Control Research Of The Converter To Direct-drive Permanent Magnet Wind Generation System

Permanent magnet direct-drive synchronous generator (PMSG) which eliminates the gearbox and reduces the maintenace has become an important research subject besides the Double-fed inductor generator . The full scale power converter is a key part of the wind power system.In the traditional wind power system the two-level converter is mostly adopted. With the increasing of unit capacity,the full power three-level converter with switch voltage stress reducing is suitable to a direct drive wind power system .This paper analyzes the mathematical model of the full power converter of the direct drive wind generator. The converter use the diode damped three-level inverter as its topology. It also analyzes the dynamic and operating characteristics of the wind turbine and studies the control strategy which takes the method to track the optimal speed under the rated wind speed.This paper also analyzes the grid side of the three-level inverter mathematical model and the three-level SVPWM modulation principle. It adopts the mid-point voltage balancing hysteresis factor to inhibit the midpoint voltage offset.Through the grid voltage-oriented vector control, the DC-side of the three-level grid inverter achieves a stable DC bus voltage and by controling the reactive power current, the reactive power is regulated independently.The study of vector control of the direct-drive permanent magnet synchronous wind turbines based on three-level converter is carried out in this paper. Further more, a detailed comparative study of two-level system and three-level system is conducted. The simulation results, three-phase current waveforms, the electromagnetic torque waveform are given. The analysis results show that the current harmonics are significantly reduced and the electromagnetic torque ripple is improved after the application of three-level converter.In the end, three-level grid converter experiment equipments are designed, which conclude main circuit of three-level inverter, drive and protect circuit and auxiliary power.