National Semiconductor has introduced the ‘SolarMagic’ arc detection reference design, comprised of analog front end integrated circuits (ICs) and multi-band dynamic filtering firmware. According to the company this is the first commercially available chipset to detect hazardous DC arc faults in PV systems.
In PV systems, intermittent connections or insulation deterioration (faults) can cause DC circuits to generate arcs of considerable energy. The arc, reaching temperatures of over 3,000 degrees C, poses safety risks to surrounding infrastructure and personnel. The 2011 U.S. National Electrical Code (NEC) 690.11 requires an arc-fault circuit detect and protect system as part of all new PV system installations. 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 wide 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 a state-of-the-art abstracted pattern recognition approach that does not require the arc signature to match a rigid, pre-described, absolute shape.
Arc detection for solar modules.
National's SolarMagic chipset is an analog front end (AFE) featuring three highly integrated ICs. The SM73201MM 16-bit, 50 to 250 kSPS, differential input, micropower ADC digitizes 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 mid-point for the arc-detect AFE. The SM73307MM dual precision, 17 MHz, low noise, CMOS input amplifier provides gain and filtering of the arc signature signal. Additional National power management chips enable various support functions.
SolarMagic arc detection chipset is available now and offered in a variety of industry-standard electronic packages and priced at US$7.90 in quantities of 1,000 including a license for the MBDF firmware.