Research On Coordinated Control Strategy Of Inverter In New Energy Microgrid System Based On Virtual Synchronous Generators

With the intensification of energy consumption and environmental pollution,the trend of grid connection of clean new energy power generation systems is further expanding.However,the new energy power generation system with inverter as the grid connection interface does not have enough inertia and damping.At the same time,due to the volatility of new energy output,large-scale new energy grid connection has not only changed the structure of modern power grid,but also threatened the stable operation of power grid,and posed a more serious challenge to ensure the power quality.Aiming at the above problems,the virtual synchronous generator(VSG)technology is used to control the inverter,so that the new energy generation system has damping and inertia,thus improving its voltage regulation and frequency regulation capability.Therefore,on the basis of previous studies,this paper studies the stability control of inverter based on VSG technology.First,the structure of the microgrid system and the basic principle of VSG are briefly introduced,and the two most widely studied VSG models are mainly introduced,and the third-order VSG mathematical model is established with three control links of angle,frequency and torque;At the same time,the method of coordinating the output of photovoltaic and energy storage and stabilizing the bus voltage at the DC side of the microgrid is given,which provides a preliminary basis for subsequent research.Secondly,an adaptive integral sliding mode backstepping control strategy based on VSG is proposed to improve the transient stability of single VSG system.In the design process of the controller,based on the idea of backstepping control,the integral sliding surface is used to construct the controller,which can restrain the adverse effect of disturbance on the system to a certain extent.And the adaptive disturbance estimation technology is introduced to increase the accuracy of the controller.The simulation results verify the effectiveness of the strategy.Then,aiming at the problem of coordinated operation control between different VSGs,a power distribution strategy is proposed.On the premise of ensuring power distribution,a coordinated adaptive integral sliding mode backstepping control strategy based on VSG is designed to further stabilize the transient operation process of the system.To ensure the consistency of dynamic response of multi-VSG system under disturbance,the frequency correlation term of adjacent VSGs is introduced on the basis of traditional VSG model,and an improved VSG model is obtained.On the basis of this model,some parameters are selected through power distribution strategy,and the controller is redesigned according to the design idea in Chapter 3,which improves the transient performance of the system.The differential expansion problem is solved by the command filter.The simulation results verify the effectiveness of the strategy.Finally,in order to further improve the transient performance of the system and solve the problem of frequency error caused by the long time existence of load change,a VSG-based Frequency Error-free Coordination adaptive integral sliding mode backstepping control strategy is proposed.The torque error compensation term was introduced to further improve the VSG model,and some parameters of the model are selected to ensure that the power distribution can still be achieved in steady-state;At the same time,combined with the design idea in Chapter 4,the controller is redesigned to realize that the system operating frequency can be stabilized near the rated frequency when the load exists for a long time,so that the system transient performance can be effectively improved.The simulation results verify the effectiveness of the strategy.