Pseudo-open-loop low-speed control of induction motors

Between the extremes of simplicity and complexity of control lie many applications which require an intermediate level of performance. It is this problem that the authors address. The motor is operated open-loop in respect of torque, with a constant steady-state flux magnitude. The coupling of torque and flux during a transient is tolerated in the same way as it is when the machine is operated `on-line´. The major failing of V/f ratio control, the inability to account for the current dependency of the stator winding resistance voltage drop (V_Rs), is overcome by using a very simple feedback loop within the invertor controller. For this reason the scheme is termed pseudo-open-loop steady-state control. The controller is realised by considering simple machine models, and by using only one transducer within the inverter