Direct power control with common mode voltage reduction of grid-connected three-level NPC inverter

This paper proposes three new direct power control (DPC) algorithms which minimise the variation of the common mode voltage (CMV) provided by a transformerless grid-connected three-level neutral point clamped (3L-NPC) inverter. The proposed techniques make use of three reduced switching tables designed with the aim to control the active and reactive powers and to minimise the variation of the CMV. The first switching table uses large, medium and zero vectors of the space vector diagram; it is therefore named large medium zero vectors DPC. The second table uses the medium and zero vectors. It is referred to as medium zero vectors DPC. The third one namely medium vectors DPC, uses only medium vectors. Numerical simulations and experimental tests carried out on a laboratory prototype of the 3L-NPC inverter confirm the feasibility and effectiveness of the proposed algorithms.