Analysis Of Sub-Synchronous Oscillation Characteristics Of Doubly-Fed Wind Farm And Research On Multi-Turbine Cooperative Mitigation Strategy

Because wind power generation is clean and environmentally friendly,has little impact on the environment,and its technology is relatively mature,it has developed rapidly in the world in recent years.With the development of wind power technology in China,the installed capacity of wind power is increasing and the scale of wind farms is expanding.But as a result of domestic wind resource centers do not agree with the center of the load,wind power should be transmitted over a long distance,using series capacitor compensation technology which is widely applied and can effectively solve the problem of wind power long-distance transmission.But at the same time,the Sub-synchronous Control Interaction(SSCI)between the doubly-fed wind power generator control loop also bring risk of subsynchronous oscillation(SSO).Therefore,this paper mainly studies the subsynchronous oscillation of the doubly-fed wind farm with series compensated power grid.In this paper,the impedance model of doubly-fed wind turbine considering the grid-side converter(GSC),the roter-side convertor(RSC)and the phase-locked loop(PLL)is established,and the time-domain simulation model is built in Simulink.The correctness of the impedance model is verified by frequency scanning method.On this basis,method of building the impedance model of multi-DFIGs and the corresponding impedance stability criterion are put forward,and followed by the doubly-fed wind power subsynchronous oscillation stability criterion and the quantitative analysis method.Take the two-machine system as an example,builds the corresponding simulation model to verify its correctness,laying the foundation for subsequent influencing factor analysis and mitigation strategy design.Secondly,the calculation methods of frequency-domain normalized sensitivity and interval average sensitivity are proposed,and the effects of the proportion and integral parameters of rotor side converter current loop,grid side converter current loop and phase-locked loop on the system impedance and subsynchronous oscillation characteristics are analyzed in detail by this method,and the main influencing parameters are found out.Based on the impedance model and impedance stability criterion of the two-machine system,the influence of different wind speeds and control parameters on the SSO characteristics of the whole grid-connected system between closer wind turbine and further wind turbine is compared and analyzed.The simulation model verifies the correctness of the analysis results.Finally,two subsynchronous oscillation mitigation strategies for doubly-fed wind farms are proposed.First one SSO mitigation shceme for wind farms based on the multiple machines speed coordinating control is proposed,at the expense of a few loss of active power,by limiting part of the minimum rotate speed of low wind speed unit to improve the system stability at subsynchronous frequency,in which the minimum rotational speed command coordination optimization for different units is used to minimize the loss of active power.Then,a controller parameter optimization method based on orthogonal experimental optimization,comprehensive weight analysis and particle swarm optimization is proposed.By optimizing the main influencing parameters of sub-synchronous oscillation for wind turbies at different positions,the dynamic performance of the unit and the system stability in sub-synchronous frequency band are both improved.Finally,the effectiveness and superiority of the two mitigation strategies proposed in this paper are verified by simulation.