The state of health（SOH） estimation for sodium-ion batteries is crucial for their safe and efficient applications, which is also a key to large-scale energy storage implementations. However, sodium-ion batteries exhibit usage-induced degradation with unclear mechanisms and are sensitive to operating conditions and environmental factors, posing a challenge to the accurate SOH estimation. In this paper, a data-driven SOH estimation method for sodium-ion batteries is proposed. The charging data is correlated with capacity degradation, and variance filtering, grey relational analysis and recursive feature elimination are integrated for feature selection. In addition, four machine learning methods including multiple linear regression, support vector machine, Gaussian process regression and error back propagation neural network are applied to formulate the corresponding estimation methods. Test results reveal that the root mean square errors for the four methods are all less than 1.6%, with Gaussian process regression showing an error rate below 0.8%, indicating a precise SOH estimation for sodium-ion batteries.

Aimed at the problem that DC-DC converters with coreless transformers must operate at high frequen-cies, a DC-DC converter with a coreless transformer based on free decay oscillation is proposed. First, a circuit model in series-series topology with no excitation sources is established, the evolution of the eigenvalue is discussed, and the free decay oscillation behavior of the system is analyzed. Second, the DC-DC converter with a coreless transformer based on free decay oscillation is designed. The switching frequency of this converter can be significantly lower than the operating frequency of the coreless transformer, and the output power from the converter and the operating frequency of the core-less transformer can be described by the eigenvalue of the free decay oscillation system. Finally, an experimental proto-type was constructed, which was under constant duty control. The switching frequency of the converter was reduced to one half（103 kHz） and one third（69 kHz） of the operating frequency of the coreless transformer（206 kHz）, respective-ly. The converter efficiency achieved 91.2%, and the transformer efficiency was always higher than 96%.

The insulated-gate bipolar transistors（IGBTs） have been widely applied in the modern power electronics technology, and the paralleling of IGBTs has become an economical and feasible method in some working scenarios where one single device cannot meet the design requirements. The paralleling of IGBT modules can simplify the circuit structure, increase the converter output power, and improve the power density of devices. During the operation of IGBTs in parallel, the current imbalance, which may be caused by the difference in IGBTs' characteristics in a static or dynamic mode, the inconsistency of junction temperature, the asymmetry of a drive circuit or power loop, as well as the aging or failure of IGBTs due to long-term use, will affect the system's reliability and stability. The research hotspots of parallel-operating IGBTs at home and abroad are investigated. The principle and influence of static and dynamic current imbalance are summarized, and the difference in the current-sharing control principles is analyzed. The performance characteristics of current-sharing control are summarized and compared from the aspects of power loop current-sharing control and drive circuit current-sharing control. Furthermore, the development of current-sharing technologies for parallel-operating IGBTs in the future is also prospected.

A design method for small- and medium-power DC/DC converters suitable for low-orbit commercial aerospace is given in this paper. A synchronous rectifier flyback topology and surface mounted devices are adopted, which can meet the demands for common single- and multi-output DC/DC converters applied in aerospace, with advantages of low cost, high performance, high reliability, and mass production. To further improve the conversion efficiency and power density, gallium nitride（GaN） FETs are also used. In addition, the losses of main power devices in the topology under different operating conditions are calculated and compared. Finally, a DC/DC converter with a wide range of input voltage（23-47 V） and output of 5 V and 30 W was built for verification.

Owing to its obvious advantages such as high control flexibility, no commutation failure and strong dynamic reactive power support capability, the voltage sourced converter based high-voltage direct-current（VSC-HVDC） transmission technology has been widely applied in scenarios including point-to-point transmission, back-to-back interconnections and DC grids. As a core piece of equipment in VSC-HVDC transmission engineering, the VSC valve achieves AC/DC energy conversion through frequent switching of power electronic devices. In this paper, the key design requirements for VSC valves in different application scenarios are systematically summarized by combining with practical experiences accumulated in engineering, the commonly used power devices and VSC valve topologies in VSC-HVDC transmission engineering are compared and analyzed, and their development trends are projected. In addition, different schemes for two typical application scenarios in the future are also compared, providing reference for the applications of VSC-HVDC transmission technology in high-voltage, large-capacity and long-distance transmission scenarios.

A Super-Boost converter can greatly reduce the mass and volume of power supply and improve the cor-responding power density by replacing the traditional charging and discharging module, so it has a broad application prospect in space power system. However, due to the existence of multiple power components and the reverse flow char-acteristics of inductance current, its power supply mode and output ripple voltage are more complex than those of the traditional Boost converter. To provide a theoretical guidance for the analysis and design of the Super-Boost converter, its power supply mode and output ripple voltage are studied. It is found that there exists continuous conduction mode, pseudo continuous conduction mode and pseudo discontinuous conduction mode in both inductor L₁ and L₂. The analyti-cal mathematical models of critical inductance and output ripple voltage in each operation mode are established, the re-lationship between peak current and inductance is discussed, and the minimum capacitance and minimum inductance that meet the design requirements are obtained. On this basis, a design method for the converter parameters is given, and experimental results verify the theoretical analysis.

Silicon carbide metal-oxide-semiconductor field effect transistor (SiC MOSFET) has attracted attention from the industry owing to its excellent characteristics such as high voltage, high frequency and low conduction loss. However, compared with the silicon-based IGBT, the problem of gate oxide reliability caused by the high defect density at the SiC/SiO₂ gate oxide interface has become a key bottleneck restricting the large-scale applications of SiC MOSFET devices. By sorting out and analyzing the research results of the gate oxide reliability of SiC MOSFET at home and abroad in recent years, the causes of the gate oxide reliability problems at present were elaborated upon, and various commonly-used gate oxide reliability evaluation methods were summarized and compared. Finally, the gate oxide reliability of SiC MOSFET under extreme operating conditions and the development status of technologies for improving its performance were discussed.

Accurately obtaining the electromagnetic characteristics of high-voltage and high-power switching devices is crucial for predicting the electromagnetic interference in a system in which the devices are located. Research is focused on an equivalent method of switch waveforms for analyzing the electromagnetic characteristics of high-voltage and high-power switching devices. Aimed at the problem that the existing equivalent waveforms are too ideal to reflect the complex spectral components in the switching transients of devices, an analytical model for the electromagnetic characteristics of devices considering their switching processes is proposed. Starting from the time-domain analytical formula for the analytical model and based on the Fourier transform theory, the frequency-domain analytical formula for the analytical model is derived, and the spectral envelope characteristic parameters are analyzed to obtain the spectral characteristics of the analytical model. The theoretical analysis was verified by using the measured switching waveforms of Si IGBT and SiC MOSFET devices.

Aimed at the particularity of an isolated DC/DC converter when it is applied in a space radiation environment, the isolated magnetic feedback circuit is usually used to improve the feedback accuracy and stability. The working principles for several commonly used amplitude modulation magnetic feedback circuits are introduced, and a forward-flyback amplitude modulation bidirectional magnetic feedback circuit is introduced and optimized to solve the problem of the need for an additional secondary power supply voltage. Under the premise of realizing the same function, a two-winding transformer is used to replace the three-winding transformer, which effectively reduces the volume of the magnetic core and simplifies the circuit structure. The working principle for the circuit and the design method for a pulse sampling circuit and a magnetic feedback transformer are analyzed in detail. In addition, based on the magnetic feedback circuit, a DC/DC converter prototype with 100 W output was built. Simulation and experimental results show the effectiveness of the proposed isolated magnetic feedback circuit, providing a theoretical guidance for engineering design.

For practical conditions where both the load and coupling coefficient may vary obviously, a novel nonlinear topology of wireless power transfer(WPT) based on ferro-resonance is proposed. First, the working principle is qualitatively analyzed using the Duffing equation and phasor analysis method. Second, the finite element software for circuit simulation is used to verify the principle. Finally, a prototype of nonlinear topological WPT system with power up to 566 W and efficiency up to 93.5% was built. Experimental results show that the proposed nonlinear LCC-LCC topology can tolerate the drastic changes in coupling coefficient from 0.1 to 0.5 and load resistance from 72 Ω to infinity under 200 V secondary output voltage, indicating an excellent anti-misalignment capability and load stability. With a novel principle and a simple structure, the proposed topology has the potential to be applied in engineering.

The advancements in research on automotive power device packaging have significantly improved the dynamic performance and driving range of electric vehicles, making them more efficient and reliable. With the continuous optimization of automotive power device packaging, the electric vehicle industry is expected to embrace a broader market prospect and development space. In recent years, power device packaging modeling, packaging structure and optimization, thermal management and junction temperature monitoring, gate drive and applications, reliability analysis, and online monitoring have become current research hotspots and have received sustained attention from both the academic and industrial sectors. To promote discussions on the challenges and hot issues related to automotive power devices packaging and their applications, a special issue titled “High Reliability Power Device Packaging and Assistant Technology in EV Application” has been launched in the Journal of Power Supply.

Silicon carbide（SiC） is a promising wide-bandgap semiconductor material owing to its excellent electrical and thermal characteristics. Power metal-oxide-semiconductor field-effect transistors（MOSFETs） based on SiC are suitable for high-power fields, and their high-temperature gate oxide reliability is one of the most concerned characteristics. In this paper, the high-temperature gate oxide reliability of self-developed SiC MOSFETs is compared with that of the foreign SiC MOSFETs of the same specification by positive and negative high-temperature gate bias（HTGB） tests. The negative HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is almost equal to that of the foreign SiC MOSFETs, and the maximum discrepancy between them is about 4.52%. However, the positive HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is smaller than that of the foreign SiC MOSFETs, with a maximum discrepancy of 11%. The reason for the better performance of self-developed devices is that an appropriate amount of nitrogen is added to the SiC/SiO₂ interface, which can passivate interface defects and reduce the generation of fast interface states, so that the total interface state density is minimized.

A soft-switching DC-DC converter with low current ripple and high gain is proposed, which can be applied to new energy generation systems. Based on the conventional interleaved Boost converter, the proposed converter can achieve high gain by introducing a coupled inductor, diodes and a capacitor Boost unit. The coupled inductor transmits energy during the entire switching cycle, thus improving the utilization rate of magnetic core. The input Boost stage works in an interleaved mode, and the current ripple of the two-phase inductor can cancel each other, so as to obtain a lower input current ripple. Due to the existence of leakage inductance of the coupled inductor, the reverse recovery problem of rectifier diodes are alleviated. Meanwhile, an active clamp circuit is adopted to absorb the leakage inductance energy, thereby achieving the zero-voltage soft-switching of all switches, restraining the turn-off voltage spike of switches, and improving the converter’s conversion efficiency. The working principle, circuit characteristics and soft-switching realization method of the converter are analyzed in detail. Finally, a 200 W experimental prototype was built to verify the theoretical analysis.

In this paper, the modulation scheme for a dual active bridge（DAB） bidirectional DC/DC converter is stud-ied. The main advantage of the DAB converter is that it has characteristics such as symmetrical structure, bidirectional power flow capability, wide soft switching range and flexible control capability. The simplest way to control this topology is to control the direction and magnitude of power transmission by adjusting the phase shift angle between the primary and secondary bridges. However, when the input or output voltage of the converter varies widely, a large amount of reac-tive power will be generated under light load conditions. Meanwhile, the zero voltage switching（ZVS） operation of part of switches cannot be maintained, which directly leads to a low conversion efficiency. Therefore, to improve the efficiency of the DAB converter, a hybrid phase shift modulation（PSM） scheme is proposed, which can reduce the inductor root-mean-square（RMS） current and extend the soft switching range on the basis of keeping the control simple, thereby improving the performance of the converter. First, by making the controllable variables in the extended phase shift（EPS）, dual phase shift（DPS） and triple phase shift（TPS） modulation schemes equal, four different PSM schemes are obtained. Then, the steady-state characteristics of these modulation schemes are compared and analyzed, including their transmission power capacity, inductor current level and soft switching performance. On this basis, a hybrid PSM scheme is formulated. Fi-nally, an experimental platform was built to verify the effectiveness and correctness of the proposed modulation scheme.

A mobile relay wireless charging system can realize bidirectional wireless power transfer between the ground-side power supply and load, thereby providing increased portability and flexibility for energy storage and charging and facilitating unmanned and intelligent electrical equipment. As a novel wireless charging system, the mobile relay wireless charging device has many focuses and challenges in its design, one of which is the bidirectional power conversion. Therefore, a novel topology for the power conversion in mobile relay bidirectional wireless charging was proposed, and specific parameters for implementation were designed, which were further validated through simulation and experimental results. A simulation model of the bidirectional wireless charging system was established, and simulations were conducted under different values of mutual inductance, load, and output power. In addition, a 10 kW bidirectional wireless charging system was constructed for relevant experimental studies, and it was found that the simulation results and experimental data were consistent, further confirming the correctness and feasibility of the proposed topology and the overall system.

The development of power modules towards high temperature, high power and high density raises higher requirements for the packaging structures of modules. Compared with the traditional wire-bond structure, the double-sided structure has attracted more and more attention owing to its characteristics such as high heat dissipation capacity and low parasitic inductance. However, the mismatch of thermal expansion coefficient between materials used in the double-sided structure makes the structure suffer tremendous thermo-mechanical stress, thus reducing the reliability of power module. Therefore, to develop double-sided bi-directional modules with low thermo-mechanical stress, the effects of chip layouts on the heat dissipation performance of modules and the parasitic inductance were analyzed by simulations at first. Then, a flexible buffering spacer with low Young's modulus is proposed accordingly. The feasibility of reducing the thermo-mechanical stress and improving the reliability of the module was preliminarily proved by simulation and experimental results.

The phenomenon of dynamic avalanche occurring during the IGBT turn-off process is one of the important reasons for its failure. To study the dynamic avalanche failure mechanism of IGBT, the Silvaco software was used to simulate and analyze this mechanism. Through the simulation and analysis of the breakdown mechanism, current density distribution and temperature distribution of dynamic avalanche, it is concluded that dynamic avalanche can generate moving current filaments and dead filaments which are either moving slowly or fixed. However, the failure of the device is caused by the dead filaments formed by dynamic avalanche. The dead filaments will lead to a sharp increase of local temperature in the IGBT, and the IGBT will eventually fail because the local temperature is too high to burn the device. On this basis, the causes of dead filaments are analyzed, and specific measures to prevent the dynamic avalanche failure of IGBT are also put forward.

Aimed at the problems of fast loss and high capacity configuration of battery energy storage equipment in microgrid, an optimal configuration model of battery energy storage capacity of microgrid considering life loss is established in this paper. In addition, a cost calculation method for the battery energy storage life loss based on fixed daily cycle times is also proposed. This method combines the piecewise linearization idea and the scenario analysis method, and it can effectively extend the lifetime by optimizing the discharging depth and daily cycle times of battery energy storage. Moreover, considering the uncertainties in wind power output and load power, a two-stage robust optimization model is introduced, which is further solved by the column-and-constraint generation algorithm. Finally, the effectiveness of the novel model under different uncertainties and different unit prices of battery energy storage is verified by numerical examples.

The wireless power transfer(WPT) technology is an effective means to solve the endurance problem of underwater equipment. However, it will be affected by the marine environment when applied underwater. In this paper, aimed at an underwater magnetically-coupled resonant wireless power transfer(MCR-WPT) system, the system composition of an MCR-WPT system is discussed, and a circuit model of the underwater MCR-WPT system is established. In addition, the eddy current loss generated under the marine environment is quantitatively analyzed, and the influence of seawater current impact on the MCR-WPT system is analyzed according to the marine environment. Finally, an experimental platform was set up for verification.

To address the issues of large volume and weight of a magnetic coupler for onboard wireless charging of electric vehicles as well as the susceptibility of ferrite fragmentation, a magnetic coupler with a composite shielding layer composed of ferrite magnetic sheets, nanocrystalline strips and aluminum foil was proposed in this paper. The performances of ferrite and four types of nanocrystalline magnetic cores were analyzed and compared by Maxwell, respectively. Based on machine learning, the optimal magnetic core structure of the magnetic coupler was obtained, and the structure of composite shielding layer and material composition ratio of each part were optimized. Compared with the traditional magnetic couplers composed of ferrite magnetic sheets and aluminum plates, the volume and weight of the magnetic coupler with the proposed composite shielding layer were reduced, while its mutual inductance and coupling coefficient were improved by 8.2% and 0.7%, respectively. In addition, its cost was reduced by 47%. Finally, a 2.5 kW experimental platform with a transmission distance of 12 cm was built for verification.

In a double-load wireless power transfer(WPT) system, the problem of coupling interference between sec-ondary-side coils becomes a critical factor that seriously limits the system performance. To solve this problem, a single-transmitter dual-receiver magnetic coupling mechanism is proposed, which aims to solve the problem of coupling inter-ference between two secondary-side coils. In addition, the same power output for both loads is achieved through the de-sign of the primary-side coil. Without using shielding materials or control methods, this mechanism can achieve complete decoupling of two secondary-side coils only through the design of coil structure. Experimental results show that the ener-gy transfer efficiency of the WPT system with this mechanism can achieve 88.7% under double-load. Moreover, the two loads can operate independently with no interference.

In practical applications, the relative position change between the two coupling coils of a wireless power transfer system will change the system parameters, resulting in system detuning as well as a lower power transmission efficiency. For the problem of system detuning, a variable capacitance tuning control strategy is proposed. By controlling the charge and discharge time of the capacitor, the capacitance is equivalent to a variable capacitance, so that the equivalent capacitance value and the coil inductive reactance value can meet the resonant condition requirements. As a result, the system is always maintained in a resonant state, and the highest transmission efficiency between the transmitting and receiving coils of system will be kept. A simulation model was established, and an experimental prototype of magnetically-coupled resonant wireless power transfer system based on a series-series resonance compensation topology was built. The variable capacitance tuning control experiments were carried out, and experimental results show that the protype can realize stable and reliable wireless power transfer with a resonant frequency of 100 kHz and an input voltage of 20 V, thus verifying the effectiveness of the proposed variable capacitance tuning control method.

As a novel and extensively applied switching device, silicon carbide metal-oxide-semiconductor field-effect transistor（SiC MOSFET） offers a faster switching speed and lower device loss in practical applications, thereby enhancing the converter efficiency and delivering a superior performance. Aimed at the driving characteristics of SiC MOSFET, the influence of parasitic parameters on its performance was analyzed. To investigate the relationship between the gate-source voltage and turn-on time of SiC MOSFET, a two-pulse experimental platform was also established. However, there are certain drawbacks with the existing domestic SiC MOSFET. Based on the experimental platform and other power products, the changes in conduction time, driving loss and negative voltage amplitude after replacing the imported SiC MOSFET with domestic devices were analyzed.

In a weak grid, due to the existence of grid impedance, the natural resonant frequency of a new energy grid-connected LCL filter will shift, and the traditional active damping control strategy cannot guarantee the system stability. Moreover, as the proportion of new energy power generation in the power system continues to grow, how to reduce the operating costs is a hot topic for research. Therefore, a novel control strategy based on grid-connected current and common coupling voltage feedback is proposed in this paper, which not only provides active damping to suppress LCL resonance, but also reduces the use of sensors. In addition, it has a strong adaptability under wide-ranging changes in grid impedance. Simulation and experimental results show that, compared with that under the traditional control strategy, the practical range of weak grid under the improved strategy increases, the system stability is enhanced, and the capability to suppress harmonics is raised, indicating that the quality of grid-connected current is well improved.

The magnetron is used by most of the existing high-power wireless power transfer(WPT) systems as radio frequency(RF) power supply. However, its narrow bandwidth and big mass are not conducive to system integration despite its high output power. To solve this problem, a solid-state microwave power source(MPS) with adjustable power and frequency was designed, which realized a wide bandwidth range and a wide output power range by using broadband amplifiers and feedback regulation. The system was integrated into a box with a size of 28 cm×19 cm×10 cm, and it had advantages such as a small volume, high reliability, a good heat dispersion performance and a small mass, showing its engineering application value to systems of WPT or RF energy harvesting in the environment(simulating the RF energy generation equipment in the environment, such as a base station and WIFI). Finally, the measurement results at room temperature show that the solid-state MPS designed had an adjustable frequency range of 0.7-2.8 GHz, with a frequency step of 1 MHz and a maximum frequency offset less than 0.3 MHz. In addition, it had an adjustable power range of 20.0-39.5 dBm, with a maximum output power error of ±0.5 dB. The design method proposed provides guidance for the study and design of high-power MPSs.

Aimed at a coaxial rotating magnetic-coupling wireless power transfer(MC-WPT) system, a power and signal parallel transfer method based on coaxial ring six-winding(CRSW) coupler is proposed. First, a mathematical model of the CRSW coupler is established, and the expression for the cross-coupling parameters of the power and signal channels is derived. Second, with the combination of finite element simulation, the positional relationship between each winding and the relationship of cross-coupling between the two channels are analyzed, and the conditions for achieving decoupling are given accordingly. Third, the parameters and characteristics of compensation network for the power transmission part of the system are analyzed and designed, and the signal transfer circuit including signal transmitting and receiving parts is presented. Finally, an experimental prototype of the magnetic-coupling wireless power and signal transfer(MC-WPST) system was constructed, and results demonstrate that the proposed CRSW coupler exhibited a better suppression effect on the power crosstalk and switch noise in the fundamental frequency component. The signal transmission rate reached 19 200 bit/s based on amplitude shift keying when the system output power was 150 W.

Aimed at the problem of DC voltage fluctuations caused by load switching, power fluctuations and dou-ble-frequency injection in DC microgrids, a dynamic compensation control strategy for a Buck-type bidirectional DC-DC converter based on model predictive control（MPC） is proposed. First, the corresponding discrete state space matrix is es-tablished, and the input current is used as the disturbance. Second, the model-based inner-loop current predictive control and outer-loop voltage control of the Buck-type bidirectional DC-DC converter is designed. Third, a dynamic compensa-tion control structure based on a residual generator is designed for the current disturbance, and the dynamic compensa-tion controller Q（z） is solved. At the same time, the recursive least squares algorithm is used for parameter identification to reduce the influence of model uncertainty on the dynamic compensation control strategy. Finally, a comparative ex-periment was designed on the PSCAD/EMTDC simulation platform to verify the effectiveness of the proposed control strategy. Experimental results show that the compensation control structure can effectively solve the problem of DC bus voltage fluctuations and enhance the robustness of the entire system without changing the original predictive control.

To ensure the safety of new energy vehicles during the entire period of use, it is necessary to conduct health monitoring for the full life cycle of lithium-ion batteries. Aimed at the low learning rate due to the small capacity of training data set for the remaining useful life（RUL） prediction model based on neural network and the duplicate collinearity of the extreme learning machine（ELM） method, a method for augmenting the training data set is proposed. In addition, based on the improved ELM, an RUL prediction model for the full life cycle of lithium-ion battery is built. First, the early operation data of battery is extracted to formulate health factors, and the Akima interpolation method is used to augment the amount of training data. Then, the salp swarm algorithm is used to improve the ELM network, and the RUL prediction model for the full life cycle of lithium battery is established. Finally, the NASA battery data set is used to validate the model. Experimental results show that the proposed method for augmenting the training data capacity is effective, the capacity tracking capability of the RUL prediction model in full life cycle is strong, and the prediction error is small.

Based on the fact that inductance and capacitance are of fractional-order, the nonlinear dynamic characteristics of a fractional-order Boost converter are studied. The predictor-corrector model of the Boost converter is established using the predictor-corrector algorithm of fractional-order calculus. On this basis, the bifurcation diagrams with the reference current, input voltage and orders of capacitance and inductance as bifurcation parameters are obtained. The period doubling bifurcation and chaotic behaviors of the fractional-order Boost converter are studied, and its nonlinear dynamic behavior is compared with that of an integer-order Boost converter at the same time. Results show that under certain operating conditions, some nonlinear phenomena such as bifurcation and chaos will appear in the fractional-order Boost converter with changes in some circuit parameters. Under the condition of the same circuit parameters, the parameter stability domains of integer- and fractional-order converters are different. Compared with that of the integer-order converter, the parameter stability region of the fractional-order converter is smaller, which more truly reflects the nonlinear dynamic characteristics of the Boost converter.

Aimed at the problem of limited available resonant frequencies in shared channel transmission and inability to ensure the carrier transmission efficiency in the simultaneous wireless power and information transfer(SWPIT) technology, a three-frequency resonant SWPIT technology based on double-LCC circuit is proposed to achieve 3FSK modulation. Compared with the traditional 2FSK modulation circuit, the proposed circuit has the following advantages. First, three-frequency resonant frequency bands are adopted and all the system carriers use resonant frequencies, which avoids the defects such as a low utilization rate of system resonant frequency and a low transmission efficiency. Second, the system is enabled to operate normally at three frequencies, thus achieving full duplex and improving the working efficiency. The work includes an analysis of resonant conditions for low- and high-order circuit resonators, parameter design and frequency selection, and demodulation of signals. In addition, 150 kHz, 177 kHz and 48 kHz experimental platforms were built by Simulink simulation and an experimental prototype, thereby verifying the feasibility of the proposed 3FSK energy modulated technology. The experimental prototype showed that at three frequencies, the output voltage on the receiving side was stable and its amplitude was 4/π times that of DC input voltage, achieving the goal of constant-voltage output.

The design of DC-DC converters which are applied to vehicle auxiliary power modules (APMs) is taken as a research object, the topology of a two-stage DC-DC converter consisting of a three-level Boost (TL-Boost) topology and a half-bridge LLC resonant topology is proposed, and its working principle is analyzed. The front-stage TL-Boost topology converts a wide range of input voltage into a stable voltage, ensuring the high-efficiency operation of the back-stage half-bridge LLC resonant topology. The feasibility and correctness of the proposed DC-DC converter were verified by establishing an experimental platform and carrying out relevant experiments.

The conventional Buck-type power factor correction（PFC） converter has a disadvantage of high harmonic current, which limits its applications. A Buck-type single-switch integrated PFC converter is proposed and analyzed. This converter is composed of a Buck-type PFC converter and a Buck-Boost PFC converter, and they are integrated by only one active switch, thereby simplifying the control. Under the constant on time（COT） control, the dead zone of input current in the Buck-type PFC converter is eliminated. With advantages of Buck and Buck-Boost converters, this converter can achieve a high power factor and a high efficiency in universal-input applications. The circuit structure, working principle, steady-state characteristics and design considerations of the proposed converter are introduced and analyzed. Finally, a 56 W prototype was built, and experimental results verified the analysis results.

The silicon carbide（SiC） device is considered as a semiconductor device with high temperature resistance, and a careful study on its loss and heat dissipation is required when it is applied to high-power-density and high-tem-perature scenarios. The maximum current conduction capability of SiC MOSFET power module at high temperature is stud-ied, and the relationship between electrical performance and heat dissipation is taken into account. Based on an electro-thermal coupling model of SiC MOSFET device and a heat dissipation model of the cooling system, the mechanism of thermal runaway process is analyzed. A co-simulation is conducted to determine the current conduction capability of one SiC power module at high temperature, and the simulation error with respect to the experimental result is about 4%, which verifies the effectiveness of the proposed method.

As power lithium-ion batteries play a key role in the electric vehicle industry, ensuring their working reliability has become a research hotspot at present. In this paper, the materials and manufacturing processes of lithium-ion batteries are reviewed. The battery state estimation and remaining useful life prediction methods are summarized in detail, and the advantages and disadvantages of these methods are discussed. From the perspective of battery management system, the relevant knowledges of equalization management system and thermal management system are sorted out in turn. From the perspective of electric vehicle hybrid energy storage system, the performance degradation mechanism under actual working conditions and the relevant technologies are elaborated upon. Finally, the status quo of key technologies related to the reliability of power lithium-ion batteries used in electric vehicles is summarized from four aspects, and the development possibilities in the future are forecasted.

Aimed at the problem that the output current and voltage from a magnetic coupling resonant LCC-S wireless charging system are easily affected by external disturbance or its own parameter disturbance during its working process, as well as the problem of how to respond to disturbances quickly and accurately, a secondary-side two-stage closed-loop control method of constant-current and constant-voltage based on active disturbance rejection control(ADRC) is proposed. First, the relationship between the output characteristics of LCC-S resonant network and system parameters is studied through the circuit analysis. Second, the state equation model of a secondary-side Buck converter is established to achieve the closed-loop precise regulation of system output, and the tracking differentiator, extended state observer and nonlinear state error feedback in ADRC are designed accordingly. Finally, an experimental platform of wireless charging based on ADRC was built. The control effect is compared between the ADRC and PI controllers under multi-parameter disturbance, and results show that the former shows a better dynamic regulation capability.

The data acquisition and information processing of an underwater wireless power transfer(WPT) system are systematically studied in this paper. For this system, its transmission of power and information is affected to a certain degree considering the complex and changeable underwater environment. Since the marine environment is disturbed by some environmental factors such as temperature and pressure, the medium of underwater power transfer is uncertain, which will affect the electromagnetic field coupling between the power transmitting terminal and the power receiving terminal. As a result, the stability of underwater WPT will be affected, leading to changes in the transmission power and transmission efficiency of the WPT system under seawater conditions. Therefore, it is necessary to acquire the underwater marine environment information in real time and analyze the influences on circuit parameters and transmission efficiency of the underwater WPT system. An information acquisition and processing system based on a variety of sensors was built to realize real-time marine data acquisition, thus effectively solving the problem of underwater data acquisition and improving the data acquisition and data processing efficiency. The influences of the relative permeability, electrical conductivity, and relative permittivity of seawater on the system information and energy transfer are studied. In particular, the influences of temperature and pressure on WPT are analyzed in detail.

The circuit topology of a novel three-phase quasi-Z source AC-AC converter is proposed, and the basic working principle and structure of the circuit are analyzed. In addition, the relationship between input voltage and output voltage is also derived. This circuit topology is controlled by a pulse width modulation method, which can achieve the effect of changing the output voltage. MATLAB/Simulink is used to build a simulation model, and the simulation results are analyzed. Finally, an experimental circuit was built on the basis of the simulation model, and experimental results verified the feasibility of the proposed circuit topology and the correctness of circuit analysis.

A UAV wireless charging coupling mechanism based on dual coupling coils is designed to meet the wireless charging requirements of medium and large UAVs, which has a high transmission energy efficiency and certain offset resistance while satisfying the lightweight design on the UAV side. The dual receiver coils are mounted at the bottom bracket positions on both sides of the UAV, and the dual transmitter coils are mounted on a trapezoidal transmitter platform with the same tilt angle as the UAV bracket to reduce the large range of UAV deflections. Meanwhile, a cascading series connection is used to ensure the uniformity of wireless charging. A series-series(S-S) compensation structure is also used. The finite element simulation is applied to compare and analyze the influence of different parameters of coupling coils on the transmission efficiency, and the design of coupling coils is optimized based on the principle of light weight. A UAV wireless charging experimental system was built, and results show the proposed coupling mechanism can effectively charge the UAV battery at 1.2 kW power with a transmission efficiency of 95.554%. The mass of the UAV-side coupling mechanism was 320 g, which meets the requirements of lightweight design of UAV coupling mechanism and also has certain offset resistance.

Based on the time-sharing working principle, a main-auxiliary(MA) cooperative receiving coil with a lower space occupation rate and a simple control is proposed in this paper, which can effectively improve the anti-misalignment capability of a dynamic wireless charging(DWC) system. First, the structure and circuit topology of the MA coil are designed, and the two auxiliary coils are connected in reverse series and symmetrically placed on both sides of the main coil. Second, the output performance of the MA-coil in the y-direction is calculated based on the time-sharing working principle, and the auxiliary coil only works and enhances the total output power when the misalignment occurs. Third, the most suitable ratio of w_M to w_A is determined through simulations, and the effective misalignment range and anti-misalignment capability are compared between the MA and square coils in this case. Finally, an experimental prototype was built, and it was found that the effective misalignment range of the MA coil reached 0.183τ, which is 23% higher than that of the square coil of the same size.