A Robust Load Adaptability Method to Suppress AC Harmonic for Series-Connected 12-Pulse Rectifier With DC Side Active Harmonic Injection Circuit

Though the DC side harmonic reduction methods of multipulse rectifiers can improve AC side power quality, they are applicable to large inductive load only. This paper proposes a novel active harmonic injection circuit (AHIC) for seriesconnected 12-pulse rectifier to achieve lower input current total harmonic distortion (THD) with non-ideal inductive load. First, the harmonic suppression effect of two representative passive and active harmonic reduction circuits (HRCs) under load ripple current conditions is analyzed and the mechanism of poor load adaptability is revealed. On this basis, the AHIC realized by twostage DC-AC-AC three-port converter is installed at DC side as two independent current sources. By extracting harmonics from load current and superimposing them on original triangular current, the AHIC generates specific injection circulating currents to offset the undesired harmonics of rectifier output current. The resulting rectifier draws a near-sinusoidal input current with less than 3% THD during complex conditions. The proposed AHIC has the merits of low voltage stress (5%Udc), small design capacity (2.5%PL), and elimination of the necessary magnetic devices of existing methods. An experimental prototype is established to validate the performance of proposed rectifier.