Robust adjustable speed drive with active filtering and regenerative braking capability

Power conversion structures for adjustable speed drives usually include a diode bridge as input stage. The current harmonics generated by the bridge rectifier contribute strongly to the degradation of the utility current quality. To avoid this problem the diode bridge could be replaced by an active front-end rectifier which provides a low total harmonic distortion, power factor correction and bidirectional power capability. However, this input stage is more expensive and has lower energy efficiency than the bridge rectifier. Furthermore, it has to be designed for the whole power of the adjustable speed drive. A well know alternative to the active front-end rectifier consists of using active filters to cancel the harmonics generated by the diode bridge. This solution has no bidirectional power capability and is often used in medium-voltage electrical drives that do not require controlled braking. This paper proposes the connection of the dc links of the diode bridge rectifier and the active filter by means of two diodes and a common-mode inductance. This new solution achieves low total harmonic distortion, unitary power factor and it also provides a robust speed drive with regenerative braking capability that can be very interesting for many applications.