Research On Grid-connected Control Of Double-fed Fan Based On Virtual Synchronous Generator

Wind power has been the most mature of new energy power generation technologies in recent years.However,as the installed capacity of wind power generation connected to the power system increases year by year.The fluctuation and unpredictability of wind power have become important factors affecting the stability of grid-connected operations.The grid-connected inverter does not have a stationary component of the moment of inertia and cannot have the role of inertia to support the frequency adjustment of the system like a synchronous machine.Aiming at the above problems and drawing on the operating experience of traditional power systems,a control system for gridconnected wind turbine power generation based on the principle of Virtual Synchronous Generator(VSG)was proposed.The interface characteristics of the parallel output of the energy storage system and the wind farm are used to simulate the external characteristics of the synchronous generator,which is equivalent to a virtual synchronous generator to compensate the inertia of the wind farm.Reflecting the characteristics of synchronous generators to the power system,the inverter power output has a certain inertia and damping,which improves the frequency stability of the system when it is subjected to load disturbances and fluctuations in new energy output,which effectively improves the efficiency of the grid-connected wind turbine power generation system.This paper first combines the mathematical model of the grid-connected inverter and the mathematical model of the synchronous generator to derive the control algorithm of the virtual synchronous generator,analyzes the implementation principle of the virtual synchronous generator.The controller is modeled and simulated,including active frequency controller,reactive voltage controller and ontology algorithm.And the establishment of doubly-fed fan model,including wind speed model,wind turbine operating characteristics and motor,and listed mathematical models,analyzed its power characteristics,and verified the effectiveness of the control strategy.Then use simulation software to build system models of VSG and droop control strategy.Through comparison and simulation,it is verified that the VSG control strategy can increase the effect of the system’s equivalent inertia.At the same time,the key control parameters in VSG control are studied,mathematical models of inertia,damping and adjustment coefficient parameters are given.A small-signal model of the inverter power supply is established,and its influence on the dynamic stability of the system is discussed.Finally,simulation verification is performed for three different operating conditions.The frequency stability law is obtained to provide a certain reference for the selection of control parameters.Finally,the structure of a double-fed wind turbine grid-connected power generation system based on a virtual synchronous generator control strategy is introduced.The virtual synchronous inertia-controlled energy storage device is applied to the grid connection of the doubly-fed wind power generation system.The interface characteristics of the parallel output of the energy storage system and the wind farm are simulated to simulate the external characteristics of the synchronous generator,which is equivalent to a virtual synchronous generator.Based on the Matlab platform,the external characteristics of the virtual synchronous generator and the grid-connected regulation characteristics are simulated and verified.The simulation verified that the designed VSG doublyfed fan can effectively simulate the inertial response characteristics and frequency response characteristics of actual synchronous generators.When subjected to external disturbances,the virtual inertia control strategy can quickly suppress the output power fluctuation and assist the wind farm to achieve virtual inertia control,and reduce the range of system frequency fluctuations to enhance the stable operation of the system.