اینورتر جدید چند سطحی اساسی با تعداد عناصر سوئچینگ کاهش یافته New Fundamental Multilevel Inverter with Reduced Number of Switching Elements

I. INTRODUCTION In recent years, high-power medium-voltage multilevel inverters applications have been increased due to producing good output voltage harmonic spectrum and easy control. Multilevel inverters structures are used in some applications, including FACTS devices, HVDC transmissions, AC motors drives and active filters to overcome the voltage and current limitation on semiconductors switch [1]–[3]. Multilevel inverters are suitable for high-power applications due to good characteristic such as high-power generation, low voltage common-mod, better output harmonic waveforms and lower dv/dt. Other important advantages of multilevel inverters are reducing THD, losses; electromagnetic interference and the stress of power electronic switches [4,5]. Different structures have been presented for multilevel inverters. The neutral point diode clamped multilevel inverters, flying capacitors multilevel inverters and H-bridge cascaded multilevel inverters are part of the basic structures [6,7]. Cascaded H-bridge multilevel inverter is one of the most popular structures compared to other classical structures due to the use of lower number of power electronics devices for producing high number of voltage levels. The biggest advantages of the cascade H-bridge multilevel inverters are: [8,9] 1. Regular circuit structure due to the same structure of each cell. 2. No additional clamping diodes compared to the diodeclamped multilevel inverters. 3. No need to flying capacitors compared to flying capacitors multilevel inverters. 4. To produce the specified voltage levels need to lower number of power electronic devices in compared to classical multilevel inverters. However despite all the advantages mentioned, the cascaded H-bridge multilevel inverter have disadvantages such as: voltage generation is independent to DC links in each cell, nonflexibility in increasing the output voltage range and high number of DC links and power switches for generating high number of voltage levels [10]–[12]. Recently, new cascaded multilevel inverters structure has been a topic of investigation by many researchers [13]–[17]. Although, researchers have made great efforts on multilevel inverter, it seems further research on multilevel inverter structures can still be done in order to define an optimal structure for increasing number of output voltage levels. Therefore, in this research, firstly a new fundamental inverter for cascaded multilevel inverters is introduced, which reduces the number of switching elements and independent power supplies. Secondly, a cascaded inverter is suggested linked to z number series of fundamental inverter. Subsequently, three methods to define values of DC links are presented. To check the advantage and disadvantages of the suggested cascaded structure a comparison is made with traditional structures aspects of the number of switching elements and DC links. Lastly, to verify the performance of the inverter a single-phase 15-levels fundamental inverter is simulated in PSCAD/EMTDC environments.