Air Flow Control And Compressor Anti-surge Control Of Automotive Fuel Cell Based On Model Predictive Control

Proton exchange membrane fuel cell(PEMFC)is a new type of energy conversion device with no carbon emission.In recent years,the device has attracted extensive attention from the automotive industry.The flow of hydrogen and oxygen required by the electrochemical reaction in the device should change with the different driving conditions of the vehicle.However,due to the high concentration of hydrogen at the anode of PEMFC comes from the high-pressure hydrogen tank,its flow response is faster,while the air needed at the cathode comes from the air extracted by the compressor,its flow control is more difficult.Therefore,the control of fuel cell air system is of great significance to ensure the stable operation and improve the performance of the system.This paper puts forward ideas and new methods for air flow control in fuel cell air system and anti-surge control of compressor under extreme working conditions.The main work contents are as follows:(1)In this paper,the key components of fuel cell air supply circuit are modeled,including compressor,supply manifold,stack cathode gas partial pressure and return manifold.The model effectively reflects the air pressure at each position in the air circuit under the change of compressor air flow rate.On the basis of the model,the oxygen excess ratio(OER)is used as the control index to evaluate the oxygen shortage problem of fuel cell air system,and the common control strategies in the academic field were designed,including PID control strategy and one-dimensional and two-dimensional fuzzy control strategy.The control effects of the three strategies are compared in terms of steady-state error,overshoot,transient input and convergence time.(2)In order to promote the performance of oxygen excess ratio control,a linear adaptive model predictive control strategy(MPC)is proposed to control the air flow in the cathode air supply loop.In this paper,the state space model of fuel cell oxygen supply system is derived,and it is linearized and discretized at each sampling moment,so that the linear model and discrete model can accurately describe the original nonlinear model.In this paper,the discrete model is combined with the cost function which considers the minimum error of oxygen ratio to optimize the cost function,and the optimal sequence is obtained.The simulation results show that the response speed of oxygen excess ratio under MPC controller is faster than that of traditional control strategies,and the overshoot phenomenon is not obvious.(3)In addition,when the system load is too small,the air flow through the compressor will be lower than the limit value.At this time,the air flow rate and pressure in the system and the compressor body vibrate,which means that the compressor enters the surge state.Based on the predicted value of air flow in model predictive control,this paper predicts whether the compressor will enter surge.Then,before the compressor enters the surge zone,the control variable output by the MPC controller is modified to quickly restore the air flow and finally stabilize the compressor operating point at the early warning line.