Efficiency Optimization and Control of Auxiliary Power Unit for Extended Range Electric Vehicles

Abstract

How to determine the target engine operation point is a key issue of APU (Auxiliary Power Unit) control, which has a significant influence on fuel consumption of the system. Conventionally, engine operation point was decided by ensuring that the engine works in its maximum efficiency area. However, System efficiency of APU equals the product of engine efficiency and generator efficiency. Conventional method did not pay special attention to the generator efficiency. Based on analysis of how generator efficiency and engine efficiency influence fuel consumption of the system, a fuel optimal control method with consideration of both engine and generator efficiencies is proposed. Numerical models of generator efficiency and engine efficiency are established based on experiment data. An backward optimization algorithm is proposed to calculate optimal engine operation points in order to achieve highest overall efficiency of the engine-generator system. A simulation model is established to validate the optimal algorithm, simulation results indicates that the fuel consumption of the system is reduced by more than three percent after optimization.