Space Vector Modulation (SVM) is widely used in traditional three-phase converters, but it suffers from issues of heavy computation cost and intense memory usage when extended to multilevel converters. This paper proposed a novel simplified SVM algorithm based on a new coordinate system, referred to as H-D coordinates, and the mapping table method. The calculation based on H-D coordinates is independent of voltage level. Its computation cost is the least compared with other orthogonal and non-orthogonal coordinate systems. The mapping table method enables SVM algorithm to achieve a constant space complexity for storage and it can be further simplified when combined with H-D coordinates. For the problem of selecting switching state, the criteria of minimum common-mode voltage is adopted. Thus obtaining the switching state is quite simple. Based on the statements above, the proposed algorithm is suitable for large level-number converters like modular multilevel converters (MMCs). Simulations in various operating conditions are given.