Audible noise and losses in variable speed induction motor drives with IGBT inverters-influence of the squirrel cage design and the switching frequency

This paper describes a large number of experiments comparing audible noise, losses and efficiency of different induction motors supplied by an IGBT inverter. The influence of the switching frequency on the motor behaviour is analysed. As a comparison the motor is also supplied directly from the mains. Furthermore two different motors are compared to study the influence of the rotor cage design on the motor behaviour. It is shown that the choice of the switching frequency has a large influence on the audible noise produced by induction motors. By taking higher switching frequencies, the time harmonics move to a nonaudible region. At some higher switching frequencies subharmonics appear, having a bad influence on the audible noise. At higher fundamental frequencies the audible noise of the fan dominates. The switching frequencies can cause pure tones that are very disturbing to the human ear. The influence of the switching frequency on the efficiency is rather small. Minimal overall losses appear around 3 and 4 kHz. The voltage-frequency ratio should be taken constant from the point of view of the efficiency