Research For The Low Voltage Ride Through Technology Of Direct-driven PM Wind Power Generation System

As one of the cleaner renewable energy sources, development and utilization of wind energy has received worldwide attention and has a broad prospect of the market.In the trend of countries vigorously developing wind power technology, it is found that the voltage drop which will do great harm to the wind power generation system, so the problem of low voltage ride through has gradually become the research hotspot in the world. Many countries set out the guidelines according to their actual research status of wind power technology to solve the problem of low voltage ride through technology.This paper mainly studies on the Low Voltage Ride Through Technology of Direct-driven PM Wind Power Generation System.The main work is as follows:1. The mathematical model of the main parts of the system is established under dq coordinates system. Among them, machine side converter which is used in the rotor field-oriented vector control, the grid-side converter base on net voltage field-oriented vector control.2. Simulation of the system when the voltage sag 50%, 80%, and analyse the system’s operating mechanism and converter over-voltage damage caused by voltage drop.3. Adding the power dissipative crowbar in DC-link and control strategy of reactive power compensation in grid-side are proposed, and take the simulation and analysis by Matlab/simulink software. From the simulation waveform chart of the system can be seen, the proposed protection strategy can make a very good system control of DC-link voltage and provide reactive power compensation for grid, support the recovery of the grid under balanced fault of three-phase grid voltage.4. when the system operation under unbalanced fault of grid voltage, due to grid-side voltage producing negative sequence component, and in the grid-side and DC side will produce the double frequency disturbance, Traditional control strategy cannot make grid side voltage of positive and negative sequence separation, at this time grid side d, q-axis voltage will produce double frequency disturbance, so that the system is not stable enough.Therefore, this paper take the second order generalized integrator phase locked loop(SOGI-PLL) to replace the traditional PLL, grid side voltage of positive and negative sequence separation can be realized by SOGI-PLL. Simulation results show that the SOGI-PLL can not only eliminate grid-side d, q-axis voltage the double frequency disturbance, but also can improve the DC link voltage fluctuation.Based on the above research, the proposed protection strategy can achieve the low voltage ride through technology of the system when the grid symmetrical drop and the asymmetric fall.