A surplus power absorption strategy in MMC-MTDC systems based on master-slave energy control

Modular multilevel converter based multi-terminal direct current (MMC-MTDC) systems rely on energy-dissipating devices to handle surplus power caused by AC-side faults at the receiving-end, which suffers from poor economic efficiency and significant energy waste. To fully exploit the inherent surplus power absorption capability of MMC-MTDC systems and reduce dependence on energy-dissipating devices. A master-slave energy coordination strategy is proposed for interactive power absorption among multiple converter stations. Firstly, an MMC-MTDC control model is established, and the feasibility of surplus power absorption through energy-based control is analyzed. Subsequently, a three-dimensional energy model of the MMC is introduced to achieve decoupled energy control for each pole of the converter stations. Based on a simplified MMC-MTDC system model, active energy control schemes are designed for different types of converter stations. Furthermore, inspired by the master-slave control concept, a timing-based energy coordination logic is developed to address various AC-side fault scenarios at different receiving-end stations and two categories of surplus power levels, thereby enabling coordinated utilization of available energy margins across multiple converter stations. Finally, a MMC-MTDC system is implemented in PSCAD/EMTDC for simulation validation. Results demonstrate that the proposed strategy effectively coordinates multiple converter stations energy control without requiring energy-dissipating devices. The strategy can adapt to diverse surplus power conditions and successfully achieve fault ride-through.