A method of water temperature control for a fuel cell stack

Abstract

The application discloses a fuel cell stack water temperature control method, and belongs to the field of fuel cell safety control. The fuel cell stack water temperature control method comprises a stack cooling path subsystem, the stack cooling path subsystem comprises a water pump, a thermostat, a heater, a radiator, and a temperature sensor, and the radiator comprises a first group of fans and a second group of fans. In the system operation process, the opening and closing of the two groups of fans are controlled by setting a switching parameter, stable control of the stack water temperature is realized, two control variables of a demand target temperature and a control target temperature are adopted, the control target temperature can be adjusted according to the actual system, dynamic PID parameter control can quickly respond to the temperature change of the system, and fine control of the stack water temperature is realized.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell safety control, and more specifically to a method for controlling the water temperature of a fuel cell stack. Background Art

[0002] Fuel cell stacks generate electricity and water through the electrochemical reaction of hydrogen and oxygen. During system operation, the water temperature in the stack cooling water circuit must be maintained stable to prevent overheating and damage to the stack. Different operating currents of the fuel cell require different water temperature control requirements, necessitating a fuel cell temperature management system to control the outlet water temperature of the fuel cell stack. However, because the fuel cell hydrothermal system is a nonlinear system with large capacitive hysteresis, control is challenging.

[0003] Chinese invention patent application publication number CN 114447379A discloses a fuel cell coolant temperature control method, system, and controller. The temperature control method includes: collecting data such as the real-time coolant outlet temperature of the fuel cell stack; finding the coolant outlet target temperature, temperature difference set value, and initial number of fans based on the scheduled current; determining whether the difference between the coolant outlet target temperature and the real-time temperature is less than the temperature difference set value; if so, activating a fan control strategy, calculating the fan duty cycle; and then determining whether the fan duty cycle is greater than or equal to the minimum set duty cycle and less than or equal to the maximum set duty cycle. If so, directly outputting the fan duty cycle to control the fan speed. If the fan duty cycle is less than the minimum set duty cycle, the number of fans is reduced and the fan duty cycle is calculated to control the fan speed. If the fan duty cycle is greater than the maximum set duty cycle, the number of fans is increased, and the fan startup delay is taken into account to calculate the fan duty cycle to control the fan speed. This patent only uses the coolant outlet target temperature as the control variable, and the minimum and maximum set duty cycles are fixed. However, since the coolant temperature is in a dynamic change process, the control accuracy of the coolant temperature is not high enough with this single variable and fixed minimum and maximum duty cycle setting values. Summary of the Invention

[0004] The present invention provides a fuel cell stack water temperature control method to overcome the shortcomings of the existing control method using a single variable and fixed minimum and maximum duty cycle setting values, such as insufficient fuel cell stack water temperature control accuracy.

[0005] The present invention adopts the following technical solutions:

[0006] A fuel cell stack water temperature control method includes a stack cooling circuit system, the stack cooling circuit system including a water pump, a thermostat, a heater, a radiator, and a temperature sensor. The radiator includes a first set of fans and a second set of fans, and decoupling control of the two sets of fans is achieved through a low-voltage wiring harness. The specific steps are as follows:

[0007] S1. According to the current working current of the battery stack, query and obtain the corresponding target water outlet temperature T of the battery stack. demand ;

[0008] S2. Confirm the target temperature value T of the control ctrl and by formula T ctrl =T demand -T cur Calculate T ctrl , in the formula T cur It is a set of parameter values ​​obtained through system calibration;

[0009] S3, when the actual water outlet temperature of the stack is T act Greater than the control target temperature value T ctrl When , the first set of fans starts to turn on, and the duty cycle setting value of the fan is set to FANPWM_PID. FANPWM_PID is calculated using the PID algorithm, and its expression is: Where: T ctrl is the target water outlet temperature of the stack, T act is the actual water outlet temperature of the stack, e(j) = T ctrl -T act is the difference between the current target water temperature and the current actual water temperature, n is the total number of steps in the integral calculation period, e(j-1) is the difference between the historical target water temperature and the historical actual water temperature, FAN_PWM(j) is the fan duty cycle setting value, k p 、k i 、k d They are adjustable parameters, Δt is the running step size;

[0010] S4. When the duty cycle FANPWM_PID of the first fan group exceeds the set turn-on threshold FAN2_SetPWM of the second fan group, the second fan group is turned on, and the duty cycle of the second fan group is increased according to the set slope FAN2_Rat.

[0011] S5. When the duty cycle of the second fan group increases to the set opening threshold FAN2_Open, the duty cycle of the second fan group is set to FANPWM_PID. From this point on, the duty cycle setting values ​​of the first and second fan groups are both FANPWM_PID calculated by PID.

[0012] S6. When one of the following conditions is met, the duty cycle setting value of the first group of fans is retained, and then the second group of fans is turned off: (1) the fan duty cycle setting value FANPWM_PID is less than the second group fan closing threshold FAN2_Close; (2) the stack current is less than the set current value Stack_LowCur during system load reduction; (3) the fuel cell system shutdown is completed.

[0013] Specifically, the PID algorithm in step S3 above uses a dynamically changing PID. A set of parameter tables is obtained by measuring the error between the actual outlet water temperature and the target temperature of the stack cooling subsystem. The PID control parameters in the table are obtained by system calibration. The table is expressed as follows: where k p k i k d They are PID control parameters, function k p [], k i [], k d [] are the parameter values ​​corresponding to the water temperature errors.

[0014] Furthermore, in step S5 , the opening threshold FAN2_Open of the second set of fans is determined based on the ambient temperature. When the ambient temperature is greater than the set threshold TO, FAN2_Open=FAN2_Open_0; when the ambient temperature is greater than the set threshold T1, FAN2_Open=FAN2_Open_1, and T0<T1.

[0015] Furthermore, during the operation of the FC system, when the speed of the second group of fans starts to decrease, if the system is in a stable power loading process, when the FC system inlet water temperature deviation is detected to be greater than a degree Celsius, the speed n0 of the first group of fans is increased; if the inlet water temperature deviation exceeds b degrees Celsius, b>a, the speed n1 of the first group of fans is increased; if the system is in a loading process, when the FC system inlet water temperature deviation is detected to be greater than a degree Celsius, the speed n1 of the first group of fans is increased; if the inlet water temperature deviation exceeds b degrees Celsius, the speed n2 of the first group of fans is increased; if the system is in a load reduction process, when the FC system inlet water temperature deviation is detected to be greater than -a degrees Celsius, the speed of the first group of fans is maintained unchanged; when the FC system inlet water temperature deviation is detected to be greater than -b degrees Celsius, the speed n3 of the first group of fans is reduced.

[0016] Preferably, the above-mentioned a is 0.5, b is 1; and the rotation speed n1<n2<n3.

[0017] Furthermore, during the entire operation of the FC system, when the actual water temperature is lower than the control target water temperature, both sets of fans are turned off.

[0018] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention divides the radiator into two groups and controls the on and off of the two groups of fans by setting switching parameters to achieve stable control of the stack water temperature. Two control variables are used: the demand target temperature and the control target temperature. The control target temperature can be calibrated and adjusted according to the actual system. Furthermore, dynamic PID parameter control can quickly respond to system temperature changes, achieving refined control of the stack water temperature.

[0020] 2. The opening threshold of the second group of fans of the present invention is determined according to the environmental conditions. Different set values ​​are adopted in combination with the current different ambient temperatures, which can further improve the control accuracy of the water temperature of the fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a control principle diagram of the fuel cell system of the present invention.

[0022] Figure 2 Flowchart of the present invention. DETAILED DESCRIPTION

[0023] The following describes specific embodiments of the present invention with reference to the accompanying drawings. Numerous details are provided below to provide a comprehensive understanding of the present invention, but those skilled in the art will appreciate that the present invention can be practiced without these details. Well-known components, methods, and processes are not described in detail below.

[0024] The present invention provides a fuel cell stack water temperature control method, which is based on the stack cooling circuit system. Figure 1 The stack cooling subsystem includes a water pump 1, a thermostat 2, a heater 3, a radiator, and temperature sensors. The radiator includes a first set of fans 41 and a second set of fans 42, which are decoupled and controlled via a low-voltage wiring harness. The temperature sensors include a first temperature sensor T1 and a second temperature sensor T2. T1 indicates the stack outlet water temperature, and T2 indicates the stack inlet water temperature.

[0025] Reference Figure 2 The above fuel cell stack water temperature control method has the following specific steps:

[0026] (1) After receiving the power-on command, the system starts up and the system is in normal operation.

[0027] (2) According to the current working current of the battery stack, the corresponding target water outlet temperature T of the battery stack is obtained. demand .

[0028] (3) Confirm the target temperature value T of the control ctrl and by formula T ctrl =T demand -T curCalculate T ctrl , in the formula T cur It is a set of parameter values ​​obtained through system calibration.

[0029] (4) When the actual water outlet temperature of the stack is T act Greater than the control target temperature value T ctrl When , the first set of fans starts to turn on, and the duty cycle setting value of the fan is set to FANPWM_PID. FANPWM_PID is calculated using the PID algorithm, and its expression is: Where: T ctrl is the target water outlet temperature of the stack, T act is the actual water outlet temperature of the stack, e(j) = T ctrl -T act is the difference between the current target water temperature and the current actual water temperature, n is the total number of steps in the integral calculation period, e(j-1) is the difference between the historical target water temperature and the historical actual water temperature, FAN_PWM(j) is the fan duty cycle setting value, k p 、k i 、k d are adjustable parameters, and Δt is the running step size.

[0030] The PID used in the above PID algorithm changes dynamically. A set of parameter tables is obtained through the error between the actual outlet water temperature and the target temperature of the stack cooling system. The PID control parameters in the table are obtained through system calibration. The table is expressed as follows: where k p k i k d They are PID control parameters, function k p [], k i [], k d [] are the parameter values ​​corresponding to the water temperature errors.

[0031] (5) When the duty cycle FANPWM_PID of the first fan group exceeds the set second fan group start threshold FAN2_SetPWM, the second fan group is turned on, and the duty cycle of the second fan group increases according to the set slope FAN2_Rat.

[0032] (6) When the duty cycle of the second fan group increases to the set opening threshold FAN2_Open, the duty cycle of the second fan group is set to FANPWM_PID. From this moment on, the duty cycle setting values ​​of the first and second fan groups are both FANPWM_PID obtained by PID calculation.

[0033] The load setting threshold FAN2_Open after the second set of fans are turned on is mainly determined based on the ambient temperature. When the ambient temperature is greater than the setting threshold T0, FAN2_Open=FAN2_Open_O. When the ambient temperature is greater than the setting threshold T1, FAN2_Open=FAN2_Open_1. Generally, TO<T1.

[0034] (7) When one of the following conditions is met, the duty cycle setting value of the first group of fans is retained, and the second group of fans is turned off: ① The fan duty cycle setting value FANPWM_PID is less than the second group fan closing threshold FAN2_Close; ② During the system load reduction process, the stack current is less than the set current value StacK_LowCur; ③ The fuel cell system is shut down.

[0035] When the second group of fans begins to reduce their speed, if the system is in a stable power loading process and the FC system inlet water temperature deviation exceeds a degree Celsius, the speed of the first group of fans is increased by n0. If the inlet water temperature deviation exceeds b degrees Celsius, where b>a, the speed of the first group of fans is increased by n1. If the system is in a loading process and the FC system inlet water temperature deviation exceeds a degree Celsius, the speed of the first group of fans is increased by n1. If the inlet water temperature deviation exceeds b degrees Celsius, the speed of the first group of fans is increased by n2. If the system is in a load shedding process and the FC system inlet water temperature deviation exceeds -a degrees Celsius, the speed of the first group of fans remains unchanged. If the FC system inlet water temperature deviation exceeds -b degrees Celsius, the speed of the first group of fans is reduced by n3. In this embodiment, a is preferably 0.5 and b is preferably 1.

[0036] During the entire operation of the FC system, when the actual water temperature is lower than the control target water temperature, both sets of fans are turned off.

[0037] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A fuel cell stack water temperature control method, comprising a stack cooling circuit system, wherein the stack cooling circuit system includes a water pump, a thermostat, a heater, a radiator, and a temperature sensor, characterized in that: The radiator includes a first set of fans and a second set of fans, Use the low-voltage wiring harness to achieve decoupling control of the two sets of fans. The specific steps are as follows: S1. According to the current working current of the battery stack, query and obtain the corresponding target water outlet temperature T of the battery stack. demand ; S2. Confirm the target temperature value T of the control ctrl and by formula T ctrl =T demand -T cur Calculate T ctrl , in the formula T cur It is a set of parameter values ​​obtained through system calibration; S3, when the actual water outlet temperature of the stack is T act Greater than the control target temperature value T ctrl When , the first set of fans starts to turn on, and the duty cycle setting value of the fan is set to FANPWM_PID. FANPWM_PID is calculated using the PID algorithm, and its expression is: Where: T ctrl is the target water outlet temperature of the stack, T act is the actual water outlet temperature of the stack, e(j) = T ctrl -T act is the difference between the current target water temperature and the current actual water temperature, n is the total number of steps in the integral calculation period, e(j-1) is the difference between the historical target water temperature and the historical actual water temperature, FAN_PWM(j) is the fan duty cycle setting value, k p 、k i 、k d They are adjustable parameters, Δt is the running step size; S4. When the duty cycle FANPWM_PID of the first fan group exceeds the set turn-on threshold FAN2_SetPWM of the second fan group, the second fan group is turned on, and the duty cycle of the second fan group is increased according to the set slope FAN2_Rat. S5. When the duty cycle of the second fan group increases to the set opening threshold FAN2_Open, the duty cycle of the second fan group is set to FANPWM_PID. From this point on, the duty cycle setting values ​​of the first and second fan groups are both FANPWM_PID calculated by PID. S6. When one of the following conditions is met, the duty cycle setting value of the first group of fans is retained, and then the second group of fans is turned off: (1) the fan duty cycle setting value FANPWM_PID is less than the second group fan shutdown threshold FAN2_C1ose; (2) the stack current is less than the set current value Stack_LowCur during system load reduction; (3) the fuel cell system shutdown is completed.

2. A fuel cell stack water temperature control method according to claim 1, characterized in that: The PID algorithm in step S3 uses a dynamically changing PID. A set of parameter tables is obtained by calculating the error between the actual outlet water temperature and the target temperature of the stack cooling system. The PID control parameters in the table are obtained by system calibration. The table is expressed as follows: where k p k i k d They are PID control parameters, function k p [], k i [], k d [] are the parameter values ​​corresponding to the water temperature errors.

3. A fuel cell stack water temperature control method according to claim 1, characterized in that: In step S5 , the opening threshold FAN2_Open of the second set of fans is determined based on the ambient temperature. When the ambient temperature is greater than the set threshold T0 , FAN2_Open=FAN2_Open_0 . When the ambient temperature is greater than the set threshold T1 , FAN2_Open=FAN2_Open_1 , where T0 < T1 .

4. A fuel cell stack water temperature control method according to claim 1, characterized in that: During operation of the FC system, when the speed of the second group of fans starts to decrease, if the system is in a stable power loading process, and the FC system inlet water temperature deviation is detected to exceed a degree Celsius, the speed n0 of the first group of fans is increased; if the inlet water temperature deviation exceeds b degrees Celsius, b>a, the speed n1 of the first group of fans is increased; if the system is in a loading process, and the FC system inlet water temperature deviation is detected to exceed a degree Celsius, the speed n1 of the first group of fans is increased; if the inlet water temperature deviation exceeds b degrees Celsius, the speed n2 of the first group of fans is increased; if the system is in a load reduction process, and the FC system inlet water temperature deviation is detected to exceed -a degrees Celsius, the speed of the first group of fans is maintained unchanged; if the FC system inlet water temperature deviation is detected to exceed -b degrees Celsius, the speed n3 of the first group of fans is reduced.

5. A fuel cell stack water temperature control method according to claim 4, characterized in that: The a is 0.5, b is 1; the rotation speed n1<n2<n3.

6. A fuel cell stack water temperature control method according to claim 1, characterized in that: During the entire operation of the FC system, when the actual water temperature is lower than the control target water temperature, both sets of fans are turned off.

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