Research On Fault Ride-through Strategy For Direct-drive Permanent Magnet Wind Power System

As a kind of important renewable energy, wind energy has drawn the world’s attention. Because wind power generation is one of the most effective forms to utilize wind energy, it has made a rapid development. With the increasing percentage of wind power, the reliability of wind farms during faults has a great influence on the safety and stability of grid. So most countries have proposed strict standards for the fault ride-through performance of the wind power generation system. Due to the high efficiency, wide range of applicable areas and easily maintenance, wind energy generation based on the direct-driven permanent magnet synchronous generators (PMSG) has accounted for a large proportion in low wind speed land wind farms and offshore wind farms. So the research on the fault ride-through methods of the direct-driven PMSG wind-power system has great significance.Because of the low switching frequency of the converter, there are many harmonic components in the the grid voltage. Then the current is rich in low-frequency harmonics too, which results in reduced motor life and the descent of wind-farms’power quality. This paper presents the proportional multi-resonant (P-MR) current loop controller to improve the performance of current harmonic suppression and tracking performance, especially to improve the performance of current controller under the poor quality of the voltage during grid faults. The controller is verified by simulation and experiment. The results indicated the higher harmonic suppression performance and tracking control ability of this type of controller.The conventional grid-connected control during the unbalanced grid faults will produce pulsation of grid-connected power and the DC bus voltage. To suppress the power fluctuation and ensure the maximum output power of the converter at the same time, the paper proposed a control strategy to maximize the output active power of the grid-side converter. To solve the unbalance problem of the wind turbine input power and grid-connected output power during grid faults, this paper presents a control strategy of the motor-side converter based on the rotor energy storage of the wind turbine. At last, this paper conducted a variety of simulations under different grid fault conditions to verify the above control strategies. The results show that the proposed control strategy can successfully ensure the safety and stability of wind turbine under the grid failure.Finally, this paper made a summary and prospected about the work, by indicating unsolved problems and the direction of further improvement.