A control method for low temperature cold start of a flow battery system

Abstract

The application provides a control method for low-temperature cold start of a flow battery system. The flow battery system comprises an electric pile and positive and negative electrolyte circuits. The positive and negative electrolyte circuits respectively comprise a main circuit and an auxiliary branch. The main circuit comprises an electrolyte storage tank, an electric pile liquid inlet pipeline and an electric pile liquid outlet pipeline. The auxiliary branch is connected to the electric pile liquid inlet pipeline and the electric pile liquid outlet pipeline. The control method comprises the following steps: obtaining the current temperature of the electrolyte storage tank; and dynamically adjusting the distribution ratio between the flow rate of electrolyte backflowing to the electrolyte storage tank through the electric pile liquid outlet pipeline and the flow rate of electrolyte backflowing to the electric pile liquid inlet pipeline through the auxiliary branch according to the current temperature, so as to ensure that the electrolyte temperature entering the electric pile liquid inlet pipeline is always in a stable transition state during the entire heating process, avoid a sharp temperature drop caused by a large amount of low-temperature electrolyte in the storage tank pouring into the liquid inlet pipeline, and thus guarantee the service life of the heating device, the stability of the electric pile inlet temperature and the safety of the electric pile operation.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage system technology, and specifically to a control method for low-temperature cold start of a flow battery system. Background Technology

[0002] Vanadium redox flow batteries, with their advantages of high intrinsic safety, long cycle life, and support for deep charge and discharge, have become one of the mainstream technologies in the field of long-term energy storage for new energy applications. As energy storage power stations in my country are gradually deployed on a large scale in the cold northern regions, low-temperature environmental adaptability has become a key technical bottleneck restricting the reliable operation of the units.

[0003] In winter conditions in northern my country, the temperature of the large amount of electrolyte in the storage tank often drops to 5°C or below after prolonged standing. This low temperature significantly increases electrolyte viscosity, reduces ionic conductivity, and deteriorates electrochemical reaction kinetics, leading to increased stack polarization, a sharp drop in system efficiency, and rendering the unit unable to operate under load directly. Therefore, flow battery energy storage systems must be equipped with cold-start preheating devices to raise the electrolyte temperature to the rated operating range (typically 25-30°C) before grid connection.

[0004] Currently, most energy storage power stations adopt a "two-position on / off valve hard switching + independent small-circuit preheating" scheme. This scheme has two parallel pipelines at the stack outlet: a return branch and an overflow branch. The return branch is equipped with a two-position on / off valve with only two extreme states: fully open and fully closed. The overflow branch is directly connected to the positive and negative electrolyte storage tanks. Its standardized cold start process is divided into two independent stages: (1) Preheating small circulation stage. Start the circulation pump and set the reflux switch valve to the fully open state. Most of the electrolyte forms a closed small circulation loop between the stack and the reflux pipeline. The circulating electrolyte is heated in a concentrated manner by the electric heater connected in series in the loop until the electrolyte temperature in the loop reaches the set threshold.

[0005] (2) Heating switching stage. When the electrolyte temperature in the small circulation loop reaches the set value, the controller sends a command to the reflux switch valve to completely close the reflux switch valve at once. All the high-temperature electrolyte is then diverted to flow directly into the low-temperature electrolyte storage tank through the overflow branch, completing the switching from "small circulation preheating" to "large circulation operation".

[0006] While existing cold start solutions have the advantages of simple piping structure and easy implementation of basic control logic, they have the following technical drawbacks in practical engineering applications: Firstly, the sudden temperature drop causes frequent start-ups and shutdowns of the heater, resulting in high energy consumption and a short equipment lifespan. After a single on / off switch of the two-position switching valve, the high-temperature electrolyte mixes with a large amount of low-temperature raw liquid in the tank, resulting in a limited temperature rise in the entire tank. The electric heater needs to be restarted at full power and repeatedly heated. This not only increases the required installed capacity of the heater and causes significant energy loss, but also accelerates the thermal fatigue aging of the heating elements, shortening their service life. Simultaneously, the existing binary switching mode lacks a gradual heat transfer mechanism, making it difficult to smoothly and evenly raise the electrolyte level in the entire tank to the rated operating temperature, resulting in a significant temperature gradient always existing within the tank.

[0007] Secondly, severe SOC stratification occurs during the small-cycle phase, posing a high risk of vanadium salt precipitation. During the closed-loop preheating stage, the electrolyte continuously flows through the fuel cell stack and participates in electrochemical reactions, leading to a continuous enrichment of vanadium ions at both the positive and negative electrodes. This causes the difference between the circuit SOC and the tank SOC to easily exceed the safety threshold. When high-temperature, high-SOC electrolyte is injected into the tank all at once, the electrolyte concentration distribution within the tank becomes severely uneven, with localized areas exhibiting supersaturation of pentavalent vanadium ions. Under the coupling effect of a sudden temperature drop, vanadium salts are easily crystallized and precipitated. These precipitates not only cause permanent electrolyte capacity loss, but their solid particles can also clog fuel cell stack channels, pipelines, and valves, significantly increasing system maintenance costs and the risk of system downtime.

[0008] Therefore, there is an urgent need for a new control method that can enable flow battery energy storage systems to achieve uniform and safe cold start in low-temperature environments.

[0009] The above background information is provided only to aid in understanding the concept and technical solution of this application. It does not necessarily belong to the prior art of this application, nor does it necessarily provide technical guidance. In the absence of clear evidence that the above information was disclosed before the filing date of this application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0010] The purpose of this invention is to provide a novel control method for low-temperature cold start of a flow battery system, so as to achieve uniform and safe cold start of the flow battery energy storage system in a low-temperature environment.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a control method for low-temperature cold start of a flow battery system. The flow battery system includes a battery stack, a positive electrolyte circuit, and a negative electrolyte circuit. The positive electrolyte circuit is connected to the positive electrode side of the battery stack, and the negative electrolyte circuit is connected to the negative electrode side of the battery stack. The positive electrode electrolyte circuit and the negative electrode electrolyte circuit each include a main circuit and an auxiliary branch; The main circuit includes an electrolyte storage tank, a fuel cell stack inlet pipe, and a fuel cell stack outlet pipe. The electrolyte storage tank, the fuel cell stack inlet pipe, the fuel cell stack, and the fuel cell stack outlet pipe are sequentially connected to form a circulation loop. The fuel cell stack inlet pipe is sequentially equipped with a fuel cell stack inlet valve, a main circulation pump, and a heating device along the electrolyte flow direction. A first flow meter is also provided on the fuel cell stack inlet pipe downstream of the main circulation pump, and a first valve is provided on the fuel cell stack outlet pipe. One end of the auxiliary branch is connected to the fuel cell stack inlet pipe at the position upstream of the main circulation pump, and the other end of the auxiliary branch is connected to the fuel cell stack outlet pipe at the position upstream of the first valve. The auxiliary branch is equipped with a second valve and a second flow meter. The first valve and / or the second valve are adjustable regulating valves; The control method includes: Obtain the current temperature of the electrolyte storage tank; Open the battery stack inlet valve, start the main circulation pump, and adjust the heating power of the heating device to maintain the temperature of the electrolyte entering the battery stack through the battery stack inlet pipeline within the set temperature range; Based on the current temperature, adjust the opening of the first valve and / or the second valve to control the distribution ratio between the flow rate returning to the electrolyte storage tank via the fuel cell outlet pipeline and the flow rate returning to the fuel cell inlet pipeline via the auxiliary branch. As the current temperature increases, the flow rate returning to the electrolyte storage tank via the fuel cell stack outlet pipeline tends to increase, while the flow rate returning to the fuel cell stack inlet pipeline via the auxiliary branch pipeline tends to decrease.

[0012] In some implementations, when the current temperature is greater than a set temperature threshold, all the electrolyte flowing out of the fuel cell stack flows back to the electrolyte storage tank through the fuel cell stack outlet pipeline, and the auxiliary branch is in a shut-off state.

[0013] In some specific embodiments, a first temperature threshold, a second temperature threshold, and a third temperature threshold are set, wherein the first temperature threshold < the second temperature threshold < the third temperature threshold; Obtain the first flow value detected by the first flow meter and the second flow value detected by the second flow meter, and calculate the ratio of the second flow value to the first flow value; When the current temperature is less than or equal to the first temperature threshold, adjust the opening of the first valve and / or the second valve so that the ratio is equal to the first set value; When the current temperature is greater than the first temperature threshold and less than or equal to the second temperature threshold, increase the opening of the first valve and / or decrease the opening of the second valve so that the ratio is equal to the second set value; When the current temperature is greater than the second temperature threshold and less than or equal to the third temperature threshold, increase the opening of the first valve and / or decrease the opening of the second valve so that the ratio is equal to the third set value; When the current temperature is greater than the third temperature threshold, the first valve is fully opened and the second valve is closed. Wherein, the first setting value > the second setting value > the third setting value.

[0014] In some specific implementations, the first set value ranges from 0.75 to 0.85, the second set value ranges from 0.60 to 0.70, and the third set value ranges from 0.45 to 0.55.

[0015] In some specific implementations, the first temperature threshold is less than or equal to 5°C, the second temperature threshold is greater than 5°C and less than or equal to 12°C, the third temperature threshold is greater than 12°C and less than or equal to 19°C, and the set temperature threshold is equal to the third temperature threshold.

[0016] In some embodiments, the control method further includes controlling the main circulation pump to operate at a first flow rate for a first preset time, and then increasing the flow rate of the main circulation pump to a second flow rate; Wherein, the second flow rate is greater than the first flow rate.

[0017] In some embodiments, the control method further includes: setting a fourth temperature threshold, the fourth temperature threshold being greater than the third temperature threshold; When the current temperature is greater than or equal to the fourth temperature threshold, the heating device is turned off.

[0018] In some embodiments, the flow battery system further includes an auxiliary circulation loop, which includes a bypass pipe disposed outside the electrolyte tank and connected between the auxiliary outlet and the auxiliary return port, a circulation distribution pipe assembly disposed inside the electrolyte tank, and an auxiliary circulation pump disposed on the bypass pipe. The circulation distribution pipe assembly includes a distribution pipe disposed at the bottom of the electrolyte tank and a distribution connecting pipe connected between the auxiliary return port and the distribution pipe. The distribution pipe has multiple distribution holes configured to allow the electrolyte in the distribution pipe to flow out at an upward angle. The auxiliary circulation pump drives the electrolyte in the electrolyte tank to flow out through the auxiliary outlet, flow through the bypass pipe, enter the circulation distribution pipe assembly, be ejected from the distribution holes, and flow back into the electrolyte tank. The control method further includes: Obtain the first SOC value of the electrolyte in the electrolyte storage tank and the second SOC value of the electrolyte in the electrolyte outlet pipeline of the stack, and calculate the absolute value of the difference between the first SOC value and the second SOC value, denoted as ΔSOC; When the ΔSOC is greater than or equal to the first set threshold, the auxiliary circulation pump is started; When the ΔSOC is less than the first set threshold, the auxiliary circulation pump is turned off.

[0019] Furthermore, the distribution pipe is arranged circumferentially around the electrolyte storage tank and is coaxial with the electrolyte storage tank.

[0020] Furthermore, the distribution tube has a non-closed, circumferential tubular structure.

[0021] Furthermore, the plurality of liquid distribution holes are arranged at equal intervals along the axial direction of the distribution pipe.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: This invention dynamically adjusts the flow rate between the electrolyte returning to the electrolyte storage tank via the stack outlet pipe and the flow rate returning to the stack inlet pipe via the auxiliary branch, based on the current temperature of the electrolyte storage tank. During the low-temperature stage, most of the heated electrolyte returns to the stack inlet pipe via the auxiliary branch, mixes with the cold electrolyte output from the storage tank, and is reheated; only a small amount of hot electrolyte returns to the storage tank. As the storage tank temperature gradually increases, the proportion of the flow rate returning to the storage tank via the stack outlet pipe gradually increases, while the proportion of the flow rate returning to the stack inlet pipe via the auxiliary branch gradually decreases. This control method ensures a stable temperature rise in the storage tank throughout the heating process, while the electrolyte temperature entering the stack inlet pipe remains in a stable transition state. This avoids a sharp temperature drop caused by a large influx of low-temperature electrolyte from the storage tank into the inlet pipe, thereby ensuring heater lifespan, stability of the stack inlet temperature, and safety of stack operation.

[0023] Furthermore, throughout the entire heating process, a portion of the hot electrolyte is always directly returned to the storage tank via the main circuit, actively participating in the mixing and homogenization of the electrolyte in the tank. Simultaneously, the hot liquid returned from the auxiliary branch mixes with the cold liquid in the storage tank and re-enters the stack, ensuring that the SOC of the electrolyte at the stack inlet and the SOC of the storage tank always gradually approach each other, effectively guaranteeing the stability of the electrolyte capacity. Attached Figure Description

[0024] Figure 1 A simplified structural diagram of a flow battery system provided by the present invention; Figure 2 A simplified structural diagram of the positive electrode side of a flow battery system provided by the present invention; Figure 3 This is a schematic diagram of the structure of an electrolyte storage tank provided by the present invention; Figure 4 A cross-sectional schematic diagram of an electrolyte storage tank provided by the present invention; Among them, 1. fuel cell stack; 2. Electrolyte circuit; 21. Electrolyte storage tank; 211. Outlet; 212. Return port; 213. Auxiliary outlet; 214. Auxiliary return port; 215. First UV-Vis spectrophotometer; 22. Fuel cell stack inlet pipeline; 221. Fuel cell stack inlet valve; 222. First filter; 223. Main circulation pump; 224. First flow meter; 225. Electric heater; 226. Cooler; 23. Fuel cell stack outlet pipeline; 231. First valve; 232. Second UV-Vis spectrophotometer; 24. Auxiliary branch; 241. Second valve; 242. Second flow meter; 3. Bypass pipeline; 31. Auxiliary circulation pump; 32. Second filter; 33. Circulation distribution pipe assembly; 331. Distribution pipe; 332. Distribution connection pipe; 333. First liquid distribution hole.

[0025] 4. Liquid distribution pipe assembly; 41. Central pipe; 42. Liquid distribution branch pipe; 43. Second liquid distribution hole. Detailed Implementation

[0026] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0027] In the description of the embodiments of the present invention, it should be understood that the terms "upper part," "bottom part," etc., indicate the orientation or positional relationship based on the appendix. Figure 1 The orientations or positional relationships shown are merely for the purpose of facilitating the description of embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of the present invention.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0029] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0030] The following disclosure provides many different implementations or examples for carrying out different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0031] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0032] Example 1: This embodiment provides a control method for low-temperature cold start of a flow battery system, specifically a vanadium redox flow battery system.

[0033] like Figure 1 As shown, the vanadium redox flow battery system includes a stack 1 and two electrolyte circuits 2 connected to the positive and negative electrode sides of the stack 1, respectively. The stack 1 can adopt a conventional structural design of existing vanadium redox flow battery stacks in the art. Exemplarily, it includes, but is not limited to, a configuration formed by sequentially stacking and pressing end plates, current collectors, bipolar plates, electrode frames, and ion-conducting membranes. The material selection and dimensional parameters of each component can be adaptively adjusted according to actual power requirements, which will not be elaborated here. The electrolyte circuit 2 connected to the positive electrode side of the stack 1 is the positive electrolyte circuit, and the electrolyte circuit 2 connected to the negative electrode side of the stack 1 is the negative electrolyte circuit. The positive and negative electrolyte circuits have the same or substantially the same structure, both including a main circuit and an auxiliary branch 24. The main circuit and auxiliary branch 24 of the positive electrolyte circuit will be further described below.

[0034] like Figure 2 As shown, the main circuit includes an electrolyte storage tank 21, a fuel cell stack inlet pipe 22, and a fuel cell stack outlet pipe 23. The electrolyte storage tank 21, the fuel cell stack inlet pipe 22, the fuel cell stack 1, and the fuel cell stack outlet pipe 23 are sequentially connected along the electrolyte flow direction to form a circulation loop. Wherein: like Figure 3 and Figure 4 As shown, the electrolyte storage tank 21 is a vertical cylindrical tank, and its internal cavity volume is configured to match the electrolyte demand of the fuel cell stack 1 without specific limitations. The electrolyte storage tank 21 has independently located outlet 211 and return port 212. Specifically, outlet 211 is located at the bottom of the electrolyte storage tank 21 to ensure that the electrolyte can be smoothly extracted even when the liquid level is low. Return port 212 is located at the top of the electrolyte storage tank 21. Both outlet 211 and return port 212 have independent interfaces connecting to external pipelines. Furthermore, the top of the electrolyte storage tank 21 is equipped with a nitrogen sealing interface, which is connected to an external compressed nitrogen source via a gas supply pipeline. A pressure regulating valve is installed at the nitrogen sealing interface to automatically replenish nitrogen when the internal pressure falls below a preset threshold, maintaining a slightly positive pressure nitrogen environment inside the tank. Preferably, the electrolyte storage tank 21 is provided with an injection port at the top, which is connected to an external electrolyte supply source via an injection pipeline. The injection pipeline is equipped with a switch valve to open during the injection operation and close after the injection is completed, so as to maintain the tank's seal.

[0035] The fuel cell stack inlet pipeline 22 is equipped with a fuel cell stack inlet valve 221, a main circulation pump 223, a first flow meter 224, and a heating device. Preferably, these components are arranged sequentially along the electrolyte flow direction. Specifically, the fuel cell stack inlet valve 221 controls the opening and closing of the fuel cell stack inlet pipeline 22. The main circulation pump 223 provides driving force for the circulating flow of the electrolyte and is preferably a variable frequency pump. As a further preferred embodiment, the main circulation pump 223 can first operate at a first flow rate for a first preset time (e.g., 50% of the rated flow rate for 5 minutes) to expel gas from the pipeline; then, the flow rate of the main circulation pump 223 is increased to a second flow rate (e.g., 70%~80% of the rated flow rate), which is the reference flow rate for low-temperature cold start. The first flow meter 224 detects the electrolyte flow rate within the fuel cell stack inlet pipeline 22. In other embodiments, it can also be located between the heating device and the fuel cell stack 1 (i.e., downstream of the heating device). The heating device is used to heat the electrolyte in the fuel cell stack inlet pipe 22. It can be a conventional heating device in the art, including but not limited to a heat exchanger or an electric heater 225. In this embodiment, an electric heater 225 is used.

[0036] Furthermore, the fuel cell stack inlet line 22 may optionally be equipped with a first filter 222 and a cooler 226. The first filter 222 is preferably located between the fuel cell stack inlet valve 221 and the main circulation pump 223. It can be a Y-type filter, a basket filter, or an automatic backwash filter with self-cleaning function. Its filtration accuracy can be selected according to the electrolyte properties and the flow channel size of the fuel cell stack 1. The cooler 226 is preferably located between the heating device and the fuel cell stack 1. Normally, the cooler 226 is in a closed or bypass state and does not participate in the cold start process. If the downstream electrolyte temperature temporarily overshoots due to the thermal inertia of the heating device, the cooler 226 can be activated to rapidly cool the overshoot electrolyte, quickly restoring the fuel cell stack 1 inlet temperature to the set range, thus preventing high-temperature electrolyte from directly entering the fuel cell stack 1 and causing thermal damage to the membrane material and seals. The cooler 226 can be a liquid-cooled heat exchanger or an air-cooled radiator.

[0037] A first valve 231 is installed on the liquid outlet pipeline 23 of the fuel cell stack.

[0038] One end of the auxiliary branch 24 is connected to the electrolyte inlet pipe 22 of the fuel cell stack, located upstream of the main circulation pump 223, and the other end of the auxiliary branch 24 is connected to the electrolyte outlet pipe 23 of the fuel cell stack, located upstream of the first valve 231. A second valve 241 and a second flow meter 242 are sequentially installed on the auxiliary branch 24 along the electrolyte flow direction.

[0039] At least one of the first valve 231 and the second valve 241 is a continuously adjustable regulating valve, used to regulate the electrolyte flow rate returning to the electrolyte storage tank 21 via the fuel cell outlet pipeline 23 and the electrolyte flow rate in the auxiliary branch 24. The regulating valve may be an electrically operated or pneumatically operated regulating valve. In this embodiment, the first valve 231 is a regulating valve, and the second valve 241 is a shut-off valve.

[0040] The flow battery system also includes a controller and multiple temperature sensing elements (not shown). At least one of the multiple temperature sensing elements is located inside the electrolyte storage tank 21, used to detect the electrolyte temperature in the electrolyte storage tank 21 in real time and transmit the temperature signal to the controller. This temperature sensing element is preferably located inside the electrolyte storage tank 21 or at the outlet 211. At least one of the multiple temperature sensing elements is located on the battery stack inlet pipe 22 between the heating device and the battery stack 1 inlet, used to detect the electrolyte temperature in real time before entering the battery stack 1 after being heated by the heating device. The temperature sensing element can be a thermocouple temperature sensor, a resistance temperature sensor, or an integrated digital temperature sensor, which can be flexibly selected by those skilled in the art according to the detection accuracy requirements and cost budget. The controller is signal-connected to the first valve 231, the second valve 241, the first flow meter 224, the second flow meter 242, each temperature sensing element, and the heating device. The controller is used to send control commands to the first valve 231 and / or the second valve 241 and the heating device according to the received temperature signal and the detection value of each flow meter, according to a preset control logic.

[0041] The low-temperature cold start control method provided in the embodiments of the present invention will be described in detail below with reference to the above-described flow battery system structure.

[0042] The control method includes the following steps: Step 1: Obtain the current temperature of electrolyte storage tank 21.

[0043] When the flow battery system is in a low-temperature shutdown state and requires a cold start, the controller obtains the current temperature of the electrolyte in the electrolyte storage tank 21 in real time through a temperature sensing element installed in the electrolyte storage tank 21. When the current temperature is lower than the lower limit of the system's preset rated operating temperature range (e.g., below 5°C), the controller starts the cold start control program.

[0044] It should be noted that the low-temperature cold start described in this invention refers to the startup process where, under conditions where the ambient temperature is low, causing the electrolyte temperature to be below its normal operating temperature range and the unit cannot be directly operated under load, the electrolyte temperature is raised to a temperature range suitable for load operation through preheating. This invention does not limit the initial value of the current temperature; as long as the current temperature is below the lower limit of the system's preset rated operating temperature range, the control method of this invention can be executed.

[0045] Step 2: Open the battery stack inlet valve 221, start the main circulation pump 223, and adjust the heating power of the heating device to maintain the temperature of the electrolyte entering the battery stack 1 through the battery stack inlet pipe 22 within the set temperature range (e.g., 26℃~28℃).

[0046] The controller sends an opening command to the stack inlet valve 221, opening the valve and connecting the electrolyte storage tank 21 to the stack inlet pipeline 22. Simultaneously, the controller starts the main circulation pump 223, which operates at a set flow rate, pumping the electrolyte from the storage tank 21 into the stack inlet pipeline 22 to drive the electrolyte circulation throughout the flow battery system.

[0047] The controller also adjusts the heating power of the heating device based on the electrolyte temperature at the inlet of fuel cell 1, fed back by a temperature sensing element located between the heating device and the inlet of fuel cell 1, to maintain the electrolyte temperature entering fuel cell 1 through fuel cell inlet pipe 22 within a set temperature range. Specifically, when the electrolyte temperature at the inlet of fuel cell 1 is lower than the lower limit of the set temperature range, the controller increases the heating power of the heating device; when the electrolyte temperature at the inlet of fuel cell 1 is higher than the upper limit of the set temperature range, the controller decreases the heating power of the heating device or shuts down the heating device. Through the above closed-loop control, it is ensured that the electrolyte temperature entering fuel cell 1 is always within a suitable range for the safe operation of fuel cell 1, avoiding excessive polarization of fuel cell 1 due to excessively low temperature or damage to the internal materials of fuel cell 1 due to excessively high temperature.

[0048] It should be noted that the execution order of steps one and two is not strictly limited. Preferably, steps one and two can be executed simultaneously, that is, the tank temperature is acquired and the circulating pump and heating device are started at the same time the system initiates the cold start procedure. As another optional implementation, step one can be executed first to acquire the tank temperature, and after confirming that a cold start procedure is required, step two can be executed to start the circulating pump and heating device. Those skilled in the art can flexibly adjust according to the actual control logic.

[0049] Step 3: Adjust the opening of the first valve 231 and / or the second valve 241 according to the current temperature to control the distribution ratio between the flow rate returning to the electrolyte storage tank 21 via the fuel cell outlet pipeline 23 and the flow rate returning to the fuel cell inlet pipeline 22 via the auxiliary branch 24.

[0050] The controller determines the temperature range of the current temperature based on the current temperature obtained in step one, and controls the opening degree of the first regulating valve and / or the second regulating valve according to the temperature range.

[0051] In this invention, the controller acquires the first flow value detected by the first flow meter 224 and the second flow value detected by the second flow meter 242, calculates the ratio (i.e., the ratio of the flow of the auxiliary branch 24 to the total flow of the fuel cell inlet pipeline 22), and adjusts the opening of the first regulating valve and / or the second regulating valve to make the ratio correspond to the temperature range of the current temperature.

[0052] Since the sum of the flow rate in auxiliary branch 24 and the flow rate returning to electrolyte storage tank 21 via fuel cell outlet pipe 23 equals the total flow rate in fuel cell inlet pipe 22, the change in this ratio reflects the change in the proportion of the flow rate in auxiliary branch 24 to the flow rate returning to electrolyte storage tank 21 via fuel cell outlet pipe 23. As the current temperature increases, the ratio gradually decreases, meaning the proportion of the flow rate in auxiliary branch 24 gradually decreases, and / or the proportion of the flow rate returning to electrolyte storage tank 21 via fuel cell outlet pipe 23 gradually increases.

[0053] Specifically, the controller has preset a first temperature threshold, a second temperature threshold, and a third temperature threshold, where the first temperature threshold < the second temperature threshold < the third temperature threshold. Preferably, the first temperature threshold ≤ 5℃, 5℃ < the second temperature threshold ≤ 12℃, and 12℃ < the third temperature threshold ≤ 19℃. The controller compares the current temperature with the above three temperature thresholds and executes the corresponding control strategy based on the comparison result. (1) First temperature control stage: The current temperature is less than or equal to the first temperature threshold.

[0054] When the controller determines that the current temperature is less than or equal to the first temperature threshold, the system enters the first temperature control stage. The controller sends control commands to the first valve 231 and / or the second valve 241 to adjust the opening degree of the corresponding valves so that the ratio equals the first set value. At this time, most of the hot electrolyte needs to be returned to the fuel cell inlet pipe 22 through the auxiliary branch 24, mixed with the cold electrolyte output from the storage tank, and then reheated. Therefore, the first set value is relatively large. Preferably, the range of the first set value is 0.75~0.85.

[0055] As a first option, the controller can send control commands only to the first valve 231, causing the opening of the first valve 231 to change according to a preset trend, while the second valve 241 maintains its current opening. As a second option, the controller can send control commands only to the second valve 241. As a third option, the controller can send control commands to both the first valve 231 and the second valve 241 simultaneously, causing their openings to change in opposite directions in a coordinated manner. Those skilled in the art can flexibly choose any of the above methods according to the actual control accuracy requirements and valve response characteristics. Regardless of the method used, the first valve 231 and the second valve 241 must achieve continuous and smooth changes in their openings during their respective adjustment processes to avoid flow shocks and temperature fluctuations caused by sudden changes in opening. The following explanation uses the first option as an example.

[0056] During this stage, the electrolyte flowing out of fuel cell stack 1 is divided into two paths: one path flows back to the electrolyte storage tank 21 via the first valve 231 on the fuel cell stack outlet pipeline 23 (accounting for a small proportion); the other path flows back to the fuel cell stack inlet pipeline 22 via the second valve 241 on the auxiliary branch pipeline 24, located upstream of the main circulation pump 223 (accounting for a large proportion). This mixture is then pumped by the main circulation pump 223, reheated by the heating device, and finally enters fuel cell stack 1. This method avoids a sharp drop in temperature caused by a large influx of low-temperature electrolyte from the storage tank into the fuel cell stack inlet pipeline 22, thus ensuring the service life of the heating device, the stability of the fuel cell stack 1 inlet temperature, and the safety of fuel cell stack 1 operation.

[0057] During the control process, the controller acquires the detection values ​​of the first flow meter 224 and the second flow meter 242 in real time, calculates the real-time ratio, and compares it with the first set value. If the ratio deviates from the first set value, the opening of the corresponding valve can be adjusted through algorithms such as PID regulation or fuzzy control until the ratio equals the first set value and stabilizes at that value. This closed-loop control process continues until the temperature sensing element detects that the current temperature is greater than the first temperature threshold, at which point the next temperature control stage begins.

[0058] (2) Second temperature control stage: The current temperature is greater than the first temperature threshold and less than or equal to the second temperature threshold.

[0059] When the controller determines that the current temperature is greater than the first temperature threshold and less than or equal to the second temperature threshold, the system enters the second temperature control stage. At this time, the tank temperature has increased to a certain extent, which allows for an increase in the electrolyte flow rate into the fuel cell stack inlet pipe 22.

[0060] The controller sends a control command to the first regulating valve 231, increasing the opening of the first valve 231. Consequently, the flow rate of electrolyte entering the second valve 241 decreases, making the ratio equal to the second set value, wherein the second set value is less than the first set value. Preferably, the second set value is in the range of 0.60 to 0.70.

[0061] In this stage, the proportion of flow returning to the electrolyte storage tank 21 via the fuel cell stack outlet pipe 23 is higher than in the first stage, while the proportion of flow returning to the fuel cell stack inlet pipe 22 via the auxiliary branch pipe 24 is correspondingly lower. Similar to the first stage, the controller acquires the ratio in real time and performs a closed-loop comparison with the second set value, continuously adjusting the opening of the first valve 231 and the second valve 241 until the ratio stabilizes at the second set value. This process continues until the temperature sensing element detects that the current temperature is higher than the second temperature threshold, at which point the next temperature control stage begins.

[0062] (3) Third temperature control stage: The current temperature is greater than the second temperature threshold and less than or equal to the third temperature threshold.

[0063] When the controller determines that the current temperature is greater than the second temperature threshold and less than or equal to the third temperature threshold, the system enters the third temperature control stage. At this time, the tank temperature is close to the lower limit of the optimal operating temperature range, and the proportion of hot electrolyte directly returned to the tank can be further increased.

[0064] The controller sends a control command to the first valve 231 to further increase the opening of the first valve 231, that is, to further reduce the electrolyte flow rate entering the second valve 241, so that the ratio is equal to the third set value, wherein the third set value is less than the second set value. Preferably, the value of the third set value is in the range of 0.45 to 0.55.

[0065] During this stage, the proportion of flow returning to the electrolyte storage tank 21 via the fuel cell stack outlet pipeline 23 further increases, while the proportion of flow returning to the fuel cell stack inlet pipeline 22 via the auxiliary branch 24 further decreases.

[0066] (4) Fourth temperature control stage: The current temperature is greater than the third temperature threshold.

[0067] When the controller determines that the current temperature is greater than the third temperature threshold, the system enters the fourth temperature control stage. At this time, the tank temperature has reached or exceeded the lower limit of the optimal operating temperature range, and the flow battery system is ready for load operation.

[0068] The controller sends control commands to the first valve 231 and the second valve 241, controlling the opening of the first valve 231 to be fully open and simultaneously closing the second valve 241. At this time, all the electrolyte flowing out of the fuel cell stack 1 flows back to the electrolyte storage tank 21 through the fuel cell stack outlet pipeline 23, the auxiliary branch 24 is in a completely shut-off state, and the system enters the normal operating mode.

[0069] At this stage, the flow battery system can be put into operation under load according to the grid dispatch instructions.

[0070] Step 4: Real-time monitoring and cyclical control.

[0071] During the execution of step three, the controller monitors the current temperature in real time through a temperature sensing element installed in the electrolyte storage tank 21, and continuously executes the control logic of each stage in step three according to temperature changes. At the same time, the controller monitors the electrolyte temperature at the inlet of the fuel cell stack 1 in real time through a temperature sensing element installed between the heating device and the inlet of the fuel cell stack 1, and continuously adjusts the heating power of the heating device accordingly to ensure that the temperature of the electrolyte entering the fuel cell stack 1 is always maintained within the set temperature range (e.g., 26℃~28℃).

[0072] The two closed-loop control processes described above are independent and executed in parallel: the temperature distribution proportional control loop adjusts the distribution of the two return liquid flow rates according to the tank temperature, and the heating power control loop adjusts the heating power according to the inlet temperature of fuel cell stack 1. Together, they ensure that the tank temperature rises steadily and the inlet temperature of fuel cell stack 1 remains stable and controllable during the low-temperature cold start process.

[0073] If the temperature of the storage tank drops due to fluctuations in ambient temperature or changes in system load, the controller can automatically readjust the control strategy to the appropriate stage based on the temperature drop, ensuring that the system always maintains a stable working state.

[0074] To further shorten the cold start time of flow battery energy storage systems and solve the grid connection delay problem caused by the sequential execution of preheating and SOC mixing processes in existing technologies, enabling energy storage power stations to respond quickly to grid dispatch and improve power generation and ancillary service revenue, this invention optimizes the flow battery system and further develops a method that coordinates the completion of heating and SOC balancing, allowing direct grid connection once the temperature reaches the standard, thus significantly reducing the cold start time.

[0075] Specifically, the auxiliary circulation loop includes a bypass pipe 3, a circulation distribution pipe assembly 33, and an auxiliary circulation pump 31. The bypass pipe 3 is located outside the electrolyte storage tank 21 and connects between the auxiliary outlet 213 and the auxiliary return port 214 at the bottom of the electrolyte storage tank 21. The auxiliary circulation pump 31 is installed on the bypass pipe 3 to draw electrolyte from the electrolyte storage tank 21 through the auxiliary outlet 213 and deliver it to the auxiliary return port 214 through the bypass pipe 3. This auxiliary circulation loop is completely decoupled from the main loop in terms of physical and hydrodynamics, and is not affected by the flow rate of electrolyte entering the electrolyte storage tank 21 from the main loop. Preferably, the bypass pipe 3 is equipped with a second filter 32, which is similar to the first filter 222, and will not be described in detail here. A circulation distribution pipe assembly 33 is disposed inside the electrolyte storage tank 21. It includes a distribution pipe 331 located at the bottom of the electrolyte storage tank 21 and a distribution connecting pipe 332 connecting the auxiliary return port 214 and the distribution pipe 331. The distribution pipe 331 has multiple distribution holes (i.e., first distribution holes 333), which are configured to allow the electrolyte in the distribution pipe 331 to flow out at an upward angle. When the auxiliary circulation pump 31 operates, it drives the electrolyte in the electrolyte storage tank 21 to flow out through the auxiliary outlet 213, pass through the bypass pipe 3, and then enter the circulation distribution pipe assembly 33 through the auxiliary return port 214. Finally, the electrolyte is ejected at an upward angle towards the inner wall of the tank through the first distribution holes 333. The spray rate can be controlled independently by the auxiliary circulation pump 31, providing sufficient spray power to prevent SOC stratification. Preferably, the distribution pipe 331 is arranged circumferentially around the electrolyte storage tank 21 and is coaxial with the electrolyte storage tank 21. In this embodiment, as Figure 3 , Figure 4 As shown, the distribution pipe 331 has a non-closed, circular tubular structure with rounded bends to reduce local resistance loss. In other embodiments, the circulation distribution pipe assembly 33 can also adopt a closed annular tubular structure or other circular arrangement, as long as it can achieve the distribution of return liquid along the circumference of the storage tank.

[0076] Furthermore, multiple first liquid distribution holes 333 are evenly distributed along the axial direction of the distribution pipe 331, and one or more first liquid distribution holes 333 are provided in each of the four regions (front, back, left, and right) of the distribution pipe 331. Since the first liquid distribution holes 333 are distributed throughout the entire area of ​​the distribution pipe 331, the electrolyte, after being ejected from the first liquid distribution holes 333, can cover the entire circumferential area of ​​the inner wall of the storage tank, avoiding the existence of liquid distribution blind spots and improving the uniformity of electrolyte mixing within the tank. The angle between the axial direction of each first liquid distribution hole 333 and the radial horizontal direction of the electrolyte storage tank 21 is preferably 30°~60°, such as 45°.

[0077] To obtain the SOC values ​​of different regions in the flow battery system, the flow battery system also includes a detection component communicatively connected to the controller. The detection component includes a first detection element and a second detection element. The first detection element is located at the bottom of the electrolyte storage tank 21 and is used to detect the state parameters of the electrolyte at the bottom of the tank. The second detection element is located in the electrolyte outlet pipe 23 and is used to detect the state parameters of the electrolyte within the outlet pipe 23. Preferably, both the first and second detection elements are spectral detection elements used to detect the absorbance or transmittance of the electrolyte at a specific wavelength to calculate the state of charge (SOC) of the electrolyte. The concentration of each valence ion can be calculated based on Lambert-Beer's law, and then the corresponding SOC value can be calculated, as detailed in existing technologies. As an example, the spectral detection element can be a UV-Vis spectrophotometer, i.e., the first and second detection elements are a first UV-Vis spectrophotometer 215 and a second UV-Vis spectrophotometer 232, respectively. It is understood that the detection element can also be other sensing elements that can reflect the SOC value of the electrolyte, such as redox potential detection elements or conductivity detection elements, which can be selected by those skilled in the art according to actual needs.

[0078] The control method also includes: Obtain the first SOC value of the electrolyte in the electrolyte storage tank 21 and the second SOC value of the electrolyte in the electrolyte outlet pipeline 23 of the stack, and calculate the absolute value of the difference between the first SOC value and the second SOC value, denoted as ΔSOC (e.g., 0.05). When the ΔSOC is greater than or equal to the first set threshold, the auxiliary circulation pump 31 is started; When the ΔSOC is less than the first set threshold, the auxiliary circulation pump 31 is turned off.

[0079] The above settings enable simultaneous temperature rise and SOC balancing, thus shortening the cold start time.

[0080] In addition, the flow battery system may optionally include a liquid distribution pipe assembly 4. The liquid distribution pipe assembly 4 is located inside the electrolyte storage tank 21, with one end connected to the return port 212 and the other end extending into the electrolyte storage tank 21. The liquid distribution pipe assembly 4 has multiple second liquid distribution holes 43. The electrolyte, after undergoing the electrochemical reaction in the fuel cell stack 1, is transported to the return port 212 via the return pipe, enters the liquid distribution pipe assembly 4 from the return port 212, and is dispersed outwards through the second liquid distribution holes 43, flowing back into the electrolyte storage tank 21 to mix the electrolyte in the tank. The liquid distribution pipe assembly 4 may refer to existing technologies in the art and is not specifically limited. As an example, the liquid distribution pipe assembly 4 includes a central pipe 41 and multiple liquid distribution branch pipes 42 connected to the outer wall of the central pipe 41. The central pipe 41 extends axially along the electrolyte storage tank 21 and is coaxially arranged with the electrolyte storage tank 21. One end of the central pipe 41 is connected to the return port 212. One end of each distribution branch pipe 42 is connected to the bottom of the central pipe 41 and communicates with the central pipe 41. The other end extends radially outward along the electrolyte storage tank 21. Multiple distribution branch pipes 42 are distributed circumferentially along the central pipe 41, and each distribution branch pipe 42 has multiple second distribution holes 43 opened along its axial direction. Preferably, the angle between the axial direction of the second distribution hole 43 and the radial horizontal direction of the electrolyte storage tank 21 is 30°~60°, such as 45°, so that the electrolyte is injected into the electrolyte storage tank 21 at an oblique upward direction. During the upward process, the jet mixes fully with the original electrolyte in the tank and drives the electrolyte in the bottom area to move upward, suppressing the stratification of the electrolyte in the storage tank.

[0081] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A control method for low-temperature cold start of a flow battery system, characterized in that, Based on a flow battery system, the flow battery system includes a stack, a positive electrolyte circuit, and a negative electrolyte circuit, wherein the positive electrolyte circuit is connected to the positive electrode side of the stack, and the negative electrolyte circuit is connected to the negative electrode side of the stack. The positive electrode electrolyte circuit and the negative electrode electrolyte circuit each include a main circuit and an auxiliary branch; The main circuit includes an electrolyte storage tank, a fuel cell stack inlet pipe, and a fuel cell stack outlet pipe. The electrolyte storage tank, the fuel cell stack inlet pipe, the fuel cell stack, and the fuel cell stack outlet pipe are sequentially connected to form a circulation loop. The fuel cell stack inlet pipe is sequentially equipped with a fuel cell stack inlet valve, a main circulation pump, and a heating device along the electrolyte flow direction. A first flow meter is also provided on the fuel cell stack inlet pipe downstream of the main circulation pump, and a first valve is provided on the fuel cell stack outlet pipe. One end of the auxiliary branch is connected to the fuel cell stack inlet pipe at the position upstream of the main circulation pump, and the other end of the auxiliary branch is connected to the fuel cell stack outlet pipe at the position upstream of the first valve. The auxiliary branch is equipped with a second valve and a second flow meter. At least one of the first valve and the second valve is a regulating valve with an adjustable opening. The control method includes: Obtain the current temperature of the electrolyte storage tank; Open the battery stack inlet valve, start the main circulation pump, and adjust the heating power of the heating device to maintain the temperature of the electrolyte entering the battery stack through the battery stack inlet pipeline within the set temperature range; Based on the current temperature, adjust the opening of the first valve and / or the second valve to control the distribution ratio between the flow rate returning to the electrolyte storage tank via the fuel cell outlet pipeline and the flow rate returning to the fuel cell inlet pipeline via the auxiliary branch. As the current temperature increases, the flow rate returning to the electrolyte storage tank via the fuel cell stack outlet pipeline tends to increase, while the flow rate returning to the fuel cell stack inlet pipeline via the auxiliary branch pipeline tends to decrease.

2. The control method for low-temperature cold start of a flow battery system according to claim 1, characterized in that, When the current temperature is greater than the set temperature threshold, all the electrolyte flowing out of the fuel cell stack is returned to the electrolyte storage tank through the fuel cell stack outlet pipeline, and the auxiliary branch is in a cut-off state.

3. The control method for low-temperature cold start of a flow battery system according to claim 2, characterized in that, A first temperature threshold, a second temperature threshold, and a third temperature threshold are set, wherein the first temperature threshold < the second temperature threshold < the third temperature threshold; Obtain the first flow value detected by the first flow meter and the second flow value detected by the second flow meter, and calculate the ratio of the second flow value to the first flow value; When the current temperature is less than or equal to the first temperature threshold, adjust the opening of the first valve and / or the second valve so that the ratio is equal to the first set value; When the current temperature is greater than the first temperature threshold and less than or equal to the second temperature threshold, increase the opening of the first valve and / or decrease the opening of the second valve so that the ratio is equal to the second set value; When the current temperature is greater than the second temperature threshold and less than or equal to the third temperature threshold, increase the opening of the first valve and / or decrease the opening of the second valve so that the ratio is equal to the third set value; When the current temperature is greater than the third temperature threshold, the first valve is fully opened and the second valve is closed. Wherein, the first setting value > the second setting value > the third setting value.

4. The control method for low-temperature cold start of a flow battery system according to claim 3, characterized in that, The first set value ranges from 0.75 to 0.85, the second set value ranges from 0.60 to 0.70, and the third set value ranges from 0.45 to 0.

55.

5. The control method for low-temperature cold start of a flow battery system according to claim 3, characterized in that, The first temperature threshold is less than or equal to 5°C, the second temperature threshold is greater than 5°C and less than or equal to 12°C, the third temperature threshold is greater than 12°C and less than or equal to 19°C, and the set temperature threshold is equal to the third temperature threshold.

6. The control method for low-temperature cold start of a flow battery system according to claim 1, characterized in that, The control method further includes controlling the main circulation pump to run at a first flow rate for a first preset time, and then increasing the flow rate of the main circulation pump to a second flow rate; Wherein, the second flow rate is greater than the first flow rate.

7. The control method for low-temperature cold start of a flow battery system according to claim 1, characterized in that, The control method further includes: A fourth temperature threshold is set, which is greater than the third temperature threshold. When the current temperature is greater than or equal to the fourth temperature threshold, the heating device is turned off.

8. The control method for low-temperature cold start of a flow battery system according to any one of claims 1 to 7, characterized in that, The flow battery system further includes an auxiliary circulation loop, which comprises a bypass pipe located outside the electrolyte tank and connected between the auxiliary outlet and the auxiliary return port of the electrolyte tank, a circulation distribution pipe assembly located inside the electrolyte tank, and an auxiliary circulation pump located on the bypass pipe. The circulation distribution pipe assembly includes a distribution pipe located at the bottom of the electrolyte tank and a distribution connecting pipe connected between the auxiliary return port and the distribution pipe. The distribution pipe has multiple distribution holes configured to allow the electrolyte in the distribution pipe to flow out at an upward angle. The auxiliary circulation pump drives the electrolyte in the electrolyte tank to flow out through the auxiliary outlet, pass through the bypass pipe, enter the circulation distribution pipe assembly, be ejected from the distribution holes, and flow back into the electrolyte tank. The control method further includes: Obtain the first SOC value of the electrolyte in the electrolyte storage tank and the second SOC value of the electrolyte in the electrolyte outlet pipeline of the stack, and calculate the absolute value of the difference between the first SOC value and the second SOC value, denoted as ΔSOC; When the ΔSOC is greater than or equal to the first set threshold, the auxiliary circulation pump is started; When the ΔSOC is less than the first set threshold, the auxiliary circulation pump is turned off.

9. The control method for low-temperature cold start of a flow battery system according to claim 8, characterized in that, The distribution pipe is arranged around the circumference of the electrolyte storage tank and is coaxial with the electrolyte storage tank.

10. The control method for low-temperature cold start of a flow battery system according to claim 8, characterized in that, The distribution tube has a non-closed, circular tubular structure; And / or, the plurality of liquid distribution holes are arranged at equal intervals along the axial direction of the distribution pipe.

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