Reducing both Torque and Flux Ripple in the DTC of IPMSM by Incorporating Duty Cycle Calculation Method and Dithering Technique

The Direct Torque Control (DTC) of Interior Permanent Magnet Synchronous Motor (IPMSM) offers simple structure and fast torque response. The conventional Switching Table-based DTC (ST-DTC) presents some disadvantages like high torque and flux ripple and also variable switching frequency. This paper investigates the improved ST-DTC strategies to reduce both torque and flux ripple in DTC of IPMSM with emphasis on structure simplicity and fast dynamics. New switching table with only two active vectors for each sector is introduced and the torque control hysteresis band is replaced by duty cycle calculation unit. For flux ripple reduction, conventional hysteresis-based controller is replaced by simple dithering technique. The duty cycle calculation unit is implemented to operate on each selected vector with the aim of torque ripple RMS minimization. The increase of switching frequency in ST-DTC because of delay in torque and flux estimation process, actually, is not possible; even when hysteresis bands are sufficiently diminished. This paper incorporates the combination of duty cycle modulated DTC and dithering technique to enlarge switching frequency. It therefore provides smoother waveform concurrently for the motor torque and the flux. In the proposed method waveform comparison structure for duty cycle calculation is used; hence, the merits of classical ST-DTC, such as fast dynamic and simple structure, are mostly preserved