A shunt active power filter for a medium-voltage 12-pulse current source converter using open loop control compensation

AC-side compensation for current source converters using a shunt active power filter (SAPF) is affected by delays introduced into the reference signals and/or the actual injected current. The delays should be identified and compensated to eliminate distortion from the supply current extracted from the point of common coupling, such that the total harmonic distortion complies with standards. An improved distortion factor is achieved if the delay for each harmonic order is considered individually. This paper introduces an open-loop control strategy for the SAPF, which is capable of mitigating specific and predetermined harmonic orders and consequently achieves low total harmonic distortion. The delays are minimized or eliminated when extracting the reference current and controlling the filter current. The control technique is applied on a medium-voltage asymmetrically controlled 12-pulse ac to dc current source converter, which follows a specific power locus with the SAPF connected via taps on the star connected secondary winding of the front end transformer, to compensate the mains current dominant harmonics (5th, 7th, 11th, and 13th). Medium voltage simulation results are verified experimentally using a scaled prototype.