A Systematic Approach of Improving a Fault Tolerant Fuel Cell Bus Powertrain Safety Level

This paper focuses on the safety issue of fuel cell bus powertrain system. It demonstrates a systematic way of evaluation and refinement of the safety degree to advance the confidence of a kind of fuel cell bus powertrain system, and meanwhile a specific approach of safety level evaluation is used. Via functionally summing up the potential faults which may appear and cause economic losses or occupant injury, the deficiency of the powertrain is located. Based on the occurrence, the severity and the detecting possibility, the numerical expressions of the faults property are measured. Through combining these evaluating results, a general safety level can be achieved, which directly reflects the inappropriateness that should be adjusted or redesigned. Continuous improvement, including using the passive methods of hardware redundancy and the active methods of fault diagnosis, detection and fault tolerant control in the electric control system is carried out, leading to a much more reliable system and the updated safety level shows the enhanced confidence of the fuel cell powertrain system. In order to get a more practical control system, a hardware in the loop test bench is set up to test the performance of the controllers, the core of the powertrain system, under different working conditions, especially those when faults appear. The actual execution of the approach shows that it is an objective analysis method for the innovative powertrain system and can help to improve the system reliability of the fuel cell bus systematically.