Research On Electric Vehicle V2G System And Charging And Discharging Control Strategy

The Vehicle to Grid(V2G) technology to regulate bi-directional power flow between electric vehicles and the grid is attracting researchers from worldwide. Through V2 G technology, low adequacy, efficiency, and renewable energy integration capability for power systems can be improved. And the charging/discharging flexibility and economic concerns of electric vehicles can also be enhanced.As a multi-disciplinary research topic covering power systems, electric vehicles, batteries and control theories, V2 G technology is still in its early stages at home and abroad. The thesis focuses on the temporal and spatial V2 G load prediction, consumer charging/discharging strategy optimization, local V2 G power conversion systems, and bi-directional battery charger.A V2 G temporal and spatial load prediction method is presented in the thesis to analyse the load distribution with time and locations. Starting from the angle of traffic planning, parking demands are first evaluated based on traffic(OD matrix), land occupation and vehicle usage. A load model is established to predict the temporal and spatial load characteristics based on Monte Carlo simulation. The load characteristics of different suburbs in an example city are simulated and compared to analyse the impacts of reserve driving capacity, single EV charging and discharging power and daily average driving range on V2 G load.In order to realize maximization of the economic benefits of vehicle owners during participating V2 G, basic electric power services are analyzed to find the service suitable for V2 G. On this basis, taking hierarchically controlled park lot as the study object, this thesis proposes user side optimal V2 G control strategy for Service Type I(slow charging + frequency modulation) and Service Type II(slow charging + frequency modulation + peak power). A method to calculate the depletion of batteries is also presented based on typical operating cycle. The economic returns of vehicle owners and the service provider in the parking lot, affected by the power rating of chargers and daily mileage, are estimated for the two service types, to offer operation guidelines for both vehicle owners and the service provider.To find energy conversion system structure suitable for V2 G, disadvantages of traditional charging system are analyzed and a novel active front end V2 G power conversion topology with a common dc bus is presented, which can overcome the drawbacks of conventional topologies, by dealing with reactive compensation and harmonic suppression in a unified approach. The presented active front-end conversion system is analyzed, modelled, and simulated(3k V 2MVA 5-level cascaded) to validate its performance.Aiming at active front end controller with common DC bus energy conversion structure, an on-board V2 G charger design scheme is presented. Firstly, the requirements of V2 G system and services for on-board bi-directional charger are analyzed, and considering on-board charger’s low efficiency problem in light load, a dual active bridge is chosen as the topology used in DC/DC converter, which can realize wide power range soft switching combing single PWM phase shift control strategy. The charger is designed and established in the laboratory to verify its feasibility.