Minimizing power pulsations seen by a dc source feeding unbalanced single-phase ac distribution circuits through voltage source converters

When a three-phase voltage source converter feeds three asymmetric single-phase circuits at the same frequency, the current from the dc source pulsates. Most of these pulsations are at twice the fundamental frequency and are undesirable for certain dc sources, such as fuel cells. These second harmonic pulsations can be minimized, and in some cases eliminated, by adjusting the relative phase angles of the voltages in the individual single-phase circuits, while maintaining the voltage magnitudes. Large filter capacitors or supercapacitors are not required. This paper presents a control Lyapunov function based voltage angle controller that minimizes the second harmonic power pulsations in the dc current and explains its limitations. The theory is validated through computer simulations and laboratory experiments.