The Research Of Doubly Fed Induction Wind Generator’s Riding Through Low Voltage

In conventional energy depletion and actively promote the development of new energy background, wind power has become a hot research object in the world. With the development of wind power generation technology, the capacity of single machine is rising, and the power of wind power is becoming more and more important position in the power system. Because of the characteristics of wind power, wind power system once appeared fault, the disturbance of power grid and wind turbine system itself is greater than the traditional thermal power and hydropower. All the countries in the world have made the corresponding provisions of grid connected wind power generation system, the most important point is that the wind power system must have a low voltage ride through capability in provisions, the grid voltage can’t exceed the standard of drop range. During the period of the fault, it is necessary to ensure that the wind turbines are not separated from the power grid in a certain range, to supply the stable and efficient power, wind turbine itself supplies reactive power to support power grid, helps to restore the grid that can work the normal voltage level, makes the whole system work the normally.In this paper, according to the working principle of double fed induction generator, utilize the ideal mathematical model of doubly fed induction generator, accomplish the system simulation of low voltage ride through of doubly fed induction generator. Finishing and summarizing the control strategy and hardware protection of the doubly fed induction generator proposed by domestic and foreign scholars. Study vector control strategy, direct power control strategy, direct torque control strategy, comparing the traditional technology with the new improvement of the control technology, expound the advantages and disadvantages of them; and study the circuit protection technology of rotor side and DC side, such as Crowbar and Chopper of the hardware protection equipment. Secondly, with the help of Simulink electrical module in MATLAB simulation software, create the simulation structure of grid connected doubly fed induction generator. Through the simulation of double fed generation system, the simulation of the grid is symmetrical and asymmetrical fault, voltage drop depth is different, through the simulation of doubly fed induction generator, according to the stator and rotor of the corresponding output waveform, analysis the changing characteristics of current parameters of stator and rotor, the voltage drop is serious, DFIG rotor loop current is bigger, it need to add protection device on the rotor side. Finally, the factors affecting the effect of Crowbar protection circuit are studied, how to choose the resistor of active Crowbar circuit, based on the principle and formula derivation, to select the appropriate energy release resistance. Design Crowbar simulation module of IGBT type, establish doubly fed wind turbine system simulation model with energy release resistance of IGBT Crowbar circuit, the simulation of transmission line occur three kinds of fault cases, grid voltage drops, to observe double fed induction generator of the improvement with Crowbar circuit. Through the validation of simulation experiment, the design Crowbar protection circuit inhibits surge current in the rotor circuit, preventing protection device will cut doubly fed wind power generator set off the grid, effectively enhances low voltage ride through ability of the doubly fed wind turbines.