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To reduce output voltage waveform distortion and associated harmonic loss, multilevel converter voltage levels count must be increased. While for symmetric cascaded converter levels count increases linearly with modules count, for asymmetric converter levels count grows exponentially. However, a symmetric converter is modular and it is possible to stabilize its voltage levels by charge balance control methods while asymmetric converter modules are different and voltage levels stabilization is not possible. To set up a compromise between converter levels count and its modularity and voltage levels stability, it is suggested to use a hybrid asymmetric converter comprised of a low resolution symmetric and high resolution - symmetric or asymmetric - parts. Utilization of full dynamic range of a high resolution part for each low resolution level provides the increased levels count, reduced and uniform high resolution part power consumption at the expense of increased high resolution part switching frequency.
Date of Conference: 3-5 Dec. 2008