| With the swift depletion of traditional fossil fuels,climate warming and environmental pollution caused by the emission of a large number of carbon dioxide and harmful gases make people must pay more attention to the progress and exploitation of green energy.In the past few years,because of its widely distributed,it contains large amount of wind power,the advantages of recycling has been the research hot spot of people.Electricity from wind power is environmentally friendly.As the rapid increase in the proportion of grid-connected wind turbines in the power grid,the safety and reliability of wind power systems plays an increasingly important role in complex power systems,at the same time,wind farms must adopt more stringent requirements,low voltage across ability is indispensable for a wind farm.When the voltage drop fault occurs in the power grid,the wind turbine can operate on the grid in a short period of time,which greatly improves the reliability of power supply in the power system,which means that the wind turbine must have higher operating requirements and must adopt certain control strategies to achieve fault crossing,otherwise it will not only lead to the converter damage of the unit,but also lead to a larger area of off-grid accidents of the unit Therefore,the study of fault traversing strategy plays an important role in the operation control of doubly-fed units.Doubly-fed wind turbine is the main research object in this paper.And in this paper,briefly describes its basic operation theory,deduces and establishes the mathematical models of basic electrical quantities in different coordinate systems,and studies and analyzes the general vector control strategy of rotor-side converter under ideal grid conditions.The mathematical expression of the related electrical quantity of doubly-fed motor when the voltage sag occurs in the grid is emphatically analyzed,and the possible adverse effects of the voltage sag on the unit are pointed out.In the two-phase static coordinate system,the analysis of the mathematical expression shows that the cause of the rotor fault overcurrent is the slow attenuation of the DC component of the flux linkage.To restrict large over current in order to protect the safety of the rotor side converter,this paper USES the virtual resistance control strategy,through additional resistance in the rotor of the equivalent circuit,on the one hand,from the intuitive increases the circuit the total resistance so as to decrease the rotor current,on the other hand can accelerate flux attenuation quickly to the dc component of the rotor current limit within the scope of the permit.Virtual resistance tolerance due to the inconvenience setting,if a given improper will cause the problem of high rotor voltage rise.In this paper,fuzzy control is used to adjust the resistance of virtual resistance for the first time,under several different depth of voltage drop failure.By using the control strategy proposed in this paper,the peak current of the rotor can be limited while the rotor voltage is not too high,and the value of virtual resistance given more flexible,which extremely simplifies the control strategy,the low voltage ride through strategy of doubly-fed wind power generator is improved in the meantime.Firstly,the model is established on Matlab/Simulink platform,and the power control and variable speed constant frequency control of doubly-fed wind turbine are simulated and verified under ideal grid conditions.Secondly,under the condition of voltage sags of different depths,the changes of related electrical quantity are analyzed and studied.Virtual resistors are added and the effectiveness of traditional control strategy is verified.Then,based on the traditional control strategy,a fuzzy controller was designed to verify the control strategy using fuzzy control virtual resistance.And the feasibility of the conventional strategy and the fuzzy control strategy presented in this paper were compared under the same voltage drop depth.Finally,the hardware circuit involved in this paper is debugged on the experimental platform of doubly-fed wind power generation system,and related software programs are designed for the control strategy.Combined with software and hardware,the improved control strategy in this paper is experimented and verified. |
