Low Resistance Hot-Spot Diagnosis and Suppression of Photovoltaic Module Based on I-U Characteristic Analysis

In the hot-spot fault of photovoltaic modules, there is a low resistance hot-spot fault caused by crystal defects, such as internal crack and PN junction failure. When the faulty area is partially shaded, it will produce severe temperature rise, accelerate the aging of battery unit, and even cause fire, which will affect the safe operation of the photovoltaic system. In this paper, the low resistance hot-spot fault endangering the safe operation of photovoltaic modules is taken as the research object; the shunt effect of equivalent low resistance caused by crystal defects under local shadow occlusion is explained by using the reverse characteristic of PN junctions of battery units, and its failure mechanism is analyzed. The three working states of the power generation system and the formation conditions of hot-spots in the process of power generation are analyzed in detail. By building a simulation model, the heating power distribution characteristics of hot-spots under different external local shadow occlusions are simulated, and finally, the fault characteristics and the fault diagnosis criterion of low resistance hot-spots are obtained. A control algorithm for low resistance hot-spot diagnosis and suppression based on I-U characteristic analysis is designed, and verified by simulation and experiment. The experimental results show that the control algorithm proposed in this paper can use the I-U characteristics of photovoltaic modules to determine whether there is a low resistance hot-spot fault, and carry out real-time control according to the judgment results. If it is judged that a low resistance hot-spot module is partially shaded, actively fixing the working point of the system near the safe voltage will protect the safety of the photovoltaic module. Otherwise, performing global MPPT will ensure the maximum power output of the system.