International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) Volume No.3 Issue No.6, pp : 818-822 1 June 2014 IJSET@2014 Page 818 Comparative Analysis of Three Topologies of Three-Phase Five Level Inverter H.S.Sangolkar, P.A.Salodkar Department of Electrical Engineering, RCOEM, Nagpur, India. harshada.sangolkar@gmail.com, salodkarpa@gmail.com Abstract —This paper presents the simulation and analysis of the three topologies of three phase 5-level inverter. We have considered the Flying Capacitor Multilevel Inverter (FCMLI), the Neutral Point Clamped or the Diode Clamped Multilevel Inverter (NPCMLI or DCMLI) and the Cascaded H-Bridge Multilevel Inverter (H-bridge MLI). The comparison between these inverters is based on the %THD present in the output voltage. Each inverter is controlled by the multi-carrier sinusoidal pulse width modulation (SPWM). The analysis shows that the total harmonic distortion (THD) is approximately 23% for DCMLI and 22% for PWM H-Bridge topologies, and it is about 24% for the FCMLI topology. The comparative results of the harmonic analysis have been obtained in MATLAB/SIMULINK. Keywords—Multilevel, Cascade, Harmonics, Modulation, MATLAB/SIMULINK, THD I. Introduction In the recent years, multilevel inverters (MLI) are increasingly being used for medium voltage and high power applications due to their various advantages such as low voltage stress on the power switches, low electromagnetic interferences (EMI), low dv/dt ratio to supply lower harmonic contents in the output voltage and current. Comparing two-level inverter topologies of the same power ratings, MLIs also have the advantages that the harmonic components of line-to-line voltages fed to the load are reduced owing to its switching frequencies [1]. In this paper, constant switching frequency multicarrier, sinusoidal pulse width modulation method is used for the multilevel inverter. Multilevel inverter is an effective solution for increasing power and reducing harmonics of an ac waveform. The control objective is to compare the reference sine wave with multicarrier waves for the three phase five level inverters. The elementary concept of a multilevel inverter to achieve higher power is to use a series of power semiconductor switches with several dc sources to perform the power conversion by synthesizing a staircase voltage waveform. Capacitors, batteries, and renewable energy sources can be used as the multiple dc voltage sources. The multilevel inverter output voltage has less number of harmonics [2, 3]. The most common MLI topologies are classified into three types: neutral point clamped (NPCMLI) or diode clamped MLI (DCMLI), flying capacitor MLI (FCMLI), and Cascaded H- Bridge MLI (CHBMLI). The basic topologies of the MLI are shown in Fig.1. The diode clamped inverters, particularly, the three-level structure have a wide popularity in motor drive applications besides other multilevel inverter topologies. However, it would be a limitation of complexity and number of clamping diodes for the DCMLIs, as the level exceeds. The FCMLIs are based on balancing capacitors on phase buses and generate multilevel output voltage waveform clamped by capacitors instead of diodes. The FCMLI topology also requires balancing capacitors per phase at a number of (m - 1) * (m - 2)/2 for an m-level inverter and it will cause to increase the number of required capacitor in high level inverter topologies and complexity of considering DC-link balancing [1]. Nowadays, the multilevel inverters have become more attractive for researchers and manufacturers due to their advantages over conventional three-level pulse width- modulated (PWM) inverters. They offer improved output waveforms, smaller filter size, low EMI, lower total harmonic distortion (THD). Multilevel inverter topology has the least components for a given number of levels. Cascaded H-Bridge- MLI topology is based on the series connection of H-bridges with separate DC sources. Since the output terminals of the H- bridges are connected in series, the DC sources must be isolated from each other. The need of several sources on the DC side of the inverter makes multilevel technology attractive for photovoltaic applications. Owing to this property, CHB-MLIs have also been proposed in order to achieve higher levels [1, 4, 5]. The Cascaded Multilevel (a)