Research On Low Voltage Ride Through Control Strategy Of Virtual Synchronous Generator

With the rapid development of renewable energy power generation technology represented by photovoltaics,in order to improve the operating characteristics of grid-connected inverters,this article introduces Virtual Synchronous Generator(VSG)technology,by drawing on the operating characteristics of synchronous generators,The inverter has the characteristics of inertia,damping and frequency regulation.However,the traditional VSG technology does not have the capability of low voltage ride through when the power grid falls.In response to this problem,this thesis takes the photovoltaic grid-connected power generation system based on VSG control as the research object,and proposes a low-voltage ride-through control strategy that combines power-limited improved balanced current method and DC voltage regulation.First,through the analysis of the second-order mathematical model of the synchronous generator,the active frequency controller and the reactive voltage controller of the virtual synchronous generator are designed,and the design of the virtual synchronous generator power loop is completed.The control requirements are designed for current and voltage closed-loop control.Secondly,a low-voltage ride-through control strategy combining power-limited improved balanced current method and DC voltage regulation is proposed.Analyzed the positive and negative sequence separation method,detailed analysis of the balanced current method control strategy,put forward the power limit control strategy,and improved the balanced current method using mixed-order linear auto-disturbance control to suppress the inrush current and the instantaneous voltage drop of the grid Steady-state over current to achieve three-phase current balance.At the same time,a DC voltage stabilization control strategy based on linear auto-disturbance control is designed to quickly absorb the excess energy during thepower grid drop and stabilize the DC bus voltage around the rated value.Finally,this thesis builds a low-voltage ride-through simulation model based on VSG control on the MATLAB/Simulink simulation platform.The symmetrical and asymmetrical drops of VSG were simulated separately,and the simulation results were analyzed to verify the effectiveness and reliability of the control strategy proposed in this thesis.