Design Considerations of Tri-mode Intelligent Solid State Circuit Breaker Using GaN Transistors

The purpose of this paper is to introduce a bidirectional, GaN based, autonomously operated, intelligent solid-state circuit breaker (SSCB) or iBreaker. The iBreaker features tri-mode operation of three distinct operation states: ON, OFF, and PWM Current Limiting (PWM-CL) for a wide range of conditions such as short circuit fault interruption and startup inrush current in both current directions. While the conventional ON/OFF states allow the iBreaker to conduct normal load currents or interrupt fault currents, the PWM-CL state allows gradual charging of the input capacitor of an electronic load at a limited inrush current level during startup. The iBreaker can switch from PWM-CL to OFF state if a true short circuit fault is determined after a short detection time window. The bidirectional iBreaker is based on the concept of operating a back-to-back buck converter with a variable frequency PWM technique, and combines programmable digital control with fast acting analog control. The experimental results on a 380V/20A iBreaker prototype using commercial 650V GaN FETs are reported. Special design considerations related to the use of GaN FET are discussed in detail in this paper, including thermal design, damping of GaN switching di/dt, and overvoltage protection due to the fact that GaN FETs lack avalanche capability.