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In this study, analysis of extending the linear modulation range of a zero common-mode voltage (CMV) operated n-level inverter by allowing reduced CMV switching is presented. A new hybrid seven-level inverter topology with a single DC supply is also presented in this study and inverter operation for zero and reduced CMV is analysed. Each phase of the inverter is realised by cascading two three-level flying capacitor inverters with a half-bridge module in between. Proposed inverter topology is operated with zero CMV for modulation index <86% and is operated with a CMV magnitude of V dc /18 to extend the modulation range up to 96%. Experimental results are presented for zero CMV operation and for reduced common voltage operation to extend the linear modulation range. A capacitor voltage balancing algorithm is designed utilising the pole voltage redundancies of the inverter, which works for every sampling instant to correct the capacitor voltage irrespective of load power factor and modulation index. The capacitor voltage balancing algorithm is tested for different modulation indices and for various transient conditions, to validate the proposed topology.

This study presents a 17-level inverter-based induction motor drive for high-resolution multilevel voltage space-vector (SV) generation. The proposed topology consists of a three-level inverter and a seven-level inverter connected to an open-end winding induction machine. The two inverters are powered by two unequal DC supplies, resulting in a low component count, with just 12 switches and three floating capacitors per phase. The voltage SVs applied by the two inverters are chosen to eliminate circulating power flow and prevent DC bus overcharging. In addition, the switching states of both inverters are chosen in order to keep voltages of all floating capacitors well-controlled. Since the capacitors voltages are controlled using the phase currents, additional pre-charging circuitry is not required. A modulation scheme using level-shifted carriers has also been developed, which can be used with both V/f control and d-q control. The high-voltage inverter has a low effective switching frequency and the low-voltage inverter has a high effective switching frequency, reducing the switching loss. The included results of steady-state and transient testing of an experimental prototype demonstrate that the proposed scheme is suited for industrial drives and traction applications.