Reduction of current and flux distortions of VSI-fed induction motors with direct self-control

Direct self-control (DSC) of an inverter-fed induction machine is a signal processing technique based on two-level hysteresis controllers of the machine flux and torque. The attractiveness of DSC is its simplicity and high dynamic performance even using high power, low switching frequency converters. One disadvantage of DSC, however, is that the output inverter current is not sinusoidal, containing harmonic components typical of those in six-pulse, square wave inverters. A method is proposed which is based on processing a stator flux trajectory. The method offers the possibility of flux self-compensation at low speed. It is shown that this method can be easily extended to drives with a discrete PWM which do not use zero vectors. It is also shown that by dividing a stator flux trajectory into two areas, in which different hysteresis width of a torque controller is applied, reduction of motor current active distortions at speed close to nominal can be achieved