Power factor improvement of three‐phase unbalanced loads with non‐sinusoidal supply voltage

Three‐phase load asymmetry causes a useless current loading of the supply source and this loading increases even more if the supply voltage is non‐sinusoidal. This loading can be expressed quantitatively with the unbalanced current iu of RMS value ||iu||. A whole compensation of the unbalanced current iu was proved to be possible with reactive balancing circuits, however, it may be very complex. This paper shows that a substantial minimization of the unbalanced current iu may be achieved with such a circuit, but of much lower complexity. The method suggested requires that the unbalanced admittances An of the load for harmonic frequencies are known. A harmonic analysis that provides the complex RMS values of the phase voltages and currents harmonics in a cross‐section between the load and the source enables us to determine these admittances and design the balancing circuit. It was shown, moreover, that the reduction of the unbalanced current iu can be integrated with the reactive current ir minimization. Copyright © 1993 John Wiley & Sons, Ltd