Drop the Droop

Abstract

This paper presents the case against the use of droop control in DC traction grids when integrating third-party users, energy storage, or DC-side renewables. The primary argument is that the voltage behavior and the requirements of traction grids should not be mistakenly compared to those of residential distribution grids or microgrids, as no sufficient control input can be derived from the complex power flow of traction grids. In one example, it is shown that droop control can trigger a traction substation to charge the batteries by 41% of their load demand instead of harvesting the available braking energy. This paper also identifies key directions for traction grid state estimators and warns of the narrow applicability of every estimator to the specific energy supply architecture for which it was designed.