An Improved DTC Technique for Low-Speed Operation of a Five-Phase Induction Motor

In this paper, an improved direct torque control (DTC) technique of a two-level inverter-fed five-phase induction motor (FPIM) drive for low-speed operation is presented. The operation of the FPIM with distributed winding requires the elimination of third-harmonic voltage, which, if not taken care of, would generate distorted stator current. For this, the concept of virtual vectors (VVs) is utilized. Before selecting the VVs for the DTC operation, a theoretical analysis is carried out to find the effects of these VVs on the torque and flux response of the FPIM under different speed and loading conditions. It is found that the rotor speed plays a crucial role in the selection of VVs. A particular VV has different effects on the torque change as speed varies. This analysis helps in the selection of VVs, hysteresis torque bandwidth, flux bandwidth, and efficient formation of sectors. Furthermore, in this paper, the performance of the FPIM during low-speed operation is improved by avoiding the demagnetization of the stator flux. To achieve this, a new modified lookup table is proposed. Superiority of the proposed method over the reported approaches is illustrated by experimental results.