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Space Vector Sequence Comparison for Low-Switching Frequency Current Source Rectifiers

Fig. 1. THD factors of switching currents up to 19th harmonic, sequences SQ1-SQ5.
High-power applications operate at low-switching frequency to have higher efficiency, which normally produces significant amount of low-order harmonics (LOH). This is highly undesirable property of current source rectifiers (CSRs) and different space vector sequences produce different amount of LOH. Furthermore, CSR is usually not used for high-power applications, because it has worse efficiency than voltage source rectifiers (VSR). This paper compares five different space vector modulation (SVM) sequences that are suitable for low-switching frequency CSR. Furthermore, simple operating point analysis for CSR is presented and explained.

Different space vector sequences that are suitable for CSR are simulated in MATLAB\simulink. Harmonic content of sequences is compared as well as total harmonic distortion (THD) factor of switching current of different sequences. THD and harmonics for each sequence are completely analyzed and shown in part III of the paper. Based on that, two sequences are found to be more convenient for CSR applications. Figure 1 shows THD factor up to 19th harmonic of switching current of all five SVM sequences for different values of modulation index. Clearly, all five SMV sequences have pretty similar THD factors up to 19th harmonic. Figure 2 shows THD factors up to 16th harmonic of switching currents of all five SVM sequences for different values of modulation index. Comparing THD factors up to 16th harmonic we can see that sequences SQ2 and SQ3 have small 17th and 19th harmonic and have greater LOH. Sequences SQ1, SQ4 and SQ5 have higher 17th and 19th harmonic and have much smaller LOH. Sequences SQ4 and SQ5 are better than sequence SQ1, so those two are more suitable for CSR applications that require small THD of input currents.

Fig. 2. THD factor of switching currents up to 16th harmonic, sequences SQ1-SQ5.
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