Comparison between DC Voltage Droop Schemes and Grid-Following & Grid-Forming Control in AC Systems in View of Interoperability of MTDC grids

This paper explores the fundamental characteristics of two typical DC voltage droop control schemes, namely the direct droop where the power setpoint is adjusted in proportion to the DC-voltage deviaiton, and the inverse droop where the DC-voltage setpoint is adjusted in proportion to the power deviation. We draw an analogy between these two droop controls for DC voltage regulation and and the grid-following and grid-forming controls in AC systems. Simulation results show that, for the security of the DC grid, it is crucial to specify the desired characteristics of droop-controlled stations in both steady state and transient.