Investigations on Fault Diagnosis in DC Side of Solar Photovoltaic (PV) Systems

Abstract

The solar energy conversion into electricity is a very promising technique, knowing that the source is free, clean and abundant in several countries. Solar photovoltaic (PV) systems contribute 2% of the world’s total energy consumption. India’s solar installed capacity has reached 37.62 GW as of 31st march 2020. In view of increasing grid connected solar PV plants and environmental conditions there are possibilities of faults (line-ground, line-line, open circuit and partial shading) occurring in solar PV arrays. The conventional protection devices are unable to detect the faults in PV array under lower module mismatch (one module), severe partial shading conditions and low irradiation levels because of PV’s nonlinear characteristics, lower magnitudes of fault current and active Maximum Power Point Tracking (MPPT’s). Once the fault is diagnosed, should be cleared in minimum time. The faults (line-ground, line-line, open circuit) can be cleared manually but partial shading cannot be cleared manually. So, to reduce the effect of partial shading the PV array can be reconfigured without changing the electrical connections. Therefore, fault analysis in solar photovoltaic (PV) arrays is a fundamental task to increase reliability, efficiency and safety in PV systems. Firstly, to identify and localize the faults in the PV array, a Diagonal Sensor Arrangement (DSA) method is proposed. This DSA method works on the principle of measurement of differential voltage across two different potential points in the solar PV array. The proposed DSA method is verified in simulation (4kW system) and hardware (0.16kW system) for a 4×4 PV array. The conditions of short circuit faults with one, two module mismatch within the string and between the strings are analyzed. Also, the characteristics of PV array under open circuit faults and partial shading faults are discussed. A comparative analysis is done between the proposed DSA method and various methods available in the literature which shown the efficacy of the proposed SDA method. Partial shading in photovoltaic (PV) arrays is a common and challenging issue that significantly impacts the overall performance and efficiency of solar energy systems. Partial shading leads to formation of hot spots and

multiple peaks in characteristic curves. Several techniques are reported in the literature to mitigate the effects of partial shading. Configuration of the PV array plays an important role in increasing the output power. The conventional PV array configurations are Series-Parallel (SP), Bridge Link (BL), Honey Comb (HC) and Total Cross Tied (TCT) configurations. Among which TCT configuration is able to generate more output under partial shading conditions. However, TCT configuration has more number of cross ties which increases the cost of wire required for connecting the modules. Hence, a novel Reduced Cross Tied (RCT) PV array configuration with reduced cross ties which is capable of generating output power closer to TCT configuration is proposed. It is implemented on 8×8 and 7×7 PV arrays and verified in simulation and experimental environments. The PV array output power can be further increased by re configuring the PV modules without changing the electrical connections. This report presents a new static reconfiguration technique -Cyclic Back Shift (CBS) method to mitigate the effects of partial shading.The proposed CBS method is implemented on 9Ö9 PV array and verified in simulation (20.25kW system) and experimental (0.81kW system) environments. From the results obtained, it is observed that proposed CBS method is able to enhance the output power and improves efficiency of PV systems under partial shading conditions. Further, a new static reconfiguration technique Modified Odd Even Prime (MOEP) is proposed to mitigate the effects of partial shading. The proposed MOEP method is implemented on 9Ö9 and 8Ö8 PV arrays and verified in simulation (20.25kW system and 16kW system) and hardware (0.81kW system and 0.64kW system) environments. A detailed qualitative and quantitative comparative analysis is made between the proposed MOEP method and various other techniques in the literature. From the results obtained, it is observed that proposed MOEP method is able to enhance the output power and improves efficiency of PV systems under partial shading conditions. All the developed algorithms are simulated in MATLAB/Simulink.