Modeling and control of flexible HEV charging station upgraded with flywheel energy storage

This paper deals with the design of a fast DC charging station (FCS) for hybrid electric vehicles (HEVs) that is connected at a remote location. Power rating of this new technology can go up to a hundred kW and it represents a main challenge for its broad acceptance in distribution systems. In that sense, growing number of these stations, if operated in a non-flexible regime, will start to cause problems in future distribution systems such as overloads of local network´s corridors and reduction of its total equivalent spinning reserves. A power balancing strategy based on a local energy storage system (ESS) is proposed in this paper. Flywheel has been selected as the means of storing energy as it provides high power density and does not have significant performance degradation along its lifetime. Implemented control algorithm uses the energy stored in flywheel to compensate for the peak of power introduced by HEV charger, avoiding big initial stress in grid converter and also is able to limit the maximum extracted power. In addition, feed-forward compensation has been implemented to reduce the voltage dip within the station. Real time simulation results, that prove the validity of proposed approach, have been presented.