On control strategy of auxiliary power unit for series hybrid city bus

Auxiliary Power Unit (APU) is one of the two power sources of series hybrid city bus. The diesel engine of APU is directly mechanically connected with the generator. The electricity power output of generator will fluctuate the engine speed, at the same time, the engine speed changes would affect the power output of generator. So there are very strong coupling characteristics between the engine and the generator. Since the working of the APU may cause the system bus voltage too high to damage the electrical components, the design of integrated APU control system has taken the active voltage control into account. The designed APU control strategy is used to the test of the series hybrid city bus which drives under Chinese typical city cycle in laboratory. The experimental results show that The APU control performance is good enough to meet the engineering needs, and the designed APU control strategy is feasible and effective.