Search Results (8)

In medium- and high-power-density applications, silicon carbide (SiC) metal-oxide semiconductor field effect transistors (MOSFETs) are often connected in parallel increasing the current capability. However, the current sharing of paralleled SiC MOSFETs is affected by the mismatched technical parameters of devices and the deviated power circuit parasitic inductances, even if power devices are controlled by a single gate driver. This leads to unevenly distributed power losses causing different stress between SiC MOSFETs. As a result, unbalanced current sharing increases the probability of severe power switch(es) and system failures. For over a decade, the current imbalance issue between parallel-connected SiC MOSFETs has concerned the scientific community, and many methods and techniques have been proposed. However, most of these solutions are impossible to realize without the necessity of screening power devices to measure their technical parameters. Consequently, system costs significantly increase due to the expensive equipment for screening SiC MOSFETs. Also, transient current imbalance is the main concern of most papers, without addressing static imbalance. In this paper, an innovative approach is proposed, capable of suppressing both static and transient current imbalance between paralleled SiC MOSFETs, under both symmetrical and asymmetrical layouts, through an improved active gate driver and without the requirement for any power device screening process. Additionally, the proposed solution employs a self-sustaining algorithmic approach utilizing current sensors and a field-programmable gate array (FPGA). The functionality of the proposed solution is verified through experimental tests, achieving current imbalance suppression between two paralleled SiC MOSFETs, actively and autonomously. Full article

In this research, a ferroresonant (SATFORMER) inverter, optimized in terms of power efficiency, noise reduction, and reliability, is analyzed and described. This modified SATFORMER inverter can be used as a standalone inverter. In the proposed topology, the variable DC input is converted to an AC square wave by a thyristor-based modified current source inverter and additionally applied to primary winding, which is divided into four sub-windings, that are wound on the saturable core portion, via six relays with one change-over (CO) contact. The proposed ferroresonant inverter is innovative, to the best of our knowledge. A method for reducing the power losses of the proposed inverter is described and analyzed. A 150 VA model of a constant voltage transformer (ferroresonant transformer) is tested in order to experimentally investigate its basic characteristics. The circuit and simulated results of the modified current source inverter are presented in detail. The experimental results of our 150 VA model are presented. A precise term is introduced to describe the operation of the converter’s magnetic components. The occurring phenomenon is thoroughly explained, and a meaningful, perceptive, and newly incorporated term is introduced to provide a clearer understanding of the phenomenon. Full article

The energy carrier infrastructure, including both electricity and natural gas sources, has evolved and begun functioning independently over recent years. Nevertheless, recent studies are pivoting toward the exploration of a unified architecture for energy systems that combines Multiple-Energy Carriers into a single network, hence moving away from treating these carriers separately. As an outcome, a new methodology has emerged, integrating electrical, chemical, and heating carriers and centered around the concept of Energy Hubs (EHs). EHs are complex systems that handle the input and output of different energy types, including their conversion and storage. Furthermore, EHs include Combined Heat and Power (CHP) units, which offer greater efficiency and are more environmentally benign than traditional thermal units. Additionally, CHP units provide greater flexibility in the use of natural gas and electricity, thereby offering significant advantages over traditional methods of energy supply. This article introduces a new approach for exploring the steady-state model of EHs and addresses all related optimization issues. These issues encompass the optimal dispatch across multiple carriers, the optimal hub interconnection, and the ideal hub configuration within an energy system. Consequently, this article targets the reduction in the overall system energy costs, while maintaining compliance with all the necessary system constraints. The method is applied in an existing Smart Microgrid (SM) of a typical Greek 17-bus low-voltage distribution network into which EHs are introduced along with Renewable Energy Sources (RESs) and Electric Vehicles (EVs). The SM experiments focus on the optimization of the operational cost using different operational scenarios with distributed generation (DG) and CHP units as well as EVs. A sensitivity analysis is also performed under variations in electricity costs to identify the optimal scenario for handling increased demand. Full article

Nowadays, with the need for clean and sustainable energy at its historical peak, new equipment, strategies, and methods have to be developed to reduce environmental pollution. Drastic steps and measures have already been taken on a global scale. Renewable energy sources (RESs) are being installed with a growing rhythm in the power grids. Such installations and operations in power systems must also be economically viable over time to attract more investors, thus creating a cycle where green energy, e.g., green hydrogen production will be both environmentally friendly and economically beneficial. This work presents a management method for assessing wind–solar–hydrogen (H₂) energy systems. To optimize component sizing and calculate the cost of the produced H₂, the basic procedure of the whole management method includes chronological simulations and economic calculations. The proposed system consists of a wind turbine (WT), a photovoltaic (PV) unit, an electrolyzer, a compressor, a storage tank, a fuel cell (FC), and various power converters. The paper presents a case study of green hydrogen production on Sifnos Island in Greece through RES, together with a scenario where hydrogen vehicle consumption and RES production are higher during the summer months. Hydrogen stations represent H₂ demand. The proposed system is connected to the main power grid of the island to cover the load demand if the RES cannot do this. This study also includes a cost analysis due to the high investment costs. The levelized cost of energy (LCOE) and the cost of the produced H₂ are calculated, and some future simulations correlated with the main costs of the components of the proposed system are pointed out. The MATLAB language is used for all simulations. Full article

Silicon carbide (SiC) MOSFETs tend to become one of the main switching elements in power electronics applications of medium- and high-power density. Usually, SiC MOSFETs are connected in parallel to increase power rating. Unfortunately, unequal current sharing between power devices occurs due to mismatches in the technical parameters between devices and the layout of the power circuit. This current imbalance causes different current stress upon power switches, raising concerns about power system reliability. For over a decade, various methods and techniques have been proposed for balancing the currents between parallel-connected SiC MOSFETs. However, most of these methods cannot be implemented unless the deviation between the technical parameters of semiconductor switches is known. This requirement increases the system cost because screening methods are extremely costly and time-consuming. In addition, most techniques aim at suppressing only the transient current imbalance. In this paper, a simple but innovative current balancing technique is proposed, without the need of screening any power device. The proposed technique consists of an open-loop system capable of balancing the currents between two parallel-connected SiC MOSFETs, with the aid of two active gate drivers and an FPGA, actively and independently of the cause. Experimental test results validate that the proposed open-loop method can successfully achieve suppression of current imbalance between parallel-connected SiC MOSFETs, proving its durability and validity level. Full article

In this study a four-wheel independent steering (4WIS) system for an electric vehicle (EV) steered by stepper motors is presented as a revolutionary real-time control technique employing neural networks in combination with fuzzy logic, where the use of the neural network greatly simplifies the computational process of fuzzy logic. The control of the four wheels is based on a variation of a Hopfield Neural Network (VHNN) method, in which the input is the error of each steering motor and the output is processed by a hyperbolic tangent function (HTF) feeding the fuzzy logic controller (FLC), which ultimately drives the stepper motor. The whole system consists of the four aforementioned blocks which work in sync and are inseparable from each other with the common goal of driving all the steering stepper motors at the same time. The novelty of this system is that each wheel monitors the condition of the others, so even in the case of the failure of one wheel, the vehicle does not veer off course. The results of the simulation show that the suggested control system is very resilient and workable at all angles and speeds. Full article

In the prospect of greener transportation means and global emission limitations for the protection of the environment, the electric vehicles’ market share is constantly increasing. It is expected that 32% of new vehicles sold in 2030 will be pure electric or plug-in hybrids. As all electric vehicles utilize lithium batteries to power the powertrain, the need for rare earth materials, like lithium or nickel, exceeds the planet’s ability to provide the required capacities. Additionally, even though lithium-ion batteries provide high energy density, they have some disadvantages like a limited range and durability at high-temperature operation. This issue can be improved greatly with the implementation of a hybrid energy storage system consisting of batteries and ultracapacitors. In this paper, the power efficiency of this storage system will be analyzed. Finally, when the cells reach below a specific capacity threshold, they can be removed from the vehicle to be installed in renewable energy plants for storing surplus energy production. Therefore, environmental waste is minimized while simultaneously assisting grid power demands, before being recycled to recover a portion of the rare metals used. Full article

The current paper presents an inclusive survey about the AC to DC and DC to DC converters for brushed DC Motor Drives. An essential number of different AC to DC and DC to DC topologies and control techniques, applied on the brushed DC motor drives are presented. This extensive literature review exposes advantages, disadvantages and limitations besides giving the basic operating principles of various topologies and control techniques. Full article