Dynamic control of fuel cell air supply system with power management

Abstract

A power management system is introduced to control the current flow between a Polymer Exchange Membrane fuel cell and a Li-Ion battery. Depending on the load current and the battery state of charge, the power management system decides the amount of the load power shared with each power source. The hybrid system operating power is divided into three categories which are named as Start-up state, Charging state and High power state based on the propulsion motor current. A unidirectional DC/DC power converter boosts the fuel cell system voltage and operates in voltage control mode or current control mode depending on the operating power state. Similarly, a bidirectional power converter is developed to boost the battery voltage to the DC bus voltage during the high power state. The bidirectional converter operates in buck mode during the charging power state. Based on the fuel cell current decided by the power management system, the fuel cell air supply system controller varies the inlet air pressure and flow rate to prevent the fuel cell oxygen concentration loss. The referenced model is used to obtain the optimum air pressure which produces maximum net power from the fuel cell system. Then, the air supply system is controlled to obtained the optimum pressure ratio and hence maximized the net power output. The fuel cell system power output with optimum compressure power is compared with the constant compressure power. The results shows that, the dynamic control of the air supply system with the power management decisions increase the fuel cell system net power output considerably.