Filter-based power splitting in ultracapacitor-battery hybrids for vehicular applications

Control strategies for power supplies with actively controlled battery-ultracapcitor combinations are investigated for vehicular applications. Simple filters for allocation of load between battery and ultracapacitor can introduce phase shift that degrades performance. When used with a nonlinear algorithm for voltage control of the ultracapitor bank, a simpler frequency-independent gain factor gives better performance. A low-phase-shift filter design is introduced and shown to produce better results than a frequency-independent gain factor. A physical test system has validated simulation results.