DC voltage deviation-dependent voltage droop control method for VSC-MTDC systems under large disturbances

Along with the increasing demand of large power transfer and integration of renewable energy sources, voltage source converter based multi-terminal high-voltage DC (VSC-MTDC) technology has represented both challenges and opportunities. However, the DC voltage of the droop-controlled VSC station may exceed the DC voltage limits when facing large disturbances, thereby losing the DC voltage control and power sharing capabilities. To tackle this problem, a DC voltage deviation-dependent voltage droop control method (VDM) is proposed to change the droop coefficients adaptively when large disturbances occur, not only retaining the advantages of the fixed VDM in the steady state, but also preventing frequent adjustments of the droop coefficients in the transient state. The basic analytical model of droop-controlled VSC is analysed first, and then the generalised linear model of VSC-MTDC is derived based on the restrict requirements of DC voltage deviation. The DC voltage deviation-dependent VDM is derived from the generalised linear model of the VDC-MTDC. Case studies and simulations of a +/- 320 kV VSC-MTDC system are conducted in PSCAD/EMTDC software to validate the effectiveness of the proposed DC voltage deviation-dependent VDM.