Modular multilevel converters (MMC) have become established in the state of the art as the favored topology for high-voltage and high-power applications. The advantageous properties of an MMC, such as redundancy and fail-safety, high efficiency, industrial scalability, and the ability to electronically manage faults, are particularly suitable for use in high-voltage DC transmission (HVDC). For a holistic utilization of these advantages, as well as for the fulfillment of the demanding requirements in modern applications, adapted control concepts are necessary in addition to improvements of the hardware (submodule topologies and semiconductor components). In this work, the concept of direct multivariable control (MVC) is presented, which allows decoupled and highly dynamic control of all six degrees of freedom (direct current, alternating currents, circulating currents and common mode voltage). Individual tolerance bands are introduced for each of these variables, which strictly limit the deviations from the reference values and are maintained even in fault scenarios. This is achieved by the direct current control included in the concept, which results in minimum dead times and robustness against changing system parameters. Based on a simulation model and a scaled hardware setup with 96 full-bridge submodules, the steady-state and dynamic performance of the MVC is analyzed.     «

Modular multilevel converters (MMC) have become established in the state of the art as the favored topology for high-voltage and high-power applications. The advantageous properties of an MMC, such as redundancy and fail-safety, high efficiency, industrial scalability, and the ability to electronically manage faults, are particularly suitable for use in high-voltage DC transmission (HVDC). For a holistic utilization of these advantages, as well as for the fulfillment of the demanding requirement...     »