Losses investigation in SPWM-controlled cascaded H-bridge multilevel inverters

The application of voltage source multilevel inverters, in medium voltage-high power applications, is growing enormously. These inverters generate a near sinusoidal staircase output voltage waveform. Key attractions of multilevel inverters, compared to conventional two level inverters, are: higher output voltage can be achieved at low switching frequency, low voltage stress(dv/dt), lower total harmonic distortion (THD), less electro-magnetic interference (EMI), smaller output filter and higher fundamental output. However, loss evaluation of a multilevel inverter is much more complicated compared to a two level inverter. The scope of this paper is to investigate the loss performance in multilevel voltage source inverters. The study implements an on-line model to evaluate the conduction and switching losses precisely. As a case study, a single-phase 7-level cascaded H-bridge (CHB-MLI) with IGBT's as switching devices has been considered. SPWM has been applied in order to control the inverter. The inverter loss was analyzed at different switching frequencies, different modulation indexes and different loads. MATLAB-SIMULINK is used for the modelling and simulation.