Study On Low Voltage Ride Through Of PMSG Wind Power Generation System

The low voltage characteristics of direct drive permanent magnet wind power generation system are studied in detail. On the basis of analyzing the traditional hardware protection circuit and control strategy,an improved feed-forward control strategy is proposed, and the practicability and reliability of the scheme are verified by simulation analysis and experimental verification.Firstly, the basic characteristics of the wind turbine are studied, the conversion principle of wind energy to mechanical energy and the power characteristics of the wind turbine are described. The mathematical model of PWM converter is established. The traditional steady state control strategy is analyzed. The validity of the mathematical model and the control strategy are verified by simulation.Secondly, analyzed the transient drop under the voltage of direct drive permanent magnet synchronous wind energy machine, the protection circuit has been designed based on Crowbar, this paper gives a method of judging mainly, supplemented by DC voltage DC input output power difference, as switching circuit based on Crowbar, and the grid voltage different sags were simulated, results show that, the method solves the problem of single use of DC side voltage unloading resistance problems of frequent switching, and can make the grid side converter in low voltage fault quickly by the unit power factor mode conversion to reactive power compensation mode(STATCOM), effectively improve the low voltage ride through capability of direct drive wind power system.Finally, the combination control strategy is proposed to improve the low voltage ride through capability of the unit, which is based on the control of the side speed, the reactive power compensation mode and the Crowbar circuit. The simulation results show that the control strategy canmake the DC voltage more stable when the grid voltage drops. Then the experimental platform was designed and developed.