Dynamic Emulation of a PEM Electrolyzer by Time Constant Based Exponential Model

The main objective of this paper is to develop a dynamic emulator of a proton exchange membrane (PEM) electrolyzer (EL) through an equivalent electrical model. Experimental investigations have highlighted the capacitive effect of EL when subjecting to dynamic current profiles, which so far has not been reported in the literature. Thanks to a thorough experimental study, the electrical domain of a PEM EL composed of 3 cells has been modeled under dynamic operating conditions. The dynamic emulator is based on an equivalent electrical scheme that takes into consideration the dynamic behavior of the EL in cases of sudden variation in the supply current. The model parameters were identified for a suitable current interval to consider them as constant and then tested with experimental data. The obtained results through the developed dynamic emulator have demonstrated its ability to accurately replicate the dynamic behavior of a PEM EL

Self-Heating Induced Instability of a Non-Linear Inductor in a SMPS: a Case Study

This paper proposes a case study to show that the non-linear operation of a power inductor in a SMPS can induce instability of the control system leading to overheating of the inductor beyond its allowable temperature and to an excessive peak of the maximum current. The case study is performed by a commercial ferrite inductor employed in a synchronous boost converter encompassing a control system to adjust the duty cycle, assuring a constant output voltage. The thermal transient is described by the time domain waveforms and thermal images

Optical Nanoantennas for Energy Harvesting

In the last decade, the increasing demand for renewable energy has been leading to the development of new devices, which overcome the disadvantages of the traditional photovoltaic conversion and exploit the thermal radiation created by the Sun, that is transferred in the form of electromagnetic waves into free space and finally absorbed by the surface of the Earth [1-2]. These new devices, called nanoantennas, have only recently been considered thanks to the development of electron beam lithography and similar techniques. Nanoantennas operate at nanometers wavelengths and their dimensions range from a few hundred nanometres to a few microns. They exhibit potential advantages in terms of polarization, tunability, and rapid time response. Furthermore, the nanoscale dimensions, combined with the high electric field enhancement in the antenna gap, enable a small device footprint, making it compact enough to be monolithically integrated with electronics and auxiliary optics [3]. Similar to traditional RF antennas, nanoantennas capture the incident visible or infrared electromagnetic wave causing an AC current onto the antenna surface, such that it oscillates at the same frequency of that of the wave. The movement of the electrons produces an alternating current in the antenna circuit. A proper rectifier coupled with nanoantenna is used in order to produce a DC power [3]. This rectifier contains one or more diodes whose power loss and fast response can influence the whole device efficiency. This circuit is known as rectenna and the typical block diagram and the equivalent circuit are shown in figure 1-2 [3-4]. Infrared nanoantennas are also coupled to a metallic thermocouple. The rectification mechanism is based on the Seebeck effect, a thermoelectric voltage generation due to the infrared irradiation induced currents in the antenna. Figure 3 shows the electric equivalent circuit of the antenna-coupled thermocouples [5]. The purpose of this contribution is to critically compare advantages and disadvantages of new optical nanoantennas for energy harvesting, focusing on the state of the art and its perspectives. Nanoantennas for visible radiation reveal better upper bound limits in terms of efficiency and available power density, table 1 [4]. Infrared nanoantennas can work even in the absence of solar radiation, but the efficiency is still very low. Some technological issues have to be taken into account before these commercial devices are put on the market. They mainly regard the circuits between the antenna and the load. Nonetheless, they show a greater efficiency than traditional PV solar cells and could be an alternative to the latter in the energy harvesting process in the next future

NON-LINEAR INDUCTOR CONTRIBUTION TO HARMONIC SPECTRUM IN POWER CONVERTERS

The paper investigates the harmonic content in DC/DC power converters where the inductor is operated in the non-linear region. This operation is often exploited to use lighter and cheaper inductors; as a drawback, an increasing number of harmonics is noticeable. A theoretical analysis is proposed. It is based on a polynomial model of the inductor used in a boost converter. Results are given by the spectra of the output voltage performed on a circuit prototype

Non-Linear Inductors Characterization in Real Operating Conditions for Power Density Optimization in SMPS

The exploitation of power inductors outside their linear region in switching converters can be achieved by raising the current until a decrease in the inductance can be noticed. This allows using a smaller magnetic core, increasing the power density of the converter. On the other hand, a detailed description of the magnetization curve including the temperature is required. Since this information is often not included in the inductor’s datasheets, this paper shows how to identify the behavior of an inductor when it is operated up to saturation and its temperature rises. In order to characterize the inductor in real operating conditions, a dedicated measurement rig was developed. It consists of a switching converter that encompasses the inductor under test and is controlled by a virtual instrument developed in LabVIEW. The characterization system was tested by retrieving the inductance and the magnetization curves vs. current for two commercial inductors at core temperatures up to 105 °C. The magnetic core was then characterized by the saturation current vs. inductance, obtaining an expression for the whole family of inductors sharing the same core. Finally, we experimentally analyzed the thermal transient of the inductors in operating conditions, confirming the fundamental role of the temperature in changing the current profiles and the core saturation condition

GaN and SiC Device Characterization by a Dedicated Embedded Measurement System

This work proposes a comparison among GaN and SiC device main parameters measured with a dedicated and low-cost embedded system, employing an STM32 microcontroller designed to the purpose. The system has the advantage to avoid the use of expensive laboratory measurement equipment to test the devices, allowing to obtain their behavior in operating conditions. The following KPIs (Key Performance Indicators) are measured and critically compared: threshold voltage, on-resistance and input capacitance. All the measurements are carried out in a short time interval and on a wide range of switching frequencies, ranging from 10 kHz to 1 MHz. This investigation is focused on the deviation of the figures of merit when the switching frequency changes, since it is crucial for wide-bandgap devices. The devised, low-cost, microcontroller unit allows high flexibility and system portability, while the employed equivalent-time sampling technique overcomes some issues related to the need of high sampling frequency. It allows good performances with common microcontroller embedded AD converters. To validate the proposed system, the obtained results have been compared with the time-domain waveforms acquired with a traditional laboratory oscilloscope and a study of the system’s measurement errors has been carried out. Results show that GaN devices achieve a higher efficiency with respect to SiC devices in the considered range of switching frequencies. The on-resistance exhibited by GaN devices shows, as expected, an increase with frequency, which happens to switching losses, too. On the other hand, GaN devices are more sensitive to parasitic effects and the high dV/dt, due to the reduced switching times, can excite unwanted ringing phenomena

Automatic EMI filter design for power electronic converters oriented to high power density

In this paper, a complete computer aided procedure based on the power density concept and aimed at the automatic design of EMI filters for power electronic converters is presented. It is rule-based, and it uses suitable databases built-up by considering information on passive components available from commercial datasheets. The power density constraint is taken into consideration by imposing the minimization of the filter volume and/or weight; nevertheless, the system in which the automatically designed filter is included satisfies the electromagnetic compatibility standards limits. Experimental validations of the proposed procedure are presented for two real case studies, for which the performance and the size of the best filter design are compared with those related to a conventionally designed one

Implementazione con scheda STM32 NUCLEO® di un algoritmo per la modulazione della larghezza d’impulso di tipo casuale (Random PWM)

La tecnica di modulazione dei convertitori statici di potenza è fondamentale per garantire le prestazioni richieste e per minimizzare le emissioni elettromagnetiche. Infatti utilizzando una frequenza portante fissa si generano armoniche multiple della fondamentale sovrapposte alla tensione di uscita; se invece si fa variare la frequenza della portante le emissioni sono distribuite più uniformemente nello spettro di frequenze e si limita il contributo di singole frequenze. In commercio esistono vari circuiti integrati in grado di generare un segnale PWM con portante a frequenza fissa, tuttavia se si vuole studiare il comportamento facendo variare la frequenza in modo casuale è necessario implementare un algoritmo possibilmente su un sistema a basso costo. In questo rapporto tecnico sono descritti i metodi di simulazione e sperimentali adottati per implementare il controllo della commutazione di un convertitore DC-DC, di tipo elevatore (Boost) realizzato in laboratorio. La prassi adottata in tali metodi ha previsto la programmazione di un micro controllore (μCC), per la generazione del segnale di controllo. In particolare saranno confrontate due tipologie di controllo, denominate rispettivamente “tecnica di controllo con segnale PWM classico” e “tecnica di controllo con segnale Random PWM”. Tale confronto viene effettuato sull’analisi del fenomeno della ondulazione (Ripple), presente nella tensione e nella corrente di uscita ai convertitori. Il codice è stato implementato in modo da poter variare quando funziona in modalità random, sia la frequenza di scostamento rispetto alla frequenza centrale fissata pari a 20 kHz, sia il numero di impulsi di pilotaggio da applicare al gate dell'IGBT prima di aggiornare il valore della frequenza di switching secondo un numero random. La disponibilità di questi due gradi di libertà sarà utilizzata per minimizzare la densità spettrale della potenza, all’uscita del convertitore nel campo delle emissioni condotte

Implementation and Comparison of SiC and GaN switches for EV Fast Recharging Systems

Wide bandgap material-based devices allow faster switching frequency and exhibit smaller losses than traditional Si devices; nevertheless, a complete understanding of the functioning of these new devices remains poorly understood. A fast battery charger for electric vehicles based on a converter employing SiC and GaN devices is here reported Besides, these two technologies are experimentally compared, in the same layout, to highlights their performance in terms of electrical dynamic and electromagnetic compatibility

The role of autophagy in resistance to targeted therapies

Autophagy is a self-degradative cellular process, involved in stress response such as starvation, hypoxia, and oxidative stress. This mechanism balances macro-molecule recycling to regulate cell homeostasis. In cancer, autophagy play a role in the development and progression, while several studies describe it as one of the key processes in drug resistance. In the last years, in addition to standard anti-cancer treatments such as chemotherapies and irradiation, targeted therapy became one of the most adopted strategies in clinical practices, mainly due to high specificity and reduced side effects. However, similar to standard treatments, drug resistance is the main challenge in most patients. Here, we summarize recent studies that investigated the role of autophagy in drug resistance after targeted therapy in different types of cancers. We highlight positive results and limitations of pre-clinical and clinical studies in which autophagy inhibitors are used in combination with targeted therapies. Refereed/Peer-reviewe