Current harmonic controller in multiple reference frames for series active power filter integrated with 18-pulse diode rectifier

The paper presents the control system and selected results of experimental tests of the AC/DC power converter consisting of an 18-pulse diode rectifier based on coupled reactors and a serial active power filter. Proportional integral controllers with decoupling components are implemented in multiple reference frames for selective line current harmonic suppression. The regulator is provided with a backtracking anti-windup mechanism of sorts in which a signal proportional to the saturated control reference is subtracted from the error signal in each reference frame. The fundamental harmonic filter based on the DFT algorithm with phase correction is used for grid synchronization and current harmonic detection. Three configurations of the 15 k VA converter were tested experimentally and then compared: the 18-pulse diode rectifier with and without an additional grid reactor, and the rectifier integrated with an active power filter. The applied control method of active filter significantly reduces harmonic distortion and unbalance of the grid current, which is particularly advantageous under non-ideal supply voltage and low loads conditions.