Study on the New SVPWM Method for three-level Inverter of Brushless Doubly-Fed Machine

Brushless doubly-fed machine (BDFM) is a new type of AC induction motor. It has a good applicable prospect as the variable frequency motors or the variable speed constant frequency generators. Although the advantage of the three-level inverter, there are also some problems of neutral point voltage balance in this method such as the unbalance of neutral point voltage. And the traditional principle of Three-level inverter space vector pulse width modulation method is to estimate the sectors and calculating a lot of trigonometric functions. To solve these problems, a novel method for the virtual space vector concept in G-H coordinate system is presented in this paper. The method proposed can omit the judging process of the sectors, reduce the calculating burden, and maintain the balance of neutral-point voltage between capacitances within a certain index modulation. The results of simulation are given to validate the improved virtual space vector modulation.