DC Output Research Articles

An energy efficient modified passive power filter for power quality enhancement in electric drives

In most industrial applications, AC drives are used. These drives require power electronic modules to convert AC to DC and also DC to AC. The power modules used for power conversion consist of power semiconductor switches. There is distortion in the voltage and current obtained from the power modules due to non-linear behaviors of semiconductor switches. To reduce the distortion in the input current, inductors are used along with the line impedance. A high value of inductance is required to maintain the percentage of THD within limits set by the latest standards. Along with the increased size and cost, it also reduces the power factor and output DC voltage at higher loads. The use of a passive power filter (PPF) is the conventional method followed for the reduction of percentage THD and promotion of the power factor. PPFs comprise passive elements such as the resistor, inductor, and capacitor. These passive elements are connected at the point of common coupling (PCC) in shunt to compensate for the harmonics present in the input current. In this study, a modified multi-tuned passive filter is considered to reduce the source current harmonics. A bridge rectifier with resistive load, three-phase induction motor drive, and linear resistive–inductive load is connected at the point of common coupling to analyze the harmonics present in the source current, and also unbalanced created in one phase. To achieve proper selection of the resistance value for the passive filter, the class topper optimization technique is used. To validate the simulation results obtained for the multi-tuned passive filter, the hardware is implemented with a three-phase AC induction motor drive load, in which the speed of the motor is controlled with voltage by a frequency control algorithm using an FPGA controller; The 50% THD is reduced by using the fifth-order filter alone, 75% by combining the fifth- and seventh-order filters, 85% by combining the 5th-, 7th-, 11th-, 13th-, and higher-order filters, and 90% for varying loads. For single-phase AC induction motor load, THD % is reduced to 4%, and for three-phase AC induction motor drive, THD % is reduced to 10% with the same value of the filter.

A New Compact Triple-Band Triangular Patch Antenna for RF Energy Harvesting Applications in IoT Devices.

This work proposes a new compact triple-band triangular patch antenna for RF energy harvesting applications in IoT devices. It is realized on Teflon glass substrate with a thickness of 0.67 mm and a relative permittivity of 2.1. Four versions of this antenna have been designed and realized with inclinations of 0°, 30°, 60° and 90° to study the impact of the tilting on their characteristics (S11 parameter, radiation pattern, gain) and to explore the possibilities of their implementation in the architectures of electronic equipment according to the available space. The antenna is also realized on waterproof paper with a thickness of 0.1 mm and a relative permittivity of 1.4 for biomedical domain. All the antennas (vertical antenna, tilted antennas and antenna realized on waterproof paper) have a size of 39 × 9 mm2 and cover the 2.45 GHz and 5.2 GHz Wi-Fi bands and the 8.2 GHz band. A good agreement is obtained between measured and simulated results. Radiation patterns show that all the antennas are omnidirectional for 2.45 GHz and pseudo-omnidirectional for 5.2 GHz and 8.2 GHz with maximum measured gains of 2.6 dBi, 4.55 dBi and 6 dBi, respectively. The maximum measured radiation efficiencies for the three antenna configurations are, respectively, of 75%, 70% and 72%. The Specific Absorption Rate (SAR) for the antenna bound on the human body is of 1.1 W/kg, 0.71 W/kg and 0.45 W/kg, respectively, for the three frequencies 2.45 GHz, 5.2 GHz and 8.2 GHz. All these antennas are then applied to realize RF energy harvesting systems. These systems are designed, realized and tested for the frequency 2.45 GHz, −20 dBm input power and 2 kΩ resistance load. The maximum measured output DC power is of 7.68 µW with a maximum RF-to-DC conversion efficiency of 77%.

Experimental Validation of the Boost Power Factor Corrector Converter Based on Smart Intuitive Control Law

This paper discusses the simulation and experimental validation of a curative solution, called power factor correction (PFC), intended to improve the power quality of the single-phase AC/DC converter. A modern control law combined between two methods which are the fuzzy logic theory and the predictive technique is proposed in this research work. The first is reserved to guarantee an intelligent regulation of the DC output voltage while the second aims to the intuitive power switch governance of the boost chopper constituting the PFC. The adopted solution ensures the delivery of a source current of sinusoidal shape, respecting the imposed international standards and the operation of the treated system under a power factor very close to unity. The effectiveness and practical use of the intelligent intuitive PFC control have been experimentally proven using the dSPACE 1104 card for different operating conditions, resulting from the variation of the load and the reference output voltage. The practical results in terms of power quality identified by a total harmonic distortion of the source current of 2.8% and a power factor of 0.995 respect the international standard IEEE 519-2014. Also, they are very convincing compared to those existing and recently published in the literature.

Simulation Studies of Energy Recovery in a BLDC Motor-Based Kinetic Energy Storage

This paper presents research conducted on the development of an innovative system to increase the amount of energy recovered from a high-speed kinetic energy storage based on a three-phase permanent magnet brushless (PM BLDC) motor/generator (mogen) with a flywheel-shaped rotor, compared to the efficiency obtained for standard solutions with power electronics systems. This kinetic energy storage is currently under development. In the system presented in the paper, the regulated DC output voltage of the 6T thyristor bridge is controlled with a tolerance within ±10% of the reference voltage for a variable power load. The input voltage of the rectifier is a three-phase trapezoidal-shaped voltage from the rotating mogen, whose amplitude can vary from 0 to 650 V and frequency from 0 to 250 Hz voltage. The article presents example results of simulation tests of the mogen-based kinetic energy storage model with the thyristors’ firing angle control system. As part of the research, a prototype of the rectifier was built on a laboratory scale, to confirm the validity of the assumptions regarding the synchronization and control method of the bridge using a new design of the thyristor gate drivers.

A high step-up DC–DC converter based on ASL and VMC for renewable energy applications

In this paper, a new high step-up non-isolated DC–DC converter has been proposed and analyzed. The proposed topology provides a high DC output voltage, which is adjustable by two different duty cycles. Moreover, low voltage stress across the power switches can be marked as another advantage of this structure. The inequality of the switches’ duty cycles helps obtain high output voltage with moderate duty cycles in this converter. Four inductors based on two magnetic cores, four capacitors, two diodes, and three switches make up the converter’s components. Operational modes of the proposed topology are investigated under steady-state analysis in continuous conduction mode (CCM), discontinuous conduction mode (DCM), and boundary condition mode (BCM). In addition, mathematical calculations of voltage, current, and efficiency are provided in this paper. In addition, a comparison study of the proposed converter and other related structures is conducted to determine the advantages it offers. The proportion of losses and efficiency calculation are analyzed. Finally, a (500 W, 50 kHz) laboratory prototype is assembled and analyzed to validate the analytical findings in this paper.

Dual Band Rectenna for Wireless Energy Harvesting in the 2.40 GHz and 5.38 GHz

The objective of this study, reflected in this document, was to implement a rectenna for 2.45 GHz and 5.38 GHz wireless local area applications. For this purpose, the antenna dimensions were set to 18 mm × 44 mm, which is simulated using the optimization software CST Studio, manufactured on FR4 substrate with a thickness of 1.6 mm, where the conductive material has a thickness of 0.035 mm. Likewise, the rectangular slot technique was used to improve the bandwidth of the antenna; this technique consists of inserting slots in the structure to modify the displacement of the surface current. The above presented a gain of 2.49 dB at the 2.45 GHz frequency and 4.01 dB at the 5.38 GHz frequency. The proposed antenna for RF energy harvesting applications exhibits a dipole type radiation pattern, which enhances the capture of RF energy from various directions. The triple slotted-band rectifier with T-shaped impedance matching network was designed in FR4, using a Schotkky HSMS-286C diode for AC to DC RF control switching. A tp-link TL-WR940N wireless router was used as the RF emitting source at 30 cm separation between it and the proposed rectenna. The DC output of the rectenna is 3 volts with a generated signal power of 20 dBm at 2.4 GHz. The low-cost rectenna can be used for power-charging applications in the Internet of things (IoT) systems.

Design and Analysis of Front Side Modular Multilevel Converter for Smart Transformer in 15 kV Arba Minch Distribution Network Using Diverse Controllers and Multicarrier Modulation

This paper presents design and analysis of a bidirectional medium voltage (MV) front-side converter of smart transformer (ST) for Arba Minch Town distribution system. A modular multilevel converter (MMC) configuration is used in the MV side of the ST. The grid side MV is 15 kV RMS line value and the desired MVDC voltage is 24.5 kV for ensuring bidirectional operation of the converter in the time of grid outage. A half bridge semiconductor power module is used to model the front-side MMC. Based on the MV DC voltage requirement, the number of submodules per phase leg is designed to be four (four in the upper arm and four in the lower arm). Multicarrier modulation techniques such as phase-shifted PWM and level-shifted PWM are used to generate gate signals. The model is developed in MATLAB/Simulink, and its performance with respect to input side voltage harmonics, current harmonics, and output DC voltage value has been tested by carrying out several case studies under different controllers such as proportional integrator(PI), fuzzy inference system (FIS), and adaptive neuro fuzzy inference system (ANFIS) for obtaining reference signal for modulation. Level-shifted PWM is used with PI, FIS, and ANFIS, whereas phase-shifted PWM with a technique of introducing DC bias is used with PI controller alone. From the simulation results, it has been observed that better power system current quality of FS-MMC is obtained for PS-PWM (2.16%) than level-shifted PWM (5.22%). Use of FIS and ANFIS with level shift PWM method slightly brings down the current THD values to 2.98% and 2.72%, respectively (decrease by 2.5%). Also, a maximum output DC voltage of 24650 V is obtained for ANFIS with level shift PWM as compared to values obtained by PI with level shift PWM and PI with phase shift PWM.

Dynamic piezotronic effect modulated AlGaN/GaN HEMTs with HfZrOx gate dielectric

High electron mobility transistors (HEMTs) based on AlGaN/GaN heterojunctions show promising applications in high-performance power electronics. Having to face the limited device performance caused by electrically unstable issues, high-κ gate dielectric has been brought into HEMTs (forming MOS-HEMTs) to make a breakthrough. Impressively, a high-κ HfZrOx (HZO) dielectric has been proved to enable the HEMTs to exhibit enhanced performances, e.g., higher output performance, lower leakage current, and better surface properties. Additionally, by coupling piezoelectric and semiconductor properties, piezotronic effect also provides a novel approach for optimizing HEMTs with the use of external stress. Here, we present dynamic piezotronic effect of AlGaN/GaN HEMTs with HZO gate dielectric in pulse voltage modes. When the GaN layer is suffered from tensile stress, the DC and pulse output characteristics of the MOS-HEMTs show significantly decreased trends, and the gate leakage current shows a slight increase. Moreover, theoretical analysis based on Crosslight simulation and a self-consistent model shows that the applied tensile stress can effectively improve the energy band height of triangular potential well and affect the energy states of defects. This work not only provides an inspiration for the modulated device performance in dynamic piezotronic effect, but also expands the application prospect of HEMTs in a strain-controlled platform.

Line‐transient enhancement techniques for multi‐path hybrid DC–DC converter with <1% output overshoot/undershoot

This letter presents two transient enhancement techniques for multi-path switched-capacitor-inductor (MP-SCI) hybrid DC–DC converters to eliminate the line-transient-induced voltage coupling to the converter output. Since the existing input-feedforward method is hard to apply to the MP-SCI converter, the proposed techniques tackle the intrinsic hard-charging property with the MP-SCI topology, preventing the line-coupling current through topology operation reconfiguration and power-switch modulation. The proposed controller also achieves adaptive line-transition detection and automatic flying-capacitor voltage balancing, ensuring a fast line regulation feature. Implemented with an MP-SCI topology for a 9 to 14 V-input to 5 V-output conversion, the proposed control techniques provide an output (VOUT) overshoot and undershoot as low as 0.5% of the output DC level under a 3-V input voltage step. From the simulation, the corresponding output variation reduction can be more than 94% when compared with the existing MP-SCI operations. Besides, the proposed controller is compatible with a voltage-mode (VM) V2 pulse-width modulation (PWM) function, achieving a fast load-transient recovery in six switching cycles and a VOUT variation of 75 mV at a 5 V DC level under a 0-to-3 A load step. The peak conversion efficiency can be as high as 95.5%, and the targeted load current delivery is up to 3 A.

An Intra-Body Power Transfer System With 1-mW Power Delivered to the Load and 3.3-V DC Output at 160-cm of on-Body Distance.

This paper presents an intra-body power transfer (IBPT) system that can deliver power greater than 1 mW across an on-body distance of 160 cm. A system simulation model is built for the characterization of the channel and optimization of the power transfer. Our system analysis and experimental validation demonstrate that 1 MHz is an optimal carrier frequency for IBPT in terms of power delivered to the load (PDL) and power efficiency (PE). Prototype TX and RX boards were built, and an IC was fabricated in a 180-nm CMOS process for the RX. The proposed RX IC consists of a voltage doubler (VD) and a charge pump (CP) to obtain a sufficiently high voltage conversion ratio (VCR). Among various rectifier topologies, the VD is the optimal topology for the power receiver front-end because the parasitic ground coupling capacitances, which inevitably exist in the IBPT system, act as an inherent input-coupling capacitance for the VD. The implemented VD utilizes a dynamic VTH compensation (DVC) for its diode components. Compared to the conventional static VTH compensation (SVC), DVC in the VD reduces the reverse leakage current of the diode, thus maximizing the power conversion efficiency (PCE) and VCR. In addition, the PDL is enhanced by inserting an inductor on the TX board. It reduces the backward-path impedance without increasing the RX volume, boosting the PDL by up to 9.9 times compared to the PDL without the inductor insertion. The proposed IBPT system delivers up to 178.8 μW of power at 11.7% of maximum power efficiency with 3.3-V DC output voltage and even 1.385 mW of power with the inductor insertion, supporting various biomedical wearable sensors, such as ECG sensor modules.

The charging performance in contact electrification of fluorinated ethylene propylene surfaces by electrode bridge

Triboelectricity utilizes triboelectric nanogenerators (TENG) that transfer negative charges between two material surfaces that are in contact. Incomplete flow of charges results in charge accumulation on the material surfaces. In this study, we demonstrated that the accumulated charges could enhance induced output by contact electrification using electrode bridge (EB) to improve charge transfer mechanism. Triboelectric nanogenerator electrode bridge (TENG-EB) was fabricated using synergistic combination of polymer-polymer, polymer-metal, and metal-metal contacts during contact-electrification. Fluorinated ethylene propylene (FEP) film was fabricated using hot pressing technique. FEP crystallinity reached 85.8%, maximum temperature for ε r of FEP was 145 °C, and remanent polarization of FEP polymer was 4.2 µC mm – 2 . The individual events of the charge transfer during contact and separating of TENG-EB could be studied with a single electrode measurement. Separation of FEP, EB and electrode surfaces led to induced output of which signal was 4 times higher than TENG with non-EB. This mechanism utilized DC output that enhanced AC output signal for a given tapping frequency across a rectifier circuit. This new route is proposed for further research, development and invention in alternative energy field including energy harvesting and flexible electronic devices. • Charges event is demonstrated using electrode bridge (EB) induced output performance. • Triboelectric nanogenerator electrode bridge (TENG-EB) was fabricated based on synergistic combination of polymer-polymer, polymer-metal, and metal-metal contacts. • FEP-Al hot pressing is fabricated for electron blocking layer (EBL) has also played a vital role in blocking the electron overflow between a negative material and an electrode. • Output signal of TENG-EB is 4 times higher than that of a TENG non-EB.

A Patch Rectenna With an Integrated Impedance Matching Network and a Harmonic Recycling Filter

A new compact patch rectenna is presented in this letter. It consists of a rectangular patch antenna, a Schottky diode, and a harmonic filter with impedance matching to improve the rectifying efficiency. The filter is realized by a series short-ended one-eighth-wavelength microstrip transmission line, which also balances the capacitive impedance of the diode. The impedances of the diode and patch antenna are matched well by tuning the patch antenna and short-ended transmission line. A meander line is used to build a dc output path. For validation, a rectenna working at 2.45 GHz is designed, manufactured, and measured. A maximum rectifying efficiency of 82.2% is realized when the dc load is 400 Ω at an input power of 22.5 dBm. The proposed patch rectenna has potential applications such as rectenna arrays in wireless power transmission.

Analysis of mm-Wave Multi-Stage Rectifier and Implementation

In the mm-wave frequency band, the rectifier’s sensitivity is the bottleneck of a wireless-powered IoT transponder’s distance. At a meter’s distance, the received power is weak, and transistors in a front end of a wireless power receiver operate in the weak inversion region. This article presents a mathematical analysis of the mm-wave multi-stage rectifier in the low-power region. A design methodology of a 57–64-GHz fully integrated eight-stage rectifier with a bulk-drain connection in 40-nm CMOS technology is presented. Parasitic effects on a multi-stage rectifier are analyzed. Based on the analysis, an intrinsic threshold voltage modulation is applied to improve the sensitivity. A tree-type power splitter is also proposed for the RF power signal’s phase balance. With this method, the RF signal arrives at each stage with an equal phase, and its suppression at the output is improved by 16 dB. This mm-wave rectifier achieves −7.1-dBm input sensitivity at 57 GHz with 1-V dc output voltage. The overall sensitivity from 57 to 64 GHz is better than −4.5 dBm. Compared to other mm-wave silicon-based rectifier state of the arts, the proposed mm-wave rectifier achieves better sensitivity while maintaining a compact size.

Controlling of Cascaded Voltage Source Two Level Inverter Based Grid Connected PV System by Using SVPWM and Quadratic Boost Converter

In this paper, two cascaded voltage source grid-connected inverters (VSI) with Quadratic boost converter (QBC) has been described and simulated as more attractive for a grid to interface with the PV system. The simulation is carried out by using the open loop control method to synchronize the grid with the photovoltaic system and these two inverters are controlled with the Sinusoidal Pulse Width Modulation (SPWM) approach and SV Pulse Width Modulation (SVPWM) skill technique for dynamic behavior. These two inverters individually operate as two-level inverters and after cascading with the transformer will get the three-level output voltage and it is interfaced to a three-phase ac grid. To interface PV system with Grid here using a two-stage method which includes DC to DC converter, three-phase voltage source inverters and cascaded transformer for analyzing dc output voltage, active power and harmonic distortion of current. The Quadratic Boost Converter (QBC) is used to convert from DC to DC for injecting DC supply voltage into the cascading three-phase inverters. In this paper, the entire system is carried out by using with QBC and without QBC and compares the output voltages and total harmonic distortion of current at the grid side.

Integrated PV–BESS-Fed High Gain Converter for an LED Lighting System in a Commercial Building

The demand for electricity is rapidly growing and renewable energy sources such as solar, wind and tidal energy can compensate the demand to a substantial level. Among these, solar energy is abundant, scalable and is cheaper. The generated energy can be used in an efficient way if the DC output is directly supplied to the load instead of converting it to AC. Every electrical system is capable of operating in DC and, for example, energy efficient Light Emitting Diode (LED) lights have become popular as they provides more lumens with less power consumption and also can be directly operated from DC. LED lighting system in large commercial buildings has irradiance levels which vary sigificantly during operation. Extracting maximum power from the energy system and maintaining constant voltage output at different loads is another challenge. This paper proposes a solar Photo Voltaic (PV)-based energy system including Battery Energy Storage System (BESS) for supplying LED lamps to a commercial building through a modified high gain Luo converter. The Perturb and Observe control algorithm has been used for maximum power extraction from a PV cell whereas PI (Proportional Integral) controllers maintain constant output voltage from PV–BESS against different irradiance levels. To supply the desired voltages to the LED lighting system, a modified high gain Luo converter is designed. To make the output voltage constant at different load currents, PI and Sliding Mode Controllers (SMC) are designed with the help of the state-space average model. It is found that the sliding mode controller outperforms the PI controller in terms of behavior in the transient period and tracking capability. The system is simulated using MATLAB/Simulink®. The Sliding Mode Controller has a 95% less transient period and is 75% faster in tracking capability when compared to other controllers. The system could be incorporated with the PV source to obtain green energy.

Design of a Power Regulated Circuit with Multiple LDOs for SoC Applications

In this paper, a power regulated circuit (PRC) is proposed for system-on-a-chip (SoC) applications. The proposed PRC is composed of a limiter, a bandgap reference (BGR), three low-dropout regulators (LDOs), and a bias generator. A high output voltage of an active rectifier is given to the limiter, which limits it to a desired supply voltage for circuits in PRC. The curvature-compensated BGR robust to process, voltage and temperature (PVT) variations are designed to provide a stable reference voltage for three LDOs. The three LDOs are implemented to generate regulated output dc voltages. The proposed PRC is designed and fabricated in 130 nm bipolar-CMOS-DMOS (BCD) technology with die area of 1.9 mm × 0.860 mm, including pads. The measurement results show that the limiter limits the input voltage of (6 V to 20 V) to 5.3 V. The BGR produces a stable reference voltage of 1.24 V with a power supply rejection ratio (PSRR) of −58.6 dB and −51.9 dB at 10 Hz and 1 kHz, respectively. The LDO_5V, LDO_3V, and LDO_1.5V generate regulated output dc voltages of 5 V, 3 V, and 1.5 V, respectively, with dc load regulations of 0.43 mV/mA, 0.70 mV/mA, and 0.28 mV/mA while delivering load currents of 300 mA, 100 mA, and 100 mA, respectively.

Wireless charging for cardiac pacemakers based on class‐D power amplifier and a series–parallel spider‐web coil

AbstractBiomedical implants (BMIs) and biomedical sensors (BMSs) help to improve quality of life, detect diseases, provide monitoring of vital signs, and take over the role of malfunctioning organs. These implants and sensors require continuous battery power to work effectively, but the batteries used are restricted by their limited capacity and lifetime. This research reported here involved the design and implementation of a wireless charging system based on a series–parallel spider‐web coil (WPT‐SP‐SWC), specifically for cardiac pacemakers. The experimental design investigated several important parameters, including air gap, applied source voltage, coil size, and operating frequency. Performance metrics were evaluated in terms of output DC voltage, delivered output power, and power transfer efficiency. The target voltage was 5 V, which is adequate to charge a BMI such as a pacemaker, and three source voltages (5, 15, and 25 V) were tested. The design was examined at six operating frequencies, ranging from 1.78 MHz to 6.78 MHz. The most favorable results were achieved at 1.78 MHz. Power transfer efficiencies at a 10 mm air gap were 95.75% and 92.08% for applied voltages of 5 V and 15 V, respectively. The effectiveness of the proposed system was also validated by comparing the findings with previous articles.

Control the Output of an HTS Dynamo With a DC Background Field

This paper proposed and demonstrated a feedback control method for a high temperature superconducting (HTS) dynamo, which was based on an additional DC coil. This method was based on the theory of macroscopic magnetic coupling effects (MMCE) discovered by Wang and Coombs, "Macroscopic magnetic coupling effect: The physical origination of a high-temperature superconducting flux pump," <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Phys. Rev. Appl.,</i> by using this theory, we had realized very flexible and accurate control of the pumped current in the HTS closed-loop. In this experiments, we had shown that the DC background field has a significant impact on the DC output of HTS dynamo, for instance, by applying a reversed DC bias field to the AC travelling wave generated by the HTS dynamo, we had managed to reverse the pumped current from 69.5A to -28.7A in the YBCO coil, without changing the rotation of HTS dynamo. Based on this experiment, we had developed a feedback control system, i.e., by controlling the direction of the DC bias field, we had managed to control the direction of HTS dynamo's DC output. By doing this, we had realized the adaptive control of the pumped current in the HTS closed-loop, with the control accuracy reached up to about 0.15A. This work verified that the state of superconducting magnetic flux quanta plays an important role in HTS dynamo's DC output, as had been explained in the theory of MMCE. This work had proven the “four-quadrant control” method proposed in MMCE, which may have important implications in HTS applications, especially in applications with high current accuracy such as in magnetic resonance imaging, etc.

Dynamical response and vibrational resonance of a tri-stable energy harvester interfaced with a standard rectifier circuit.

This paper investigates the dynamical response and vibrational resonance (VR) of a piecewise electromechanically coupled tri-stable energy harvester (TEH), which is driven by dual-frequency harmonic excitations. To achieve a stable DC output, the TEH is interfaced with a standard rectifier circuit. Using the harmonic balance method combined with the separation of fast and slow variables, a steady-state response together with the analytical expressions of displacement and harvested power is derived. The multi-solution feature in the amplitude-frequency response is observed and can improve the harvesting performance of the TEH under a low-frequency environment. There is an optimal time constant ratio and electromechanical coupled coefficient to maximize the harvested DC power. Meanwhile, the VR phenomenon of the TEH is explored through the response amplitude of the low-frequency input signal, which implies that an appropriate combination can induce the occurrence of VR and improve the rectified voltage. Similarly, the nonlinear stiffness coefficients can be adjusted by changing the magnet distance to induce the appearance of VR. The theoretical solutions are well supported by numerical simulation and experimental verification. Specifically, the theoretical analysis and experimental evidence illustrate that the harvested power under the VR effect is much higher than that without VR.

A Kilo-Amp Linear-Motor Type Flux Pump

A kilo-amp linear-motor type flux pump with the maximum output DC current exceeding 1610 A had been designed and manufactured. We had optimized the large-current flux pump based from the previous design, and shortened the travelling wavelength of the flux pump, and simulated its magnetic density distribution with COMSOL Multiphysics, and obtained the present design parameters after analysis. We had placed 12 superconducting single loops side by side in the air gaps on both sides of the flux pump, and had used the flux pump to charge them. We had applied different magnetic flux density in the air gap, the maximum DC output current of the flux pump was measured at 1619 A in the liquid nitrogen at 77 K. We have carried out theoretical analysis on the direction of the pumped current on both sides of the flux pump, while had changed the polarities of the DC windings to make sure that the current directions on both sides are the same. Comparing with the traditional superconducting power supply of the same output current level, this flux pump had not only eliminated the current leads, but also reduces the cost, size and energy consumption of the power source by at least one order. Finally, we designed the prototype of the kilo-amp linear-motor type flux pump to measure the critical current of the superconducting cables.