DC Link Capacitor Voltage Balancing Technique For Cascaded H-Bridge Multi-level Inverter /

Abstract

to-medium power system applications. They while providing high quality power also utilizes lesser number of components as compared to their counter parts. The complication that has hindered the path of development of Cascaded H-Bridge Multi-level inverter is unbalancing of Dc-Link capacitor. This unbalancing occurs due to number of reason, one of them is the occurrence of fault in the system resulting in to un-balancing. This needs to be resolved for the proper functioning of the inverter and to be with in the limit of the IEEE standards. Over the years, research has been focused on developing an balancing techniques that could be used to reduce the un-balancing and enhance the quality of power that can be integrated into the grid. One of many solutions floating around the market is being proposed in this thesis, having the ability to reduce the un-balancing while at the same time keeping the harmonic content in check. Unbalancing in introduce using three phase faults in the system. Zero sequence injection method calculates the zero sequence voltage in case of Y-connected multi-level inverter and zero sequence current in case of delta-connected multi-level inverter and feed it back in to the system allowing the system to gain its stable voltage and current values again. This method also has its own limitation like the fact that required zero voltage and current reach un-attainable values under certain circumstances. System was able to gain stability in regards to voltage and current when the zero sequence is fed back in to the system. Current controller takes 0.02 seconds for achieving the new reference voltages level to produce the proper switching when fault was introduce in the system. Zero sequence method is one of the most advance method for un-balancing problem because of its robustness. It takes minimum amount of time among the existing system because it is not dependent upon the PI controller loop but it does take some time when calculating as the un-balancing has to occur for it to calculate.