THD Analysis of a 13 Level Asymmetric Hybrid Cascaded Multilevel Inverter for Industrial Applications

This paper proposes asymmetric cascaded H-bridge multilevel inverter with reduced number of switches suitable for industrial applications and renewable energy too. Cascade Multilevel Inverters are very popular and have many applications in electric utility and for industrial drives. When these inverters are used for industrial drive directly, the THD contents in output voltage of inverters are very significant as the performance of drive depends very much on the quality of voltage applied to drive. There are two types of cascaded H-bridge inverter based on input voltage from different sources namely symmetric and asymmetric inverter.The proposed asymmetric cascaded H-bridge topology consists only one H-bridge(with 4 switches) and 3 more switches totally 7 switches for 13 level output voltage. The new topology is well suited for drives and renewable energy applications. THD depends on modulation index and the switching angles for different levels of multilevel inverters. Therefore, the switching angles are calculated first by using N-R (Newton Raphson) method where certain number of harmonic components has been eliminated. THD is reduced to 9.23% by using SPWM technique.THD analysis is carried out for each switch of firing angle calculated analytically as well as using MATLAB/SIMULINK. The proposed topology is verified with hardware prototype of single phase 13 level inverter using FPGA based Xilinx SPARTAN 3E processor. This processor provides appropriate gating signals for switches using SPWM where the modulation index can be varied manually and THD is observed. By using low pass filter with minimum value, further the THD is reduced to 1.08%.all the results are validated experimentally.