Overall Currents Unbalance Assessment for Several Three-Phase Loads under Sinusoidal Conditions of Four-Wire Circuit

The paper deals with complex-valued negative and zero sequences current unbalance factors, which in addition to the magnitudes ratios also take into account the phase differences between the negative and positive sequences' currents and between the zero and positive sequences' currents. These coefficients allow uniquely locate any currents asymmetry modes. The equations for calculating the general complex negative sequence current unbalance factor and zero sequence current unbalance factor according to the known similar coefficients for each separate three-phase load of a four-wire circuit under sinusoidal voltages and currents conditions are presented. Also the equations for the desired phase currents to be drawn from the power network by a balancing device (in particular a passive or/and active filter or some other type compensator) to eliminate both the negative and zero currents components are offered. Thus, the approach makes it possible to assess the overall current asymmetry and the necessary measures to eliminate it even before connecting three-phase loads, without directly metering the total circuit currents values. An example of calculating the above complex current unbalance factors, based on metering in a PSIM model magnitudes and initial phase angles of currents, is considered. The compensated mode is also demonstrated via using AC current sources of the PSIM model.