Research On The Virtual Synchronous Generator Control Strategy Based On The Battery Energy Storage System

Renewable energy has been highly valued as an effective solution to the contradiction between social development needs and resource reserves,as well as distributed power generation(DG)technology and microgrid technology based on it.However,the large-scale access of power electronic converters under traditional control strategy will reduce the stability of the power grid.Therefore,the virtual synchronous generator(VSG),which can simulate the external characteristics of synchronous motors,has become a research hotspot.The energy storage system is an undipensable component of microgrid containing DGs.Through VSG control of energy storage system,the microgrid can actively participate in the primary frequency regulation(PFR)and inertia and voltage support response in gridconnected state,be independently loaded in isolated state,and realize seamless switch between these states.So,VSG is a promising control strategy for adapting to the high propotion of DGs.Some progress has been made in the research of the VSG control strategy based on battery energy storage system(BESS),but problems are still present for engineering applications and researhes on these problems are not perfect,such as the adaption problem of strong and weak power grids and non-ideal loads,and the optimization under different state of charge(SOC).This article will focus on these aspects and the main work is as follows:Firstly,based on the review of the energy storage converter control strategy and the development and current status of VSG technology,the steady-state model and small-signal model of two types of VSG are established,and the PFR and dynamic response characteristics of them are analyzed.An improved VSG control strategy is proposed,which can combine the advantage of both two types of VSG.Secondly,an adaptive VSG control method based on online detection of grid strength is proposed,which can maintain good operating characteristics under different grid conditions,thus solve the problem of degraded VSG control performance under significant changes in grid strength.Thirdly,aiming at VSG running with unbalance and non-linear load in low-voltage distribution network,the application of negative sequence voltage compensation and specific harmonic voltage compensation is discussed,which can improve the power quality of distribution.Fourthly,the state-of-charge(SOC)model of Li-ion battery is established and influence of SOC to VSG is analyzed.An adaptive method based on SOC is proposed,which can keep VSG in the optimal SOC range,prolong the running time of VSG in low SOC level and maintain power margin to participate in the subsequent adjustment.Finally,a hardware-in-the-loop platform based on the real-time digital simulator(RTDS)is built,and a microgird model is eastablish on this platform which contains BESS,photovoltaics and diesel generator sets.Expeiments have been done on this platform to prove the correctness of the analysis above.Also,some research results have been applied to the factory microgrid pilot project to verify the effectiveness of the control strategy.