Abstract
Traditional Hybrid Multilevel inverter produces (2n+1) levels at output voltage of inverter for n number of sources by a switching mechanism which requires 4n number of switches. However, one underlying problem of single phase multilevel inverter is that it requires isolated sources which render it inappropriate except where isolated energy sources are available. In this paper, firstly, a new technique is proposed for generating multiple isolated Buck-Boost DC sources of variable voltages from a single DC source. Secondly, a new switching algorithm is proposed by which number of output voltage levels can be increased by 80%, 157% and 833% while reducing number of switch count by 0%, 16.66% and 25% keeping voltage stress across the switches unhampered for two, three and four source inverter respectively compared to traditional multilevel inverter. As a result, conspicuous improvement is achieved in terms of harmonic distortion dropping it down to 4% and less than 1% for three and four source inverter respectively even without using output filters or sinusoidal PWM switching signals. A meticulous analysis of the circuit configuration and switching algorithm along with detailed performance analysis is provided throughout the paper.
Highlights
Multilevel inverter has become popular especially in high power applications due to its inherent capability of reducing voltage stress across semiconductor devices
Multilevel inverter is capable of producing higher output voltage which contains lesser harmonics and subharmonics [1]
Traditional cascaded H-bridge multilevel inverter (CHB-MLI) requires n isolated DC sources for an output voltage which exhibits (2n+1) discrete voltage levels which precludes its universal implementation for high power applications [5]
Summary
Multilevel inverter has become popular especially in high power applications due to its inherent capability of reducing voltage stress across semiconductor devices. Traditional CHB-MLI requires n isolated DC sources for an output voltage which exhibits (2n+1) discrete voltage levels which precludes its universal implementation for high power applications [5]. An adroit switching arrangement can increase number of voltage levels, reducing harmonic distortion. This approach demands unequal source voltage for each hybrid inverter block [4,5,6,7,8,9]. High frequency PWM signals can be used to reduce THD instead of increasing discrete voltage levels, but it hampers one fundamental advantage of MLI [11,12,13,14,15]. Isolated DC sources are generated from a single DC source by slightly modifying typical Buck-Boost circuit arrangement and connecting them parallel. Cost, weight, size and other corresponding attributes of the overall circuit reduces and reliability and longevity of the package increases
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