An Improved Modulation Technique With Minimum Switching Actions Within One PWM Cycle for Open-End Winding PMSM System With Isolated DC Bus

Due to the application of dual inverters in the structure of open-end winding permanent-magnet synchronous machine system with isolated dc bus, the double number of switching devices are employed and thus the switching actions within one pulsewidth modulation (PWM) period are relatively high. To reduce the switching actions, an improved modulation technique is proposed in this letter. In the proposed technique, the reference voltages in the synchronous coordinate system are transferred to the three-phase stationary frame through Park transformation and thus the duration time corresponding to the three-phase windings can be directly obtained. On this basis, by synchronously adjusting the duration time of three phases, the maximum one can be adjusted to be the control period while their resultant voltage remains constant. Furthermore, the switching actions are assigned to the switching devices based on the polarity of duration time for each phase, with the principle of keeping the switching device on one side clamped. The novelty of the proposed technique is that it can be universally applied to minimize the number of switching actions within one PWM cycle for any kind of voltage ratio of the system without sector identification. The experimental validation of the proposed scheme is given to validate its effectiveness.