting is based on experimental data of vanadium ion concentration and self-discharge rate, which not only ensures the effectiveness of control but also avoids energy waste caused by premature start-up.

[0022] In some embodiments, the low frequency range is 20%-40% of the rated frequency.

[0023] By adopting the above technical solution, the frequency of the circulating pump is controlled at 20%-40% of the rated frequency. This optimized range has been verified by experiments to minimize energy consumption while maintaining the necessary flowability, and at the same time avoid the risk of sedimentation caused by excessively low frequency.

[0024] In some embodiments, the preset temperature threshold is ≥35℃, and the preset temperature range is 25℃-30℃.

[0025] By adopting the above technical solution, a reasonable temperature control threshold is set, namely, ≥35℃ for startup, and a reasonable target range is set, namely 25℃-30℃. This can not only suppress the self-discharge heat release effect in time, but also avoid energy waste and equipment damage caused by excessive cooling.

[0026] Secondly, this application provides a self-discharge control system for a flat-structure VRFB under high SOC conditions, applying the self-discharge control method for a flat-structure VRFB under high SOC conditions as described in the first aspect, including a positive electrolyte storage tank, a negative electrolyte storage tank, an electrolyte circulation pump, a fuel cell stack, an evaporator, and a control module; the positive electrolyte storage tank, the negative electrolyte storage tank, the electrolyte circulation pump, and the fuel cell stack form a main circulation path through pipes and valves, and the electrolyte circulation pump, the fuel cell stack, and the evaporator form a self-circulation path for the fuel cell stack through pipes and valves;

[0027] The control module is used to monitor the SOC value of the fuel cell stack in real time and determine whether the current SOC value meets the preset high SOC condition. If the current SOC value meets the high SOC condition and the system enters the idle mode, the inlet and outlet valves of the positive and negative electrolyte storage tanks are closed, the self-circulation valve is opened, and the operating frequency of the electrolyte circulation pump is reduced to a preset low frequency range. The control module is also used to monitor the electrolyte temperature in real time. If the temperature reaches a preset temperature threshold, the evaporator is started to dissipate heat and control the electrolyte temperature within the preset temperature range.

[0028] By adopting the above technical solution, a complete hardware execution system was constructed based on the collaborative design of pipeline valve layout and control modules. In particular, the parallel design of the stack self-circulation path and the main circulation path enables flexible switching of operating modes without increasing complexity. Addressing the unique electrolyte distribution characteristics of flat-structure VRFBs—high retention rate within the stack—the above solution proposes a "shut down main circulation - start self-circulation" control logic. Combined with the collaborative control of multiple parameters such as SOC and temperature, it solves the problem of self-discharge defects in flat-structure vanadium redox flow battery systems at high SOC, which is difficult to effectively suppress in existing technologies. In particular, the design of integrating the evaporator into the self-circulation path, and the linkage control of pump frequency and valves, constitute significant advantages over conventional electrolyte circulation and heat dissipation solutions.

[0029] In summary, this application includes at least the following beneficial technical effects:

[0030] 1. By establishing a self-circulation path for the battery stack and installing self-circulation valves and an evaporator, specific circulation control can be achieved under high SOC conditions. Real-time monitoring of the battery stack SOC value and determination of whether high SOC conditions are met allows for timely detection of high SOC states. Closing the inlet and outlet valves of the positive and negative electrolyte storage tanks, opening the self-circulation valves, and reducing the operating frequency of the electrolyte circulation pump can avoid ineffective circulation of high SOC electrolyte between the storage tank and the battery stack, reduce vanadium ion permeation, maintain low-speed electrolyte flow, and prevent local accumulation of high-concentration vanadium ions. Real-time monitoring of electrolyte temperature and activation of the evaporator for heat dissipation when a preset temperature threshold is reached can control the electrolyte temperature within a preset range, preventing the accumulation of self-discharge heat, reducing self-discharge reactions and high-temperature shocks under high SOC, extending the life of the battery stack diaphragm, and improving electrolyte stability. Ultimately, this effectively overcomes the shortcomings of existing flat-layer vanadium redox flow battery systems, such as severe self-discharge heat release and rapid SOC decline during high SOC idle periods.

[0031] 2. A complete exit mechanism is provided when the SOC drops to a safe range or the system needs to be restarted. First, shutting down the evaporator avoids unnecessary energy consumption, and extending the self-circulation time before stopping the pump ensures thorough mixing and cooling of the electrolyte, preventing localized concentration imbalances or residual temperature, and guaranteeing a smooth transition of the system state.

[0032] 3. Based on the collaborative design of pipeline valve layout and control modules, a complete hardware execution system was constructed. In particular, the parallel design of the stack self-circulation path and the main circulation path enabled flexible switching of operating modes without increasing complexity. Addressing the unique electrolyte distribution characteristics of flat-structure VRFBs—high retention rate within the stack—a control logic of "closing the main circulation and starting the self-circulation" was proposed. Combined with the collaborative control of multiple parameters such as SOC and temperature, this solved the problem of self-discharge defects in flat-structure vanadium redox flow battery systems under high SOC, which is currently unsustainable in existing technologies. In particular, the design of integrating the evaporator into the self-circulation path, and the linkage control of pump frequency and valves, constitute significant advantages over conventional electrolyte circulation and heat dissipation solutions. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating a self-discharge control method for a flat-structure VRFB under high SOC conditions, provided in this application embodiment;

[0035] Figure 2 An architecture diagram of a self-discharge control system for a single-story VRFB under high SOC conditions, provided for an embodiment of this application;

[0036] Figure 3 The flowchart illustrates the operation of the control module provided in this embodiment. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other. The application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0038] like Figure 1 As shown in the figure, this application provides a self-discharge control method for a flat-structure VRFB under high SOC conditions, and the specific steps are as follows.

[0039] Step 101: Establish a self-circulation path for the fuel cell stack and install self-circulation valves and evaporators along this path. By establishing a self-circulation path and installing self-circulation valves and evaporators, specific circulation control can be achieved under high SOC conditions.

[0040] Step 102: Monitor the SOC value of the fuel cell stack in real time and determine whether the current SOC value meets the preset high SOC condition. By monitoring the SOC value of the fuel cell stack in real time and determining whether the high SOC condition is met, the system can be promptly detected to be in a high SOC state. In some embodiments, the high SOC condition includes: SOC ≥ 80%, preferably 80%-95%. This setting quantifies the judgment standard for the high SOC state, and the threshold setting is based on experimental data of vanadium ion concentration and self-discharge rate, which ensures the effectiveness of control and avoids energy waste caused by premature start-up.

[0041] Step 103: If the current SOC value meets the high SOC condition and the system enters idle mode, close the inlet and outlet valves of the positive and negative electrolyte storage tanks, open the self-circulation valve, and reduce the operating frequency of the electrolyte circulation pump to a preset low frequency range. The idle mode refers to the idle mode after the system has completed normal charging and shut down. By clearly defining the applicable scenario as the idle state after charging, this optimization design under specific operating conditions is more targeted. Furthermore, in some embodiments, the low frequency range is 20%-40% of the rated frequency. By controlling the circulation pump frequency to 20%-40% of the rated frequency, this optimized range has been experimentally verified to minimize energy consumption while maintaining necessary flowability, and to avoid the risk of precipitation caused by excessively low frequencies. By closing the inlet and outlet valves of the positive and negative electrolyte storage tanks, opening the self-circulation valve, and reducing the operating frequency of the electrolyte circulation pump, ineffective circulation of high SOC electrolyte between the storage tank and the stack can be avoided, reducing vanadium ion permeation, maintaining low-speed electrolyte flow, and preventing localized accumulation of high-concentration vanadium ions.

[0042] Step 104: Monitor the electrolyte temperature in real time. If the temperature reaches the preset temperature threshold, start the evaporator to dissipate heat and control the electrolyte temperature within the preset temperature range. Further, in some embodiments, the preset temperature threshold is ≥35℃, and the preset temperature range is 25℃-30℃. By setting a reasonable temperature control threshold, i.e., starting at ≥35℃, and setting a reasonable target range, i.e., 25℃-30℃, the self-discharge heat effect can be suppressed in a timely manner, while avoiding energy waste and equipment damage caused by excessive cooling. This step, by monitoring the electrolyte temperature in real time and starting the evaporator to dissipate heat when the preset temperature threshold is reached, can control the electrolyte temperature within the preset range, avoid the accumulation of self-discharge heat, reduce self-discharge reactions and high-temperature shocks under high SOC, extend the life of the fuel cell stack diaphragm, and improve electrolyte stability.

[0043] Furthermore, in some implementations, the method further includes: when SOC is detected to be ≤10% or a system startup command is received, shutting down the evaporator, extending the self-circulation time, and then stopping the electrolyte circulation pump. This approach provides a complete exit mechanism when SOC drops to a safe range or the system needs to be restarted. Shutting down the evaporator first avoids unnecessary energy consumption, and extending the self-circulation time before stopping the pump ensures thorough mixing and cooling of the electrolyte, preventing localized concentration imbalances or residual temperature, and guaranteeing a smooth transition of the system state.

[0044] Furthermore, in some implementations, upon receiving a discharge command, the self-circulation valve is closed, the frequency of the electrolyte circulation pump is restored to the rated frequency, and the inlet and outlet valves of the positive and negative electrolyte storage tanks are opened, allowing the system to enter normal discharge operation mode. This scheme designs a rapid response mechanism for discharge demands. Through rapid valve state switching and pump frequency restoration, the system can transition from energy-saving self-circulation mode to normal operation mode in the shortest possible time, ensuring both energy conservation and system response speed.

[0045] The above overall solution can reduce ineffective electrolyte cycling, lower the probability of self-discharge reaction, and simultaneously control the stack temperature. Ultimately, it effectively overcomes the shortcomings of existing flat-structure vanadium redox flow battery systems, such as severe self-discharge heat generation and rapid SOC drop during high SOC idle periods. Example 2

[0046] Based on the self-discharge control method for a flat-structure VRFB under high SOC conditions provided in Embodiment 1, this Embodiment 2 provides a self-discharge control system for a flat-structure VRFB under high SOC conditions, applying the self-discharge control method for a flat-structure VRFB under high SOC conditions as described in Embodiment 1.

[0047] refer to Figure 2As shown, the self-discharge control system of the flat-structure VRFB in this application under high SOC conditions includes a positive electrolyte storage tank, a negative electrolyte storage tank, an electrolyte circulation pump, a fuel cell stack, an evaporator, and a control module. The positive electrolyte storage tank, the negative electrolyte storage tank, the electrolyte circulation pump, and the fuel cell stack form a main circulation path through pipes and valves, and the electrolyte circulation pump, the fuel cell stack, and the evaporator form a self-circulation path for the fuel cell stack through pipes and valves. The control module is used to monitor the SOC value of the fuel cell stack in real time and determine whether the current SOC value meets the preset high SOC condition. If the current SOC value meets the high SOC condition and the system enters the idle mode, the inlet and outlet valves of the positive and negative electrolyte storage tanks are closed, the self-circulation valve is opened, and the operating frequency of the electrolyte circulation pump is reduced to a preset low frequency range. The control module is also used to monitor the electrolyte temperature in real time. If the temperature reaches a preset temperature threshold, the evaporator is started to dissipate heat and control the electrolyte temperature within the preset temperature range.

[0048] It should be noted that vanadium redox flow batteries are an energy storage technology that achieves the reciprocating conversion of chemical energy into electrical energy through changes in the valence state of vanadium ions, thereby realizing the storage and release of electrical energy. A conventional vanadium redox flow battery system generally includes an electrolyte tank, an electrolyte circulation pump, a stack, and a control system. The electrolyte tank includes a positive electrolyte tank and a negative electrolyte tank; the electrolyte circulation pump includes a positive pump and a negative pump; the stack also includes positive and negative electrodes; and the control system typically employs a battery management system (BMS) and a pump control system. The positive electrode of the stack, the positive pump, and the positive electrolyte tank are connected through pipes and valves to form the main positive circulation path; the negative electrode of the stack, the negative pump, and the negative electrolyte tank are connected through pipes and valves to form the main negative circulation path. The battery management system is connected to both the positive and negative main circulation paths.

[0049] Specifically, the electrolyte storage tank is the system's "energy warehouse," directly determining the system's energy storage capacity (kWh). The positive electrode electrolyte storage tank stores the positive electrode active material and mainly contains a sulfuric acid solution with VO²⁺ (which becomes VO2⁺ after charging). The negative electrode electrolyte storage tank stores the negative electrode active material and mainly contains a sulfuric acid solution with V³⁺ (which becomes V²⁺ after charging).

[0050] The electrolyte circulation pump is the "heart" of the system, responsible for circulating the electrolyte. Its functions include: pumping the electrolyte from the storage tank to the fuel cell stack and returning the reacted electrolyte to the storage tank; the continuous circulation ensures a constant concentration of active material delivered to the fuel cell stack, thus providing stable power output; the power consumption of the electrolyte circulation pump is one of the main energy losses during the entire system operation. Both the positive and negative electrode pumps are electrolyte circulation pumps and can be collectively referred to as circulation pumps.

[0051] The fuel cell stack is the "powerhouse" of the system, the site of the interconversion of electrical and chemical energy, and directly determines the system's output power (kW). A fuel cell stack consists of dozens or even hundreds of stacked individual cells. Each individual cell contains electrodes, an ion exchange membrane, and a bipolar plate. The electrodes are typically porous carbon felt or graphite felt; they do not directly participate in the chemical reaction but provide a reaction site for the redox reaction of vanadium ions, requiring high conductivity, high specific surface area, and good chemical stability. The ion exchange membrane, located between the positive and negative half-cells, is the core component of the fuel cell stack. Its function is to allow H⁺ (hydrogen ions) to pass freely, maintaining the charge balance of the entire circuit, while simultaneously preventing the mixing of the positive and negative electrolytes; this prevents cross-contamination of active materials and ensures the system's cycle life. The bipolar plate, located between two individual cells, has one side as the positive electrode of the previous cell and the other side as the negative electrode of the next cell. The bipolar plate is responsible for collecting current and connecting the individual cells in series, while also uniformly distributing the electrolyte across the electrode surfaces.

[0052] The control system is the "brain" of the system, responsible for monitoring, managing, and optimizing the operation of the entire system. The Battery Management System (BMS) monitors parameters such as voltage, current, and temperature of the battery stack to prevent overcharging and over-discharging, ensuring the stack operates in optimal condition. The pump control system intelligently adjusts the pump speed according to load (power) requirements to match the electrolyte flow rate; it increases the flow rate under high power and decreases the flow rate under low power or standby conditions to save pump energy.

[0053] Based on the above configuration, the self-discharge control system of the flat-structure VRFB in this application under high SOC conditions adds a stack self-circulation path to the original system architecture. This self-circulation path incorporates branches and valves on the original positive and negative main circulation paths, directly bypassing the positive and negative electrolyte storage tanks. This allows the positive electrode and positive pump to directly form a positive self-circulation path through the branches and valves, and the negative electrode and negative pump to directly form a negative self-circulation path through the branches and valves. An evaporator is also installed on the positive and / or negative self-circulation paths. For details, refer to... Figure 2 As shown, the original negative electrode electrolyte storage tank was equipped with valves 1 and 4 on both sides, valve 2 was installed between the negative electrode pump and the negative electrode of the fuel cell stack, valves 5 and 7 were installed on both sides of the positive electrode electrolyte storage tank, and valve 6 was installed between the positive electrode pump and the positive electrode of the fuel cell stack. In this application, one end of the negative electrode side branch is located between valve 1 and the negative electrode pump, and the other end is located between valve 4 and the negative electrode of the fuel cell stack. Valve 3 is installed on this negative electrode side branch, thus forming a self-circulating path for the negative electrode of the fuel cell stack, and an evaporator is installed on this path. One end of the positive electrode side branch is located between valve 7 and the positive electrode pump, and the other end is located between valve 5 and the positive electrode of the fuel cell stack. Valve 8 is installed on this positive electrode side branch, thus forming a self-circulating path for the positive electrode of the fuel cell stack.

[0054] The flat-layer VRFB of this application adds a control module to the self-discharge control system under high SOC conditions. The control module can be integrated into the original battery management system or used as a separate control module, depending on the requirements.

[0055] refer to Figure 3 As shown, during normal system operation, the positive and negative pumps operate at the set frequency. At this time, electric valves 1, 2, 4, 5, 6, and 7 are open, while valves 3 and 8 are closed. After normal charging, the system continuously monitors the vanadium ion concentration and battery voltage until charging is complete and the system shuts down. Afterward, the control module continuously performs real-time SOC monitoring: the current SOC value of the fuel cell stack can be obtained in real time through the system's original SOC monitoring module; a high SOC threshold (preferably 80%-95%), such as 95%, is preset. If the detected current SOC value is greater than 95%, after a period of pause, a switching of the circulation path is required, i.e., closing valves 1, 4, 5, and 7, and opening valves 3 and 8 to cut off the connection between the electrolyte and the storage tank; simultaneously, the circulation pipeline between the fuel cell stack and the evaporator remains unobstructed. Next, start the circulation pump and adjust the frequency: reduce the operating frequency of the electrolyte circulation pump to 20%-40% of the rated frequency (maintaining only low-speed electrolyte flow to avoid local accumulation of high-concentration vanadium ions); further, implement temperature control: monitor the circulating electrolyte temperature in real time through the evaporator, and when the temperature is ≥35℃, activate the evaporator's heat dissipation function to control the electrolyte temperature within the range of 25℃-30℃; when the system SOC is detected to be ≤10% (or a system start command is received), shut down the evaporator function, extend the circulation time, and then stop the circulation pump. If a discharge command is received at this time, exit the self-circulation mode, restore the circulation pump frequency to the rated frequency, open the inlet and outlet valves between the fuel cell stack and the storage tank, and allow the system to enter the normal discharge operation mode.

[0056] Based on the above settings, under high SOC conditions, closing the tank valve cuts off the connection between the electrolyte and the tank, preventing ineffective circulation of the high SOC electrolyte between the tank and the stack, and reducing vanadium ion permeation. At the same time, it controls the risk of heat release, and the low-frequency circulating pump can maintain the low-speed flow of the electrolyte. Combined with the real-time heat dissipation of the evaporator, it avoids the accumulation of self-discharge heat, reduces self-discharge reaction and high-temperature shock under high SOC, and can extend the life of the stack diaphragm by 15%-20% and improve the stability of the electrolyte by more than 10%.

[0057] By adopting the above technical solution, a complete hardware execution system was constructed based on the collaborative design of pipeline valve layout and control modules. In particular, the parallel design of the stack self-circulation path and the main circulation path enables flexible switching of operating modes without increasing complexity. Addressing the unique electrolyte distribution characteristics of flat-structure VRFBs—high retention rate within the stack—the above solution proposes a "shut down main circulation - start self-circulation" control logic. Combined with the collaborative control of multiple parameters such as SOC and temperature, it solves the problem of self-discharge defects in flat-structure vanadium redox flow battery systems at high SOC, which is difficult to effectively suppress in existing technologies. In particular, the design of integrating the evaporator into the self-circulation path, and the linkage control of pump frequency and valves, constitute significant advantages over conventional electrolyte circulation and heat dissipation solutions.

[0058] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A self-discharge control method for a flat-layer structure VRFB under high SOC conditions, applied to a self-discharge control system for a flat-layer structure VRFB under high SOC conditions, the self-discharge control system for a flat-layer structure VRFB under high SOC conditions comprising a positive electrolyte storage tank, a negative electrolyte storage tank, an electrolyte circulating pump, an electrolyte stack, an evaporator, and a control module; the positive electrolyte storage tank, the negative electrolyte storage tank, the electrolyte circulating pump, and the electrolyte stack form a main circulating path through pipes and valves, and the electrolyte circulating pump, the electrolyte stack, and the evaporator form an electrolyte stack self-circulating path through pipes and valves. The control module is used for monitoring the SOC value and the electrolyte temperature of the stack in real time, characterized in that, It comprises: An auto-circulation path of the stack is established, and an auto-circulation valve and an evaporator are arranged on the auto-circulation path of the stack; The SOC value of the stack is monitored in real time, and it is judged whether the current SOC value meets a preset high SOC condition, the high SOC condition comprising: SOC≥80%; If the current SOC value meets the high SOC condition and the system enters an idle mode, the inlet and outlet valves of the positive electrolyte tank and the negative electrolyte tank are closed, the auto-circulation valve is opened, and the operating frequency of the electrolyte circulating pump is reduced to a preset low frequency range, the low frequency range being 20%-40% of the rated frequency; The electrolyte temperature is monitored in real time, and if the temperature reaches a preset temperature threshold, the evaporator is started to dissipate heat, and the electrolyte temperature is controlled within a preset temperature range, the preset temperature threshold being≥35℃, and the preset temperature range being 25℃-30℃.

2. The self-discharge control method of the flatbed structure VRFB under high SOC working condition according to claim 1, characterized in that, It further comprises: When it is detected that SOC≤10% or a system starting instruction is received, the function of the evaporator is closed, the time of auto-circulation is prolonged, and then the operation of the electrolyte circulating pump is stopped.

3. The flat-layer structure VRFB self-discharge control method under high SOC working condition according to claim 2, characterized in that, If a discharge instruction is received, the auto-circulation valve is closed, the frequency of the electrolyte circulating pump is restored to the rated frequency, and the inlet and outlet valves of the positive electrolyte tank and the negative electrolyte tank are opened, so that the system enters a normal discharge operation mode.

4. The flatbed structure VRFB self-discharge control method under high SOC working conditions according to claim 1, characterized in that, The idle mode is an idle mode after the system is normally charged and stopped.

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