Research On Control Strategy Of Inverter Based On Virtual Synchronous Generator

With the increase of the capacity of new energy power generation connected to the power grid,the proportion of traditional synchronous generators with inertia and damping in the power grid is becoming smaller,resulting in the entire power grid exhibiting low damping characteristics,responding to load fluctuations and frequency changes Capacity is increasingly insufficient.Therefore,it is imminent to improve the control strategy of grid-connected inverters,and the new type of Virtual Synchronous Generator(VSG)control technology is to solve this problem.The VSG control strategy not only enables the inverter to have the damping and inertia of the synchronous generator,but also allows it to participate in frequency and voltage regulation of the power grid like a synchronous generator.Therefore,it is of great significance to study the key technologies of virtual synchronous generators.The mathematical model of the three-phase bridge inverter is established,and the electrical and mechanical mathematical model of the VSG is established by studying the model of the traditional synchronous generator.Analyze the voltage and frequency regulation function of traditional synchronous generators on the power grid,and design the control link of VSG.The simulation verifies the correctness of the control technology of the virtual synchronous generator.An improved cooperative adaptive control method of moment of inertia and damping coefficient is proposed.Analyze the effect of moment of inertia and damping coefficient on the output power and frequency of VSG.By analyzing the power angle curve and the angular frequency oscillation curve of the synchronous generator,the relationship between the frequency change rate and frequency increment and the moment of inertia and the damping coefficient is determined.Therefore,a coordinated adaptive control strategy for moment of inertia and damping coefficient is designed,and the correctness and superiority of the proposed control strategy are verified by simulation.This paper proposes a differential LVRT control strategy for VSG.The technical requirements of VSG low-voltage ride-through are given,and the effect on the virtual synchronous generator in the event of a short-circuit fault in the power grid is analyzed.In order to make the grid-connected inverter comply with the requirements of low voltage ride-through when the power grid is short-circuited,the fault short-circuit current is differentiated.When the short-circuit current is small,a virtual resistance control method is used,and when the short-circuit current is large,a direct quasi-PR control Current control method.The simulation verifies the correctness of the proposed differential LVRT control strategy of the virtual synchronous generator.A balanced current control strategy based on voltage-compensated stationary coordinate system is proposed.To analyze the output current characteristics of VSG when the grid voltage is unbalanced in three phases,in order to balance the three-phase current output of the VSG,a control strategy balance of positive and negative sequence separation control in static coordinates is proposed.In order to be able to suppress the power double-frequency oscillation,the positive sequence voltage is compensated before the balanced current control,and the negative sequence voltage is suppressed.The simulation verifies the balance effect of the proposed control strategy on the gridconnected current and the suppression effect of the power double frequency.The paper has 55 figures,3 tables,and 89 references.