V2G Control Research Articles

Frequency droop control with scheduled charging of electric vehicles

Vehicle-to-grid (V2G) control of electric vehicles (EVs) has the potential to provide frequency regulation for power system operation. The authors study the frequency droop control with EVs’ participation. The challenge is to simultaneously suppress frequency fluctuation and satisfy transportation usages of EV owners. A V2G control consisting of frequency droop control and scheduled charging is developed to overcome this challenge. Frequency droop control can suppress frequency fluctuation by responding to frequency deviation signal, while scheduled charging can achieve the charging demands of EV owners. Although uncertain regulation may result in deviation of the battery energy levels from the expected, the scheduled charging made based on the departure time, the real-time, the real-time battery energy levels, and the expected battery energy levels can compensate this change in real time. The proposed V2G control can ensure different types of charging demands such as holding battery energy levels and elevating battery energy levels, unlike existing methods in which different V2G control strategies have to be developed. Simulations on a two-area interconnected power grid using real power grid data in China validate the effectiveness of the proposed V2G control in suppressing frequency fluctuation and achieving the charging demands of EV owners.

Aggregated optimal charging and vehicle‐to‐grid control for electric vehicles under large electric vehicle population

Effective charging and vehicle-to-grid (V2G) control strategies can utilise the properties of electric vehicles (EVs) to obtain various benefits. EVs are modelled as individuals in existing charging control algorithms. In this study, a new modelling method of EVs and an optimal charging control strategy are proposed so that all EVs in a control area can be regarded as a single object in the optimisation process. The strategy minimises the total charging cost of EVs, and can be further expanded to serve V2G control. With the new modelling method, the computational burden of the optimisation algorithm can be reduced significantly and does not increase with the number of EVs. Thus the strategy is extremely effective when the number of EVs becomes large, and the implementation cost could be more reasonable since less computational capacity is required. Case studies are presented to illustrate the performance of the strategy.

Vehicle-to-Grid Control for Supplementary Frequency Regulation Considering Charging Demands

Electric vehicles (EVs) as distributed storage devices have the potential to provide frequency regulation services due to the fast adjustment of charging/discharging power. In our previous research, decentralized vehicle-to-grid (V2G) control methods for EVs were proposed to participate in primary frequency control. In this paper, our attention is on bringing a large number of EVs into the centralized supplementary frequency regulation (SFR) of interconnected power systems. An aggregator is the coordinator between EVs and the power system control center. The aggregator calculates the total frequency regulation capacity (FRC) and expected V2G (EV2G) power of EVs based on the data communicated between the aggregator and individual EVs or EV charging stations. With FRC and EV2G power, a V2G control strategy is proposed for the aggregator to dispatch regulation requirements to EVs and EV charging stations. In individual EV charging stations, the FRC is calculated on the basis of the V2G power at present time, and EV2G power is presented considering both frequency regulation and charging demands. Besides, V2G control strategies are developed to distribute regulation requirements to each EV. Simulations on an interconnected power grid based on a practical power grid in China have demonstrated the effectiveness of the proposed strategies.

Implementation of autonomous distributed V2G to electric vehicle and DC charging system

Vehicle-to-Grid (V2G) has potential for providing the distributed spinning reserve to the power system. We proposed an autonomous V2G control scheme managing the vehicle user's convenience, the battery condition during the idle time, and the contribution to the power system, simultaneously. V2G power is controlled corresponding to the frequency deviation detected at the plug-in terminal and the desirable battery State-of-Charge for the plug-out. In this paper, the proposed control scheme is implemented to an electric vehicle and charging system. Performances of the interface, communication and control structure, and system efficiency and time response are verified by using the test system coordinating an electric vehicle battery test bed with a DC charging port, a controllable bi-directional power conditioner, and an integrated interface controller.

Robust LFC in a Smart Grid With Wind Power Penetration by Coordinated V2G Control and Frequency Controller

In the smart grid, the large scale wind power penetration tends to expand vastly. Nevertheless, due to the intermittent power generation from wind, this may cause a problem of large frequency fluctuation when the load-frequency control (LFC) capacity is not enough to compensate the unbalance of generation and load demand. Also, in the future transport sector, the plug-in hybrid electric vehicle (PHEV) is widely expected for driving in the customer side. Generally, the power of PHEV is charged by plugging into the home outlets as the dispersed battery energy storages. Therefore, the vehicle-to-grid (V2G) power control can be applied to compensate for the inadequate LFC capacity. This paper focuses on the new coordinated V2G control and conventional frequency controller for robust LFC in the smart grid with large wind farms. The battery state-of-charge (SOC) is controlled by the optimized SOC deviation control. The structure of frequency controller is a proportional integral (PI) with a single input. To enhance the robust performance and robust stability against the system uncertainties, the PI controller parameters and the SOC deviation are optimized simultaneously by the particle swarm optimization based on the fixed structure mixed H2/H∞ control. Simulation results show the superior robustness and control effect of the proposed coordinated controllers over the compared controllers.

Decentralized Vehicle-to-Grid Control for Primary Frequency Regulation Considering Charging Demands

Vehicle-to-grid (V2G) control has the potential to provide frequency regulation service for power system operation from electric vehicles (EVs). In this paper, a decentralized V2G control (DVC) method is proposed for EVs to participate in primary frequency control considering charging demands from EV customers. When an EV customer wants to maintain the residual state of charge (SOC) of the EV battery, a V2G control strategy, called battery SOC holder (BSH), is performed to maintain the battery energy around the residual SOC along with adaptive frequency droop control. If the residual battery energy is not enough for next trip, the customer needs to charge the EV to higher SOC level. Then, a smart charging method, called charging with frequency regulation (CFR), is developed to achieve scheduled charging and provide frequency regulation at the same time. Simulations on a two-area interconnected power system with wind power integration have shown the effectiveness of the proposed method.

Research on V2G Control Strategy for EV Charge and Discharge Equipmen

In this paper, the fundamental structure of charge and discharge device of V2G is analyzed. As for three phase voltage source PWM converter’s control, this paper presents that the control strategy of direct power control PWM rectifier is adopted under charging operation and constant power control strategy is used under discharging operation. For bidirectional DC/DC converter control strategy, dual closed-loop control of external voltage loop and internal current loop is put into use. The whole system of charge and discharge device of V2G is modeled and simulated by using the toolbox of PSCAD/EMTDC. Two-way power energy and information interaction of electric vehicle and power grid has been realized, current harmonic on grid side is decreased, power factor and power quality are improved.

Autonomous Distributed V2G (Vehicle-to-Grid) Satisfying Scheduled Charging

To integrate large scale renewable energy sources in the power grid, the battery energy storage performs an important role for smoothing their natural intermittency and ensuring grid-wide frequency stability. Electric vehicles have not only large introduction potential but also much available time for control because they are almost plugged in the home outlets as distributed battery energy storages. Therefore, vehicle-to-grid (V2G) is expected to be one of the key technologies in smart grid strategies. This paper proposes an autonomous distributed V2G control scheme. A grid-connected electric vehicle supplies a distributed spinning reserve according to the frequency deviation at the plug-in terminal, which is a signal of supply and demand imbalance in the power grid. As a style of EV utilization, it is assumed that vehicle use set next plug-out timing in advance. In such assumption, user convenience is satisfied by performing a scheduled charging for the plug-out, and plug-in idle time is available for the V2G control. Therefore a smart charging control is considered in the proposed scheme. Satisfaction of vehicle user convenience and effect to the load frequency control is evaluated through a simulation by using a typical two area interconnected power grid model and an automotive lithium-ion battery model.