Reference Design Detects Hazardous DC Arc Faults

National Semiconductor has introduced the Solarmagic arc-detection reference design - the first commercially available chipset to detect hazardous DC arc faults in photovoltaic (PV) systems. Comprised of analogue front-end integrated circuits (ICs) and multi-band dynamic filtering firmware, the Solarmagic arc-detection reference design will be exhibited in its booth in Hall A1.151 at the Intersolar Europe Conference in Munich, Germany, on 8-10 June.

National's new Solarmagic arc detection reference design includes analogue front-end ICs and multi-band dynamic filtering (MBDF) firmware. Together, they detect the arc-fault condition and provide an alert to shut down the system power, extinguishing the arc. Arcing events in PV arrays are very difficult to detect. An electric arc does not leave a uniquely identifiable electronic signature. In addition, the power lines of a PV array act as very effective antennas for a range of electromagnetic interference in the vicinity of the array; inverters also contribute additional noise that is induced onto the power lines.

A sophisticated signal processing approach is required to reliably detect the entire range of dangerous arcing events without false alarms when the PV array is operating under safe conditions. National Semiconductor has developed a patent-pending signal-processing approach. The MBDF firmware uses an abstracted pattern-recognition approach that does not require the arc signature to match a rigid, pre-described, absolute shape.

The Solarmagic chipset is an analogue front end (AFE) featuring three highly integrated ICs. The SM73201MM 16-bit, 50 to 250kSPS, differential input, micropower ADC digitises the arc signal after the AFE gain and filtering stage, and sends the digital signal to the microcontroller. The SM73308MG low-offset, low-noise, RRO operational amplifier provides the Vref midpoint for the arc-detect AFE. The SM73307MM dual precision, 17MHz, low-noise, CMOS input amplifier provides gain and filtering of the arc signature signal.

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