Digital Techniques in the Evaluation of High-Efficiency Induction Motors for Inverter Drives

An inexpensive method of measuring the efficiency of high-efficiency ac motor drive with an inverter power source is described. The method uses simultaneous sampling of waveforms, storing data in memory, and transferring the data to a personal computer for processing. The method yields an estimated precision of 0.25 percent in measuring motor electrical power. With the availability of the actual waveforms in the computer, it is possible to apply them to a motor model and use the results to separate the losses into inverter waveform-induced losses, magnetic losses, and resistance losses. The results show excellent correlation with calculation using a specially designed induction motor, so that extending the digital analysis method to analysis of an unknown motor should yield good results.