Direct torque control of induction motor-variable switching sectors

An induction motor drive based on direct torque control (DTC) allows high dynamic performance to be obtained with a very simple hysteresis control scheme. In this paper, the problem of stator flux drooping at low speeds has been investigated. By rotating the original flux sectors defined for conventional DTC near the sector boundaries, it is possible to maintain stator flux within the prescribed hysteresis bands and therefore improve the stator flux in the machine as well as the harmonic contents of stator currents. Moreover, the use of the proposed scheme also results in a reduction of overall inverter switching frequency. The effectiveness of the proposed scheme is evaluated through simulation studies, and is also supported with experimental results obtained from a 1.5 kW induction motor driven in a laboratory environment.