In this paper, a novel technique for the control of an AC/DC boost converter aimed at efficiently extracting power from magnetostrictive vibration energy harvesters (MVEHs) is proposed and experimentally tested. The proposed Inductor Current Multi Peaks (ICMP) technique automatically detects the optimal turn ON/OFF of the converter switches. In this way the MVEH internal inductance is charged/discharged multiple times per period, with a consequent increase of the extracted power with respect to the state-of-the-art techniques (characterized instead by only two charge/discharge cycles per period). Moreover, the ICMP technique avoids the need for a maximum power point tracking function by extracting maximum power over a large interval of DC voltage values. Experimental tests of a proof-of-concept prototype confirm the theoretical findings and the predicted behavior.

Hot-spots represent a significant failure mechanism in photovoltaic (PV) modules, typically attributable to electrical mismatching. However, thermo-optical degradation of the encapsulant, including discoloration and delamination, can both trigger and amplify mismatch by inducing localized optical losses and temperature rise. The present paper proposes a compact circuit-level electro-thermal–optical model that explicitly captures the short-term closed-loop interaction between mismatching, cell temperature, and temperature-dependent optical properties. The photogenerated current is formulated as a function of irradiance, cell temperature, and encapsulant degradation, enabling dynamic feedback between heating and optical losses. Numerical simulations are carried out on a commercial 40-cell PV module under four representative operating static scenarios. The results demonstrate that, even in the absence of shading, optical degradation can generate multimodal P–V characteristics, drive cells into reverse bias, and produce hot-spots. When optical degradation coexists with irradiance mismatch, the feedback loop significantly amplifies mismatching and shifts the maximum power point toward thermally unsafe operating conditions. These findings demonstrate that maximizing instantaneous power does not necessarily maximize lifetime energy yield, underscoring the need for thermal-aware MPPT strategies and providing a practical framework for early detection of thermo-optical faults in PV modules.

The last years have seen the increasing development of innovative railway pantographs based on smart materials and equipped with monitoring features based on wireless sensor nodes. In this scenario, one of the most important challenges is the power supply of pantograph sensors. Energy harvesting systems have been proposed for powering monitoring sensors in a variety of applications, including railway pantographs. These systems convert ambient energy sources into electrical energy. The use of energy harvesting systems coupled with storage devices, such as rechargeable batteries or supercapacitors, can be a very promising solution for making the sensors self-powered, thus avoiding the drawbacks associated with supplying from the main grid or disposable batteries. In this paper, the operating principles of the main technologies used for energy harvesting in railway pantographs are described in detail, together with some examples of laboratory prototypes and commercial devices. The proposed analysis focuses on the perspectives and challenges of various energy harvesting technologies and can help select the most suitable technology for the development of innovative sensorized pantographs.

An SSHI-based interface circuit for piezoelectric vibration energy harvesters is presented and experimentally validated. The developed solution relies on current-driven regulation of the rectifier output voltage downstream of a parallel SSHI stage. By measuring only the rectifier output current, the proposed Current-Driven SSHI (CD-SSHI) interface directly and continuously sets the rectified DC voltage to its optimal value under time-varying vibration conditions, without resorting to the perturbative approaches of classical Maximum Power Point Tracking (MPPT) techniques. The CD-SSHI reaches and tracks the Maximum Power Point (MPP) without the steady-state oscillations typical of perturb and observe MPPT, and without the power interruptions characteristic of the fractional open circuit voltage MPPT. Moreover, the proposed CD-SSHI interface significantly increases dynamic performance compared to an SSHI coupled with a conventional implementation of the P&O MPPT control. A theoretical analysis based on a general equivalent circuit model is developed to support the proposed circuit. Experimental results obtained from a prototype implementation demonstrate the effectiveness of the CD-SSHI interface in terms of both steady-state efficiency and dynamic response.

This paper investigates a ball-screw energy harvester shock absorber (BS-EHSA) equipped with a DC motor/generator and driven by an external sinusoidal force. A comprehensive parametric study examines the effect on the power delivered to the load of varying the sprung mass, external electrical resistance, and spring constant. A simulation study is also performed to demonstrate how the resonance frequency of the system impacts energy recovery. Numerical simulations are carried out in the MATLAB environment, providing insights into optimizing system parameters for maximum power efficiency.

This paper presents an innovative approach to the modeling and dynamic analysis of DC–DC converters in photovoltaic applications. Departing from traditional studies that focus on the transfer function from duty cycle to output voltage, this work investigates the duty cycle to input voltage transfer function, which is critical for accurate dynamic representation of photovoltaic systems. A notable contribution of this study is the integration of the PV panel behavior in the small-signal representation, considering a model-derived differential resistance for various operating points. This technique enhances the model’s accuracy across different operating regions. The paper also validates the effectiveness of this linearization method through small-signal analysis. A comprehensive comparison is conducted among several non-isolated converter topologies such as Boost, Buck–Boost, Ćuk, and SEPIC under both open-loop and closed-loop conditions. To ensure fairness, all converters are designed using a consistent set of constraints, and controllers are tuned to maintain similar phase margins and crossover frequencies across topologies. In addition, a gain-scheduling control strategy is implemented for the Boost converter, where the PI gains are dynamically adapted as a function of the PV operating point. This approach demonstrates superior closed-loop performance compared to a fixed controller tuned only at the maximum power point, further highlighting the benefits of the proposed modeling and control framework. This systematic study therefore provides an objective evaluation of dynamic performance and offers valuable insights into optimal converter architectures and advanced control strategies for photovoltaic systems.

Photovoltaics represents one of the key sources of clean energy to help reduce the carbon footprint and fight climate change, enabling the so-called green energy transition. To maximize photovoltaic production in any irradiation and temperature conditions, Maximum Power Point Tracking techniques must be implemented to determine and set the working point at which the photovoltaic panel delivers the maximum power. Such techniques usually exploit real-time measurements of voltage and current on the photovoltaic cell, and possibly of the operating temperature. This paper proposes an assessment of the effects of measurement uncertainty on the maximum power point calculation. We compare the sensitivity to measurement noise of different tracking algorithms, including perturb and observe, incremental conductance and feedforward neural networks. The results show that neural networks become the most attractive solution when measurement uncertainty is introduced in the system.

We present an experimental and numerical study of a piezoelectric energy harvester driven by broadband vibrations. This device can extract power from random fluctuations and can be described by a stochastic model, based on an underdamped Langevin equation with white noise, which mimics the dynamics of the piezoelectric material. A crucial point in the modelisation is represented by the appropriate description of the coupled load circuit that is necessary to harvest electrical energy. We consider a linear load (resistance) and a nonlinear load (diode bridge rectifier connected to the parallel of a capacitance and a load resistance), and focus on the characteristic curve of the extracted power as a function of the load resistance, in order to estimate the optimal values of the parameters that maximise the collected energy. In both cases, we find good agreement between the numerical simulations of the theoretical model and the results obtained in experiments. In particular, we observe a non-monotonic behaviour of the characteristic curve which signals the presence of an optimal value for the load resistance at which the extracted power is maximised. We also address a more theoretical issue, related to the inference of the non-equilibrium features of the system from data: we show that the analysis of high-order correlation functions of the relevant variables, when in the presence of nonlinearities, can represent a simple and effective tool to check the irreversible dynamics.

In this article, a novel MPPT technique is proposed and experimentally tested. It is called "grid-connected photovoltaic (PV) systems maximum power point tracking (MPPT) technique driven by the power factor correction (PFC) controller" (CICERONE). It generates, for both single stage (SS) and double stage (DS) grid-connected PV systems, the bulk voltage reference by exploiting only the internal (not coming from sensors) PFC control signal. CICERONE leads to a piecewise ramp bulk voltage whose slope is updated to maximize the average power injected into the grid. Experimental results show that CICERONE exhibits better performance and robustness than the Perturb and Observe MPPT technique, especially in case of dynamic irradiance conditions. In addition, CICERONE can be applied without modifications to both SS and DS grid-connected PV systems. Hence, differently from a traditional DS system, in a CICERONE based DS system, the dc-dc converter can be operated with a fixed duty-cycle and can work in the highest efficiency conditions. Moreover, CICERONE operates without using external signals coming from sensors and affected by measuring noise (such as PV voltage, PV current, grid current, or their derivatives), but it performs the MPPT using only an internal signal already used for PFC purposes.

A single stage active AC/DC electronic interface able to emulate the optimal load impedance of a Resonant Piezoelectric Vibration Energy Harvester (RPVEH) is proposed. As theoretically shown, unlike an electronic interface that emulates an optimal load generator, an interface that emulates an optimal load impedance does not require adaptation to the acceleration of input vibrations. This allows the use of a very simple control, avoiding the implementation of Maximum Power Point Tracking algorithms that require lossy microcontrollers. Thus, the proposed interface is equipped with a simple analog controller allowing the RPVEH to work in its Maximum Power Point in both steady-state and variable conditions of vibrations, without recurring to multivariable perturbative approaches, as it happens for the most of single stage AC/DC interfaces proposed in the literature. The absence of perturbative techniques allows a significant improvement of both stationary and dynamic performances. Experimental tests of a prototype of the proposed interface confirm the theoretical findings and the predicted behavior.

We consider the problem of assessing the non-equilibrium behavior of a system from the study of time series. In particular, we analyze experimental data from a piezoelectric energy harvester driven by broadband random vibrations where the extracted power and the relative tip displacement can be simultaneously measured. We compute autocorrelation and cross-correlation functions of these quantities in order to investigate the system properties under time reversal. We support our findings with numerical simulations of a linear underdamped Langevin equation, which very well describes the dynamics and fluctuations of the energy harvester. Our study shows that, due to the linearity of the system, from the analysis of a single variable, it is not possible to evidence the non-equilibrium nature of the dynamics. On the other hand, when cross-correlations are considered, the irreversible nature of the dynamics can be revealed.

A self-supplied circuit that is able to significantly increase the power delivered to a bridge rectifier by a Resonant Piezoelectric Vibration Energy Harvester (RPVEH) is presented and discussed. The proposed circuit, called the Energy Harvester Power Optimizer (EHPO), is implemented by means of a switch-mode converter that emulates a negative capacitance. Unlike switch-mode impedance emulators, based on sophisticated tracking algorithms requiring lossy microcontrollers, EHPO exploits a very light control circuit based on a hysteresis comparator. The EHPO is self-supplied since it does not need an external supply, but it draws the energy for its operation directly from the RPVEH. Moreover, it is developed without the assumption of purely sinusoidal vibrations. Experimental results show that the EHPO can significantly increase the power delivered to a rectifier, both in the case of sinusoidal vibrations (percent gain of the net extracted power up to about 190%) and non-sinusoidal vibrations (percent gain of the net extracted power up to about 245%), regardless of the shape of the forcing acceleration and regardless of the RPVEH resonance frequency.

A droplet electrical generator (DG) is an energy harvester able to scavenge energy from water droplets sliding on its surface. A compact electrical model of a droplet generator is here presented together with a black-box identification procedure. Even if previous research works have shown the great potential of the droplet generator in terms of extracted power and have investigated the optimization of the device, a simple equivalent electrical circuit is not available, which is fundamental for predicting its behavior and for designing its electronic interface, devoted to maximizing the power extraction under varying source and load conditions. A detailed identification procedure for the model parameters is also presented, in order to overcome the issues due to the high voltage, low current, high bandwidth, and unknown time-waveform of the time-varying capacitances. It is also shown how the proposed model allows the designer to predict analytically and numerically the energy that can be extracted by the generator. Finally, experimental tests are presented to show that the proposed model and the outlined procedure are able to effectively predict with good accuracy the system behavior under different operating conditions.

This paper is focused on resonant piezoelectric vibration energy harvesters loaded by diode bridge rectifiers. Typically, in such applications the voltage at the output of the rectifier is properly regulated by a DC/DC converter for maximum power point tracking purposes. Resistance emulation and voltage adaptation are the strategies that are usually adopted. In this paper, an optimal shape of the voltage profile at the output port of the rectifier is identified. The proposed voltage profile can lead to the extraction of a higher average power with respect to both resistance emulation and voltage adaptation techniques. In the framework of the fundamental harmonic analysis, the proposed optimal voltage profile allows the emulation, at the harvester terminals, of an ohmic-inductive passive load as required by the maximum power transfer theorem.

This paper is aimed at experimentally investigating the performance of a Water Droplet Energy Harvester (WDEH) as a function of the main harvester characteristics. A prototype of a WDEH composed of two electrodes and a PolyTetraFluoroEthylene (PTFE) layer is implemented and tested. The PTFE is placed between an upper electrode (a simple conductive terminal) and a lower electrode (a conductive layer). A fundamental characteristic for the operation of the WDEH is the very good charge storage capability and stability of the PTFE. In particular, by means of a continuous water droplets impingement on the PTFE surface, negative charges are stored on it. In this way, a pre-charged variable capacitance is formed during the flowing of droplets over the upper electrode, and a current flow is obtained when the upper and lower electrodes are connected to an electrical load. The experimental tests that are presented and discussed in this paper are aimed at highlighting the variation of the performance of the considered WDEH prototype as a function of the characteristics of the source of energy, of the device structure and of the electrical load.

This article focuses on the dynamic optimization of the operating conditions of two types of ac–dc converters, a diode bridge rectifier and a full bridge active rectifier, which are used for interfacing regenerative rail vehicle suspensions based on ac electromagnetic generators. A theoretical analysis shows that, for both types of converters, the optimal operating conditions, leading to the maximization of the extracted power, can be predicted from the measurement of the generator speed. In particular, as regards the diode bridge rectifier, it is shown that the optimal value of the dc side voltage is related to the generator speed. As regards the active full-bridge rectifier, it is shown that a relationship exists between the optimal converter duty cycle and the generator speed. Experimental results validate the proposed theoretical models both in case of ideal constant generator speeds, and in case of more realistic time-variable generator speeds. The proposed analysis enables the design of high-performance speed-driven maximum power point tracking techniques for regenerative vehicle suspensions.

In this paper a circuital emulation technique for resonant electromagnetic vibration energy harvesters is proposed and discussed. The idea of circuital emulation is here proposed for the first time in the field of electromagnetic vibration harvesters. In particular, a circuital emulation technique based on a cheap hardware system with easily adjustable parameters is much more easy, fast and practical, at least for a preliminary though very important and necessary analysis. This is particularly relevant when the analysis is focused on the AC/DC electronic interfaces between harvesters and DC loads. Starting from the characteristics that are typically provided by manufacturers of harvesters, the parameters of the harvester circuital model are derived and used for the implementation of a simple and fully electronic circuital emulator based on an op-amp inductor realization. Experimental results are presented and discussed.

The power generation capability of an electromagnetic vibration energy harvester augmented with an additional coil was investigated and compared with that of a standard single coil electromagnetic energy harvester. A single degree of freedom model and the corresponding equivalent electric circuit were employed for the analysis of the standard and of the augmented harvesters. The harvester model was validated by means of an accurate experimental characterization of a commercial electromagnetic harvester, i.e., the model-D by ReVibe. The electric circuits for the standard and for the augmented harvesters were implemented by electronic components and experimentally tested to determine the maximum power they are able to generate in four test conditions. Results from simulations and from experiments showed significant improvement of the power extraction performance exhibited by the double coil energy harvester, particularly at frequencies lower than the harvester mechanical resonance frequency.

A theoretical analysis aimed at predicting the power extracted from resonant piezoelectric vibration energy harvesters feeding synchronous switching-type electronic interfaces under variable mechanical excitation is proposed. In particular, for the widely used synchronous electric charge extraction (SECE) and synchronized switching harvesting on an inductor (SSHI) switching interfaces, the nonlinear equations describing the circuit behavior are solved under reasonable assumptions, and closed-form expressions of the extracted power are derived as a function of the circuit parameters and of the vibration characteristics, in the case of modulated mechanical vibrations. Numerical and experimental results validate the proposed closed-form expressions and show their usefulness for design purposes.

Backpack energy harvesting systems are very promising solutions for powering portable devices without primary batteries, especially in excursionist and military applications. During human walking, they allow the conversion of the backpack mechanical vibration energy into electricity. In this paper the attention is focused on a backpack regenerative system based on a mechanical motion rectifier, which is able to convert the up-and-down oscillation of the backpack into a unidirectional rotation of a DC generator. Such a system needs a power electronic interface for optimizing the operating point that maximizes the extracted power. In particular, two types of ideal power electronic interfaces are analyzed and compared. The first one is based on the adaptation of the voltage at the DC generator output, while the second one is based on the matching of the resistance at the DC generator output. Through a numerical analysis, the average power extracted by the two interfaces are compared under different input displacement characteristics. The proposed analysis can be useful for the identification of the optimal voltage profile to set at the DC generator output for the maximization of the extracted electrical energy.