| With the aggravation of the energy crisis and the continuous deterioration of the environment,the contradiction between economic development and environmental protection is becoming more and more significant.In order to alleviate the consumption of fossil energy by a large number of fuel locomotives and the pollution of exhaust gas to the environment,electric vehicles(EVs)with good energy storage characteristics and environment-friendly characteristics emerge as the times require.As the representative of new EVs,EVs have been recognized as the main direction of the development of automobile industry in the 21 st century.EVs can be used as load or as mobile energy storage unit to provide auxiliary services for grid by using V2 G technology.By formulating reasonable control strategy,EVs can be used to promote the safe and stable operation of the grid.Due to the fast charging and discharging characteristics of power batteries,which meet the requirements of system frequency regulation(FR),a large number of EVs can provide auxiliary FR service support for the power grid.The reasonable FR control strategy should consider the interests of grid,user’s and electric vehicles.Based on this,the following research is carried out.Firstly,aiming at the problems of inertia and damping loss caused by a large number of EVs entering the grid through power electronic equipment and the impact on the power grid caused by too fast response,the virtual synchronous generator(VSG)model is established by using the VSG technology,which makes the V2 G of EVs have similar inertia damping characteristics and FR characteristics as the synchronous generator,realizing the friendly network access of EVs.Then,the feasibility of EV participating in FR is analyzed from the aspects of response mode,FR capacity,response time and economy.In order to solve the problem of battery capacity decline during FR,based on the battery test data of the University of Maryland,and considering the two key factors of average cycle SOC and cycle charge and discharge interval,a capacity decline model during FR was established.Through the analysis of the established model and the charging behavior of user’s,the FR range and principle are determined to reduce the decline of battery capacity in the process of FR.Aiming at the problem of auxiliary FR of EVs,a FR control strategy for EVs is proposed,which considers battery capacity decline and user charging demand.First,a factor reflecting the degree of user’s charging demand is put forward.Secondly,according to the size of the factors,two operational modes of FM and planned charging are designed,in which FM mode mainly considers reducing the loss of batteries.The planned charging mode mainly considers to meet the charging needs of user’s,and the two modes are applied to the primary and secondary FR.The primary FR is realized by the method of adaptive droop coefficient,while the secondary FR is realized by the design of fuzzy controller.In the same mode,the primary and secondary FR cooperate with each other to achieve the goal of reducing capacity decline and meeting the needs of user’s,and realize the intelligent charging and discharging of EVs.Finally,the VSG model and the FR model of EV in single area system are established in Matlab/simulink.Different examples are designed to verify the proposed control strategy.Simulation results show the effectiveness of the proposed control strategy. |
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