Optimization of multilevel voltage source converters for medium-voltage DC transmission systems

In the past, the market of generation, transmission and distribution of electricity was dominated by large power utilities. At present, the market for electrical power is being liberalized in multiple regions of the world, To guarantee power quality, new power electronic systems are being installed as they offer economic solutions. These systems are usually based on voltage source inverter (VSI) topologies. In this paper, transformerless systems are considered to offer higher power density and lower cost. However, to provide high waveform quality without high switching frequencies, multilevel converter topologies are essential. The aim of this paper is to find an optimal converter topology for a medium-voltage DC transmission system (MVDC). Different multilevel topologies are compared and the best topology is chosen to examine in detailed with respect to harmonic content of output voltages and dynamic response behavior during load changes.