Currently

researches on electric vehicles for frequency regulation in power system

mainly regard them as distributed generation

while relatively few take them as controllable load. However

electric vehicles are equally important either as distributed generation or as controllable load in frequency regulation. Therefore

a model with charging and discharging static frequency characteristics of electric vehicles is developed first. Then

a charging and discharging coordinated control strategy for electric vehicles is proposed to realize their role conversion between distributed generation and controllable load. Finally

considering charging and discharging of electric vehicles

a load frequency control model each for single and two-area power systems is developed. A simulation study is carried out to demonstrate that electric vehicles for frequency regulation as distributed generation and controllable load

can not only effectively improve power system responsiveness and reduce frequency deviation

but also remarkably decrease the reserve capacity of traditional frequency regulation units.