Sensorless Estimation of the Rotor Speed for the Use in V/f Control Systems of IM Drives

The paper deals with a sensorless V/f control system of induction motor drive. The control system consists of two loops intended to regulate the shaft angular speed and an active component of the stator current. Rotor speed estimation is based on the linearized relationship between the rotor current frequency and active component of the stator current obtained for IR-compensation scheme. Active current is calculated via the measured alpha-beta components of the generalized current vector as a sum of their projections on the vector of basic harmonic voltage, the position of which is predetermined by the generalized vector of PWM modulating signals. A computer model of the control system with proposed rotor speed observer has been developed to estimate accuracy of the observer for different rotor speeds. The control range of the rotor speed has been determined under conditions of a static error kept less than 1%.