Multilevel inverter topology survey
[Examensarbete på avancerad nivå]
Multilevel inverters have become more popular over the years in electric high power application with the promise of less disturbances and the possibility to function at lower switching frequencies than ordinary two-level inverters. This report presents information about several multilevel inverter topologies, such as the Neutral-Point Clamped Inverter and the Cascaded Multicell Inverter. These multilevel inverters will also be compared with two-level inverters in simulations to investigate the advantages of using multilevel inverters. Modulation strategies, component comparison and solutions to the multilevel voltage source balancing problem will also be presented in this work. It is shown that multilevel inverters only produce 22% and 32% voltage THD while the two-level inverter for the same 1kHz test produces 115% voltage THD. For another simulation, while using lower switching frequency, it is shown that when the two-level inverter generates 25.1W switching losses, the tested multilevel inverters only produce 2.1W and 2.2W switching losses.
Nyckelord: Multilevel inverter, topologies, modulation, voltage balance, comparison