Investigation of Zero Sequence Injection Method For Balancing of Multi-level Cascaded-H Bridge Inverter

The main complication that hinders the progress of multilevel inverters is the matter of unbalancing in DC-Link capacitor. This keeps on accumulating when moving towards higher voltage levels. The aim of this paper is to investigate the possibility of injecting the zero sequence voltage and current, that could be used to mitigate the unbalancing introduced in the Multi-level Cascaded-H bridge inverter. The mathematical model has been developed and arrayed with the purpose of calculating the zero sequence voltage and current to be injected accordingly. Development of the semiconductor devices has led not only to the usage of Pulse Width Techniques causing low harmonics in the system but also produce high quality power fed in to the gird, lowering the filter size. Singularity, existing in the cascaded-H bridge inverter leads to the limitation of zero sequence injection method. Seventeen level Multi-Level Cascaded-H Bridge inverter has been simulated in MATLAB using Alternate Phase Opposition Disposition Pulse Width Modulation, technique used for removal of unbalancing has also been developed in MATLAB showing promising results within the limits of grid requirement.