Balancing distribution systems with three‐phase active front end rectifiers: field experiment results

Abstract

This study describes field tests of alternative methods to control three-phase active rectifiers to reduce voltage unbalance in low-voltage (LV) distribution systems. The tests show that per-phase control of active power of two residential loads can significantly reduce unbalance throughout an LV feeder shared by 25 homes. Different algorithms, designed to either reduce negative sequence voltage, or phase–neutral (P–N) voltage unbalance using active or reactive power (four algorithms in all), were tested. The algorithm designed to reduce P–N voltage unbalance using active power showed the greatest reduction in median P–N voltage unbalance at the prototypes terminals (up to 87%), the greatest reduction in median current unbalance at the feeder's substation (38%), and was also effective at reducing negative sequence voltage in the feeder. The algorithms controlling reactive power reduced negative sequence voltage, but did not show significant effects on P–N voltage unbalance. Two prototypes were tested at different locations on the same feeder, and the average combined effect of the two prototypes was well predicted by the sum of their individual effects. Some of the results are inconsistent with earlier simulations and laboratory tests which used simple constant impedance load models, highlighting the importance of field trials to validate controller designs.