# Comprehensive Diagnostic Assessment of Inverter Failures in a Utility-Scale Solar Power Plant: A Case Study Based on Field and Laboratory Validation

## TL;DR

This paper investigates inverter failures in a solar power plant using lab and field data to identify causes and suggest design improvements for better reliability.

## Contribution

The study introduces an integrated method combining lab simulations and field validation to diagnose and address inverter failure mechanisms.

## Key findings

- Negative DC input terminal faults lead to multi-phase short-circuits and sustained ground-fault arcs due to inadequate protection.
- Field data confirmed lab findings, showing identical fault signatures in real-world inverter failures.
- Design enhancements like advanced DC-side protection and rapid fault-isolation mechanisms are recommended to prevent failures.

## Abstract

Recurrent catastrophic inverter failures significantly undermine the reliability and economic viability of utility-scale photovoltaic (PV) power plants. This paper presents a comprehensive investigation of severe inverter destruction incidents at the Kopli Solar Power Plant, Estonia, by integrating controlled laboratory simulations with extensive field monitoring. Initially, detailed laboratory experiments were conducted to replicate critical DC-side short-circuit scenarios, particularly focusing on negative DC input terminal faults. The results consistently showed these faults rapidly escalating into multi-phase short-circuits and sustained ground-fault arcs due to inadequate internal protection mechanisms, semiconductor breakdown, and delayed relay response. Subsequently, extensive field-based waveform analyses of multiple inverter failure events captured identical fault signatures, thereby conclusively validating laboratory-identified failure mechanisms. Critical vulnerabilities were explicitly identified, including insufficient isolation relay responsiveness, inadequate semiconductor transient ratings, and ineffective internal insulation leading to prolonged arc conditions. Based on the validated findings, the paper proposes targeted inverter design enhancements—particularly advanced DC-side protective schemes, rapid fault-isolation mechanisms, and improved internal insulation practices. Additionally, robust operational and monitoring guidelines are recommended for industry-wide adoption to proactively mitigate future inverter failures. The presented integrated methodological framework and actionable recommendations significantly contribute toward enhancing inverter reliability standards and operational stability within grid-connected photovoltaic installations.