The Study Of Low Voltage Ride Through For The Variable Speed Constant Frequency Doubly-Fed Induction Generator

With the background of highly rise demand of energy, gradual exhaustion and huge waste of traditional energy, new energy has a very fast developing speed, and wind energy has been seen as the first choice of new energy. With the installed capacity of wind power becoming larger, wind power has become more and more important in power system, the grid also proposes higher requirements for wind power technologies. The low voltage ride through(LVRT) technology is one of the most important technologies.At first, this passage introduces the current research conditions of wind power and LVRT, and some usual LVRT technologies. Then do analysis on variable speed constant frequency doubly-fed induction generator (DFIG)and dual PWM model, the mathematical models of DFIG, grid side converter (GSC)and rotor side converter (RSC)are set up in dq coordinate system, the stator flux oriented control and improved control strategies are researched based on the mathematical models.Then the voltage dip and LVRT are studied, as well as the transient response of DFIG. After the comparison in the advantages and disadvantages of active and passive Crowbar circuit, this passage chooses the active Crowbar circuit based on GTO to achieve the LVRT. After the voltage dip, rotor current rises sharply, triggering the Crowbar circuit, short circuit the RSC. When the current recovers to some value, cut off the Crowbar, to shift the RSC into normal work. And the range of resistor value is gotten from the limitation of rotor current and bus voltage.At last, simulation model is set up in Matlab/Simulink, the optimal value of Crowbar resistor is determined through simulation. At small value voltage dip and large value voltage dip conditions, the comparison of simulation results with Crowbar and without it, shows that this method can do a better control of rotor overcurrent, bus overvoltage and torque oscillation; it can also provide passive power to grid during the fault. So this method satisfies the requirements of LVRT...