Y-Type Solid-State Circuit Breaker for Fast DC Fault Protection

Background

The protection of direct current (DC) power systems is a critical aspect of modern electrical engineering, necessitating advanced circuit interruption technologies. Unlike alternating current systems, DC systems lack natural current zero-crossings, making the rapid interruption of high fault currents significantly more challenging. Solid-state circuit breakers (SSCBs) have emerged as a vital solution in this field, utilizing semiconductor devices to achieve ultrafast fault isolation without the mechanical delays of traditional breakers. Reliable DC protection requires these breakers not only to interrupt short-circuit and overload faults rapidly, but also to quickly reclose and rebreak the circuit to ensure continuous system stability and safety.

However, existing SSCB topologies face significant operational and reliability limitations. Designs utilizing insulated-gate bipolar transistors (IGBTs) suffer from high steady-state conduction losses and limited current interruption capabilities. Conversely, while thyristor-based breakers offer lower losses, current architectures relying on single-capacitor commutation circuits require hundreds of milliseconds to seconds to recharge the capacitor, resulting in unacceptably slow preparation times between reclosing and rebreaking operations. Furthermore, in many conventional designs, metal-oxide varistors (MOVs)—which are essential for clamping voltage and dissipating energy—remain connected to the power line even when the breaker is in the OFF state. This continuous exposure leads to premature MOV degradation, compromises overall system reliability, and restricts the maximum allowable voltage utilization of the main switch.

Technology

The Y-type DC solid-state circuit breaker (Y-SSCB) is a thyristor-based protection system designed to rapidly and reliably interrupt DC fault currents. The architecture integrates a main switch, an auxiliary switch, two diodes, two resistors, a metal-oxide varistor (MOV), and a complementary commutation circuit featuring a unique dual-capacitor pair. During normal operation, the second capacitor remains pre-charged. When an overload or short-circuit fault occurs, the auxiliary switch triggers, transferring energy between the two capacitors to inject a countercurrent pulse. This mechanism rapidly turns off the main thyristor and diverts the fault current. The MOV then clamps the resulting voltage and dissipates remaining energy before the auxiliary switch naturally turns off, safely returning the system to an off state.

This solution is differentiated by its dual-capacitor configuration and strategic MOV placement, which overcome critical limitations of conventional single-capacitor breakers. Because the MOV is completely disconnected from the power line during normal and off states, component degradation is prevented, extending the MOV’s lifespan and increasing voltage utilization by at least 20%. Furthermore, the capacitor-capacitor structure reduces preparation time for rebreaking from seconds to mere milliseconds, ensuring fast, repeatable reclosing cycles alongside a 99.8% operational efficiency and higher power density.

Benefits

• Fast commutation and fault current interruption via countercurrent pulse injection
• Rapid preparation for rebreaking within milliseconds after reclosing
• Improved reliability and extended lifespan of metal-oxide varistors by disconnecting them during the off state
• Increased voltage utilization, allowing for at least a 20% higher DC bus voltage
• High overall operational efficiency of approximately 99.8% with low steady-state conduction loss
• High current interruption capability for protection against both short-circuit and overload faults
• Higher power density and reduced thyristor count compared to alternative designs
• Capability for both autonomous operation and manual tripping

Applications

• DC microgrid fault protection
• Electric vehicle charging station protection
• Data center DC power protection
• Renewable energy grid integration
• Electric ship power distribution protection

Additional info

Fei Lu is an Associate Professor in the Department of Electrical and Computer Engineering at Lehigh University. His areas of research include: Electrical Engineering, Power Electronics, High Voltage DC Power Systems, Semiconductor Device Packaging, Renewable Energy

Assignee: Lehigh University; the patent record also identifies Drexel University as an assignee