Control Methods for a Bi-directional DC-DC Converter in Fuel Cell Hybrid Vehicle Applications

This paper presents methods adapted for the control of a bi-directional DC-DC converter in fuel cell hybrid vehicle applications. To interconnect the high voltage battery to the DC bus, a cascaded hard-switched buck and boost converter is chosen to allow operation of the electric drive train with overlapping input and output voltages. Specifically, current, power and voltage control are investigated for the boost and buck modes based on dynamic averaging converter models. The design shows that using active compensation of the input and output voltages, the same controller settings can be used for both modes of converter operation, and in particular, these settings are specified independently of the load. Furthermore, the methods demonstrate that at constant current flow, control deviations are avoided by dynamically applying a correction to the control voltage during the transition from boost to buck mode and vice versa. A case study with representative voltage and power values for a fuel cell hybrid vehicle verifies the suggested methods by means of simulations.