Induction motor speed measurement using motor current signature analysis technique

As the procedure of nonintrusive method for field efficiency estimation of induction motor requires the actual motor speed from direct measurement by using shaft-mounted speed encoder or optical tachometer which reduces the reliability and also increases the cost. In this paper, the sensorless speed measurement scheme using implementation of motor current signature analysis (MCSA) is proposed. Both line-fed (sinusoidal) and inverter-fed (nonsinusoidal) motors with different operating frequencies are considered. In this technique, neither equivalent circuit parameters nor structures of machine are required. Moreover for inverter-fed motor, the information of inverter such as switching frequency and switching PWM scheme are not required. This proposed technique is verified from the experimental results of measured speeds of 2.2 and 4.0 kW three-phase induction motors operated under various load torques. The experimental results show that the overall speed estimation accuracy is approximately within 2 rpm errors.