Multilevel inverters (MLIs) are being used in wide range of power electronics applications. These converters that are attracted a lot of attentions during recent years have different topologies with similar basic concept. This paper presents five main submodules (SMs) that are used as the basic structures of MLIs. The paper reviews the common multilevel inverter topologies with the structural point of view. The topologies are divided to main SMs to show conventional MLIs configuration and future topologies that can be created from the main SMs. The comparative study on topologies is investigated with details. The MLIs are categorized and investigated with due attention to some indexes such as the number of components, the ability to create inherent negative voltage, working in regeneration mode and using single DC source.

This paper presents a new reconfiguration module for asymmetrical multilevel inverters in which the capacitors are used as the DC links to creates the levels for staircase waveforms. This configuration of multilevel converter makes a reduction in DC sources. On the other hand, it is possible to generate 13 levels with lower DC sources. The proposed module of multilevel inverter generates 13 levels with two unequal DC sources (2VDC and 1VDC). It also involves two chargeable capacitors and 14 semiconductor switches. The capacitors are self-charging without any extra circuit. The lower number of components makes it desirable to use in wide range of applications. The module is schematized as two back-to-back T-type inverters and some other switches around it. Also, it can be connected as cascade modular which lead to a modular topology with more voltage levels at higher voltages. The proposed module makes the inherent creation of the negative voltage levels without any additional circuit (such as H-bridge circuit). Nearest level control switching modulation (NLC) scheme is applied to achieve high quality sinusoidal output voltage. Simulations are executed in MATLAB/Simulink and a prototype is implemented in the power electronics laboratory which the simulation and experimental results show a good performance.

In this paper, design and analysis of an isolated low-profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) power transformer was presented. For obtaining the stringent height switch mode power supplies, a multilayered coreless PCB power transformer of approximately 4:1 turn's ratio was designed in a four-layered PCB laminate that can be operated in megahertz switching frequency. The outermost radius of the transformer is 10 mm with achieved power density of 16 W/cm². The energy efficiency of the power transformer is found to be in the range of 87-96% with the output power level of 0.1-50 W operated at a frequency of 2.6 MHz. This designed step-down transformer was utilized in the SRC and evaluated. The supply voltage of the converter is varied from 60-120 VDC with a nominal input voltage of 90 V and has been tested up to the power level of 34.5 W. The energy efficiency of the converter under zero-voltage switching condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75 MHz. By using a constant off-time frequency modulation technique, the converter was regulated to 20 VDC for different load conditions. Thermal profile with converter loss at nominal voltage is presented.

Power converters with an extended range of line voltage are the main requirement in today's industrial applications like photovoltaic and supercapacitors based energy systems. The variation in the line voltage severely degrades the performance of power converters, because of the extended freewheeling interval, more circulation current, narrow range of zero voltage switching and increased EMI. This work suggests a modified Phase-Shifted Full-Bridge converter that cuts the freewheeling interval and minimizes these problems. It extends the input voltage range by keeping the operational duty cycle of the converter high over the wide range of input voltage while maintaining the performance stable. The proposed converter consists of four low profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a series mode and a parallel mode, which can be configured with changes in the operational conditions. The operation of the proposed converter with high switching frequency improves power density. Additionally, the use of multiple transformers minimizes heat management efforts and reduces the overall volume of the converter. The proposed work is validated in hardware characterization for a wide range of input voltage 100-400Vdc and up to the load power of 1kW. The measured energy efficiency of the proposed converter remains stable over the complete range input voltage 100-400Vdc.