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.

Owing to environmental protection and transportation convenience, the proportion of electric bicycles（E-bikes） is increasing. However, the safety and convenience of charging has become a bottleneck for the wide applications of E-bike. Therefore, the wireless charging for E-bike has become an alternative development direction in the future. The current status of wired charging of E-bike is briefly described, the wireless charging technology for E-bike is introduced, and the research status both at home and abroad is reviewed. Then, the relevant standards and industrial status of wireless charging for E-bike are presented. Finally, the key problems and development trend of wireless power transmission technology for E-bike are discussed, thus providing technical reference for the research and development of E-bike wireless charging.

To solve the problem that the conventional single-inductor dual-output（SIDO） Buck converter has a low step-down ratio, a quadratic type unit is introduced and a dual-output Buck converter with a high step-down ratio is proposed. The working principle for this converter is analyzed in depth, and it is found that there exist four working modes. The voltage gain expression of this converter is formulated, the critical inductance in each working mode is obtained, and the relationship among the working mode, inductance and load is summarized. The analytical expressions of output ripple voltage（ORV） in each working mode are established, and the relationship between ORV and inductance is analyzed. The inductance ripple current and capacitance ripple voltage are taken as constraint conditions, and the design formulas of inductance and capacitance are obtained. An experimental platform was set up, and experimental results verified the theoretical analysis.

SiC MOSFET has a high operating frequency and a good temperature stability, which can reduce the system loss and improve the system efficiency when applied to a three-level Buck converter. However, its high-frequency charac-teristics will make its voltage spike more serious during the switching process. To solve this problem, its switching process in the three-level Buck converter is analyzed, and the generation mechanism of transient voltage spikes is explored. Based on the optimization and improvement of a traditional charge-discharge RCD snubber, a low-loss RCD snubber is designed as a voltage spike suppression method. First, the working principle and loss of the charge-discharge RCD snubber and the improved low-loss RCD snubber were compared and analyzed. Second, a three-level Buck converter experimental unit was built, and the absorption capacitor and resistance of the low-loss RCD snubber were parameterized. Finally, the effectiveness of the low-loss RCD snubber and the rationality of the parameter design were verified experimentally. The combination of theoretical analysis and experimental results indicate that the three-level Buck converter with the low-loss RCD snubber has a lower system loss than that with the charge-discharge RCD snubber.

The traditional single-stage Boost LLC resonant AC/DC converter has been widely concerned because of its advantages such as less conversion stages, a high power factor and soft switching. However, due to its disadvantages such as a high DC bus voltage and a large stress in switching devices, it is generally applied in power grids with voltage below 110 V. To overcome this problem, a novel type of Buck-Boost LLC resonant AC/DC converter for 220 V power grid is proposed, which not only has the characteristics of traditional structures, but also has the advantage of adjustable bus voltage in the case of a high input voltage. The working process of the converter controlled by pulse frequency modula-tion（PFM） is analyzed, the realization mechanism of power factor correction and soft switching are elaborated upon, and a design method for the key parameters of its main circuit is also given. Finally, an experimental prototype with 170-230 V input and 48 V/100 W output was built, and experimental results verified the theoretical analysis and the grid applicability of the proposed topology.

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 conventional frequency-controlled LLC resonant converter is unsuitable for wide voltage range applications, and it suffers from a large circulating current, which makes it difficult to achieve a high conversion efficiency. To cope with these issues, a simple fixed-frequency PWM control strategy is proposed. The rear arm of the resonant converter is controlled by a fixed switching frequency, and the switching frequency is equal to the resonant frequency. Then, the front arm adopts PWM control to convert the input voltage of the resonant network into a multi-level voltage, so that the voltage gain adjustment range of the resonant converter is doubled. Under this control strategy, the gain range is independent of load and magnetizing inductance, which can simplify the design of resonant parameters. By designing a larger magnetizing inductance, the conduction loss of circuit and turn-off loss are reduced to improve the conversion efficiency. Simulation results show that the resonant converter can achieve a wide output voltage range. In addition, the circulating current and turn-off current are reduced. Finally, the feasibility of the proposed control strategy was verified by experimental results.

With the increasing demand for electric bicycles（E-bikes）, there exist safety risks in the traditional wired charging technology. The wireless charging technology for E-bike has a great development space owing to its advantages such as safety, reliability and flexibility. However, the design of a wireless charging device for E-bike which can meet the needs of consumers and then gradually replace the traditional wired charging device is still a serious challenge. The wireless power transmission technology for E-bike is analyzed from the aspects of circuit topology, magnetic coupler, constant current and constant voltage control, and foreign object detection methods. In addition, the research direction of this technology in the future is pointed out.

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 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.

With the increasing power density in the design of a compact inverter, the electromagnetic compatibility（EMC） problems caused by the rapid switching process of power components are becoming more and more prominent. To make the inverter operate stably under various environmental conditions, EMC design is particularly critical. Aimed at the common-mode interference problem of the inverter, the three paths of common-mode interference conduction are analyzed. Based on the ANSYS electromagnetic simulation platform, the equivalent model of inverter common-mode interference is established, and the propagation channel and action principle of the interference signal are analyzed. The relationship between common-mode interference voltage and parasitic capacitance is obtained. After the verification by experimental results, two effective methods of common-mode suppression by reducing parasitic capacitance are proposed. Conclusions are drawn based on the principle analysis and simulation results, which are further verified by two case studies, providing a practical guidance for the EMC design of inverter and a solution to its common-mode interference problem.

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.

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.

Owing to its characteristics of high voltage gain and low voltage stress, the modified SEPIC converter is widely applied in fields such as photovoltaic and uninterruptible power supply. At the same time, because of its satisfying soft switching characteristic, it can also be applied to high-frequency scenarios to improve the power density. To expand the load range and improve the dynamic response, the establishment of a mathematical model is important. In this paper, the generalized state-space averaging method is adopted to model a quasi-resonant modified SEPIC converter based on switched inductor, the corresponding small signal model is established, and the transfer function of system output is obtained. The K-factor method is used to design a compensator, thus optimizing the system's dynamic performance. A digital control method of constant-current output was designed, which was further verified by experimental results.

Aimed at the power equalization problem of input independent output parallel（IIOP） modular dual active bridge（DAB） converters when the parameters of modules do not match or the input voltages are not equal, a power compensation equalization control（PCEC） algorithm based on dual phase shift（DPS） control is proposed to improve the dynamic performance and efficiency of the converter and achieve the transmission power equalization of the modular DAB converter. In addition, considering the large transmission power, a power compensation cooperative control（PCCC） algorithm is additionally proposed to realize the full use of each module. Finally, based on the DSP28335 hardware-in-the-loop simulation platform, the proposed power equalization scheme was compared and verified experimentally.

For on-board charger applications, the conventional frequency-controlled LLC resonant converter is difficult to achieve a wide voltage range, and it is also not conducive to the optimal design of on-board chargers. To solve these problems, based on a resonant converter with a hybrid rectifier, some control strategies are proposed to achieve the wide output voltage. In this topology, two auxiliary switches between the secondary-side rectifier diode of the converter and the output filter capacitor are reversely connected in series to form a full-half bridge hybrid rectifier. Then, a frequency control with a narrow frequency range and a fixed-frequency PWM control are proposed, so that the resonant converter can achieve the wide voltage range. Compared with the conventional frequency-controlled resonant converter, the proposed converter has advantages such as a wide voltage range, a low circulating loss and a narrowed frequency range. Finally, the effectiveness and feasibility of the converter and its control strategy were verified by MATLAB/Simulink simulations and experimental results.

To improve the input voltage range of an LLC resonant converter, a hybrid control method is proposed to improve the gain of the LLC resonant converter circuit. The whole control is divided into three modes, i.e., full-bridge mode, half-bridge mode and hybrid mode. In the hybrid mode, the distribution weights of a half-bridge LLC resonant converter and a full-bridge LLC resonant converter are obtained by PI calculations, and the control signals are generated by a digital signal processor DSP28335, so that the whole circuit can operate in the mode of the full-bridge LLC resonant converter within a certain time of the control cycle and in the mode of the half-bridge LLC resonant converter in the rest of the time. Through the analysis and simulations at an early stage, the optimal control scheme for the control mode can be determined. Finally, an experimental prototype with 50-150 V DC input and 12 V/5 A output was used to verify the correctness and rationality of the proposed control mode.

The light-emitting diode (LED) driver usually needs a large electrolytic capacitor to reduce its low-frequency current ripple. Therefore, the short life of the electrolytic capacitor is an important factor restricting the life of LED driver, and eliminating the electrolytic capacitor is a key to the long-life LED driver. Under this background, a two-switch electrolytic capacitor-less LED drive circuit topology based on flyback converter is proposed. The auxiliary power balance circuit and flyback converter are integrated, and a balance between the instantaneous input power and output power is realized through two switches. The electrolytic capacitor is eliminated, the low-frequency ripple of output current is suppressed, and a high power factor is realized. The working principle of this topology is analyzed in detail, and a control strategy for its circuit topology is put forward. Finally, a 30 W prototype was built, and experimental results verified the feasibility of the proposed topology.

Insulated gate bipolar transistor（IGBT） power modules have been widely applied in the field of high-voltage and high-power electric energy conversion, where a high reliability is increasingly requested. First, the IGBT power modules and their market scale and demand are summarized and predicted. Then, from the perspective of life prediction mechanism, the prediction methods for IGBT power modules are classified into two categories, i.e., model-based and data-driven. Afterwards, the research status, basic principle, implementation of prediction process, application scope, advantages and disadvantages of each category are analyzed and summarized. Finally, the research results in the last ten years are statistically analyzed, and the development trend of life prediction methods for IGBT power modules is also discussed.

Owing to its advantages such as small size, low installation cost, and stable energy extraction, the capacitor energy extraction power supply has become the local energy extraction power supply for pole-mounted switch with primary and secondary fusion in 10 kV power systems. To further improve the energy extraction power under the limitation of drawn current, the power supply characteristics of output voltage and energy extraction power are studied based on a simplified energy extraction model, and the power supply characteristics under different compensation relations are pointed out. The design parameters affecting the upper limit of energy extraction power are analyzed, and the design principle under the maximum energy extraction power is obtained. Considering the dynamic characteristics of typical loads such as pole-mounted switch, simulations are carried out under the equivalent load of energy storage capacitors, constant-power load and instantaneous high-power load, which show the power supply characteristics under different dynamic loads and verify the theoretically calculated power supply characteristics.

To adapt to the large voltage gap between the output from renewable sources and battery banks in a distributed energy storage system, a novel Buck converter with a large step-down ratio and a low switch voltage stress is studied in this paper. This converter is formed by low-side switch step-down stage cascaded with switched-inductor step-down stage. Based on the introduction of its operation modes and steady-state characteristics, the power loss and electrical stress of its components are analyzed in detail. According to the analysis results, the optimal selection of components and the optimal design of circuits are performed. The SIMPLIS tool was employed to conduct simulations, and a 750 W experimental prototype with 94.6% peak efficiency was also tested. Test results demonstrate that an extremely high step-down capability and a low electrical stress of component can achieved by the proposed converter, and a relatively high conversion efficiency can be maintained.

To suppress the common-mode conducted noise of ordinary BOOST PFC converters, a common-mode conducted EMI suppression method for BOOST PFC converters based on chaotic spread spectrum and lossless absorption is proposed. Through the analysis of the EMI conduction path of the converter, a common-mode interference equivalent circuit is established, and the mechanism of lossless absorption and suppression of high-frequency EMI is clarified. On this basis, the spread spectrum technology is introduced, the frequency spectrum distributions of fixed-frequency, periodic and chaotic spread spectrum PWM are analyzed, and the superiority of chaotic spread spectrum technology applied in suppressing the EMI in switching converters is discussed. Simulation and experimental results show that, compared with the fixed-frequency PWM common-mode conduction EMI spectrum, the lossless absorption chaotic PWM has improvements of 5~20 dBμV and 12~22 dBμV in 100 kHz~1 MHz and 1~30 MHz, respectively. This method does not require any auxiliary switching tube, and it realizes zero-voltage turn-off of the switching tube by absorbing the circuit resonance. Aimed at the disadvantage that the lossless absorption cannot suppress the low- and medium-frequency noise, chaotic spread spectrum is used to further suppress the common-mode noise of the converter. Test results show that after the introduction of chaotic PWM, the output ripple and efficiency fluctuation range of the converter were both within 1%.

As the working frequency of a converter jumps from tens of kHz to tens of MHz, it also faces many new challenges while significantly reducing the volume of passive components, reducing the overall weight and cost and improving the system’s transient response speed. First, the typical topologies, driver and control modes of multi-tens MHz DC-DC converters are described briefly in this paper. Then, the key technologies such as parasitic inductance suppression, improvement in wide input and wide output capability and power density are introduced, which aims to provide reference for subsequent related research.

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.

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.

With the increasing proportion of new energy power generation, it is necessary to design a high-power converter with a high efficiency and a wide input range. In this paper, a Sigma converter composed of a Buck-boost LLC converter and an LLC based on DC trsnsformer（LLC-DCX） converter is proposed based on the existing research, which can meet the requirements of a high efficiency and a wide input range. The Buck-boost LLC converter can effectively decrease the number of components and reduce loss through bridge arm integration. However, all the input current flows through its Buck-boost inductor, which will cause a lot of loss in high-power scenarios. Therefore, the Sigma structure and the concept of partial power transmission are adopted to reduce the loss caused by the Buck-boost LLC converter. Finally, experimental results demonstrated the superior voltage regulation characteristics and high efficiency of the proposed topology.

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.

The two-switch Buck-Boost converter has been widely applied in step-up and step-down scenarios. However, it usually operates under hard switching conditions in the existing various control and modulation modes. In addition, its interleaved control circuit is usually complicated. A three-switch interleaved Buck-Boost circuit with co-directional coupling inductor and its control method are given based on the characteristics of co-directional coupling inductor. First, the coupling process of the coupling inductor during the switching process is analyzed under a large coupling coefficient, based on which the circuit’s fundamental operating principle is given in detail. Then, it is concluded that the extended duty cycle and soft switching of Boost-side power switches can be achieved in the discontinuous self-induction current mode, so as to avoid the synchronous and current-sharing circuits in the two-phase interleaved control circuit, thus obviously simplifying the control circuit. Finally, simulation and experimental results verified the analysis results.

With the rapid development of new energy technology, the performance of DC-DC converters continuously increases. In this paper, a novel high-gain DC-DC converter is proposed, which is improved based on the quasi-Z-source topology. Owing to the use of the topology in which three capacitors discharge together to the load, a higher voltage gain is obtained while the voltage stress of capacitors is reduced. The proposed converter has advantages of the traditional quasi-Z-source converter such as simple control, continuous current and small current ripple. The working principle for this converter is analyzed. In addition, its performance was verified through simulation experiments and prototype experiments.

For the DC charging module in an electric vehicle which is applied under three- or single-phase input compatible scenarios, a single-phase Vienna rectifier structure and its three modulation methods are proposed based on a three-phase Vienna rectifier structure. For the first modulation method, two teams of switches have a common modulation signal, and they are turned on or off at the same time. For the second modulation method, one team is always turned on, while the other operates in a high-frequency PWM mode. For the third modulation method, two teams have two independent modulation signals, respectively. The comparison results indicate that the third modulation method has advantages of a wide output voltage range and output voltage balance, based on which a mathematical model of the proposed rectifier is established and the corresponding control method with two control loops of output voltage u_pn and output voltage difference Δu_pn is proposed. Simulation and experimental results of arectifier with 110 V input voltage shows that only with the third modulation method, the rectifier can generate 200-380 V output voltage and maintain the output voltage balance with imbalanced output capacitors and load resistors.

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.

The losses caused by the switching process of a power MOSFET in a synchronous rectifier and its driving circuit are increasingly prominent with the increase of switching frequency, especially in the low-voltage and high-current applications. To solve this problem, a single-inductor resonant driving circuit for dual MOSFETs is proposed in this paper, which can use a single inductor to drive the dual power MOSFETs with non-common sources. The operation principle and characteristics of the circuit are analyzed in detail, and the parameter design method is given as well. In addition, simulation and experimental verifications were carried out. Results show that the driving circuit has advantages such as a low driving loss, a fast driving speed, a strong anti-interference capability and easy integration, which is suitable for synchronous rectifiers with high frequency and high power density.

The unipolar sinusoidal pulse width modulation（SPWM） has advantages of low switching loss, high efficiency and better output waveforms. However, circulating current may be induced in a parallel inverter system when using the unipolar SPWM method, which will lead to a lower system efficiency, current waveform distortion and even damage to devices. From the comparison of circulating current in the parallel system when using four different unipolar SPWM methods, it is found that only the unipolar PWM in double-armed chopped driving mode will induce circulating current, and the corresponding cause is analyzed from the perspective of control structure. In addition, in the case of using the unipolar SPWM in double-armed chopped driving mode, a control method without adding extra hardware cost is proposed, which can avoid inducing circulating current in the parallel inverter system. Simulation and experimental results verified the feasibility and effectiveness of the proposed method.

In the application of wide output voltage range, some problems exist in an LLC resonant converter under the traditional frequency control, such as a wide switching frequency regulation range, a large circulation current and difficulty in high-efficiency operation. To solve these problems, a dual-full-bridge LLC resonant converter under a fixed-frequency phase-shift and fixed-frequency PWM hybrid control strategy is proposed, which is suitable for the wide range of output voltage. This converter is composed of two full-bridge LLC resonant converters sharing one bridge arm, and the output voltage is modulated by the hybrid control, so that a quadruple voltage gain and a wider output voltage range of the resonant converter can be realized. Meanwhile, the problems that the large circulation current exists under the traditional frequency control and the soft switching cannot be realized at a small phase shift angle are solved, thus improving the system efficiency. The switching frequency of the converter is always equal to the resonance frequency, and the voltage gain is independent of load, which is helpful for the design of the magnetic element. At the same time, the soft switching can be realized in the full load range. Finally, a detailed analysis of the circuit principle was given, which was further verified by simulations. An experimental platform was also established to validate the feasibility and effectiveness of the proposed converter.

The dual-active-bridge (DAB) converter is a key device in a bidirectional power transmission system. In this paper, its fundamental operation principle and topologies are reviewed at first. Then, four basic modulation strategies for the DAB converter are introduced, including single-phase-shifted, dual-phase-shifted, extended-phaseshifted and triple-phase-shifted strategies. Moreover, the modeling and optimization methods based on these four modulation strategies are compared and analyzed. Finally, some problems faced by practical applications and the corresponding solutions are discussed. Along with the development of DC power distribution, energy storage and distributed energy resources, DAB converters will have broad application prospects.

To reduce the cross-regulation of a single-inductor dual-output Boost converter, a compound control scheme is proposed in this paper. An affine nonlinear mathematical model of the converter is established, and it is proved that this model satisfies the exact feedback linearization condition based on the differential geometry theory. The corresponding output function is constructed to realize the linearization and decoupling of the original system, and an internal model controller and a state feedback controller are designed for the linear system, respectively. In addition, the selection of feedback coefficients that meet the stability requirements of the control system is analyzed. Simulation results show that compared with the existing control method, the proposed control scheme has better dynamic regulation characteristics, better control performance and smaller cross-regulation. Moreover, experimental results verified its feasibility.

The stability of a grid-connected inverter will be threatened by phase-locked loop（PLL） under a weak grid environment. An output impedance model of inverter considering the influence of PLL and a transfer function of the traditional synchronous reference frame PLL（SRF-PLL） are established, and the stability of the inverter with the traditional PLL is analyzed based on the impedance analysis method. Then, a composite generalized integral PLL（CGI-PLL） based on reduced-order generalized integral and second-order generalized integral is studied, and the corresponding parameter design method is given. The transfer function of CGI-PLL is obtained using the harmonic linearization method, and the stability of the inverter with the novel PLL under the weak grid environment is analyzed. Considering the influence of system frequency offset on the phase-locked accuracy, a frequency adaptive structure is designed. The theoretical analysis and simulation results show that the grid-connected inverter with CGI-PLL can operate stably under a large grid impedance, and the quality of grid-connected current is high.

Compared with a Si device under the same voltage rating, the GaN device has a lower on-resistance（R_ds（on）） and gate charge（Q_g）, which can significantly reduce the drive and switching loss and is helpful in improving the converter's efficiency and power density. In a very-high-frequency（VHF） resonant flyback converter under a low-voltage and low-power scenario, an air-core transformer integration method is proposed, thereby significantly reducing the printed circuit board（PCB） area and improving the power density. Meanwhile, a prototype structure is designed using the finite element analysis（FEA） to ensure that the transformer magnetic field does not affect other components. This scheme was applied to three VHF resonant flyback converters（input of 5 V and output of 5 V/2 W） operating at 20 MHz with Si, 30 MHz with GaN, and 50 MHz with GaN, respectively. The 50-MHz GaN prototype achieved a power density of 39.4 W/in³, which was 41% higher than that of the 20-MHz Si prototype. Moreover, under the premise of similar efficiencies, the overall height of all the three prototypes was less than half of the commercial products.

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.