In previous works [2] [3], we assumed the linear characteristic
in charging power control as shown in Fig. 1. PHEVs charge at
500W per car when the frequency is 50Hz; then, decrease the
charging power with decreasing frequency and increase the
charging power with increasing frequency. These controls are
equivalent to the governor with speed-droop operation of thermal or hydro power generator. We can derive the frequency
characteristic per PHEV, 2500 [W/Hz], from the gradient in