Decoupled Modulation Scheme for Three-Phase Four-Leg Four-Wire Three-Level T-Type Inverter

The three-phase four-leg four-wire (3P4L4W) three-level (3L) inverter, constituted by three 3L phase-legs and a fourth two-level (2L) phase-leg, is capable of feeding both balanced and unbalanced loads. In this paper, a closed-loop common-mode (CM) load-voltage control incorporated decoupled modulation scheme (CL-DMS), which combines the advantage of the three-dimensional space-vector modulation (3D-SVM) with the closed-loop control for the CM part in the load voltages and the advantage of the carrier-based modulation scheme with the low complexity for implementation, is proposed for the 3P4L4W3L inverter. In doing so, the 3L phase-legs are modulated to attain both the voltage balancing control for the split dc-bus voltages and the closed-loop control for the differential-mode (DM) load voltages, whereas the fourth leg is independently modulated to realize the closed-loop control for the CM load voltage. The proposed work has been verified on a 10-kVA 3P4L4W3L inverter. The experimental results show that the proposed decoupling modulation scheme benefits the 3P4LW3L inverter with well-balanced split dc-bus voltages and well-balanced load voltages with low total-harmonic-distortion (THD) for both balanced and unbalanced loads.