Research On Frequency Control Of Microgrid

With the increasingly prominent fossil energy crisis and environmental problems,development and utilization of new energy become the inevitable trend of world energy resources development.As an effective way to absorb new energy,microgrid has become a hot topic of domestic and foreign scholars.However a lot of fluctuant micro power,fast response of power electronic devices,plus load variability,lead frequent shift of microgrid,the power quality of microgrid is seriously affected.frequency control of microgrid is studied in this thesis,the main work as follow:In order to further improve the accuracy of pv virtual synchronous generator modeling,pv virtual synchronous generator model integrating the tracking of pv output maximum power point,energy storage and inverter is presented.Considering the output characteristics of pv array and battery energy storage,the mathematical model of active power output is obtained by modeling dc part.Combination of maximum power point tracking of pv output and double loop control of energy storage,considering power factor of photovoltaic virtual synchronous generator dynamic is adjustable,photovoltaic virtual synchronous generator could be divided into four kinds of operation mode,which are normal excitation mode,overexcitation mode,leading phase mode and phase modulation mode,and four kind modes of photovoltaic virtual synchronous generator output static model is set up.Photovoltaic virtual synchronous generator model is built on matlab platform to verify its accuracy.Aiming at the frequency control problem of microgrid,a control strategy of photovoltaic virtual synchronous generator based on frequency stratification is proposed,based on the three-level frequency control of traditional power grid.The first layer is the first level control based on the photovoltaic virtual synchronous generator,which is the main frequency modulation unit,and photovoltaic virtual synchronous generator simulates the external characteristics of active power frequency modulation and reactive power voltage regulation of traditional power grid synchronous generator set.The second layer is the secondary control of diesel generator based on PI control or photovoltaic virtual synchronous generator with small capacity.The third layer is the three-level control based on the central control center of microgrid.By means of the layered frequency control,the flexible frequency control of the microgrid can be realized,so as to ensure the real-time power balance of the source-load end of the microgrid system.The effectiveness of control strategy presented in this thesis is verified by comparing the simulation results with and without the participation of the photovoltaic virtual synchronous generator in frequency modulation and the participation of multiple micro power sources in frequency modulation.