Uniform state-of-charge control strategy for plug-and-play electric vehicle in Super-UPS

Abstract

To prevent electric vehicles (EVs) from overcharging and discharging in a Super-uninterrupted power system (UPS) and to evaluate the influence of plug and play of EVs on the voltage of direct-current (dc) bus, a sliding-mode control method based on the multi-agent technology is employed in this article, and the output voltage, current, and the state of charge (SoC) of each EV's lithium battery are considered as the control object. The control design considers the current unitary value of each EV's lithium battery connected to a Super-UPS, the battery's SoC, and the average SoC of their adjacent EVs' lithium batteries. To prevent chattering and to consider the stability and authenticity of simulation, an improved sliding-mode function is presented, and the real-time capacities of EVs' lithium batteries are taken into account. Finally, the voltage stability of dc bus and the consistency of SoC of EVs' lithium batteries connected to Super-UPS are achieved by the new control scheme. The reliability and effectiveness of the proposed new control design method are confirmed by simulations.