3D-SVM algorithm and capacitor voltage balancing in a 4-leg NPC converter operating under unbalanced and non-linear loads

In this paper analysis and simulation of a 3D-Space Vector Modulation (SVM) for a 4-Leg Neutral-Point-Clamped (NPC) Inverter, including the capacitor voltage balancing is presented. In order to analyze the capacitor voltage balancing, different regions are defined in the α-β-γ space. The analysis and simulations results show that for sinusoidal, symmetric, balance or unbalanced voltages reference and linear loads, the NP voltage oscillate naturally around the middle point of the DC-Link voltage. In addition, the analysis explains the low frequency oscillation of the NP voltage and the feasibility to balance the NP voltage under generalized voltage references and unbalanced loads.