Papers by Dr. Kamran Ali Khan Niazi
Energies
This research presents an optimal scheme for the integration of renewable resources with the util... more This research presents an optimal scheme for the integration of renewable resources with the utility grid to minimize the operational cost of the residential and industrial microgrids. With the changing paradigm of solar photovoltaic in low-voltage distribution networks, utilities have allowed net metering and feed-in tariff (FiT). These incentives encourage residential and industrial consumers to contribute toward energy generation. However, in conventional mode, the system may underperform if resources are not scheduled optimally. To compensate for the price difference during off-peak and on-peak hours, the energy should be taken from the grid when electricity prices are lower and supplied to the grid when the electricity price is higher. The proposed models will therefore allow optimal resource utilization considering intermittent renewable generation as well as a time-varying utility tariff. A complete comparative analysis of on-grid and off-grid models was carried out. The resu...
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)
Partial shading reduces energy production and affects the lifetime of the overall PV system. To m... more Partial shading reduces energy production and affects the lifetime of the overall PV system. To mitigate the mismatch effects caused by partial shading, several PV cell-or sub-panel-level techniques employing power electronics have been proposed in the literature, where discrete passive components, e.g., inductors and capacitors, are also used. In this paper, a differential power processing (DPP) technique, which utilizes only the intrinsic capacitance of solar cells, is introduced for small-scale PV applications. The developed DPP topology mitigates the mismatch effects by operating all PV cells at or near to their corresponding maximum power points (MPPs) even under mismatch conditions. The analysis of the topology and its comparison with the frequently used series-and series-parallel (SP)-connected techniques, are presented to validate its efficacy and operational capabilities, through simulation results. Moreover, a prototype is built to verify the topology. The experimental results confirm the elimination of multiple power peaks under mismatch along with maintaining the same voltages across the PV panels.
Electronics
Partial shading and other non-ideal conditions cause electrical mismatches that reduce the output... more Partial shading and other non-ideal conditions cause electrical mismatches that reduce the output power generated by a photovoltaic (PV) system. It affects the overall performance and efficiency of PV systems. Therefore, a model is developed in MATLAB, which analyses the performance of the PV systems under real irradiance profiles and temperatures for various available mismatch mitigation methodologies, i.e., bypass diode, DC power optimizer, and differential power processing (DPP). More specifically, this study will help to understand the best mismatch reduction methodologies for a solar PV system under different scenarios. The results also are validated by comparing them with a similar PV system installed in SolarTechLAB, which also operates under the same irradiance and temperature conditions under which these models are tested. This study also presents novel results, covering discussions on the reverse voltage distribution under mismatch scenarios among bypass diode, DC power op...
2019 IEEE Applied Power Electronics Conference and Exposition (APEC)
The deployment of solar photovoltaic (PV) systems is increasing. The performance degradation of P... more The deployment of solar photovoltaic (PV) systems is increasing. The performance degradation of PV systems can happen, which is potentially induced by partial shading, also referred to as mismatch faults. Conventional PV modules are connected in series and are sensitive to mismatch faults. Bypass methods and other solutions are thus used to reduce the mismatch effect. This paper compares the performances of the bypassing techniques using traditional (Schottky) bypassing diodes with smart bypassing diodes (SBD). The benchmarking results show that the SBD can be employed to improve the performance during shading in PV systems. More specifically, the use of SBDs with series-connected MOSFETs leads to a reduction of the reverse voltage with a higher output power under various shading conditions, when compared to the case with traditional bypassing diodes. The reduction in the reserve voltage contributes to lowered temperature in shaded cells, and thus increases the reliability of the PV modules.
Partial shading affects the performance and reliability of thin-film and crystalline-silicon (c-S... more Partial shading affects the performance and reliability of thin-film and crystalline-silicon (c-Si) photovoltaic (PV) modules. In this paper, the thin-film and c-Si modules are experimentally benchmarked by introducing various partial shading patterns over the modules. More specifically, experiments are performed using SPISUN 5600 SLP-based test-rig. The benchmarking reveals that thin-film and c-Si technologies behave differently under the same shading patterns. Furthermore, thermographic images are also presented to explore the effect of partial shading on both modules.
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC), 2018
Photovoltaic (PV) modules are subject to various internal or external stresses due to their opera... more Photovoltaic (PV) modules are subject to various internal or external stresses due to their operation in solar PV based power systems. Therefore, monitoring and maintenance are critical issues to ensure reliability of PV modules which in turn would affect the reliability of any PV system. In this paper, we categorize operational solar panels into two categories (Defective and Non-Defective panels) using a machine learning technique i.e. texture features through thermography assessment. Further, the panels are also categorized for diagnostic perspective using nBayes classifier. Results from an investigation for a 42.24 kWp PV system showed a mean recognition rate of 98.4% for a set of 260 test samples.
2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019
Energy harvesting from solar photovoltaic (PV) modules is affected by partial shading (contribute... more Energy harvesting from solar photovoltaic (PV) modules is affected by partial shading (contributes to mismatch issues), which in turn affects the entire system efficiency. Various power electronics converters have thus been investigated to address the mismatch issue due to partial shading, where the charges between PV submodules (typically, three submodules in a PV module) are redistributed. As a representative of the power electronic-based techniques, differential power processing (DPP) converters can improve the power extraction from the series-connected PV submodules. In this paper, a switched-capacitor-inductor (SCL)-based DPP converter is proposed to mitigate the mismatch effect for PV modules. The proposed converter only processes the differential power, enabling extraction of the maximum power from the PV module at a submodule level. The proposed topology is analyzed and compared with the traditional (Schottky) bypassing technique through simulations. Partial shading experiments are also performed for the traditional technique. A benchmarking with the prior-art DPP converters and experimental tests on the switched-inductor (SL)-based DPP topology are presented in this paper.
2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019
In present times, the concerns over severe environmental pollution, fluctuations, and fossil-fuel... more In present times, the concerns over severe environmental pollution, fluctuations, and fossil-fuel consumption caused by immensely dynamic loads (pulsed loads) have captured attention in shipboard microgrids. In order to make such power system stable and reliable, presently, more generators are kept online that operate much below their efficient point. Therefore, in order to boost the fuel efficiency of shipboard microgrids, the minimum generator operation with N-1 safety can be considered as a possible solution, which is a trade off between reliability and fuel economy. For that, one of the efficient solution is to interface an energy storage system (ESS) by removing the backup generator or removing one of generator and operate rest of the generators close to their efficient point. Energy storage devices that have been frequently in use in different applications consist of batteries, flywheel, ultra-capacitor, and fuel cell. Lithium-ion among the different type of batteries is one of the most used battery in fully electric zero-emission commercial ferries that sails on shorter routes. This paper therefore presents Lithium-ion based Battery Energy Storage System (BESS) as a feasible solution to the prior mentioned concerns. At first, in order to cater with the fluctuation caused by the propulsion motor with the varying sea conditions, BESS is interfaced without the use of buck-boost converter in parallel with the DC-link capacitor. Secondly, the same BESS is interfaced with the point of common coupling (PCC) in order to cater with pulsed loads. The proposed methodology is simulated and verified using MATLAB/SIMULINK software environment.
Energies, 2021
Partial shading affects the energy harvested from photovoltaic (PV) modules, leading to a mismatc... more Partial shading affects the energy harvested from photovoltaic (PV) modules, leading to a mismatch in PV systems and causing energy losses. For this purpose, differential power processing (DPP) converters are the emerging power electronic-based topologies used to address the mismatch issues. Normally, PV modules are connected in series and DPP converters are used to extract the power from these PV modules by only processing the fraction of power called mismatched power. In this work, a switched-capacitor-inductor (SCL)-based DPP converter is presented, which mitigates the non-ideal conditions in solar PV systems. A proposed SCL-based DPP technique utilizes a simple control strategy to extract the maximum power from the partially shaded PV modules by only processing a fraction of the power. Furthermore, an operational principle and loss analysis for the proposed converter is presented. The proposed topology is examined and compared with the traditional bypass diode technique through ...
Partial shading affects the performance and reliability of thin-film and crystalline-silicon (c-S... more Partial shading affects the performance and reliability of thin-film and crystalline-silicon (c-Si) photovoltaic (PV) modules. In this paper, the thin-film and c-Si modules are experimentally benchmarked by introducing various partial shading patterns over the modules. More specifically, experiments are performed using SPISUN 5600 SLP-based test-rig. The benchmarking reveals that thin-film and c-Si technologies behave differently under the same shading patterns. Furthermore, thermographic images are also presented to explore the effect of partial shading on both modules.
Electronics, 2021
A reconfiguration technique using a switched-capacitor (SC)-based voltage equalizer differential ... more A reconfiguration technique using a switched-capacitor (SC)-based voltage equalizer differential power processing (DPP) concept is proposed in this paper for photovoltaic (PV) systems at a cell/subpanel/panel-level. The proposed active diffusion charge redistribution (ADCR) architecture increases the energy yield during mismatch and adds a voltage boosting capability to the PV system under no mismatch by connected the available PV cells/panels in series. The technique performs a reconfiguration by measuring the PV cell/panel voltages and their irradiances. The power balancing is achieved by charge redistribution through SC under mismatch conditions, e.g., partial shading. Moreover, PV cells/panels remain in series under no mismatch. Overall, this paper analyzes, simulates, and evaluates the effectiveness of the proposed DPP architecture through a simulation-based model prepared in PSIM. Additionally, the effectiveness is also demonstrated by comparing it with existing conventional D...
2019 21st European Conference on Power Electronics and Applications (EPE '19 ECCE Europe), 2019
The partial shading on parallel-connected photovoltaic (PV) modules introduces severe mismatch is... more The partial shading on parallel-connected photovoltaic (PV) modules introduces severe mismatch issues in PV systems, which significantly affects the overall output power. Distributed maximum power point tracking (DMPPT) is considered as an effective solution to the resultant mismatch in parallel-connected PV sub-modules. In this context, this paper proposes a sub-module level switched-inductor (SL) based differential power processing (DPP) technique for parallel connections to alleviate the mismatch effect. The technique can achieve the maximum output power under mismatch by equalizing the sub-module voltages. The proposed technique is analyzed and compared through simulations with a traditional (Schottky diode) bypassing technique.
2019 9th International Conference on Power and Energy Systems (ICPES), 2019
Due to increasing environmental concerns associated with the fossil fuel consumption and greenhou... more Due to increasing environmental concerns associated with the fossil fuel consumption and greenhouse emissions by marine vessels, world is moving towards sustainable energy resources such as solar, wind and so on. Renewable energy sources are found out to be a significant source of energy as they are sustainable and clean as compared to traditional generation sources, for instance, the burning of fossil fuels, diesel generators, steam engines, etc. As solar energy is one of the cheapest, abundant and cleanest source of energy, therefore, it has the potential to be the most utilized source of energy along with energy storage systems (ESS) for future yachts and ferries. However, partial shading effect and intermittent nature of photovoltaic (PV) systems cause fluctuations in voltage that can potentially disturb the voltage profile, therefore may instigate instability in shipboard microgrids, if not properly managed. This paper, therefore, proposes a hybrid energy storage system (HESS) comprising of Lithium-ion (Li-ion) battery and ultracapacitor having the capability to mitigate fluctuations caused by the partial shading effect in PV panels. The control system is based on frequency sharing approach in which high-frequency components are handled by the ultra-capacitor whereas lowfrequency components are handled by the Li-ion battery. The proposed methodology is simulated using MATLAB/ SINULINK and various scenarios of power sharing are highlighted for the validation of the proposed scheme. Index Terms-Frequency sharing, hybrid energy storage systems (HESS), shipboard microgrids, battery energy storage system (BESS), partial shading, photovoltaic (PV) systems.
The 10th International Conference on Power Electronics, Machines and Drives (PEMD 2020), 2021
Mismatch effects are common in photovoltaic (PV) systems, which affect the overall system perform... more Mismatch effects are common in photovoltaic (PV) systems, which affect the overall system performance and the PV module life. A mismatch causes an imbalance in the PV module voltages, and therefore, it is not recommended to connect PV modules in parallel due to increased power losses and stresses. To mitigate the effect of mismatch, module-level power electronics converters are considered as an effective solution. Accordingly, this paper introduces a differential power processing (DPP) converter based on switched-capacitors (SCs) for parallel-connected PV strings. The proposed DPP converters are connected across each PV module, which equalizes the PV module voltages. The technique can help to generate more output power regardless of mismatch between PV modules and make the parallelization of PV strings possible. The proposed architecture is analyzed through simulations and compared with parallel-connected PV strings using Schottky diodes.
Energies, 2019
Photovoltaic (PV) energy has been competitive in power generation as an alternative to fossil ene... more Photovoltaic (PV) energy has been competitive in power generation as an alternative to fossil energy resources over the past decades. The installation of grid-connected solar energy systems is expected to increase rapidly with the fast development of the power electronics technology. As the key to the interface of the PV energy and the grid, power converters should be reliable, efficient and comply with the grid requirements. Considering the nature of PV energy, the power conversion should be flexible (e.g., high step-up DC-DC conversion and harmonic-free DC-AC conversion). Accordingly, many power electronic converters have been reported in literature. Compared with isolated inverters, transformerless inverters show great advantages. This paper thus presents an overview of the transformerless step-up single-phase inverters for PV applications based on the dc-link configurations. Grid-connected PV inverters are classified as constant dc-link voltage structures, pseudo-dc-link voltage...
Energies, 2019
In recent times, concerns over fossil fuel consumption and severe environmental pollution have gr... more In recent times, concerns over fossil fuel consumption and severe environmental pollution have grabbed attention in marine vessels. The fast development in solar technology and the significant reduction in cost over the past decade have allowed the integration of solar technology in marine vessels. However, the highly intermittent nature of photovoltaic (PV) modules might cause instability in shipboard microgrids. Moreover, the penetration is much more in the case of utilizing PV panels on ships due to the continuous movement. This paper, therefore, presents a frequency sharing approach to smooth the effect of the highly intermittent nature of PV panels integrated with the shipboard microgrids. A hybrid system based on an ultra-capacitor and a lithium-ion battery is developed such that high power and short term fluctuations are catered by an ultra-capacitor, whereas long duration and high energy density fluctuations are catered by the lithium-ion battery. Further, in order to cater ...
Solar Energy, 2019
Monitoring and maintenance of photovoltaic (PV) modules are critical for a reliable and efficient... more Monitoring and maintenance of photovoltaic (PV) modules are critical for a reliable and efficient operation. Hotspots in PV modules due to various defects and operational conditions may challenge the reliability, and in turn, the entire PV system. From the monitoring standpoint, hotspots should be detected and categorized for subsequent maintenance. In this paper, hotspots are detected, evaluated, and categorized uniquely by using a machine learning technique on thermal images of PV modules. To achieve so, the texture and histogram of gradient (HOG) features of thermal images of PV modules are used for classification. The categorized hotspots are detected by training the machine learning algorithm, i.e., a Naive Bayes (nBayes) classifier. Experimental results are performed on a 42.24-kWp PV system, which demonstrates that a mean recognition rate of around 94.1% is achieved for the set of 375 samples.
Applied Sciences, 2019
The paper investigates the system efficiency for power distribution in residential localities con... more The paper investigates the system efficiency for power distribution in residential localities considering daily load variations. Relevant system modeling is presented. A mathematical model is devised, which is based on the data from the Energy Information Administration (EIA), USA, for analysis. The results reveal that the DC distribution system can present an equivalent or even better efficiency compared to the AC distribution network with an efficiency advantage of 2.3%, averaged over a day. Furthermore, the distribution systems are compared under various capacities of solar PV accounting for the effect of variation in solar irradiation over time.
Energies, 2019
Partial shading on photovoltaic (PV) arrays reduces the overall output power and causes multiple ... more Partial shading on photovoltaic (PV) arrays reduces the overall output power and causes multiple maximas on the output power characteristics. Due to the introduction of multiple maximas, mismatch power losses become apparent among multiple PV modules. These mismatch power losses are not only a function of shading characteristics, but also depend on the placement and interconnection patterns of the shaded modules within the array. This research work is aimed to assess the performance of 4 × 4 PV array under different shading conditions. The desired objective is to attain the maximum output power from PV modules at different possible shading patterns by using power electronic-based differential power processing (DPP) techniques. Various PV array interconnection configurations, including the series-parallel (SP), total-cross-tied (TCT), bridge-linked (BL), and center-cross-tied (CCT) are considered under the designed shading patterns. A comparative performance analysis is carried out b...
The Journal of Engineering, 2019
In this work, a dual-loop control strategy is applied to a highly distributed architecture of pho... more In this work, a dual-loop control strategy is applied to a highly distributed architecture of photovoltaic (PV)/batterybased DC microgrid, suitable for swarm electrification of developing regions. Typically, in such schemes, resource sharing among the spatially dispersed PV generation and battery storage resources is enabled via communication-based control methodologies, which adds cost and complexity to the overall system. Alternately, a communication-less and decentralised control methodology is proposed which utilises inner loop current control and outer loop voltage droop (V-I droop) control for the coordinated resource sharing among the distributed resources. Various scenarios of power sharing among the contributing households are evaluated and the efficacy of the proposed control scheme is validated through simulations on MATLAB/ Simulink. Results show that the proposed decentralised control strategy is capable of ensuring stable and coordinated operation without any dedicated layer of communication among the dispersed generation/storage resources.
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Papers by Dr. Kamran Ali Khan Niazi