A design of DC bus control system for EVs based on battery/ultracapacitor hybrid energy storage

This paper presents the design of a control system suitable for EV DC bus voltage sag compensation based on the voltage PI controller and load current feedforward compensator. The superimposed PI controller and feedforward compensator references are distributed between the inner battery and ultracapacitor current-controlled DC/DC converters so that the ultracapacitor takes on the highly-dynamic (transient) current demands, while the battery covers for steady-state loads. In order to avoid deep discharges of the ultracapacitor, the DC bus control system is also equipped with auxiliary state-of-charge (SoC) controller. The functionality of the superimposed DC bus voltage control system and inner current and SoC control loops has been verified by means of simulations and experimentally on a downscaled battery/ultracapacitor experimental (NIL) setup.