Improvement of a stator-flux-oriented speed-sensorless control of an induction motor

Simulations have predicted high performance control characteristics in the torque and speed sensorless control algorithm which uses a stator-flux-controlled V/f PWM inverter. However, in the actual control system, different problems occurred. Among these problems, there are the fluctuation of the inverter input voltage and the voltage error due to switching time lag of power transistors and to voltage drop in inverter power devices. These voltage errors are a big effect on the flux estimation and cause oscillations of the torque and even instability of the drive system especially at low speeds. This paper investigates these problems and proposes solutions to improve the accuracy of the control system. A very simple implementation of these solutions has shown considerable improvement of dynamic as well as steady-state control characteristics.<<ETX>>