Electric Power Devices Research Articles

Enhanced Antenna Design for Rectenna Application in the 2.45 GHz ISM Band

In this paper a two layers microstrip antenna design at 2.45 GHz ISM band with Harmonic rejection filter embedded on the ground plane is presented. The two roger substrates with relative permittivity of 2.2 are separated by an air gap which enhances the antenna gain. The design is simulated using Computer Simulation Technology (CST) Studio Suite 2015. Different aperture couplings slots such as rectangular and triangular aperture coupling slots are studied and compared. It is found that the antenna with triangular aperture coupling slot enhances the antenna performance by suppressing 2 nd and 3 rd harmonics at 5 GHz and 8 GHz, respectively, increasing the antenna gain and providing a better circular polarization behavior. The simulated antenna design achieves a gain of 9 dB, return loss of -23.6dB, axial ratio of 1.27dB and axial-ratio bandwidth of 40.8% (2 ~ 3 GHz). The proposed antenna shows an enhancement in the antenna performance which makes it a suitable candidate for rectifying antenna or rectenna application as it can increase the total conversion efficiency resulting in a high output DC voltage used to power low power electronic and electrical devices such as wireless sensor.

Progress in and prospects for electrical insulating materials

The performance of electrical equipment and devices is determined to a great extent by the properties of their insulating materials. In power systems and electrical devices, insulating materials have to work in extreme circumstances that can include high temperature differences, intense radiation, and strong electric fields. Such conditions demand high-quality insulating materials with superior electrical, thermal, and mechanical properties as well as resilience to other environmental stresses. This study focuses on advances in insulating materials since the early 20th century and reviews the many developments in their properties and applications, including electric breakdown strength, thermal conductivity, temperature resistance, corona resistance, and specific energy storage in dielectrics. Some research progress on other properties is also covered, such as non-linearity and radiation resistance. Investigations into the properties of insulating materials can greatly assist in understanding their interface effects and composite structures, which in turn is helpful for discovering methods to improve the performance of electrical devices. Future directions for research are proposed to guide new investigations and support the development of even better insulating materials.

Multidimensional materials and device architectures for future hybrid energy storage.

Electrical energy storage plays a vital role in daily life due to our dependence on numerous portable electronic devices. Moreover, with the continued miniaturization of electronics, integration of wireless devices into our homes and clothes and the widely anticipated ‘Internet of Things', there are intensive efforts to develop miniature yet powerful electrical energy storage devices. This review addresses the cutting edge of electrical energy storage technology, outlining approaches to overcome current limitations and providing future research directions towards the next generation of electrical energy storage devices whose characteristics represent a true hybridization of batteries and electrochemical capacitors.

Propagation of overvoltages transferred through distribution transformers in electric networks

The increasing requirements for improved reliability of electrical power devices and optimisation of dielectric insulation design means that the analysis of impact due to overvoltages is of high importance. This analysis should also consider propagation of overvoltages transferred through power transformer windings to other parts of the electrical network. Hazard levels of overvoltages affected the insulation systems of electrical devices are determined by wave propagation conditions of overvoltages as well as the protection level of applied overvoltages protection. The analysis of overvoltages transferred to low voltage networks is very important due to the increasing number of electrical devices and electronic apparatus with low resistance to overvoltages. This study presents a detailed analysis of the propagation of overvoltages transferred through distribution transformer windings, in typical medium and low-voltage electrical networks. The analysis is based on simulation results carried out by the use of electromagnetic transients program–alternative transients program (EMTP–ATP). A high-frequency model for transformers done on the basis of frequency characteristics of admittance measurements was used in simulations. Detailed analysis of influence of length of medium- and low-voltage lines connected to the distribution transformers and metal oxide surge arresters on switching overvoltages transferred to low-voltage networks are presented in the study.

(Invited) Improved GaN Based Hydrogen Sensors

Recently, there are many interests in hydrogen as alternative energy source and carrier. Hydrogen is emission-free fuel when reacted with oxygen to produce the heat of combustion of 141.9 kJ/g while 47.0 and 45.0 kJ/g are for gasoline and diesel. Electrochemical cells and combustion in internal engines are used to transport hydrogen-generated energy to power vehicles and electric devices. Great efforts have been devoted on the researches to produce hydrogen in efficient and economical ways such as photoelectrochemical water splitting, photocatalytic water splitting, radiolysis, and photobioligical water splitting. Hydrogen is consumed in the petrochemical plant for hydrodealkylation, hydrodesulfurization, and hydrocracking, as a coolant in power stations due to its highest specific thermal conductivity of all gases, as an energy carrier in fuel-cell vehicles, in the propulsion of spacecraft, and in the semiconductor industry. Hydrogen gas is colorless, odorless, extremely reactive with oxygen, and has low ignition energy. When it leaks from pressurized container, its temperature rises up due to its negative Joule-Thomson coefficient, which can induce spontaneous flammable ignition. Therefore, hydrogen gas detection is very important issue in various hydrogen related industrial processes and equipments. Not only for early flammability alarm, a hydrogen sensor is also essential to monitor feed stream in the fuel-cell vehicle for efficient energy conversion. GaN based material system is very suitable to construct hydrogen sensor. Wide bandgap of GaN enable devices to operate at high temperature and harsh radiative environment, and mechanical and chemical robustness of GaN ensures reliability and durability of the device. Many types of GaN based hydrogen sensing devices including Schottky diode, metal oxide semiconductor (MOS) diode, GaN nanowire and AlGaN/GaN high electron mobility transistors (HEMTs) which employ platinum or palladium film as a catalytic active layer have been developed for fast and sensitive detection of hydrogen . In this study, effect of crystal polarity and plane on hydrogen sensing characteristics of GaN based diodes was investigated. Also, AlGaN/GaN HEMT hydrogen sensors with dramatically increased active sites on platinum nanostructure and GaN diode sensors with etched large surface area will be introduced as an approach to improve the sensitivity of hydrogen sensors.

Nano-scale, planar and multi-tiered current pathways from a carbon nanotube-copper composite with high conductivity, ampacity and stability.

New lithographically processable materials with high ampacity are in demand to meet the increasing requirement for high operational current density at high temperatures existing in current pathways within electronic devices. To meet this demand, we report an approach to fabricate a high ampacity (∼100 times higher than Cu) carbon nanotube-copper (CNT-Cu) composite into a variety of complex nano-scale, planar and multi-tiered current pathways. The approach involved the use of a two-stage electrodeposition of copper into a pre-patterned template of porous, thin CNT sheets acting as the electrode. The versatility of this approach enabled the realization of completely suspended multi-tier, dielectric-less 'air-gap' CNT-Cu circuits that could be electrically isolated from each other and are challenging to fabricate with pure Cu or any metal. Importantly, all such complex structures, ranging from 500 nm to 20 μm in width, exhibited ∼100-times higher ampacity than any known metal, with comparable electrical conductivity as Cu. In addition, CNT-Cu structures also exhibited a superior temperature stability compared to the ∼10-times wider Cu counterparts. We believe that the combination of our approach and the properties demonstrated here are vital achievements for the future development of efficient and powerful electrical devices.

Analysis on Development and Application of Power Electric Device and Variable Frequency Technology

Today, with rapid development of science and technology in the 21<sup>st</sup> century, China has also obtained great achievements drawing world’s attention regarding application and research in power electronics technology and variable frequency technology field. This paper has intensively studied and discussed development and application of power electronic device and variable frequency technology. This paper has first analyzed current application situation and trends of power electronic device in new energy and power system, rail transit and electric car, energy saving of industrial motor, consumption electronics, and national defense and war industry, then discussed development history of variable frequency technology, hazards brought by power electronic device and countermeasures, and finally demonstrated future development of power electronics technology and expected a broad development prospect of variable-frequency regulating speed technology in the future.

Benefits and Challenges of Mechanical Spring Systems for Energy Storage Applications

Storing the excess mechanical or electrical energy to use it at high demand time has great importance for applications at every scale because of irregularities of demand and supply. Energy storage in elastic deformations in the mechanical domain offers an alternative to the electrical, electrochemical, chemical, and thermal energy storage approaches studied in the recent years. The present paper aims at giving an overview of mechanical spring systems’ potential for energy storage applications. Part of the appeal of elastic energy storage is its ability to discharge quickly, enabling high power densities. This available amount of stored energy may be delivered not only to mechanical loads, but also to systems that convert it to drive an electrical load. Mechanical spring systems’ benefits and limits for storing macroscopic amounts of energy will be assessed and their integration with mechanical and electrical power devices will be discussed.

Performance test of the cryogenic cooling system for the superconducting fault current limiter

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

Intermag 2015 Chairman’s Foreword

On behalf of the Organizing Committee of the International Magnetics Conference 2015 (Intermag 2015), it is our pleasure to present this issue of the IEEE T ransactions on M agnetics comprising selected papers from Intermag 2015. These categories this year included: Magnetic Recording, Spintronics and Applications, Sensor/MEMS or RF Materials and Devices, Electric Machines and Power Devices, Life Sciences and Applications, Magnetic Thin Film and Nanostructures, Functional Magnetic Materials, Soft Magnetic Materials, Permanent Magnet Materials, and Microscopy Imaging and Characterization.

Development of 1 kW Stirling cryocooler using a linear compressor

Cryogenic cooling systems for HTS electric power devices require a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed a dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of the fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has a gamma-type configuration. The piston and displacer are supported with a flexure spring. A slit-type heat exchanger is adopted for the cold and warm-end, and the generated heat is rejected by cooling water. In the cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. The developed cryocooler reaches 47.8 K within 23.4 min. with no-load. Heat load tests shows a cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

Cool-down test of cryogenic cooling system for superconducting fault current limiter

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

Development and Test of a Cooling System for a 154 kV Superconducting Fault Current Limiter

The superconducting fault current limiter (SFCL) is an electric power device that limits the fault current immediately in a power grid. Korea Electric Power Corporation (KEPCO) has been developing a 154 kV, 2 kA SFCL since 2011 to protect power grids from increasing fault current and improve the stability and quality of electric power. This SFCL adopts 2G YBCO wires and operates at 71 K and 5 bars. In this paper, a cooling system for the 154 kV SFCL and its cooling test results are reported. This cooling system uses a Stirling-type cooler to make sub-cooled liquid nitrogen (<TEX>$LN_2$</TEX>), which cools the superconductor modules of the SFCL. The <TEX>$LN_2$</TEX> is circulated between the cooler and the cryostat that contains superconductor modules. The <TEX>$LN_2$</TEX> also plays the role of a high voltage insulator between the modules and the cryostat, so the pressure was maintained at 5 bars for high insulation performance. After installation in a test site, the cooling characteristics of the system were tested. In this operation test, some important data were measured such as temperature distribution in <TEX>$LN_2$</TEX>, pressure change, performance of the heat exchanger, and cooling capacity of the total system. Consequently, the results indicate that the cooling system operates well as designed.

Enhancement of Distributed Generation by Using Custom Power Device

Wind energy (WE) has become immensely popular for distributed generation (DG). This case presents the monitoring, modeling, control, and analysis of the two-level three-phase WE based DG system where the electric grid interfacing custom power device (CPD) is controlled to perform the smart exchanging of electric power as per the Indian grid code. WE is connected to DC link of CPD for the grid integration purpose. The CPD based distributed static compensator, i.e. the distributed static synchronous compensator (DSTATCOM), is utilized for injecting the wind power to the point of common coupling (PCC) and also acts against the reactive power demand. The novel indirect current control scheme of DSTATCOM regulates the power import and export between the WE and the electric grid system. It also acts as a compensator and performs both the key features simultaneously. Hence, the penetration of additional generated WE power to the grid is increased by 20% to 25%. The burden of reactive power compensation from grid is reduced by DSTATCOM. The modeling and simulation are done in MATLAB. The results are validated and verified.

Characterization of a Second Generation HTS Coil for Electrical Power Devices

Due to the electrical characteristics of second generation (2G) high temperature superconductor (HTS) wires, such as higher critical current density and superior performance than first generation (1G) HTS wire under magnetic fields, they have been chosen for use in the development of several superconducting devices for electric power applications. Since the majority of the electrical devices are designed using a conductor coil, it is necessary to understand the electrical characteristics of superconducting coils under different situations, to develop these equipment. An important aspect that should be considered in the project of 2G HTS coils is the influence of its self field. This effect could lead to a reduction in the 2G HTS wire critical current value resulting in damages due to heterogeneous quenching Therefore, this work aims the construction of a HTS coil using 2G wires, and the determination of its DC critical current under different conditions. The influence of the coil bending radius, by going to the minimum value recommended by the manufacturer, was also investigated. These measurements are essential for the development of electric power devices.

A review on piezoelectric material as a source of generating electricity and its possibility to fabricate devices for daily uses of army personnel

Energy harvesting, a process of capturing ambient waste energy and converting it into usable electricity, has been attracting more and more researchers' interest because of the limitations of traditional power sources. In this study, fabrication of flexible piezo composite material was investigated using lead zirconate titanate PZT powder 3 µ and 1 µ particle size, multiwalled carbon nano tubes MWCNT diameter 5-20 nm, length up to 10 µ, polydimethyl siloxane PDMS synthetic silicone rubber and solvents THF, chloroform. These materials have been tested for their peak performance, lifetime and durability under different conditions. The foremost aim will be to extract usable power which can run various devices having low power requirement such as mobile devices and wireless sensor networks and the recent advent of the extremely low power electrical and mechanical devices such as micro electromechanical systems MEMS.

AC Loss Measurements of a Trapezoidal Shaped HTS Coil Using an Electrical Method

High temperature superconducting (HTS) coils of different shapes (typically circular or trapezoidal) wound on iron or ironless core are fundamental components of many superconducting electrical power devices. A 150-turn (75 turns/pancake) trapezoidal coil in double pancake configuration has been designed and realized in our laboratory of ENEA Frascati. Various epoxy resins and YBCO tapes have been tested in the temperature range room to liquid nitrogen, leading us to the choice of AmSC (American Superconductor) tape for the winding and araldite resin for the impregnation process. The trapezoidal shape has been chosen because of its suitable geometry for practical applications, the results being complementary to what was previously achieved on round shaped HTS coils. The AC transport current losses have been measured using a compensated electrical method and expressed in terms of a linearly frequency dependent resistance. A linear dependence of the losses resistance from frequency was expected and found in agreement with previous results. The current-voltage curve has been measured in zero externally applied field condition, the results being in good agreement with a numerical simulation. The magnetic field distributions, at different air gaps from coil top and zero externally applied filed condition, have been simulated and reported as well.

Vision Inspection Methods for Uniformity Enhancement in Long-Length 2G HTS Wire Production

With much effort devoted by many research groups, the performance of 2nd generation (2G) superconducting wires, also called coated conductors (CC), was drastically improved, leading to many meaningful and impressive demonstrations of electric power devices. Now that the performances such as critical current, in-field characteristics, and mechanical strengths became sufficient to the application, the attention has moved to how we can produce long 2G wires with high uniformity. Many in-line inspection tools are tested and introduced to address these challenges. In this paper, we describe two methods that we adopted for in-line monitoring and feedback control of layer deposition. One is for texture control of ion beam assisted deposition (IBAD) of an MgO layer through reflection high-energy electron diffraction (RHEED) pattern monitoring and analysis. The other is for composition control of a superconducting layer through surface color observation and control of metal source evaporation rates. By applying the above two methods, we achieved in-plane texture of about 4.8 ° in the MgO layer, as measured by FWHM of phi-scan of (220) peak, and the critical current of 750 A/12 mm width in the GdBCO layer along the length of more than 650 m, with excellent uniformity.

Examining the trends of technological development in hydrogen energy using patent co-word map analysis

Hydrogen fuel is a zero CO2 emission fuel which uses in electrochemical cells, or internal combustion engines, to power vehicles and electric devices. It is also can potentially be mass-produced for various applications and be used in propulsion of spacecraft with safely high pressure storage. Therefore, it is an interesting subject to identify the technological trends of hydrogen energy. This study suggests a patent co-word map analysis (PCMA) to examine the trends of technological development in the area of hydrogen energy. The PCMA provides a systematic procedure to demonstrate the overall relationship among patents and produces the important technological insights regarding hydrogen energy. The results of analysis firstly indicate that the technological trends of worldwide hydrogen energy focus on the converting and application of hydrogen. Furthermore, critical technologies obtained from three patent sub-maps can be identified as the production, storage and conversion for hydrogen energy. Finally, hydrogen application is taken for the key factor in sustainable energy research works to improve the use for hydrogen.

Powering electronic contact lenses: current achievements, challenges, and perspectives

The recent media hoopla regarding ‘smart’, ‘bionic’, or more appropriately, electronically augmented contact lenses is analyzed in terms of real achievements coupled to the critically important issue of power management. Not depending on the availability, currently or in the near future, of to-the-purpose discrete or integrated electronic devices, power management, including delivery/supply and temporal sustainability, will be an outstanding issue if present-day technology should remain the only option. Radically different approaches have been taken to deliver electric power to electronically augmented contact lenses, that is, ranging from quite simplistic wire-based delivery assemblies, grossly inappropriate for end users, to various elaborate wireless designs drawing on over-the-air power delivery, as well as solar and electrochemical cells. Nonetheless, given the complex restrictions offered by a contact lens, conventional, even state-of-the-art, power management technology is at an impasse, and to ensure a bright future for smart lenses, radical technological measures need to be taken. Bridging the conceptual gap between fuel cells and supercapacitors, an ingenious novel approach to on-lens power management is presented: a charge-storing fuel cell, or alternatively, a self-charging capacitor, that is, a hybrid electric power device.