A variable-voltage ultra-capacitor/battery hybrid power source for extended range electric vehicle

Abstract

Energy storage system of extended-range electric vehicle faces great challenges in working efficiency and energy utilization to meet the requirement of various working conditions of vehicle, efficient ultra-capacitor/battery hybrid power source is an effective way to tackle these challenges. This paper takes an ultra-capacitor/battery hybrid power source based on series-parallel switchover technology of ultra-capacitors as the research object, launches a fundamental study on its operation principle, control method and simulation/experimental verification. A significative series-parallel switchover technology of ultra-capacitors is adopted to achieve variable-voltage output of the hybrid power source, which overcomes the technical limitation of the existing hybrid power source with only a fixed working voltage output, enables the voltage-conversion ratio of the power converter to be controlled in a highly efficient range. The bi-directional four working modes of the hybrid power source that can fit the various working conditions of vehicle are analyzed. Following this, an incremental digital PID controller suitable for this energy storage system is presented. After that, a comprehensive comparison and analysis of the simulation and small-power experiment based on the simulated working conditions of vehicle are performed. The results have verified the feasibility and effectiveness of the proposed hybrid power source and its control method.