A Voltage-supportive Controller for Ultra-fast Electric Vehicle Chargers in Islanded DC Microgrids

Abstract

This paper presents a controller for fast and ultra-fast electric vehicle (EV) charging stations. Without affecting the charging efficiency, the proposed controller enables the charger to provide support to the interconnection voltage to counter and damp its transients. Existing solutions are either hardware-based such as using supercapacitors and flywheels which increase the cost and bulkiness of the charging station, or software-based such as $P/V$ droop methods which are still unable to provide a robust and strong voltage support. This paper proposes an emulated supercapacitor concept in the control system of the ultra-fast EV charger in an islanded DC microgrid. Thus, it converts the EV from a static load to a bus voltage supportive load, leading to reduced bus voltage oscillations during single and multiple ultra-fast EV charging operations, and rides through and provides supports during extreme external disturbances. Detailed analysis and design guidelines of the proposed controller are presented, and its effectiveness and improved performance compared with conventional techniques are shown for different case studies.

Keywords

• Electric vehicle (EV)
• charging station
• ultra-fast charging
• DC microgrid
• voltage support
• capacitor emulation