Small DC Research Articles

Suppressing DC Current Injection in Transformerless Grid-Connected Inverter Using a Customized Current Sensor

Transformerless grid-connected inverters are widely applied due to their low cost and small volume. But the dc current injection (DCI) is one of the main problems that need to be solved. It is difficult to measure milliamperes dc current mixed in large (≥10 A peak) ac current, which causes it difficult to suppress the DCI using the ordinary current sensor (CS). To solve this problem, a novel CS is proposed. It uses a current transformer (CT), a power amplifier, and an additional winding to cancel the ac magnetic field in a commercial current sensor (CCS). Under this circumstance, the CCS is used to detect the remaining small dc magnetic fields. As the range of CCS does not need to be large, the dc current measurement error is significantly reduced. Meanwhile, the CT can measure the ac current and provide feedback to control the inverter. In this way, the proposed CS can replace the original CS instead of adding a new CS to the inverter, which relatively reduces the cost. The volume of CT is relatively small; hence, the CT can be integrated with the CCS, which achieves a relatively small volume of the sensor. A dc current suppression experiment using a 1.5-kVA transformerless grid-connected inverter verified the effectiveness of the proposed technique.

Interference effects induced by a precessing easy-plane magnet coupled to a helical edge state

The interaction of a magnetic insulator with the helical electronic edge of a two-dimensional topological insulator has been shown to lead to many interesting phenomena. One of these is that for a suitable orientation of the magnetic anisotropy axis, the exchange coupling to an easy-plane magnet has no effect on DC electrical transport through a helical edge, despite the fact that it opens a gap in the spectrum of the helical edge [Meng {\em et al.}, Phys.\ Rev.\ B {\bf 90}, 205403 (2014)]. Here, we theoretically consider such a magnet embedded in an interferometer, consisting of a pair of helical edge states connected by two tunneling contacts, at which electrons can tunnel between the two edges. Using a scattering matrix approach, we show that the presence of the magnet in one of the interferometer arms gives rise to AC currents in response to an applied DC voltage. On the other hand, the DC Aharonov-Bohm effect is absent at zero temperature and small DC voltages, and only appears if the applied voltage or the temperature exceeds the magnet-induced excitation gap.

Current switching of valley polarization in twisted bilayer graphene

Twisted bilayer graphene (TBG) aligned with hexagonal boron nitride (h-BN) substrate can exhibit an anomalous Hall effect at 3/4 filling due to the spontaneous valley polarization in valley resolved moir\'e bands with opposite Chern number [Science 367, 900 (2020); Science 365, 605 (2019)]. It was observed that a small DC current is able to switch the valley polarization and reverse the sign of the Hall conductance [Science 367, 900 (2020); Science 365, 605 (2019)]. Here, we discuss the mechanism of the current switching of valley polarization near the transition temperature, where bulk dissipative transport dominates. We show that for a sample with rotational symmetry breaking, a DC current may generate an electron density difference between the two valleys (valley density difference). The current induced valley density difference in turn induces a first-order transition in the valley polarization. We emphasize that the intervalley scattering plays a central role since it is the channel for exchanging electrons between the two valleys. We further estimate the valley density difference in the TBG/h-BN system with a microscopic model and find a significant enhancement of the effect in the magic angle regime.

Photonics-Based RF Signal Phase Detector With Wide Operating Frequency Range and High Resolution

A new topology that generates a DC voltage whose value is depending on the phase difference of two input RF signals is presented. It is implemented by the mixer concept. With the use of microwave photonics, the mixer-based phase detector can be operated over a very wide frequency range. It also has the advantages of high phase detection resolution, small phase detection error, and small DC offset and phase offset. The phase detector can be constructed using off-the-shelf components including a single integrated optical modulator and a low-speed balanced detector. Measured results on the phase detector demonstrate a 0° to 180° RF signal phase difference detection range for 3.5 GHz to 18 GHz input RF signal frequencies, less than ±3° phase detection error and 2° phase detection resolution.

Trends in the Evolution of Small DC Motors to Reduce Environmental Load

Trends in the Evolution of Small DC Motors to Reduce Environmental Load

Simultaneous and continuous characterization of reversible and irreversible heat of lithium-ion battery using wavelet transform technique

Entropy coefficient and internal resistance of lithium-ion batteries are the key thermal properties needed for an optimal design of thermal management systems. Currently, these two parameters are measured separately with either potentiometric or calorimetric method and electrochemical impedance spectroscopy (EIS) or hybrid pulse power characterization (HPPC) method, respectively, which requires different equipment and extra experimental time. In addition, both results are discrete at given state of charge (SOC) points, which does not provide the values in-betweens. In this paper, we proposed a fast and highly efficient calorimetric method based on an isothermal calorimeter that allows for simultaneous and continuous characterization of these two parameters. The method is developed using the wavelet analysis technique, where a sinusoidal AC current with a small DC current offset is used as an input for battery and the heat generation rate is measured as an output using the calorimeter. Then, the two parameters are determined simultaneously in time-frequency domain. The results are compared with those measured by the potentiometric method and EIS analysis, respectively with respect to measurement time and accuracy. The saved time is 95%, and the proposed method maintains the accuracy. In addition, the obtained parameters are used to calculate the total heat generation, which shows a good agreement with the experimental measured one both in the shape and tendency.

Modelling of magnetostrictive vibration and acoustics in converter transformer

The converter transformers are susceptible to more noise and vibration when compared to power transformers due to the presence of DC bias in the DC transmission line. DC bias occurs mostly due to inaccuracies in valve firing resulting in a small residual DC oscillating around zero. Measurement of magnetostriction becomes significant as it influences the vibration and noise from the core. Hence, a magnetostrictive model of a high-voltage DC converter transformer has been developed. This work analyses the vibration and noise acoustics under such an occurrence. First, the core of the transformer model is designed in the stepped configuration for 240 MVA; then, magnetostrictive vibration is analysed by using suitable modules of COMSOL Multiphysics at different magnitudes of DC bias. The physics of noise has been interfaced using the Acoustics Module, and the results are recorded. Finally, artificial neural network model is developed for the prediction of vibration and noise characteristics of the model. The fitting process of neural network was then remodelled using various optimisation techniques, namely teaching–learning-based optimisation, particle swarm optimisation, biogeography-based optimisation, simulated annealing and binary coded genetic algorithm, and their results were compared to obtain the best-suited method using % mean-squared-error evaluation.

Stacked Low-Inertia Converter or Solid-State Transformer: Modeling and Model Predictive Priority-Shifting Control for Voltage Balance

This article presents control challenges of stacked low-inertia converter (SLIC) or cascaded reduced dc-link solid-state transformer (SST) and proposes a novel model predictive priority-shifting (MPPS) control with implicit modulator and a discrete-time large-signal model for voltage balancing and dc-link regulation. Low-inertia converters, featuring small electrolytic capacitor-less dc links, dramatically reduce cost, size, and weight compared to conventional solutions. However, without a large dc-link buffer, the input and output are tightly coupled, leading to significant control challenges. The control becomes even more challenging with these converters stacked input-series output-parallel (ISOP) for medium-voltage (MV) grid, which causes coupling between the modules besides the coupling within each module. This article analyzes the multiobjective, multidegree of freedom control problem, using the modular soft-switching solid-state transformer (M-S4T) as an example of the SLIC. First, distribution of control efforts under controller saturation is critical because multiple control objectives can be conflicting, especially when the module voltages are unbalanced and are being restored. The MPPS can shift the priorities to address this issue. Second, due to the low inertia and high dc-link ripple, classic space vector pulsewidth modulation, average model with small-ripple assumption, and control design based on small-signal model cannot accurately modulate, model, and control the nonlinear reduced dc link. Therefore, a discrete-time large-signal model of the M-S4T is established to derive the predictive control in the MPPS. The MPPS and the PI control are compared in MV simulations to show the issue of applying the PI to the SLIC and the effectiveness of the MPPS for voltage balancing and dc-link regulation in a deadbeat manner. Finally, the proposed control is tested on a 5-kV ISOP SiC SST prototype to verify priority shifting to address controller saturation issue and fast and robust voltage balancing.

PI-like fuzzy based synchronous SEPIC converter control for PV-fed small scale irrigation DC pump

For off-grid, standalone solar-fed water pumping has become a very viable option for small householder farmers. Appropriate configuration and control to suit this specific application are required. Buck, boost, and buck-boost converters are used to ensure impedance adaption between the solar PV generation and the load. However, these converters have switching harmonic problems. This problem is solved by the use of a single-ended primary inductor converter. Thus, a single-ended primary inductor converter is designed to overcome these drawbacks. Therefore, the objective of this paper is to design a single-ended primary inductive converter with a PI-like fuzzy controller. In this paper, synchronous SEPIC converter with PI-like fuzzy controller for PV-fed pumping system is modeled and designed. The system performance at different input conditions is evaluated. PI and PI-like fuzzy controllers have been compared using MATLAB/SIMULINK. PI-type fuzzy controller is less sensitive to input parameters variation than PI due to auto-tuning capability. Less than 2% output variation is recorded between 200 and 1000 W/m2 irradiance. This show that output voltage is less sensitive to the input solar radiation with this SEPIC converter control. The steady-state result obtained in speed and flow rate were 141.4 rpm and 1.56 l/s, respectively, and the voltage error was 1.4 V. Thus, PI-like fuzzy controller was used to reduce the steady-state error. The results obtained with PI-like fuzzy controller in speed and flow rate were 143.6 rpm and 1.624 l/s at 6 m head, respectively. The voltage error is 0.2 V which is less than the PI converter error (1.4 V).

Design of a flyback high-efficiency switching power supply

Switching power supplies are widely used in automotive, aviation, and DC speed control fields. Its biggest requirement is stable output and high efficiency. It is usually realized by resonant converters, but its control circuit is complex and the output ripple is large. In this paper, a new type of flyback switching power supply is designed using a flyback conversion circuit and a single-tube self-excited conversion circuit. Experiments have shown that the designed switching power supply improves the efficiency and reliability of the power supply while obtaining a small ripple, continuously adjustable, and stable DC voltage.

Neural Networks Based Shunt Hybrid Active Power Filter for Harmonic Elimination

The growing use of nonlinear devices is introducing harmonics in power system networks that result in distortion of current and voltage signals causing damage to power distribution systems. Therefore, in power systems, the elimination of harmonics is of great significance. This paper presents an efficient techno-economical approach to suppress harmonics and improve the power factor in power distribution networks using Shunt Hybrid Active Power Filters (SHAPF) based on neural network algorithms like Artificial Neural Network (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Recurrent Neural Network (RNN). The objective of the proposed algorithms for SHAPF is to enhance system performance by reducing Total Harmonic Distortion (THD). In our filter design approach, we tested and compared conventional pq0 theory and neural networks to detect the harmonics present in the power system. Moreover, for the regulation of DC supply to the inverter of the SHAPF, the conventional PI controller and neural networks-based controllers are used and compared. The applicability of the proposed filter is tested for three different nonlinear load cases. The simulation results show that the neural networks-based filter control techniques satisfy all international standards with minimum current THD, neutral wire current elimination, and small DC voltage fluctuations for voltage regulation current. Furthermore, the three neural network architectures are tested and compared based on accuracy and computational complexity, with RNN outperforming the rest.

基于STC单片机的小型直流电机变频调速控制器系统设计

基于STC单片机的小型直流电机变频调速控制器系统设计

PENGARUH JUMLAH SUDU PADA PROTOTYPE PLTMH DENGAN MENGGUNAKAN TURBIN PELTON TERHADAP EFISIENSI YANG DIHASILKAN

Turbine is a component that plays an important role as an energy converter to be ableto generate electricity in the Micro Hydro Power Plant (MHP). The turbine used in this prototypeis a Pelton tubine. The Pelton turbine is a type of impulse turbine consisting of two blades as aprelude receiver for water jets from the nozzles by utilizing high water heads even though thewater discharge is small. This research will discuss the effect of the number of blades on therotation produced by the Pelton turbine and generator so that it can be seen the voltage,current, power produced that affects the torque value and efficiency obtained on the prototypeMHP. This study aims to obtain a turbine runner with the number of blades that can produce thehighest efficiency, then a variation of the pelton turbine runner is made with different number ofblade parameters from the runner with the number of blades according to the calculationobtained from the reference. Variations in the number of blades used are 14 blades, 16 blades,18 blades, 20 blades, and 22 blades. The results showed that the addition of the number ofblades starting from the smallest caused the performance of MHP to increase, the highestoutput obtained was using a turbine runner with a number of 22 blades which resulted in aturbine rotation of 852.2 rpm before the generator coupled and 497.2 rpm after coupling thegenerator. Generator rotation is 2133.8 rpm, Generator Voltage is 15.72 volts, Generator poweris 33.7 Watts and Torque is 0.6 Nm. The efficiency value using a runner with a number ofblades 22 is 4.54%. The resulting efficiency value is very low because the MHP prototype in generation is less effective and uses a small generation capacity DC generator, so it cannotgenerate power as much as hydraulic power.

Analysis of DC Motor Current Waveforms Affecting the Accuracy of “Sensorless” Angle Measurement

A typical approach for “sensorless” angle or speed measurement of dc machines is to evaluate periodic oscillations in the electrical motor signals which is also known as ripple counting. This method is usually applied to the current signal and very susceptible to counting errors due to different waveforms caused by various influences. In this article, the steady-state current waveforms of a small dc machine are investigated to identify the causes leading to incorrect counting results. The focus is on production tolerances and changes over the service life of the motor. This is done both by the experimental and simulative investigations and analysis of the signals in the time and frequency domains. For the simulative investigation, much attention is paid to suitable modeling for this particular task and parameter variations are performed to separate the influences on the current signal. The goal is a better understanding of the different waveforms and their causes as a basis for the development of future error-free counting algorithms.

Electrical Safety Considerations of Neutral Blocker Placements for Mitigating DC

The dc in a power network might be caused by geomagnetic disturbances that result from either a geomagnetic storm or a high-altitude nuclear detonation. The augmenting trend of inverter-based resources is also acting as a source of small dc injection into the power systems. As the resultant, dc could lead toward a possible power system failure, a myriad of neutral blocking devices (NBDs) have been proposed, where, these devices are installed between the neutral and ground of wye-grounded transformers. However, the electrical safety assessment of these devices is critical prior to adding them to the grid as they might raise serious concerns both for the power equipment and the power system maintenance staff. This work is the first effort toward hazard identification and quantitative risk assessment associated with NBDs. It proposes a risk management framework for augmented electrical safety pertinent to these devices. Later, it analyzes the proposed neutral blocking strategies and highlights the associated risks to the operational safety of these installations, particularly concerning electromagnetic pulse (EMP) attacks, cyber threats, and equipment malfunction. Finally, an ideal NBD operational design is proposed incorporating a variety of risk reduction measure to avoid any hazardous situation arising from such installations. This work could provide a guideline for the electric utilities and academic researchers to consider these safety implications prior to proposing or installing these devices.

Tuning the dynamics in Fe3O4 nanoparticles for hyperthermia optimization

The AC magnetic susceptibility (ACS) of Fe3O4 nanoparticles was measured between 10 kHz and 4 MHz at different temperatures and in applied DC fields. In this frequency range, magnetostatic interactions impact magnetization dynamics even for dilute assemblies. The ACS spectrum of relaxation frequencies changes both with temperature and the addition of a small DC field. Because both the relaxation peak frequency and amplitude can be tuned with the DC field, these results could be applied to magnetic hyperthermia applications to optimize heat delivery.

Apparatus for loss measurements under multidirectional and dc-bias flux in electrical steel laminations

Conventional standardized power loss measurements for electric steels are performed at flux densities with a single sinusoidal and unidirectional excitation. However, the flux inside electrical steel laminations can deviate significantly from the standard condition, and the loss is sensitive to such deviations of the flux in time and space. In this article, we describe the design and construction of an apparatus for loss measurements under two scenarios: (1) The main flux in the rolling direction is superimposed with flux in either the transverse or normal direction, while varying magnitude and phase angle between two fluxes and (2) the main flux having a dc-bias. The main flux in the rolling direction is generated in a square lamination frame by the current in excitation coils. The transverse and normal direction fluxes are generated by the current in auxiliary excitation coils wound around powder cores. The dc-bias flux is created either by an ac current with a small dc offset in the excitation coils or by a separate coil excited by a dc current. We implement and compare the two dc-bias methods and discuss the commons and differences. Finally, we present experimental results showing the possibilities for loss measurements under the combined action of magnetic flux in different directions and under dc-bias.

Current-induced generation of skyrmions in Pt/Co/Os/Pt thin films

We report the generation of skyrmions under the combined influence of applied perpendicular magnetic fields and electrical currents in Pt/Co/Os/Pt thin films. Under no electrical current, skyrmions are found to nucleate at specific defect sites distributed throughout the film and remain pinned at these sites for small dc electrical currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$ . For larger currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$, skyrmions can either move or elongate in the direction of the current flow to form stripe domains. We further observed the current-induced generation of skyrmions through two specific processes: (i) stripe domains depinning from defect sites and collapsing into skyrmions, or (ii) skyrmions breaking off from pinned stripes; the rate of these stripe-to-skyrmion creation phenomena is proportional to the applied current density. Additionally, we observe a sudden increase in the skyrmion population immediately after the applied current is removed----a behavior attributed to stripe domains previously elongated by the electrical current collapsing back into skyrmions.

Magnetic Nanoparticle Detection by Utilizing Nonlinear Magnetization for Sentinel Lymph Nodes of Breast Cancer Patients

To minimize the invasiveness and improve the patient's quality of life, sentinel lymph node (SLN) biopsy with magnetic nanoparticles (MNPs) containing superparamagnetic iron oxide is performed on breast cancer patients. Identifying the first SLN by quantification of the amount of MNPs can help to investigate the cancer metastasis. We developed the device for performing iron quantification during surgery. The compact desktop-size device can be easily introduced into operation rooms, and simple system of the device enables identification of the first SLN. We investigated the optimum nonlinear magnetic responses that are attributed to magnetic relaxations under moderate small ac and dc magnetic fields (~1 mT) and found that ac magnetic fields with <; 5 kHz are effective in the detection of MNPs. In addition, our clinical trials revealed more iron (40 μg) in the first lymph node than in the second lymph node (10 μg), clearly indicating intraoperative quantification in the first node.

Design and Construction of PIC-Based DC Motor Speed Controller for Small Robots

Because of their good speed control and high torque, DC motors are widely used in many industrial and robotic applications. Robotic application of DC motors often required, in addition to driving loads at constant speed or torque, the ability to vary the speed of the motor. An efficient and economically feasible intelligent DC motor speed controller is designed and constructed based on the rules of closed loop feedback control system. There are two main parts in the hardware development: PIC16F873A microcontroller and its support circuitries and external interface circuitries between motors and microcontrollers. Data processing and control program (firmware program) was run on PIC microcontroller and its on-chip A/D converter, PWM module and external circuitry was used to send and receive the data signal from the motor for control application. The firmware program was written in assembly language and converted to machine language (Hex code) by using Microchip MPASM macro assembler. These machine codes are downloaded into the PIC microcontroller by using EPIC microcontroller programmer. Through prototyping and implementing on a PIC microcontroller, the system was then be tested and used to control the speed of a small DC motor until the required criteria were achieved.