Line harmonics reduction in high power systems using square-wave inverters

This paper presents a hybrid parallel active filter scheme using small rated square-wave inverters for supply line harmonic current reduction for high power nonlinear loads in the range of 1-50 MW to meet IEEE 519 harmonic standards. The active filters are connected in series with 5th and 7th passive filters. A synchronous reference frame based controller which achieves harmonic isolation for dominant 5th and 7th harmonic load currents in presence of supply voltage harmonics is presented. The impact of mistuned passive filters on the operation and rating of the hybrid parallel active filter is examined. Simulation results validate the proposed harmonic isolation controller under mistuned 5th and 7th passive filter conditions and supply voltage distortion. The proposed scheme is general and applicable for high power 12 pulse rectifier loads. The proposed use of small rated-2%-square-wave inverters increases the cost effectiveness and practical viability of hybrid parallel active filter scheme for high power applications