An Improvement on A Simplified Space Vector Modulation Algorithm to Solve the Inherent Three-Phase Unbalance

Abstract

Space vector modulation (SVM) is widely used in traditional three-phase converters, but when extended to multilevel converters it suffers from issues of heavy computation cost and intense memory usage. Researchers have proposed many simplified SVM algorithms, but they are still impractical in some respects. This paper examines a simplified SVM algorithm based on H-D coordinates, which has simpler calculations than simplified algorithms based on other coordinate systems. Then, this paper analyzes this simplified algorithm and finds it has an inherent three-phase unbalance problem. There are two reasons for the unbalance: the unbalance of generation rules and the directionality of H-D coordinates. Then, based on the feature of HD coordinates, we propose an improved SVM algorithm. The proposed algorithm divides the hexagonal vector space diagram into three diamond-shaped areas equally and can take full advantage of the similarities among them. Consequently, the unbalance problem is solved and the calculations are still compact. In addition, the proposed algorithm has another two features: simplified calculation in a condition of overmodulation and better balance performance when switching frequency equals a multiple of 150 Hz. Based on our findings, we believe the proposed SVM algorithm is more practical than others and is suitable for large level-number applications like three-phase modular multilevel converters. Simulations in various operating conditions are done.