Fault Detection in Solar Inverters: A Technical Overview

A recent study has organized all existing fault detection and localization strategies for grid-connected PV inverters. The summary also sorts out the different ways parts can break and what might be causing those issues. The use of solar energy as a clean, renewable energy source is increasing significantly. The cumulative capacity of photovoltaic solar power is expected to reach 2,626 GW by 2023, a significant increase from the current capacity of about 500 GW 1. By converting the direct current (DC) from solar panels into alternating current (AC) for consumption, solar inverters are essential for this system. However, several issues can arise with solar inverters that could adversely impact their functionality or even cause major harm. In this section, we are going to explain the technical aspects of solar inverter fault detection and protection systems.

Types of Faults

Undervoltage and Overvoltage

Undervoltage faults occur when the DC bus voltage falls below the inverter’s undervoltage detection value. One of the most frequently observed issues affecting the functioning of your panels is overvoltage, which arises when the grid voltage rises above 258 volts and when more solar energy is produced than is consumed ². The inverter signals an undervoltage fault to protect the circuit. According to the national standard, the protective range for undervoltage and overvoltage at the AC output side is between 85% and 100% of the rated voltage. The solar inverter’s operation should be stopped when it goes over this range. The single-phase grid has a rated voltage of 230V ³.

Overcurrent

Overcurrent is the result of a current exceeding its average flow, either by increasing or surging. The primary causes of overcurrent are short circuits and overloads. Many things, including shade on the solar panels, bad connections, or flaws in the internal parts of the inverter, could result in excessive current flow. It is essential to have overcurrent protection to protect the inverter and other parts from damage.

Islanding

When a residential solar power system keeps producing electricity even when the grid is down, this occurrence is known as solar islanding. This happens when an inverter keeps the grid power during a grid outage. Many people would consider this a good thing, as your home still has power from your solar panels while everyone else has no power. Utility personnel may be at risk of islanding because they might not be aware that a circuit is still energized even when there is no power coming from the grid.

Ground Faults

When any component of your solar power system comes into touch with the ground, your inverter will display a Ground Fault error. Unintentional connections between the DC or AC side of the inverter and the ground are also known as ground faults. These can be the consequence of poor wiring, failing insulation, or external conditions. Hazards from electric shock are avoided using ground fault detection.

Temperature

A variety of environmental factors can affect solar inverters. Damage and decreased efficiency might result from overheating caused on by high temperatures or inadequate airflow. Monitoring and protection systems for temperature are important. Heat has an impact on photovoltaic modules. They are rated and tested at 25ºC, and the generation of electricity decreases by as much as 5% for each degree over the temperature ⁶.

Solar Mechanisms Fault Detection

Voltage and Current Sensors

The electrical properties of the inverter are continually monitored by sensors measuring voltage and current. A current sensor is a device that measures the electric current flowing through a wire and outputs a signal that is proportionate to the current. The signal that is produced might be a digital output, analogue voltage or current, or both. Voltage sensors are capable of measuring DC voltage as well as AC voltage. To identify overvoltage, undervoltage, overcurrent, and short circuits, they provide real-time data.

Monitoring of Phase and Frequency

It is possible to identify inconsistencies that can point to problems by keeping an eye on the frequency and phase of the AC output. When standard values vary, preventative action is taken. The standard frequency for electric utilities is 60 hertz (Hz). In order to operate, solar electric inverters need the utility frequency to be at or near 60 Hz ⁸.

Detecting Ground Faults

Specialized sensors are used in ground fault detection to track possible differences between the system and the ground. The inverter disconnects from the grid to avoid dangers if it detects an unusual condition. Monitoring insulation resistance and using residual current detectors (RCDs) are two methods for finding DC ground faults. Every morning, you should measure the resistance to the ground by doing a grounding test using an insulating resistance meter.

Sensors for Temperature monitoring

According to IEC 60904-10:2020, the optimal test conditions for photovoltaic cells are 25 °C, 1,000 W/m2 sun irradiation, and 1.5 AM (air mass) ⁹. The temperature of important parts of the inverter is monitored by temperature sensors positioned strategically inside. If the temperature rises above acceptable limits, safety precautions including decreasing power output or turning off appliances might be taken.

Solar Panel Fault Detection Proactive Actions

Switching Off the Output

If there is a problem, the inverter has to be disconnected from the grid right once to stop further damage. Relay devices and switches can be used to do this.

Shutdown of Inverters

To avoid irreparable damage, the inverter may need to completely shut down in extreme situations. This is especially important when there is an overcurrent or overheating. The National Electrical Code (NEC) has set a safety requirement called “rapid shutdown,” which mandates that solar panels include switches to quickly cut off the energy flowing through the system. Your home is protected against a fast fire by rapid shutdown, which lowers the voltage of electrical conductors in wires and cables.

Communication with Monitoring Systems

With the use of communication interfaces, modern inverters can send problem information to operators or monitoring systems. This makes maintenance and response possible on time.

To ensure the safe and effective operation of solar inverters, fault detection, and protection systems are essential parts of the device. Through the use of an array of sensors, monitoring systems, and preventative measures, solar inverters can reduce the probability of several kinds of problems. Improvements in fault detection and protection will be essential to maintaining system safety and dependability as the solar energy sector expands.