Distributed Virtual Synchronous Generator Based Control Stategy With Pmsg For System Active Support

In recent years,wind power has developed rapidly because of its many advantages.However,with the increase of the wind power proportion,the problems due to the decline of inertia and damping of the power grid have emerged,which affect the stability of frequency and voltage in power system.Therefore,it is imperative for wind power to participate in the voltage and frequency regulation of the system.To solve the above problems,this paper applies the control strategy of virtual synchronous generator(VSG)to the grid-connected control of permanent magnet synchronous generator(PMSG)based wind turbine.The machine side converter adopts constant DC voltage control to maintain the DC voltage.And the grid-side converter adopts VSG control strategy to control strategy.Compared with traditional control strategy of the converter,the control strategy of VSG with voltage source model can simulate the active power-frequency and reactive power-voltage dynamic characteristic of synchronous generator.Meanwhile,it can also adjust the moment of inertia and damping and impedance of the system.It is great significance to participate in the voltage and frequency regulation of the system and enhance the capacity of wind turbines active support.Firstly,the topological structure and model of PMSG based wind turbine and the control strategies about it’s active power are analyzed.The virtual inertia of wind turbine is modeled and analyzed the principle and function between inertia support and primary frequency modulation in active support control strategy.Then,a control strategy of voltage source based VSG is discussed in detail.Compared with the traditional synchronous generator,the exciter and frequency modulator and inner loop controller are designed.The actual physical parameters of the system are combined into the virtual winding design to eliminate its influence on the converter control.At the level of electromagnetic transient,the transfer function of the controller is deduced,and the influence of controller parameters change to the system stability is analyzed in the complex frequency domain by using the bode diagram.At the same time,the relationship between the power allocation of high wind power proportion system and the parameters design of VSG is analyzed.Through the above analysis,the comprehensive selection principle of VSG parameters is discussed.Finally,the control strategy is extended from single machine to multiple machines,the equivalent model of multiple parallel PMSG based wind turbine is constructed,and the parallel DC control strategy of multiple wind turbines based on DC together is proposed.The active support capability of VSG based multi-machine DC grid-connected system is studied.The parallel control strategy of multiple units based on DC convergence can effectively avoid voltage synchronization and harmonic problems in AC convergence control strategy.It can also reduce the number of grid-side converters and improve the economy.According to different control modes of DC bus voltage,the difference between master-slave control and DC droop control strategy is analyzed and compared.And then,the method of using DC capacitance to provide virtual inertia is proposed.In order to verify the proposed control strategy,a simulation model was built in PSCAD/EMTDC to verify the correctness of the proposed control strategy under different operating conditions and modes.