An Improved abc-coordinate-based 3D Space Vector Modulation for Neutral-Point Voltage Balancing in Three-Phase Four-Leg Three-Level Converters

Four-leg three-Level neutral-point-clamped converter is a popular solution for DC/AC or AC/DC conversion. However, simple and effective control algorithm for the switch modulation and capacitor voltage balancing is a key issue. In this paper, an improved three-dimensional (3D) space vector modulation (SVM) strategy for four-leg three-level converter in abc coordinate is proposed and investigated. Compared with the previous 3D SVM strategies, the proposed method presents the over-modulation scheme for limiting the reference voltage in the interior of the modulation region, and the selection scheme of redundant vectors for balancing the positive and negative DC-link capacitor voltages. This implementation technique involves few logic comparisons and arithmetic operations, so the computation time is easily affordable and the method can also be migrated to other multilevel converters. Simulations and experimental results verify the validity of the proposed modulation strategy.