Multilevel inverters generate high-level voltage with high quality and low-harmonic distortion, and these unique properties have increased their applications in renewable energy sources. However, these inverters require several passive components and a complex pulse width modulation (PWM) control method. Besides, they suffer from voltage balancing problems. In this work, a new inverter has proposed that generates seven-level voltage from one DC source by reduced number of switches which does not exhibit any voltage balancing problem. The proposed inverter without any extra boost circuit is able to increase the input voltage. The voltage stress on all the switches in the proposed inverter is the same. In this study, variable amplitude phase disposition PWM control method that is compatible with the proposed inverter is developed. Moreover, extended structure of the proposed inverter and its new algorithm in generating all odd and even voltage levels are proposed. To validate the performance of the inverter, a prototype has been built and tested and also its performance has been modelled using PSCAD/EMTDC software package. Very good agreement has been achieved between experimental results and simulations.

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A new three-phase hybrid multilevel inverter configuration is proposed. The proposed inverter is modular and consists of three single-phase H-bridge inverters, one three-phase H-bridge inverter and auxiliary modules for increasing the number of output voltage levels. The performance of the proposed inverter has been compared with some of the commonly used inverters within the literature in terms of the number of components, blocking voltage and overall losses. The proposed multilevel inverter has lower number of insulated-gate bipolar transistors and gate drivers and subsequently requires a relatively simple control strategy for generating the desired output voltage. Finally, the performance of the proposed inverter has been validated via a laboratory-scale prototype along with numerical simulation.

Cascaded multilevel inverters (MLIs) have been proposed that utilise transformers in the basic unit. The proposed inverters primarily serve to step up the input voltages in addition to using lower number of components in comparison to traditional MLIs. In order to generate all voltage levels (even and odd) at the output, three different algorithms are proposed to determine the magnitude of DC voltage sources and transformer turn ratios. Also, the basic inverter unit was further developed and two new flexible MLI structures have been obtained. The developed structures increase the input voltage with no need for an additional boost converter. A reduction in the number of power switches, the peak inverse voltage, and the number of DC voltage sources are other advantages of the proposed topologies. Also, a simple cost model was developed and the dimensionless cost coefficient was determined. The overall cost of the proposed MLIs was compared to the similar MLIs from the literature. It was shown that the proposed MLI decrease the overall cost of the system if the cost coefficient is selected appropriately. To verify the performance of the proposed topologies simulated by the mathematical model; several lab-scale inverters were built and tested and good agreement was achieved.

A 15-level flying capacitor multi-cell based inverter with new control method is proposed. The main benefit of this topology is minimising the number of components (switches, insulated-gate bipolar transistor (IGBTs), diodes, flying capacitors and DC sources with minimum variety number) that are used for producing the same number of output voltage levels. The proposed novel control strategy is capable of regulating voltage of flying capacitors on desired values, which results in increased number of output voltage levels. Another feature of the proposed control strategy is robustness against the load changes. Moreover, a new algorithm is presented for determining the voltage rating of flying capacitors. Simulations carried out in PSCAD/EMTDC software package and the experimental data were validated against numerical results.