A light-emitting diode, also known as an LED, is a modern lighting technology that consumes 70% to 85% less energy than other lighting technologies. However, an LED is a nonlinear load that generates harmonic distortion, thereby distorting the sinusoidal waveforms. A larger number of LED installations in buildings may lead to severe power quality issues, and there is a lack of research on LED harmonic monitoring and laboratory testing, with underdeveloped innovation in practical power harmonic monitoring of LED lamps. To monitor the harmonic level in the system, the study aimed to design and develop a low-cost power-harmonic monitoring device for LED systems. The comparison of the Fluke 1736 power logger with a prototype using a low-cost ESP32 microcontroller with current and voltage sensors involved an experimental setup comprising a single LED and 18 LED tubes operated in a low-voltage, also known as an LV network, single-phase, 60Hz. The Total Harmonic Distortion or THD measurement method was applied, and the harmonic results were validated against specific IEC standards. It was observed that a single FSL T8 18W LED had a 236.3V and a 0.14A, with 0.51 pf, 94.7% total current harmonic distortion (THDi), and 1.5% total voltage harmonic distortion (THDv). For the 18 LED tube orientation, it produced 242.7V and 2.2A, with 0.56 pf, 133.8% THDi, and 1.7% THDv. The absolute error of the prototype is ±0.5V and ±0.02A, with THDi and THDv at ±1.35% and ±0.04%, respectively, which are within acceptable error limits of the IEC standards for low-cost instrumentation Class II and S. The findings showed that the FSL T8 18W LED has a poor power factor with a high THD content. The current harmonic distortion is directly related to the number of LED installations. The study revealed that it is essential to monitor power harmonics in modern lighting technology, and this can be achieved with a low-cost power-harmonic monitoring device.

The increasing penetration of photovoltaic generation in residential buildings has intensified the temporal mismatch between electricity availability and thermal demand, particularly in heat pump-based heating systems. Thermal energy storage represents a key enabling technology to increase on-site renewable energy self-consumption and system flexibility. Among available options, latent thermal energy storage (LTES) based on phase change materials (PCMs) offers high energy density and compact system layouts, which are especially attractive for space-constrained residential applications. Organic PCMs are of particular interest due to their chemical stability, predictable phase change behavior, and absence of supercooling-related issues. Nevertheless, the practical integration of PCM-based storage into real heat pump systems remains challenging due to heat transfer limitations and internal temperature non-uniformities. As a result, latent storage solutions cannot be considered plug-and-play components and require careful experimental validation under realistic operating conditions. Within this context, the LIFE ITS4ZEB project adopts an application-driven approach, focusing on industrially feasible configurations rather than idealized laboratory concepts.

This work presents the experimental characterization of a medium-temperature latent thermal storage unit based on an organic phase change material and integrated with a hydraulic loop representative of residential heat pump systems. The storage module consists of an aluminum tank with an internal volume of approximately 0.1 m³, filled with a commercial organic PCM with a phase change temperature suitable for space heating applications. The resulting nominal storage capacity is approximately 8 kWh. Heat exchange between the water loop and the PCM is provided by a commercial finned-tube heat exchanger adapted for latent storage use, representative of compact and cost-oriented industrial solutions. Charging and discharging tests were carried out by varying inlet water temperature differences (10–20 K) and volumetric flow rates (4–8 L/min), covering a range of operating conditions relevant to residential heat pump operation. Thermal power, cumulative stored and released energy, and internal temperature distribution were monitored using calibrated instrumentation. A distributed network of thermocouples enabled the analysis of thermal stratification and spatial temperature non-uniformities within the PCM volume.

The experimental results show that the performance of the organic PCM-based storage is strongly influenced by the imposed boundary conditions. Increasing the inlet temperature difference leads to higher peak thermal power and shorter charging and discharging times, while enabling a more effective utilization of the available storage capacity. At constant temperature difference, increasing the flow rate significantly boosts peak power but may reduce the total usable energy when an application-oriented power threshold is adopted to define the end of the process. Charging and discharging behaviors are largely symmetric, reflecting the stable and repeatable phase change characteristics of the organic PCM. Internal temperature measurements reveal the development of thermal stratification during both operating phases, with temperature gradients increasing under more aggressive conditions. Although such non-uniformities do not prevent correct operation, they influence charging and discharging dynamics and limit the uniform participation of the PCM volume in the phase change process.

The experimental investigation confirms that organic PCM-based latent thermal storage can deliver energy and power levels compatible with residential heat pump applications, albeit with a lower energy density compared to inorganic solutions. The absence of supercooling contributes to stable and predictable operation, but heat transfer limitations and thermal stratification remain key design challenges. System performance is highly sensitive to operating conditions, and excessive emphasis on peak power may compromise temperature uniformity and effective energy utilization. These results demonstrate that, even for organic PCMs, latent thermal energy storage cannot be considered a plug-and-play solution. Careful system design, appropriate selection of operating conditions, and experimental validation under realistic boundary conditions are essential to achieve a balanced compromise between performance, robustness, and industrial feasibility. Within the ITS4ZEB framework, the investigated configuration represents a reliable and scalable solution for enhancing renewable energy self-consumption in residential heat pump systems.

The increasing penetration of renewable energy resources such as solar photovoltaic and wind power has introduced significant challenges in the operation and control of modern power systems. One of the critical issues is maintaining voltage stability and minimizing power losses while ensuring efficient reactive power management. Optimal Reactive Power Dispatch (ORPD) plays a vital role in enhancing the operational performance of power systems by optimally controlling reactive power sources, transformer tap settings, and voltage magnitudes of generators. However, the nonlinear, nonconvex, and highly constrained nature of the ORPD problem makes it difficult to solve using conventional optimization techniques.

This study presents an Improved Salp Swarm Algorithm (ISSA) for solving the optimal reactive power dispatch management problem in power systems integrated with renewable energy resources. The proposed ISSA is an enhanced version of the Salp Swarm Algorithm inspired by the swarming behavior of salps in the ocean. The algorithm improves the exploration and exploitation capability of the conventional SSA by incorporating adaptive control parameters, improved leader–follower updating strategies, and enhanced convergence mechanisms. These modifications help avoid premature convergence and improve global search ability when solving complex power system optimization problems.

In the proposed framework, renewable energy sources such as solar and wind generation units are integrated into the distribution network, and their uncertainties are considered during optimization. The ORPD problem is formulated as a multi-objective optimization problem with the primary goals of minimizing active power losses, improving voltage profile, and maintaining voltage stability across the system. Control variables include generator voltages, transformer tap positions, and reactive power compensation devices such as shunt capacitors. System constraints such as power balance equations, generator limits, voltage limits, and reactive power limits are also incorporated into the optimization model.

To validate the effectiveness of the proposed method, the Improved Salp Swarm Algorithm is applied to standard benchmark test systems including the IEEE 33-bus, IEEE 69-bus, and IEEE 85-bus distribution networks with renewable energy integration. Load flow analysis is performed using the backward–forward sweep method suitable for radial distribution networks. The results obtained using ISSA are compared with several well-known optimization algorithms such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and Orangutan Optimization Algorithm (OOA). Simulation results demonstrate that the proposed ISSA achieves superior performance in terms of reducing power losses, improving voltage profiles, and achieving faster convergence compared to conventional algorithms.

The numerical results show that the ISSA-based reactive power dispatch strategy significantly enhances system performance under renewable energy integration scenarios. Furthermore, the algorithm provides stable and reliable solutions even under varying load conditions and renewable energy uncertainties. The improved convergence characteristics and robustness of the proposed approach make it a promising tool for solving complex optimization problems in modern smart grids.

Overall, this research highlights the potential of the Improved Salp Swarm Algorithm for efficient reactive power management in renewable energy-based power systems. The proposed approach can assist power system operators in maintaining voltage stability, reducing power losses, and improving overall system efficiency in future smart grid environments with high renewable energy penetration.

Accurate and effective optimization of photovoltaic (PV) systems is still a challenging task because solar cell current–voltage (I–V) characteristics are strongly sensitive to environmental conditions, which behave nonlinearly. This paper presents an analytical, non-iterative method to achieve the global maximum power point (MPPT) of PV cells and panels based on the Lagrange Multiplier Method (LMM). Compared with traditional iterative and empirical methods, the proposed method can obtain a mathematical optimization solution directly for output power maximization of PV systems in terms of single-diode and double-diode equivalent circuit models with series and parallel resistances.

An objective function and a constraint are set up for the optimization problem, consisting of the desired output power and nonlinear current–voltage solar cell equation. The problem becomes a matter of a reduced analytical approach by normalizing the variables with respect to current and voltage, which leads to the application of constrained optimization theory. Then, the Lagrange Multiplier Method is used under standard regularity and optimality conditions such as the KKT, Fritz John, Mangasarian–Fromovitz (MFCQ), or Linear Independence Constraint Qualification. These statements ensure that there is an optimal solution, which further means that the condition of optimality is satisfied.

Regarding the single-diode model, an analytical solution results in a second-order polynomial equation that describes the efficiency gap against the current density [12], which is of third-order type for the double-diode model. The optimal current, voltage, and load resistance corresponding to the maximum power point are analytically obtained in closed forms. The physical meaning of the Lagrange multiplier is also presented, emphasizing its connection with the characteristic resistance of the solar cell at the maximum power point.

To assess the efficiency and applicability of the proposed method, a series of simulations are performed based on experimental data recorded from R.T.C France (silicon solar cell) and Photowatt-PWP 201 (photovoltaic module). Further validation is carried out on the different PV technologies, such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, and copper indium diselenide (CIS) modules. The results indicate that the analytically calculated maximum power point corresponds well with experimental current–voltage and power–voltage characteristics for various operating temperatures and technologies.

The Lagrange-based optimization is an effective, fast, and low-cost approach compared to the conventional heuristic search techniques of AI for MPPT. Its non-iterative nature, analytical transparency, and versatility make it especially well-suited for real-time PV analysis, system sizing, and performance estimation tasks, as well serving as a bridge rom optimization environments to larger PV plant and system hybrids.

Introduction

The development of advanced electrode materials capable of delivering high energy and power densities while maintaining long-term operational stability remains a central challenge in electrochemical energy storage. Organic pseudocapacitive materials have emerged as promising candidates in this context, as they offer fast redox kinetics, molecular-level tunability, mechanical flexibility, and compatibility with low-energy, solution-based fabrication processes. In particular, electropolymerized conjugated polymers enable direct, binder-free growth of electroactive films on conductive substrates, ensuring intimate electrical contact and precise control over film thickness and morphology, features that are highly desirable for advanced energy materials.

Porphyrins constitute a unique class of redox-active molecular scaffolds owing to their extended π-conjugation, multielectron redox chemistry, and exceptional chemical robustness. Fully fluorinated porphyrins are especially attractive building blocks, as their strongly electron-withdrawing substitution pattern confers outstanding electrochemical stability and enhanced resistance toward oxidative degradation. When functionalized with polymerizable conjugated substituents, porphyrins can be integrated into extended polymer networks that combine molecular redox activity with efficient charge transport and structural durability. However, the electropolymerization of porphyrin derivatives remains nontrivial, and subtle variations in molecular architecture (such as the number and nature of polymerizable units) can critically influence polymer growth, electrochemical stability, and long-term pseudocapacitive performance. Establishing clear structure–property–performance relationships is therefore essential for advancing porphyrin-based electropolymers toward practical energy storage applications.

Herein, we present a comparative study of two structurally related fluorinated porphyrin monomers, P-4E, bearing four 3,4-ethylenedioxythiophene (EDOT) units, and P-3E-BDT, incorporating three EDOT units and one benzothiadiazole substituent, which were used as precursors for the electropolymerized films p-P-4E and p-P-3E-BDT, respectively. These polymer systems provide an ideal platform to elucidate how the nature and distribution of conjugated substituents influence electrochemical stability, rate capability, and pseudocapacitive behavior.

Methods

Electropolymerization of the porphyrin monomers was performed by oxidative cyclic voltammetry using a conventional three-electrode configuration. Glassy carbon (GC), platinum, and indium tin oxide (ITO) electrodes were employed as working electrodes, with a platinum wire counter electrode and a silver wire quasi-reference electrode. Polymer growth was carried out in dichloromethane solutions containing 0.10 M tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte, applying consecutive potential cycles at a scan rate of 0.1 V s⁻¹ within the anodic window required to promote EDOT coupling. After deposition, the electrodes were rinsed and transferred to monomer-free electrolyte solutions for electrochemical characterization.

Spectroelectrochemical measurements were conducted using polymer-coated ITO electrodes in a UV–Vis transparent electrochemical cell. Film morphology and surface texture were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) measurements were performed using a 5 mV AC perturbation amplitude over a frequency range of 100 kHz to 0.1 Hz. Galvanostatic charge–discharge (GCD) measurements at different current densities were used to evaluate gravimetric capacitance, rate capability, and cycling stability, including extended cycling tests.

Results

Both fluorinated porphyrin monomers were efficiently electropolymerized, yielding uniform and strongly adherent films on GC and ITO substrates. Cyclic voltammetry revealed reversible redox processes associated with both the porphyrin macrocycle and the conjugated EDOT backbone, indicating effective electronic communication within the polymer network.

p-P-4E exhibited a highly reproducible electrochemical response upon extended cycling, whereas p-P-3E-BDT displayed more pronounced changes over repeated cycles. GCD measurements confirmed pseudocapacitive behavior for both materials, with nearly linear discharge profiles within the selected potential windows. Spectroelectrochemical measurements revealed reversible, potential-dependent spectral changes consistent with the formation of radical species during oxidation, involving both the EDOT backbone and the porphyrin macrocycle and confirming preservation of the porphyrinic framework during cycling.

At a current density of 5 A g⁻¹, p-P-3E-BDT delivered a gravimetric capacitance of approximately 240 F g⁻¹, whereas p-P-4E reached higher values of around 320 F g⁻¹ under identical conditions. Moreover, p-P-4E showed improved capacitance retention with increasing current density and retained ~90% of its initial capacitance after 3000 charge–discharge cycles, demonstrating excellent durability. Capacitance values derived from GCD were independently corroborated by EIS. SEM and AFM analyses revealed more porous and textured morphologies for p-P-4E, consistent with its superior electrochemical performance.

Conclusions

This work demonstrates that molecular engineering of fluorinated porphyrin electropolymers provides an effective approach to access stable and high-performance pseudocapacitive materials. The investigated EDOT–porphyrin polymer networks exhibit reversible redox activity, efficient charge storage, and robust electrochemical behavior over extended cycling. While both systems display pseudocapacitive characteristics, the polymer incorporating a larger number of EDOT units (p-P-4E) exhibits enhanced gravimetric capacitance and cycle stability within the investigated current-density range. The combined analysis of galvanostatic charge–discharge and electrochemical impedance spectroscopy confirms a consistent pseudocapacitive response. These results highlight the importance of molecular architecture in porphyrin-based electropolymers and establish fluorinated EDOT–porphyrin systems as promising candidates for advanced organic electrode materials in electrochemical energy storage.

The transition from conventional air-insulated substations (AISs) to hybrid and fully digital substations constitutes a structural transformation in power system architecture, communication infrastructure, protection philosophy, and asset management practices. This transition redefines not only primary and secondary equipment interfaces but also engineering workflows, interoperability requirements, and operational performance expectations. Although numerous studies address specific technologies and pilot implementations, a comprehensive and methodologically rigorous synthesis of migration strategies, enabling standards, and deployment challenges remains limited. This paper presents a systematic literature review aimed at identifying dominant technological pathways, implementation barriers, reported benefits, and emerging research directions associated with digital substation transformation.

The review was conducted following a structured systematic review protocol inspired by PRISMA guidelines to ensure transparency and reproducibility. A comprehensive search was performed in IEEE Xplore and ScienceDirect for peer-reviewed publications published between 2005 and 2025. Predefined Boolean search strings combined terms such as “digital substation,” “IEC 61850,” “process bus,” “station bus,” “substation automation,” and “protection and control modernization.” After duplicate removal, titles and abstracts were screened against explicit inclusion criteria (peer-reviewed journal articles and conference papers addressing substation architecture, communication infrastructure, protection and control integration, or migration strategies) and exclusion criteria (non-technical reports, non-English publications, and studies lacking architectural or implementation relevance). Full-text assessment was subsequently conducted, and the final set of eligible studies underwent structured data extraction using predefined classification variables. All screening stages and eligibility decisions were documented to guarantee methodological consistency.

The selected studies were systematically categorized according to substation architecture level (conventional, hybrid, fully digital), communication layer (station bus, process bus, or combined), measurement interface type (conventional CT/VT versus Non-Conventional Instrument Transformers), scope of protection and control integration, and migration strategy (incremental retrofit, phased modernization, or greenfield deployment). A comparative synthesis was performed to evaluate architectural features, interoperability performance, communication determinism, time synchronization requirements, engineering complexity, cybersecurity implications, and reported operational performance indicators.

The review confirms that IEC 61850-based architectures—particularly the coordinated implementation of station bus and process bus—represent the dominant technological foundation of digital substations. The deployment of Intelligent Electronic Devices (IEDs), Merging Units (MUs), and communication mechanisms based on Sampled Values (SV) and GOOSE messaging is consistently identified as the core enabler of interoperability and functional integration. Reported benefits include substantial reduction of copper wiring, improved measurement fidelity, enhanced personnel safety through elimination of high-energy secondary circuits, faster and more selective protection response, and improved system observability and asset diagnostics capabilities.

Despite these advantages, large-scale adoption remains constrained by several technical and organizational challenges. These include multi-vendor interoperability limitations, strict latency and synchronization requirements for process-bus applications, increased engineering and configuration complexity, testing and commissioning difficulties, workforce skill gaps, and heightened cybersecurity exposure in highly interconnected digital environments. Furthermore, heterogeneous implementation practices and limited standardization in validation procedures continue to restrict widespread deployment.

Significant research gaps are identified in long-term reliability and availability assessment, standardized interoperability validation frameworks, systematic cyber-resilience evaluation methodologies, and documented large-scale field deployment experiences. Emerging research directions include the integration of digital twins for real-time simulation and decision support, artificial intelligence for engineering automation and predictive maintenance, cloud- and edge-based automation platforms, and software-defined protection architectures.

By explicitly defining a transparent and reproducible review protocol, this work provides a structured reference framework to support utilities, manufacturers, system integrators, and researchers in the systematic evaluation and implementation of reliable, cost-effective, and resilient migration strategies toward fully digital substations.

Lightweight metallic porous materials with high energy absorption efficiency are of increasing interest for advanced energy materials, impact mitigation, and structural protection applications. Such structural and high-performance energy-absorbing materials are mostly used in automotive, aerospace, and protective applications, which drive innovation in metallic foams. Silicon carbide (SiC)-reinforced aluminum alloy (AlSi10Mg) attracts attention across the globe in a variety of areas, ranging from aerospace, automotive, heat exchangers, electronic components, and biomedical implant scaffolds. The porous AlSi10Mg-SiC composite material provides good mechanical properties and wear resistance, and is applied to lightweight structural components and tribological parts. The materials are mostly designed for energy absorption and impact resistance applications, where the mechanical properties are strongly influenced by the porosity, pore size, and SiC content in the materials. In this investigation, porous AlSi10Mg and AlSi10Mg-SiC are investigated under compressive loading conditions. The samples were manufactured using a replication casting process that provides microstructural uniformity in the material. The porous structure was designed with an average pore size of 0.8 – 1.2 mm. Quasi-static compression testing was performed at strain rates of 0.01 s⁻¹ and 0.001 s⁻¹. Quasi-static uniaxial compression tests were conducted to evaluate compressive strength, plateau stress, and energy absorption capacity. The material deformation behavior under compressive loading was analyzed by stress–strain curves from the available data resources. The work absorption behavior and its efficiency were analyzed in a material deformation regime. This research indicates that the energy absorption behavior is primarily influenced by the strain rate rather than the size of the porous structure. Additionally, higher strain rates exhibit higher energy absorption characteristics than lower strain rate deformations. Both porous AlSi10Mg and aluminum composites (AlSi10Mg -SiC) show similar behavior during compressive deformation process. These findings are necessary for understanding the potential of replication-cast AlSi10Mg-based porous structures as high-performance advanced energy materials for applications in impact protection, vibration damping, and energy-related structural systems.

1. Introduction

Advanced energy materials play a critical role in the continued development of photovoltaic technologies, particularly crystalline silicon solar cells, which continue to dominate the global renewable energy market [1]. Despite their high degree of technological maturity, the performance of silicon photovoltaic devices remains fundamentally limited by non-radiative recombination losses occurring at surfaces, interfaces, and within defect-rich bulk regions. These recombination pathways directly reduce the achievable open-circuit voltage and, consequently, the overall power conversion efficiency.

Among the various surface engineering strategies, hydrogenated silicon nitride (SiNₓ:H) has emerged as a key passivation layer due to its dual functionality: chemical passivation of dangling bonds and field-effect passivation arising from fixed charges within the dielectric layer [2]. Nevertheless, further improvements in passivation quality require characterization techniques capable of resolving recombination dynamics with both temporal and spectral selectivity.

Spectrally selective open-circuit voltage decay (OCVD) analysis represents an advanced transient diagnostic method that is particularly well suited for probing charge carrier recombination in silicon photovoltaic energy materials [3,4]. By exploiting the wavelength-dependent absorption coefficient of silicon, this technique enables depth-resolved investigation of recombination processes, offering direct insight into the relative contributions of surface, emitter, and bulk regions.

2. Methods

A spectrally selective OCVD system was developed to investigate recombination dynamics in monocrystalline (c-Si) and multicrystalline (mc-Si) silicon photovoltaic energy materials. Industrial p-type Al-BSF solar cells fabricated using standard industrial processes were examined in both full-area devices (10 × 10 cm²) and mini-cell configurations (2 × 2 cm²) in order to capture global as well as localized recombination behavior.

Pulsed optical excitation was provided by light-emitting diodes operating at discrete wavelengths of 458, 524, 633, and 864 nm. These wavelengths were selected to enable depth-resolved carrier generation, ranging from near-surface excitation to bulk-dominated absorption, in accordance with the spectral absorption characteristics of silicon. Pulse generation, timing, and synchronization were controlled using an Arduino-based system interfaced with MATLAB/Simulink, providing microsecond-scale temporal resolution.

To assess the impact of passivation on recombination dynamics, a low-temperature thermal annealing treatment at 115 °C for 3 minutes was applied. The resulting OCVD transients were analyzed using exponential fitting procedures, allowing extraction of characteristic decay times corresponding to the effective minority carrier lifetime under different excitation conditions.

3. Results

The spectrally selective OCVD analysis reveals pronounced differences in recombination dynamics between monocrystalline and multicrystalline silicon solar cells. Under broad-area, high-injection excitation, full-size c-Si devices exhibited voltage decay times exceeding 15 ms, indicative of superior crystalline quality and reduced bulk defect density. In contrast, localized excitation in mini-cell configurations resulted in decay times in the microsecond regime, highlighting the strong influence of injection level and probing scale on recombination kinetics.

Short-wavelength excitation at 458 nm, which predominantly probes the near-surface and emitter regions, produced a marked increase in both open-circuit voltage and decay time following thermal annealing. This behavior confirms the effectiveness of hydrogen-related defect passivation in reducing surface recombination velocity. Conversely, near-infrared excitation at 864 nm, which is primarily sensitive to bulk recombination processes, showed minimal change after annealing, particularly in multicrystalline silicon. This observation indicates the persistence of bulk defect-related recombination associated with grain boundaries and extended defects.

Excitation at intermediate wavelengths exhibited coupled surface–bulk recombination behavior, further validating the depth-resolved capability of the spectrally selective OCVD approach.

4. Conclusions

This work demonstrates that spectrally selective OCVD analysis is a powerful, non-destructive characterization technique for investigating recombination dynamics in silicon photovoltaic energy materials. By enabling clear separation of surface and bulk recombination mechanisms, the method provides direct insight into the effectiveness of passivation treatments. The results confirm that low-temperature thermal annealing primarily enhances surface passivation, with a more pronounced impact on monocrystalline silicon compared to multicrystalline material. Through the integration of wavelength-resolved excitation and high temporal resolution, the proposed approach offers a robust pathway for guiding material optimization and passivation engineering in next-generation high-efficiency silicon photovoltaic technologies.

References

[1] M. A. Green et al., « Solar Cell Efficiency Tables (Version 66) », Progress in Photovoltaics, vol. 33, n^o 7, p. 795‑810, juill. 2025, doi: 10.1002/pip.3919.

[2] S. P. Muduli et P. Kale, « State-of-the-art passivation strategies of c-Si for photovoltaic applications: A review », Materials Science in Semiconductor Processing, vol. 154, p. 107202, févr. 2023, doi: 10.1016/j.mssp.2022.107202.

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The rapid growth of photovoltaic (PV) systems has made them a central component of renewable energy integration. However, PV inverters, which are responsible for converting direct current (DC) into alternating current (AC) for grid compatibility, remain highly vulnerable to faults. Issues such as sensor offsets, partial shading, and grid disturbances can cause performance degradation, instability, and even disconnection from the grid. These challenges pose significant risks to system reliability. Conventional control strategies, including proportional–integral–derivative (PID) controllers, often fail to adapt dynamically to such disturbances. Similarly, standard Model Predictive Control (MPC) approaches with fixed parameters may be ineffective under fault conditions. This has created the need for advanced fault-tolerant control (FTC) methods.

Recent studies have explored residual-based fault detection, where discrepancies between expected and actual outputs are monitored to identify faults, as well as finite-state-machine (FSM)-based frameworks to govern system behavior under different operating conditions. However, integrating these approaches directly into MPC for real-time adaptation has been relatively unexplored, particularly for PV inverters.

This work introduces a novel FSM-guided adaptive MPC framework aimed at detecting faults and adjusting control strategies on the fly. The proposed scheme is designed not only to identify fault conditions but also to reconfigure its optimization priorities to maintain stability and performance despite variations in operating conditions and reference signals. The approach is validated using a detailed discrete-time simulation of a PV inverter, where fault offsets and varying reference signals are introduced to stress the system.

The FSM operates with two modes: normal and faulty. Fault detection relies on monitoring the residual, which measures the deviation between the system’s actual and nominal outputs. When the residual surpasses a threshold, the controller switches to the faulty mode, assigning greater importance to minimizing output errors while allowing for sharper control actions. Once the residual returns below a recovery threshold, the FSM transitions back to the normal mode with smoother control behavior.

Simulation results over 350 time steps show that the proposed adaptive MPC effectively maintains stability and tracking performance under fault conditions. When a disturbance is applied, the FSM correctly identifies the fault and transitions the controller to a more aggressive setting. This reduces tracking error compared to the normal operating mode and ensures the inverter output closely follows the reference despite the disturbance. Once the disturbance subsides, the controller smoothly transitions back to its original configuration. Additional analyses, such as state trajectories, phase plots, and control cost evaluations, confirm both the stability and robustness of the system.

Overall, the FSM-adaptive MPC framework improves fault tolerance in PV inverters by combining residual-based detection with dynamic tuning of control parameters. The method shows significant improvement in tracking accuracy during faults while maintaining overall system stability. Beyond its strong simulation performance, this framework addresses pressing reliability challenges in renewable energy integration. Future work will focus on expanding the FSM to multiple states, refining fault detection thresholds, and conducting hardware-in-the-loop experiments to demonstrate its practicality for real-world grid-connected PV systems.

Quasi-solid-state supercapacitors (QSSCs) utilizing bio-derived polymers represent a pivotal technology for sustainable energy storage, bridging high power density with environmental compatibility [1]. This study proposes an integrated, sequential layer-by-layer fabrication strategy for QSSCs that exploits the multifunctional properties of carboxymethylcellulose (CMC). This protocol uniquely employs CMC as a bifunctional material, acting simultaneously as a sustainable, biodegradable binder in the electrodes and as the host polymer matrix in the electrolyte [1]. This dual role ensures superior chemical and mechanical compatibility between components [1, 2].

Unlike conventional methods relying on fluorinated binders and toxic solvents, the electrode paste preparation adopts a green aqueous processing route. The formulation adapts the standard 80:10:10 mass ratio of Activated Carbon (AC), Carbon Black (CB), and binder established [3], strategically substituting the conventional binder with CMC. To ensure the integrity of the conductive network, the mixture undergoes ultrasonication (10–30 min); this homogenization step induces cavitation forces critical for uniformly dispersing the amphiphilic CMC and breaking down particle agglomeration, thereby yielding a robust dry electrode with optimized percolation pathways [4, 5].

Device assembly is performed in a single stage directly on metal current collectors. The applied electrode paste undergoes controlled pre-drying at 60–70 °C. This specific thermal range is critical; it is sufficient to evaporate free water (thermal peak onset ≈ 62.76 °C [6]) while strictly preserving coordinated water, which is vital for cation solvation and ionic mobility within the polymer matrix [6, 7]. Subsequently, the highly viscous CMC/Na₂SO₄ gel electrolyte [8] is deposited, followed by the application of the second electrode layer. The resulting sandwich structure is consolidated under a controlled contact pressure of 0.5 MPa [5, 7]. This mechanical compression optimizes interfacial contact by promoting conformal adhesion and filling surface roughness, effectively reducing equivalent series resistance (ESR) without the need for external separators [5, 7].

Finally, device validation employs a comprehensive characterization suite. Structural properties and polymer-salt complexation are investigated via X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) [6]. Surface morphology and electrode/gel interfacial integrity are examined by Scanning Electron Microscopy (SEM) [6]. Thermal stability, free and coordinated water management, and polymer degradation transitions are investigated using Thermogravimetric Analysis (TGA) coupled with Derivative Thermogravimetry (DTG) and by Differential Scanning Calorimetry (DSC) [6, 7]. Electrochemical performance is rigorously evaluated using Electrochemical Impedance Spectroscopy (EIS) across a frequency range of 100 mHz to 10 kHz [8], alongside Cyclic Voltammetry (CV) and Galvanostatic Charge/Discharge (GCD). These assays are designed to confirm operational stability within extended potential windows and validate the efficiency of ionic transport across the quasi-solid interface [8].

This integrated fabrication protocol represents a methodological framework for developing fully bio-derived supercapacitors using CMC in dual functional roles. By consolidating the literature evidence regarding CMC processability, polymer-salt chemistry, and electrochemical device assembly, this approach offers a rational design strategy for quasi-solid-state energy storage systems. If validated through experimental implementation, this methodology could enable the development of supercapacitors with reduced reliance on fluorinated polymers and synthetic separators, potentially expanding the applicability of bio-derived materials in energy storage and grid-scale applications. The sequential layer-by-layer assembly strategy presented herein provides a foundation for future optimization of bio-based electrochemical device architectures.

References

[1] Akhlaq, M., et al(2023). Carboxymethyl cellulose-based materials as an alternative source for sustainable electrochemical devices: A review. RSC Advances, 13(9), 5723–5743. https://doi.org/10.1039/D2RA08244F

[2] Landi, G., et al. (2022). Electrochemical performance of biopolymer-based hydrogel electrolyte for supercapacitors with eco-friendly binders. Polymers, 14(20), 4445. https://doi.org/10.3390/polym14204445

[3] Demarconnay, L., et al. (2010). A symmetric carbon/carbon supercapacitor operating at 1.6 V by using a neutral aqueous solution. Electrochemistry Communications, 12(10), 1275–1278. https://doi.org/10.1016/j.elecom.2010.06.036

[4] Gordon, R., et al. (2020). Effect of polymeric binders on dispersion of active particles in aqueous LiFePO4-based cathode slurries as well as on mechanical and electrical properties of corresponding dry layers. ACS Omega, 5(20), 11455–11465. https://doi.org/10.1021/acsomega.0c00477

[5] Xu, L., et al. (2023). Nanocellulose-carboxymethylcellulose electrolyte for stable high-rate zinc-ion batteries. Advanced Functional Materials, 33(16), 2302098. https://doi.org/10.1002/adfm.202302098

[6] Darmawan, D. A., et al. (2023). Fabrication of solid polymer electrolyte based on carboxymethyl cellulose complexed with lithium acetate salt as Lithium-ion battery separator. Polymer Composites, 45(1), 273-285. https://doi.org/10.1002/pc.27902

[7] Tombolesi, S., et al. (2023). A sustainable gel polymer electrolyte for solid-state electrochemical devices. Polymers, 15(14), 3087. https://doi.org/10.3390/polym15143087

[8] Li, Z., et al. (2019). High-energy quasi-solid-state supercapacitors enabled by carbon nanofoam from biowaste and high-voltage inorganic gel electrolyte. Carbon, 149, 273–280. https://doi.org/10.1016/j.carbon.2019.04.056