Abstract:
Cascade Multilevel Inverters are very popular and have many applications in electric utilities and for industrial drives. When these inverters are used for industrial drives directly, the THD in the output voltage of inverters is very significant as the performance of drive depends very much on the quality of voltage applied to drive. A multilevel inverter in high power ratings improves the performance of the system by reducing harmonics. This paper presents the simulation of single phase nine level, eleven level and thirteen level inverters. Detailed analysis of these inverters has been carried out and compared with different loads. PWM control strategy is applied to the switches at appropriate conducting angles with suitable delays. These different level inverters are realized by cascade H-Bridge in MATLAB/SIMULINK. The inverters with a large number of steps can generate high quality voltage waveforms. The THD depends on the switching angles for different units of multilevel inverters. It has been found that the fifteen level CMLI satisfies this limit while seven and eleven level CMLI do not meet this limit.

Keywords: Cascaded H-bridge inverter, PWM, THD