A Controllable Membrane-Type Humidifier for Fuel Cell Applications—Part II: Controller Design, Analysis and Implementation

摘要

A membrane-based gas humidification apparatus was employed to actively manage thenamount of water vapor entrained in the reactant gas supplied to a fuel cell stack. Thenhumidification system utilizes a gas bypass and a series of heaters to achieve accuratenand fast humidity and temperature control. A change in fuel cell load induces a reactantnmass flow rate disturbance to this humidification system. If not well regulated, this disturbancencreates undesirable condensation and evaporation dynamics, both to the humidificationnsystem and the fuel cell stack. Therefore, controllers were devised, tuned, andnemployed for temperature reference tracking and disturbance rejection. Two heater controllerntypes were explored: on-off (thermostatic) and variable (proportional integral), tonexamine the ability of the feedback system to achieve the control objectives with minimalnhardware and software complexities. The coordination of the heaters and the bypassnvalve is challenging during fast transients due to the different time scales, the actuatornconstraints, and the sensor responsiveness.