International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, Volume-7 Issue-5S2, January 2019 200 Published By: Blue Eyes Intelligence Engineering & Sciences Publication Retrieval Number: ES2030017519/19©BEIESP Abstract: Applications of multi level inverters have been broadly accepted for high power AC drives purposes. In this paper a multi level inverter with reduced number of components has been designed. The power quality of the output waveforms are controlled by proper selection of switching angles for different levels of the output. A simplified optimal THD modulation algorithm is used to calculate the proper switching angles of the output. This algorithm greatly reduces the computational efforts required than the conventional computation methods and also produces better output performances. The simulation model of 9-level asymmetrical inverter with reduced number of components is built to validate its operation and the results are presented. Keywords: Multi Level Inverter, Reduced Number of Components, Optimal THD Modulation, and Harmonic Distortion. I. INTRODUCTION Now-a-days, the demand for high power equipments has been augmented. High power equipments are typically connected to the medium-voltage network. It is hard to connect a single power semiconductor device directly to the medium-voltage network. For these reasons, a family of Multi Level Inverters (MLIs) has emerged as the solution for high power medium or high voltage applications. It has gained increasing awareness in industry and research since it was introduced in 1980s [1]. A MLI is an array of power semiconductor devices. The advantages of this method over the conventional two-level inverter approach are: improved output power quality, lower voltage stress on the switches and load, improved amplitude of fundamental components and lower electromagnetic interference [2]. The basic function of MLI is to sum up several small DC sources with appropriate switching sequences to the array of power switches so as to obtain a stair-case waveform which resembles the AC sine waveform. Hence inverter action is obtained. The merits of the MLI can be enhanced by increasing the number of steps in the output waveform. There are three types of basic MLI topologies: Neutral Point Clamped (NPC) [3], Flying Capacitor (FC) [4] and Cascaded H-Bridge (CHB) [5] multi level inverter. Among these topologies CHB multi level inverter (CHBMLI) becomes more trendy, because of its superior reliability arising from its modularity and lesser number of hardware devices. Cascade connection of a number of H-bridge inverters forms a CHBMLI. Each H-bridge inverter can Manuscript received January 25, 2019. V. Karthikeyan, Department of Electrical and Electronics Engineering (Marine), AMET University, 135, East Coast Road, Kanathur, Chennai, Tamilnadu, India. V. Jamuna, Department of Electrical and Electronics Engineering, Jerusalem College of Engineering, Velachery Main Road, Narayanapuram, Chennai, Tamilnadu, India. generate three voltage levels in the output. These inverters are classified as: symmetric (each H-bridge is fed by equal DC sources) and asymmetric (each H-bridge is fed by unequal DC sources) MLIs. An asymmetric CHBMLI is preferred to produce more number of output levels with same number of power switches. Conventionally, there are two asymmetrical configurations: binary and ternary. There are various other asymmetrical MLI topologies proposed by many researchers [6]. Since the MLI topologies require reduced voltage stress on the power switching devices, we can realize the high power inverters with low power matured semiconductor technology [7]. MLIs have been used in many applications, such as variable speed AC drives, power quality devices and renewable energy generation such as photovoltaic, wind and fuel cells [8]- [10]. The power quality of the MLI increases as the number of levels in the output increases. The main disadvantage of MLI is the circuit complexity increases, hence the overall cost and size of the system with the increase in the number of levels at the output. To defeat these disadvantages, many topologies are introduced with reduced number of components [11]-[14]. Another major disadvantage with the conventional MLI is the requirement of small isolated DC voltage sources or series bank capacitors. This is overcome by using the renewable energy sources. The performance of the MLI is mainly depends on the modulation technique used to generate the required gating signals. Different modulation techniques have been introduced to improve the performance of the MLIs [2],[10],[15]-[18]. The commonly used modulation techniques are Selective Harmonic Elimination (SHE) [15], [16], Carrier Based PWM (CBPWM) [17] and Space Vector Modulation (SVM) [18]. In this paper, a Reduced Switch Reverse Voltage (RSRV) multi level inverter with asymmetrical DC sources and reduced number of components is considered. This topology requires lesser number of components than the conventional topologies. The performance of the inverter is controlled by a simplified algorithm of optimal THD modulation for calculating the proper switching angles for different levels of the output. This algorithm reduces the computational complexity of the switching angles of the different levels of output. The operation and performance of the 9-level RSRV-MLI with asymmetrical DC sources are presented and validated through the simulation results. A Simplified Optimal THD Modulation Algorithm for Multi Level Inverter with Reduced Components V. Karthikeyan, V. Jamuna