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A DC-link Balancing Control Strategy for NPC Three-level Shunt Active Power Filter

In this paper, a quantitative mathematical model of neutral current and DC-link balancing voltage is established for neutral point clamping (NPC) three-level shunt active power filter. Based on the established model, a three-level voltage balance control method is proposed. By introducing a coefficient representing the relationship between the neutral current and the DC-link capacitor voltage difference, the reasonable value of the injected neutral current can be directly calculated according to the voltage difference between the upper and lower capacitors. At the same time, the influence of DC-link voltage difference on SAPF compensation performance can be restrained by selecting filter parameters and sampling frequency reasonably. Simulation and experimental results show that the proposed control strategy can eliminate the DC-link voltage difference at the upper and lower capacitor without affecting the SAPF compensation effect.