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MMC based multi-terminal HVDC subsea power transmission system with the integration of offshore renewable energy

Typical 2-level and 3-level converters are still widely implemented in offshore renewable and deep-water oil and gas applications due to their simplicity and maturity in these fields. However, it is difficult for these converters to operate in higher dc bus voltage due to the switching transients, large voltage stress on each switches and large losses. Therefore, Modular Multilevel Converter (MMC) has been gaining popularity over these converters in the field of high voltage and high power applications such as HVDC. In this paper, control of MMC based multiterminal HVDC transmission system for offshore wind energy integration and subsea oil and gas application are presented. Different strategies to regulate the DC link voltage, active and reactive power flow and AC grid voltage of the passive subsea grid in a 3-terminal offshore HVDC grid have been presented.