High Power Density Interleaved ZCS 80-kW Boost Converter for Automotive Applications

Abstract

High system efficiency at all power levels is desired for electric vehicle (EV) propulsion systems. Conventional boost converters employed in EV traction architectures exhibit significantly lower efficiencies at low-power levels when operated under traditional fixed-frequency pulsewidth modulation (PWM) techniques. Also, low system power densities are associated with conventional boost converters due to their bulky inductors. These two shortcomings are addressed here through a comprehensive design methodology for an 80-kW interleaved boost converter stepping a low battery voltage up to an 800-V dc link. The designed converter employs a discontinuous conduction mode (DCM) variable-frequency control strategy to achieve an efficiency increase at low-power levels and, thus, a fairly constant efficiency throughout the entire drive schedule. A system loss model is developed to decompose analytically the loss mechanisms and, thus, determine the optimized design parameters for the variable-frequency control strategy and converter magnetics. Moreover, a custom inductor design based on distributed air gaps and aggressive thermal management through potting is integrated into the design methodology to further increase the converter power density. An 80-kW prototype is fabricated achieving a total power density of 55.6 kW/L, and experimentally tested, yielding system efficiencies above 96% for all power levels.