Harmonics reduction in low switching frequency space vector modulated current source converters

High power current source converters (CSC) are usually implemented with GTOs which present a maximum switching frequency of a few kHz. Space vector modulation (SVM) offers a very elegant way of generating CSC gating signals on-line with increased gain and reduced switching frequency. However, for very low frequency, as required by GTOs, SVM results in non-characteristics low order (5^th and 7^th ) harmonics. The reduction of the magnitude of these harmonics has been sought mostly through new sequences of space vectors (states), which present better performance for different ranges of modulation index and power factor. Moderate improvement can be obtained by calculating the states on times at once in the middle of a cycle. This paper shows that larger reductions can be achieved by calculating the states on times at different moments, as the states are used. The effectiveness of the proposed technique for different states sequences is demonstrated by means of simulations.