Reduction of low-order harmonics and new topologies of current source converters

Two CSCs related issues are investigated. The first is the reductions of Low Order Harmonics (LOH) in Low Switching Frequency (LSF) CSCs. High power CSCs operate with LSF. This is not an ideal scenario for Space Vector Modulation (SVM), resulting in non-characteristics LOH, 5th and 7 th (HD5-7). Researchers have attempted to reduce these harmonics by creating new sequences of space vectors (states) or different sampling techniques. New approaches based on the fact that HD5-7is affected by states ON times calculation process are proposed. Results show that by using a new technique called Record Middle (RM), one can obtain a smaller HD5-7. Also, results for calculating states ON times as the reference vector rotates by new SVM equations show that one can get a significant reduction in HD5-7. Another alternative effective with large overlap periods is minimizing LOHs in LSF-SVM-CSCs with Minimum Harmonic Tracking (MHT) technique. Fuzzy logic dependent states ON times calculation give fixed states ON times adjustment during steady state and fast response. Those techniques allowed the usage of reduced size ac-side filters with high cut-off frequencies.;The second issue is on new hybrid current source converters (HCSCs). Three SCRs and four IGBTs HCSC has similar characteristics, less capital cost and less power losses compared to the 6-switches CSC. Two types of modulation are proposed. The first is Hard Switching Space Vector Modulation technique (HS-SVM). HS-SVM is presenting low maximum modulation index (ma.max), resulting in LOH distortion and requiring multiple mandatory switching inside a cycle. The second modulation technique achieves line-commutation or soft switching (SS) of the SCRs whenever possible, thus being called Soft Switching Space Vector Modulation technique (SS-SVM). SS-SVM increases the ma.max while reducing LOH, the switching frequency and switching losses. Comparisons between the 6-switches CSC and the HCSCs are provided. Cost analysis showing the importance of HCSCs is carried out. A case study is presented to show that the HCSC is economically viable in medium and high power ranges. Besides having lower capital cost, the HCSC can operate with lower power losses than 6-switches CSC.