Spread Spectrum Time Domain Reflectometry (SSTDR) and Dictionary Matching to Measure Capacitance for PV cells

The health of photovoltaic (PV) cells and modules can be determined from its capacitance. In this paper we describe a reflectometry method that can be used to determine capacitance on live electrical systems such as PV systems. Spread spectrum time-domain reflectometry (SSTDR) is used to measure the impedances as a function of distance from low-voltage transient reflections. The capacitances are determined from the reflectometry responses using a dictionary matching approach. The dictionary is built from simulated SSTDR reflections for a range of capacitances, and the measured SSTDR reflections are is compared with each simulated reflection through crosscorrelation. To validate this method, we measured twelve ceramic capacitors ranging from 1pF to 450pF using a 12 MHz SSTDR.