Fault Protection in Medium Voltage DC microgrids

摘要

We define an approach Local Information Based Fault Protection (LIFP) for robust protection against short-circuit faults that does not rely on microgrid-wide communications. Using a monopolar bus as an example, we show how each entity connected to the dc bus, including current-limiting power converters and non-load-breaking disconnect switches, can autonomously detect, identify, and appropriately react to the presence of a short-circuit arcing fault based only on its own local observations of voltage and current. The method for LIFP was previously reported for systems where the effective resistance of short-circuit faults was small compared to the resistance of the bus work or cabling [1][2]. But the effective resistance of an arc can sometimes be large compared to that of the bus cables, and the arc resistance can vary randomly in time with large bandwidth; these characteristics complicate implementation of the LIFP method. We describe the system design constraints, and then we report the effectiveness of applying the method for a reference system over a wide range of system operating conditions (e.g. system current), and fault conditions (arc location, arc length). Simulation results show that the LIFP method can successfully protect the system.