Revolutionising DC Marine Microgrids: Advanced Solid State Circuit Breaker with Soft Switching for Inrush Current Control

DC microgrids have gained popularity for electrifying marine vessels, aircraft, and rail transport due to their seamless integration with power electronics devices and battery energy storage systems. This integration reduces system weight and size and minimizes the need for harmonic filters and inverters required in AC marine systems to interface with batteries. Additionally, DC microgrids allow generators to operate within a more comprehensive frequency range, enhancing overall efficiency by eliminating the need to maintain a specific frequency value. However, DC microgrids in marine systems often face challenges due to their low inductance and impedance, stemming from their limited wiring length and high capacitor density. These factors make fault management a daunting task, given the rapid rise of fault currents and elevated overall fault current levels, which can potentially cause mechanical circuit breaker (MCB) failure. Moreover, the absence of zero crossings exacerbates arcing in MCBs during fault current interruptions unless artificially induced. Solid-state circuit breakers (SSCBs) address these challenges by employing power semiconductor switches to interrupt fault currents swiftly, resulting in lower fault current levels and no arc production. Nevertheless, a quick restart of the DC microgrid requires rapid charging of the DC bus capacitor, leading to high inrush currents and potential damage to the SSCB and the other equipment in the DC microgrid. This Black-start is typically done using energy stored in the DC microgrid’s energy system storage (ESS) without external sources. To mitigate these issues, a soft switching strategy is proposed for reconfigurable battery ESS and SSCB. This strategy aims to limit grid inrush current while reducing grid restoration time, thus enhancing the reliability and performance of DC microgrids in marine applications. Simulation results demonstrate the smooth charging of the DC microgrid capacitor, thus avoiding an inrush current and speeding up capacitor charging time, leading to lower Black-Start time.