Photovoltaic Conversion System Research Articles

Feasibility study of coffee husk char-derived carbon dots to enhance solar photovoltaic-thermal applications

Coffee is one of the most traded commodities in the world. Coffee husk makes up the majority of the solid debris generated during the dry processing of coffee, which is between 30% and 50%. Pyrolysis is a reliable and feasible technology to valorise the coffee husk. The present study proposes and investigates a novel method for producing carbon dots from coffee husk char through pyrolysis. Nanomaterials are becoming more popular to improve the thermal and optical properties of working fluids used in solar photovoltaic and thermal conversion systems. The coffee husk-char derived carbon dot (CHC-CD) nanofluids are prepared with different char concentrations (1%, 2%, 3% and 4%). The chemical and optical properties of the nanofluid produced from coffee husk char (CHC-CD nanofluid) are investigated. The morphology, size and particle size distribution of the CHC-CD particles were studied using field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The particles were found to have an average size of 5.38 nm. The CHC-CD nanofluid had a basic pH and negative zeta potential, which was found to decrease with an increase in the char concentration and pH. The nanofluid prepared with 2% char was found to have a zeta potential of −61.4 mV. It was evident from the UV–vis transmittance spectra that the CHC-CD nanofluid prepared with a char concentration of 2% had very limited transmittance in the UV region and good transmittance above 735 nm. This transmittance range is found to be favourable for the smooth and efficient operation of silicon-based solar PV cells. The CHC-CD nanofluid also showed a maximum intensity emission wavelength of 522 nm at an excitation wavelength of 450 nm. Characterisation of the carbon phase, surface functional groups, and surface defects was also done using XRD, FTIR, and Raman spectroscopy, respectively. The optical and chemical properties indicate that the developed CHC-CD nanofluid can find application not only in solar photovoltaic and thermal systems but also in applications in biomedical and chemical sensor applications.

Sustaining the DC Micro-Grid Bus Voltage through the Implementation of Finite Control Sets Model Predictive Control in a Photovoltaic Converter System

Sustaining the DC Micro-Grid Bus Voltage through the Implementation of Finite Control Sets Model Predictive Control in a Photovoltaic Converter System

Current Source Inverter (CSI) Power Converters in Photovoltaic Systems: A Comprehensive Review of Performance, Control, and Integration

Grid converters play a central role in renewable energy conversion. Among all inverter topologies, the current source inverter (CSI) provides many advantages and is, therefore, the focus of ongoing research. This review demonstrates how CSIs can play a pivotal role in ensuring the seamless conversion of solar-generated energy with the electricity grid, thereby facilitating stable and reliable integration. This study extensively investigates various categories of single-stage CSI photovoltaic inverters, categorizing them into two-level, three-level, and multi-level architectures. Furthermore, these inverters are classified based on construction attributes, power factor, and total harmonic distortion values to assess their compliance with the standards, such as IEEE 1547 and IEC 61727. This review also delves into diverse control strategies for seamless grid integration. This comprehensive assessment serves as a resource for researchers in the field, enabling them to effectively choose the most suitable CSI for their specific applications. Additionally, it offers a quick reference point to steer research endeavors toward refining the integration of CSIs within photovoltaic systems.

Bounded Region for Tracking by Two Fuzzy Rules Based Perturb and Observe Technique with Fractional Order based Proportional Integral Controller for Photovoltaic Conversion System

Maximum power from PV system is tracked by using Maximum power point (MPP) tracking techniques. In this paper the Two fuzzy rules based perturb and observed (2F-P&O) with Fractional order based PI (FOPI) controller is developed to track the global MPP under Partial shading conditions (PSCs). The two rules based fuzzy systems are implemented to provide the voltage boundaries under which the P&O starts to track GMP. FOPI controller is used to minimize the error and gives an accurate response under PSCs. The performance analysis of 2F-P&O based MPP technique is showing along with cases as diagonal & column based shading patterns, irradiance change conditions under several PSCs. The 2F-P&O with FOPI based technique compared with traditional P&O, Artificial neural network and Particle swarm optimization, Moreover from the comparative analysis 2F-P&O has higher efficiency, less oscillations and convergence time. This paper is validated using Opal-RT simulator and MATLAB/ Simulink Software.

A Reliability-Optimized Maximum Power Point Tracking Algorithm Utilizing Neural Networks for Long-Term Lifetime Prediction for Photovoltaic Power Converters

The reliability of power converters in photovoltaic systems is critical to the overall system reliability. This paper proposes a novel active thermal-controlled algorithm that aims to reduce the rate of junction temperature increase, therefore, increasing the reliability of the device. The algorithm works alongside a normal perturb and observe maximum power point tracking algorithm, taking control when certain temperature criteria are met. In conjunction with a neural network, the algorithm is applied to long-term real mission profile data. This would grant a better understanding of the real-world trade-offs between energy generated and lifetime improvement when using the proposed algorithm, as well as shortening study cycle times. The neural network, when applied to 365 days of data, was 28 times faster than using standard electrothermal modeling, and the lifetime consumption was predicted with greater than 96.5% accuracy. Energy generated was predicted with greater than 99.5% accuracy. The proposed algorithm resulted in a 3.3% reduction in lifetime consumption with a 1.0% reduction in the total energy generated. There is a demonstrated trade-off between lifetime consumption reduction and energy-generated reduction. The results are also split by environmental conditions. Under very variable conditions, the algorithm resulted in a 4.4% reduction in lifetime consumption with a 1.4% reduction in the total energy generated.

Optimization of flexible thin-film photovoltaic converters based on CdS/CdTe heterosystem for integration with solar thermal collectors

The paper introduces the concept of a photoenergy system based on film photovoltaic converters using the CdS/CdTe heterosystem. The goal is to develop a design solution for a flexible thin-film photovoltaic converter system that can be directly mounted on a heat collector plate, integrating photovoltaic converters with thermal collector systems. The paper highlights the limitations of traditional silicon-based photovoltaic converters and propose using flexible photovoltaic converters based on CdS/CdTe, which have concentrated absorption within the visible range and allow unobstructed flow of long-wave solar radiation for efficient thermal energy generation. The paper discusses the methods of obtaining samples of flexible photovoltaic converter ITO/CdS/CdTe/Cu/Au solar cells, including the deposition of layers on polyimide films, chloride treatment, and annealing processes. Analysed the impact of the “chloride” treatment on the structural and optical characteristics of the base layers and present the overall appearance of the thin-film photovoltaic converter samples. The structural analysis of the cadmium telluride films is conducted using X-ray diffractometry techniques, while the optical properties are investigated using a spectrophotometer. The light-voltage characteristics of the photovoltaic converter samples are measured under illumination conditions, and various output parameters and characteristics of the photovoltaic converter are determined. The authors emphasize the significance of optimizing the performance of the cadmium telluride layer in the flexible photovoltaic converter structure and discuss the variation of technological parameters to enhance efficiency. Paper presents the output parameters and light diode characteristics corresponding to different thickness ranges of the CdS layer. Overall, this paper provides valuable insights into the development of flexible film photovoltaic converters based on the CdS/CdTe heterosystem for integrated photovoltaic and thermal collector systems. The experimental methods and results contribute to the understanding of optimizing the performance of the photovoltaic converters and offer potential applications for autonomous heat supply systems.

Improve the energy efficiency of PV systems by installing a soft switching boost converter with MPPT control

<span lang="EN-US">To improve the energy consumption rate of solar cells and reduce switching loss, a maximum power point tracking (MPPT) control approach is presented to manage the boost converter and achieve soft switching. A method for determining the optimal values of the soft switching boost converter design parameters has been proposed, by determining the ideal values for the inductor, capacitor, and duty cycle of the boost converter with soft switching, this method enables the key matching of the PV system with the DC/DC converter configuration. In addition to presenting an analysis of several MPPT methodologies, the entire design of the PV converter system is also included. This study compares the perturb-and-observe (P&O) method and the incremental conductance (IC) method for maximum power point tracking (MPPT) in the MATLAB/Simulink application. The PV systems with both MPPT algorithms have been simulated beginning with an implemented model of the photovoltaic (PV) array together with the soft switching boost converter and its MPPT control. The simulation results based on irradiance and temperature are then shown. In the end, soft-switching is more efficient than hard-switching, especially when operating at full load.</span>

Analysis and Control of Chaos in Current Mode Controlled Superbuck Converter for Photovoltaic Systems

Background: Superbuck converter is a strong nonlinear system. However, with the changes in parameters, Superbuck converter performance may be reduced due to nonlinear phenomena, such as bifurcation, chaos, etc. Current mode controlled Superbuck converters have been extensively applied in photovoltaic (PV) systems that require a stable output voltage. Superbuck converters, as nonlinear circuits, exhibit plentiful nonlinear phenomena, such as bifurcation and chaos. In this study, we analyze and control the nonlinear phenomena in the current mode controlled Superbuck converter. The piecewise switching model and discrete iteration mapping model of the Superbuck converter are established. The evolution process of the Superbuck converter from steady state to bifurcation and chaos is revealed when the reference current, input voltage, and load are used as bifurcation parameters, and the bifurcation forms of the converter are all period-doubling bifurcations. The stability criterion of Superbuck converter under current mode has been deduced from reference current by analyzing the stability of the converter. Through the resonant parametric perturbation (RPP) method, the chaos control of the Superbuck converter has been realized for the first time. The converter changes from a chaotic state to a stable single-cycle state about 0.4ms after control and the output voltage ripple is reduced from 3.905V to 0.679V, which effectively improves the output stability of the converter. Objective: This study aimed to analyze and control nonlinear phenomena in current-mode controlled Superbuck converters. Method: Bifurcation diagram, time-domain waveform diagram, phase portrait and Poincare section are used as analytical methods for the nonlinear dynamic characteristics of Superbuck converters. The chaotic control method of the Superbuck converter is Resonant Parameter Perturbation (RPP). Results: After applying RPP control to the Superbuck converter in the chaotic state, it is converted into a single-cycle stable state in about 0.4ms. After the converter is controlled, the output current ripple is reduced from 0.71479A to 0.31A, and the output voltage ripple is reduced from 3.905V to 0.679V. Conclusion: With the increase in the reference current, the decrease in the input voltage, or the increase in the load, the system enters the chaotic state through the period-doubling bifurcation path. In this study, the chaos control of the Superbuck converter is carried out for the first time, and the control method used is the resonant parametric perturbation method. After RPP control, the converter is changed from an unstable, chaotic state to a stable period state in about 0.4ms.

Design and analysis of isolated high step-up Y-source DC/DC resonant converter for photovoltaic applications

ABSTRACT This paper presents the design and analysis of an isolated high step-up Y-source DC/DC converter for photovoltaic systems. At high switching frequencies, the conventional impedance source converter (ISC) experiences higher switching losses. To mitigate this, a high gain soft-switched frequency-modulated Y-source DC/DC converter is proposed. Here, soft switching is implemented on the Y-source impedance converter by creating quasi-resonance during a shoot-through instant. Thus, quasi-resonance occurs by an LC resonant tank, and it is formed using a resonant capacitor and leakage inductance of a transformer. It ensures that all the active switches are turned off with zero current switching (ZCS) and the voltage stress on each switch is much lower than the output voltage with lower turn-off voltage spikes. Thus, it eliminates the need for a snubber circuit. The output voltage is regulated by frequency modulation with the ON period of all four active switches kept constant. The converter can also deliver a continuous input current (CIC) and high voltage gain with a small shoot-through duty ratio . The galvanic isolation of the converter helps to eliminate the leakage current issues and safety hazards faced by the non-isolated counterparts. The proposed topology has all the inherent characteristics of a typical impedance source DC/DC converter with higher conversion efficiency over a wide range of output loads. The proposed converter achieves 96.46% of full load efficiency. Finally, a 200W prototype is built and tested in the laboratory to verify the converter design and performance.

Low-Voltage Photovoltaic System Based on a Continuous Input/Output Current Converter

Low-voltage photovoltaic systems are being widely used around the world, including their introduction into the power grid. The development of these systems requires the adaptation of several power converters, their static and dynamic modeling, the design of passive elements, and the design of the controller parameters, among other actions. Today, power converters are key elements in the development of photovoltaic systems, and classical power converters such as buck converters produce discontinuous input and output currents, requiring a high input capacitance and impacting the output power quality of these systems. This paper presents a proposal for a low-voltage photovoltaic system that uses a continuous input/output current buck converter, which enhances the operation of the classical buck converter in photovoltaic systems. The methodology describes the proposed photovoltaic system, including the power converter, its detailed operation, and the analysis of its waveforms. Moreover, the methodology includes a mathematical model of the photovoltaic system’s dynamic behavior and the design of a sliding-mode controller for maximum power extraction and perturbation rejection. The photovoltaic system is validated in two ways: first, a comparison with the classical buck converter highlighting the advantages of continuous input/output currents is presented; then, an application example using commercial devices is described in detail. The application example uses a flowchart to design the power converter and the sliding-mode controller, and a circuit simulation confirms the advantages of the continuous input/output current buck converter with its controller. In the circuit simulation, the control strategy is formed by a perturb and observe algorithm that generates the voltage reference for the sliding-mode controller, which guarantees the system stability, tracks the maximum power point, and rejects the double-frequency oscillations generated by an intended microinverter.

A single‐loop and current‐sensorless control for on‐grid seven‐level photovoltaic microinverter

AbstractThis paper proposes a single‐phase transformerless photovoltaic (PV) microinverter for low and medium‐voltage applications. The proposed approach comprises a suitable combination of multilevel boost/buck and H‐bridge topologies with a current‐sensorless control scheme, where the system controller only needs a straightforward‐to‐implement control loop to reach the desired attributes in solar PV conversion systems. Compared with other microinverters, this proposal significantly reduces the number of hardware components and required software resources, considerably attaining industrial and production advantages; guaranteeing: (i) a high DC elevation factor; (ii) an extraction of maximum power from solar PV panels; (iii) a multilevel output voltage; (iv) a low total harmonic distortion; and (v) a power factor close to unity. The multilevel microinverter's feasibility and effectiveness are assessed by a comprehensive mathematical model, whose simulation results are evaluated using MATLAB‐Simulink, and the experimental results are validated by means of an on‐grid low‐scale prototype, generating a power capacity of 1.5 kW.

Single Phase High Frequency AC Link DC/AC Converter for Photovoltaic Systems

In this article, an isolated high-frequency AC link bidirectional AC/DC Push-Pull converter is proposed for photovoltaic systems. Conventional DC/AC converters, such as back-to-back converters, are multi-stages converter with a common DC link. These converters due to their huge DC link capacitor, despite the simplicity of control, have some drawbacks such as high size and volume, low reliability and short life span, and fault ride-through (FRT) problems. In this article, a DC/AC converter with high-frequency AC link and transformer is proposed for the integration of photovoltaic (PV) arrays to a single-phase AC grid or load. The presented converter, beside the reduced number of active switches and cost, due to the lack of intermediate bulky energy storage element, has none of the conventional converter disadvantages. Modulation and commutation techniques of the proposed converter are also presented. The performance of the proposed system is proved using simulation in the MATLAB/SIMULINK environment and using a laboratory setup.

Multi-Functional Isolated Three-Port Bidirectional DC/DC Converter for Photovoltaic Systems

This paper proposes a novel multi-function isolated three-port bidirectional DC–DC converter for a stand-alone photovoltaic (PV) system. The proposed topology was composed of a unidirectional step-up converter and a bidirectional step-up/step-down converter that only required one set of complementary PWM signals to control any operation mode and used multiple operating stages to improve the practicability of the converter. In addition, the proposed topology had the function of inductance energy leakage recovery to improve the conversion efficiency and used synchronous rectification technology to reduce the conduction losses from passive components. This paper implemented a 500 W converter to verify the feasibility of the proposed converter by theoretical analysis, simulation, and experiment results. The experimental results show the highest efficiency of 95.5% for the PV step-up to the DC bus, 97.8% for the PV step-down to the battery terminal, 94.5% for the battery terminal step-up to the DC bus, and 93.4% for the DC bus step-down to the battery terminal, respectively.

Novel High-Step-Up/Step-Down Three-Port Bidirectional DC/DC Converter for Photovoltaic Systems

This paper presents a novel three-port high-step-up/step-down bidirectional DC/DC converter with a coupled inductor for photovoltaic (PV) systems. The proposed converter combines a high-step-up converter, which is used to step-up the PV module to DC bus 200 V, and a battery charge/discharge bidirectional converter to form a three-port bidirectional converter. When sufficient energy is supplied from the PV modules, the converter can step-up the output of the PV modules and provide energy to the DC bus while charging the battery simultaneously. However, when no energy is supplied from the PV modules, the DC bus voltage is provided by the battery. Moreover, the energy stored in the leakage inductor is recycled to the DC-blocking capacitor, and synchronous rectification is conducted in the switch during the step-up mode to reduce switch loss and thereby increase the system’s overall efficiency. Finally, a 500 W three-port bidirectional converter is implemented to verify the feasibility and practicability of the proposed converter. The maximum efficiency of the proposed converter is 95.4%, 94.3%, and 94.7% when operated in the high-step-up mode, battery step-up mode, and step-down mode for the PV modules, respectively.

Assessing the potential and utilization of solar energy at the building-scale in Shanghai

The assessment of potential and utilization of solar energy for each building has become an essential precondition of urban sustainable development. Currently, there are two challenges, namely high computation cost for an assessment within a large city and missing rooftop information for each building. In this study, by taking the downtown area in Shanghai as sample, a grid scheme with buffer was proposed to alleviate the computational burden and successfully estimate solar radiation with an accuracy of 0.91. Also, a quadrant-based segmentation method was developed to classify rooftop types with an overall accuracy of 83.63%, which helps better calculate solar energy utilization cost. Finally, we assumed PhotoVoltaic conversion (PV) systems or Domestic Solar Water Heater (DSWH) systems are installed on all suitable rooftops and analyzed their utilization cost, as well as economic and ecological benefits. The results show that 165,529 and 52,131 buildings are suitable for PV and DSWH systems, respectively. PV system's average payback time is about five years with reducing standard coal consumption of 1.85 × 1011kg. The DSWH system requires three more years to balance the cost and benefits. The criteria of further solar energy planning are also concluded from three perspectives: building height and density, and rooftop structure.

Modeling and simulation of novel dynamic control strategy for grid-connected photovoltaic systems under real outdoor weather conditions using Fuzzy–PI MPPT controller

ABSTRACT This paper proposes the modeling and simulation of a novel dynamic control strategy for 2.4 kWp single-phase grid-connected photovoltaic systems under real outdoor weather conditions using an intelligent Fuzzy–PI MPPT controller. The PV array in the first case is fixed and tilted at a 32° angle, whereas the PV array in the second is equipped with dual-axis sun tracking. The objective is to deliver the maximum power from the PV array and to improve the drawbacks of the classical MPPT control. The optimization is performed using a real-time daily profile of Ghardaia, Algeria (32.24°N – 3.24°W). The proposed MPPT controller (Fuzzy PI MPPT) is optimized under different climatic scenarios based on four selected typical days: the first two days in winter and the second two days in summer. An analysis of the performance and simulation of a photovoltaic conversion system associated with a solar tracker, comparing it from an energy point of view with a fixed photovoltaic converter, has been carried out in Matlab/Simulink software. The results show that grid-connected PV with dual solar tracking enhances the PV array output power efficiency by about 25% compared to a similar fixed PV system. The results show that higher injected power quality is achieved and the overall system has higher efficiency.

Enhancing reliability of photovoltaic power electronic converters under dynamic irradiance conditions

This paper presents a novel temperature-controlled maximum power point tracking (MPPT) algorithm for lifetime improvement of a photovoltaic (PV) converter under dynamic irradiance conditions. The proposed algorithm controls and limits the junction temperature change rate of switching devices, reducing the thermal stress and drastically reducing the damage received, hence improving the reliability and lifetime of power converters in PV systems. To evaluate the damage reduction, a lifetime estimation technique is applied which is composed of a Foster thermal model, a rainflow counting algorithm and an empirical lifetime model. Moreover, in this paper the energy and life consumption are calculated with the application of lookup tables to reduce computation time. The effectiveness of the proposed algorithm is verified using extensive simulations and by comparing energy generated and life consumption under irradiance profiles for different cloud conditions. The temperature-controlled algorithm is applied in parallel with a normal MPPT algorithm to a 10 kW photovoltaic system and results are compared using irradiance data from the province of Quebec, Canada to validate its efficacy. The obtained results show that for very variable cloud conditions, the modified algorithm managed to reduce the life consumption by 4.68 % at no extra cost, with just 0.08 % of energy generation reduction, proving its effectiveness.

A sliding mode control method based on improved reaching law for superbuck converter in photovoltaic system

Due to the influence of input voltage fluctuation, output load mutation, inductance and capacitance parameter perturbations, the DC bus voltage of photovoltaic power generation system will fluctuate accordingly. In order to maintain the stability of the bus voltage, a PID-type sliding mode control based on the improved reaching law is proposed. Using the saturation function sat(s), an improved fast reaching law is constructed to weaken the inherent chattering effect of sliding mode control, the finite time reachability property of the reaching law is verified, and the disturbance stability bound of closed-loop sliding mode control system in the presence of bounded disturbance is derived. Compared with PID control method and sliding mode control method based on power reaching law and exponential reaching law, the results show that the proposed control method weakens the influence of chattering, improves the dynamic response speed of the system by about 23% in the start-up stage. At the same time, the proposed control method has good dynamic performance and global robustness when subjected to external disturbances.

Fuzzy Observer Design for PV Conversion System with Fault Effects

This paper proposes a new approach to design an observer for the Photovoltaic conversion system. Originally, the PV conversion system is modeled under the nonlinear framework that is difficult for designing the observer. Thus, in this work, the original nonlinear form of the PV conversion system will be transformed to the T-S fuzzy model with the existence of the disturbance. Unlike the previous articles, the PV conversion system in this work is affected by the faults, and the fault impacts not only the system but also the output. The observer is designed to estimate the unknown states and the faults of the PV conversion system asymptotically as well as eliminate the impact of the disturbance. The augment technique is employed to modify the PV conversion system. With the aid of the Lyapunov theory and Linear Matrix Inequality (LMI) technique, the conditions for observer design have been proposed in the main theorem. Finally, the simulation results are also provided to prove the success and merit of the proposed method.

Analysis of Residual Current Flows in Inverter Based Energy Systems Using Machine Learning Approaches

Faults and unintended conditions in grid-connected photovoltaic systems often cause a change of the residual current. This article describes a novel machine learning based approach to detecting anomalies in the residual current of a photovoltaic system. It can be used to detect faults or critical states at an early stage and extends conventional threshold-based detection methods. For this study, a power-hardware-in-the-loop approach was carried out, in which typical faults have been injected under ideal and realistic operating conditions. The investigation shows that faults in a photovoltaic converter system cause a unique behaviour of the residual current and fault patterns can be detected and identified by using pattern recognition and variational autoencoder machine learning algorithms. In this context, it was found that the residual current is not only affected by malfunctions of the system, but also by volatile external influences. One of the main challenges here is to separate the regular residual currents caused by the interferences from those caused by faults. Compared to conventional methods, which respond to absolute changes in residual current, the two machine learning models detect faults that do not affect the absolute value of the residual current.