The harmonic elimination strategy for a 24-pulse converter with unequal-impedance phase-shift transformers

This paper proposed a compensation strategy to reduce the 24n ± 1th harmonics existing in a traditional 24-pulse diode converter. Moreover, the strategy also overcomes the unequal-shared line currents of the two phase-shift transformers, which provide four set of three phase ac sources with 15° phase angles with respect to the adjacent sources. The 24-pulse converter used in this paper is parallel at the dc side through inter-phase transformers (IPTs) including two first-stage IPTs and one second-stage IPT. Each first-stage IPT has an extra winding for injecting compensation current to eliminate the overall ac line current harmonics and obtain the equal-shared primary line currents of the two phase-shift transformers. The compensation currents for the two first-stage IPTs are generated by an inverter and a digital signal processor (DSP) is used as the controller to generate the required trig signals for the switches in the inverter. A 6kW prototype is established to verify the validity of the proposed scheme. Both simulation and experimental results demonstrate the correctness and performance of the proposed method.