Auxiliary power unit control for hybrid electric vehicles

The control of a typical Auxiliary Power Unit for series type hybrid electric vehicles is considered. The APU is equipped with an internal combustion engine and with an electrical induction motor used as starting motor and as battery charging generator. Dynamic models of both engine and motor are considered and exploited for the design of the APU controller. A field oriented control scheme and a decoupling controller with two independent current control loops is used for the motor whereas a torque controller regulates the engine transients. The control of the whole APU is thus designed by coupling the engine and motor controllers through a cascaded feedback control approach. Different APU control strategies are used depending on the shaft speed and on the power requested by the battery management system. Simulation results are carried out with Matlab/Simulink. Small oscillations in the battery charging current and small power tracking error confirm the effectiveness of the proposed controller both in steady state and during transients.