The Research Of Low Voltage Ride-through Technology Based On Doubly-fed Induction Generators

With the large-scale centralized wind farms constructing, wind power is with an increasing proportion in the power system. The construction speed of network is far behind relatively, so the grid security and stability can not be ignored influenced by wind power. Many Countries have already established the standard of low voltage ride-through according to their own national conditions. During grid faults, the doubly fed induction wind generators have some defects, so the research to DFIG of low voltage ride through technology has very important significance.This paper mainly investigates the double-fed induction wind generator. Analyze the operation principle and establish the mathematical model of wind speed, wind turbine, transmission structure, double-fed induction generator and the converter on DFIG system. A two-loop vector control based on decoupling active power and reactive power of DFIG mathematical model is established. The mathematical model of stator phase transient current which is under the condition of the voltage drop is derived. The low voltage operation characteristics based on doubly fed induction wind generator is simulated and analyzed. The results indicate :when the voltage drop is at a low range, the DFIG can ride through with primary controls; but the voltage drop is at a high range, the DFIG security will be faced with severe threaten because of the appearance of over voltage and over current. In order to improve the low voltage ride through capability of DFIG, the paper adopts two kinds of the measure which are crowbar protection circuit of rotor side and consumption energy Circuit in DC link. Finally, the effect of crowbar protection is analyzed with three factors. The simulation results indicate that the rotor side and DC link equipping with the protection circuit can inhibit the rotor side over-current and over voltage in DC link during grid voltage drop so as to protect generator and converter. The study of this paper shows that the designed protection circuit can be better achieved a low through voltage to confront with the new requirements of grid.