An Improved DTC Based Five-phase Induction Motor Drive with Minimum Torque Ripple and Constant Switching Frequency

Variation in switching frequency with operating speed and high torque ripples are two important limitations of the Direct Torque Control or DTC technique. The potentiality of the switching device cannot be fully exploited for variable switching frequency (in the case of lowest frequency) whereas high torque ripples lead to vibrations and acoustic noise in the motor. A five-phase induction motor (FPIM) based on DTC technique is presented here to overcome these drawbacks. A five-level Proportional-Integral (PI) based torque controller using waveform comparison is employed in the drive. The PI controller will process the torque error whose output is then compared simultaneously with four constant frequency triangular waves to achieve constant switching frequency. The gains of PI controller are designed using linear control theory for minimum torque ripples. Stator current distortion due to the presence of auxiliary subspace in the five-phase system is also minimized. The demagnetization of stator flux during low-speed operation is mitigated through the selection of voltage vectors that are present thirty-six degrees within the sector boundaries. Experimental results have been presented for validating the steady state and dynamic performance of proposed DTC technique.