Advanced active output filter for low acoustic noise adjustable speed drive (ASD) system

In recent years, manufactures of adjustable speed drive (ASD) make effort to reduce the acoustic noise emitted by electric motors. Traditionally, LC passive filters can be employed to mitigate the pulse-width modulation (PWM) generated current harmonics in the audible noise range. However, the bulky passive filters contribute to additional volume and cannot effectively eliminate harmonics at low switching frequency. In this paper, an active output filter (AOF) is proposed to replace passive filters to achieve higher power density and lower acoustic noise. The proposed AOF can be envisioned as a power semiconductor filter block and is implemented by the harmonic injection strategy, which can compensate voltage/current harmonics at the arbitrary frequency. Advanced wide-band gap devices can be employed in AOF to achieve low power loss and high switching frequency. Experimental results from a 2/3 horsepower ASD prototype verifies the advantages of the proposed AOF.