Effect of the Variable Switching Frequency and DPWM Switching Schemes on the Losses of Traction Drives

This paper studies different switching schemes for loss reduction in a traction motor drive. The system under examination is composed of a battery, a 2 level Voltage Source Inverter, and an Interior Permanent Magnet motor. Discontinuous PWM (DPWM) control strategy is widely used in this type of motor drive for the reduction of losses. In some publications, the effect of the DPWM modulation scheme is compared to the reduction of the switching frequency which can also cause a reduction in switching losses of the inverter. Extensive studies have examined the effect of variation of the switching frequency on the motor and inverter losses. However, the effect of applying both switching schemes simultaneously has not been explored. This paper will use a system that is operated at a fixed switching frequency as the baseline. Afterwards, three different switching schemes will be studied and compared to the baseline. The first scheme (S1) will decrease the losses by optimizing the switching frequency in different regions of the torque-speed envelope. The second strategy (S2) will achieve the same goal by keeping the base switching frequency the same and introducing DPWM operation to the map. Finally, the third scheme (S3) will use S1’s switching frequency map and apply DPWM to that. Through experimental validation, this paper will paper will demonstrate that the loss reduction of S1 and S2 will be very similar to one another and S3 will not provide a considerable advantage compared to S1 or S2.