ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering (An ISO 3297: 2007 Certified Organization) Vol. 2, Special Issue 1, December 2013 Copyright to IJAREEIE www.ijareeie.com 288 Modified Multilevel Inverter Topology for Driving a Single Phase Induction Motor Divya Subramanian 1 , Rebiya Rasheed 2 M.Tech Student, Federal Institute of Science And Technology , Ernakulam , Kerala, India 1 Asst. Prof, Federal Institute of Science And Technology , Ernakulam , Kerala, India 2 Abstract: The multilevel inverter utilization has been increased since the last decade. These new type of inverters are suitable in various high voltage & high power application due to their ability to synthesize waveforms with better harmonic spectrum and faithful output.. This paper presents a multilevel inverter configuration which is designed by insertion of a bidirectional switch between capacitive voltage sources and a conventional H-bridge module. The modified inverter can produce a better sinusoidal waveform by increasing the number of output voltage levels. By serial connection of two modified H-bridge modules, it is possible to produce 9 output voltage levels including zero. Multicarrier phase-shifted pulse-width modulation method is used to generate control signals. The analysis of the output voltage harmonics is carried out. From the results, the proposed inverter provides higher output quality with relatively lower power loss as compared to the other conventional inverters with the same output quality. Also the hardware implementation was made with induction motor load. Keywords: Cascaded H-bridge multilevel inverter (CHB), phase shifted modulation, multicarrier pulse-width modulation, total harmonic distortion (THD). I. INTRODUCTION Over the past two decades, multilevel inverters have attracted wide interest both in the scientific community and in the industry. The reason for the increased interest is that the multilevel inverters are a viable technology to implement controlled rotational movement in high-power applications. Multilevel inverters include an array of power semiconductors and capacitor voltage sources, the output of which generate voltages with stepped waveforms. The commutation of the switches permits the addition of the capacitor voltages, which reach high voltage at the output, while the power semiconductors must withstand only reduced voltages. Multilevel converters have a lot of advantages to offer in medium- to high-voltage range of applications. These include variable speed motor drives and power system applications. Multilevel converters can synthesize waveforms using more than two voltage levels, Small filter components are required and sometimes they can be left out altogether. Disadvantages of multilevel topologies include: high number of semiconductor devices, complex control as a result of the large number of controlled devices, large number of gate drive circuits, several DC voltage sources are required, need to balance voltages across capacitors used in voltage divider circuits. There are different types of multilevel circuits involved. The first topology introduced was the series H-bridge design. This was followed by the diode clamped converter, which utilized a bank of series capacitors. A later invention detailed the flying capacitor design in which the capacitors were floating rather than series-connected. Another multilevel design involves parallel connection of inverter phases through inter-phase reactors. In this design, the semiconductors block the entire dc voltage, but share the load current. Several combinational designs have also emerged some involving cascading the fundamental topologies. These designs can create higher power quality for a given number of semiconductor devices than the fundamental topologies alone due to a multiplying effect of the number of levels. The multilevel inverters are mainly classified as diode clamped, Flying capacitor inverter and cascaded multilevel inverter. The cascaded multilevel control method is very easy when compare to other multilevel inverter because it doesn’t require any clamping diode and flying capacitor. In this paper, we are using a new topology of cascaded H-bridge multilevel inverter for producing nine output voltage levels and for that we are using multicarrier modulation technique. This paper is organized as follows: the inverter’s configuration is presented in Section II, the PWM modulation strategy in Section III, analysis of output voltage and harmonics in Section IV, the hardware implementation in Section V and Section VI is the conclusion.