Modeling and Controls of a Fuel Delivery System With Dual Recirculation Lines for a PEM Fuel Cell System

A fuel delivery system with dual recirculation lines is investigated in this paper, which can reuse the exhausted gas from the outlet of anode flow channel. In the automotive application, the fuel delivery system regulates the hydrogen pressure and flow rate from the tank to the anode flow channel that change dynamically with load. The control objectives of fuel cell stack require that a slight pressure difference between the anode and cathode be maintained to prevent the damage of the membrane. In addition, the unconsumed hydrogen is circulated to a supply line by the recirculation lines. The fuel delivery system analyzed in this paper consists of two supply lines and two recirculation lines. The supply line with a low pressure regulator accounts for the supply of fuel at relatively low load demands. The other supply line with a flow controller starts to provide additional fuel with controllable flow rate at high load demands. The recirculation line with an ejector allows for mixing the unconsumed hydrogen with the supplied fuel. The other recirculation line with a blower is used to improve the controllability of the recirculation flow rate. Analysis of the fuel delivery system with dual recirculation lines is carried out by modeling and simulating an integrated system, where the components are modeled involving the dynamic characteristics. The major components of fuel delivery and recirculation system are an ejector, a blower, and a pressure regulator. In addition, the linearization of the integrated system is expressed in the approach of state equations to form the control problem of the system. Then the linear controllers are designed based on the decentralized proportional and integral control, and the state feed-back control. The systems with the different controllers are simulated at different operating points to evaluate their tracking performance by comparing the dynamic response curves.