The increase in the High Voltage Direct Current HVDC technology is growing rapidly and the use of multilevel converter the must However the increase in the levels of converters leads to complexity Besides the interconnection for converting DC AC DC and to interface renewable systems like solar and wind farm is another issue should be taken into the account This paper proposes a high frequency system for DC AC DC utilizing lower switching losses modular multilevel converter and alternate arm converters rather than conventional two or three level converters In fact the DC link capacitors required for interconnection increases by increasing levels in conventional as well as in proposed converter Hence the high frequency operation is the best solution for a significant reduction in the volume of capacitors and transformers The proposed 50 MW 350 Hz converter was verified with efficient characteristics by simulation using MATLAB Index Terms DC DC power conversion high frequency converters HVDC converters multilevel converters pulse width modulation I INTRODUCTION The invention of Modular multilevel converter MMC was started in 2003 by Marquardt and Lesnicar 1 and has a promising solution for HVDC transmission systems HVDC systems are developed or planned to be built up to 1000MW 2 The HVDC systems are proposed to control and to provide wide power range high efficiency and reliability in steady state and transient state as well as healthy and faulty conditions at dc side is challenged 3 4 In particular the generalized MMC benefits from its scalability with power IGBTs and power IGCTs by providing wide power and voltage ratings 1 5 Since a huge structure of IGBTs is necessary to block high voltages even with low switching frequency techniques can also achieve acceptable output waveforms 6 The low switching frequency design always suggests a high efficient modulation with large number of capacitors 7 In addition to the efficiency very important factor to be considered is reliability for designing the high power converters
