Low speed control improvements for classic Direct Torque Control of a 2-level 5-phase inverter-fed induction machine

A novel technique that improves the low-speed performance of a 5-phase induction machine driven by a 2-level inverter using the classic DTC technique is presented. Demagnetization of the stator flux using DTC is investigated when the induction machine runs at lower speeds and a solution is provided to overcome this phenomenon. The proposed technique reduces the demagnetization phenomenon by using the ±36° displaced voltage vectors during low-speed operation but employs the ±72° displaced voltage vectors otherwise. Demagnetization of the stator flux is shown by simulation to be eliminated using the proposed technique and this is confirmed through experiment. The proposed technique improves the rate of change of stator flux and the torque response at low speeds compared to the traditional method.