Performance and Scalability of Voltage Controllers in Multi-Terminal HVDC Networks

TL;DR

This paper compares the transient performance of different voltage control schemes in multi-terminal HVDC networks, showing that distributed controls outperform slack bus control especially as network size increases.

Contribution

It provides a quantitative comparison of transient performance between slack bus, droop, and DAPI controllers using the H2 metric, highlighting advantages of distributed control.

Findings

Distributed controls have better transient performance than slack bus control.

H2 norm remains bounded with droop and DAPI control as network size grows.

Slack bus control performance deteriorates significantly in larger networks.

Abstract

In this paper, we compare the transient performance of a multi-terminal high-voltage DC (MTDC) grid equipped with a slack bus for voltage control to that of two distributed control schemes: a standard droop controller and a distributed averaging proportional-integral (DAPI) controller. We evaluate performance in terms of an H2 metric that quantifies expected deviations from nominal voltages, and show that the transient performance of a droop or DAPI controlled MTDC grid is always superior to that of an MTDC grid with a slack bus. In particular, by studying systems built up over lattice networks, we show that the H2 norm of a slack bus controlled system may scale unboundedly with network size, while the norm remains uniformly bounded with droop or DAPI control. We simulate the control strategies on radial MTDC networks to demonstrate that the transient performance for the slack bus controlled system deteriorates significantly as the network grows, which is not the case with the distributed control strategies.