The preferred design principle for the EV charging station is to have enough power to serve most EVs to charge as fast as possible and never be cut off. Therefore, the choice of EV charger specification mostly goes to 22 kW EV charger. This is to ensure the capability to serve all available EV on-board chargers in the market, for example, 7.4kW, 11kW, and 22kW. One of the major costs of an EV charging station is the installation cost, where the concerns are the cable, raceway costs especially the main feeder and transformer. With the electrical design to prepare total power to serve the case that all charged EVs of 22kW on-board charger is very expensive, and the chance of this case is very low.

Therefore, most of the time, the design for EV charging stations is to support the case that charged EVs are all 11kW on-board as it will applied to the case of mixed EVs on-board chargers. However, the case that there were many EVs with 22kW on-board charger charging at the same time is unlikely but possible; it may cause the main circuit breaker to trip, which is unacceptable. The Energy Management Device (EV-EM1) is designed to ensure support in this case.