A Thermal Management System for a PEM Fuel Cell System in Commercial Vehicles

Polymer electrolyte membrane (PEM) fuel cell operating in commercial vehicles produces a relatively high amount of heat. In order for securing durable operations, the produced heat should be rejected to keep the temperature in the cell under the limit. High temperature increases the rate of electrochemical reactions and mobility of water vapor. However, a thermal stress imposing on the thin layers of catalysts and membranes can accelerate degradation processes. Therefore, proper design of a thermal management system (TMS) and the associated control is required for ensuring highly reliable and efficient operations of the system. A typical thermal circuit consisting of a radiator, a fan, a reservoir and a coolant pump has been used to reject the excessive heat from the fuel cell. However, the capability of heat rejection is limited by sizes of the components that cannot be employed in heavy duty vehicles. In this study, we used two coolant loops, where the inner circuit consists of a bypass valve, a heat exchanger, a reservoir and a water pump and the outer circuit includes a radiator, a fan, a reservoir and a coolant pump. A state feedback control for the two loops was designed. Objectives for the controls were to maintain the temperature at the set value and to reduce the parasitic loss of the system. The controllers were tested on a dynamic model of a stack developed in the laboratory. Included is analysis of dynamic performance of the designed controllers at multiple step currents and FUDS. As a result of the proposed thermal management system, the size of radiator and the capacity of the pumps for proposed design become 10% smaller than those for the typical one. In addition, the overall net power of the fuel cell system increases to 5%.