Research On MMC Based Grid-Connected Infrastructure And Control For Large Scale Electric Vehicle Fleet

Because of the increasingly adverse environmental pollution and exhaustion of fossil energy sources,electric vehicles(EV)and renewable energy generation have been attracting extensive attentions from industries and academics.The integrated EVs can play an important role in increasing penetration of the renewable power generation into existing power system and keeping the power system stability without adding more fixed energy storage system(ESS).It is a key of EV integrating into gird how to make full use of the character of EV bidirectional power while take the EV owner's demands into accounts.Modular Multilevel Converter(MMC)may be one of the possible topologies to integrate EV fleet into utility efficiently.But unlike the traditional MMC,it is a big challenge to control MMC-based EV integration system(MMC-based EVIS)such that its output three-phase power is kept balanced because different power demand of individual EVs means different values of SOC and DC voltage of individual MMC sub-modules,which may give rise to big circulation current.The paper is focused on the application of MMC in integrating EV fleet into utility;the main works and innovation are as follows.1.In this paper,the MMC is used as a power electronic interface for integrating EV fleet into utility by embedding the EVs into each sub-modules of MMC.The network structure and operation are analyzed,and the mathematical model is derived for designing the parameters of simulation cases.2.For the interactive energy management strategies between EVs and power system,this paper proposes a multi-objective power management strategy for MMC-Based EV fleet integrated into smart grid based on a virtual SOC model and by taking advantages of controlling the circulating current.The proposed objectives include the charging/discharging power differential control and interactive power management between EVs and utility,while keeping power quality of MMC interface to the grid.3.This innovated solution for the integration of EVs into future smart grid is investigated by establishing a concrete MMC-based EV integration model with 72 EVs in Matlab/Simulink and simulation for five charging/ discharging cases.The simulation results verify that power of individual EVs can be controlled differently and the power among three phase-units or six arms can be coordinately allocated according to the EV owners' demands and gird dispatching command while the output current THD lower than 5% the power quality is ensured,proving that power control strategies based on circulation current control and V-SOC are effective.