Hybrid control strategy for effective frequency regulation and power sharing in multi-terminal HVDC grids

This study proposes a hybrid control (HC) strategy for improved frequency regulation and power sharing in multiterminal HVDC (MTDC) integrated AC grids. The proposed method uses the topology of bi-polar converters in the MTDC system to improve power sharing and frequency regulation. In this methodology, the two voltage source converters (VSCs) in a bi-polar topology are operated with individual specified control methods. In the proposed HC method, one of the converters operate in voltage square frequency droop (PV(2)f) and another in power frequency droop (Pf) control methods. This HC strategy is implemented for grid side voltage source converters in MTDC grids. Further, the performance of frequency regulation and autonomous power sharing of the proposed HC technique is compared with the conventional voltage and frequency droop (PVf) and improved PV(2)f control methodologies. In order to validate the proposed method, two AC-MTDC systems are considered. In both the systems, mesh typed MTDC CIGRE B4 DC test system is in common, it is integrated with two-area power system and New England IEEE 39-bus system to form two different AC-MTDC systems.