Factors Affecting Losses in Induction Motors with Non-Sinusoidal Supply

Abstract

This paper presents the results of an investigation into the factors affecting losses in induction motors operating with non-sinusoidal supply. It is well known that the losses in machines increase when a non-sinusoidal supply is used. However, the specific causes of the increase in loss and resultant techniques required to mitigate these losses are not fully known. The paper investigates the efficiency of an induction motor under different loading and supply conditions. As expected losses are a function of fundamental voltage waveform, load condition and PWM switching conditions. It is also shown that the additional stray loss caused by PWM supply (when compared to sinusoidal supply) is a function of these factors.

Determination of the Harmonic Losses in an Induction Motor Fed by an Inverter

“…The parameters of the fundamental equivalent circuit at 50Hz supply are given in Table I. The iron-core and the mechanical loss resistances and <= are varied with air-gap voltage and their relations are generated by the curve-fitting technique as given in ( 6)- (7). The iron core resistance is reflected on the stator and rotor circuits to stay in the dynamic model of the 4 th order, although the iron core is considered in the model.…”

“…There is also an increase in the machine iron losses due to the flowing of harmonic currents [1][2][3][4][5]. At low harmonic frequency (< 2.5kHz), the harmonic losses are also increased with the machine load due to the slight reduction of the machine inductances caused by the saturation effect [6][7]. Measuring the harmonic losses in electrical machines is a very complex task, and its determination by subtracting the output power from the input power is very sensitive to errors of measurement [8].…”

Performance of a High-Speed Motor Drive System Using a Novel Multilevel Inverter Topology

“…The situation is a little more complex for induction motors, with several cause and effects, but the end re- sult is the same-a lowering of machine power rating. In brief, for high-speed induction motors, high rotor losses, for example, due to high-frequency current ripple, increase the rotor resistance, which, in turn, forces the machine to operate at a higher slip speed, which, in turn, increases the rotor losses further and lowers the machine efficiency, torque, and power rating [6]. The machine power rating is lower primarily because operating at higher slip speeds also increases the machine fundamental current for a given torque, causing larger fundamental losses due to copper heating and iron losses.…”