Algebraic Modulation Strategy for Direct Matrix Converter With Adaptation to Unbalanced Grids

Owing to the direct coupling between the input and output, the input/output currents of the direct matrix converter (DMC) are sensitive to grid disturbances, especially unbalanced grids. To mitigate the adverse effects caused by unbalanced grids, an algebraic modulation strategy is developed for the DMC in this article. Based on the algebraic theory, the general solution of the modulation vector is first derived. By utilizing the free variables, sinusoidal input/output currents are ensured despite whether the grid is balanced or not. The impact of offset variables is analyzed and they are designed to realize three-level output characteristics. Furthermore, the switching sequence is arranged without bipolar operating mode. The presented algebraic modulation strategy has the following features: 1) easy to implement; 2) three-level output voltage synthesis; 3) effective under either balanced or unbalanced grids. The effectiveness of the algebraic modulation strategy is validated by laboratory experiments.