Measuring equipment for the electric quantities at the terminals of an inverter-fed induction motor

The electric quantities at the terminals of an inverter-fed induction motor are difficult to measure because of the large distortion on both the voltage and current signals. Special care must be taken in evaluating the rms values and power. A measuring device is proposed for the measurement of voltage and current rms values, their frequency, their frequency-domain components and the active power consumed by the motor. The measuring instrument is based on digital signal-processing techniques and is organized as a Virtual Instrument. The results of some experimental work done on a 3 kW induction motor supplied by a six-step inverter are reported.