Proposal of Smart Storage for Ubiquitous Power Grid

—Autonomous Distributed Vehicle-to-Grid of Electric Vehicle—

Abstract

Penetrating large amount of renewable energy sources into power system, battery energy storage performs an important role for smoothing their natural intermittency, ensuring grid-wide frequency stability, and suppressing voltage rise caused by reverse power flow. The ubiquitous power grid concept has been proposed as a smart grid in Japanese context, where the total battery capacity can be optimized by coordinating renewable energy sources, controllable distributed generators, and controllable loads on demand side, for example, heat pump based water heater with heat storage, and plug-in hybrid vehicle or electric vehicle with onboard battery, and so on. In this paper, we propose an autonomous distributed vehicle-to-grid (V2G) control scheme. The proposed V2G control has droop characteristics against power system frequency measurement at 200/100V plug-in terminal, and battery state-of-charge (SOC) is balanced within designable range by restraining V2G gain according to estimated SOC. Of course, the convenience for vehicle user is considered by V1G charge, which is one-way charging control for plug-out. Self terminal frequency measurement algorithm, model based battery SOC estimation method, and the proposed autonomous distributed V2G control are implemented to automotive power electronics circuit and electric control unit. These concepts are summarized as Smart Storage in ubiquitous power grid applications.