Showing papers by "Yongjian Li published in 2022"

Analysis of Magneto-Mechanical Coupling Model of Anodic Saturable Reactor Considering Anisotropy with UHVDC Converter Valve

Abstract: As a vital component in the converter valve of Ultra-high Voltage (UHV) DC transmission, the anodic saturable reactor is often affected by the effect of magnetic, thermal and stress field in actual operation, so the simulation under ideal circumstances cannot accurately evaluate the performance of the reactor. In order to simulate the complex effect of magnetic and mechanical field, a coupled finite element model of the anodic saturable reactor core considering anisotropy is established, which includes electromagnetic anisotropy parameters, mechanical anisotropy parameters and magneto-mechanical coupling parameters. Besides, the vibration testing platform is built. The magnetic flux density and vibration acceleration are measured at different magnetic induction intensity levels of the core. The reasons for the difference between simulation and measurement results are analyzed. This research is helpful to increase the accuracy of calculation in the magneto-machine coupling simulation research of electrical equipment and provide reference for the optimization direction of magneto-machine coupling model.

Improvement of core loss model under AC–DC hybrid excitation and verification based on TEAM P21 extended model

Abstract: HVDC (High Voltage Direct Current) transmission equipment generally works under AC–DC hybrid excitation (with both DC-bias components and harmonics), increasing the loss of magnetic components and even causing local overheating. In order to study the influence of AC–DC hybrid excitation on the performance of magnetic materials, the loss properties of electrical silicon steel under AC–DC hybrid excitation are measured and modelled. This paper improves the iron loss model based on the Bertotti loss model by introducing a new term caused by DC bias. In addition, the improved loss model is combined with the transient loss model, and the iron loss calculation is performed based on the results of the TEAM P21 extended model. The comparison between the calculated and measured loss shows that the improved loss model is more accurate than the traditional one.

MIS-Based GaN Schottky Barrier Diodes: Interfacial Conditions on the Reverse and Forward Properties

Abstract: In this work, we have conducted systematic studies on the interfacial conditions for gallium nitride (GaN)-based trench metal/insulator/semiconductor (MIS)-type barrier Schottky rectifier (TMBS) with the help of the T-CAD tools. Our results show that the donor-type traps tend to reduce the Schottky barrier height ( ${q}\varphi _{s}$ ), which weakens the charge coupling effect, increases the leakage current, and finally reduces the breakdown voltage (BV). On the contrary, the acceptor-type traps at the contact interface and mesa sidewall will increase ${q}\varphi _{s}$ and the turn-on voltage ( ${V}_{\mathrm{ON}}$ ) because they can capture electrons in the mesa region and show the negative polarity. This then enhances the electron depletion at the contact interface and the mesa sidewall, resulting in an increase in ${q}\varphi _{s}$ and ${V}_{\mathrm{ON}}$ . Therefore, this process can increase the reverse blocking characteristics. However, for solving the complicated interfacial conditions in the Schottky contact region, we propose using an MIS structure with a 1-nm Al2O3 insulation layer for the GaN-based TMBS rectifiers. Based on the results, the tunneling process and thermionic-emission (TE) process take into account for the current transport mechanism for the MIS-TMBS rectifiers. Meanwhile, the 1-nm thick Al2O3 interlayer increases the effective Schottky barrier height ( ${q}\varphi _{s} + {q}\varphi _{T}$ ), which significantly reduces the reverse leakage. In addition, this design offers more freedom in selecting the Schottky contact electrode for the MIS-TMBS rectifier.

Multiobjective Particle Swarm Optimization Design of Permanent Magnet Machine for Torque Density Improvement and Torque Ripple Suppression

Abstract: Multiobjective particle swarm optimization (MOPSO) is applied to optimize six structural parameters of a 27-slot/30-pole permanent magnet synchronous machine (PMSM) with external rotor, including slot opening, magnet height, stator outer radius, thickness of rotor yoke, width of tooth, and stack length. Three conflicting objectives, namely torque, torque ripple, and volume, are improved simultaneously after applying MOPSO. MOPSO is combined with Kriging surrogate model (KSM) of torque and torque ripple, which reduces number of times to use time-consuming finite element analysis (FEA) in the process of machine optimization. KSMs are established based on samples obtained by FEA, which reflects relations between various structural parameters of machine and torque and torque ripple.

Localized magnetic properties measurement of interlocking core laminations

Abstract: Purpose In rotational alternating current machines, interlocking is a commonly used manufacturing method to fix laminated silicon steel cores. The purpose of this study is to measure the localized magnetic properties more comprehensively and to analyze the deteriorated magnetic properties caused by interlocking more accurately. Design/methodology/approach A movable B–H sensor is designed in this paper. The localized magnetic properties measurement was performed to investigate the magnetic properties around the interlocks with various sizes, various orientations and various numbers of laminations. Then, the damaged area caused by the interlocking was quantified, and the magnetic degradation of different degrees is layered. Findings The measurement results have shown that the interlocks with larger sizes, along the transverse direction and on 10-layer laminate, will lead to more serious magnetic degradation, and the maximum loss increment can reach up to 70%. Originality/value This work is an improvement and optimization based on the previous overall magnetic measurement of the interlock. The quantitative results of the localized magnetic measurement will have a certain significance for the accurate modeling and simulation of the electrical machines and provide valuable guidance for the optimization of the actual production process of the motor.

Punching effects on local magnetic properties near the edge of nonoriented electrical steels

Abstract: Purpose The purpose of this study is to investigate the effect of punching on the local magnetic properties of the nonoriented electrical steel sheet. Design/methodology/approach A microcomposite B–H sensor consisting of a pair of B probes with a spacing of 2 mm and a 1.8 × 1.8 mm2 H coil is designed. The region and degree of local magnetic properties degradation caused by punching can be quantitatively analyzed by flexibly moving the composite B–H sensor. The influence and physical mechanism of punching on the hysteresis loss, eddy current loss and excess loss are analyzed based on the Bertotti loss separation theory. Findings This study investigates the deterioration effect of the punched nonoriented electrical steel. The permeability near the edge decreases, and the core loss as well as the microhardness increases. The region of magnetic property deterioration is dependent on the area of work hardening. Originality/value The microcomposite B–H sensor can be used to measure the magnetic properties near the edge of electrical steel sheets under different processing conditions. This study provides the possibility of precise magnetic property model of the motor core after punching, especially valuable for motors without annealing process.

A Novel Derivative Free Methodology for Topology Optimization

Abstract: Most existing methods for topology optimization update the material distribution iteratively based on the derivative information. However, the calculation of gradient is of low accuracy and even unavailable in some cases. To this end, this paper proposes a novel derivative free methodology for TO based on affine transformations and Boolean operations. Specifically, the proposed method selects the basic structures to constitute a new topology. Affine transformations and Boolean operations are employed to represent the evolvement and the way of combinations of the basic structures. The numerical result has validated the proposed method.

Magnetic Properties Measurement and Loss Modeling of Nanocrystalline Cores with Different Stack Thicknesses

Abstract: Nanocrystalline materials are often used to make cores for high-frequency transformers and reactors. It is important to reduce core loss for their reliable operation. In this paper, the loss of nanocrystalline core with different stack thicknesses at different frequencies is measured. The hysteresis loss and dynamic loss are obtained by the loss separation model, and the variation of two losses with stack thickness and frequency is shown. A modified loss separation model related to the stack thickness is obtained. The calculated loss obtained from the loss model show great agreement with the measured results. This loss model would be helpful for the design and manufacture of high frequency transformers and reactor cores.

A hybrid dynamic hysteresis model based on the Preisach model and stacked auto-encoder

Abstract: With the increase in power electronic equipment in power system, the excitation of ferromagnetic materials often involves a large number of harmonics. Therefore, it is necessary to construct an accurate dynamic hysteresis model to adapt to this complicated operating state of electrical equipment. In this paper, a Hybrid Dynamic Hysteresis Model (HDHM), which can effectively characterize the harmonic excitation of materials is studied based on the Preisach model and Stacked Auto-Encoder (SAE) model. The static part of this model takes the form of the inverse Preisach model. And the Multiple Dynamic Hysteresis Model Set (MDHMS) is constructed by multiple dynamic models of eddy currents and excess characteristics of the ferromagnetic materials. The dynamic part of the HDHM takes the form of the model structure combining the Stacked Auto-encoder and the MDHMS. The calculation results of the hysteresis loop and ferromagnetic loss in the harmonic condition of silicon steel sheet proves the validity of this model. Moreover, compared with the conventional dynamic hysteresis model, the HDHM has better accuracy and generalization ability.

Optimal Design and Verification of Stacking-Hole in Transformer Core Based on Analysis of Magnetic-Fluid-Thermal Coupling

Abstract: The loss and local temperature of the transformer core increases due to the stacking hole. To minimize the impact of the hole, a novel shape of the hole is designed and proposed in this paper. The finite element method and the experimental method are used to verify the optimization effect of the proposed novel hole. Based on the finite element method, the model of the core with the hole is established to simulate and calculate the core loss of the transformer under no-load condition. Subsequently, the loss as heat source maps into the thermal field to establish the magnetic-thermal-fluid coupling model. Considering the dependence of temperature on material properties, the convective heat transfer process is simulated and the temperature rise is calculated. The impacts of the traditional hole and novel hole on the transformer performance are compared and analyzed. Based on the experimental method, the loss and local temperature rise caused by the traditional hole and novel hole are quantitatively measured and compared. The simulation and experimental results show that, compared to the core without the holes, the loss is increased by 10-15% due to the traditional holes, the loss caused by the novel holes increases by 3-6% and the maximum optimization of the loss is up to 11%. The core with novel holes achieves an excellent performance which is superior to the core with current holes.

Anti-saturation Shielding Coil with Coupling Enhancement for Wireless EV Charging

Abstract: The digest proposes a shielding coil featuring anti-saturation and coupling enhancement for wireless electric vehicle (EV) charging. The shielding coil is powered by the induced current and operates under reactive shielding mode using a tunable capacitor. By adjusting the connection of the dotted terminals, the direction of the current in each part of the shielding coil is designated. The coupling enhancement is achieved by the inner shielding coil carrying the current in-phase with the trans-mitting coil. The solenoids wounded on four edges of the ferrite generates opposing fluxes on corresponding edges to reduce the magnetic flux density in the ferrite to prevent saturation. The outer shielding coil carries current in a reversed direction of the transmitting current to reduce the leakage field outside of the target area. The proposed design significantly reduces the magnetic flux intensity in the ferrite to prevent saturation while not distinctively impact the coupling enhancement in one coil design.