DC bus feed-forward/feedback control for EVs with battery/ultracapacitor energy storage system

A DC bus control strategy of an actively-controlled battery/ultracapacitor hybrid energy storage system for a full EV is presented in this paper. The control strategy is based on the PI DC bus voltage controller, wherein the DC bus voltage target is determined based on motor voltage demand. A feed-forward load compensator is also included in order to suppress DC bus voltage excursions under highly-variable driveline torque conditions. The superimposed controller commands the current references to the inner current control loops, so that ultracapacitor takes on the highly-dynamic (transient) current demands, while the battery covers for steady-state loads. The proposed control strategy has been verified by means of simulations for the case of electric vehicle being subject to NEDC driving cycle and constant acceleration/deceleration modes in order to reflect realistic EV power-train operating regimes.