Design and analysis of a modulation strategy for a seven output voltage levels on a HNPC topology

In this paper a new modulation strategy for the single-phase H-bridge neutral point clamped (HNPC) topology is presented. The proposed modulation scheme allows the conventional five levels multilevel inverter to generate a seven levels output voltage waveform, without any changes in the structure of the HNPC topology. For this purpose a modulation scheme based on the typical Level Shift Pulse Width Modulation (LS-PWM) is designed. In order to obtain the seven output voltage levels, the DC-link is split in asymmetric form, that is one of the DC-side capacitor voltage is the double of the other one. Numerical results were obtained for a grid-tied photovoltaic system in order to evaluate the performance of the proposed modulation technique. An efficiency analysis of the proposed modulation strategy is also shown to illustrate the advantage of this scheme.