A Pareto Based Comparison of DC/DC Converters for Variable DC-Link Voltage in Electric Vehicles

Abstract

High battery voltages increase inverter switching and harmonic losses of the electric machine. These losses dominate at low speeds in the partial load range, where the customer relevant Worldwide Harmonized Light Vehicles Test Procedure (WLTC) driving cycle is located. By installing a bidirectional DC/DC converter between the inverter and the battery, the input voltage of the inverter can be adjusted to various torque/speed conditions, thereby enhancing the efficiency and range of the electric sports car. Outside of the WLTC, the DC/DC converter is not operated and is short-circuited by a bypass. Additionally, the utilization of synchronous modulation methods, as opposed to space vector pulse width modulation (SVPWM), within the WLTC is made possible by the variable DC-Link voltage, further reducing switching and harmonic losses. In this paper, different topologies of DC/DC converters are proposed. The investigations are conducted on an 800 V system. To facilitate this, a script-based toolchain was developed based on analytic and fast calculating waveform models. The impact of the DC-Link voltage on energy efficiency during the WLTC is examined, and sensitivities are presented. A multi-objective optimization is carried out based on the WLTC driving cycle to demonstrate the maximum trade-offs between increasing the electric range and the power density of the DC/DC converter.