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Abstract Potential uses for electromagnetic launchers in defense systems, space exploration, and transportation have recently emerged. In addition, this accelerator has many applications, such as deploying small satellites into low-earth orbit and accelerating high-speed trains (e.g., bullet trains and Hyperloop) with a low-cost propulsion system instead of expensive linear motors, particularly in space applications. Therefore, the full capability and optimization of these launchers’ efficiency are still required. Therefore, this paper focuses on presenting a new design to decrease the coil’s magnetic circuit reluctance and boost the magnetic flux lines by adding a laminated iron yoke surrounding the coil. This design makes the inductance value of the iron-yoked accelerator twice the inductance in case of the absence of the iron-yoke at its peak. Additionally, the initial inductance of the iron-yoked accelerator is approximately 65% higher than that of the coil without the iron yoke. Consequently, the modified design proposed an efficiency of 17.5%, which represents a 60% improvement over the efficiency of the regular accelerator. In addition, the introduced design eliminates the suck-back force using a fast-switching device (IGBT) to switch the coil off when the projectile reaches half of the coil. Moreover, a mathematical model for the iron-yoked accelerator is built on MATLAB Simulink and validated experimentally. An artificial intelligence optimization technique, the gravitational search algorithm (GSA), is used to optimize the accelerator parameters, such as the number of turns, capacitor value, and capacitor voltage. Finally, the experimental evaluation of the GSA-optimized system demonstrated an additional 15% enhancement in efficiency, bringing the total efficiency to 20%.

Summary LLC resonant converter has been widely employed in electric vehicle (EV) charging applications. Compared with single‐phase LLC converters, three‐phase LLC converters provide a smaller current ripple, higher power capacity, and higher power density at higher power levels. However, the conventional three‐phase LLC converter, which adopts pulse frequency modulation (PFM), has the issue of limited gain range. In this paper, a three‐phase LLC resonant converter with variable magnetizing inductance is proposed. A two‐stage control strategy of PFM and fixed‐frequency magnetizing inductance modulation (MIM) is proposed. The wide gain range needed for EV charging is realized by modulating magnetizing inductance and frequency. Finally, a 2.7 kW prototype with 400 V input and 280–420 V output range verifies the theoretical analysis and parameter design. The experimental results show that the converter can achieve soft switching and a wide gain range and the peak efficiency is 97.7%. [ABSTRACT FROM AUTHOR]

Rotary electromagnetic fault current limiter (FCL) is an emerging technology for limiting fault currents in the power network. The device consists of two movable air-core spherical reactor rings (i.e., inner and outer rings). The movable feature allows the reactor rings to rotate, and form a proper mutual positional displacement. This can limit the fault current since the effective inductance of the device is dependent to the mutual angular position of the reactor rings. Due to the unconventional structure, to this date, the design process has solely been based on finite element (FE) method. This paper aims to analytically validate the theory and the overall functionality of the device in both the steady state and transient regime. For this propose, the resistance and the inductance of the device are first computed at normal operating condition using the basic theory of engineering electromagnetics. Next, performance characteristics such as electromagnetic torque, rotational displacement of the reactors, effective inductance of the device, and the network current are calculated at the faulty condition. For verification purposes, analytical results are compared with via FE simulation and experimental test.

Eddy current sensors are an attractive choice due to their high resolution, reliability, and durability in harsh environments while being able to measure in a noncontact manner. This article presents a novel design to realize a thin eddy-current-based angle sensor. It is realized by converting the shaft, whose rotation angle is to be measured, into the sensing element. The modification to the shaft is minimal; a small surface groove is introduced without affecting the mechanical strength. The stationary part of the sensor consists of two layers of flexible square-planar coils. Depending on the angular position of the shaft, the inductances of the planar coils get modified. These are measured using a specially designed circuitry, optimized for this sensor. The output for the entire circle range (360°) is derived from the inductance values of each coil using a successive approximation algorithm developed for this purpose. Finite-element analysis was employed to design the sensor and analyze the axial/radial misalignment of the rotor. A sensor prototype was built and tested. The output showed a resolution of 0.1° and the worst case linearity error of 0.9%. The prototype sensor dimensions are designed to fit in a standard steering column. The proposed sensor is thin, easy to manufacture at low cost, tolerant to axial vibration by design, and has a 360° sensing range.

Recent developments in electromagnetic launchers have created potential applications in transportation, space, and defense systems. However, the total efficiency of these launchers has yet to be fully realized and optimized. Therefore, this paper introduces a new design idea based on increasing the magnetic flux lines that facilitate high output velocity without adding any excess energy. This design facilitates obtaining a mathematical equation for the launcher inductance which is difficult to analytically represent. This modification raises the launcher efficiency to 36% higher than that of the ordinary launcher at low operating voltage. The proposed design has proven its superiority to traditional launchers, which are limited in their ability to accelerate microsatellites from the ground to low Earth orbit due to altitude and velocity constraints. Therefore, an aircraft is used as a flying launchpad to carry the launcher and bring it to the required height to launch. Meanwhile, it is demonstrated experimentally that magnetic dipoles in the projectile material allow the launcher coil’s magnetic field to accelerate the projectile. This system consists of the launcher coil that must be triggered with a high amplitude current from the high DC voltage capacitor bank. In addition, a microcontroller unit controls all processes, including the capacitor bank charging, triggering, and velocity measurement.

DC microgrids with power electronic converter units are prone to become unstable due to the well-known negative impedance characteristic of constant power loads. For such systems, the global stability cannot be assumed. It is known that the transient stability of the system can be degraded by large and fast disturbances due to the reduced stability region. As a result, the system gets to operate outside the stability region and becomes unstable even if the steady-state operating point is in the stable region. To overcome this problem, a dynamic stabilizer that controls the stability region using variable inductor is proposed to guarantee stable operation during transient-states. The proposed scheme is straightforward and can be implemented with minimal power consumption. Furthermore, it is robust for parameter variation. The feasibility of the proposed method is verified experimentally. [ABSTRACT FROM AUTHOR]

Parametric transformers are magnetic components which employ a variable inductance to generate parametric oscillations in a secondary resonant tank. Power conversion with parametric transformer can provide constant output voltage regulation, short‐circuit protection, input over‐voltage and under‐voltage protection, and bidirectional filtering. In spite of these benefits, parametric transformers did only experience small scientific attention during the 1970s. Due to the low energy density and low efficiency of the topologies developed at the time, parametric transformers were discarded in favour of the more common power converters based on the magnetic amplifier. In spite of the great developments in power semiconductors, magnetic amplifier control still remains a competitive option in present‐day power electronic applications benefiting from its high robustness. This publication presents a new topology of parametric transformer based on permanent magnet (PM)‐inductors, presenting higher efficiency and higher energy density. Finite element method magnetics simulations are used to analyse the variable inductance mechanisms. A physical prototype is developed and tested empirically in an AC/DC power converter. The prototype verifies all the mentioned benefits of parametric power conversion, and presents an efficiency and energy density equivalent to presently employed solutions for voltage regulation, using power semiconductor magnetic amplifiers. [ABSTRACT FROM AUTHOR]

This article proposes a half-bridge LLC resonant converter applying a simple circuit with a variable magnetizing inductance scheme for hold-up time requirement. By changing the magnetizing inductance of the main transformer, the proposed converter can satisfy the hold-up time requirement without sacrificing efficiency, featuring small conduction, and turn-off switching losses of the primary switches in the nominal status. In addition, the proposed converter can relieve the burden of the additional components by positioning them on the signal path, and the proposed circuit is self-powered by adding only one additional winding instead of the isolated power supply. Therefore, those of the size and cost of the proposed circuit can be reduced compared to the previous studies. The feasibility of the proposed method was verified with a 350 W prototype converter (56 V/6.25 A), and the improved circuit for the transient mode was also presented. The experimental results validated the theoretical analysis and showed the effectiveness of the proposed converter for high-efficiency applications, especially in light-load conditions. [ABSTRACT FROM AUTHOR]

This paper presents the design and development of a novel, linear, eddy current-based noncontact angle sensor with 360° range. Although the eddy current proximity sensors are known for high reliability, resolution, and insensitivity to moisture and oil, the approach has not been exploited to develop full-circle range angle sensors with such features. The proposed sensor consists of a rotary conducive hollow tube (e.g., made of aluminum) part and a stationary part with four identical flexible coils. The tube has a simple but special groove. The position of the groove modifies the value of the inductance of the stationary coil as a function of the sensing angle. The design is such that the inductance of each coil varies linearly for a specified range of the angle. From this piecewise linear characteristic, an output that is linear for the full-circle range is obtained using a simple yet effective algorithm. A suitable signal conditioning circuit is developed to obtain an output that is proportional to the change in the inductance of the coil. In order to optimize the design, first, the sensor structure was studied using finite-element analysis. Then, a prototype of the sensor was built and tested in the laboratory. The prototype sensor has a resolution of 0.08° and a maximum nonlinearity of 0.25%. The possible sources of error of the sensor have been analyzed and quantified. The sensor has no electrical contact to the rotary part and its output is immune to moisture, dust, and oil. [ABSTRACT FROM AUTHOR]

Designs of saturated-cores fault current limiters (FCLs) usually implement conducting or superconducting DC coils serving to saturate the magnetic cores during nominal grid performance. The use of coils adds significantly to the operational cost of the system, consuming energy, and requiring maintenance. A derivative of the saturated-cores FCL is a design implementing permanent magnets as an alternative to the DC coils, eliminating practically all maintenance due to its entirely passive components. There are, however, various challenges such as the need to reach deep saturation with the currently available permanent magnets as well as the complications involved in the assembly process due to very powerful magnetic forces between the magnets and the cores. This paper presents several concepts, achieved by extensive magnetic simulations and verified experimentally, that help in maximizing the core saturation of the PMFCL (Permanent Magnet FCL), including optimization of the permanent magnet to core surface ratios and asymmetrical placement of the permanent magnets, both creating an increase in the cores’ magnetic flux at crucial points. In addition, we point to the importance of splitting the AC coils to leave the center core point exposed to best utilize their variable inductance parameters. This paper also describes the stages of design and assembly of a laboratory-scale single phase prototype model with the proposed PMFCL design recommendations, as well as an analysis of real-time results obtained while connecting this prototype to a 220 V grid during nominal and fault states.

Magnetic-resonant wireless power transfer (WPT) has become a reliable contactless source of power for a wide range of applications. WPT spans different power levels ranging from low-power implantable devices up to high-power electric vehicles (EV) battery charging. The transmission range and efficiency of WPT have been reasonably enhanced by resonating the transmitter and receiver coils at a common frequency. Nevertheless, matching between resonance in the transmitter and receiver is quite cumbersome, particularly in single-transmitter multi-receiver systems. The resonance frequency in transmitter and receiver tank circuits has to be perfectly matched, otherwise power transfer capability is greatly degraded. This paper discusses the mistuning effect of parallel-compensated receivers, and thereof a novel dynamic frequency tuning method and related circuit topology and control is proposed and characterized in the system application. The proposed method is based on the concept of switch-mode gyrator emulating variable lossless inductors oriented to enable self-tunability in WPT receivers. [ABSTRACT FROM AUTHOR]

This paper deals with an analytical model of the virtual air gap (VAG) function in order to define design rules when this technique is used inside complex devices. The establishment of those design rules constitutes the main originality of the developments presented in this paper, which are about a single-phase magnetic core. It is based on the definition of a nonlinear reluctance network that takes simultaneously into account the effects of dc and ac magnetic flux components in the disturbed area that contains the VAG. The results are validated using a finite-element analysis and experimentally. [ABSTRACT FROM AUTHOR]

Within a German government funded project with the partners Siemens and KIT, we present the concept and first results for a full-scale inductive superconducting fault current limiter. It is based on the well-known shielded core concept but does not need the deployment of an iron core. Aim of the project is the construction and test of one phase with a nominal current I = 600 A and a voltage of U = 10 kV, i.e., a protected power of P = 10 MVA for the three-phase system. The shielding is provided by a stack of superconducting rings, i.e., YBCO-tapes soldered to closed rings, with a radius of R = 0.7 m. To obtain a sufficient coupling between the reactor (primary coil, warm) and the shielding stack, the minimization of the gap between both is crucial. The paper presents numerical work with respect to the overall geometry and the physical properties (limitation behavior, ac-losses) of the device. Also a suitable superconducting material had to be qualified. Finally, a test equipment for single components (rings) was built up and successful tests of first superconducting full size components are reported. [ABSTRACT FROM PUBLISHER]

A wide-band LC-tank CMOS voltage controlled oscillator (VCO) employing a transformer-based variable inductance structure is presented. The variable inductance is obtained through a switching scheme that controls the current path in a transformer and allows four different inductances to be delivered by the structure. Additionally, an electric model of the transformer obtained through the simulated data and equations based on its physical properties is proposed. The inductance and quality factor from the variable structure were extracted from the transformer's electromagnetic simulations and model's scattering parameters. The model showed and error lower than 4% in all modes of operation inside of the desired range (from 1 to 6 GHz). The proposed VCO is simulated and shows a percentual tuning range of 87.9% around a central frequency of 4.12 GHz, while consuming less than 3.3 mW of power and exhibiting a maximum phase noise of -108 dBc/GHz occupying an area of 0.45 mm 2. • An 87.6% tuning range wide-band VCO with variable inductance is simulated. • The variable inductance utilizes 3 switches to deliver 4 different inductance values. • A body floating technique is used to mitigate the switches' impact on the inductance. [ABSTRACT FROM AUTHOR]

This paper presents the development of a universal electronic ballast for TL5 lamps. The intent is to efficiently operate the maximum number of TL5 lamps with different power ratings at nominal power, using a resonant variable inductance, provided by a magnetic regulator, while maintaining the switching frequency constant. A microcontroller and additional digital circuitry are used to command a dc-dc buck converter to supply the necessary dc control current to the magnetic regulator and to regulate the switching frequency of the half-bridge resonant inverter that supplies the lamp. The selection of the resonant capacitance is done in order to comply with the SoS limits established for each lamp. Experimental results with lamps ranging from 14 to 49 W, operating with high efficiency and high output, are presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a new technique for controlling dc-dc resonant converters is investigated. A variable inductance is used to control and regulate the dc output voltage maintaining constant switching frequency for the half-bridge transistors. The output voltage characteristics of the series resonant and parallel resonant converters under the proposed magnetic control are obtained and analyzed. In order to evaluate the proposed technique, a laboratory prototype for a 48 V-input 5 V/10 A-output 500 kHz parallel resonant converter is presented. A methodology for obtaining the converter dynamic response using a step response test is carried out. From the dynamic response, a compensator for operating the converter at closed loop is developed and tested in the laboratory. The results prove that the proposed technique is suitable for controling resonant inverters at constant frequency using a low-cost half-bridge inverter. [ABSTRACT FROM AUTHOR]

A new type of pressure sensors with extremely high sensitivity is introduced. Unlike piezoresistive, capacitive, and linear-variable-differential-transformer-based pressure sensors, the new sensor is based on a technique for substantially changing the inductance of a coil. The prototype device has demonstrated a change in inductance of approximately 34.5 mH over a pressure range of 10 kPa. The sensor offers a number of desirable features, including linearity, low temperature, and pressure hysteresis, in addition to small size. [ABSTRACT FROM PUBLISHER]

In this paper, a digitally controlled electronic ballast is presented. The ballast corresponds to the so-called universal or multiwatt ballasts, which are intended to operate different lamps with different power ratings without performing any change in the hardware. Thus, the ballast must incorporate some kind of circuitry so that the rated power of the connected lamp can be identified. The ballast must also adjust some of its parameters in order to supply the lamp adequately, which usually means the following: 1) as close as possible to the nominal power and 2) with the best efficiency. In the proposed ballast, the parameters selected to adapt the power circuit to each lamp are the switching frequency and the resonant tank inductance. The resonant tank inductance is varied by means of a magnetic regulator whose inductance can be adjusted through a dc bias current. Due to the relatively high complexity of the proposed converter, a digital control circuit is developed to control both the resonant inverter used to drive the lamp and the dc–dc converter employed to supply the control winding of the magnetic regulator. Experimental results from a laboratory prototype for lamp powers ranging from 15 to 58 W are provided. [ABSTRACT FROM AUTHOR]

To create an active phase‐gradient metasurface relying on variable inductance, an impedance converter is used to realise positive inductance values. By varying the inversion coefficient, a variation of the inductance can be achieved electronically. A prototype of the circuit is fabricated and tested. Different inductance values are obtained with respect to the inversion coefficient used. Such circuit can be readily applied to an LC resonant cell to control the phase responses. A potential application for beam steering is further numerically verified. [ABSTRACT FROM AUTHOR]

A low-profile power inductor fabricated using low-temperature cofired ceramic (LTCC) technology has been demonstrated to improve the light-load efficiency of a converter, without the use of additional control circuitry. This is brought about by the material and the geometry, which causes a change in inductance with load current. Variation in inductor geometry is performed experimentally to study the effects on the light-load efficiency of a converter. By decreasing the conductor width of the inductor, the light-load efficiency can be further improved by 30% in comparison with using commercial inductors of similar inductance. Sufficient core thickness is necessary to have sufficient inductance, since an inductance value which is too low is detrimental from the system power loss point of view, as demonstrated experimentally. From the circuit point of view, there seems to be a critical inductance value, whereby increasing the inductance further, does not result in significant improvement in power stage efficiency. Changing conductor thickness in the range of 260 to 550 μm does not result in significant improvement in the overall efficiency of the converter. Variation in the number of parallel conductors in a multiconductor structure does not have significant effect on light-load efficiency improvement. [ABSTRACT FROM AUTHOR]

Nowadays, there are few commercial types of ballasts that are able to control fluorescent lamps with different power ratings. One of the main issues is how to get optimum operation for each lamp in this condition. This paper tries to demonstrate how to accomplish this objective using a magnetic regulator, i.e., using a variable inductor. This variable inductor is controlled by a dc current delivered by a forward converter directly supplied from the ballast dc bus voltage. This control current allows changing the resonant tank and adapting it to the working parameters imposed by each lamp, ensuring near-resonance working conditions. Design criteria and practical verifications are included to confirm this new technique. Theoretical predictions are verified with the experimental results for three TLD Philips fluorescent lamps, from 18 to 58 W. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis and experiments of resonant tanks for magnetically controlled electronic ballasts, focusing on their behavior and performance when driving hot cathode fluorescent lamps. Four different resonant tanks are analyzed: LC, LCC, capacitive impedance inverter, and CLL. The analysis is performed using a 36-W fluorescent lamp, which has been previously tested and modeled experimentally. The lamp model is used to derive the dimming characteristics of the different resonant tanks when using the resonant inductance as a control parameter. Analysis and experiments showed that instabilities appear when the lamp power is decreased below a minimum value, which effectively limits the dimming range of the ballast. Nevertheless, the proposed control method can be used to control lamp power in an adequate range provided that the resonant tank should be selected and designed properly. [ABSTRACT FROM AUTHOR]

The EIE core variable inductor is a device of variable inductance that is controlled by DC current. This device controls the cancellation of AC magnetic flux and thus always maintains the flux density on the magnetic path within the saturation flux density in control mode. It cancels high harmonic distortion and does not require gaps, which reduce distortion. Thus, it is simply structured and easy to scale up. This paper describes the basic structure and characteristics of the device, and presents examples of its application to electrical power equipment. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(4): 22–33, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10140 [ABSTRACT FROM AUTHOR]

Designs of saturated-cores fault current limiters (FCLs) usually implement conducting or superconducting DC coils serving to saturate the magnetic cores during nominal grid performance. The use of coils adds significantly to the operational cost of the system, consuming energy, and requiring maintenance. A derivative of the saturated-cores FCL is a design implementing permanent magnets as an alternative to the DC coils, eliminating practically all maintenance due to its entirely passive components. There are, however, various challenges such as the need to reach deep saturation with the currently available permanent magnets as well as the complications involved in the assembly process due to very powerful magnetic forces between the magnets and the cores. This paper presents several concepts, achieved by extensive magnetic simulations and verified experimentally, that help in maximizing the core saturation of the PMFCL (Permanent Magnet FCL), including optimization of the permanent magnet to core surface ratios and asymmetrical placement of the permanent magnets, both creating an increase in the cores' magnetic flux at crucial points. In addition, we point to the importance of splitting the AC coils to leave the center core point exposed to best utilize their variable inductance parameters. This paper also describes the stages of design and assembly of a laboratory-scale single phase prototype model with the proposed PMFCL design recommendations, as well as an analysis of real-time results obtained while connecting this prototype to a 220   V grid during nominal and fault states. [ABSTRACT FROM AUTHOR]