A Seven-Level Inverter Topology for Induction Motor Drive Using Two-Level Inverters and Floating Capacitor Fed H-Bridges

A multilevel inverter topology for seven-level space vector generation is proposed in this paper. In this topology, the seven-level structure is realized using two conventional two-level inverters and six capacitor-fed H-bridge cells. It needs only two isolated dc-voltage sources of voltage rating V-dc/2 where V-dc is the dc voltage magnitude required by the conventional neutral point clamped (NPC) seven-level topology. The proposed topology is capable of maintaining the H-bridge capacitor voltages at the required level of V-dc/6 under all operating conditions, covering the entire linear modulation and overmodulation regions, by making use of the switching state redundancies. In the event of any switch failure in H-bridges, this inverter can operate in three-level mode, a feature that enhances the reliability of the drive system. The two-level inverters, which operate at a higher voltage level of V-dc/2, switch less compared to the H-bridges, which operate at a lower voltage level of V-dc/6, resulting in switching loss reduction. The experimental verification of the proposed topology is carried out for the entire modulation range, under steady state as well as transient conditions.