Adaptive Master-Slave Control Strategy for Medium Voltage DC Distribution Systems Based on a Novel Nonlinear Droop Controller

To ensure accurate active power-sharing and an improved dynamic response to DC voltages in a medium voltage DC distribution system (MVDCDS), this paper presents an adaptive master-slave (AMS) control strategy based on a novel nonlinear droop (ND) controller. This ND controller, which is based on an improved sigmoid nonlinear function, is applied to the slave converter stations. An improved sigmoid function is designed to achieve a continuous and nonlinear droop curve. Through use of the proposed ND controller, the proposed AMS strategy can achieve seamless switching between the master-slave control and droop control modes automatically. Consequently, the AMS control strategy not only guarantees precise control of the active power in the steady state but also allows a superior dynamic performance to be achieved in the transient state, during which the system suffers from both large-scale disturbances and communication failures. The effectiveness and superiority of the proposed AMS control strategy are illustrated by theoretical analyses and validated by performing hardware-in-the-loop (HIL) tests in a ±10 kV MVDCDS.