This study presents a new solution for harmonic optimisation of multi-level inverters using variable DC sources. The new approach is based on converter utilisation ratio consideration for total harmonic distortion (THD) minimisation. In the proposed solution, switch utilisation ratio (SUR) is introduced as an indication of efficient operation of multi-level converters and is maximised in the final THD minimisation objective functions for both phase and line-line voltages. According to the calculated formula, by SUR maximisation, the DC-link voltages of the cells are minimised which is essential for medium-and high-voltage applications. Alterable DC sources are also considered as degrees of freedom in the final target functions which results in feasible solution for the entire range of the modulation indices. In order to investigate the proposed technique, the simulations are performed for 5-, 7-, 9-and 11-level cascaded H-bridge inverters. Finally, experimental results validate the effectiveness of the suggested scheme for five-and seven-level inverters.

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In this paper, a new technique for harmonic optimization in cascaded H-bridge 7-level inverters is proposed. The suggested strategy is based on minimizing an objective function which simultaneously optimizes the converter utilization and Total Harmonic Distortion (THD). The Switch Utilization Ratio (SUR) is formulized for both the phase and line-line voltages of a 7-level inverter and is considered in the final objective functions. Based upon the SUR formula, utilization ratio enhancement will reduce the value of feeding DC links, which improves the efficiency and lifetime of the circuit components due to lower voltage stresses and losses. In order to achieve more effective solution in different modulation indices, it is assumed that the DC sources can be altered. Experimental validation is presented based on a three-phase 7-level inverter prototype.

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