Design of Shunt Resonant Solid-State Circuit Protection for μs-level Protection Coordination and Enhanced Fault Limitation in MVDC Systems

The extremely high di/dt rates during line-to-line faults present a significant challenge in achieving selective coordination between circuit breakers in compact Medium Voltage Direct Current (MVDC) systems. Existing Time-Current-Curve (TCC) based methods incur coordination delays, leading to excessive fault current and severe system repercussions. Although di/dt sensing circuits have been explored to reduce the delay, their wide bandwidth increases susceptibility to noise and the risks of mis-tripping. Alternatively, DC inductors have been used to directly limit the di/dt rate. However, their bulky size limits their adoption under compact system requirements. Moreover, the additional energy stored in the inductors requires larger metal-oxide varistors (MOVs) and prolongs fault isolation time. To tackle these challenges, this paper proposes a solid-state protection method based on a shunt resonant fault limiter circuit. During line-to-line faults, the resonant circuit automatically limits fault current and accelerates the response of the upstream circuit breaker closest to the fault. This enables microsecond level selective protection coordination without worsening the fault current or compromising noise immunity in sensing circuits. Compared to the existing pure inductive fault limiter, the proposed resonant fault limiter demonstrates much better current limiting capability with the same inductance, allowing for a more compact inductor design. The effectiveness of the proposed method has been validated through both simulation and test.