A Realtime APF Method for Battery Ripple Current Reduction in HESS-Based Electric Vehicles

This paper presents an active power filtering (APF) method to reduce battery ripple currents negative to battery lifetime extension, in hybrid energy storage system (HESS) based electric vehicles (EVs). Deriving theoretical basis, the DC bus current is decomposed by improved Fast Fourier Transform (FFT) in real time, without knowing the driving cycle profile. With integration of motor information, the problem of FFT fundamental frequency and phase decision is solved for the first time in spite of its application to a DC system. A bidirectional DC-DC converter using chattering-free fixed-boundary-layer sliding mode (FBLSM) control helps the ultracapacitor deal with high-frequencies and part of low frequencies. Thus battery ripple currents can be reduced and its lifetime is extended. Simulated results validate the proposed method applied to HESS-based EVs.