Enhancing VA sharing between the shunt and series APFs of UPQC with a modified SRF-PAC method

This study proposes a synchronous reference frame (SRF) theory-based modified power angle control (PAC) method for unified power quality conditioner (UPQC). In the steady state of conventional UPQC, shunt active power filter (APF) supplies total reactive power demand, and series APF sits idle, leading to unbalanced VA loading of the two APFs and increase in overall VA rating of UPQC. PAC methods of UPQC have been devised for reducing the unbalance in VA loading of series and shunt APFs of UPQC by sharing reactive load power between the two APFs. SRF-based PAC methods are robust, but existing ones support only small values of power angle, and thereby limit the improvement in unbalance of VA loading of series and shunt APFs. In this work, a modified SRF-PAC method is proposed to support larger values of power angle, to load the two APFs in proportion to their VA ratings and thus yield smaller unbalance in VA loading of the two APFs of UPQC. Also, a modified power angle estimation is proposed to ensure that voltage and VA load on series converter does not go beyond the rated values. Controller hardware in loop simulations and hardware experiments validate the proposed control method.