Research On Control And Fault Diagnosis Strategy Of Fuel Cell Air Supply System

As one of the key points of energy revolution in the 21 st century,hydrogen energy has the advantages of cleanliness,high calorific value,safety and controllability.Proton exchange membrane fuel cell is an important form of hydrogen energy application.As one of the power sources of new energy vehicles,it has received strong support and promotion from the government.In the vehicle-mounted environment,the complex road environment and frequent acceleration and deceleration place high requirements on the power and safety of the fuel cell system.The dynamic performance of the fuel cell system is mainly determined by the air supply system.Improper control of the air intake parameters will cause the output performance to decrease and damage the life of the stack.Therefore,studying the safe and efficient control of the fuel cell air supply system is of great significance for ensuring the stable operation of the fuel cell and improving the dynamic performance of the system.This thesis models the external operating behavior of the fuel cell system,and proposes accurate air system control methods and fault diagnosis strategy based on a simplified model.The main work and innovations are as follows:1)In view of the multi-parameter and multi-variable dynamic characteristics mod-eling of the fuel cell system,the influence of different parameters and environmental conditions on the output performance of the fuel cell is analyzed,and the electrochemi-cal model of the fuel cell stack and the empirical model of the air supply subsystem are constructed,which effectively reflects the changes in the pressure,flow and composi-tion of the air at various positions in the system under dynamic conditions,as well as the changes in the electrical output performance of the stack;in view of the non-linear,complex structure and difficult application of the fuel cell system model,a simplified version is proposed.With the help of methods such as parameter fitting and nonlinear system theory,a control-oriented fuel cell system model is established.2)Aiming at the time delay problem of fuel cell air supply,the oxygen excess ratio is used as the control index,an air flow control strategy based on fuzzy predictive control is proposed.In order to simplify the complexity of the controller design,a fuel cell system model simplification method based on T-S fuzzy theory is proposed.The complex nonlinear model is simplified to a linear model through dynamic linearization,and the direct correspondence between the peroxygen ratio and the control variable is obtained.A generalized predictive controller based on the T-S linear model is proposed to control the oxygen excess ratio in real time.In addition,in order to improve the output performance and efficiency of the system,an oxygen excess ratio control index based on the optimal principle of net output power is proposed.Finally,it is verified that the method can effectively reduce the overshoot of the air supply and improve the dynamic response speed of the system under the step current condition of the full working range.3)Aiming at the problem of fuel cell air pressure and flow coupling,the nonlinear system model is decoupled through input and output feedback linearization to obtain the direct correspondence between controlled variables and the control variables;For the pressure observation problem,an extended state observer is proposed to estimate the cathode pressure in real time.Based on the feedback linearized model,a predictive sliding mode control is proposed for the joint control of pressure and flow.The relative order of the system to is used design the slide surface and the corresponding predic-tive model.Simulation experiments prove that the proposed sliding mode predictive control algorithm can achieve stable pressure and flow coordinated control,and has the advantages of high precision,fast response and strong robustness.4)In view of the fault diagnosis of the air flow,the fault signals are considered as additional states of the system to construct an augmented model of the system.The dynamic small-signal models at different operating points are used for weighting to form a linear variable parameter model of the full working range of the system,and the corresponding augmented state observer is then developed.Furthermore,the influence of system disturbance and noise are considered in the observer design,and the gain of the observer is designed using the Lyapunov stability theorem to minimize the influence of these system uncertainties on fault diagnosis.In addition,an oxygen excess ratio estimator is designed based on the flow fault value estimated by the augmented state observer,and a corresponding fault-tolerant control method is further proposed.Finally,the effectiveness of the fault diagnosis method under different fault types is verified through dynamic working conditions,thereby ensuring the safety of the system and maintaining stable and efficient dynamic output performance.5)Aiming at the problem of safe and efficient management and control of fuel cell power system,a control strategy for vehicle fuel cell system is designed,which provides a solution for the application of the fuel cell control strategy.The control strategy can effectively realize the system’s start and stop control,air supply control,tail exhaust,water and heat management,and fault diagnosis.The control strategy is integrated into the hardware system,and the effectiveness and reliability of the control strategy are verified through the simulation platform.