Analysis and Control of an Input-Parallel Output-Series Connected Buck-Boost DC–DC Converter for Electric Vehicle Powertrains

Abstract

Many electric vehicle powertrains use a boost type dc-dc converter to step-up the battery voltage for optimization and improving vehicle performance. The converter allows variation of inverter dc-link voltage to further reduce losses. By focusing on boost operation only, previously proposed drivetrains have not fully utilized the benefits of variable dc-link. This paper describes a new non-isolated bidirectional dc-dc converter capable of voltage step-down as well as high-gain voltage step-up operation. Such wide voltage range operation can lead to improved efficiency of electric vehicle drivetrains. The proposed converter comprises two non-inverting buck-boost modules, configured to operate in various optimized modes depending on the load requirement. Compared to existing bidirectional buck-boost converters, the proposed converter offers lower switch stress, reduced converter size and better efficiency. The operation of the converter in different modes is described in detail, followed by small-signal modeling and an outline of the control scheme. Experimental results obtained in an all-SiC 5 kW prototype show stable operation while the converter emulates the behaviour of the dc-dc stage in a variable dc-link EV powertrain under the ECE 15 drive cycle. The prototype demonstrated peak efficiencies of more than 98.5% and 98% for voltage step-up and step-down operations, respectively.