Temperature control method for vehicular proton exchange membrane fuel cell system

Abstract

A temperature control method for a vehicular proton exchange membrane fuel cell system comprises the following steps: detecting a cooling loop inlet temperature of a fuel cell stack by using a temperature sensor, and inputting the temperature into a controller to achieve cooling fan control based on the controller, wherein the cooling fan control comprises fuzzy logic self-adaptive proportional integral control and feedforward compensation control, gain parameters of the proportional integral control are self-adaptively updated by a fuzzy logic algorithm, a load current of the fuel cell serves as disturbance and is used for feedforward compensation, and meanwhile, the opening degree of the fan is determined by the total cooling capacity requirement and the number of cooling fans; and finally, inputting a control signal output by the controller into an actuator of a thermal management subsystem, and conducting cooling inlet temperature control of the fuel cell stack.

Claims

1. A temperature control method for a vehicular proton exchange membrane fuel cell system, comprising the following steps: step S1: measuring a coolant inlet temperature of a cell stack; step S2: evaluating a difference between a target coolant inlet temperature and an actually measured coolant inlet temperature to obtain a temperature deviation value; step S3: inputting the temperature deviation value and the actually measured coolant inlet temperature into a proportional integral (PI) control module to obtain a control quantity of a cooling fan, wherein the control quantity comprises a rotation speed of the cooling fan, and the PI control module comprises a proportional integral PI module and a fuzzy logic module specifically as follows: the proportional integral PI module is used for obtaining the rotation speed of the cooling fan by calculation, and the fuzzy logic module is used for adjusting PI parameters in real time according to the temperature deviation value and a variation quantity of the temperature deviation value, an input membership function of the fuzzy logic module is described by a triangular distribution, an output of the fuzzy logic module is a proportional parameter correction and an integral parameter correction, an output membership function is described by a Gaussian distribution, and a centroid method is adopted for the calculation of the output; and step S4: inputting the control quantity of the cooling fan obtained in the step S3 into a cooling system controller through a control unit of a fuel cell system to achieve temperature control of the fuel cell system, wherein in the step S3, in consideration of a large difference value between the target coolant inlet temperature and the actually measured coolant inlet temperature in an initial warming-up process, the following processing is specifically conducted: introducing an integral separation method in the proportional integral PI module to separate an integral in the proportional integral PI module in the initial warming-up process, specifically as follows: 1) Setting a threshold value ε for controlling the temperature deviation value according to actual system control requirements; 2) when the target coolant inlet temperature is an initial warming-up temperature and the difference value between the target coolant inlet temperature and the actually measured coolant inlet temperature is greater than the threshold value ε, adopting a proportional control; and 3) In a target coolant inlet temperature reduction process, not starting the proportional integral PI module in the cooling process, maintaining a current opening degree of the cooling fan unchanged until the difference value between the actually measured coolant inlet temperature and the target coolant inlet temperature is less than a certain threshold value, and then starting the proportional integral PI module to adjust the rotation speed of the cooling fan in real time.

2. The temperature control method for the vehicular proton exchange membrane fuel cell system according to claim 1, wherein, in the step S3, the rotation speed is regulated in advance through the cooling fan under a working condition that a load current changes is greater than 10 A, the load current is regarded as disturbance to be used for a compensation calculation, and then a compensation calculation result is integrated with the output of the fuzzy logic module: when a compensation action needs to be started, a disturbance-based feedforward compensation control expression is as follows:
u(t).sub.fed=k.sub.cI wherein k.sub.c is a feedforward control parameter; a total opening degree output control expression of the cooling fan is as follows:
u=k.sub.cI+(k.sub.p_c+Δk.sub.p_FL)e(t)+(k.sub.i_c+Δk.sub.i_FL)∫.sub.0.sup.te(t)dt

3. The temperature control method for the vehicular proton exchange membrane fuel cell system according to claim 2, wherein, in the step S3, before inputting an obtained total opening degree output control value of the cooling fan into a controller of a cooling subsystem, a total opening degree control output quantity is limited, so that an upper control duty ratio of each cooling fan is 90%.

4. The temperature control method for the vehicular proton exchange membrane fuel cell system according to claim 1, wherein, the step S3 further comprises a step of distributing the cooling fans, so that the output duty ratio is averagely distributed, with specific principles as follows: when a PI output duty ratio D is that D is equal to or greater than 0 and is less than 5%, no cooling fan is started; when the PI output duty ratio is that D is equal to or greater than 5 and is less than 15%, the duty ratio of each cooling fan is 15%, and one cooling fan is started; when the PI output duty ratio is that D is equal to or greater than 15% and is less than 30%, the duty ratio of each cooling fan is D, and one cooling fan is started; when the PI output duty ratio is that D is equal to or greater than 30% and is less than 60%, the duty ratio of each cooling fan is D/2, and two cooling fans are started; when the PI output duty ratio is that D is equal to or greater than 60% and is less than 90%, the duty ratio of each cooling fan is D/3, and three cooling fans are started; when the PI output duty ratio is that D is equal to or greater than 90% and is less than 120%, the duty ratio of each cooling fan is D/4, and four cooling fans are started; when the PI output duty ratio is that D is equal to or greater than 120% and is less than 150%, the duty ratio of each cooling fan is D/5, and five cooling fans are started; when the PI output duty ratio is that D is equal to or greater than 150% and is less than 180%, the duty ratio of each cooling fan is D/6, and six cooling fans are started; when the PI output duty ratio is that D is equal to or greater than 180% and is less than 210%, the duty ratio of each cooling fan is D/7, and seven cooling fans are started; and when the PI output duty ratio is that D is equal to or greater than 210% and is less than 240%, the duty ratio of each cooling fan is D/8, and eight cooling fans are started.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow diagram of a temperature control method of an embodiment of the present invention.

(2) FIG. 2 is a principle diagram of a fan control algorithm of an embodiment of the present invention.

(3) FIG. 3 is a logic block diagram of a fan control opening degree calculation algorithm in an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

(4) To understand the objective, features and advantages of the present invention more clearly, the present invention is further described below with reference to accompanying drawings and embodiments. Numerous specific details are set forth in the following description to facilitate a thorough understanding to the present invention, however, the present invention may be implemented in other ways than those described herein and is therefore not limited to the specific embodiments disclosed below.

(5) The embodiment provides a temperature control method for a vehicular proton exchange membrane fuel cell system, as shown in FIG. 1, comprising the following steps:

(6) step S1, measuring a coolant inlet temperature of a cell stack, and setting a target coolant inlet temperature;

(7) step S2, calculating a temperature deviation, evaluating a difference between an actual value measured by a temperature sensor (an actually measured coolant inlet temperature) and a target set value (the target coolant inlet temperature) to obtain a temperature deviation value, and serving the temperature deviation as an input of a PI control module;

(8) step S3, inputting the temperature deviation value and the actually measured coolant inlet temperature into the PI control module to obtain a control quantity of a cooling fan, wherein the control quantity comprises a rotation speed of the cooling fan; and

(9) step S4, inputting the control quantity of the cooling fan obtained in the step S3 to a cooling system controller through a control unit of a fuel cell system to achieve temperature control of the fuel cell system.

(10) In the step S1, the temperature sensor is used for detecting the coolant inlet temperature of a fuel cell stack, and the coolant inlet temperature is used as a control target for temperature stabilizing control. To prevent a fuel cell engine controller from transmitting an abnormal set value, the target coolant inlet temperature (set value) needs to be limited, and the specific working temperature range is based on that provided by a cell stack manufacturer. The target temperature is determined by the magnitude of the working current of the cell stack, and the most appropriate operating temperature under different operating currents can be found through experimental calibration generally; meanwhile, the temperature difference of a coolant inlet and a coolant outlet needs to be within a certain range and generally needs to be controlled within 5-10° C., and the specific temperature difference is determined by a cell stack supplier and can be specifically set according to actual conditions, which would not be repeatedly described in detail here.

(11) In the step S3, the main control object is the rotation speed of the cooling fan, and the implementation steps are as shown in FIG. 2, mainly including PI control module tuning, compensation calculation, control quantity output, fan pre-starting, fan distribution and the like, specifically as follows:

(12) (1) fuzzy PI control module tuning: aiming at a nonlinear time-varying system, a derivation module is easy to introduce high-frequency measurement noise, and a filtering time constant is difficult to determine. Therefore, in the embodiment, the PI control module does not contain the derivation module to guarantee stability of a closed-loop control system, specifically as follows:

(13) the fuzzy PI control module comprises a proportional integral PI module and a fuzzy logic module;

(14) the proportional integral PI module is basic framework of the whole control algorithm, and is used for calculating a control quantity of an actuator, i.e., a rotation speed of the cooling fan, as shown in FIG. 3, the specific expression is as shown in (1):
u(t).sub.PI=k.sub.pe(t)+k.sub.i∫.sub.0.sup.te(t)dt  (1)

(15) wherein u(t).sub.PI is control output calculated by the proportional integral PI module, e(t) is a difference value between the target temperature and the actually measured temperature, k.sub.p and k.sub.i are a proportional gain and an integral gain respectively.

(16) The fuzzy logic module is used for adjusting PI parameters in real time according to the temperature deviation and variable quantity of the temperature deviation to improve a response speed and control accuracy of the PI control module, an input thereof is temperature deviation e of the target temperature and the actually measured temperature and the variable quantity Δe of the temperature deviation, input membership function is described by a triangular distribution, an output of the fuzzy logic module is a proportional parameter correction Δk.sub.p and an integral parameter correction Δk.sub.i, an output membership function is described by Gaussian distribution, and a centroid method is adopted for output calculation.

(17) To ensure that the temperature is not excessively overshoot in the heating process, a larger proportional parameter is generally selected at the initial moment; however, the temperature cannot be close to the target temperature due to the overlarge proportional parameter, so that the larger proportional parameter cannot be selected when the deviation value is small. Hereby, the fuzzy rule between the input and the output employs a rule in Table 1. Wherein NB denotes negative large, NM denotes negative medium, NM denotes negative small, ZO denotes zero, PS denotes positive small, PM denotes positive medium, and PB denotes positive large.

(18) Table 1 PI Fuzzy Logic Control Rule Table

(19) Proportional correction Δk.sub.p_FL and proportional parameter correction Δk.sub.i_FL output by the fuzzy logic module are summed with fixed proportional parameters k.sub.p_c and integral parameters k.sub.i_c calibrated in advance, i.e., the proportional integral parameters in the proportional integral PI module are corrected in real time based on an output result of the fuzzy logic module, with expressions as follows:
k.sub.p=k.sub.p_c+Δk.sub.p_FL  (2)
k.sub.i=k.sub.i_c+Δk.sub.i_FL  (3)

(20) wherein, in consideration of large difference value between the target temperature and the actually measured temperature in the warming-up starting process, if the integral module is started at the moment, the error can be continuously accumulated to cause serious lagging in fan start-up. To reduce error accumulation, an integral separation method is introduced into the proportional integral module PI. To this end, the integral in the PI module is separated in the initial warming-up process, with specific methods as follows:

(21) 1) setting a threshold value ε for controlling the deviation according to actual system control requirements;

(22) 2) when the target temperature is the initial warming-up temperature and the difference value between the target temperature and the actually measured temperature is greater than the threshold value ε, adopting proportional control to avoid adverse impact of the integral as well as make the system have faster dynamic response; and

(23) in addition, in the target temperature reduction process, to avoid downward overshoot of the temperature, not starting the proportional integral PI module in the cooling process, maintaining a current opening degree of the fan unchanged until the difference value between the actually measured temperature and the target temperature is less than a certain threshold value, and then starting the proportional integral PI module to adjust a rotation speed of the fan in real time.

(24) (2) Compensation calculation: compensation is mainly applied to a working condition with great load current change, the rotation speed of the fan can be adjusted in advance to avoid temperature overshoot. Due to small range of change of the current, the proportional-integral PI module can perform adjustment by itself, so that the compensation effect is not started when the current changes in a small range. By taking the situation that control quantity is compensated by taking 10 A as a current change threshold value as an example, i.e., when the load current change of the fuel cell engine is more than the threshold value, a feedforward compensation effect is adopted.

(25) The current is regarded as disturbance for compensation control calculation. The current I is obtained by table look-up according to a current power demand, and when the compensation action needs to be started, the disturbance-based feedforward compensation control expression is as follows:
u(t).sub.fed=k.sub.cI  (4)

(26) Wherein k.sub.c is a feedforward control parameter, and the specific feedforward control coefficients need to be judged and calibrated according to different current magnitudes of an actual system at present. Then, as shown in FIG. 3, a compensation calculation result is integrated with an output result of a fuzzy logic module.

(27) Hereby, the total opening degree output control expression of the fan is as follows:
u(t)=k.sub.cI+(k.sub.p_c+Δk.sub.p_FL)e(t)±(k.sub.i_c+k.sub.i_FL)∫.sub.0.sup.te(t)dt  (5)

(28) (3) Control quantity output: before inputting a calculated total opening degree output control value of the cooling fan to a controller of a cooling subsystem, the total opening degree control output quantity of the cooling fan needs to be limited to prevent the total opening degree control output quantity from exceeding the upper output quantity limit capable of being reached by the fan. In the embodiment, the power of the fuel cell system is 90 kW, eight cooling fans need to be adopted, and the upper control duty ratio of each cooling fan is 90%, i.e., the fan output upper limit of the whole fuel cell engine is 720%.

(29) (4) Fan pre-starting: in the warming-up process, as shown in FIG. 3, an extra pre-starting temperature compensation value is added after evaluating a difference between the target temperature and the actually measured temperature, the extra pre-starting temperature compensation value is input to the fuzzy logic module together with the difference value for calculation, due to the fact that the fan has a relatively serious lagging characteristic, this step is to start the fan in advance in the warming-up process to prevent the temperature from upward overshoot.

(30) (5) Fan distribution: the output duty ratio needs to be averagely distributed, if some fans are kept started all the time, then other fans need to be frequently started and turned off, resulting in non-uniform service life of the fans. To guarantee the service life consistency of the fans, the following fan distribution rule is adopted. For example, when the total calculated opening degree of the fan is 3%, no any fan needs to be started; when the total calculated opening degree of the fan is 10%, No. 1 fan needs to be started, and the opening degree of the No. 1 fan is 10%; when the total calculated opening degree of the fan is 40%, No. 1 and No. 5 fans need to be started, and the opening degree of each fan is 20%, and so on. (The engine in the embodiment is provided with two coolers, each cooler having four fans).

(31) TABLE-US-00001 TABLE 2 Fan distribution rule table Duty ratio Number of Serial number of PI output duty ratio of each fan started fans started fans .sup. 0 <= D < 5% 0 0 —  .sup.  5 <= D < 15% 15% 1 1 15% <= D < 30% D 1 1 30% <= D < 60% D/2 2 1, 5 60% <= D < 90% D/3 3 1, 5, 2  90% <= D < 120% D/4 4 1, 5, 2, 6 120% <= D < 150% D/5 5 1, 5, 2, 6, 3 150% <= D < 180% D/6 6 1, 5, 2, 6, 3, 7 180% <= D < 210% D/7 7 1, 5, 2, 6, 3, 7, 4 210% <= D < 240% D/8 8 1, 5, 2, 6, 3, 7, 4, 8

(32) Step S4, the control signal is input to the actuator through a control unit of the fuel cell system to control a coolant inlet temperature of the cell stack. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention in other forms, any skilled person familiar with the present professional may change or modify the technical content disclosed above to an equivalent embodiment with an equivalent change to be applied to other fields. However, any simple modifications, equivalent changes and adaptations made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of protection of the technical solution of the invention.