The magnetic properties and loss characteristics of oriented silicon steel sheets exhibit significant deviation under stress. The traditional loss separation model generally overlooks the impact of mechanical stress on the loss characteristics, resulting in calculation errors. In recent years, most studies on the loss characteristics of oriented silicon steel sheets under mechanical stress have focused on qualitative analysis, with only a few studies making quantitative improvements to the loss separation model. This paper develops an improved loss separation model based on the traditional loss separation model by introducing stress terms into the hysteresis loss and excess loss.

Firstly, measurements from a single sheet tester with unidirectional stressing are utilized to analyze the stress dependency of the loss characteristics of the oriented silicon steel sheets. The experimental results demonstrate a significant enhancement in loss under compressive stress while exhibiting a slight decreasing trend under tensile stress. The magnetization mechanism in ferromagnetism explains the variation of the loss characteristics under mechanical stress. Secondly, the hysteresis loss and excess loss under stress are calculated based on the Bertotti traditional loss separation model. Since the stress component is not introduced into the hysteresis loss in the traditional loss separation model, the effect of stress on the hysteresis loss is only reflected by the hysteresis loss coefficient, leading to a significant error in the calculation of the hysteresis loss under stress. Although the excess loss parameter ${{V}_{0}}$, currently expressed by a constant coefficient, embodies the effect of stress, it fails to capture the effect of the applied mechanical stress on the losses of each magnetic induction intensity. Consequently, computational inaccuracies arise when employing the Bertotti traditional loss separation model.

Based on the correlation between parameters ${{V}_{0}}$ in excess loss, hysteresis loss, and stress, the traditional separation formula for losses is improved by introducing stress components into the excess loss parameters ${{V}_{0}}$ and hysteresis loss. An improved loss separation model is established and verified by varying the frequency of excitation and the type of oriented silicon steel sheet. The results indicate that the improved loss separation model can accurately separate and calculate the losses of oriented silicon steel sheets under different stresses while maintaining a remarkable precision level.

Experimental measurement and calculation analysis are performed, and the conclusions are as follows. (1) The excess loss parameter ${{V}_{0}}$ is correlated with stress, and incorporating the stress component into the excess loss parameter can effectively mitigate the calculation error caused by stress in the traditional loss separation model. (2) An improved loss separation model is proposed based on the traditional mode by incorporating the excess loss and hysteresis loss into stress-related functions. (3) The improved loss separation model is confirmed through testing with different frequency excitations and oriented silicon steel sheets, demonstrating its ability to accurately separate losses under different stresses.

In non-destructive testing (NDT), there is a growing demand for simulation tools that can predict magnetic characteristics, enhance understanding, and avoid harsh and uncertain experimental expectations. Due to the high sensitivity and non-destructive nature, the measurement and simulation of magnetic barkhausen noise (MBN) have become important in NDT.

This paper measured the MBN signals of soft magnetic materials under different stress conditions at a magnetic frequency of 10 Hz. The experimental results revealed the significant impact of tensile and compressive stresses on the MBN signals. Specifically, as tensile stress increases, the spacing between magnetic domain walls decreases, reducing energy loss in the movement of domain walls. The migration rate of the domain walls is accordingly increased, which in turn causes the MBN signals to rise. At the same time, due to the presence of additional domains in oriented silicon steel, the MBN signals exhibit a double-peak structure. As tensile stress increases, these additional domains are suppressed. Hence, peak-to-peak values one and two increase, and the increase in peak value two is significant. When a magnetic field and compressive stress are applied along the rolling direction, the compressive stress increases the energy of the magnetic domain walls, reducing their migration rate and weakening the MBN signals. Ithelpsto better understand the changes in the magnetic properties of soft magnetic materials under different stress conditions.

Existing MBN models can not accurately simulate the MBN signals of different soft magnetic materials under stress. This paper proposes a mathematical model based on the improved S-J-A hysteresis model. This model simulates MBN signals by considering the irreversible motion of magnetic domain walls in soft magnetic materials, thereby increasing the accuracy of the simulation. Specifically, the improved S-J-A hysteresis modelsimulates the irreversible hysteresis loops of soft magnetic materials, considering the relationship between magnetic anisotropy, model parameters, and stress. Then, these irreversible hysteresis loops are linked with the MBN envelope line to establish a mathematical model for the MBN envelope curve. Next, the MBN signals are simulated by modulating white noise in the 1~50 kHz range with this envelope curve. Finally, three different soft magnetic materials are selected: oriented electrical steel sheet (30QG120), non-oriented silicon steel (35WW230), and amorphous alloy (1K101). The proposed MBN model simulates MBN signals under different mechanical stress conditions.

The proposed MBN model accurately simulates the MBN signals of the oriented electrical steel sheet (30QG120), non-oriented silicon steel (35WW230), and amorphous alloy (1K101) under stress. A comparison of MBN signals between oriented silicon steel, non-oriented silicon steel, and amorphous alloy is conducted, revealing that the double-peak structure exhibited by oriented silicon steel under tensile stress is related to its anisotropy. Microscopic analysis gains a deep understanding of the stress effects on the magnetism of soft magnetic materials and the generation mechanism of MBN. The proposed MBN model provides a reliable tool in material characterization and non-destructive testing (NDT) applications, laying the foundation for further engineering applications.

As the power source of the robotic manipulators, the motors inside the joint servo systems generally start with a load directly and cannot execute position calibration due to the operating conditions. Therefore, the commonly used position acquisition scheme is the Hall position sensor during motor start-up. However, this scheme cannot start the motor with the maximum starting torque, as the Hall position sensor only provides the present sector of the motor rather than the precise angle. The traditional processing method utilizes a square-wave voltage to start up or take the middle value of the Hall sector as the angle input to the motor drive algorithm, thereby obtaining a large torque across the entire angle range of the Hall sector. These methods are simple but lose some torque in the event of a significant deviation in the position estimation.

This paper proposes a quick-startup method for surface-mounted permanent magnet synchronous motors (SPMSMs) based on a Hall position sensor. Firstly, the start-up process of different curves of random initial angles is analyzed. The deviation between the actual rotor position and the imprecise estimated position decreases the starting torque, as the Hall sector spans an angle range of 60°. Under these conditions, combined with the field-oriented control (FOC) algorithm and the maximum torque per ampere (MTPA) strategy, the quick start-up method is proposed, and the critical start-up curve parameters are numerically calculated. Although the initial and precise angles during the start-up process are not available, the proposed curve can be close to the average locus to a great extent.

The simulation and an experiment are conducted using an actual servo motor under different initial angles. The results show that when the initial rotor position is close to the minimum angle of the Hall sector, the proposed method exhibits a pronounced acceleration effect. Due to the short stroke, although the position tracking of the proposed method is slightly behind the traditional method, the time difference is negligible when the initial position approaches the maximum angle. Combined with the average start-up time of the entire initial angle in the Hall sector, the proposed method can effectively reduce the average start-up time.

A quick start-up method for SPMSM based on a Hall position sensor is proposed. In the conventional control method, the maximum starting torque and the minimum statistical value of the start-up time cannot be achieved over the entire range of initial angles. Therefore, the novel position curve is designed to improve the start-up time for small initial angles in each Hall sector while considering the start-up process at other angles. Statistical analysis has demonstrated a significant reduction in the start-up time expectation of the entire initial rotor positions. The method optimizes the torque reduction problem during the start-up process, which is caused by imprecise positioning in the first Hall sector. Moreover, the ease of transplantation allows the method to be applied to various motor drive algorithms.

The maximum torque per ampere (MTPA) control strategy can fully use the reluctance torque to output the maximum torque per unit stator current and improve the operating efficiency of interior permanent magnet synchronous motors (IPMSMs). Still, the traditional formula method or the high-frequency signal injection method requires the installation of at least two phase-current sensors to obtain the current information of the motor. Once the current sensor fails, the closed-loop control of the system will fail and cause unpredictable damage. The paper proposes an MTPA control strategy for IPMSM without current sensors. The strategy can accurately realize the MTPA control of the permanent magnet synchronous motor by calculating the optimal voltage control instruction only from the rotational speed information and the mathematical model of the system.

Firstly, the relationship between the control voltage command and the rotational speed is calculated using the formula method according to the mathematical model of the IPMSM and the conditions of the MTPA control. Secondly, inverter nonlinearity can cause the inverter output voltage to deviate from the commanded voltage, resulting in the motor deviating from the MTPA operating point. Therefore, the mean value compensation method is proposed to compensate the command voltage for the nonlinearity. Thirdly, the effect of current estimation error on the calculated voltage compensation value is analyzed. The analysis shows that even if the current estimation error exists, the average error of the voltage compensation value based on the estimated current is still 0. Finally, the effect of parameter deviation on the control strategy is analyzed, and the influence of parameter deviation on the optimal voltage command amplitude and the response current is given.

The experimental results for steady-state conditions show that the A-phase current fundamental wave amplitude of the motor with the proposed strategy is smaller than that with the traditional strategy. The effectiveness of the proposed method is verified. The experimental results at the same load torque under different speeds show that the current vector amplitude error of the MTPA control with the proposed method is small. Its maximum error does not exceeding 0.5%, while the traditional method is 14%~30%. The experimental results at the same speed with different load torques show that the current vector magnitude error of MTPA control with the proposed method is small, with the maximum error not exceeding 1%. In contrast, the traditional method’s maximum error is in the range of 2%~37%. The experimental results of dynamic operation and loaded starting conditions show that the proposed control strategy is robust to parameter deviations and has good dynamic performance.

The following conclusions can be drawn. (1) The proposed method can realize MTPA control of IPMSM without current sensors, which is of great significance to the fault-tolerant control capability of current sensor failures in the IPMSM drive system. (2) The proposed method has good dynamic performance and is robust in the variation of motor parameters. (3) The proposed MTPA control strategy considers the effect of VSI nonlinearity, and the control voltages are compensated, effectively improving the running accuracy in MTPA.

The linear induction machine (LIM) drive system can get direct thrust and linear motions without transmission, which enjoys strong climbing capability, high acceleration or deceleration ratio, and small mechanical losses. The LIM drive systems have been developed and commercialized in over 20 linear metro lines worldwide. However, due to the large air gap, end effects, and high-power, low-switching frequency drive, the LIM drive system in urban rail transit needs better efficiency. Although the existing efficiency optimization control strategies have improved machine efficiency, the parameter robustness and system efficiency still need to be addressed. This paper proposes a robust efficiency optimization strategy for three-level inverter-fed LIM systems under low switching frequency.

Firstly, the primary flux-based LIM loss model considering end effects is built, where the loss is expressed as a convex function of primary flux. Its parameter sensitivity and limitation are analyzed. Furthermore, combined with the gradient descent method, a hybrid optimal primary flux search method is proposed to eliminate the influence of parameter changes on optimal flux selection. Then, the cost function containing multiple objectives, such as primary flux control, switching frequency constraint, and neutral point voltage balance, is derived. A model-free predictive flux control based on the nonlinear-extended state observer is proposed to manipulate optimal flux flexibly under low switching frequency.

Finally, experimental comparisons with the existing methods on a 3 kW LIM confirm that efficiency and parameter robustness can be improved for the drive system under low switching frequency. The system efficiency with the proposed method can be improved by 1.22% and 0.64% compared with the mature control strategy and the existing efficiency optimization strategy under the working conditions of 8 m/s and 200 N.

The following conclusions can be drawn. (1) The proposed method takes the minimum DC-link current as the search objective, which considers the harmonic loss and inverter loss, thus improving the system’s efficiency. (2) Considering multiple objectives, such as the switching frequency constraint and neutral point voltage balance, a model-free predictive flux control with adaptive switching frequency regulation is developed. (3) By combining the hybrid optimal primary flux search method with model-free predictive flux control, the proposed method effectively avoids the influence of parameter changes and modeling errors on optimal flux selection and manipulation. In this way, the parameter robustness of the efficiency optimization control strategy is significantly enhanced.

Due to the advantages of high power level, small torque ripple, and strong reliability, dual three-phase permanent magnet synchronous motors (DTP-PMSM) have been widely used in electric vehicles, ship propulsion, and aerospace power systems. The high fault-tolerant capability for open-phase faults is an important application feature of DTP-PMSM. Developing fault-tolerant control strategies is crucial for improving fault-tolerant performance. While both the minimum loss (ML) and maximum torque (MT) control strategies offer their advantages, stator copper loss and torque output capacity cannot be simultaneously considered. The full range minimum loss (FRML) control strategy comprehensively considers both ML and MT optimization objectives. The stator copper loss is effectively reduced without sacrificing the output torque range. Currently, the FRML control strategies usually add the restriction of sinusoidal current mode. However, the restriction of the sinusoidal current mode narrows the solution space of the current reference and prevents further improvement of the fault-tolerant performance. Therefore, a FRML control strategy based on harmonic current injection is proposed.

Firstly, considering the control complexity and optimization effect, third harmonics are injected into the fault-tolerant phase current to expand the solution space. By optimizing the current references, the fault-tolerant performance of ML and MT control strategies is further improved. Secondly, considering the stator copper loss and torque output capacity holistically, an allocation coefficient is introduced to combine the ML and MT strategies nonlinearly. The fault-tolerant trajectory can be smoothly switched online by adjusting the allocation coefficient under various load conditions. The proposed FRML control strategy simplifies the implementation complexity and produces a unified expression of current reference, which effectively reduces stator copper loss over the torque range. Finally, the proposed control strategy is verified on a surface-mounted DTP-PMSM platform. The quasi-proportional resonance controllers ensure accuracy in tracking the AC current reference. Both ML and MT control strategies achieve smaller stator copper loss and larger torque output capacity after the third harmonic injection than the sinusoidal current mode. When the FRML control strategy based on harmonic current injection is applied, the allocation coefficient is modified in real-time with the change of load condition. Under the rated load of 65.5%, 67.7%, and 69.7%, the stator copper loss is lowered by 6.2%, 4.91%, and 3.1%, respectively, compared to the MT control strategy. The fault-tolerant control strategy is verified.

The following conclusions can be drawn. (1) The strategies with the injection of third harmonic exhibit the superior performance of copper losses and torque output capability than that with sinusoidal current mode thanks to the more thorough current optimization. Therefore, the fault-tolerant control strategy based on third harmonic injection is more favorable for the stator copper loss optimization in the full torque range. (2) The proposed FRML control strategy based on harmonic current injection can further expand the range of torque optimization and enhance adaptability to various load conditions. (3) The proposed fault-tolerant control strategy is scalable. Future work will be focused on extending the applicability of the proposed control strategy to other polyphase motors, such as nine-phase motors.

Developing high-voltage silicon carbide (SiC) devices has enabled breakthroughs in voltage levels, power density, and efficiency in power electronic systems. Research institutions and manufacturers have recently created high-voltage SiC devices with ratings over 10 kV and 15 kV. These devices can increase the voltage level of large-capacity converters to 10 kV or higher and achieve megawatt power levels using only two- or three-level topologies. However, as voltage levels rise, the isolated power supplies for the SiC device drive circuits face greater challenges in voltage-withstand capability. These isolated power supplies draw power from the low-voltage side to supply the high-potential drive circuits. While they only need a few watts, they must withstand isolation voltages from several kilovolts to tens of kilovolts because they connect to the main circuit of the converter.

The high-frequency current transformer (HCT) is a promising isolated power supply structure known for its strong resistance to dv/dt. This advantage comes from the high integration of ultrahigh-frequency electromagnetic coupling and the low coupling capacitance of single-turn coils on the primary side. However, current research on HCT-isolated power supply mainly targets optimizing transmission efficiency, power, and coupling capacitance. There has been little systematic study of its unique insulation characteristics. As a result, the optimization design methods are unclear, and assessing insulation voltage capacity is challenging.

This paper investigates the insulation characteristics of the HCT-isolated power supply for high-voltage SiC devices. It examines six key structural factors: the inner diameter, height, and thickness of the magnetic core, as well as the winding method and wire diameter for both primary and secondary windings. This paper proposes an electric field optimization design method under compact size constraints. Additionally, a high voltage experimental platform was established to clarify the relationship between key structural parameters and the initiation voltage and discharge magnitude of partial discharges. The voltage withstand characteristics of the HCT isolated power supply were also verified. Simulation and experimental results indicate that using concentrated winding for the secondary winding results in a more uniform electric field within the structure. The inner diameter and height of the magnetic core, as well as the turns and diameter of the secondary winding, have significant effects on the electric field and partial discharge. However, the thickness of the magnetic core has a relatively weak influence on insulation capability. This study provides a theoretical basis for the design and optimization of the HCT-isolated power supply and experimentally verifies the specific effects of key structural parameters on insulation performance.

Traditional control parameter design methods of grid-connected converters (GCCs) are usually carried out under rated operation conditions. The stability margin is generally characterized by the magnitude margin (GM) and phase margin (PM). The bandwidth of the phase-locked loop (PLL) needs to be sacrificed for enough system stability margin, which ensures that the system can operate safely under non-rated working conditions. Therefore, traditional parameter design methods make it difficult to achieve a compromise between the stability and rapidity of GCC. Furthermore, the relationship between the stability margin and the output limit of the system is difficult to obtain, which relies on simulations or experiments. To address this issue, this paper proposes a control parameter design method based on the system stable operation domain, which com- prehensively considers the variable working conditions and different stability requirements.

Firstly, the complex vector open-loop transfer function G_s(s) is derived, which can analyze the stability of the system in a wide operating range or under different parameters. Secondly, varying the values of the PLL and current loop control parameters, the feasible domain of control parameters can be obtained by numerical analysis. PLL and current loop are coupled to each other due to the grid impedance. Therefore, the phase-locked loop parameter has a stable parameter boundary. Thirdly, based on the upper limit of the obtained PLL parameter, the three-dimensional diagram between the PLL parameter and the output current of the dq-axis is plotted, which shows the stable operation boundaries of GCC under different PLL parameters. Finally, taking the operation margin as the stability margin, the PLL parameter can be flexibly designed to realize the balance between the stability margin and the dynamic performance. Theoretical analysis results show that the control parameter design method based on the stable domain can ensure the safe and reliable operation of the system. Compared with traditional parameter design methods, determining the value of control parameter based on operation margin can improve the dynamic performance of PLL. At the same time, the corresponding relationship between different stability margin and the output current limit of the system can be obtained. Finally, the simulation and experiment results verify the correctness of the theoretical analysis and the effectiveness of the proposed design method.

The following conclusions can be drawn from the theoretical analyses: (1) The derived open-loop complex transfer function can be used to plot the control parameter feasible domain and the stable operation domain of GCC. The PLL control parameter satisfying the operation margin can be obtained quickly without repeated trial and error in the parameter design. (2) The analysis results show that the grid strength is positively correlated with the parameter feasible domain and the PLL cutoff frequency is negatively correlated with the stable operation domain. The cutoff frequency value of PLL is limited by the current loop parameter. The smaller the operating current in the parameter design, the wider the range of PLL cutoff frequency, and the better the dynamic performance of the PLL. (3) The control parameter design method based on the stable operation domain can directly quantify the influence of stability margin on the limit of the output current, which can be used for obtaining the stable boundaries under different stability margin. At the same time, the control parameters of PLL can be flexibly designed according to the actual needs of rapidity.

LLC converters are widely used in the power stage of battery energy storage converters due to their excellent soft switching performance and low output impedance. Under low voltage and high current conditions, matrix transformers are often used on the secondary side of LLC to reduce current stress. In practical circuits, the volume of matrix transformers accounts for about 25% of the total main power, which seriously restricts the improvement of device power density. This paper proposes an integrated optimization design of LLC four-element-matrix planar transformer considering loss and parasitic parameters. Decoupling the influence of various structural parameters of transformers on parasitic parameters this method achieves efficient operation of transformers and controllable parasitic parameters. Voltage drop and oscillation are effectively suppressed.

Firstly, establish an accurate transformer loss model based on the proposed distributed magnetic core loss calculation method. Select the key parameters of the magnetic core that meet the efficiency and volume requirements: the radius of the magnetic core's central pillar r and the total width of the winding c. Afterward, select the winding layer structure. Establish a leakage inductance model based on transformer leakage magnetic field energy, determine the feasibility of leakage inductance integration through PCB thickness constraints, and design leakage inductance values.

The experiment shows that the secondary-side V_ds voltage oscillation is significantly reduced after integration optimization, reducing the parasitic capacitance value. By matching the resonant inductance to ensure that LLC operates in critical continuous mode at 300 kHz, the magnitude of the transformer's primary leakage inductance before and after integration can be calculated. The resonant inductance before integration is 1.8 μH, indicating the original edge leakage is 0.7 μH. After integrated optimization, the resonant inductance is 2.3 μH, indicating the original edge leakage is 0.2 μH. When operating in reverse, with the same input voltage of 3.2 V, the LLC output voltage rises from 34 V to 35 V. This means that the secondary edge leakage has decreased after integration. After resonance point matching, the secondary leakage inductance can be reduced from 33 nH to 12 nH. The secondary side V_ds oscillation caused by parasitic capacitance is close and small, which verifies the control effect of parasitic parameters.

This method can achieve the following effects. (1) The proposed distributed magnetic core loss calculation method for planar transformers based on P-B curves eliminates the influence of uneven magnetic density distribution on the accuracy of the magnetic core loss model, achieving accurate modeling of integrated transformer losses. (2) This method provides a judgment method for the feasibility of leakage inductance integration. (3) The prototype parasitic parameters can be controlled by accurately modeling the leakage inductance and parasitic inductance. This method provides theoretical support for designing and optimizing energy storage converters in LLC low-voltage and high-current scenarios.

Due to its shared structure, the dual Buck/Boost-CLLC three-port converter has a simple structure and few power devices. The integrated interleaved parallel Buck/Boost unit significantly reduces input current ripple, while the integration of CLLC units endows the converter with excellent buck-boost conversion capability and soft-switching capability. However, the large number and volume of magnetic components in the shared structure are the main factors limiting the size of the power converter. Increasing the switching frequency or using magnetic integration can increase the power density of the power converter. However, in some studies, some schemes integrate two energy storage inductors and the resonant inductor in the converter to enhance coupled inductor current sharing and converter power density. Nonetheless, these schemes can only integrate full inverse coupling at a fixed duty cycle and cannot control the inverse coupling coefficient. Integration schemes with controllable coupling coefficients have been proposed, but two magnetic components remain after integration.

This paper proposes a fully integrated magnetic structure based on a dual Buck/Boost-CLLC three-port converter. By unevenly distributing the windings and establishing low reluctance paths, all magnetic components are integrated into a single magnetic element under variable duty cycle and coupling coefficient conditions. The proposed fully integrated magnetic component achieves inverse coupled inductor current sharing and ripple reduction, thereby enhancing system stability. Additionally, by integrating all magnetic components into a single magnetic element, the increased magnetic flux cancellation within the core further reduces core losses. Fig.A1 shows the proposed fully integrated magnetic structure, which consists of a cover magnetic core and a base magnetic core.

Fig.A1 Structure of the topology and fully integrated magnetic component structure

Firstly, based on the partially integrated structures and the proposed fully integrated structure, magnetic circuit models were established for both partially integrated and fully integrated magnetic components. The magnetic flux distribution and cancellation with different integration methods were compared. It is shown that the proposed fully integrated structure exhibits more magnetic flux cancellation and has lower losses. Next, the

performance-influencing parameters were analyzed, and a loss model was developed. Low losses for the fully integrated magnetic component were achieved through finite element parameterization scanning. Finally, a 500W prototype platform was built, and comparative experiments of non-integrated, partially integrated, and fully integrated magnets were conducted. Steady-state and dynamic experiments verified the feasibility of the integrated magnetic design. Efficiency and temperature comparison experiments validated the effectiveness of the integrated magnetic design.

The results show that the proposed fully integrated magnetic component maintains the same volume and footprint and exhibits more magnetic flux cancellation and uniform temperature distribution. The fully integrated magnetic component achieves an efficiency of 94.6% under full load, demonstrating higher power density and efficiency compared to non-integrated and partially integrated structures.