An active in-line notch filter for reducing acoustic noise in drives

Manufacturers of drives of have put in much effort in recent years to reduce the acoustic noise of their systems by improving the motors and by paying attention to the PWM schemes that are used. In this project inserting an active filter between the inverter and the induction machine reduces the acoustic noise, and in this way the acoustic behavior of an existing drive can be improved without needing to replace components or modifying the drive. An active notch filter is proposed that uses a switched capacitor. Tests results on a 3 kW drive show that the active notch filter works well and that it is possible to achieve a reduction of 15 dB in the line current and stator vibrations. This is a significant reduction and could reduce the radiated noise at a troublesome acoustic frequency substantially.