An Improved Droop Control Method for VSC- MTDC Considering Power Mismatch Allocation

Converter control of voltage-source-converter multi-terminal DC (VSC-MTDC) grids interconnecting offshore wind farms over long distance is an important research area grabbing much attention in academia and industry. When a converter outage happens in VSC-MTDC grids or the active power injected into DC grids varies, how to determine the power mismatch allocation is a critical issue. To overcome the problem of inaccurate estimation of power mismatch distribution based on local voltage measurements, this paper proposes an improved droop control method that can establishes a common DC voltage signal across the VSC-MTDC grids. Further, a method to determine the droop constants is also developed. The effectiveness of the proposed control strategy on power sharing of is verified by time-domain simulation studies of a four-terminal VSC-MTDC system in PSCAD/EMTDC.