Research On Electric Vehicle Aggregation Modeling And Regulation Strategy Of Participation In Power System Auxiliary Service

Chinese EV industry is developing rapidly.Mobile energy storage of EV is a new way to alleviate energy and environmental problems,which has attracted extensive attention.Through vehicle-to-grid technology,energy storage and rapid response characteritics of EV can be fully utilized.And Reasonable regulation of EV charging and discharging behavior has become a new way to alleviate the pressure of power grid frequency regulation in new power system.Therefore,this paper mainly studies the aggregation modeling of AEVs and the regulation strategy of participating in frequency regulation service.The main work of this paper is as follows:(1)At present,AEVs aggregation models mostly rely on high-quality and real-time communication and the calculation speed is limited by the number of EV.Based on Markov chain theory,this paper establishes a linear controllable aggregation model of AEVs for power grid frequency regulation.The model can predict the state transition of AEVs,estimate the adjustable ability of AEVs off-line,and simulate the dynamic evolution process of aevs off-line.Firstly,considering the difference of battery capacity,this paper proposes a transfer probability calculation method for the dynamic change process of electric vehicles based on Markov theory,derives the transfer probability distribution function of state of charg e,constructs charging load aggregation model of AEVs.Then,combined with the charging,discharging,idle state aggregation model and state switching process,the multi-state switching controllable aggregation model of aevs is constructed,and the model only communicates when interference factors appear,then updates the model parameters which reduces the communication pressure.Considering different charging modes,this paper establishes an extended aggregation model.The simulation results show that the aggregation modeling method can transform large-scale EV into a low dimensional controllable aggregation model,and can accurately simulate the dynamic evolution process of AEVs.(2)For the area with abundant EV resources,in view of the problem that the current frequency regulation command allocation of traditional units and AEVs doesn’t make full use of the fast response characteristics of EV batteries and doesn’t fully consider the economy of frequency regulation,this paper proposes a frequency regulation control strategy of AEVs based on variational mode decomposition(VMD)algorithm and double-layer model predictive control(MPC).Firstly,based on the AEVs aggregation model built in this paper,the underlying controller is designed to convert the aggregation cluster into AEVs frequency modulation units,and a single-area multi-generator LFC model involving AEVs is established;then,considering the response characteristics of traditional units and EV,the original regulation command is preliminarily allocated through VMD and reconstructed into low-frequency and high-frequency components.Then,in order to improve the economy of frequency regulation,the control strategy of double-layer MPC is used to realize the redistribution and tracking control of commands;The upper layer uses EMPC to redistribute the low-frequency and high-frequency components,so as to reduce the regulation cost and accelerate regulation process.Lower layer uses MPC is to adjust various resources to track command to complete the frequency regulation.The simulation results show that the control strategy can reasonably allocate and coordinate the output of various resources,optimize the economy of frequency modulation and improve the dynamic regulation performance of the system.(3)The command signal decomposition method is not applicable in the area with small scale EVs.In order to give full play to the energy storage characteristics of AEVs,improve the frequency regulation performance of the system,and optimize the economy of the dynamic regulation process on the premise of ensuring the frequency stability of the system,this paper proposes the frequency regulation control strategy of AEVs auxiliary power grid,based on Lyapunov-based economic model predictive control(LEMPC).Firstly,a generator-EV combined frequency regulation framework based on typical two-area interconnection system is established.Then,dual-mode frequency regulation strategy based on LEMPC is proposed.Mode 1 optimizes the comprehensive performance function in the stability region through economic predictive control;Mode 2 uses an auxiliary controller to ensure system stability and track the steady-state optimal set point.The simulation results show that the control strategy can optimize the economy of the dynamic regulation process,ensure the frequency stability of the system,improve the dynamic regulation performance of the frequency and track the steady-state set point.To sum up,this paper transforms the large-scale electric vehicle into a low dimensional controllable aggregation model,which can reduce the pressure of system communication and calculation;At the same time,based on the aggregation model,the corresponding frequency control strategy is designed for different scales of AEVs,which gives full play to the energy storage characteristics and optimizes the economy and dynamic performance of system frequency regulation.The research provides a new idea for aevs to participate in power grid frequency regulation and alleviate the pressure of power grid frequency regulation under new energy power system.