PhD defence by Kamran Ali Khan Niazi
15.09.2021 kl. 13.00 - 16.00
Kamran Ali Khan Niazi, AAU Energy, will defend the thesis "Mismatch Effects and its Mitigation Techniques in the Solar Photovoltaic Systems"
Mismatch Effects and its Mitigation Techniques in the Solar Photovoltaic Systems
Kamran Ali Khan Niazi
Associate Professor Tamas Kerekes
Yongheng Yang, Zhejiang University
Dezso Sera, Queensland University of Technolog
Associate Professor Dong Wang
Associate Professor, Kaiyuan Lu, Aalborg University (Chairman)
Professor Ing Jens Schneider, Fakultät Maschinenbau und Energietechnik, Nieperbau
Professor George Georghiou, University of Cyprus
The installed capacity of solar photovoltaic (PV) systems is continuously increasing due to decreasing costs and increasing environmental concerns. The energy obtained from the solar PV systems is clean and green energy. However, it is highly affected by the non-ideal environmental conditions, e.g., partial shading. These non-ideal conditions lead to a mismatch in the electrical characteristics of the solar PV system, which compromises of few to thousands of PV panels in series and parallel to achieve the system requirement. Due to mismatch, the entire PV system performance is affected along with the system life, which is degraded due to the stresses generated by the mismatch in the PV system.
To analyze, diagnose, and mitigate the effect of mismatch in the solar PV system, this Ph.D. study is divided into two parts. In the first part, crystalline-silicon (c-Si) and thin-film solar PV panels technologies are considered to analyze them by using infrared thermography, temperature measurement, and power-voltage (P-V) characteristics under various mismatch conditions. Additionally, infrared thermographic images are also used in the diagnoses of the mismatch effect through a machine-learning (ML)-based algorithm, i.e., Naive Bayes (nBayes) classifier. The ML classifier is used to detect the hotspots in c-Si PV panels. The developed algorithm categorizes the PV panel's infrared images into three various categories, e.g., normal, defective, and hotspot by achieving an efficiency above 94%.
In the second part, the techniques based on power electronics have been developed to reduce the impact of mismatch in a solar PV system. The developed techniques use smart bypass diodes and distributed power electronic topologies focusing on differential power processing (DPP) techniques to reduce the impact of mismatch. The developed topologies improve the extraction of energy from the system by reducing the stresses over the components in the topology by minimizing the peak-peak mismatch current ripples, better voltage equalization, and improving the performance under severe mismatch conditions as compare to already existed solutions. Additionally, the DPP processes only a small part (mismatched power) of power instead of processing a complete power. Hence, the size of the DPP converters is small therefore, they can easily be integrated into a PV panel junction box. Moreover, the DPP converters eliminate the multiple power peaks (MPPs) issue in the solar PV system, which reduces the complexity for maximum power point tracking (MPPT) algorithms. The proposed topologies are analyzed through simulation and experimentation. Additionally, the DPP converter along with DC optimizer is also compared with state-of-the-art solution, i.e., bypass diode technique under various mismatch scenarios to analyze the effectiveness and performance of these three techniques.
In continuation, the Ph.D. study also explores the integration of DPP topologies on various PV string interconnection schemes, e.g., series-parallel (SP), total-cross-tied (TCT), bridge-linked (BL), and central-cross-tied (CCT), to analyze their applicability on them. For this purpose, a system of 4x4 PV array is considered for analysis under various mismatched conditions. The results show that the DPP converters are only applicable to SP and CCT connections due to the inherent DPP converter structure. However, the integration with SP and CCT shows an improvement in overall energy yield. Thus, the integration of DPP with various integration schemes may be a promising solution to enhance the performance and efficiency of large PV systems.
THE DEFENCE will be IN ENGLISH - all are welcome.
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Pontoppidanstræde 101, Room 1.011