Harmonic elimination, reactive power compensation and load balancing in three-phase, four-wire electric distribution systems supplying non-linear loads

Abstract

In this paper, a new control scheme of a three-phase active power filter (APF) is proposed to eliminate harmonics, to compensate reactive power and neutral currents and to remedy system unbalance, in a three-phase four-wire electric power distribution system, with unbalanced non-linear loads. The APF is realized using three single phase IGBT based PWM-VSI bridges with a common dc bus capacitor. A hysteresis rule based carrierless PWM current controller is used to derive gating signals for the IGBTs. Three-phase balanced reference supply currents are estimated using load currents, dc bus voltage and supply voltages. The reference currents of the APF are derived by taking the difference of corresponding reference supply current and load current. The APF forces the compensating currents to conform to the desired reference currents. The APF is found effective to compensate reactive power and neutral current while eliminating harmonics with load balancing.