Shunt active filter with three-phase four-wire NPC inverter

A three-phase four-wire active filter with neutral- point-clamped topology is adopted to eliminate harmonics, to compensate reactive power and to balance the source current for the balance loads. The voltage rating of the power switches in the adopted system is equal to half the dc bus voltage. Using the equal current control scheme, the balanced line currents are drawn from the ac mains. The neutral current of the linear or nonlinear loads is compensated by the neutral current of the active filter such that the source neutral line current is close to zero. The compensated current commands of the active filter are tracking using the carrier-wave current control scheme. Three voltage levels v_dc/2, 0, -v_dc/2 are generated on the ac terminal of the inverter. Experimental results based on a laboratory prototype are provided to verify the effectiveness of the proposed control scheme.