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.

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 6.78 MHz operating frequency and 19.6 V and 29.7 V output DC voltages.

Vibration suppression is an extremely important aspect in mechatronic equipment, and the placement of actuators/ sensors and control system design greatly impacts vibration control performance. In this study, a simultaneous optimal design system for the actuator position and control system is constructed. As a preliminary study, the vibration suppression problem of a flexible cantilever using a piezoelectric element as an actuator is addressed. The simultaneous optimal design system reproduces the motion behavior of the mechanism, including the control system, by simulation using multi-body dynamics software, and searches for the optimal actuator position and compensator parameters in combination with optimization algorithms. The multi-body dynamics software calculates the vibration response based on the elastic deformation of the cantilever and reproduces the force generated by the piezoelectric actuator on the analytical model. The validity of the constructed system is verified through simulations and experiments.

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.

In this study, we have developed a driver advisory system using a speed estimation technique developed for freight trains aiming to ensure energy-saving and punctuality. The driver advisory system focuses cruising driving operation for a freight railway by maintaining the planned time of passage station. The driver advisory system proposes a recommended driving operation for each passage station.

First, we discuss an energy saving driving method called cruising driving for freight railways considering the running resistance and motor efficiency. As a result of an energy calculation, we found that is necessary to use constant-speed and saw-toothed driving operations properly depending on speed and load characteristics, including hauling mass and gradient of running line. Then, we have developed a driving operation assignment method using the speed estimation, which switches between constant-speed and saw-toothed driving operations depending on speed and load characteristics. Finally, we present a trial result focusing on energy consumption. We confirm the energy-saving effect comparing the energy consumption with or without the developed driver advisory system.

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.

Model predictive current control (MPCC) is a fast and accurate current control method for interior permanent magnet synchronous motors (IPMSMs), which controls the current on the basis of current values predicted using a mathematical model of the IPMSM. MPCC requires accurate motor parameters, and a parameter estimation using a current ripple caused by MPCC has been proposed. As this ripple causes acoustic noise and vibration, a voltage smoother has recently been proposed to suppress the ripple. High-performance current control necessitates an appropriate combination of both parameter estimation and voltage smoothing; however, combining them is difficult. Suppression of the current ripple makes parameter estimation difficult. Therefore, a novel estimation method based on dynamic regressor extension and mixing (DREM) is proposed for realizing high-performance current control in MPCC-controlled IPMSM. Experimental results demonstrate the validity of the proposed approach.

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, 1700 V-rated SiC JFETs and 650 V-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.

This paper proposes a novel optimal control method for operating each powertrain component of a series hybrid electric vehicle (SHEV) while reducing the total energy loss during a trip with a given speed profile. The proposed method formulates the SHEV energy management problem (EMS) as a novel optimization problem. This study has novel aspects: 1) The proposed method simultaneously optimizes the ignition on/off timing and operating points of powertrain components without involving any binary variable. 2) Function 1) is realized by defining the reference values and actual values of ignition on/off timing, engine output torque, and inverter conversion rate as continuous variables separately, setting the reference values as optimization variables and including a designed function in the performance function to avoid engine ignition when the engine speed is lower than the idling speed. 3) The entire brake-specific fuel consumption (BSFC) map is modeled for optimization instead of restricting the engine operating point to the optimal line of BSFC. 4) A rule-based control method is established according to the control method used on commercial SHEVs to validate the effectiveness of the proposed method. 5) The control results under four initial conditions are compared to validate the rationality and effectiveness of the rule-based and proposed methods in reducing the total energy loss. Both methods can efficiently control the powertrain components. However, in all four case studies with different initial state of charge values, the proposed method and the rule-based method generate different ignition timing and operating points for the components in the powertrain. The proposed method reduces the total energy loss and fuel consumption by over 19.41% and 13.75%, respectively. Moreover, the proposed method eliminates the chattering of the engine ignition on/off switch.

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 DClink 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.

In modular three-phase wireless power transfer (WPT) systems, efficiency is crucial, and the consistency of the resonant frequency in each phase module directly affects efficiency. This paper discusses an effective resonant frequency stabilization (RFS) technique for adjusting the resonant compensation capacitor parameters to correct the unbalanced resonant frequency in each phase caused by coil misalignment or variations in the transmission gap and the natural tolerance of the transmitter (Tx)/receiver (Rx) coil geometry. The method compensates for misalignment tolerance and enhances overall system performance by making these adjustments. To validate the proposed concept, experimental results have been conducted, demonstrating that the system is capable of transferring 11 kW over a distance of 180 to 250 mm. A significant improvement in power transfer efficiency (PTE) can be achieved, up to a 3.10% increase (saving 406.3W of power) under coil alignment. Additionally, even with a 100 mm misalignment between Tx/Rx coils, the optimized system can still achieve an efficiency improvement of up to 4.09% (saving 599.7W of power). Finally, the main contribution of this paper is introducing a modular three-phase WPT system design method, offering an effective solution for stabilizing resonant frequencies compared to alternative topologies, and is well-suited for commercial purposes.

Silicon carbide (SiC) power modules have witnessed significant advancements in recent years, and adopted in a wide range of power electronics applications. The long-term reliability of SiC power modules is key for the replacement of conventional Si power modules. Although several reliability test methods for SiC power modules have been conducted, SiC MOSFETs still have concerns regarding changes in electrical characteristics owing to electrical or thermal stresses. It can cause errors in junction temperature estimation, especially in the power cycling test, which utilizes the electrical characteristics of MOSFETs to detect mechanical deterioration of power module packages. In order to accurately assess the long-term reliability of power module packages, it is necessary to clarify a suitable test method to avoid any electrical degradations of SiC MOSFETs. This paper experimentally investigates the changes in electrical model parameters of several SiC MOSFETs in power cycling tests. The investigation focuses on the influences of the self-heating method on large forward and reverse current flows through the SiC MOSFET.

The optimum design and development of a high-frequency transformer (HFT) is a key requirement in the development of a solid state transformer (SST) for incorporating in smart grid environment. This paper proposes an iteration-based algorithm for the optimum design of a HFT. The algorithm generate optimum design by evaluating an objective function of minimizing the total owning cost (TOC). The unique features of the algorithm developed for the optimum design of HFT include the following: it iterates eight design variables from their minimum values to maximum values and considers four design constraints for selecting the valid designs. This algorithm can work with three different core materials and can select a suitable AC test voltage based on the HFT voltage rating. A case study is conducted on a HFT incorporated in 1000 kVA, 11 kV/415 V, Dyn11 three-phase SST. It enables us to determine the optimum design parameters of HFT. In this case study, the algorithm is iterated with 121,500 design data inputs, generating 19,873 designs that satisfied all design constraints. The optimum design with minimum TOC is selected from the generated 19,873 designs. The optimum design is validated using finite element analysis in ANSYS software. The results obtained in finite element analysis are comparable with the analytical results and hence the algorithm is validated.

In this paper, we describe the control of electronic frequency converters (EFCs), which enables them to continue independent operation in the event of a fault, which is necessary to replace all the frequency conversion facilities in the Tokaido Shinkansen to EFCs. To continue independent operation of the EFCs under faults, we have developed a new overcurrent suppression control scheme applied to the three-phase AC input and output EFCs. We confirm through simulations that the new control suppresses fault current effectively and enables the EFCs to continue oper- ation through a series of operations in which short-circuit faults occur at the feeding circuit, and the circuit breaker interrupts the circuit at the location of the fault following its occurrence and re-closes it after a short interval.

This paper proposes an angle calculation method to improve the accuracy of a magnetic absolute encoder with different magnetic flux densities (MAE-DMFD). Magnetic encoders have a conflicting relationship between the absolute angle calculation and high resolution. The MAE-DMFD is a magnetic absolute encoder that is proposed to solve the relationship. It can achieve both multipolarity and absolute angle calculation by using a magnet with magnetic force difference inside the encoder to characterize the magnetic force signal. However, the angle calculated with a magnetic force difference by the characterized magnetic force signals is greatly affected by external disturbances such as harmonics and observation noise. Additionally, the conventional angle calculation system of the MAE-DMFD uses second-order phase-locked loops (SO-PLLs) based on orthogonal signals. To use SO-PLLs, the steady-state estimation error should occur when the operating velocity changes. Therefore, this paper proposes an improved angle calculation method that considers disturbances, noise, and estimation error. The proposed method uses a higher-order PLL to compensate for the steady-state error and applies an adaptive filter to the orthogonal signal to consider the effects of noise and harmonics. The proposed method can efficiently remove noise, harmonics, and angle estimation errors. The effectiveness of the proposed method is demonstrated on an actual MAE-DMFD.

We have been tackling a problem of weight estimation of steel cylinders using image processing with an error of less than ±10 g. In our previous studies, the weight was estimated by capturing multiple images of an entire side of the steel cylinder, extracting the contours via image processing, and then constructing a 3D model based on the obtained data. However, the estimation performance was poor. To improve accuracy, a simple cylinder model was considered in addition to the previous method, and multiple regression analysis was applied on the weights calculated from both models. As a result, high estimation performance was achieved. However, detailed analyses and discussions of these results were insufficient. Therefore, they are investigated in this study.

This letter proposes a method to suppress copper loss due to the skin and proximity effect (AC-resistance) by splitting the conductors of a coil on a printed circuit board (PCB) into some traces and swapping them at the corner of the coil. The proposed structure for the coil is characterized as having no via, which results in an increase in cost and copper loss. The simulation results demonstrate that in the proposed coil comprising 12 corners (12c coil), splitting a conductor into three traces, the resistance is suppressed by 16.7% compared with a spiral coil, and the quality factor is improved by 11.0%. Practical experiments on the prototype of the 12c coil further revealed improvements in the resistance and quality factor by 19.7% and 18.8%, respectively.

This paper provides a general and systematic comparison of the transmission characteristics for circuits non-resonant, series resonant, and parallel resonant circuits of both Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT) systems. The transmission characteristics were CC/CV characteristic, efficiency, and output power when the power source is a voltage or current source. In terms of the compensation condition and CC/CV characteristic, S-S in IPT and P-P in CPT were superior because the compensation condition does not depend on the coupling coefficient and they had gyrator characteristic. For the efficiency, it was found that, for both IPT and CPT, it was suitable to use S or P on the receiver side for high efficiency. For the output power, in common with IPT and CPT, higher power can be obtained by choosing S on the transmitter side when a voltage source was used and P on the transmitter side when a current source was used. Therefore, it is clear that the circuits with superior compensation condition, CC/CV characteristic, optimal load, efficiency, and output power were S-S in IPT when a voltage source was used and P-P in CPT when a current source was used.

This paper provides a general and systematic comparison of the transmission characteristics of series, parallel and LCL/CLC resonant circuits of both Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT). The transmission characteristics are CC/CV characteristic, efficiency, and output power when the power source is a voltage source or a current source. In terms of maximum efficiency, it was found to be common regardless of the transmission method or circuit. In terms of output power, it was found that when using a voltage source, high power was obtained by setting the transmitter side to S in IPT and the transmitter side to S or CLC in CPT. It was also found that when using a current source, high power was obtained by setting the transmitter side to P or LCL in IPT and the transmitter side to P in CPT. Furthermore, it was found that IPT obtains high power when the transmitter side circuit has the CV characteristic and CPT obtains high power when the transmitter side circuit has CC characteristic. In conclusion, S-S, S-LCL, LCL-S, LCL-P, and LCL-LCL are superior in IPT and S-CLC, P-P, P-CLC, CLC-P, and CLC-CLC are superior in CPT.

In the domain of haptics, effective interaction with unknown environments is paramount. A key aspect of this lies in the pre-estimation of environmental impedance, a challenge addressed in this research study. Leveraging the paradigm of image-based object detection, this study introduces a novel methodology that correlates environmental impedance with object labels. By systematically applying this approach across diverse objects, the environmental impedance of unfamiliar entities can be reliably estimated based on shared image characteristics. This innovative technique not only advances the understanding of environmental interactions but also presents a proactive means of environment recognition. The methodology which is rooted in the fusion of haptics and computer vision, signifies a significant stride toward comprehensive and anticipatory environmental perception.

In this study, we examine the use of a four-switch buck-boost converter (FSBBC) as a bidirectional power flow controller (BPFC) for flexible power flow control in DC power networks. In our previous studies, a cascaded boost-buck converter has been used as the BPFC, and few studies have been conducted using other circuit topologies. In this study, we develop a power flow control method using an FSBBC. Because an FSBBC has fewer passive elements than the conventional circuit topology, it is expected to achieve higher efficiency than the conventional circuit. We verify the effectiveness of the power flow control using an FSBBC by experiments.

Automotive motors are necessary to reduce vibrations and improve reliability. Double-star permanent-magnet synchronous motors (PMSMs) improved reliability however, they generate a radial force, causing vibrations similar to those of conventional three-phase PMSMs. This study introduces a radial force suppression method using a double-star PMSM which increases the degrees of freedom of synchronous frames from two to four, and two redundant degrees of freedom. Superimposing harmonic currents on the redundant degrees of freedom suppresses the radial force. The performance of the proposed suppression scheme is evaluated using finite element analysis and experimental results. The scheme targets the generated second-order component, which is larger than the other order components. The results indicate that harmonic current can suppress the second-order radial force and second-order radial acceleration on the stator core. Superimposing the harmonic current suppresses the second-order radial acceleration from 0.0865 to 0.0082 m/s2, and the suppression effect is 90.5%.

Designing energy-efficient train operation strategies presents a significant computational challenge due to the inherent nonlinearity introduced by factors such as friction forces, motor efficiency variations, and power supply network fluctuations. Furthermore, when considering the utilization of regenerative braking energy (RBE) between trains, the complexity of collaborative train operation increases. To address this challenge while avoiding excessive computational costs, the solution space is explored focusing on the neighborhood of an empirically good initial solution, and potential solutions are assessed using multi-fidelity simulators, including a numerical simulator considering the power supply network and an analytical simulator. In addition, the proposed methodology is applied to a two-train case study where RBE exchange is feasible. The results from collaborative optimization are compared with those from single-train optimization using the Dynamic Programming method. Time efficiency is further analyzed based on single-train and two-train scenarios. The outcomes underscore the potential benefits of collaborative optimization, including reduced energy consumption and enhanced stability of overhead voltage, contributing to more sustainable and cost-effective train operations.

This study introduces an optimization method that utilizes the adaptive deadtime of the triangular conduction mode (TCM) in an interleaved four-level flying capacitor boost converter with coupled inductors for photovoltaic systems. The operation of the TCM is analyzed for the zero-voltage switching (ZVS) of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), which is required for high-frequency, high-power-density applications. Coupled inductors, created by combining two inductors from two phases, are employed to enhance the efficiency. Coupled inductors introduce a low current ripple, which improves performance while reducing costs. By analyzing the effect of the coupling coefficient and the relationship between the two inductances on the inductor current ripple and the ZVS model, a suitable coupling structure is recommended for use in the proposed converter. Consequently, design considerations are presented to maximize the advantages of incorporating a coupled inductor in the proposed converter. Finally, a 200 W prototype is developed and tested to validate its feasibility.

A wireless power transfer system has been widely developed for various applications. A parity-time symmetry WPT (PT-WPT) technology is currently attracting attention for ensuring the robustness of the coupling coefficient changes. The system uses self-oscillation, and therefore, the system does not determine the oscillation frequency. This paper proposes a PT-WPT system using asymmetric coils and a digital separate-oscillation controller. The impedance analysis concludes that the operation frequency, power, and efficiency are constant with the coupling coefficient changes and the same as in a coupled mode theory. Further, the analysis derives the phase and amplitude of the voltage and current, especially the output current. A perturbation and observer method is installed to achieve zero phase between the input voltage and current changing operating frequency. The asymmetric coil WPT system and the digital separate-oscillation controller are designed, constructed, and tested to verify the principles of operations. The experimental results are in good agreement with the calculated values. The proposed method controls the stability and unity power factor. The converged time of the proposed system is 15 ms. The output power and efficiency are 202.4 W and 90.75% and these values are constant varying the coupling coefficient.

With the rapid economic growth of Malaysia, workplace accidents have increased drastically, according to the Department of Occupational Safety and Health (DOSH). This study aimed to determine the patterns in Malaysian workplace fatal accidents. A total of 505 fatal accident cases across 15 industries were analyzed in this study using both qualitative and quantitative methods. These fatality cases were identified and recorded by the DOSH from 2010 to 2020. The data were arranged and coded in Python and analyzed in terms of frequency analysis, Spearman's rank order correlation, eta squared, chi-square, and Cramer’s V methods. Furthermore, neuro-linguistic programming was performed for word cloud and sentiment analyses. Finally, a light gradient-boosting machine learning model was used to further understand the causes of fatalities in Malaysia. The results showed that fatal falls from heights were the highest contributor to fatal accidents (32%, n=161). Workers under contract were more vulnerable to fatal accidents in the construction industry (n=324, 64%) than other workers. General workers were the most susceptible category to fatal accidents (60%, n=302). The results from this study provide valuable insights into workplace fatal accident patterns and strategies for their prevention across industries.

In the previous study on the bias torque function control (B-TFC) for slip suppression control, the maximum acceleration performance was improved for the B-TFC (T_B=13.01 [Nm]), and conventional TFC, and the method without TFC were compared. In this paper, we clarify the energy saving performance using the energy utilization ratio (EUR) and recovery performance from the slip phenomenon using phase plane analysis. The EUR reached a maximum value of 2.33×10^–3 m/Ws when T_B=13.01 [Nm]. This result shows that the EUR is maximalized under the bias torque condition that has best acceleration performance. In the phase plane analysis, the vectors without variation of the drive wheel speed are generated under a high slip ratio of 0.76 with a bias torque of 13.01 Nm. The result indicates that the recovery performance from the slip state is also improved under the bias torque with the best acceleration performance. Additionally, we claim that the vectors without variation of the drive wheel speed are required at the high slip ratio for setting the bias torque to improve recovery performance from slip.

This paper proposes a method for weld root crack detection in metal plates using nonlinear ultrasonic methods. Second harmonic components of Lamb waves are generated during propagation, which makes it difficult to distinguish them from second harmonic components generated by the nonlinear vibrations of cracks. Therefore, the Lamé mode is employed to suppress unnecessary second harmonic components. Additionally, higher-order modes, which are more likely to be generated than the fundamental modes, are selected. In the case of higher-order Lamé mode Lamb waves, the second harmonic amplitude in the defect area is suppressed by approximately 10 dB compared with conventional S0 and A0 mode Lamb waves.

High-speed switching with wide bandgap semiconductor switches is increasingly being applied to motor drive sys- tems in electric vehicles. However, the MHz ringing phenomenon caused by high-speed switching leads to an increase in losses in magnetic materials of the motors. This letter proposes a low-pass filter (LPF) to suppress the MHz ringing phenomenon. And, it demonstrates that the use of the proposed LPF results in the reduction of iron and copper losses.