Power Converter and Control Interface for a GEM Fuel Cell Vehicle

In this paper, we discuss the design and performance of a low cost, fully integrated power conversion and control system for a modified Global Electric Motors (GEM) fuel cell hybrid vehicle. The need for a custom converter and control system has become apparent as the commercial DC-DC market seems to have a void in the ranges of power and voltage required for fuel cell vehicle applications. The system incorporates a custom designed DC-DC boost converter which steps up the nominal 26 VDC fuel cell stack voltage to interface with the 72 VDC vehicle battery bus at an input power level of 1.2 kW. Additionally, several embedded control functions are implemented to integrate a Ballard Nexa™ fuel cell power module into the GEM vehicle. Design equations supported by preliminary performance data indicates that the DC-DC power converter achieves a conversion efficiency approaching 98% for a single fuel cell power module operating at full output power (1.2kW). The high efficiency allows for a simple and flexible air-cooled design with minimal heat sink requirements and cooling system weight. The control system incorporates algorithms to perform battery charging and power ramp rate, as well as fuel cell voltage, and current limiting algorithms. The control system exhibits stable performance characteristics throughout the entire vehicle load range and battery state of charge range, while tracking vehicle transient conditions.