MMC Submodule Group Control for Scalable HVDC Voltage Conversion

The patent divides the MMC system into multiple sets, where each set contains a specific number of submodules. This segmentation allows the control system to manage subsets of SMs independently, reducing the computational burden on the central controller. Each set can be controlled with a fixed number of SMs, making the control algorithm scalable and manageable even as the total number of SMs increases to achieve high voltage levels.

The patent introduces a new control dimension by organizing SMs into sets with hierarchical control structure. Instead of controlling all SMs uniformly, the system uses set-based organization where each set operates semi-independently. This dimensional organization transforms the control problem from managing N individual SMs to managing M sets with N/M SMs each, significantly reducing control complexity while maintaining the ability to achieve high DC voltage levels.

By segmenting SMs into sets, the patent enables independent control of each set's capacitor voltages. This segmentation allows the system to achieve low THD through coordinated control of multiple sets while managing circulating currents at the set level rather than system-wide, reducing overall control complexity.

The patent employs capacitor voltage balancing control that dynamically adjusts the voltage parameters of individual SMs within each set. By changing the voltage parameters of SMs in a coordinated manner across multiple sets, the system achieves low THD output while managing circulating currents through parameter optimization rather than increasing overall control complexity.

The patent segments the control function into central and local components. The central controller manages high-level coordination between sets, while local controllers handle day-to-day control of individual sets. This segmentation reduces the communication burden on the central controller and improves reliability through distributed control, as failures in one local controller do not compromise the entire system.

The patent introduces local controllers as intermediary devices between the central controller and the submodules. These local controllers act as mediators that handle communication and control tasks locally, reducing the direct communication burden on the central controller and improving system reliability through distributed intelligence. The local controllers can operate semi-independently, maintaining system functionality even when central communication is compromised.

The patent designs the control system with universal set-based modules that can handle any number of submodules. Each set is designed with the same control structure and capabilities, making the system universally applicable regardless of the total number of SMs. This multi-functionality allows the same control algorithm to scale from small to large systems without requiring fundamental redesign, maintaining both simplicity and adaptability.

The patent implements a dynamic control architecture where the number of sets and SMs per set can be adjusted based on system requirements. The control system dynamically adapts to different configurations by reorganizing SMs into appropriate sets, enabling scalability while maintaining control simplicity. This dynamic reconfigurability allows the system to evolve from initial deployment to expanded configurations without sacrificing control design simplicity.