A Series-Type Hybrid Circuit Breaker with Flying Capacitor Multilevel Voltage Injector for Ultrafast DC Fault Protection

The DC power system getting immense attention offers in the field of power transmission and distribution benefiting from excellent efficiency, reliability, and control simplicity. However, its short-fault current rises rapidly without a zero-crossing point due to the low inertia of DC systems, which places more stringent demands on the quick action of DC fault protection systems. This paper presents a series hybrid circuit breaker based on a flying capacitor multilevel voltage injector (FCM-SHCB) for ultrafast dc fault protection. The proposed FCM-SHCB avoids the conventional hybrid circuit breaker commutation process utilizing voltage injection and thus achieves a fast interruption capability. Meanwhile, utilizing multi-level injection, the proposed FCM-SHCB can modulate the fault current into a ripple current near zero, which provides a wide operating window for the mechanical switch (MS), thus enabling arc-free switching of the MS. And the proposed DC circuit breaker adopts a fly-across capacitor structure, which reduces the voltage stress between the devices and makes it possible to use the devices with small capacity for higher voltage applications. The operation principle and start-up operations of the proposed FCM-SHCB are detailed. The 10kV simulation platform is built, and the results indicated that the proposed FCM-SHCB can interrupt 200A fault current within 10us, exhibiting ultrafast dc fault protection.