Transient Control Optimization Of Full-size Power Converter Wind Turbine Based On Virtual Flux

With the increasing penetration of wind power in the power system,even in the local power grid,the impact of wind turbines on the dynamic process of power system is increasing.Wind turbine plays an important role in more and more system stability problems.Therefore,how to improve the transient support capacity of wind turbine without off grid operation has become an urgent problem.Based on the multi-scale sequential control of full-size power converter wind turbine,this paper analyzes the formation mechanism of internal voltage of fullsize power converter wind turbine,and further reveals the relationship between internal voltage amplitude frequency,terminal voltage amplitude frequency and current.Then,based on this relationship,a amplitude-frequency control method is proposed,which takes the ratio of internal voltage amplitude to frequency as the control target.Finally,the effectiveness of the method is verified by simulation,and the influence of control parameters on the transient support effect is studied.The details are as follows:(1)Based on the typical control of full-size power converter wind turbine,each control link and hardware protection circuit are introduced.According to the capacity of energy storage element and the response speed of controller,the characteristics of full-size power converter wind turbine equipment can be divided into three types: current control time scale,voltage control time scale and speed control time scale,which have the characteristics of sequential action / transient switching in multiple time scales.On this basis,the dynamic problems of grid connected system corresponding to different control time scales are further introduced.It is pointed out that the problem concerned in this paper belongs to DC voltage control time scale.(2)Based on the introduction of the basic concept of equipment internal voltage,this paper analyzes the dynamic behavior of the internal potential of full-size power converter wind turbine under the time scale of DC voltage,has a preliminary understanding of the formation path of its amplitude frequency,and explains that the internal voltage has the characteristics of time-varying amplitude frequency in the dynamic process.Based on the simple inductance circuit,the relationship between voltage and current under the excitation of time-varying amplitude frequency signal is analyzed.Under the excitation of internal voltage and terminal voltage with time-varying amplitude frequency characteristics,the relationship between the passing current on filter inductance of full-size power converter wind turbine and both is analyzed.(3)The traditional transient control method of full-size power converter wind turbine is described,and the response characteristics of the control scheme to the system voltage amplitude and frequency dynamics are summarized.Then,according to the relationship between internal voltage time-varying amplitude frequency,terminal voltage time amplitude frequency and current,it is shown that under deep fault,the internal voltage amplitude frequency can uniquely determine the current command allocation due to the saturation of converter capacity under deep fault.The ratio of amplitude to frequency of internal electromotive force is defined as "virtual flux",which shows that it can be used as a control target to generate current instructions.An amplitude-frequency control method based on virtual flux is proposed and its characteristics are analyzed.(4)The detailed time-domain simulation shows that the full-size power converter wind turbine with amplitude-frequency control has good fault ride through capability and can provide stronger transient support capability for the system compared with the traditional transient control.Based on the four machine two zone model,the effectiveness of the amplitudefrequency control is verified in the sending and receiving regions respectively.By changing the control parameters,the influence of the control parameters on the transient support capacity of the full power wind turbine is analyzed,and it is shown that there is an optimal range of the control parameters.