Active filter for a converter having a dc line

An active filter for a converter having a dc line, the converter being operable to provide a pulsed current on the dc line at a chopping frequency, the active filter comprising:

• a trap circuit tuned to a fundamental frequency component of the pulsed current;
• a first switch, coupled between the dc line and the trap circuit, for creating at least one deadband to adjust phase of current flowing through the trap circuit;
• and
• a power dissipation element and second switch coupled to the trap circuit for diverting at least some stored current in the trap circuit, the current being diverted to control amplitude of the current flowing through the tuned trap circuit;
• whereby the active filter is operable to trap the fundamental component of the pulsed current.

A method of filtering pulsed current on a dc line, the method comprising the steps of:

• trapping a fundamental component of the switched current;
• using a trap circuit and the trapped current to create a resonant frequency and at least one deadband, the deadband being controlled to control phase of the trapped current;
• and
• diverting at least some of the trapped current to control amplitude of the resonant current.