Low-Cost Inductor Current Ripple Excitation Design for Rapid Converter-Based Electrical Impedance Spectroscopy on a Monocrystalline Solar Module

Electrical Impedance Spectroscopy has been thoroughly researched on distributed energy devices for fault diagnostics using power converters. The technique uses externally generated alternating signals to create a current or voltage excitation signal. To achieve a high resolution in the excitation signal, the switching frequency of the power converter must be at least ten times higher than the impedance bandwidth of the device under test. For solar modules with higher impedance bandwidths, the design of the converter becomes complex and costly requiring significant processing power for high frequencies. This paper thus, assesses the feasibility of a converter's inductor current ripple as an excitation signal to reduce the switching frequency requirements of traditional impedance spectroscopy; with this technique, the switching frequency of the converter need only be as high as the impedance bandwidth of the device under test, thus lowering costs related to the converter and processing requirements. The design considers the power regulation requirements of the load to determine the optimal inductor current ripple for both power regulation and the device excitation. The experimental results show that the inductor current ripple is best suited to characterize the impedance of modules under well-lit conditions; under these conditions, more than 50% of the module's impedance can be characterized with good accuracy when compared against results from a commercial Frequency Response Analyzer. Under low lit conditions the inductor current ripple proves ineffective in the excitation when compared to traditional EIS implementation, characterizing less than 10% of the curve.