Research On Direct Torque Control Of Three Level Converter For Direct Drive Permanent Magnet Synchronous Wind Power Generator

As a kind of renewable energy, wind energy is an inexhaustible green energy source, and its development and utilization is of great significance to reduce the consumption of mineral resources and reduce environmental pollution.The direct drive permanent magnet synchronous wind power generation system is connected directly with the wind turbine by a permanent magnet synchronous generator, reduce the gear box transmission links, improve system reliability and reduce noise, has good low-speed performance, power efficiency etc.,which have been widely used.In order to make full use of wind energy, under the rated wind speed, the wind power generation system usually adjusts the speed of the wind turbine according to the change of wind speed. As an effective control strategy of AC motor, vector control has the advantages of good dynamic performance, but its dependence on motor parameters is large, and it needs a series of coordinate transformation.The direct torque control strategy has the advantages of simple algorithm, small dependence on motor parameters, fast dynamic response and so on.In this paper, the direct torque control of permanent magnet synchronous generator is studied.Firstly, the mathematical model of direct drive permanent magnet synchronous generator is established, and the working principle and direct torque control strategy of permanent magnet synchronous generator are analyzed. Due to the existence of direct torque control for the large torque ripple, proposed direct drive direct torque control strategy for permanent magnet synchronous generator torque and flux prediction based on the torque and flux prediction for the next time, to calculate the voltage vector to compensate. The simulation results show that the control strategy can achieve maximum wind energy tracking, and the torque ripple is greatly reduced.Secondly, this paper analyzes the causes and harms of the unbalanced voltage of the three level converter, and discusses the influence of various switching vectors on the neutral point potential. On this basis, based on the midpoint potential balance control strategy of small vector time adjustment, neutral point potential fluctuations effectively inhibited the small vector generated, but the fluctuation of neutral point potential of this control strategy can not suppress the vector caused by. Therefore, the proposed converter DC side based on zero point charge (?Q=0) the neutral point balance control strategy, through the neutral point current is zero, the fluctuation of neutral point voltage suppression. The simulation results show that the control strategy can greatly reduce the neutral point potential fluctuation, and improve the output voltage waveform, harmonic content is greatly reduced.Finally, the simulation results of the proposed control strategy on Matlab/Simulink platform are given to verify the effectiveness and correctness of the control strategy.