Photovoltaic-energy Storage System Virtual Synchronous Generator And Multi-machine Frequency Coordination Control

The Photovoltaic system connected to the grid through inverter can not provide inertia and damping.A large number of grid-connected Photovoltaic systems will seriously affect the safe and stable operation of the power system.Generation characteristics of Photovoltaic can be effectively improved by equipping photovoltaic with energy storage and adopting virtual synchronous generator control technology.Not only does the photovoltaic system have inertia and damping but also it can independently participate in the frequency and voltage regulation of the grid.This paper studies the problem of PV-ESS VSG and multi-machine frequency coordinated control.The research content of this paper is as follows:First,the control strategy of inverter,photovoltaic and energy storage device is designed.The influence of control parameters on system stability and dynamic performance is analyzed based on the small signal model of VSG.The PV-ESS VSG simulation model is built in MATLAB,and the superiority of VSG control strategy is verified by comparing with droop control.At the same time,it is verified that the PV-ESS VSG can operate stably under the grid-connected mode and islanded mode.Secondly,the adaptive control strategy of grid connected PV-ESS VSG is proposed based on the physical constraints of energy storage.The lead-acid battery is selected as the energy storage device.The value boundary of control parameters is analyzed according to battery’s physical constraints and response characteristics of VSG.The adaptive control strategy of inertia and damping coefficient of VSG is realized by using BP neural network.The effectiveness of PV-ESS VSG adaptive control strategy is verified by simulation.Thirdly,in order to ensure the stable operation of PV-ESS VSG in island state,the energy management strategy is studied to realize the power coordination control between the inverter and DC side.The additional controller of photovoltaic is designed according to the requirement of PV-ESS VSG operation state.Energy management system switches the operation state of PV-ESS VSG to realize the coordinated operation of photovoltaic,energy storage and inverter according to the supply and demand of energy storage,maximum output of photov oltaic and load.The correctness and effectiveness of PV-ESS VSG’s energy management strategy under different conditions are verified by simulation.Finally,because the central controller of microgrid can not make full use of the past regulation experience in the process of frequency regulation,the centralized frequency control strategy based on reinforcement learning is proposed according to the frequency regulation characteristics of VSG.The power shortage of microgrid is calculated by reinforcement learning algorithm.Output power of PV-ESS VSG is dynamically adjusted by Lagrange multiplier method according to the operation cost of PV-ESS.The proposed frequency control strategy is verified by simulation.