Vehicle-To-Grid Control For The Supplementary Frequency Regulation Of A Power Grid

Large-scale integration of electric vehicles(EVs) will bring challenges and opportunities to power system. As a new type of fast growing load, it will have a significant impact on power system operation and planning. At the same time, EVs can also act as mobile storage devices, it will exert a favorable influence on the grid by guiding large amounts of EVs’ charging/discharging behaviors.EVs have the potential to provide frequency regulation services due to the fast adjustment of charging/discharging power. Meanwhile, EVs must meet the charging demands from EV users as a generation of transportation. When EVs participate in system frequency regulation, the users expect to achieve earnings and meet their charging demands. It result in the price mechanisms become a significant way to coordinate frequency regulation and charging demands from EV users. Therefore, the control strategy is researched for EVs to take part in frequency regulation based on electricity price in this paper, and make sure the regulation capacity and charging demands form EV users. The detailed content is as following:In this paper, the reason of frequency fluctuation and principle of frequency regulation in the power system are included at first. And mathematical models of interconnected power system are introduced including plant-load model, governor model, tie line model and load fluctuation model, etc. Meanwhile the V2 G model considering battery state of charge and the control structure for the primary/secondary frequency control of power grid with EVs are built, and it set up a simulation platform for frequency regulation with EVs.Second, by the research of energy supply and operating mode, the feasibility of EVs participating in frequency regulation of power grid is analyzed from some angles of: frequency regulation characteristics, response mode, available time and capacitance. And it proposed the calculations for EVs frequency regulation price and earnings when analyze the economics.Then the control framework is built to EVs participating in secondary frequency regulation(SFR), and the principle of EVs participating in SFR is analyzed, and a centralized control is proposed for EVs to take part in the SFR of interconnected power systems based on the electricity price. The regulation is dispatched in real time to EVs according to the electricity price, frequency regulation capacity, etc, in the control center. An aggregator, the coordinator between EVs and the control center, is responsible for uploading frequency regulation capacity(FRC) and the expected charge/discharge power of EVs to maintain the expected state of charge levels of batteries, while performing the regulation. In EV charging stations, the FRCand expected charge/discharge power of EVs are calculated, and at the same time, the regulation is distributed to each EV according to the task from the control center.At last, in MATLAB/Simulink environment, the simulation of EVs participating in frequency regulation of power system is analyzed and discussed, and the frequency regulation earnings is calculated too. The simulation results show that the proposed SFR control strategy with EVs can not only suppress system frequency deviation but also achieve charging demand.