Observer-Based Distributed Control and Power Sharing of Multiterminal DC Transmission Systems With Switching Topology

This article investigates a distributed fixed-time secondary control (FTSC) scheme to eliminate dc voltage deviations caused by voltage-droop control (VDC) in a multiterminal dc transmission system (MTDCTS) with switching topology and achieve precise power sharing within a fixed time frame. The distributed FTSC combines a dc voltage controller and a power sharing controller. The main objective is to restore the average dc voltage of the converters to dc voltage reference of MTDCTS within a fixed time. Additionally, it also enables power sharing among the converters based on their individual capacities. Compared to conventional distributed consensus control (DCC), fixed-time control (FTC) presented in this article exhibits a shorter convergence time and is unaffected by the initial state of MTDCTS. In this article, each converter communicates exclusively with its adjacent converters via a communication network that may undergo changes over time, which helps alleviate the strain on the communication network. To test the FTSC, a five-terminal MTDCTS with two wind farm converters (WFCs) is created in power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC).