Virtual Synchronous Generator Droop Control Technology And Its Application

With the increase of distributed energy and the reduction of the installed proportion of traditional synchronous generators,the rotating capacity and moment of inertia in the power system will inevitably be reduced accordingly.As a result,the safety and stability of grid operation will be difficult to guarantee.Moreover,with the increase of power generation permeability,the characteristics of low inertia and under dampening will have a drastic effect on the operation stability.Especially when the operation of islanding,the decrease of frequency and voltage will have serious negative consequences.In addition distributed energy also has the characteristics of volatility,may cause instability in the operation,especially the inverter control strategies are also different,it is difficult to ensure that when the grid can plug and play and intelligent operation.Therefore,the concept of virtual synchronous generator(VSG)is proposed for the above grid-connected distributed generation problem.VSG can simulate the electromagnetic characteristics and electromechanical characteristics of synchronous generator through the control strategy of grid-connected inverter and PWM to generate the virtual moment of inertia.By changing the control scheme of inverter and the switching frequency of IGBT,VSG can adjust the voltage of distributed power supply And frequency,VSG can also better adjust the system distributed power of active and reactive power.Therefore,the second chapter of this paper focuses on the mathematical model of VSG and its working principle,and on this basis,analyzes the influence of different parameter adjustment on the VSG output voltage and power.Determining the damping coefficient and moment of inertia as the main influencing factors of the output power oscillation when the DG is connected to the grid,adjusting these two parameters can reduce the output time and amplitude of the oscillation and further increase the grid connection stability.Based on the above conclusions,an improved control strategy based on active-frequency droop control is proposed.Double closed-loop control can increase the damping coefficient,reduce the amplitude of active power of virtual synchronous generator and shorten the adjustment time of transient process,Greatly improving the stability of distributed power grid.In the end,this paper establishes a photovoltaic virtual synchronous generator model in PSCAD,simulates the control strategy and compares it with the traditional droop control method in terms of active power,reactive power and frequency,and concludes that the improved droop Control can effectively improve the damping coefficient of VSG and increase the grid-connected stability of distributed generation.