The coupled inductor filter: analysis and design for AC systems

Coupled inductors have been used in specific DC-to-DC converters to provide ripple-current steering. Switching ripple currents may be preferentially directed away from a source or a load. This paper shows that general purpose filters can be produced using coupled inductors and capacitors. These are equally applicable to AC and DC applications. A transfer function is developed for a filter based on a coupled inductor and capacitor. The resulting filter is third order and is significantly more effective than an inductor. The sensitivity of the filter to errors in the turns ratio is examined. Finally, results from an experimental power factor correction circuit are presented.