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.

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.

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, 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.

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.

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.

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.

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.

Hydrogen, as a clean, efficient, and high-quality energy source, is recognized as a crucial solution for decarbonizing the energy system and mitigating climate change. The electricity and hydrogen energy system, which uses electricity and hydrogen as energy carriers, represents a key pathway for integrating power systems with hydrogen energy. It helps overcome the developmental limitations of renewable energy, fosters the interconnection and complementarity of multiple energy modes, and promotes deep integration across generation, grid, load, and storage. The electro-hydrogen coupling process, central to this system, can lower operating costs through peak shaving and valley filling. However, the efficiency of electrolyzers and fuel cell remain suboptimal, resulting in significant exergy losses alongside economic benefits during the coupling process. Striking a balance between economic viability and energy saving continues to be a challenging task. Moreover, the substantial forecasting errors caused by the uncertainty of renewable energy outputs can negatively impact the supply-demand balance and the operating conditions of electrolyzers. Therefore, the uncertainty risks associated with renewable energy must be thoroughly considered in optimal scheduling. In response to the above problems, a robust optimal scheduling model based on exergoeconomic analysis is proposed, with the uncertainty set defined by the confidence interval to reduce the conservatism of robust optimization.

Firstly, considering the dynamic efficiency characteristics of the electrolyzer, piecewise linearization was applied to handle the non-convex terms introduced by this relationship. The operation model of the electrolyzer including hydrogen production power allocation and operation models of fuel cell and energy storage equipment were constructed. Secondly, the energy quality coefficients were employed to analyze the exergy loss distribution based on the equipment operation model. A cost accounting method for exergy losses, including both internal and external factors, was proposed. Internally, the cost allocation method was used to price unit exergy losses, enabling the calculation of operational loss costs based on the distribution of exergy losses. Externally, the cost of transmission line losses and penalties of wind curtailment were calculated according to current electricity prices and relevant policies. Thirdly, taking into account constraints such as electrolyzer start-stop cycles, ramping power, and energy balance, an optimal scheduling model was developed with the goal of minimizing total exergy loss costs in the electricity and hydrogen energy system. Then, the model was reformulated into a robust optimization problem based on the uncertainty set of the confidence interval，and a dual transformation method for solving the model was proposed.

In the case simulation, four cases are set up for comparative analysis, leading to the following conclusions: (1) By setting the wind curtailment penalty coefficient appropriately, with the goal of minimizing exergy loss costs, a balance can be achieved between the economic benefits and the exergy losses associated with the electricity-hydrogen coupling process, while ensuring the efficient absorption of wind power. (2) The proposed model can further improve the overall hydrogen production efficiency of the electrolyzer array by taking advantage of the flexibility of hydrogen production power allocation. (3) The confidence interval is used as the uncertainty set of robust optimization, which can take into account the probability characteristics of random variables, and reduce the conservative degree of system operation under the premise of ensuring robustness.