Optimal Designing and Construction of a New Multilevel Inverter with the Purpose of Improving the Operational Parameters

Research Gaps:
Two level voltage source inverters were mostly usable for low voltage and medium power applications because of the voltage, power and switching frequency rating limitations on power semiconductors switches and low efficiency. So MLIs are intro-duced to overcome these issues by generating more than two level stepped waveform at the output voltage to close sinusoi-dal voltage waveform without expensive passive filters and bulky transformers. In addition, many advantages such as low voltage stress across power switches, less total harmonic dis-tortion (THD) in the output voltage (the filter requirements can be greatly brought down or even eliminated), low electromag-netic interference (EMI), smaller common mode voltage, low stress dv/dt ratio, better power quality, lower switching losses compared to two level inverter. However, MLI possesses some drawbacks; to increase the output levels, the number of semi-conductor switch requirement along with peripherals devices such as gate driver circuit, protection circuit and heat sink in-creases. Increased device count makes overall system com-plex, bulky and costly and reduces the reliability and efficiency of the converter. Each of these classical topologies in addition to its own advantages, has some important limitations.
Solutions:
In view of two level and classical MLIs disadvantages, new breeds of multilevel inverters have been developed. So the concept of reduced component count (RCC-MLIs) are defined because of their advantages over classical topologies such as required less number of switches, related drivers, protection circuit and heat sink reduced complexity and reduced weight of the inverter. RCC-MLIs are generally classified as hybrid in-verter based on CHB-MLI topology, and non-hybrid inverter. In RCC-MLI topologies some important parameters should be sim-ultaneously observed in terms of: required components (includ-ing elements like switches, diodes, and DC sources), total standing voltage (TSV), DC sources magnitudes, power losses (including switching and conduction losses), reliability, switching patterns, and maximum output voltage (Vomax). In symmet-rical MLIs, a number of DC voltage sources of equal magnitude are used, whereas, in asymmetrical MLIs a number of DC volt-age sources of different magnitudes are required. Asymmetric configuration of DC sources has more levels in the output volt-age.
Conclusion:
By considering recent researches about RCC-MLIs, it is possible to improve their structure. In this improvement some parame-ters such as required components, total cost, total standing voltage and reliability should be considered. Because of more levels in the output voltage, asymmetric configuration is sug-gested for DC sources magnitude. And also, to reduce the complexity of control and make a static structure only using switches and diodes are recommended.