Method For Improving Low Voltage Ride Through Ability Of Doubly-Fed Wind Generators

With the increasing proportion of wind power capacity of total power system, wind power grid security and stability are very important. Various countries of the world have established the low voltage ride through standards consistent with their respective national conditions. Doubly-fed wind turbines defect to withstand the grid failure, and therefore the study on the low voltage through technology based on DFIG has a very important significance.Through study working principle of doubly-fed wind turbine, the DFIG system wind speed, wind turbine, doubly-fed generator and inverter in the three-phase stationary coordinate system (abc) and synchronous rotating coordinate system (dq) mathematical model were established. Double closed loop vector control mathematical model of DFIG rotor side was based on the stator flux oriented strategies of outer power ring and inner current loop. Double closed loop vector control mathematical model of DFIG DC side was based on the grid voltage oriented strategies of the outer voltage ring and inner current ring. Low-voltage operating characteristics of the double-fed wind turbine simulation study results show that:when the drop of voltage is more severe, result in over-current, over-voltage will pose a serious threat to grid security.The need to add hardware circuit method is the only solution. In order to improve the the DFIG low voltage ride through capability, the rotor side Crowbar over-current protection circuit and the DC side Chopper over voltage protection are used in the paper. Finally, the various factors that affect the protective effect are analyned through simulation. Simulation results show that this protection program can effectively suppress the rotor side over-current and the DC side over-voltage to protect the DFIG converter; it is possible to achieve a better low voltage ride through, to cope with new requirements of the grid.