DC grid control through the pilot voltage droop concept: Mitigating consequences of time delays

The control of the individual converters in a voltage-source-converter high-voltage dc (VSC-HVDC) based multi-terminal dc grid is central for the overall performance of the system. A few different variants of power drooped against dc voltage control have been proposed in the literature for the purpose of distributing the power mismatch, following a disturbance, on several converters. One such variant is the pilot voltage droop control concept which involves communication. As is always the case when communication is involved, there is a risk of latencies and even communication failure. This paper proposes a way to mitigate the consequences of latencies for the pilot voltage droop concept. The approach may also have bearing on other control problems, involving communication, where the aim is to adjust the steady state solution based on remote measurements. The proposed solution is established in a stepwise fashion starting from the basic control principle, and the performance is exemplified by time domain simulations with a four station dc grid using Digsilent's Powerfactory platform.