A study on fault ride-through strategies for mine DC power supply systems based on FBSM-MMC

Direct current(DC)power supply system is a key technology for enhancing the power supply efficiency and safety of underground mining equipment due to its excellent voltage stability and little reactive power losses. However, its inherent low-impedance is likely to induce extremely rapid rise in short-circuit fault currents, posing a severe challenge to system protection. This study therefore proposes a valve-side, non-locking DC fault ride-through strategy based on a Modular Multi-Level Converter (MMC). Drawing on the mechanism of DC bipolar short-circuit faults, this strategy enables flexible and rapid switches of AC-DC modulation ratio within the MMC valves to generate a reverse voltage on the valve side that offsets the fault voltage. This could rapidly suppress and limit the short-circuit current, thus achieving superior system fault-ride-through and active current-limiting capabilities. RTLAB-based hardware-in-the-loop simulation verification demonstrates that this strategy could limit the DC short-circuit current to below 1.0 p.u. of the rated current within 2 ms after a fault occurs. This prevents dynamic and thermal damage to power supply cables and electrical equipment caused by inrush currents, ensuring the continuity of power supply during a fault. This study offers an economical and efficient solution for short-circuit protection of DC power supply systems in underground coal mine, thus providing theoretical and engineering references for the safe and reliable application of DC power supply technology in underground environments.