Research On Active Power Control Of Large-scale Grid-connected Electric Vehicles

The contradiction between energy supply and environmental pollution is becoming increasingly more prominent,which makes the power system also experience profound changes of allowing for clean environment and being driven by energy demand.Electric vehicles(EVs),as a feasible solution for clean traffic,have attracted the attention of governments and researchers.In addition,EVs as an important role in smart grid is considered to be a key to solve the problems in respect of global energy and environment.The large-scale application and deployment of EVs will ease such problems of energy and environment;however,they will also cause serious impact on the security,stability and economic operation of the power system.Therefore,this paper focuses on the active power control of large-scale grid connection of EVs,in order to cope with the challenges of the stability and economic operation of the power system after large-scale deployment of EVs to the grid.The works done and the main research results are as follows:(1)Based on the physical characteristics and charging distribution of EV battery,this paper gives the complete concept of EV aggregator,and confirmed the services and available commercial mode for aggregator,as well as puts forward the operation framework of aggregator based on the power market and the control architecture of aggregator adapts to the micro grid control structure.Furthermore,the operation frame of the aggregator in the power market environment and the aggregator control architecture adapted to microgrids control structure are proposed.In view of such basis,it puts forward the concept of V2 G framework takes aggregator as the key entity.Such framework covers the two areas of technical management and market operation,which can not only take EV as controllable load and power / energy storage device to provide a variety of services to the power system in order to obtain benefits,but eliminate the adverse effects on the power system resulted from the access of large-scale EVs into grid on the premise meeting the basic need of EV charging.(2)Optimal scheduling framework of the EV aggregator energy and regulation services based on Grid-to-Vehicle is given.Such framework allows EVs to charge other than the peak of load and to provide regulation services at the same time of being charged.It takes the sum of the benefits of power energy transactions and regulation services of the aggregator in the energy and regulation service market as the objective function.The objective function takes into account the influence of the regulation services on the charged energy of EV battery and its restriction on EV battery charging power,thus to maximize the profit of aggregator.In addition,a regulation algorithm for the aggregator is proposed.The algorithm takes into account the constraints of EV battery capacity and reduced the traffic flow between aggregator and EVs.The simulation results show that the optimal dispatching of aggregator based on G2 V can not only increase the benefit of the aggregator,but reduce the charging cost of EV owners on the basis of meeting the charging requirements of EVs.(3)Based on the existing AGC area model,the modules of generation power out of RES plan,area control error(ACE)allocator and aggregator are added.An aggregator model for AGC is constructed and an ACE optimization allocation method for aggregators is proposed.The aggregator model gives the mathematical description of how about the aggregator participating in the regulation process and can respond quickly to the ACE signal and satisfy the power and energy constraints of EV battery.According to the regulation capacity,ramp rate and state of charge of conventional generators and aggregators,the ACE optimization allocation method is used to optimize the allocation of power between them,to minimize the cost of regulation on the premise of ensuring the performance of the AGC.As what simulation results show,in respect of integrating the aggregator into an AGC control area with the high penetration of renewable energy sources(RESs),it is appropriate to use the said ACE optimal allocation method,to achieve the optimal allocation of regulation power between conventional generators and aggregators,by which to improve the performance of AGC with the high penetration of RESs and reduce the regulation cost.(4)Through setting the system equivalent to a generator,it established the single-generator frequency response model with EV load shedding,which takes into account the role of governor.Based on the proposed V2 G conceptual framework,a three-layer frequency emergency control framework with aggregator as the core is established,and the function and scope of each layer are given.Besides,it gives the method for calculating the load shedding of dispatchable EVs.Such method takes into account the constraints of EV energy and capacity,and can injects EV discharge power into the system to balance the active power vacancy under the premise of ensuring the quality of regulation services and the demand for EVs charging.The simulation results have proved the validity of such dynamic method for the frequency evaluation of single-generator model.EVs can replace the load to achieve the emergency control of frequency.The reserve capacity for emergency control provided by the aggregator makes it possible to avoid or Less load shedding,so as to improve the continuity and reliability of the system power supply.