Power Converters for Electric Vehicles

Abstract

This thesis presents topologies and control methods to improve the efficiency and dynamic response of Electric Vehicle (EV) power converters. There are three main converters in an EV power conditioning system: a plug-in AC/DC converter, a low-voltage DC/DC converter, and a three-phase inverter. The focus of this thesis is to improve the plug-in AC/DC converter and the low-voltage DC/DC converter. A new topology is proposed to improve the efficiency and increase the reliability of the plug-in AC/DC converter. The plug-in AC/DC converter consists of a Power Factor Correction (PFC) stage, which is followed by a high voltage DC/DC converter for galvanic isolation. The proposed approach includes a simple and effective auxiliary circuit for the PFC stage, which guarantees soft-switching for the power switches. Next, a current-driven full-bridge topology is proposed for the high-voltage DC/DC conversion stage, which guarantees soft-switching and eliminates voltage spikes across the output diodes. Also, two control approaches are proposed in order to improve the dynamic response of the AC/DC converter. The first controller is based on nonlinear differential flatness theory, which can be used to improve the transient response of the AC/DC converter. The second controller is based on an optimized stabilizing control-Lyapunov function, which extends the stability margins and improves reliability. An optimized variable-frequency phase-shift controller is proposed for the low voltage DC/DC converter, which adaptively controls the amount of reactive current required to maintain soft-switching throughout the whole range of operation and minimizes the switching and conduction losses of the converter. Mathematical analysis, simulation, and experimental results are presented to verify the performance of the proposed techniques.