Abstract:
The conventional converters have inherent drawbacks. like high current harmonics, low power factor and non-sinusoidal line currents. To improve the power factor and reduce the current harmonics, several circuit topologies of the ac to dc converters have been proposed in the past few years. However " the conventional converters also have inherent drawbacks like high dv/dt, common mode voltage and high power problems. Multilevel converters are suited for high power, high voltage applications because a greater number of levels are necessitated by advantages of high
voltage ratings. Multilevel nversion topologies allows a reduced stress of semiconductor devices and useful in eduction of line harmonics and near unity power factor can be accomplished.
A control topology has been discussed and implemented which operates the multilevel converter (three-level Converter) as an active power filter or rectifier or both at• the same time. In rectification mode the converter can supply active power from the DC bus to an output bus, while keeping the input current sinusoidal and with unity power factor. As an active power filter, the converter operates, as a controllable current source injecting the current harmonics required by nonlinear loads. The main problem in multilevel converter is the capacitor voltage balancing. Howevelthe operation of control scheme also maintains the voltages across eachcapacitor constant and equal.
