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Fault Detection of Photovoltaics Panel using Impedance Measurement

Year: 2023 | Author: Jeet Panchal | Paper: H5.6
Circuit topology
Fig.1. Small Signal Injection to PV Panel
  Solar photovoltaics (PV) panels have seen rapid growth for many years and are expected to grow further with a continuous decrease in the cost of technology. Energy from the PV panel can be fetched and provided to the grid through a DC-DC converter and DC-AC inverter. PV panels are susceptible to a variety of faults, such as hot-spot faults, short-circuit faults, open-circuit faults, diode faults, ground faults, and many more. The source of the fault can be cabling, modules, converters, inverters, or protection devices. A PV panel is composed of multiple PV cells, each of which has its own series and parallel resistances and parallel capacitance. PV system operation varies by changes in voltage biasing, illumination, and temperature.

  Using power converters and inverters, a small signal is injected into the PV panel, as shown in Fig. 1, and the impedance of the PV panel is computed. The PV panel impedance under a fault condition is measured and compared using an online impedance measurement. The PV panel impedance is measured for a short-circuit fault with one PV string short-circuiting from three PV strings. Later, the PV panel impedance is measured for a hot-spot fault, in which one of the PV cells is shaded, and the bypass diode of the shaded PV cell string is removed. Fig. 2 shows the different operating points for different fault conditions in the PV panel. PV panel impedance under fault conditions is compared with the impedance under normal conditions, as shown in Fig. 2. Under the low-frequency region of the image, for the hot-spot fault, the fault indicator shows an increase in the impedance magnitude under the low-frequency region as the parallel resistance increases due to reverse characteristics of the PV cell. Under the mid-frequency region, for the hot-spot fault, the impedance phase decreases as the parallel capacitance increases for the shaded PV cell. Comparing the PV panel impedance for a short-circuit fault with a normal condition, the impedance magnitude in the low-frequency region shows a decrease in the impedance magnitude due to a decrease in the total number of PV cells, and thus the cumulative series and parallel resistance of the PV panel decreases under the short-circuit condition. This means PV panel hot-spot and short-circuit faults can be determined using online impedance measurements.
PV panel IV curve and impedance comparison
Fig.2. PV Panel Fault Detection using Online Impedance Measurement

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