**ABSTRACT:**

Multilevel inverter technology has emerged as a very important alternative in the field of medium and high power industrial drive applications. The emergence of multilevel inverters has been increasing since three decades. These new types of converters are suitable for high voltage and high power application due to their ability to synthesize waveforms with better harmonic spectrum. Several multilevel converter topologies have been developed; i) diode clamped, ii) flying capacitors, and iii) cascaded or H-bridge. Cascade Multilevel Inverter (CMI) is one of the productive topology from multilevel family. By increasing the number of output voltage levels in multilevel inverter the Total Harmonic Distortion (THD) can be minimized. This project proposes a new topology of 21 level asymmetric cascaded multilevel inverter with 11 unidirectional switches and 3 diodes and 4 DC voltages sources. Several Pulse Width Modulation techniques are available, among them Level shifting SPWM techniques such as PO, POD and Space Vector PWM are used and comparison is shown on the basis of THDs obtained. MATLAB/ SIMULINK software is used for simulation

** ****SOFTWARE:** MATLAB/SIMULINK

** ****CONCLUSION:**

In this project, a new topology for 21 levels is proposed with reduced number of switches and DC sources. The Proposed circuit is validated on MATLAB/Simulink platform. The simulation of the 21 level asymmetric cascaded multilevel inverter is successfully done using Space vector, Phase disposition and Phase Opposition disposition pulse width modulation techniques. Thus, this new circuit will require lesser hardware space, lesser cost; also the complexity of the circuit will reduce. From the FFT analysis, it is found that PD PWM and POD PWM techniques give least THD. It is observed that even after the reduction in switches and sources, the desired output is obtained.

** ****REFERENCES:**

- Jannu Ramu, S.J.V. Prakash, K. Satya Srinivasu, R.N.D. Pattabhi Ram, M. Vishnu Prasad and Md. Mazhar Hussain,” Comparison Between Symmetrical And Asymmetrical Single Phase Seven Level Cascade H-Bridge Multilevel Inverter With PWM Topology,” International Journal of Multidisciplinary Sciences and Engineering, Vol . 3, no. 4, April
- Karthikeyan, Dr.S.Chenthur Pandian,” An Efficient Multilevel Inverter System For Reducing THD With Space Vector Modulation,” International Journal of Computer Applications (0975 – 8887),Volume 23– No.2, June 2011.
- Xiaodong Yang, Chonglin Wang, Liping Shi ,Zhenglong Xia,” Generalized Space Vector Pulse Width Modulation Technique For Cascaded Multilevel Inverters,” International Journal of Control and Automation, Vol.7, No.1 (2014), 11-26
- Balamurugan M.,Gnana Prakash M.,Umashankar S.,” A New Seven Level Symmetric Inverter With Reduced Number Of Switches And Dc Sources,” Advances in Electrical Engineering (ICAEE), 2014 International
- Elyas Zamiri.,Sajjad Hamkari.,Ebrahim Babaei.,” A New Cascaded Multilevel Inverter Structure With Less Number Of Switches,” 5th Power Electronics, Drive systems and Technologies Conference, 2014 .