Switch-Clamped Modular Multilevel Converters With Sensorless Voltage Balancing Control

Modular multilevel converters (MMCs) feature an established topology for the highest voltage and power levels. For lower levels, MMCs find a wide range of applications in generation, energy storage, and electric motor drive. However, the large quantity of expensive voltage sensors as well as high data-processing requirements for the module voltage balancing remains an obstacle. Additionally, the stark cost reductions of power electronic semiconductors have reduced their share in the total cost and rendered initially uneconomical module topologies appealing in low and medium voltages. In this article, we proposed an MMC topology with an active clamping path that balances the voltage of the modules in an arm. The proposed structure can achieve sensorless voltage balancing with a minimum control effort. The sensorless operation has the added benefit of reducing the communication as well as computation demand between the modules and the central controller. As compared with the state-of-the-art voltage balancing schemes, the proposed solution achieves a balanced system operation with less power loss, fewer components, and without any measurement. The presented analysis as well as the simulation and experimental results verify the benefits of the proposed topology. The results demonstrate that even in the face of a severe imbalance, all the module voltages are maintained within tight boundaries.