Liquid path temperature control system suitable for all-vanadium redox flow battery

Abstract

The invention relates to a liquid path temperature control system suitable for an all-vanadium redox flow battery, and the system comprises a capacity box which is located in an electrolyte main circulation loop and is communicated with a galvanic pile; the liquid storage tank is communicated with the capacity box, and the liquid storage tank is used for balancing the liquid level of the capacity box; the heat exchanger is arranged on a liquid inlet or liquid outlet main pipeline of the volume box, or the heat exchanger is arranged in the liquid storage tank; the external water tank and the heat exchanger form a closed loop through a pipeline, and the closed loop is filled with a heat conduction medium; the external refrigeration compression fan is connected with an external water tank, and the external refrigeration compression fan is used for adjusting the temperature of the heat conduction medium; the temperature sensors are used for detecting the electrolyte temperature T < actual > and the medium temperature T < medium > and transmitting the electrolyte temperature T < actual > and the medium temperature T < medium > to the controller, and the controller conducts temperature control through the PID controller; the two liquid leakage sensors are arranged at the bottom of the external water tank and the bottom of the heat exchanger respectively.

Description

Technical Field

[0001] This invention relates to a temperature control system, specifically to a liquid circuit temperature control system suitable for vanadium redox flow batteries. Background Technology

[0002] During the operation of a vanadium redox flow battery, the positive and negative electrolytes involved in the reaction generate heat during the charge and discharge chemical reactions, causing the corresponding electrolyte temperatures to rise. The solubility of V(V) decreases with increasing temperature. When the temperature of the positive electrolyte is too high (above 40℃), V2O5 precipitates will form in the V(V) solution. The solubility of V(II), V(III), and V(IV) increases with increasing temperature. When the temperature is below 10℃, solids will precipitate in the V(II), V(III), and V(IV) solutions. This not only significantly damages the battery capacity, but the precipitates formed can also puncture or block the positive and negative electrode separators during operation, causing damage to the battery stack.

[0003] Based on the above, the existing temperature control measures are as follows: air conditioners, cooling fans, etc. are used to cool the battery pack in the power box, and heat tracing cables and heat exchangers in the pipeline are used to keep the electrolyte in the capacity box warm or cool it.

[0004] However, the above method has the following problems: 1. Insufficient temperature regulation accuracy: Most of them use single-mode cooling or heating equipment, which rely on simple switch control and cannot dynamically adjust the output power according to the temperature difference, resulting in large fluctuations in electrolyte temperature and affecting battery stability. 2. Low heat exchange efficiency: Heat exchangers mostly adopt a straight tube structure, which limits the contact area between the heat transfer medium and the electrolyte. Furthermore, the flow rate regulation lacks a linkage mechanism with the temperature difference, resulting in a lag in heat exchange response. Summary of the Invention

[0005] The main objective of this invention is to provide a liquid circuit temperature control system suitable for vanadium redox flow batteries, which features high-precision temperature regulation, efficient heat exchange, reliable leakage detection, and low energy consumption.

[0006] To achieve the above objectives, the present invention provides a liquid circuit temperature control system suitable for vanadium redox flow batteries, comprising: The capacity tank is located in the main electrolyte circulation loop and is connected to the fuel cell stack. The liquid storage tank is connected to the capacity tank and is used to balance the liquid level in the capacity tank. A heat exchanger is located on the main inlet or outlet pipe of the capacity tank, or the heat exchanger is located inside the storage tank. An external water tank forms a closed loop with a heat exchanger via pipes, and the closed loop is filled with a heat transfer medium. An external refrigeration compressor is connected to an external water tank and is used to regulate the temperature of the heat transfer medium. Temperature sensors are used to detect the electrolyte temperature T. 实 and medium temperature T 介 The data is then transmitted to the controller, which uses a PID controller to control the temperature. Two leakage sensors are installed at the bottom of the external water tank and the heat exchanger, respectively. Each leakage sensor includes three probes, a DC24V line, and three NKΩ resistors. The leakage alarm is achieved by calculating the current using I=24n / N, where n is the number of probes in contact with the leakage and N is the resistance value.

[0007] Preferably, the PID controller uses a dynamic PID adjustment algorithm, and the calculation formula is as follows: (1) Temperature difference formula: ΔT=T 实 -T 设 T is set as the target temperature; (2) When ΔT>0, the formula for the cooling power of the external refrigeration compressor is: P 冷 =P 冷max ×ΔT / ΔT max ; When ΔT < 0, the formula for the heating power of the external refrigeration compressor is: P 热 =P 热max ×|ΔT| / ΔT max ; (3) The formula for calculating the flow rate of the heat transfer medium is: θ = θ0 × (1 + |ΔT| / ΔT0); Among them, P 冷max P 热max ΔT is the maximum power of the equipment. max θ0 represents the maximum permissible temperature difference, θ0 is the basic opening degree of the regulating valve for controlling the flow of the heat transfer medium, and ΔT0 is the adjustment reference temperature difference.

[0008] A further preferred embodiment is the formula for calculating the output correction value of the PID controller: Integrating and differentiating formulas (2) and (3): Kp×ΔT+Ki×∫ΔTdt+Kd×d(ΔT) / dt Where Kp, Ki, and Kd are the proportional, integral, and derivative coefficients, respectively, which are dynamically adjusted according to the absolute value of ΔT. The larger |ΔT| is, the larger Kp is and the smaller Ki is.

[0009] Furthermore, the preferred method for initially determining the basic parameters Kp, Ki, and Kd is to use the Ziegler-Nichols critical proportionality method to determine the initial values: Disconnect the integral and differential actions, i.e. Ki=0, Kd=0, and gradually increase Kp until the system exhibits constant amplitude oscillation. Record the critical proportional gain Kcr and oscillation period Tcr at this point, and then calculate the initial parameters according to the formula: Kp=0.6×Kcr, Ki=2×Kp / Tcr, Kd=Kp×Tcr / 8.

[0010] Furthermore, the adjustment rule for the PID controller is as follows: Real-time adjustment based on the absolute value of the electrolyte temperature difference ΔT: When |ΔT|≥2℃, Kp automatically increases to 1.2-1.5 times the initial value, Ki decreases to 0.5-0.7 times the initial value, and Kd remains at the initial value; When |ΔT|<2℃, Kp returns to its initial value, Ki increases to 1.1-1.3 times its initial value, and Kd decreases to 0.8 times its initial value.

[0011] In a further preferred embodiment, an electric heating film is installed at the bottom of the external water tank, forming a composite temperature control system with the external refrigeration compressor fan. When T... 实 <T 设 And ΔT>ΔT max / 2 At that time, the electric heating film and the heating mode are activated simultaneously, via P 加 =P 热 ×0.3 replenishes calories.

[0012] Furthermore, an energy recovery module is also included, when T 实 -T 设 >2×ΔT max When the controller switches the heat exchanger to energy recovery mode, the excess heat of the electrolyte is transferred to the heat storage tank through the heat transfer medium, and the heat energy in the heat storage tank is used for the subsequent heating process.

[0013] Preferably, the inner surface of the titanium tube of the heat exchanger is integrally formed with spiral flow guide fins, the height of which is 1 / 5 to 1 / 4 of the inner diameter of the titanium tube, and the spiral angles of adjacent fins differ by 180° to form staggered flow channels.

[0014] Preferably, the heat transfer medium is a graphene-modified ethylene glycol solution with a graphene concentration of 0.05%-0.1%.

[0015] Preferably, the working principle of the leakage sensor is as follows: When no probe detects electrolyte, it is an open circuit, the sampled value is 0, and there is no alarm. When a probe detects electrolyte, the probe's circuit is connected, and the current value is I=24 / N, which is a level 3 alarm, only providing a notification; When the second probe detects electrolyte, its circuit is activated, and the current value is [value missing]. I = 24 × 2 / N, the current increases, indicating a level 2 alarm; When the third probe detects electrolyte, its circuit is activated, and the current value is [value missing]. I=24×3 / N, the current is at its maximum, which triggers a Level 1 alarm and the machine shuts down.

[0016] The beneficial effects of this invention are as follows: This invention utilizes an internal heat exchanger within the inlet / outlet liquid mains of a capacity tank or in the storage tank. The heat exchanger itself is constructed of corrosion-resistant titanium tubing and polymer materials. Connected to an external water tank containing a heat transfer medium, the temperature of the medium within the tank is adjusted by an external refrigeration compressor fan. The medium exchanges heat with the electrolyte through the heat exchanger, thereby achieving temperature control and maintaining low temperature fluctuations during operation, thus ensuring system stability.

[0017] Compared to previous single temperature control methods, this invention uses a single heat exchanger to achieve dual control of temperature rise and fall. By changing the medium temperature, it can both cool down and heat the electrolyte. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0019] The liquid circuit temperature control system of this embodiment includes a capacity tank, a liquid storage tank, a heat exchanger, an external water tank, a heat transfer medium, an external refrigeration compressor fan, a temperature sensor, a controller, two leakage sensors, and preferably, an electric heating film and an energy recovery module. Among these components: The capacity tank is located at the core of the electrolyte main circulation loop of the vanadium redox flow battery. Its inlet end is connected to the electrolyte preparation unit through a pipeline, and its outlet end is connected to the inlet of the stack through a pipeline. At the same time, it is connected to the outlet of the stack through a return pipeline, forming a circulation path for the electrolyte between the preparation unit, the capacity tank, and the stack, realizing the storage and stable delivery of the electrolyte.

[0020] The storage tank is installed adjacent to the capacity tank and is connected to the capacity tank through a pipeline. It is used to balance the liquid level fluctuations in the capacity tank caused by changes in the volume of electrolyte (such as temperature fluctuations or charge-discharge reactions). When the liquid level in the capacity tank is too high, the electrolyte can flow into the storage tank; when the liquid level in the capacity tank is too low, the electrolyte in the storage tank can flow back to replenish it.

[0021] The heat exchanger can be installed in the inlet or outlet main lines of the capacity tank, or directly inside the storage tank. Its main body is made of corrosion-resistant titanium tubing, with integrally formed spiral flow-guiding fins on the inner surface. The spiral angles of adjacent fins are staggered in opposite directions to form interlaced flow channels. The outer surface of the titanium tubing is covered with a layer of polymer material. The fin height is 1 / 5 to 1 / 4 of the inner diameter of the titanium tubing, and the spiral angles of adjacent fins differ by 180° to form interlaced flow channels. The heat exchanger is connected to an external water tank via pipes, forming a closed loop filled with a heat transfer medium.

[0022] An external water tank forms a closed-loop circulation loop with a heat exchanger via pipes. The tank contains a heat transfer medium, preferably a graphene-modified ethylene glycol solution, with the graphene evenly distributed in the solution through a dispersion process. An electric heating film can be installed at the bottom of the tank, and an external refrigeration compressor fan can be connected to the top or side wall, forming a composite temperature control structure. The water tank can also be connected to the heat storage tank of an energy recovery module via pipes.

[0023] The external refrigeration compressor is connected to the external water tank, and it has two working modes: refrigeration and heating. It can adjust the temperature of the heat transfer medium according to the controller command, and achieve precise control of the medium temperature in conjunction with the electric heating film.

[0024] The temperature sensor includes two sensors, one for detecting the actual temperature T of the electrolyte. 实 and the actual temperature T of the heat transfer medium 介 The detection signal is transmitted to the controller in real time.

[0025] The PID controller has a built-in PID control algorithm. After receiving the signal from the temperature sensor, it calculates and controls the operating mode and output power of the external refrigeration compressor, as well as the opening degree of the heat transfer medium flow regulating valve. At the same time, it can control the start and stop of the electric heating film and the working status of the energy recovery module.

[0026] Specifically, the system's temperature regulation is achieved by the controller executing a PID dynamic regulation algorithm, and the specific process is as follows: (1) Temperature difference calculation: The controller calculates the actual electrolyte temperature T detected by the temperature sensor. 实 With the preset target temperature T 设 Compare, according to ΔT=T 实 -T 设 Calculate the temperature difference.

[0027] (2) Based on the magnitude of ΔT, switch between cooling mode and heating mode and adjust power: When ΔT>0 (indicating that the electrolyte temperature is higher than the target temperature), the PID controller controls the external refrigeration compressor to switch to refrigeration mode and adjusts the refrigeration power proportionally (the power is positively correlated with ΔT, and the maximum refrigeration power is the inherent maximum value of the equipment).

[0028] When ΔT < 0 (indicating that the electrolyte temperature is lower than the target temperature), the PID controller controls the external refrigeration compressor to switch to heating mode and adjusts the heating power proportionally (the power is positively correlated with the absolute value of ΔT, and the maximum heating power is the inherent maximum value of the equipment).

[0029] (3) Heat transfer medium flow rate regulation: The PID controller adjusts the opening of the flow regulating valve proportionally according to the absolute value of ΔT. Based on the basic opening, the larger the temperature difference, the larger the opening and the higher the medium circulation flow rate. Conversely, it will fall back to the basic opening to ensure that the heat exchange efficiency matches the temperature difference requirement.

[0030] Specifically, PID dynamic correction: By integrating and differentiating formulas (2) and (3), the PID controller corrects the power and flow regulation mentioned above using the proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd. The correction value is calculated by "proportional term (Kp×ΔT) + integral term (Ki×∫ΔTdt) + derivative term (Kd×d(ΔT) / dt)", where the initial values ​​of Kp, Ki, and Kd are determined by the critical proportionality method and dynamically adjusted according to the absolute value of ΔT (Kp increases and Ki decreases when the temperature difference is large, and the opposite is true when the temperature difference is small).

[0031] Specifically, the initial determination method for the basic parameters Kp, Ki, and Kd is to use the Ziegler-Nichols critical proportionality method to determine the initial values: Disconnect the integral and differential actions, i.e. Ki=0, Kd=0, and gradually increase Kp until the system exhibits constant amplitude oscillation. Record the critical proportional gain Kcr and oscillation period Tcr at this point, and then calculate the initial parameters according to the formula: Kp=0.6×Kcr, Ki=2×Kp / Tcr, Kd=Kp×Tcr / 8.

[0032] In this embodiment, the adjustment rule of the PID controller is as follows: Real-time adjustment based on the absolute value of the electrolyte temperature difference ΔT: When |ΔT|≥2℃, Kp automatically increases to 1.2-1.5 times the initial value, Ki decreases to 0.5-0.7 times the initial value, and Kd remains at the initial value; When |ΔT|<2℃, Kp returns to its initial value, Ki increases to 1.1-1.3 times its initial value, and Kd decreases to 0.8 times its initial value.

[0033] Additionally, when the electrolyte temperature is significantly lower than the target temperature, the electric heating film and the external refrigeration compressor simultaneously activate in heating mode to supplement heat and accelerate the heating rate. Specifically, when T... 实 <T 设 And ΔT>ΔT max / 2 At that time, the electric heating film and the heating mode are activated simultaneously, via P加 =P 热 ×0.3 replenishes calories.

[0034] When the electrolyte temperature is significantly higher than the target temperature and exceeds the set threshold, the controller switches the heat exchanger to energy recovery mode, transferring excess heat from the electrolyte to the storage tank via a heat transfer medium. This heat can then be reused in subsequent heating processes. Specifically, when T... 实 -T 设 >2×ΔT max When the controller switches the heat exchanger to energy recovery mode, the excess heat of the electrolyte is transferred to the heat storage tank through the heat transfer medium, and the heat energy in the heat storage tank is used for the subsequent heating process.

[0035] Two leakage sensors are installed at the bottom of the external water tank and the bottom of the heat exchanger, respectively. Each sensor includes three probes, a DC 24V line, and three resistors with a specific resistance value (5.1KΩ in this embodiment). The probes are connected to the resistors one by one, and the other ends of the resistors are connected to the sampling line after being interconnected, forming a leakage detection circuit.

[0036] The specific leak detection process is as follows: The leak sensor implements tiered alarms by detecting changes in circuit current. The specific logic is as follows: When no electrolyte is detected at any monitoring point, the circuit is open, the current sampling value is 0, and there is no alarm. When electrolyte is detected at a point, the circuit is connected. At this time, the current I=U / R=24V / 5.1KΩ=4.7mA, which is a level 3 alarm, only providing a notification. When electrolyte is detected at the second monitoring point, the circuit is connected. At this time, the current I=U / R=24V / 2.55KΩ=9.4mA, which is a level 2 alarm. Corresponding measures can be taken. When electrolyte is detected at the third monitoring point, the circuit is connected. At this time, the current I=U / R=24V / 0.59KΩ=14.1mA, which is a level 1 alarm, and the machine is shut down.

[0037] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A liquid circuit temperature control system suitable for vanadium redox flow batteries, characterized in that, include: A capacity tank, which is located in the main electrolyte circulation loop and connected to the fuel cell stack; A liquid storage tank, which is connected to the capacity tank, is used to balance the liquid level in the capacity tank; A heat exchanger is provided in the main inlet or outlet pipeline of the capacity tank, or the heat exchanger is provided inside the storage tank. An external water tank, which forms a closed loop with the heat exchanger through a pipe, and the closed loop is filled with a heat transfer medium; An external refrigeration compressor is connected to the external water tank and is used to regulate the temperature of the heat transfer medium. Temperature sensors, the temperature sensors being used to detect the electrolyte temperature T 实 and medium temperature T 介 The data is then transmitted to the controller, which uses a PID controller for temperature control. Two leakage sensors are respectively installed at the bottom of the external water tank and the heat exchanger. Each leakage sensor includes three probes, a DC24V line, and three NKΩ resistors. The leakage level alarm is realized by calculating the current using I=24n / N, where n is the number of probes in contact with the leakage and N is the resistance value.

2. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 1, characterized in that, The PID controller employs a dynamic PID adjustment algorithm, and the calculation formula is as follows: (1) Temperature difference formula: ΔT=T 实 -T 设 T is set as the target temperature; (2) When ΔT>0, the formula for the cooling power of the external refrigeration compressor is: P 冷 =P 冷max ×ΔT / ΔT max ; When ΔT < 0, the formula for the heating power of the external refrigeration compressor is: P 热 =P 热max ×|ΔT| / ΔT max ; (3) The formula for calculating the flow rate of the heat transfer medium is: θ = θ0 × (1 + |ΔT| / ΔT0); Among them, P 冷max P 热max ΔT is the maximum power of the equipment. max θ0 represents the maximum permissible temperature difference, θ0 is the basic opening degree of the regulating valve for controlling the flow of the heat transfer medium, and ΔT0 is the adjustment reference temperature difference.

3. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 2, characterized in that, The formula for calculating the output correction value of the PID controller is as follows: Integrating and differentiating formulas (2) and (3): Kp×ΔT+Ki×∫ΔTdt+Kd×d(ΔT) / dt Where Kp, Ki, and Kd are the proportional, integral, and derivative coefficients, respectively, which are dynamically adjusted according to the absolute value of ΔT. The larger |ΔT| is, the larger Kp is and the smaller Ki is.

4. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 3, characterized in that, The initial values ​​of the basic parameters Kp, Ki, and Kd were determined using the Ziegler-Nichols critical proportionality method. Disconnect the integral and differential actions, i.e. Ki=0, Kd=0, and gradually increase Kp until the system exhibits constant amplitude oscillation. Record the critical proportional gain Kcr and oscillation period Tcr at this point, and then calculate the initial parameters according to the formula: Kp=0.6×Kcr, Ki=2×Kp / Tcr, Kd=Kp×Tcr / 8.

5. A liquid circuit temperature control system suitable for vanadium redox flow batteries according to claim 4, characterized in that, The adjustment rules for the PID controller are as follows: Real-time adjustment based on the absolute value of the electrolyte temperature difference ΔT: When |ΔT|≥2℃, Kp automatically increases to 1.2-1.5 times the initial value, Ki decreases to 0.5-0.7 times the initial value, and Kd remains at the initial value; When |ΔT|<2℃, Kp returns to its initial value, Ki increases to 1.1-1.3 times its initial value, and Kd decreases to 0.8 times its initial value.

6. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 5, characterized in that, The bottom of the external water tank is equipped with an electric heating film, which, together with the external refrigeration compressor, forms a composite temperature control system. When T... 实 <T 设 And ΔT>ΔT max / 2 At that time, the electric heating film and the heating mode are activated simultaneously, via P 加 =P 热 ×0.3 replenishes calories.

7. A liquid circuit temperature control system suitable for vanadium redox flow batteries according to claim 6, characterized in that, It also includes an energy recovery module, when T 实 -T 设 >2×ΔT max When the controller switches the heat exchanger to energy recovery mode, the excess heat of the electrolyte is introduced into the heat storage tank through the heat transfer medium, and the heat energy in the heat storage tank is used for subsequent heating processes.

8. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 1, characterized in that, The inner surface of the titanium tube in the heat exchanger is integrally formed with spiral flow guide fins. The height of the fins is 1 / 5 to 1 / 4 of the inner diameter of the titanium tube, and the spiral angles of adjacent fins differ by 180° to form staggered flow channels.

9. The liquid circuit temperature control system for a vanadium redox flow battery according to claim 1, characterized in that, The heat transfer medium is a graphene-modified ethylene glycol solution with a graphene concentration of 0.05%-0.1%.

10. A liquid circuit temperature control system suitable for vanadium redox flow batteries according to claim 1, characterized in that, The working principle of the leakage sensor is as follows: When no probe detects electrolyte, it is an open circuit, the sampled value is 0, and there is no alarm. When a probe detects electrolyte, the probe's circuit is connected, and the current value is I=24 / N, which is a level 3 alarm, only providing a notification; When the second probe detects electrolyte, its circuit is activated, and the current value is [value missing]. I = 24 × 2 / N, the current increases, indicating a level 2 alarm; When the third probe detects electrolyte, its circuit is activated, and the current value is [value missing]. I=24×3 / N, the current is at its maximum, which triggers a Level 1 alarm and the machine shuts down.