An Improved Three-level Direct Torque Control Method of Brushless Doubly-fed Machine Based on the Fixed Synthesizing Vector

Article history: Received: 11. 09. 2013. Received in revised form: 17.10.2013. Accepted: 17.10.2013. With the rapid growth of an AC adjusted speed system application, it is necessary to control and reduce harmonic pollution since the problem brought about by the device of power electronics not only blocks the development of power electronics technology, but also causes severe harm in an electric power system. In this paper an improved three-level direct torque algorithm for brushless doubly-fed machines has been developed for reducing the torque and flux ripples in a brushless doubly-fed machine. This method based on 48 fixed synthesizing vectors is implemented in the brushless doubly-fed machine. Compared with the traditional two-level direct torque control algorithm, this new method broadens the selection range on voltage vectors. It also effectively reduces the torque ripples and improves the properties of the magnetic chain track. In addition, this algorithm improves the dynamic performance and robustness of both the brushless doubly-fed machine and its control system. To validate the proposed method, some mathematic simulations have been done so that the simulation results have shown the effectiveness of the proposed method. Moreover, this proposed method has been implemented in the brushless doubly-fed machine system showing an enhancement in the motor performance.