An auxiliary-supply-assisted twelve-pulse diode rectifier with reduced input current harmonics

Diode rectifiers have been widely used for an ac-to-dc converter. One of their problems is that they include large harmonic contents in its input current. A 12-pulse diode rectifier is useful for reducing them, but it still includes the (12m±1)^th (m: integer) current harmonics in its input. In order to further reduce the input current harmonics a single-phase square wave auxiliary voltage supply is inserted in the middle dc bus of a 12-pulse diode rectifier. The purpose is to obtain a 12-pulse diode rectifier whose harmonic contents are equivalent to those of a 24-pulse diode rectifier. Theoretical analysis of the combined 12-pulse diode rectifier with the auxiliary supply is presented, and a control method of the auxiliary supply in accordance with the dc load current is proposed. The reduction in the harmonic contents in the output currents is verified by simulation and experimental results.