Hybrid space vector modulation for low-order common-mode voltage reduction in current-source rectifier for transformerless medium voltage drives

For transformerless current-fed medium voltage drives, low-order harmonics of common-mode voltages (CMVs) are more concerned with than peak values. To mitigate low-order harmonics, the average values of CMVs should be suppressed. A hybrid space vector modulation (SVM) is proposed in this study to further reduce CMV average values generated by a current-source rectifier (CSR) compared to existing zero-state vector selection modulation. The proposed SVM is a combination of zero-state vector selection and active zero-state modulations. The transition points between two modulations are defined based on various modulating index. Power losses and efficiency of the proposed hybrid SVM are analysed in detail. Simulation on a medium-voltage CSR (1 MW/4160 V/139 A) and experiments on a scale-down CSR (2.5 kW/208 V/6.94 A) are conducted under various working conditions, which validates the effectiveness of the proposed SVM to further mitigate 180 Hz and other low-order harmonics in CMVs in contrast to that by conventional zero-state vector selection modulation.