Analysis of Residual Current Flows in Inverter Based Energy Systems Using Machine Learning Approaches

Holger Behrends,Werner Weihs-Sedivy,Anže Javornik,Dietmar Millinger,Stefan Geißendörfer,Gerold Roolfs

doi:10.3390/en15020582

Abstract

Faults and unintended conditions in grid-connected photovoltaic systems often cause a change of the residual current. This article describes a novel machine learning based approach to detecting anomalies in the residual current of a photovoltaic system. It can be used to detect faults or critical states at an early stage and extends conventional threshold-based detection methods. For this study, a power-hardware-in-the-loop approach was carried out, in which typical faults have been injected under ideal and realistic operating conditions. The investigation shows that faults in a photovoltaic converter system cause a unique behaviour of the residual current and fault patterns can be detected and identified by using pattern recognition and variational autoencoder machine learning algorithms. In this context, it was found that the residual current is not only affected by malfunctions of the system, but also by volatile external influences. One of the main challenges here is to separate the regular residual currents caused by the interferences from those caused by faults. Compared to conventional methods, which respond to absolute changes in residual current, the two machine learning models detect faults that do not affect the absolute value of the residual current.

Highlights

Residual current monitors (RCM) offer the possibility of monitoring currents flowing through earth with the same procedure and sending a message if adjustable threshold values are exceeded
Residual currents were essentially caused by insulation faults in systems and were referred to as fault currents
Due to the enormous increase in non-linear electrical loads, as well as regulated power generation systems such as photovoltaic (PV) systems with their high-frequency controlled current converter stages, we see massive amounts of so-called operation-related leakage currents taking the same path as fault currents

Summary

Introduction

In earth-grounded power supply systems, the use of residual current devices (RCD). Residual current monitors (RCM) offer the possibility of monitoring currents flowing through earth with the same procedure and sending a message if adjustable threshold values are exceeded. Both types of devices record the sum of the currents flowing to and from active conductors. If the sum of currents is not equal to zero, there are usually undesired currents flowing back to the source via the body and earth, which are generally referred to as differential currents ( known as residual currents) [1]. Modern electrical loads such as generators contain direct-current (DC) circuits with high voltages that can generate DC fault currents

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Results