An Improved PWM Method of Five-Leg VSI Fed Dual-PMSM System With Duty Cycles Regulation

The five-leg voltage source inverter dual motors system has been widely studied in recent years for its advantage of fewer power switching devices. The traditional modulation method generates the voltage vectors needed by the two motors alternately in one control period, in which active voltage vectors of one motor can operate for a short time thus limit the speed ranges of the two motors. Regarding the deficiency, the relationship between the basic active voltage vectors of the two motors is futher analyzed and an improved pulsewidth modulation (PWM) method is proposed in this article, by which the duty cycles of five-phase PWM signals are modified as a whole. Under the premise that the common leg pulse width meets the requirements of the two motors in one control period, the effective time of the active voltage vectors of the two motors is tremendously expanded with no hardware added, and the speed ranges of the two motors are thus greatly expanded. When one motor runs at a relatively low speed, the speed range of the other motor can be effectively expanded with this method, compared with the traditional one. Simulations and experiments also verify the accuracy of the theoretical analysis and the feasibility of the proposed method.