Hybrid DC switch for solar array fault protection

Photovoltaic (PV) systems have the intrinsic nature of distributed DC power generation that requires additional protection to reduce the fire and shock risks from various PV faults. Due to the current limited nature of PV generation, the short circuit current of a PV panel is typically 1.2 times of its rated current. This poses a unique overcurrent protection challenge, because traditional overcurrent protection, such as fuses and breakers, are designed for cable protection and they provide protection only for high reverse current faults in solar arrays. This paper proposes a solar fault protection system, including a hybrid DC switch based overcurrent protection device and a protection and coordination scheme. An optimized switch timing control is proposed for the hybrid DC switch. The proposed control method utilizes the parallel electromechanical contactor's arc voltage to determine the solid state device's switch timings, thus significantly reduces the solid state device rating and size. A protection and coordination scheme of using hybrid DC switches in PV system is also proposed and implemented. The proposed scheme guarantees the hybrid DC switches only need to interrupt forward fault current, so that the hybrid DC switches do not need to be sized according to the high reverse fault current. Experimental results verify that the hybrid DC switch with the proposed protection and coordination scheme can effectively protect the solar array faults.