Coordinated Secondary Frequency Regulation Strategy Of Electric Vehicles And Wind/Photovoltaic Generation In Micro-grid

Facing the carbon emission problem and energy structure crisis,the development of clean energy vehicles represented by electric vehicle as well as renewable energies such as wind and solar power have received attention from various countries.Electric vehicles and renewable energy generations are usually integrated in the form of micro-grid when connected to the grid.However,the micro-grid is small in scale and has low equivalent inertia,thus it is difficult to maintain the frequency stability through traditional frequency regulation methods.Therefore,it is of great importance to investigate the control methods and cooperative strategies of various types of distributed resources for autonomous participation in frequency regulation within the micro-grid.First,starting from the independent frequency regulation method for single-type distributed resources,the paper studies the frequency regulation control strategy for electric vehicle cluster that considers the optimization of charging load,as well as the frequency regulation model of wind turbine which is suitable for continuously varying wind speed across the whole range,and proposes a tentative coordinated frequency regulation strategy of electric vehicle and wind turbine;Then,for multiple distributed resources working together to participate in frequency regulation,through the application of virtual synchronous generator technology,a coordinated frequency regulation strategy for multiple virtual synchronous generators based on self-adaptive adjustment of relevant coefficients is designed.The main research contents of this paper are as follows:A distributed frequency regulation control strategy for electric vehicle cluster that takes into account the optimization of charging load is proposed.The minimum system load variance is taken as the goal to optimize the charging plan of grid-connected electric vehicles,and a hierarchical control framework for electric vehicle cluster based on distributed sequencing is established.Simulation results show that the proposed frequency regulation control strategy for electric vehicle cluster can mitigate the negative impact of large-scale electric vehicles’ charging load on the power grid while ensuring the system frequency regulation effect;and the hierarchical distributed control framework is more suitable for the control of electric vehicle cluster than the traditional centralized control.A frequency regulation model for wind turbine under continuous varying wind speed across the whole wind speed range is established,including a de-loading operation strategy for the purpose of obtaining frequency regulation reserve capacity,and a two-way frequency regulation control strategy that combines rotor speed and pitch angle control,then a coordinated frequency regulation strategy for wind turbine and electric vehicle considering the driver’s demand and operation economy is proposed.The simulation results show that the wind turbine can effectively suppress the frequency deviation under the condition of continuously varying wind speed in whole range through the proposed frequency regulation model,and the electric vehicle cluster can serve as an additional energy storage system to assist the wind turbine to participate in frequency regulation.A coordinated frequency regulation strategy for multiple virtual synchronous generators based on self-adaptive adjustment is designed.By self-adaptive adjustment of the secondary frequency regulation coefficients of each virtual synchronous generator,the reasonable assignment of the system frequency regulation task is realized,and the auxiliary frequency regulation strategy of traditional unit based on the day-ahead prediction of reserve capacity is proposed.The simulation results show that based on the proposed coordinated frequency regulation strategy,with the assistance of traditional unit,the electric vehicle,wind turbine,and photovoltaic array can realize the self-adaptive adjustment of their own regulation tasks in the absence of communication,as well as achieve expected frequency regulation effect,enhancing the control reliability and improving the utilization rate of frequency regulation resources.