Rotor-unmanned aerial vehicles (R-UAV) have structural irregularities and problems with docking offset. The traditional unipolar CP magnetic structure increases the wind resistance of the R-UAV due to its mechanical structure characteristics, which, in turn, affects the flight stability of the R-UAV. At the same time, the asymmetric characteristics of the original secondary side can generate high stray magnetic fields, affecting the stable operation of the R-UAV. Therefore, applying the wireless charging system to R-UAVs is challenging. In order to build a stable wireless charging system for R-UAVs, it is necessary to conduct a targeted optimization design based on the mechanical structure of the R-UAV. This paper proposes an “I工I” magnetic structure with high anti-offset and low stray magnetic field constraints for the wireless charging system of R-UAVs and designs a multi-stage constant current-constant voltage (MCC-CV) control strategy with soft switching capability based on the characteristics of series-series (S-S) networks.

Firstly, this paper comprehensively analyzes the characteristics of series-series (S-S) networks, develops an MCC-CV control strategy for wireless charging of lithium batteries, and designs a full-bridge phase-shift soft-switching half-bridge workflow to solve the output current oscillation problem caused by the energy storage characteristics of the resonant network during the multi-stage constant current switching process. By incorporating soft switching capabilities, the system can transition smoothly between different stages of the charging process, minimizing current oscillations and ensuring a stable charging experience. Then, a three-dimensional model of the “I工I” magnetic structure is proposed and established. The transmission structure of this coupling structure is a “I工I” core, while the receiving side structure is an “I” core integrated within the landing gear of the R-UAV. Integrating the magnetic structure within the landing gear allows for zero wind resistance characteristics in wireless charging of R-UAV. Based on the low magnetic resistance characteristics of ferrite cores, the design of the “I” core is completed. Through magnetic circuit analysis and finite element simulations, the magnetic circuit shaping and low stray magnetic field characteristics of the “I” core are determined, and a passive constraint magnetic circuit shaping method for stray magnetic fields is derived. The “I” core distribution is adjusted to increase the anti-offset capability of the “I工I” magnetic structure, thereby achieving a high anti-offset wireless charging system design.

Finally, a prototype of the “I工I” magnetic structure is built. It is shown that the system can maintain a constant output current under radial offset of 100 mm and rotational offset of 360°, with only a 2% fluctuation in transmission efficiency. At the same time, the distribution characteristics of the stray magnetic field outside the launch platform are measured, and a distribution diagram of the stray magnetic field is drawn. The proposed “I工I” is lightweight and efficient.

Wireless power transfer (WPT) technology provides an effective way to solve the problem of stable power supply for rotating equipment. However, in practical applications, the relative misalignment between the rotating side and the stationary side is inevitable. In the practical application of WPT system, due to the presence of ferrite cores, the misalignment of the coupling mechanism will significantly affect the self-inductance and mutual inductance parameters of the coils, resulting in output power fluctuations and efficiency reduction. In order to enhance the anti-misalignment capability of WPT systems under changes in coil parameters, this paper proposes a detuned WPT system anti-misalignment method that considers changes in coil parameters. The detuned WPT system is constructed using changes in coil self-inductance to counteract the output power fluctuations caused by changes in mutual inductance.

Firstly, using the finite element simulation software, the parameter variation laws of the rotary coupling mechanism under axial and radial offsets were summarized. The study found that the self-inductance and mutual inductance of the coupling mechanism have the same trend of change, and the degree of change is similar within a certain offset range. And based on this, the idea of using self-inductance changes to dynamically adjust the degree of system detuning to offset output fluctuations caused by mutual inductance changes was proposed.

Secondly, the influence of parameter changes on system operation was obtained through circuit analysis, and the constant voltage output conditions for the degree of receiver detuning and mutual inductance changes were derived, providing a theoretical basis for the coupling mechanism design and compensation parameters optimization. The coupling mechanism design revolves around the number of turns on the secondary side, and the compensation parameters optimization is based on the particle swarm optimization (PSO) algorithm. With the goal of constant output and efficiency improvement, the compensation topology parameters of the inductor-capacitor-capacitor-series (LCC-S) are comprehensively optimized to achieve good axial and radial anti-misalignment capabilities of the rotary WPT system.

Finally, a 170 W experimental setup was constructed to validate the effectiveness of the proposed method. The experimental results show that within the range of axial offset ±30 mm and radial offset ±5 mm, the maximum mutual inductance change of the rotary coupling mechanism is 74%, the self-inductance change is 48%, and the coupling coefficient is 0.39 to 0.89. The maximum output voltage fluctuation is only 9.5% (axial) and 2.8% (radial), and the maximum efficiency of the system is 93%. This method utilizes the equilibrium characteristic of the parameter changes for the coupling mechanism itself. Its significant advantages lie in simple and effective structure, no DC-DC converter, no communication and closed-loop control, and a more stable and reliable system. It is particularly suitable for WPT system in harsh environments such as high temperature, high voltage, and high-frequency vibration underground, reducing the failure rate of the system and improving power supply reliability.

Wireless power transfer (WPT) technology has garnered widespread attention in recent years due to its advantages in safety, reliability, and flexibility. However, these benefits are often dependent on the precise alignment of the coupling mechanism. In practical applications, as perfect alignment cannot always be ensured, misalignment leads to a reduction in the coupling coefficient, significantly degrading transmission efficiency and system performance. Traditional flat solenoid coils perform well in resisting longitudinal misalignment, but when lateral misalignment occurs, especially near the coil's edge, the coupling coefficient and efficiency drop rapidly. To address this issue, this paper proposes an improved flat solenoid coil WPT system.

First, an equivalent model of the LCC/S compensation circuit is established to analyze the effects of circuit parameters on output characteristics, and a method for configuring the parameters of resonant elements is derived, revealing key circuit parameters affecting voltage gain. Then, an equivalent magnetic circuit model is built to analyze the magnetic field distribution characteristics of the coil, demonstrating that core shape and winding configuration significantly influence the coupling coefficient. Consequently, an optimized winding distribution is proposed using an arithmetic progression for the inter-turn spacing, and the specific optimization process is provided. Additionally, the core shape of the transmitter coil in the traditional flat solenoid design is improved to better concentrate the magnetic field lines, enhancing magnetic field uniformity and increasing the misalignment tolerance of the coupling mechanism.

To verify the optimization effects, multiple simulation models were created with core shape and winding configuration as variables for comparison. Finite element simulation results show that the improved transmitter core achieves more uniform magnetic flux density distribution, significantly reducing the rate of change in the coupling coefficient. Magnetic field uniformity and misalignment tolerance are markedly improved. Finally, a 100 W WPT system prototype was built, and thermal imaging was used to analyze the system’s loss distribution.

Experimental results show that when the receiver is laterally misaligned within ±50% in both the X and Y directions, the output voltage fluctuation is controlled within 5%, and transmission efficiency reaches 89%. These results validate the effectiveness and feasibility of the proposed system.

Wireless charging technology is safer and more convenient than traditional wired charging, and has been widely used in the field of electric vehicles. However, wireless charging systems have the characteristic of separating the ground end and the vehicle end, and there are issues with the selection and measurement of power metering points. The mainstream approach is to set the measurement position of the wireless charging system on the transmitting coil. However, the current and voltage of the transmitting coil are relatively high, so that directly using sensors for measurement can lead to high sensor costs. To address the aforementioned issues, this paper proposed a non-contact measurement method for output power of transmitting coil of wireless charging systems using multi coil collaboration. This method did not require specialized high-power high-frequency current and voltage sensors, and adapted well to practical scenarios such as different power levels, horizontal and vertical ground displacement of cars, and shielding materials, and had high measurement accuracy.

The paper utilized the law of electromagnetic induction to measure the output power of transmitting coil by setting sensing coils. Firstly, it was inferred that there was a relationship between the output power of transmitting coil and the voltage product of the sensing coil. Secondly, the fitting coefficient was used to fit this relationship, and it was derived that when the positions of detection coils and transmission coil were fixed, the fitting coefficient did not shift with the receiving coil. After obtaining the fitting coefficient, only the terminal voltage of the sensing coil needed to be measured. Finally, by constructing the voltage matrix of sensing coils and the standard output power of transmitting coil matrix, the fitting coefficients were obtained, and a coupling matrix model was established between the voltage phasor of each sensing coil and the output power of transmitting coil considering horizontal offset, vertical offset, and power variation.

The experimental results show that under different power levels, the maximum measurement error of the proposed method is within 1.5% when the wireless charging system undergoes offset in both horizontal and vertical ground directions. Under the condition of 2 square sensing coils, the maximum error in power measurement was 47%. When the number of sensing coils increased to 6, the maximum error decreased to within 1.5%. This result indicates that as the number of sensing coils increases, the accuracy will further improve. Meanwhile, research has found that when the transmitting and receiving coil are square, using a square sensing coil results in more ideal accuracy. In addition, with the use of 6 detection coils, 3, 5, and 9 power sampling points were used within the measured power range. The maximum errors in power measurement were 7.8%, 3.6%, and 1.5%, respectively, indicating that the more sampling points are, the more accurate the model is. Finally, further exploration is conducted on the practical scenario of placing multiple sensing coils horizontally, which can avoid the problem of vertical stacking height affecting the short distance power measurement.

This method has been proven to be effective through simulation and experimental analysis. Through comparative analysis of the results, the following conclusions can be drawn: (1) The size and quantity of detection coils are key to ensuring the accuracy of the model. A sufficient number of sensing coils will bring higher model accuracy, but at the same time, it will also increase the number of samples in the model solving process. Therefore, in practice, a reasonable selection can be made based on the measured power error requirements. (2) For coupling devices where both the transmitting and receiving coils are square coils, the measurement accuracy using square sensing coils is more ideal compared to circular sensing coils. (3) A sufficient number of sampling points in model solving can also affect the accuracy of the entire system model. In practice, a reasonable selection can be made based on the measured power error requirements. (4) Horizontal placement of multiple sensing coils can achieve high-precision power measurement, just like vertical stacking. In practical scenarios, placing multiple sensing coils horizontally can avoid the problem of vertical stacking height affecting the short distance measurement of the transmitting and receiving coils.

The magnetic field's compactness can better increase energy's transmission distance in a near-filed wireless power transfer (WPT) system. This paper proposes a non-centrosymmetric excitation unit (NEU) design method for the WPT system with a matrix coupling mechanism to improve the magnetic flux density in the central region. The proposed method enhances the magnetic focusing performance with a flat two-dimensional structure while maintaining its misalignment tolerance without any other auxiliary coil or circuit. The self-inductance value of the transmitting coil in this design method is even smaller than that of the conventional design method under the same size and number of turns. In addition, the proposed method is applicable to all regular matrix coils. Then, a detailed design method of the coupler is given based on the circuit analysis. Finally, taking the LCL-LCC compensation WPT system as an example, the feasibility of the proposed design method is verified. Compared to traditional design methods, the proposed design method can increase the induced voltage by 24.7% at the optimal position.

The current mobile robot UAV (unmanned aerial vehicle)/AGV (automated guided vehicle) plays an important role in industrial inspection, office logistics, agricultural and forestry plant protection, and military reconnaissance and surveillance fields. A multi-level, multi-modal power supply demonstration application has been designed in intelligent parks and industrial inspections to achieve charging docking between unmanned devices. However, most power supply methods are fixed-point charging, which is complicated in the energy transmission process and faces energy loss problems. In special charging environments such as wilderness and underwater, if there is no suitable parking charging platform condition, UAV hovering charging technology has become the most necessary and perfect charging solution, and it is also the key to building wireless power transmission network environments. Based on the well-established technology of fixed-point hovering and hovering following for unmanned inspection equipment in the air-to-air, ground-to-ground, and air-to-ground scenarios, hovering and alignment energy replenishment is undoubtedly a highly efficient and cutting-edge design concept applied to unmanned inspection equipment. Nowadays, to further enhance the flexibility and reliability of wireless charging systems, more and more wireless charging systems are designed based on matrix coils. The matrix-based multi-excitation wireless charging system has gained more favor in charging applications due to its reconstruction mechanism of the magnetic field at the transmitting end and strong tolerance for voltage and current stress.

In summary, a matrix coil design method based on non-centrosymmetric excitation units is proposed, combined with an evaluation of the system's spatial field transmission capability to improve the optimization design steps and the focusing ability of the magnetic field. This design method, which has a two-dimensional planar structure, enhances the magnetic flux density at the center position without any auxiliary coils or circuits, avoiding the offset tolerance weakening of the matrix coil itself as much as possible. It reduces the self-inductance of the coil unit to improve mutual inductance utilization.

In underwater applications, such as underwater robots, autonomous underwater vehicles (AUVs), and remotely operated vehicles (ROVs), magnetic-field coupled wireless power transfer (MC-WPT) enables the transmission of electrical energy without electric contact, improving the flexibility and security of power transfer. Underwater electrical devices and base stations must achieve long-distance and high-power wireless power transfer while realizing high-speed bidirectional wireless information exchange to enable command transmission, data feedback, and closed-loop control. Many scholars have researched shared-channel magnetic-field coupled underwater simultaneous wireless power and information transfer (MC-USWPIT) technology. However, there is still a gap between the transmission distance, power transfer capacity, information transfer speed, and the requirements of engineering applications. Therefore, this paper proposes an underwater simultaneous wireless power and information transfer system with a coplanar double-coil coupler. The research focuses on rapid wireless power replenishment and high-speed bidirectional information transmission for AUVs in seawater. The goal is to achieve high-power energy transfer and high-speed bidirectional information transmission over long transmission distances.

The coupler with a coplanar double-coil and the MC-USWPIT system topology are proposed. Using the relay coil for information transmission reduces the voltage stress on the information transmission circuit and helps mitigate the crosstalk between the power and information transfer channels. By employing an injecting information method with a series of LC circuits in the information transmission channel, the LC circuit is fully compensated at the power transmission frequency. Furthermore, smaller capacitance-blocking capacitors further reduce the crosstalk between the power transmission channel and the information transmission channel, as well as the voltage stress on the information transmission channel, thereby reducing the difficulty of system design.

Subsequently, the system is analyzed and modeled, and equivalent circuit models for the power and information transfer channels are provided. A parameter design method for the MC-USWPIT system is proposed. The method reduces the eddy current losses induced by the seawater and minimizes the impact of high-power energy transmission on the information transfer speed. It enables the simultaneous improvement of transmission distance, power transfer capacity, and information transfer speed in a frequency-division multiplexed MC- USWPIT system.

Finally, a 5 kW experimental setup in simulated seawater is constructed. In an environment with a seawater conductivity of 4.15 S/m, the system achieved a transmission distance of 50 cm, an output power of 5.33 kW, and an information transfer speed of 5.68 Mbit/s. Furthermore, under varying seawater conductivities (4, 5, and 6 S/m) and transmission distances (30, 40, and 50 cm), the system still demonstrates good power transfer performance and high information transfer speed. The experimental results confirm that the proposed MC-USWPIT system and method can effectively improve the transmission distance, power transfer capability, and bidirectional information transfer speed in simulated seawater.

With the increase of power and frequency of wireless power transmission systems, requirements for the control performance of power transmission and real-time high-frequency data interaction between the power transmitter and receiver continue to increase. This paper proposes an implementation method for low-cost and highly robust wireless power and signal transfer (SWPDT). Based on the traditional magnetically coupled wireless power transfer (WPT) system structure, the two metal-shielded pole plates on the outside of the magnetically coupled coil provide an independent capacitive channel for data transmission, and the magnetically coupled mutual inductance coil provides an independent inductive channel for power transmission, which achieves decouples energy transmission and signal transmission. The six-plate capacitive coupling is constructed under the coil parasitic capacitance. The mathematical and physical models of six-plate capacitive coupling are constructed, and the fourth-order resonant network is built to achieve full-duplex communication through four blocking networks and compensation structures. The overall cost and size of the WPT system are significantly reduced. The crosstalk of power transmission on signal transmission is reduced without changing the power transmission capability, and the power transmission frequency no longer restricts the transmission frequency. Finally, a 50 W power transmission prototype is constructed. The power transmission efficiency reaches 80% under the 17 cm coil distance condition. The full-duplex parallel transmission of power and signals is achieved within a serial communication bit rate range from 240 to 800 kbit/s. The BERs can be maintained at a low level, and the effects of the pole plate offset on the signal and power transmission are verified. The transverse drift ratio reaches 87.5.0%. In the case of the pole plate offset with an 87.72% lateral drift ratio, the signal transmission efficiency of the system is only 22.66%. Under the magnetic shielding function of the metal pole plate, the signal transmission is robust under extreme working conditions, improving the reliability of the power transmission process. The shielding pole plate reduces the power transmission efficiency but has a significant shielding effect on electromagnetic leakage. Compared with the existing wireless energy and data synchronous transmission technology in transmission efficiency, transmission distance, signal rate, and BER, the correctness and feasibility of the proposed method are verified.

Magnetically coupled resonant wireless power transfer (MCR-WPT) technology has received significant attention due to its ability to realize mid-range power transfer. However, the transmission characteristics of MCR-WPT systems are susceptible to variations in coupling coefficients and loads. Parity-time (PT) symmetry has been introduced into the WPT system (PT-WPT) to achieve constant power and high-efficiency transmission over medium distances. This paper provides a comprehensive review of the PT-WPT technology.

First, the paper introduces the PT-WPT system’s basic structure and operating mechanism. It analyzes how the system balances energy gain and loss through the nonlinear saturated negative resistor, allowing it to maintain stable power transmission under varying coupling conditions. Coupled-mode and circuit models are used to construct the PT-WPT system. The two models’ similarities and differences in the energy transmission mechanism, PT symmetry conditions, and system characteristics are described. In addition, PT-WPT can be considered a novel wireless power transfer technology.

Next, the paper discusses the construction methods of nonlinear saturated negative resistors, which can be divided into two categories based on the components used: operational amplifiers and power converters. While operational amplifiers provide a simple and low-cost solution, they are limited in power output. In contrast, power converters, such as half-bridge, full-bridge, and class E inverters, enable higher power output and efficiency but require more complex control strategies. Then, the advantages and disadvantages of these methods are discussed, and directions for improving the design of negative resistors are given.

This paper introduces the different types of coupling mechanisms and the implementation of charging functions. Among the topologies of PT-WPT systems, single-transmitter-single-receiver is the most basic structure; high-order compensation networks and the introduction of relay coils are commonly used to extend the transmission distance of the PT-WPT system. Multi-transmitter/multi-receiver can also improve the system’s reliability and realize stable power transmission in multi-load systems. Furthermore, the charging control strategies are investigated to realize the constant power and constant current/voltage functions independent of the coupling coefficient and load variation, further promoting the practicalization of PT-WPT systems.

Finally, this paper summarizes the existing research on PT-WPT systems and future research issues. PT-WPT technology is expected to find broader applications in the future and promote the development of wireless charging technology.

The rapid development of power electronics technology and wireless power transmission (WPT) has broadened application prospects in consumer electronics and traditional fields like electric vehicles, implantable medical devices, and autonomous underwater vehicles. The unique nature of wireless charging scenarios often results in significant variations in transmission distance, causing rapid drops in coupling coefficient and transmission efficiency. Therefore, coil compensation is an important research area of WPT. This paper proposes a segmented coil compensation method using inter-turn capacitance to solve increased internal voltage gradients in coils caused by traditional external capacitor compensation methods. By closely fitting the adjacent turns of the receiving coil, the capacitance of the closely fitting section is increased, thereby achieving coil compensation. The coil is divided into several segments, with inter-turn capacitance to compensate for each segment.

First, the advantages of segmented coil compensation are derived using rigorous circuit theory. Next, equivalent modeling and calculation of the Litz wire wound coil are performed to analyze the factors influencing the size of the inter-turn capacitance. Finally, the overall coil with inter-turn capacitance segmented compensation is modeled, and the port impedance of the entire coil is calculated. The inter-turn capacitance of the closely fitting coil segments increases significantly, effectively replacing the external capacitors for compensation. Compared to external capacitor compensation topologies, the proposed segmented compensation topology can reduce the internal voltage gradient of the coil, voltage loss, and energy dissipation. Accordingly, the energy reception efficiency of the coil is improved. Additionally, this structure is compact, with a small size and cost.

An experimental coil is compared with a coil using external capacitor compensation. Under the same input and load conditions, the receiving power of the coil with the proposed segmented compensation is increased by 54.3%, and efficiency is improved by 27.6%, which verifies the proposed method.

The following conclusions can be drawn. (1) The tight alignment length of the turns and the dielectric constant of the wire insulation layer influence the inter-turn capacitance. When Litz wire is used for equivalent analysis, the inter-turn capacitance increases significantly with the tight alignment length and shows a linear growth trend. The capacitance also increases significantly as the equivalent dielectric constant of the insulation layer increases, effectively compensating the coil. (2) Inter-turn capacitance compensation provides adequate compensation. Compared to traditional concentrated compensation methods, the proposed segmented compensation reduces the internal voltage gradient of the coil, decreases voltage losses and energy dissipation, and enhances the energy reception efficiency of the coil.

Renewable energy systems have gained continuous attention for achieving “carbon peak” and “carbon neutrality”, especially DC conversion technologies for renewable energy conversions. Multi-port converter (MPC) has been widely applied in renewable energy systems and electric vehicles due to the characteristics of low cost, high efficiency, and high power density. The non-isolated MPC suffers poor stability due to insufficient electrical isolation between ports. In contrast, isolated converters are often more complex and less flexible. Wireless power transfer (WPT) technology offers convenience, safety, flexibility, and the ability to charge multiple devices, effectively achieving electrical isolation between input and load ports. Thus, combined with WPT and MPC technologies, this paper proposes a three-port DC-DC converter with integrated wireless power transfer capability. The proposed topology facilitates DC power transfer between multiple DC sources with the same or different voltage levels. It enables wireless power transfer between DC sources and load by introducing WPT coupling technologies. The system achieves non-contact hot plug & play between DC loads and the power grid side, which indirectly isolates the impact of the load on the power grid.

The system employs a hybrid power flow control method, with dual half-bridge micro-inverters providing the dual input ports. The load port is wirelessly coupled through an LCL-LCL-type resonant coupling network connected to a full-bridge rectifier. This three-port topology is simple and highly flexible, allowing free power transmission between dual input sources, with the two sources sharing one LCL resonant tank for power transmission to the load without any additional circuit components. System control strategies can be divided into two phases: Phase1: pulse width modulation (PWM) controls the power flow between two DC sources by controlling the average DC offset current in the LCL resonant tank, enabling bidirectional power transmission; Phase 2: phase shift modulation (PSM) control method adjusts the wireless output power for DC load. These two control loops can operate independently or be combined for comprehensive control. The absence of coupling between these methods enhances the stability and effectiveness of each control function. Additionally, the system allows for dual input ports with unbalanced voltage levels.

Firstly, a dual-sided LCL resonant coupling network model is established based on the AC impedance method to analyze its frequency limitations under constant voltage and constant current output characteristics. Secondly, the system topology’s various operating states are analyzed based on switching modes. The overall system model is developed using time-domain analysis, and a small-signal model of the resonant coupling network is established to determine the primary-side PWM control and secondary-side PSM control strategies. Thirdly, a simulation model is built in PSIM to verify the system’s functionality. Matlab/Simulink is used to optimize the parameters of the compensation network. Finally, an experimental platform is set up in a microgrid and energy storage interconnected system to evaluate the system's dynamic characteristics under different voltage levels and load conditions, efficiency variations, steady-state control performance of the closed-loop controller, and dynamic response characteristics.

Experimental results show that under dual inputs of DC 36 V with only wireless output, the system achieves a peak efficiency of 93.6% and load-independent constant current output performance. The system effectively controls the power flow direction and magnitude between the primary-side energy ports, and the designed controller maintains stable load power even under sudden changes in load resistance and voltage levels at the dual half-bridge energy ports. The controller also demonstrates good robustness and dynamic response performance.

For the wireless charging systems for electric vehicles (EVs), the misalignment phenomenon due to inaccurate parking is the most significant issue, which causes non-negligible negative impacts on the power efficiency and amount. That is because the positional misalignment between coils leads to significant changes in parameters such as mutual inductance, which in turn causes dramatic fluctuations in the system’s output voltage and efficiency. It potentially prevents the system from functioning correctly or even damages it. Therefore, research on the anti-misalignment capability of EV wireless charging systems is crucial. Current research focuses on high-frequency inverter control, coupling mechanism design, and compensation topology design. However, these methods fail to maintain a constant output voltage when both coil misalignment and large variations in load occur. This paper proposes a novel hybrid compensation topology based on the QRQP coil.

This paper uses finite element simulation software to investigate a QRQP coil and its misalignment and coupling characteristics. To reduce output voltage fluctuations caused by coil misalignment and large variations in load, a novel hybrid topology is introduced based on the QRQP coil. This topology leverages the principle of opposing output characteristics between S-LCC, LCC-S, LCC-LCC, and SS topologies. Detailed design guidelines for the parameters and optimization strategies are proposed. Meanwhile, the system’s anti- misalignment capability under different parameter selections is analyzed. Finally, optimal system parameters are selected and analyzed. The optimized system can maintain a constant output voltage under various misalignment angles and load variations within a specific range. When the receiving coil is removed, the primary-side current can be effectively limited, which ensures the system's safety.

The proposed topology has been validated through a 1 kW laboratory prototype. Experimental results show that when the load resistance varies from 20 Ω to 100 Ω, the system maintains output voltage fluctuations of less than 5% under X-axis misalignment from -140 mm to +140 mm, Y-axis misalignment from -105 mm to +105 mm, and diagonal misalignment along the XY-axis from -200 mm to +200 mm. When the load resistance varies from 20 Ω to 100 Ω and the coils’ vertical distance changes from -35 mm to 70 mm, the output voltage fluctuation can be kept within 8%. Furthermore, since the system exhibits capacitive behavior after misalignment and has no compensating inductance, it can operate with high efficiency. Analysis under extreme conditions shows that when the receiving coil is removed, the optimized hybrid topology effectively limits the primary-side current surge, preventing system damage.

The following conclusions can be drawn. (1) The proposed optimization theory for the novel hybrid topology is consistent with the experimental results. (2) The optimized hybrid compensation topology based on the QRQP coil can effectively reduce output voltage fluctuations when coil misalignment and large variations in load occur simultaneously. (3) When removing the receiving coil, the optimized hybrid topology effectively limits the primary-side current surge, preventing system damage.

The multi-phase open-winding induction motor and its adaptive H-bridge multi-phase inverter system have received extensive attention due to their advantages of small torque ripple, strong fault tolerance, and easy power capacity expansion. This paper analyzes the modeling of the multi-phase open-winding motor system and speed sensorless control technology to achieve high degrees of freedom control and low switching frequency characteristics in a twelve-phase, large-capacity, open-winding motor system. The simulation and experimental verification are conducted to enhance the operating performance of the low-switching-frequency multi-phase open-winding motor system.

The twelve-phase open-winding induction motor system and its equivalent three-phase simplified model are established. The equivalent three-phase full-order observer model and its speed estimation method are presented. The full-order observer used in speed sensorless control has the advantages of low control bandwidth requirements and a wide range of observation speeds. However, the switching frequency of the H-bridge large-capacity inverter supporting the ship’s multi-phase open-winding induction motor is low, which inevitably increases the digital discretization error of the full-order observer. This paper derives the full-order flux observer models based on the forward Euler method, the simplified second-order discretization method, and the proposed Adams fourth-order discretization method. Then, the steady-state error and observer stability are compared using the F-norm and pole diagram. Theoretical analysis reveals that the full-order observer, based on Adams' fourth-order discretization method, achieves the best discrete accuracy and stability of the observation system while minimizing the computational complexity of the digital control system.

A simulation model and a test platform for a twelve-phase, 25 kW open-winding induction motor with speed sensorless control have been developed. The results show that, compared with the forward Euler method and the simplified second-order discretization method, the observation results for speed, current, and flux based on the Adams fourth-order discretization method are almost consistent with the actual values. Through the speed sensorless closed-loop speed regulation test and load mutation test, it is further verified that the full-order observer based on Adams' fourth-order discretization method exhibits good speed regulation and load-carrying capacity, which can achieve better dynamic and steady-state performance under both extremely low and high-speed conditions. The full-order observer discretization method can provide technical support for applying speed sensorless control technology to low switching frequency multi-phase open-winding motor systems.

Line-starting permanent magnet synchronous motors (LSPMSM) are different from other permanent magnet motors due to their double-sided slotted characteristics of the stator and rotor, making it difficult to analyze the cogging torque. The overall optimization of motor cogging torque and torque ripple rate is also challenging. This paper optimizes the rotor design of the LSPMSM based on multi-objective particle swarm optimization algorithm, considering the saturation performance of the motor.

Firstly, this paper establishes the relationship between harmonic magnetomotive force and cogging torque to predict the cogging torque of the LSPMSM. The cogging torque is analyzed as a dynamic function relationship of various motor parameters, providing corresponding optimization parameters for the subsequent optimization of the prototype. At the same time, under the premise that the maximum magnetic energy product of the permanent magnet remains unchanged, the relationship between the saturation degree of the motor and the parameters of the permanent magnet is determined, and the selection range of the motor's permanent magnet parameters is determined based on this relationship. Define three working states of the motor: unsaturated, peak saturation, and after saturation, to make the analysis and optimization results of the motor more accurate.

Secondly, combined with response surface methodology (RSM) and multi-objective particle swarm optimization algorithm (MOPSO), this paper proposes a comprehensive optimization strategy to optimize key objectives such as motor cogging torque, torque ripple rate, and efficiency. The optimal design solutions in different regions can be obtained by using the response surface algorithm to classify numerical groups and shorten the computation time of the particle swarm optimization algorithm. The optimal solutions under six different conditions are determined after considering whether the stator is skewed and the three working states of the motor.

Finally, simulation analysis verifies the relationship between cogging torque and harmonics under different saturation states, the trend of no-load back electromotive force, and the main harmonic order changing with the number of slots per pole of the rotor. An experimental platform is built to verify the accuracy of theoretical and simulation analysis. This paper provides optimization solutions for the design of motors of the same type.

Accurate load torque identification helps to improve the load disturbance resistance of complex nonlinear loaded permanent magnet drive systems. The sliding mode observer (SMO) has become a commonly used algorithm for load torque identification due to its advantages of high robustness to noise, fast response speed, and simple structure. However, the shortcomings of this algorithm, such as high-frequency chattering and slow response speed, limit its application in electric drive systems. This paper proposes a new adaptive sliding-mode load torque observer to solve the problem of the inherent contradiction between the convergence speed and high-frequency chattering of conventional sliding-mode observers.

Firstly, from the perspective of quasi-sliding mode, the conventional sign function is replaced by the saturation function to suppress the high-frequency chattering of the load torque estimate. The sign function can effectively suppress the chattering phenomenon of SMO, but it still fails to balance the convergence speed and observation accuracy. Second, an adaptive convergence rate is designed to introduce an exponential convergence term based on the conventional isochronous convergence rate. The adaptive gain of the isochronous convergence term is designed to make the sliding-mode observer adaptively adjust the convergence speed along with the change of the system state. Thus, the observer has a short convergence time and strong robustness, and the high-frequency chattering phenomenon of the sliding-mode observer in the steady state is suppressed. Finally, this paper introduces the average estimated value of the load torque in the conventional slip mode identification algorithm and adds it to the feedback loop of the speed observer. The improved load torque observation algorithm can suppress the chattering of the estimated torque by adjusting the feedback gain g. Since the load torque indication signal U can characterize the load torque change without additional delay, it can be directly involved in the speed estimation. Therefore, the proposed algorithm has a fast response speed during transient processes while considering the chattering suppression of the system. Based on the principle of sliding mode variable structure control, the adaptive rate of feedback gain coefficient g is designed.

Simulation and experimental results show that under varying speed and load disturbances, the proposed adaptive SMO has less chattering than traditional SMO and super-twisting SMO. Additionally, the adaptive SMO converges faster than traditional SMO and performs comparably to super-twisting SMO. In load disturbance experiments at a reference speed of 600 r/min, the speed fluctuations for no torque feedforward, traditional SMO with torque feedforward, and adaptive SMO with torque feedforward are 72.5 r/min, 56 r/min, and 35.5 r/min, respectively, with system recovery times of 0.7 s, 0.65 s, and 0.5 s. To further verify the impact of inertia parameter mismatch on the adaptive SMO, inertia was set to 2, 5, 0.5, and 0.2 times the rated value, with the maximum deviation in load torque observation being 6.7 N·m. The results indicate that the impact of parameter mismatch is not significant.

The following conclusions can be drawn. (1) The designed adaptive SMO has a simple structure and high stability, is easy to implement, observes the load torque quickly and accurately, and requires fewer parameters. (2) Compared with the conventional SMO, the proposed adaptive SMO has less chattering and faster response speed during the transient change of the load torque. (3) The proposed adaptive SMO is more suitable for the scenario of variable load torque than the conventional SMO. The experimental results show that when the load torque recognized by the adaptive SMO is used as the feedforward term of the reference torque, the response speed and load disturbance resistance of the heavy-duty chain drive system can be effectively improved.

Permanent magnet synchronous motor (PMSM) has become a core component of complex electromechanical systems such as electric vehicles, new energy urban rail vehicles, and wind power generation due to its advantages of high efficiency, high power density, and high torque density. The model predictive control strategy based on the mathematical model of the controlled object has been widely applied in PMSMs. However, there is inevitably a mismatch between the actual parameters of the motor system and the application parameters of the model predictive controller, which seriously affects the performance of the predictive control system. This paper proposes a novel model-free stator flux sliding mode control (MF-FSMC) method to achieve high-performance control under parameter mismatch.

The model-free flux sliding mode controller is adopted to replace the model predictive control algorithm that relies on the controlled object. First, a mathematical model of PMSM is established under parameter mismatch, and an ultralocal stator flux linkage model considering parameter mismatch is constructed under a rotating coordinate system. The novel MF-FSMC method is proposed, a model-free flux sliding mode controller based on a novel reaching law is designed, and a one-beat speed predictive controller is constructed. Finally, the composite integral sliding mode disturbance observer online estimation strategy is proposed, which can effectively observe the unknown disturbance part in the ultralocal model of PMSM under parameter mismatch.

Simulation and experimental results show that the proposed method can effectively improve the steady-state performance, significantly reduce the stator flux and torque ripple, and enhance the robustness and anti- interference performance of the PMSM system under parameter mismatch. The designed composite integral sliding mode disturbance observer can accurately observe the stator flux values and unknown disturbances on the dq axis. Compared with conventional model predictive control methods, the proposed MF-FSMC method can reduce torque ripple from 75 N·m to 45 N·m in the case of flux linkage parameter mismatch. In addition, with the proposed MF-FSMC method, the distortion of stator current has also been significantly improved, and the static error of stator flux linkage has been reduced from 0.35 Wb to ±0.01 Wb. In the case of inductance parameter mismatch, the proposed MF-FSMC method can reduce torque ripple from 110 N·m to 80 N·m and the fluctuation value of stator flux linkage error from ±0.235 Wb to ±0.02 Wb.

The MF-FSMC method proposed can obtain the following conclusions: (1) The composite integral sliding mode disturbance observer can accurately observe unknown disturbances and stator flux linkage, effectively enhancing the robustness of predictive control systems under parameter mismatch. (2) The proposed model-free stator flux sliding mode control method designs a model-free flux sliding mode controller in the inner loop of the controller and constructs a one-beat speed predictive controller in the outer loop of the controller. The proposed MF-FSMC method can effectively improve the control accuracy of stator flux, significantly reduce the stator flux/torque ripple of the motor, and ensure the strong robustness of the predictive control system under parameter mismatch.

Traditional I-f control for sensorless control of the permanent magnet synchronous motor (PMSM) suffers from poor damping and disturbance rejection, which lead to large speed oscillations at motor startup and long transition time when switching to close-loop control. It is unfavorable for multi-rotor unmanned aerial vehicles and electric vertical take-off vehicles. According to the differentiation of d-axis voltage and transition strategy, this paper proposes an improved I-f control strategy with frequency compensation to increase damping and improve disturbance rejection of the I-f control based on decoupling current dynamics and angle dynamics. Speed oscillations at motor startup are suppressed significantly, and a fast transition from I-f control to closed-loop control is achieved smoothly with less mechanical dynamics.

Firstly, a small-signal perturbation model of the I-f control is deduced with detailed analyses of its damping characteristics. To increase damping and suppress speed oscillations, differentiation of the open-loop d-axis voltage is used to compensate for the open-loop frequency. Secondly, to improve the load disturbance rejection when switching to closed-loop control, the angle of the reference current vector is rotated via Park transformation. In contrast, the open loop angle is increased to gradually approach the real rotor angle obtained by the angle observer. Since the reference current vector is stationary relative to the real rotor angle during this transition process, no mechanical dynamics are generated. This transition can even be done at zero angle error between the real rotor coordinate and the open-loop coordinate, which indicates no current and angle dynamics at the switching instant. The amplitude of the reference current vector is kept unchanged throughout the whole I-f control. Therefore, the load disturbance is effectively rejected, even during the transition process. Finally, after switching to closed-loop control successfully, the d-axis current is decreased to 0 according to a certain trajectory, and normal closed-loop control takes over.

Two experiments demonstrate the improvement of system damping and load disturbance rejection. In the first experiment, the proposed strategy is compared with the traditional I-f control and the perturbation of active power in literature. The experimental results show that under traditional I-f control, significant speed oscillations occur during the starting phase, and the peak-to-peak value of speed oscillations is about 80 r/min. With perturbation of active power, speed oscillations rapidly decay in 0.1 seconds, and the peak-to-peak value of speed drops to about 10 r/min in the steady state. The motor attenuates speed oscillations fast, and the peak-to-peak value of speed drops to about 5 r/min in the steady state.

The second experiment compares the proposed transition strategy and the strategy by reducing the q-axis current in the literature. The experimental results show that reducing the q-axis current generates large mechanical dynamics at the transition stage under sudden load disturbances. The speed decreases by about 260 r/min at the load disturbance of 0.064 N·m, and the motor is out of control at the load disturbance of 0.16 N·m. Mechanical dynamics are much smaller using the proposed method. The speed decreases by about 40 r/min at the load disturbance of 0.064 N·m, and the motor can still maintain normal operation at the load disturbance of 0.512 N·m.

The proposed improved I-f control strategy has better damping effect on speed oscillations and can transition to closed-loop control with strong rejection of load disturbances.

As the demand for flexibility and efficiency in modern industrial equipment increases, motors often operate under variable speed conditions in real-world industrial applications. This poses challenges for traditional time-domain and frequency-domain fault diagnosis methods. These challenges arise primarily due to the non-linear and non-stationary characteristics of signals under variable speed conditions, which can affect fault feature extraction. Single deep learning models generally require training and test data to follow the same distribution, and domain adaptation or multi-source domain generalization methods are difficult to apply in the absence of target domain and multi-source domain data, limiting their ability to enhance the generalization of single-source domain models. To address these challenges, this study proposes a motor rolling bearing fault transfer diagnosis method that integrates angular domain resampling and feature enhancement.

First, to mitigate the issue of time-frequency characteristic offsets in vibration signals under different rotational speeds, angular domain resampling is employed. This technique processes vibration signals at varying speeds, obtaining angular domain vibration signals to minimize the offsets caused by speed changes. Second, to address the generalization limitations of deep learning models, fault data from constant speed conditions are used as the source domain for training the neural network. Covariance loss is introduced to amplify the feature differences among various classes in the source domain data. This allows the network to focus on more informative features for the classification task, thereby improving its generalization capability. Finally, the angular domain vibration signals under variable speed conditions are input into the trained model for fault classification.

The effectiveness of the proposed method is validated through several experiments. Initially, the time-frequency characteristics of vibration signals from an actual bearing inner ring fault are examined before and after angular domain resampling. Before resampling, the vibration signal intervals under variable speed conditions show significant variability. However, after resampling, the variability in the vibration intervals is significantly reduced. Furthermore, using t-SNE visualization, the study observes that networks without feature enhancement show slow gradient updates and minimal changes in feature distribution. In contrast, networks with feature enhancement exhibit continuous changes in feature distribution, even as the classification loss decreases, with increasing feature distances. The study also conducts four cross-working condition fault diagnosis experiments, comparing the proposed method with other methods. The results demonstrate that the proposed method improves fault identification accuracy by 35.04% compared to methods without angular domain resampling, especially in rolling element fault identification. When compared to methods without feature enhancement, the proposed method improves accuracy by 7.45%. Additionally, in transfer diagnosis tasks under different load conditions, the proposed method demonstrates high accuracy, recall, and F1 scores.

In conclusion, the study finds that: (1) Angular domain resampling effectively reduces time-frequency distribution differences caused by speed variations, proving its applicability and rationality in data preprocessing at different speeds. (2) The feature enhancement strategy, by increasing covariance loss between different class features, amplifies feature differences between various health status signals, enabling the network to capture more distinctive features and significantly improving generalization capability. (3) The proposed method, without requiring target domain data, achieves fault identification accuracy of up to 97.29% under variable speed conditions, demonstrating good robustness under variable load conditions.

In distributed residential photovoltaic (PV) power generation systems, microinverters have attracted significant attention due to their benefits, including component-level maximum power point tracking (MPPT), plug-and-play flexibility, and high security. However, most existing microinverters are designed for grid-connected applications and are primarily suited for single-phase two-wire systems. Additionally, the intrinsic double-line-frequency power fluctuation problem greatly limits the increase in power density and reliability of microinverters. This paper proposes a novel voltage-source high-frequency-link (HFL) microinverter with double-line-frequency power decoupling capability, which is compatible with various single-phase distribution grids.

On the primary side of the proposed microinverter, a Boost converter is integrated with the full bridge of the HFL microinverter by sharing the switches. The integration has high voltage gain and additional double- line-frequency power decoupling capability. On the secondary side, a novel structure with three-wire output is proposed to be compatible with single-phase two-wire and single-phase three-wire power systems. Due to its voltage-source-inverter (VSI) characteristics, the proposed microinverter is suitable for grid-connected and islanded applications.

This paper introduces the circuit structure of the proposed microinverter. A soft-switching modulation is proposed along with its logic implementation. Operation modes during a switching cycle and the soft-switching characteristics of each switch are analyzed. The proposed microinverter features a three-wire output, and the two phase-to-neutral output voltages are auto-balanced. Therefore, the specific balancing theory is also analyzed. The double-line-frequency power decoupling principle is presented and analyzed. To meet the required input voltage range and ensure acceptable voltage stress on switching devices, design considerations for key circuit parameters are presented, including the turns ratio of the high-frequency transformer (HFT), the average value of the decoupling capacitor voltage, the inductance of Boost inductor, and the capacitance of the decoupling capacitor.

Moreover, grid-connected and islanded closed-loop control strategies are proposed. Finally, a 600 W prototype is built to verify the proposed topology and strategies. Steady-state and dynamic test results for grid-connected and islanded operations are provided.

The following conclusions can be drawn. (1) The proposed microinverter achieves high gain and double-line-frequency power decoupling, resulting in a 22 V to 55 V wide input voltage and an MPPT efficiency above 99% with a 100μF input capacitance. (2) A special three-wire output is proposed for single-phase two-wire and single-phase three-wire distribution grids, with the two phase-to-neutral voltages auto-balanced without dedicated control. (3) The proposed microinverter operates in both grid-tied and islanded applications, and the closed-loop control strategies ensure stable steady-state operation and fast dynamic response.

In recent years, non-isolated inverters have gained widespread attention in commercial and residential PV grid-connected systems due to their cost, efficiency, and flexibility advantages. However, in practical applications, the output voltage of the PV panel is generally low. Due to the loss of the electrical isolation of the transformer, the high-frequency switching action of the conventional inverter may produce a common mode voltage applied to the parasitic capacitance between the PV array and the ground, resulting in a common mode leakage current, which affects the safe operation of the system. This paper proposes a non-isolated five-level Boost inverter with no leakage current and its dual-mode modulation strategy to enhance the applicability and practicability of the inverter.

Firstly, the circuit structure combines the dual-output Boost converter with the five-level inverter to create a five-level Boost inverter topology. The Boost capability is expanded, suitable for PV power generation applications with low DC voltage on the input side. Secondly, the dual-mode modulation strategy of unipolar carrier level shifted is studied, providing five-level output capability and increasing the equivalent switching frequency under the same carrier frequency. By comparing the PV panel’s DC output voltage and the grid voltage’s absolute value, two working modes of Boost voltage and buck voltage are realized, and the energy transmission efficiency of the converter is improved. In addition, a five-level voltage is output on the side of the bridge arm, and more levels make the output voltage closer to the sine wave, which is conducive to improving the quality of incoming current. Furthermore, the negative polarity of the DC side of the topology is directly connected to the voltage neutral of the AC side to eliminate the common mode leakage current of the stray capacitor to the ground. Finally, the working principle of the inverter circuit and the realization method of the specific modulation strategy are provided, and the key parameters are designed.

An experimental prototype was built. The experimental results show that: (1) The inverter’s two working modes overcome the limitation that the traditional multilevel inverter can only step down, making it suitable for a wide range of input voltage changes. (2) The common ground structure can effectively inhibit leakage current. (3) The output voltage V_AB of the bridge arm presents five voltage levels, and the energy storage capacitor can be charged and discharged at a high switching frequency, ensuring the stationarity of the output voltage of each level. Hence, the output voltage waveform is symmetrical in the positive and negative half cycles. At the same time, the incoming current i_g can accurately track the phase of the grid voltage V_g, producing a smooth output waveform with little distortion, which meets the requirements for grid-connected current quality. (4) The proposed inverter can output reactive power output, which meets the requirements of non-unit power factor operation in IEEE grid-connected standards.

AC-DC converters are key equipment to interface the AC grid, DC loads, and renewable generation sources. Efficiency and power density are the main factors in the design and implementation of AC-DC converters. The two-stage power conversion has low system efficiency and high cost. A single-stage AC-DC converter achieves AC-side current regulation, DC-side voltage regulation, and high-frequency galvanic isolation simultaneously through only one stage of high-frequency power conversion, which has the potential advantages of high efficiency and power density. However, the design and implementation of single-stage AC-DC converters are difficult.

This paper presents a resonant single-stage isolated AC-DC converter based on a fixed frequency pulse width modulation strategy. When the switching frequency of the converter is set to the resonant frequency of the series-resonant tank, the impedance of the resonant tank always features zero impedance. Therefore, in steady-state, the total voltage applied on the resonant tank must also be zero, which means the fundamental voltage generated by the primary-side and secondary-side switching bridges must be equal. Following this idea, the converter can operate in both voltage step-down and step-up modes, and the equivalent voltage gain of the converter is continuously adjustable in a wide range by adjusting the pulse width of the high-frequency excitation voltages applied on the resonant tank. Hence, the voltage and current regulation requirements of the single-stage AC-DC converter can be satisfied. Voltage step-down regulation can be achieved by adjusting the primary-side duty ratio D_p, while the voltage step-up regulation can be achieved by adjusting the secondary-side duty ratio D_s.

In order to realize the soft-switching of all switches within a wide voltage range, the soft-switching characteristics of the converter are analyzed in detail. It is found that the magnetizing inductance L_m and quality factor Z_r of the resonant tank must be small enough within the entire AC voltage range, leading to much higher conduction losses. When the instantaneous AC voltage is low, the switching losses of switches are also low. Therefore, it is unnecessary to achieve soft-switching within the entire AC voltage range, and trade-offs between switching loss and conduction loss must be made to design the converter’s parameters. Therefore, an optimized parameters design method is proposed for the resonant single-stage AC-DC converter.

An experimental prototype is built and tested. The experimental results indicate that through the fixed-frequency pulse-width modulation strategy, step-up and step-down power conversions, the AC and DC side voltage and current regulation, and high power factor can be realized. With the proposed parameter optimization design method, soft switching of switches can be achieved in a wide input voltage range. The efficiency of the converter is up to 94.2%. In addition, experimental results indicate that the converter has excellent dynamic and steady-state performance.

In the application of new energy, energy storage, and emerging power loads, the power supply architecture using the DC bus has more advantages than the AC bus, which is the development direction of the future power supply system. Bipolar DC microgrid systems are often used to connect various renewable energy sources and emerging loads due to their higher reliability, flexibility, and efficiency. This paper proposes a synthesis method for non-isolated bipolar output DC-DC converters. A series of bipolar output DC-DC converter topologies are deduced. In order to further improve the performance of bipolar output converter, a novel high-voltage-gain DC-DC converter with a three-winding coupled-inductor is proposed by introducing coupled- inductor and switched-capacitor step-up technology to Boost bipolar output DC-DC converter.

Based on the characteristics of the bipolar output converter, the topology synthesis principle of the proposed bipolar output DC-DC converter is given. The input ends of a positive output DC-DC converter and a negative output DC-DC converter are connected in parallel, and the output ends are in series. This paper gives a series of bipolar output DC-DC converters by classifying and combining traditional DC-DC converters. However, the boost capacity of these converters is limited, and the positive and negative output voltages are only regulated by the duty cycle of the switch. Thus, a bipolar high-voltage-gain DC-DC converter with a three-winding coupled-inductor is proposed. The bipolar output voltages can be adjusted flexibly by the turns ratio of the coupled inductor and the duty ratio. This paper gives the construction principle, operating mode, voltage gain, and stress derivation of the high-voltage-gain bipolar output converter. Compared with the converters in the literature, the proposed converter has apparent advantages in voltage gain and device voltage stress. An experimental prototype with a rated power of 200 W is designed. Experimental results show that the input current ripple is small, and the actual voltage gain of the converter is 380/32=11.875, slightly lower than the calculated (3+n₁+n₂)/(1-D)=12, which is caused by parasitic resistance and control signal delay. The efficiency of the proposed converter is 95.5% at full load and 96.7% at half load.

The following conclusions can be drawn. (1) High voltage gain can be achieved with low input current ripple and small switching device voltage spikes. (2) Symmetrical bipolar output voltage can be achieved, reducing the need for high voltage gain of power supply and load. (3) The converter power is distributed on two DC bus bars, which makes the system more efficient. (4) Part of the diode realizes zero voltage switching turn-off, reduces the diode reverse recovery loss, and improves the efficiency of the proposed bipolar output converter.

In recent years, DC-DC converters have been widely used and promoted in renewable energy power generation systems, electric vehicles, and aviation power supplies. However, the output DC voltage of renewable energy sources is low. Increasing the duty cycle can improve the high gain but brings problems such as high voltage spikes across semiconductors, high losses, and low efficiency. A high step-up and high-efficiency DC-DC converter is necessary, which can be achieved by busing switched-inductor, switched-capacitor, coupled inductor, and other techniques. Simultaneously, the practical application has imposed stringent requirements on DC-DC converters, including miniaturization and lightweight design. Using magnetic integration technology can partially fulfill the developmental needs of the converter.

Based on the quadratic Boost converter, the switched capacitor and clamping branch combination is simplified using device multiplexing. Subsequently, the coupled inductor is integrated with decoupled magnetic technology, effectively reducing the volume and number of magnetic components. Therefore, a high step-up quadratic converter is achieved with a dual-coupled inductor’s magnetic and switched capacitor. The working principle of the proposed converter is analyzed, the parameters are derived, the calculation methods for loss and efficiency are provided, and the related diagrams depicting loss proportion and efficiency analysis are generated. The structure and parameters of the integrated magnetic component are designed and simulated. The volume of the integrated magnetic component is reduced by about 13.4% compared with the discrete magnetic component. Finally, an experimental prototype is built, and the feasibility of the topology is validated.

The proposed converter’s input voltage is 12 V, switching frequency is 50 kHz, turn ratio is 1, output voltage is 185 V, output power is 200 W, and load is 170 Ω. Different output power can be obtained by adjusting the load size. When the output power is 140, 160, 180, 200, 220 and 240 W, the corresponding efficiency is 91.6%, 91.9%, 92.4%, 93%, 93.3%, and 92.7%, respectively. Under the load of 200 W, the experimental efficiency reaches 93%.

The proposed converter has the following characteristics: (1) the dual-coupled inductors improve the voltage gain. The duty cycle and turn ratio can be adjusted to obtain high voltage gain, and the switch has low voltage stress. When the duty cycle is 0.5 and the turn ratio is 1, the voltage stress is about 25% of the output voltage, and the voltage gain is 16 times. (2) The clamping structure can absorb the leakage inductor of the coupled inductor, which effectively alleviates the voltage spike on the switch. (3) The diodes experience low voltage stress, ranging from 16% to 66% of the output voltage, allowing for the selection of diodes with a low withstand voltage. (4) The decoupled magnetic integration technology is adopted, which reduces the number and volume of magnetic components.

To achieve continuous and real-time stress optimization control of the dual active bridge converter under power transmission or voltage fluctuations, it is crucial to study the patterns between modes and among optimization control variables in modes. However, current research needs depth, and functional expressions of stress optimization control variables are complex.

This paper employs genetic algorithms for stress optimization. The intrinsic laws among the optimization variables in each mode are elucidated through the optimization results. An innovative trigonometric function polar coordinate method is adopted to derive the corresponding optimization control variable function expressions.

Firstly, based on waveform equivalence simplification and the principle of waveform and energy transmission, the four locally optimal modes are identified from the twelve working modes, which exhibit low stress or effective values in different power ranges. It reduces the number of modes that require optimization, which reduces the optimization burden.

Secondly, the stress of the four modes is optimized, and the optimization results are compared to determine the laws governing the optimization variables in different power ranges with different k values. Through systematic analysis, the laws of four local optimal operating modes in the low/high power section can be obtained.

Thirdly, the expressions with optimization variables are obtained by substituting these laws into the corresponding power transfer expression. The optimized variables are converted into trigonometric polar coordinate forms through the trigonometric function polar coordinate method. The expressions for the minimum current stress function and its optimization control variables are obtained by substituting optimized variables into the stress expression to obtain the minimum stress value.

Compared with the current stress in the full power range for four local operating modes, the optimal mode and optimal control variables for each power segment across the entire power range are selected, thereby achieving global optimization control. The innovations in this study are presented.

(1) Analyze and contrast the current stress optimization results for different voltage adjustment rates k to discern the laws among the optimized variables across the four local optimal modes in various power ranges.

(2) The power constraint and trigonometric polar coordinate methods are utilized to derive a precise expression for the optimal stress control variables. The globally optimal control variables are selected by comparing the current stress of four local optimal modes.

The following conclusions can be drawn. (1) Under the buck operation conditions of stress optimization for both forward and reverse power transfer across the entire power range, mode 1.1 is globally optimal during low forward transmission power when 0<P<k²(1-k); mode 1.4 becomes globally optimal during high forward transmission power in the range k²(1-k)<P<k/2. Similarly, for low reverse transmission power, mode 2.1 is globally optimal in the range k²(k-1)<P<0, and mode 2.3 becomes globally optimal during high reverse transmission power when -k/2<P<k²(k-1). (2) The stress optimization control under TPS modulation improves the efficiency of the DAB converter compared to other modulation strategies. Notably, it exhibits a significant enhancement under the low-power segment and high-voltage mismatch scenarios.

This paper proposes a fault diagnosis method based on an improved dung beetle optimization algorithm (IDBO) to solve the problem of low accuracy of mechanical fault diagnosis of high-voltage circuit breakers. Tent chaotic mapping, a golden sine strategy, and adaptive t-distribution perturbation are incorporated to optimize a deep hybrid kernel extreme learning machine (DHKELM).

Firstly, this paper takes a TY-1S-12/630-16 single-phase vacuum high-voltage circuit breaker as the research object and builds a platform for collecting high-voltage circuit breaker closing vibration signals. Five operating conditions are simulated: normal state, cushion spring fatigue, base looseness, insulator looseness, and drive shaft jam. The laser vibrometer’s sampling time and frequency are set to 1 000 ms and 78 125 Hz. 60 groups of samples for each condition of the high-voltage circuit breaker are collected, totaling 300 sets of samples.

Secondly, the successive variational modal decomposition (SVMD) is used to decompose the acquired signals, the seven IMF components with different center frequencies are obtained after decomposition, and the power spectral entropy of each IMF component is extracted to construct the feature vector matrix. Data dimensionality reduction of the feature vectors is carried out using the t-distribution-stochastic neighborhood embedding algorithm (t-SNE) to obtain 300 by 3-dimensional feature vectors. After dimensionality reduction by t-SNE, the samples of the same state show clear clustering characteristics, while the samples of different states are separated in the mapping results of t-SNE. Hence, the problems of information redundancy and high- dimensional data are avoided.

Then, by introducing three optimization strategies-fusion Tent chaotic mapping, golden sine strategy, and adaptive t-distribution perturbation, the improved dung beetle optimization (IDBO) algorithm is proposed. The IDBO algorithm optimizes the parameters of the DHKELM for constructing the IDBO-DHKELM high-voltage fault diagnosis model. The unimodal and multimodal functions from the CEC2005 test suite are selected for performance testing. The improved IDBO algorithm is compared with traditional PSO, WOA, and DBO algorithms, verifying its superior convergence speed, optimization precision, and stability in finding the optimal solution.

Finally, a platform is built to simulate mechanical failures of high-voltage circuit breakers. The fault diagnosis results show that the proposed method’s fault diagnosis accuracy reaches 98.33%, and the average accuracy of the classification of the DHKELM model is improved by 11.67%, 5.83%, and 3.33%, respectively, compared with that of the traditional SVM, ELM, and CNN models. The DHKELM model improves the average classification accuracy by 9.16% and 7.5% compared with PSO-DHKELM and DBO-DHKELM models, and the precision rate, recall rate, and F_1-score are greatly improved.

With the increasing scale of urban power grids and the application of various advanced power equipment, the comprehensive efficiency of the power system depends on the cooperation and synergy between various power equipment. Aiming at the physical entities with dynamic and real-time changes in the state of power equipment, constructing an efficient mathematical model is essential in system-level simulation of power systems and integrated design of large electromagnetic equipment. Taking the magnetically-saturated controllable reactor (MSCR) as the object, this paper proposes a nonlinear dynamic electromagnetic network model, considering the accuracy of theoretical analysis and the efficiency of parameter calculation.

Firstly, according to the structural characteristics and magnetic field distribution characteristics of MSCR, the MSCR solution domain is meshed by domain discretization. Considering the nonlinearity of the iron core, the magnetization curve model of the MSCR iron core is established by the piecewise interpolation method. The nonlinear grid parameters are calculated according to the principle of the flux tube. The MSCR equivalent magnetic network model is generated based on the loop current method.

Secondly, the electromagnetic model of circuit-magnetic circuit separation is established. The electromagnetic coupling equivalent circuit is established using the controlled source to realize the coupling connection between the circuit and the magnetic circuit. The nonlinear dynamic electromagnetic network model of MSCR is generated. Combined with the nonlinear iterative solution of the chord-cut method, the MSCR winding current and the core flux under different magnetic saturations are calculated.

Finally, a three-dimensional finite element model of MSCR is established based on the finite element method, and field-circuit coupling joint simulation is carried out. Experimental measurements are also performed on the MSCR winding current. The MSCR nonlinear dynamic electromagnetic network model is compared with the three-dimensional finite element model and experimental measurements. The MSCR nonlinear dynamic electromagnetic network model is verified.

(1) The proposed model's calculated winding current and core flux agree with the finite element model and experimental results under different magnetic saturations. (2) The calculation speed and the storage space of the proposed model in electromagnetic parameter calculation are approximately 50~240 times and 1/10 000~1/7 000 of the finite element model. The model can improve calculation efficiency and reduce cost while meeting computational accuracy. It has unique advantages in the initial design of controllable reactors and system-level simulation of power systems.