Comprehensive Analysis of the Control Structures for MMC Applications

Early MMC applications are controlled with a centralized controller. However, recent MMC controllers are primarily based on a distributed control structure as modularity and scalability features of an MMC can be efficiently utilized with local controllers of the distributed control algorithm. However, the distributed control structure also has a centralized unit for coordinating its local controllers, and the chance of a single point of failure still exists. Therefore, in most recent MMC applications, decentralized control structures are adopted, eliminating the central control unit. Eliminating the central control unit eliminates a single point of failure risk, and the reliability of an MMC theoretically increases. However, this might not always be true for practical MMC applications, as the operation of an MMC relies overall structure of an MMC. Therefore, each arm of an MMC should operate appropriately for the safe and reliable operation of an MMC. This paper evaluates and compares the control structures for MMC applications regarding reliability and area of use.