Quantifying the Energy Efficiency of Motors on Inverters

Abstract

With an ever-Increasing focus on energy efficiency along with the more widespread application of adjustable frequency inverters, it is important to accurately quantify the energy efficiency of motors fed with adjustable frequency power. The impact of inverter waveforms on the component and overall loss of motors are dealt with in this article. This article also addresses the challenges associated with making accurate efficiency measurements on inverter-fed motors, especially those with extremely high efficiency. The effects of various filters that may be applied between the inverter and motor are also considered. Both low-voltage (LV) and medium-voltage (MV) cases are included. Three-phase AC induction motors demonstrate high efficiency levels and are able to maintain high efficiency across a substantial range of loading conditions. When fed by inverter power, there are some additional losses that occur in these motors, incrementally degrading energy efficiency. While earlier inverter waveforms, such as six step, had substantial harmonic content in the motor current, today's pulsewidth modulated (PWM) inverters are capable of producing waveforms with very few low-order harmonics. In fact, the majority of the nonfundamental frequency content in modern PWM current waveforms is at the switching frequency, which is not really a harmonic for the typical asynchronous carrier modulation schemes. is an example of a PWM current waveform that has large components at the switching frequency.