| Description |
The primary objective of this dissertation is to evaluate the application of spread spectrum time domain reflectometry (SSTDR) to monitor photovoltaic (PV) strings in power plants. SSTDR has already been commercialized for detecting faults in cables in aerospace, rail, and other industries. SSTDR can detect and spatially localize changes in the impedance of the system in real-time with the system operating normally, including at high voltages and currents. The particular challenges to applying SSTDR in PV power plants arise from the presence of complex-valued impedances and many interfaces creating multiple reflections that complicate the analysis. The first topic developed in this dissertation is a formalism for analyzing electromagnetic signal propagation through piecewise-defined transmission lines with arbitrary, series-connected impedances, representing a first model of propagation through photovoltaic modules connected by short sections of transmission line. The second topic presented in this dissertation is an investigation of SSTDR applied to asymmetric twin-lead transmission lines in which either only one conductor is disconnected, or the reflectometry instrument itself has an asymmetric circuit. The third topic of this dissertation is to describe the novel use of SSTDR for detecting and locating disconnection faults in PV strings. A technique for identifying and locating disconnection faults is described. The SSTDR technique can detect and locate disconnects through at least eight 36-cell modules. Using a new technique for signal processing, we can detect and locate disconnections within a 1-foot resolution, on average. The fourth topic presents a novel technique using SSTDR for detecting broken cells and modules in a photovoltaic (PV) system. SSTDR responses have been demonstrated to detect breaks in modules. The ability to detect a broken module is demonstrated in PV strings. Using this new signal processing technique, we can both detect and locate the broken minimodule within a 1-foot resolution. The last topic describes the use of SSTDR technique to detect accelerated degradation in PV minimodules. Preliminary results are exhibited to detect three types of accelerated degradation: damp heat (DH), potential induced degradation (PID) and humidity freeze (HF) in PV minimodules using SSTDR. |
