Development of a zero-voltage-transition bidirectional DC-DC converter for a brushless DC machine EV propulsion system

This paper presents the development of a zero-voltage-transition (ZVT) bidirectional DC-DC converter for a brushless do machine (BLDCM) electric vehicle (EV) propulsion system. The DC-DC converter serves two main purposes. Firstly, it is used as the power electronics interface required for load leveling EV batteries. By employing high power ultracapacitors, the battery energy density and peak power density requirements are decoupled, offering opportunities to design and use EV batteries that are optimized for energy density, life and low cost, with less attention being given to the peak power. Secondly, the DC-DC converter is used to achieve speed extension and constant power operation of the BLDCM. To determine how well the DC-DC converter works together with the inverter/motor, and to develop a proper control method for the whole propulsion system, mathematical analysis and Matlab/Simulink simulations were carried out based on control theories. The zero-voltage-transition (ZVT) technique has been adopted in the bidirectional DC-DC converter to solve the problems associated with high frequency operation of PWM power converters, such as high switching loess resulting in low efficiency thus requiring larger heat sinks, and severe EMI noise. The final ZVT bidirectional DC-DC converter had an efficiency of greater than 96%.