Reliability Analysis of Bypass Diodes in Photovoltaic Modules by Using Different Lifetime Estimation Models

A reduction in the lifetime of bypass diodes (BD) can result in a rapid decrease in the safety and reliability of photovoltaic (PV) modules. The lifetime of bypass diodes can be significantly reduced by four main reasons, including electrostatic discharge, reverse bias thermal runaway, forward bias overheating, and transition operation from forward-biased to reverse-biased states. Electrical and thermal parameters related to the above reasons mainly are temperature, forward current, and reverse voltage of the diodes, which can influence their degradation. Specifically, dynamic operations such as partial shading, fluctuation in solar irradiance and temperature, and short-circuit conditions in the PV system can lead to a sudden increase in the magnitudes of temperature, forward current, and reverse voltage; hence, bypass diodes can undergo thermal runaway and consequently, under random dynamic and transient operations, these bypass diodes of the system can be damaged after a certain amount of the used time. To demonstrate this assumption, this paper uses lifetime estimation models based on the junction temperature, forward current, and reverse voltage for the reliability analysis of bypass diodes in a grid-connected 8kW PV-generation testbed by practically evaluating lifetime consumption (LC), failure rate (FR), and reliability index (RI) of bypass diodes in the PV-generating system. The achieved experimental results show that a temperature-current-voltage-based lifetime estimation model can be properly and practically applied for the reliability assessment of bypass diodes under random dynamic and short-circuit cases of the PV-generating system.