Sensorless direct torque control of induction motor drive with LC filter

This paper focuses on some aspects of control and estimation problems for speed sensorless induction motor drive with inverter output LC. The filters are needed in some industrial drives with pulse width modulated (PWM) inverters. They smoothen the motor supply voltage and current so that nearly sinusoidal shapes are obtained. The filters can also limit the bearing current and shaft voltages. Because of the voltage drop and phase shift imposed by the filter, the motor voltages and currents differ from the inverter output. This fact can seriously complicate the drive operation due to the problems with the control and estimation process - especially in speed sensorless drives. To solve those problems the filter model should be taken into account in the control and estimation algorithms. In this paper a sensorless solution for induction motor (IM) with inverter output filter drives is proposed. The new contribution of the paper is the application of the solution to direct torque control. A short description and discussion of the schemes is given. Simulation and experimental results validate the proposed solution.