Advanced Impedance-based Control Design for Decoupling Multi-Vendor Converter HVDC Grids

Abstract

A progressive interconnection of existing HVDClinks to form grids and the development of completely new HVDCgrids from different vendors are expected shortly. One of thecurrent challenges of such endeavour is unintended interactionsdue to independently designed controllers. This article proposesa design methodology for decentralized controllers to mitigatesuch interactions in multi-vendor voltage source converter (VSC)-HVDC grids. The approach presented relies on the unique stand-alone input-output impedance transfer function of each VSC,and the global impedance transfer function as seen from eachterminal after interconnection with other VSCs. Subsequently,network-level controllers are designed by attempting to match theglobal responses at selected locations based on a novel interactionanalysis, to the unique transfer function model of the vendorsat the corresponding location. This approach reduces the entireproblem to an impedance matching problem. We demonstrate theefficacy and flexibility of both the methodology and the designedcontrollers in mitigating interactions due to the independentdesign of VSC controllers through nonlinear simulations on afour-terminal droop controlled HVDC grid