Fault Detection and Troubleshooting in a PV Grid-Tied Inverter

Objectives: Present work envisages fault detection along with troubleshooting methodologies conﬁrmed in solar photovoltaic workshop for grid-tied three-phase inverters. Only innovative inventions are not only necessary for the society to become advanced but also to continue the modern electrical evolution with zero carbon. Methods: Here with the help of sungrow software DSP1_20_VA_J & IDM- AC Fm ver the inverter sends a notiﬁcation about the fault with a fault status code to the HMU/LCD display. As per fault severity it may completely shut down or partially operate the inverter with reduced load. After the fault rectiﬁcation manually by the site operator again it restores the power and inject power to the grid. Finding: Here with the help of sungrow software DSP1_20_VA_J &IDM- AC Fm ver we ﬁnd various types of faults with the nature of faults i.e. insulation fault, leakage current fault, over voltage/under voltage fault, frequency faults, temperature fault, islanding with its rectiﬁcation process. The major, minor, and cautionary faults and their troubleshooting procedures are elucidated in the present study with coding of faults, and its alarm level. Novelty: In previous researches, the fault identiﬁcation was not done properly; as a result the inverters are tripping frequently. The present software helps to detect fault of the inverter within 0.023 millisecond and send a message to the service engineer for rectiﬁcation. The present research can be of immense help to the service engineers and ﬁeld workers working on solar photo voltaic sector considering popularity of photovoltaic units.


Introduction
A solar photovoltaic (SPV) system alters the solar light energy into electrical energy. The SPV system comprised of solar panel(s), charge controller (CCR) or inverter, https://www.indjst.org/ battery bank (optional), electrical and mechanical appliances (1)(2)(3) . The energy produced is either stored in a battery bank in an off-grid system or fed to the grid for supply through an on-grid or grid-tie technology. Inverters act as a brain of any SPV system. The grid-tie inverter alters direct current (DC) into a required alternating current (AC) for adding into an electrical power grid (4) . Other inverter application includes; wind turbines and micro turbines, variable frequency drives, High voltage direct current (HVDC) power transmission and uninterruptable power supply.
Modern inverters use solid state designs with microprocessor control to produce high quality AC power very efficiently (5)(6)(7)(8) . To feed electrical power competently and securely into the grid, grid-tie inverters must be synchronized with the healthy voltage, frequency and phase of the grid. Grid-tie inverters are also aimed to quickly detach from the grid if the utility grid become unserviceable. The grid tie inverter shuts down to prevent the energy it transfers from harming any line workers working on the power grid (9)(10)(11)(12)(13) .
In the present work, Sun grow make inverter with capacity 3125 kW has been used having maximum input voltage 1500 V with maximum power point tracker (MPPT) voltage range from 875-1300 V (14)(15)(16)(17) . Maximum AC output power is 3125 kW at 50-degree temperature. This inverter is installed at 20MWp Gavhankund solar project, Maharashtra.

Overview of a Grid Connected SPV System
On-grid solar power plant is one in which the power plant is fed with grid through transmission line. In on-grid solar power plant a DC power is generates through photo voltaic solar module (6,18) . With the help of grid tied inverter, DC power is converted in to AC power then routed to the nearby grid where the power is supplied for use, demonstrated in Figure 1.  (19) . PV industry is still working on the safe operation of these PV plants and developing products to prevent the several plant faults arising in grid set up demonstrated in Table 1.  (20,21) . Maximum AC output power is 3125 kW at 50-degree temperature. This inverter is installed at 20 MWp, Gavhankund solar project, Maharashtra.

Methods and Materials
Indian renewable energy sector is the fourth most eye-catching renewable energy marketplace in the world. Till November 2020 the installed capacity of renewable energy up to 90 GW. In an On-Grid solar power plant inverter plays an important role as it converts the DC power generates from module to the electrical grid in AC form (22)(23)(24) . Those faults have been identified, and mainly categorized are: 1. Major Faults, 2. Minor Faults, and 3. Warning Faults.

Major Faults
This fault will shut down the inverter and stops feeding power in to the grid. In minor faults some components of the inverter are faulty but the inverter can still feed the power to grid. Function of the inverter is normal, but the output of power drops due to external factor (25)(26)(27) .
Individually the faults are identified in the photovoltaic workshop on the basis of laboratory fault finding observations and corrective actions are reported for attending using the His-Fault software (DSP1_20_VA_J &IDM-AC Fm ver) and the results are as follows: (Table 2 and Figure 2(a) to Figure 2(h)).

Various fault detection by DSP1_20_VA_J &IDM-AC Fm ver
In the laboratory the various results obtained due to various major faults are demonstrated in Figure 2(a) toFigure 2(h).

Minor Faults
In the minor fault, some components are faulty, but the inverter is still operative to feed power into grid. Few minor faults which rises in a megawatt scale grid tied inverter are as follows; (Table 3 and Figure 3).

Warning Faults
Warning faults are those in which the inverter function is normal but the output power drops due to external factors. These type of cautionary faults do not make the circuit unserviceable or breakdown but must be attended (28,29) . These major warning faults are (1)   The reactive power of the inverter is adjusted according to the change of the grid voltage.
1. Check whether the "Q-adjust switch" is in the "QU mode".

Encoding repeat
The main cause of the encoding repeat fault is addresses of the interior modules are repeated.
1. This is a major inverter fault we have to contact manufacture immediately.

Carrier Synch Fault
The main cause of the carrier synch fault is due to the abnormal of carrier signal transmission.
1. A major inverter fault which may be attended immediately with the help of inverter manufacturer. In this present work we have studied various types of faults associated with solar grid connected inverters with its rectification methods. Here we investigate the fault and attempt the troubleshooting of various grid connected inverters. When a fault occurs in a solar inverter we are unable to pump power to the grid as a result we face power interrupted with huge amount of revenue losses. If any fault occurs due to any reason like over voltage, temperature, or insulation failure or the fault between ground and the short circuit caused by low insulation resistance may lead to electric fire, device damaged or even physical hazards. Hence, power supply and quick power restoration.

Gavhankund Solar Power Plant (Similar Project)
The installation capacity of 20 MWp/16 MW AC capacity this plant is located at Gavhankund, Amaravati, Maharashtra, latitude -21.50 • N, 78.20 • E (30,31) . With an average solar irradiation 6 kWh/m2 this plant export more than 95000 kWh/day to MAHAGENCO grid with life span of 25 years' and power purchased agreement demonstrated in Figure 5.

Results and Discussions
In this practical work we identified various faults, major, minor, and cautionary faults and their troubleshooting procedures are elucidated in the present study with coding of faults, and its alarm level. Before our studies it was very difficult for the solar inverter engineer to identify the faults and power restoration was possible after 2-3 hours. This types of fault causes a loss around 3000 kWh per MW per day. Now quick fault identification is possible with the help of Sungrow software DSP1_20_VA_J & IDM-AC Fm ver, Demonstrated in Table 5. Hence, we save huge generation loses as well as revenue. https://www.indjst.org/

Conclusion
Solar photovoltaic power plant installation in India has gained momentum and has given national importance after Paris Agreement (COP 21) 2015. The government target is to install 100 GW solar PV plant by 2022. For reliable power generation, inverter has vital role in a solar power plant. The researcher explores on various operative faults such as major, minor and warning types. Generally, voltage imbalance, frequency abnormal with leakage current and insulation failure faults are shown in many on-grid solar power plant. Modern technology need to be adopted for the proper detection of the inverter faults and its troubleshooting. For quick fault detection of the inverter, we use a modernized software DSP1_20_VA_J &IDM-AC Fm version. The software helps to detect fault of the inverter within 0.023 milli-second and send a message to the service engineer for rectification. According to earlier studies it was very difficult for the solar inverter engineer to identify the faults and power restoration was possible after 2-3 hours. This troubleshooting process mitigate the inverter faults to minimize the power plant generation loses. The present research can be of immense help to the service engineers and field workers to minimize various inverter faults, troubleshooting time, save energy of around 3000 kWh/MW per day. This will aid to the future developers and researchers for optimizing the power generation and payback period of the solar power plant.