Line Current Harmonics Reduction in Multipulse Connection of Asymmetrically Loaded Rectifiers

This paper proposes a new arrangement for the multipulse connection of asymmetrically loaded six-pulse rectifiers. This arrangement is, therefore, particularly suitable for implementing the dc voltage sources of hybrid multilevel inverters in applications with active power transfer, such as medium-voltage adjustable-speed drives. A new design methodology is proposed to determine the phase shifts among the secondaries of the isolation transformer, even when the active power levels processed by each rectifier and their input and output impedances are different. A set of phase angles is obtained to minimize, and even to eliminate, undesired low-order harmonics of the input current, in particular, the 5th harmonic, because this harmonic component presents an amplitude considerably higher than the amplitude of the other harmonics. In consequence, the proposed design methodology increases the input power factor and reduces the input current total harmonic distortion. Simulation and experimental results are presented to demonstrate the feasibility of the proposed structure.