Calculation of electromagnetic forces are applied to the design of electrical machines, such as the magnetic levitation systems, actuators, and various motors and so on. To accurately pursue the dynamics of electrical machines, the calculation of electromagnetic forces must be accurate. The calculation accuracy of the electromagnetic force using the finite element method is substantially dependent on the configuration of the finite elements. When the analysis model is discretized by the finite element mesh with bilateral symmetry, the accuracy of electromagnetic force tends to be better owing to the offset of the error components by the bilateral meshes. However, the application of an asymmetric finite element mesh affects the accuracy of electromagnetic force. This is because the offset generated by the bilateral meshes is not achieved. Since controlling the mesh distribution with bilateral symmetry has limitations due to the asymmetry of the analysis target, it is effective to estimate the numerical calculation error of the electromagnetic force rather than symmetrical mesh generation. In this study, an estimation method of the error component of the electromagnetic force is proposed and applied to the analysis model in a magnetostatic field problem. Furthermore, the error estimation for a model with the nonlinear magnetic property including an iron core is proposed. The validity of the proposed method is illustrated compared to the conventional nodal force method.

Among the various types of motors, the induction motors (IMs) are the most commonly used. One approach to improve the performance of IMs is involved using a design optimization method that combines electromagnetic field analysis with topology optimization (TO). The gradient-based method is considered superior to the other methods from the viewpoint of the convergence speed and elapsed time when dealing with IMs with long transient phenomena. The time domain adjoint variable method (TDAVM) is generally used to calculate the gradients of the objective function based on time integration. TDAVM is highly efficient in calculating objective function gradients; however, it requires the storage of state variables at all time steps for the temporal discretization. In this study, a memory reduction technique in which state variables are approximated by a discrete cosine transform (DCT-II) is proposed to reduce the memory consumption of the TDAVM in TO for an IM driven by a three-phase pulse width modulation inverter, which is applied to the strongly coupled analysis of magnetic fields and electric circuits. By applying the DCT-II to the TDAVM, an optimized structures similar to those derived from the conventional TDAVM are obtained. Moreover, 85.6% memory reduction was achieved.

This paper presents a novel topology optimization approach for the design of synchronous reluctance motors based on an autoencoder (AE) combined with the level set (LS) method. As the initial shapes of the LS method, the technique uses the shape generated by the AE, which learns the relationship between the objective function values and the design shapes in the optimization process. The proposed method trains the network parameters such that certain latent variable components represent shape features that are correlated with targeted objective functions. Consequently, shape variations that correspond to changes in multiple objective function values can be independently and continuously visualized. This enables the efficient preparation of new structures that are expected to have high performance. Finally, the AE-generated shapes are used as the initial shapes for LS optimization to derive practical Pareto solutions.

This paper presents a design of a load-independent wireless power transfer (WPT) system with multiple receivers and unified coupling coils. Various applications in each receiver require individual output voltages. In the proposed WPT system, LCC filters are adopted in front of transmission coils to improve the degree of freedom. The design theory of the LCC filter for achieving load-independent operation and the required individual output voltage is given. Consequently, the receiver can obtain the specified output voltages in each transmission coil; however, the variations of the coupling coefficient affect the output voltage. Since the load-independent operation can be maintained by satisfying specific conditions of the LCC filter, the proposed system always achieves zero-voltage switching and constant output, regardless of receiver load resistances in high power-delivery efficiency. From the experimental results, the effectiveness of the proposed WPT system and the validity of the design strategy can be confirmed. The experimental prototype of the two-receiver WPT system achieved 86.1% power-delivery efficiency at 6.78MHz operating frequency and 19.6V and 29.7V output DC voltages.

Magnetic bearings (MBs) can support a rotating shaft without any contacts using electromagnetic force. A typical five-degree-of-freedom (5-DOF) magnetic levitation system uses two radial MBs and one axial MB. However, the size of this system may become large due to the combination of three MBs, posing the issue of reduced critical speed with increased shaft length. Therefore, combined radial-axial MBs (CRAMBs) have been proposed to address these challenges. In this study, reluctance-type CRAMBs capable of providing support in three-degree-of-freedom with a high suspension force density are proposed. As the CRAMBs do not use permanent magnets, they are easy to assemble and can operate in cryogenic and high-temperature environments. This paper presents the structure designed to increase the opposing surface area where the magnetic attractive force acts, to achieve a high suspension force density. The suspension force and bearing stiffness of the proposed structure are analyzed using a three-dimensional finite element method (3D-FEM). Further, a 5-DOF magnetic levitation system is constructed using the proposed CRAMB and radial MB. The proposed system is then compared to two types of conventional 5-DOF magnetic levitation systems (Separated Type A and B) based on axis vibration analysis using 3D-FEM. Critical speed maps for the first, second, and third (bending first) modes of each system, along with their corresponding deformations, are displayed. The analysis shows that reducing shaft length in the proposed system leads to an increase in the critical speed of the first bending mode. In addition, loss characteristics when the rotor is rotated are evaluated.

The high-pressure water level control system is essential for controlling the economic benefits of power plants. The study aimed to explore the utilization of digital twin technology combined with least squares support vector machine (LSSVM) in control loop state monitoring. By constructing digital twin models and applying LSSVM, we aimed to achieve high-precision monitoring of the control system states and facilitate effective prediction of abnormal situations. During model training and error testing, the outcomes demonstrated that the model could accurately match the sample data, and the output error of the model was primarily concentrated in the [-0.1, 0.1] interval. In the case of changes in system characteristics, the model effectively adapted and maintained a low mean square error via the introduction of an online update strategy. The model exhibited a good fit and prediction accuracy for the specific monitoring of the water level control circuit of a high pressure heater. The effectiveness of the model was further validated through measurements of the water level process at different time periods. Thus, this study demonstrated the effectiveness and feasibility of combining digital twins and LSSVM in control system monitoring. The proposed method facilitated cost reduction and efficiency increase in power plants, thereby promoting their production and development level.

The operation of interior permanent magnet synchronous motors (IPMSMs) can deviate from the optimal point for vector control to magnetic saturation of inductance and variations in the magnet flux caused by changes in the magnet temperature. Torque feedback maximum torque per ampere (MTPA) control, which is known for its resilience to parameter fluctuations. This control method requires accurate torque estimation and MTPA angle estimation. However, conventional methods decreased estimation accuracy inductance or magnet flux a method to enhance the accuracy of these estimations by combining torque approximation equations derived from real motor drives. The accuracy of the proposed method in estimating the torque and MTPA angle, as well as its performance under steady-state torque control and transient conditions, validated.

This study investigates the performance of wide-bandgap-based devices integrated into a bidirectional T-type inverter topology for vehicle-to-grid (V2G) and grid-to-vehicle (G2V) applications. The designed structure incorporates wide-bandgap semiconductor devices, specifically, 1700V-rated SiC JFETs and 650V-rated GaN HEMT, operating at a 100-kHz switching frequency. This high frequency enhances the parameter performance and increases the power density. The analysis focuses on three main factors: first, the switching states of the devices in a 5-kW DC-AC bidirectional inverter controlled in real-time; second, the efficiency of a traction inverter with a buck and boost DC-DC converter operation for grid-connected electric-vehicle applications; and finally, the losses of overall combined primary switching and conduction losses of wide-bandgap devices. The system improves the efficiency to 98.09% with a combined SiC and GaN traction inverter. Simulations were conducted in the MATLAB/Simulink environment, and OPAL-RT results are presented to validate the performance of the designed T-Type three- phase 3L inverter structure.

Power electronic transformers (PETs) are promising for the high-speed traction industry owing advantages such as high power density, high efficiency, and environmental friendliness. The cascade H-bridge (CHB) rectifier at the front end of a PET constitutes a significant proportion of the overall volume and mass of the PET. Modulation strategies for CHBs are divided into three main categories: staircase, carrier phase-shift (CPS), and hybrid modulations. Within these different modulation strategies, there is a tradeoff between the DC-link capacitance and switching loss, leading in turn to a tradeoff between the volume and mass of the DC-link capacitor and heat sink. In this study, the DC-link capacitance was calculated based on a restriction set on the DC-link voltage ripple. For CPS and hybrid modulations, the capacitance was calculated using the amplitude of the second-order harmonic in the DC voltage, whereas for staircase modulation, the worst-case method was proposed to calculate the required DC capacitance. The switching and conduction losses were calculated from the loss function in the HITACHI 6500V IGBT datasheet and the switching characteristics of the different modulation methods. The volume and mass of the heat sink were calculated using the thermal model of the switching device and the switching loss. Among the three considered modulations, hybrid modulation exhibited the highest power density. The accuracy of the calculations was confirmed through experiments and real-scale simulations.

This paper presents analyses of direct-current power generation systems consisting of an interior permanent magnet synchronous machine (IPMSM), a full-bridge rectifier, and resonant capacitors (series resonant PMSG system). Furthermore, the resonant capacitor capacitance design is clarified. The behavior of the generation system at the resonant speed and other rotation speeds is analyzed considering the saliency of the IPMSM. It is found that the system operates with flux-weakening current desirable for the IPMSM above the resonance speed and that maximum torque per ampere operation can be achieved as per the design concept. In addition, numerical simulations of the series resonant PMSG system are performed using a circuit simulator to confirm that the generation system operates as in accordance with the analysis.

The automatic detection of snow-covered curb boundaries facilitates autonomous driving and assistance systems in enhancing safety and efficiency, particularly in scenarios wherein driving close to curbs is unavoidable, such as snow-removal vehicles operating near or regular vehicles approaching curbs. Most existing methods are heavily reliant on appearance-based and three-dimensional geometric features to identify curbs. These features may become ambiguous or vanish after heavy snowfall. However, even when curbs are completely obscured by snow, experienced drivers roughly estimate the curb boundaries for easy navigation. This ability relies on objects not covered by snow to assist with relative positioning. This study proposed an automated method to predict curb positions based on prior knowledge, mimicking the ability of experienced drivers to estimate curb boundaries even when obscured by snow. The proposed method leveraged Global Positioning System information to extract scenes that closely resembled current conditions from a pre-established database of snow-free scenes. By matching these scenes, the coordinates of the original curb boundaries were mapped onto snow-covered scenes to predict curb positions. Experiments on a circular route verified the effectiveness of our method. Furthermore, an evaluation metric was proposed to numerically assess the prediction results.

This study involves the design of a hybrid excitation self-contained power supply using the finite element analysis software Maxwell 3D for model construction; considering the hybrid excitation optimization design as the goal, two structural improvement plans are proposed. The first radial hybrid design is intended for magnet fixation and entails improvement strategies to effectively fix the magnet while alleviating the phenomenon of magnetic saturation. The second axial mixing plan aims to increase the power density per unit volume of the magnet for output voltage optimization. The feasibility of each improvement strategy was verified through magnetic circuit analysis, focusing on optimization of the design direction. Moreover, the suitability of hybrid excitation was proven through hardware measurements. Accordingly, in an environment where the power cable transmission current was 300A, the output voltage increased by as much as 50.18% over the pure silicon steel sheet (PSSS) type. Finally, regarding product development practices, the economic benefit was examined when specifically applied to drones. Macroscopically, applications are also considered for instances when there are no power supplies or when batteries cannot be replaced easily, such as in smart electricity meters and automated external defibrillators installed in inaccessible places.

The voltages in the powertrains and lithium-ion batteries (LIBs) of electric vehicles are increasing to 600-800V, whereas ordinary fast chargers are designed for 400-V systems. An additional on-board or internal voltage conversion stage is needed to adapt traditional chargers to high-voltage powertrains. This paper presents a resonant switched capacitor converter (RSCC) with a conversion ratio of either 1.5 or 2.0 to bridge the voltage gap between 400-V chargers and 600- or 800-V systems. The proposed RSCC contains a 3-level flying capacitor circuit that realizes the changeable conversion ratio between 1.5 and 2.0. Furthermore, a zero-voltage switching (ZVS) cell, which comprises a tiny inductor and capacitor, is added to eliminate losses due to the parasitic capacitances of MOSFETs and diodes. Experimental tests using a 1-kW prototype demonstrated power conversion efficiencies in both the 1.5x and 2.0x conversion modes that exceeded 98% in the medium- and heavy-load regions.

This paper presents a wide-bandwidth estimation method of cross-coupling factors in the dq-axis inductance for current control and position estimation in advanced position-sensorless control of interior permanent magnet synchronous motors (IPMSMs). The cross-coupling factors from the complex magnetic passes depend on the rotor position and current. These cross-coupling factors reduce robustness and position estimation accuracy in position-sensorless control methods with the d-axis high-frequency voltage injection. Since estimation errors in each estimation period change the current from the voltage injection, the cross-coupling factors vary in the high-frequency bandwidth around the voltage injection frequency. Consequently, the estimated position has errors from the static magnetic characteristics in the low-frequency bandwidth and vibration in the high-frequency bandwidth. The proposed method integrates two estimated cross-coupling factors with different frequency bandwidths. The estimated values are derived from the current variation from the injected voltage and the estimated position. Experimental results show a reduction in position estimation error, smaller vibration during rotation, and improved robustness to disturbance.

A position sensorless control strategy with improved integral fuzzy sliding mode observer and rotor position error compensation is proposed to address the low rotor-position observation accuracy of the traditional sliding mode observer for permanent magnet synchronous motors. First, an integral adaptive sliding mode current observer is developed to weaken the chattering effect caused by the switching function of the sliding mode observer, and the speed and position fluctuations are suppressed by introducing a finite integral sliding mode function and an equivalent switching control law, and a fuzzy adaptive rule is designed to adjust the back electromotive force observation gain in real time. Second, a closed-loop phase tracker is designed to correct the rotor position to compensate the position offset caused by the phase-locked loop and low-pass filter, enabling us obtain accurate rotor position. Finally, the effectiveness of the proposed method is verified by simulation and experiment. The results reveal that the proposed method can accurately observe the rotor speed and position information of the motor under different operating conditions with fast convergence and strong robustness.

To suppress residual oscillation when positioning the rotor of a stepping motor, constant-pulse-rate electronic damping in full-step mode can achieve suppression by tuning a single parameter according to attached inertial loads. However, this damping technique exhibits insufficient robustness to uncertainty. This article proposes a novel damping technique that enhances robustness by being extended to half-step mode. Experiments demonstrated the effectiveness of the proposed damping.

This letter presents a control strategy to reduce both the 12th order radial force vibration and 12th order torque ripple for double-star permanent magnet synchronous motors. Feeding 12th order harmonic current to suppress the 12th order torque ripple increases the 12th order radial force. Therefore, the 12th order radial force is suppressed via superimposition of a 6th order harmonic current. Experiments were conducted to measure the torque and acceleration of a motor. The outcomes demonstrate the effectiveness of the proposed method. During the experiment, the radial acceleration of the motor was measured instead of the radial force. As a result, the 12th order torque ripple and 12th order radial acceleration are suppressed by 68.8% and 67.7%, respectively.

This study aims to recover objects descending at low speed in the air using a fixed-wing unmanned aerial vehicle (UAV). To guide the UAV toward descending objects, updating final-state control (UFSC) is applied. However, a previous study has shown that the accuracy of reaching the target states deteriorates owing to wind influence. In this study, a minor control loop is adopted to stabilize the UAV via PD control. Therefore, UFSC is applied to an augmented system comprising the original UAV and minor control loop. The robustness of the method in wind-disturbed environments is evaluated via numerical simulations.

This letter proposes T-type 3-level (T-3level) half-bride inverters for audio use. Self-oscillating inverters are preferred for feedback control with a higher loop gain, which is important for reducing the total harmonic distortion plus noise of class-D amplifiers. However, a conventional self-oscillator cannot be applied to T-3level half-bride inverters. In this letter, a self-oscillation scheme for T-3level half-bridge inverters is proposed and verified by a simulation.