New transformerless, scalable Modular Multilevel Converters for HVDC-transmission

In this paper a novel concept of high voltage direct current converter (HVDC) is presented employing the modular multilevel converter (M2C). Converters using IGBT-power devices, are getting increased importance in order to meet the global needs for reliable and environment friendly power supply and distribution. The new topology is compared to HVDC-transmission based on two level (2level) converters with direct series connected IGBT- devices or known multilevel converters. Main design aspects, concerning the rating of the power devices, the power losses and achievable efficiencies are investigated. For this purpose, a new computation method is presented and applied. This enables clear insight into the influence of various design parameters in a generalized form. Additionally, the characteristics and the differences of the topologies, with respect to passive filters, the necessary pulse frequencies and the arm currents are examined. As an example of the results, a comparison of the semiconductor losses and the efficiencies of the different topologies are given.