Flyback converters in consumer and commercial products must adhere to strict regulatory standards for conducted and radiated electromagnetic interference (EMI). Managing EMI has become increasingly complex in modern power electronics, particularly with the integration of high-speed wide bandgap (WBG) devices into compact system layouts. A review of established modeling techniques and mitigation strategies for conducted EMI is presented, focusing on differential mode (DM) and common mode (CM) noise, alongside radiated EMI in flyback converters. The discussion encompasses solutions at both component-level design and converter system optimization.

The DC-DC converter in a switch mode power supply (SMPS) is the core part that affects the device’s volume, weight and working efficiency. As a classic DC-DC topology, the LLC resonant converter uses the soft switching technology and magnetic integration technology, which has characteristics such as a high efficiency, a high power density and harmonics suppression. The research status of optimization methods for LLC resonant converters applied in SMPS is reviewed, starting from the transformer winding structure schemes and control topology optimization schemes. In addition, suggestions on the effects of synchronous rectification and the planar transformers under an all-primary-referred (APR) magnetic integration model on the circuit are given. Finally, the optimization methods based on the third-generation wide bandgap material and electromagnetic compatibility are prospected.

The power supply system in a data center is its critical infrastructure, which provides stable and reliable power support for all the power-driven equipment therein to ensure itsnormal operation. With the rapid development of technologies such as big data, cloud computing and 5G, the number and scale of data centers in China are increasing rapidly, requiring higher reliability of power supply and increasing the overall power consumption. In addition, the problem of high carbon emissions is even more obvious because the data centers at present mainly use electricity from the traditional energy sources. Therefore, how to achieve a green, energy-saving and low-carbon power supply and distribution mode is the focus of the development of data center power supply systems. The functions and characteristics of typical power supply architectures of data center power supply system are analyzed, and the development and evolution of power supply architectures of data center are introduced. On this basis, “carbon peaking and carbon neutrality” is taken as the background, and a prospect for the power supply architectures of data center in the future is given combined with the problems encountered in the development of power supply system of data center, providing reference for its in-depth research and subsequent development.

The air gap in an integrated high-frequency transformer of an LLC resonant converter is usually placed at the center of magnetic core, and a single air gap structure is adopted. The nonlinear three-dimensional transformer models with different air gap positions are established using a finite element analysis method based on the software Ansys, and the influence of air gap position on loss is studied. Through simulations, the curves of loss versus air gap positions are obtained, and it is proved that the loss of transformer can be reduced and the converter efficiency can be improved if the air gap is located in the region of secondary windings, providing a reference for the optimal design of the integrated high-frequency transformer. On this basis, an integrated high-frequency transformer structure with three air gap magnetic circuits on the secondary side is proposed, so as to further reduce the transformer loss. Finally, an experimental prototype of a 160 W LLC dimmable LED driver was built, and experimental results verified the correctness and feasibility of the proposed method.

Aimed at the problem that it is difficult for an LLC resonant converter to strike a balance between its dynamic performance and disturbance rejection capability in applications with high dynamic demand and frequent load changes, a charge active disturbance rejection control strategy is proposed. In this method, charge control is carried out in the inner loop of the resonant converter by collecting the resonant capacitor voltage, and active disturbance rejection control is introduced in the outer loop to form a compound control strategy of dual-closed-loop control. By deducing the relationship between the resonant capacitor voltage and resonant current of the LLC resonant converter, the controller parameters in the inner voltage loop of the converter are designed by using the charge control method, and an outer voltage loop controller is designed based on linearized active disturbance rejection control, thus further improving the anti-interference capability of the whole system. An experimental prototype with rated power of 300 W was designed and built, and the feasibility and effectiveness of the improved control strategy was verified by comparing with the traditional PID-PI control.

During the dynamic process of a system, the current control of a converter realizes a balance between current and reference by adjusting the output voltage when the grid-side current changes, which is represented as voltage response under the current excitation. Since the AC voltage of the converter is generated by controlling the amplitude/frequency and the amplitude/frequency of voltage is required to be maintained during the system operation, the current control should be described as the internal voltage amplitude/frequency response under active/reactive current excitation when a power imbalance occurs. At the same time, from the perspective of a grid-connected converter’s influence on the grid, the active/reactive current response under the terminal voltage amplitude/frequency excitation is another perspective for understanding the characteristics of the grid-connected converter. Therefore, for the current control of the converter, the active/reactive current-internal voltage characteristics used in the dynamic analysis of large systems and the terminal voltage-active/reactive current characteristics from the perspective of the influence of equipment (e.g., single machine) on the grid are presented. On this basis, it is determined that the two kinds of characteristics are essentially equivalent by explaining the redundant relationship between current and terminal voltage under the current control. Finally, the equivalence is verified by simulations, and the influence of phase-locked control parameters on current control characteristics is preliminarily explored.

Bi-directional DC-DC convertersare usually used in vehicle charging pile application circuits, which have problems such as slow system dynamic response and poor output voltage stability due to load perturbations. On the basis, acapacitor-inductor-inductor-capacitor (CLLC) resonant DC-DC converter is taken as a research object, and a control method for the CLLC resonant converter based on sliding mode active disturbance rejectionis proposed. A model-assisted linear state observer is used to improve the estimation accuracy of perturbation, so as to control the stable operation of the system. Sliding mode control is used to design a linear state error feedback control law to improve the dynamic performance and rapidity of the system. Simulations and experimental verification show that the proposed control strategy can effectively improve the dynamic response of the bi-directional DC-DC converter and enhance the output voltage stability.

The typical isolated dual-active bridge (DAB) converter with a simple circuit structure and easy control is widely applied under scenarios where the bidirectional energy flow is required. Therefore, it is particularly important to study how to improve the working efficiency of the converter. First, the efficiency optimization strategies proposed by domestic and foreign scholars are compared and analyzed, and it is found that the intra-and inter-bridge phase shift angles on two sides have a strong correlation, which causes the difficulty in analyzing the working characteristics of the converter. Second, the rectified average current of the converter based on extended-phase-shift (EPS) control is optimized, a new phase shift angle is defined, and the transmission power and average current of the converter under the new phase shift angle are analyzed. Finally, a simulation platform based on Simulink and an experimental platform were set up for verification.

To address the issue that the conventional model predictive torque control algorithm for a permanent magnet synchronous motor relies on position sensors, a model predictive torque control approach based on a dual- sliding-mode observer is proposed. First, to accomplish the sensorless control, the real-time speed in the prediction model is substituted by the observed speed by coupling the back electromotive force sliding-mode observer with the optimized quadrature phase-locked loop. Second, the stator flux sliding-mode observer is used to observe the stator flux, and the observed flux introduces prediction error through feedback correction to obtain the prediction torque and flux with higher accuracy, thus improving the prediction speed and accuracy of the model predictive torque control system. By contrasting the MATLAB/Simulink simulation and experimental platform with the conventional model predictive torque control approach incorporating position sensors, the efficacy and feasibility of the proposed method are confirmed.

The accurate open-circuit voltage-state of charge (OCV-SOC) curve is a basis for ensuring the modeling accuracy of lithium-ion battery. The OCV-SOC curves of LiFeO₄ battery obtained by a low-current OCV test cannot describe the OCV characteristics at a non-testing point, while those obtained by an incremental OCV test are interfered by the polarization effect. Therefore, based on the analysis of the characteristics of LiFeO₄ battery, a high-precision OCV-SOC curve acquisition method for LiFeO₄ battery is proposed by combining the low-current OCV test and incremental OCV test. This method takes the incremental discharge curve which is fitted in piecewise form as its optimization object, designs constraints based on the low-current OCV test data and first-order RC equivalent circuit model, and uses the differential evolution method to acquire the OCV-SOC optimization curve. Experimental results show that the OCV-SOC optimization curve can accurately simulate the OCV characteristics of LiFeO₄ battery. Compared with the OCV-SOC curve obtained by the low-current OCV test, the battery modeling and SOC estimation based on the OCV-SOC optimization curve has a higher accuracy, with the model accuracy increasing by 41.8% and SOC estimation accuracy increasing by 58.3%.

With the vigorous development of electric vehicles and energy storage industries, the power electronics technology has been applied on an increasing scale. In these applications, power electronic converters not only require wide voltage gain to adapt to different scenarios, but also require a high conversion efficiency to reduce volume. Therefore, bidirectional isolated DC-DC converters with soft switching have been widely studied. On the basis, the principle of isolated DC-DC converters was analyzed, and the conversion efficiency under wide voltage gain was improved by reducing the reactive power current and implementing soft switching. First, a mathematical model was established through fundamental wave analysis to obtain the conditions for controlling the phase shift angle on the primary side, secondary side, and both the primary and secondary sides to achieve reactive power current elimination. Then, the conditions for achieving soft switching of switching devices on the primary and secondary sides were analyzed, and the dead time was designed to adjust the phase shift angle between the primary and secondary sides, so that a modulation strategy for achieving ZVS with minimal reactive power current was obtained. Finally, a 9.6 kW experimental prototype was designed to verify the feasibility of the proposed modulation strategy.

The input-series output-parallel combination technology for DC-DC converters is widely applied in high-power and high-voltage fields. To realize an average operation after the expansion and connection of modules, the characteristics of input voltage-sharing and output current-sharing after the series-parallel combination of module power supplies are studied, and a control strategy for module current-sharing on the output side is proposed, which consists of an output voltage loop and an output current-sharing loop. The common output voltage loop of all the modules samples the output voltage from the combined system for feedback regulation, while the output current-sharing loop of each module samples the output current from the module for average control. All the sampling and control chips under the proposed control strategy are on the low-voltage output side, which can eliminate an isolation unit and improve the system reliability. A half-bridge LLC resonant topology was selected as a sub-module to build a prototype, and results verified the effectiveness of the proposed output current-sharing control method.

Aimed at the problems of insufficient dynamic performance and poor robustness in the traditional linear control, a dynamic response optimization method based on the model predictive control of a multi-phase interleaved Buck converter is proposed in this paper. First, the state space model of the interleaved Buck converter is optimized, and a virtual impedance method is put forward to realize the decoupling control of each phase converter. Second, a load disturbance observer and a continuous set model predictive controller based on one-step prediction are designed. The reference current is calculated based on the load current observation and the output voltage deviation, and the optimal duty cycle in each phase is obtained by substituting it into the predictive model with an objective of minimizing the current deviation. Finally, a simulation platform was built on Matlab/ Simulink for simulation verification, and experiments were conducted on a three-phase Buck converter. Simulation and experimental results show that the proposed algorithm can effectively suppress the output voltage variations caused by load disturbances, improve the dynamic performance of the system, and ensure its robustness at the same time.

Accurately predicting the remaining useful life (RUL) of lithium-ion batteries is critical to the safe and reliable operation of new energy vehicles. First, the research status of data-driven methods for predicting the RUL of lithium-ion batteries is analyzed in this paper, and the research progress in six commonly used data-driven methods is reviewed. Then, three problems existing in the practical applications of RUL prediction of lithium-ion batteries at present are summarized. At the same time, the issue of battery dataset collection is discussed comprehensively, and the importance of battery datasets to the development of data-driven methods is also elaborated upon. Finally, the development trend in the future is prospected.

A micro inverter can be directly connected to a photovoltaic board, and it has advantages such as a simple structure, a small size and input output isolation. To expand the power range of the photovoltaic micro inverter, two flyback converters can be interleaved and connected in parallel at the front stage DC-DC section, and an active clamping circuit can be used to improve the efficiency of the micro inverter. In response to the issues of temperature rise in a high-frequency power transformer and low power density in outdoor high-temperature environments, a planar transformer applied to micro inverters is designed. First, the working principle for flyback micro inverters is analyzed. Second, the electrical parameters and winding structure of the planar transformer are designed, and the magnetic density distribution and loss of the planar transformer core are simulated using Maxwell software. Finally, a 220 W interleaved parallel flyback micro inverter prototype was built for experimental testing. Experimental results proved the effectiveness of the design, and the prototype can perform stable work.

The wireless charging technology for electric vehicles has been widely studied and applied owing to its advantages of small footprint, convenience and flexibility, low maintenance cost and strong interaction with power grid. A bidirectional wireless charging system for electric vehicles based on the dual phase shift (DPS) control strategy is proposed. Through the DPS control strategy, the phase shift angle on the primary and secondary sides is changed to change the output power. By changing the phase angle difference between voltages on the primary and secondary sides, the energy flow direction is changed, and the function of “peak shaving and valley filling” is realized eventually. First, the architecture of the bidirectional wireless charging system for electric vehicles based on the DPS control strategy is presented, and its working mode and principle are analyzed. Second, the control strategy for the bidirectional wireless charging system is described in detail, and the output power and direction of the system are adjusted by changing the phase shift angle on the primary and secondary sides, as well as the phase angle difference between voltages on the primary and secondary sides. Third, the working principle for the system and the control method to realize bidirectional charging are analyzed. Finally, a simulation model was built in MATLAB, and experimental verification was carried out. Results show that the designed bidirectional wireless charging system can achieve bidirectional energy transmission, satisfying control performance and good symmetry of positive and negative charging.

To address the problem that phase-controlled and fully-controlled rectifiers cannot combine high power level, high hydrogen production efficiency and high reliability in the field of electrolytic hydrogen production at present, a hybrid rectifier topology which consists of a main power rectifier and an auxiliary converter in parallel and its control strategy are proposed. The main power rectifier is a thyristor rectifier, and the auxiliary converter consists of a pulse width modulated voltage source converter and a phase-shifted full-bridge converter in cascade. Through an analysis of the mathematical model of the auxiliary converter, the compensation of ripple current and the absorption of harmonic current are taken as control objectives, and a current control method of repetitive control with proportional resonance control is given to realize an efficient operation of the hydrogen production unit while optimizing the input current quality. In addition, three fault-tolerant operation modes of the hybrid rectifier topology are proposed to improve its reliability. An electrolytic hydrogen production platform was built and semi-physical simulations were performed to verify the hybrid rectifier topology and its control strategy, and results proved the topology’s correctness and effectiveness.

In view of the poor tiansient response of the output-capacitorless, an output-capacitorless low dropout (LDO) regulator with fast transient response is proposed, and the voltage overshoot and undershoot suppression circuits are used to suppress voltage jumps, thus improving the transient response characteristics of the LDO regulator. An improved error amplifier is designed, whose gain is larger than that of a general error amplifier in static working states. In addition, the transient output current from the designed error amplifier can be increased when the output voltage jumps, and the charging and discharging of the power tube can be accelerated. By using Current buffer Miller compensation, the phase margin of the circuit is compensated with a smaller capacitive area. Simulation results show that when the voltage range is 2.8~3.3 V, the output voltage from the circuit is 1.8 V and the maximum load current is 50 mA. When the load current jumps between 1 and 50 mA, the undershoot amplitude of output voltage is reduced by 46 mV (51%) and the response time is 1.16 µs under the effect of the transient enhancement circuit. Meanwhile, the overshoot amplitude is reduced by 29 mV (35%), and the response time is 1.18 µs.

The gallium nitride/silicon carbide (GaN/SiC) Cascode device is a composite structure, which employs a low-voltage GaN device as an assistant switch to change the high-voltage depletion-mode SiC device into an enhancement-mode device. A normally-off GaN/SiC Cascode device was constructed by low-voltage enhancement- mode gallium nitride high electron mobility transistor (GaN HEMT) and high-voltage depletion-mode silicon carbide junction field-effect transistor (SiC JFET). The Cascode device combined the advantages of GaN HEMT such as high switching speed and simple gate-driving circuit and the high blocking voltage of SiC JFET. Both the operating principle and the switching process of GaN/SiC Cascode device were analyzed in detail, and its static characteristics were also tested. A double-pulse test platform was constructed, and the switching loss of the GaN/SiC Cascode device was compared with those of the Si/SiC Cascode device and SiC JFET at varying load current. Results show that the turn-off loss of GaN/SiC Cascode device was the lowest. In addition, the three devices were applied in an LLC resonant converter respectively, and the conversion efficiency of the converter was tested, indicating that the LLC resonant converter based on GaN/SiC Cascode device exhibited the highest conversion efficiency.

The wireless charging technology for electric boats charging applications has gradually attracted attention. Due to the long wireless charging transmission distance of electric boats, the coupling coefficient and anti-misalignment capability of a magnetic coupler will decrease sharply with an increase in the transmission distance, thus reducing the transmission efficiency and output power. A novel solenoid magnetic coupler is proposed, and the finite element simulation models of magnetic couplers with different structures are built to compare their performance. In addition, the proposed solenoid magnetic coupler is optimized, and the corresponding magnetic shielding device is configured. Compared with those of the traditional solenoid magnetic coupler, the use of magnetic core and Litz wires of the novel solenoid magnetic coupler are reduced by 32% and 38%, respectively, thus effectively improving its coupling coefficient and anti-misalignment capability. Finally, a set of wireless charging prototype was built, and the transmission efficiency can reach 88%. The experimental results were consistent with the simulation results.

Aimed at the problems that the capacity of a lithium-ion battery is difficult to obtain in the direct prediction of its remaining useful life (RUL) and the characteristic parameters are redundant or insufficient in the indirect prediction, an indirect prediction method for the RUL of lithium-ion battery based on the data preprocessing technology and improved support vector regression (SVR) is proposed. First, multiple indirect characteristic parameters are extracted at the battery charging and discharging stage. Second, principal component analysis is used to remove the redundancy of various parameters, and a fusion health indicator (HI) with sufficient information is reconstructed. Third, a fusion HI prediction model and a capacity prediction model based on the whale optimization algorithm and SVR are built, and the complete ensemble empirical mode decomposition with adaptive noise is used to decompose the fusion HI into several modal components. Each component is input into the fusion HI prediction model for HI prediction, and the prediction results are superimposed into the capacity prediction model to realize indirect RUL prediction. Finally, the NASA battery degradation data set is used for verification, and results show that the mean absolute error and root mean square error of RUL prediction results for the proposed method are controlled within 1.78 % and 2.5 %, respectively, which effectively improves the prediction accuracy of RUL. The research provides a new idea for the RUL prediction of lithium-ion batteries.

The thermal characteristic modeling of silicon carbide (SiC) power devices is a key aspect in their design and development. The structure function method is crucial for characterizing the devices' thermal characteristics, focusing on acquiring the time-constant spectrum of input data via deconvolution algorithms. However, the environmental noise inevitably affects actual tests, thereby demanding more sophisticated deconvolution algorithms for the structure function. Therefore, a deconvolution structure function algorithm based on improved Wiener filtering is proposed, effectively addressing the noise problem in the measurement data during the transient thermal analysis. First, a structure function model based on Wiener filtering deconvolution is put forward, and the algorithm's effectiveness is validated through analyzing the TDIM-Master benchmark problem. Second, different levels of noise are added to the benchmark problem to explore the signal quality and peak thermal resistance of the time-constant spectrum across various noise conditions. The accuracy and superiority of the improved method when dealing with noises are verified through a comparison with the conventional algorithm. Finally, the transient thermal resistance of two different types of SiC power devices were measured under conditions with or without thermal silicone grease, and the structure function analysis was also performed, thus verifying the stability and applicability of the proposed algorithm under real measurement environment.

With the higher requirements for the safety and stability of traditional power grids, the energy crisis and environmental pollution problems are increasing. As a result, “Green” and “Low carbon” have become the urgent needs of the development of power systems. Based on the current situation, a multi-functional photovoltaic grid-connected inverter with power quality control is proposed. First, according to an improved adaptive harmonic detection method, the harmonic component in the grid-connected current is detected. Second, the command current is tracked and controlled by quasi-proportional resonance. Through the subjective and objective criteria importance through intercriteria correlation (CRITIC) game theory combination weighting method, a comprehensive evaluation model of power quality is established to evaluate the harmonic and reactive components. Third, considering the limited capacity of the inverter in practice, a capacity matching coefficient is formulated to compensate the dominating problems. Finally, simulation results show that the harmonic and reactive components are optimized and compensated in the grid-connection process of the inverter, which improves the power quality at the grid-connected point and greatly increases the utilization rate of the inverter. Therefore, the effectiveness and feasibility of the proposed strategy are verified.

To solve the problems related to the safety and stability of regional power grids which are caused by the start-up of large-capacity motors, the mechanism and influencing factors of voltage sag caused by large-capacity motor start-up are studied. First, the dynamic process of large-capacity motor start-up and the mechanism of voltage sag are analyzed in detail, and the quantitative characterization of the severity of voltage sag is conducted using evaluation indexes. Then, the start-up of large-capacity motors in a petrochemical enterprise’s regional power grid is taken as an example, and a time-domain model based on ETAP is established to verify the theoretical analysis of voltage sag caused by large-capacity motor start-up. Finally, the influencing factors of voltage sag caused by large-capacity motor start-up are quantitatively analyzed. The influences of start-up transformer capacity and grid strength on voltage sag are studied, and a comparative analysis of voltage sag indexes for different combinations of multi-motor simultaneous start-up and different start-up modes is conducted. The research results provide a theoretical basis for reducing the risk of voltage sag accidents caused by the start-up of large-capacity motors.

Aimed at the hard-switching issues associated with the traditional zero current switching (ZCS) switched capacitor converters (SCCs), a zero voltage and zero current switching (ZVZCS) DC-DC SCC based on an LC auxiliary network is proposed, which can achieve zero voltage switching (ZVS) for all switches throughout the entire operating range. Under certain conditions, it can also simultaneously achieve both the ZVS and ZCS, significantly reducing the switching losses. On this basis, an in-depth investigation into the impact of dead time on converters is conducted, revealing a quantitative relationship between dead time selection under different load conditions and converter loss distribution. Subsequently, a design methodology for key parameters of auxiliary networks based on dead time is put forward. Finally, based on the proposed ZVZCS SCC, a 24 V DC-12 V DC experimental prototype with 100 W was constructed with a peak efficiency of 99.07%, thus validating the correctness of the theoretical analysis.

The overall development statuses and trends of hydrogen-related industries are briefly introduced at first, and different types of electrolytic water hydrogen production technologies are compared in detail. Then, the development statuses of photovoltaic (PV) power hydrogen production, wind power hydrogen generation and wind-PV complementary hydrogen generation technologies are summarized, and the development trends in the future are investigated. Finally, the research framework system of “Green Hydrogen Plant” for a large-scale new energy hydrogen production system is constructed. The research and development ideas for key technologies involved in new energy hydrogen production are provided, the demand analysis for products and solutions required by relevant projects is conducted, and suggestions for the research direction of “wind-PV-hydrogen-storage” energy comprehensive utilization in the future are put forward.

Aimed at the problems of a large number of switching devices and complex control strategy for an inverter in the multi-motor drive system of a 800 V high-voltage platform for electric vehicles, a fifteen-switch three-level dual-output inverter is proposed, which simplifies the inverter topology and reduces its cost by device multiplexing. First, a detailed analysis of the proposed inverter topology and working principle is performed, its structural characteristics are summarized, and the effective switching state and maximum voltage stress analysis are given, providing a theoretical basis for the selection of switching devices and system design. Then, a single-leg independent model prediction current control strategy is put forward, and a prediction model of single-leg dual-output port current is established, which effectively reduces the prediction operation under the premise of realizing three-leg independent prediction control and single-leg dual-output current integrated optimal control. Finally, the correctness and effectiveness of the proposed inverter and its control strategy were experimentally verified based on a Typhoon HIL 402 platform.

To improve the dynamic performance of passivity-based control (PBC) of a Boost converter with constant power load under external disturbances, a passivity-based adaptive control strategy based on neural network was proposed. Under this strategy, a passivity-based adaptive control structure with proportional and integral terms was adopted, and a single-neural network was used to optimize the injection damping, proportional coefficient and integral coefficient in real time. In addition, a power observer was used to observe the power of unknown constant power load (CPL) in real time, thus improving the dynamic and steady-state performances of the Boost converter when the CPL changes. Compared with PI+PBC and PI double-closed-loop control strategies, the passivity-based adaptive control based on neural network can make the Boost converter have a better performance. The results of computer simulations show that the proposed control strategy is feasible.

To ensure the safe and reliable operation of a three-phase bridge leg, it is necessary to set a reasonable dead-time. Due to its own characteristics, the voltage variation in the dead-time of a gallium nitride high-electron mobility transistor (GaN HEMT) is different from those of traditional Si devices. In this paper, the problem of large reverse conduction voltage drops in GaN HEMT power devices is analyzed, and an improved online dead-time compensation method based on GaN HEMT power devices is proposed. This method can not only avoid the influence of circuit noise on the judgment of current direction, but also reduce the phase voltage error and current harmonics, thus improving the circuit stability. Finally, the effectiveness of the improved online dead-time compensation method was verified by simulation experiments and the construction of an experimental platform, indicating that it has obvious advantages over the traditional dead-time compensation method under the condition of large reverse conduction voltage drops.

In the traditional prediction of lithium batteries for electric vehicles, the state-of-health (SOH) prediction is usually regarded as a whole, and the result of single SOH prediction is obtained accordingly. However, in the actual operation of a car, the single prediction of SOH has a large error, and its prediction effect is not satisfying. To improve the accuracy of battery SOH prediction for electric vehicles, a novel prediction method based on variational modal decomposition (VMD) and sparrow search algorithm (SSA) optimization of kernel-based extreme learning machine (KELM) integrated prediction model, i.e., VMD-SSA-KELM, is proposed. First, the battery SOH sequence is decomposed by VMD to reduce the influence of SOH fluctuations. Meanwhile, the Person correlation method is used to reduce the influence of noise and improve the accuracy of prediction. The KELM is introduced, which improves the accuracy of prediction while retaining the advantages of extreme learning machine. The proposed model is validated based on the operation data of four electric vehicles, and experimental results show that compared with the VMD-DBO-KELM, VMD-POA-KELM, VMD-KELM and VMD-ELM models, the proposed model has a prediction trend which is the same as that of the original data, while the results of other models fluctuate a lot. The root mean square error of results predicted by the novel model is less than 0.2%, the prediction accuracy becomes higher, the prediction efficiency is faster and the time used is shorter, indicating that the proposed method has higher accuracy and better robustness.

A cascaded H-bridge (CHB) multilevel inverter is composed of many unit modules, and the probability of failure is relatively high. The fault-tolerant operation can effectively improve the reliability and performance of a system. By injecting zero-sequence voltage to enhance the output capability after fault, the fault-tolerant control method has advantages of not adding any additional cost and simple implementation. As a result, it has attracted wide attention. The zero-sequence voltage value and fundamental component value injected by different implementation methods are different, and an excessive zero-sequence voltage will have a great impact on the motor bearing and insulation in the motor drive. Aimed at this problem, a zero-sequence voltage (containing third harmonic component) injection method is discussed to reduce the fundamental component of injected zero-sequence voltage, so as to decrease the influence of injected zero-sequence voltage on the motor operation. The effectiveness of the proposed fault-tolerant control strategy was verified by simulations and a 10 kW 7-level converter prototype.

In a flexible DC transmission system for offshore wind power generation, surplus power will be generated in the system when the land end is greatly unloaded or the AC system fails, resulting in a rapid increase in the DC transmission voltage. A DC energy-consuming device can quickly dissipate the surplus power, which is a key technical solution to ensuring smooth fault ride-through and reliable operation of the system. However, the modulation voltage of the energy-consuming valve will become negative when the surplus power is large. To solve this problem, a hybrid DC energy-consuming device based on half-bridge and full-bridge sub-modules and its modulation strategy are proposed in this paper. By using the negative-voltage output capability of the full-bridge sub-module, the matching range of the surplus power can be expanded, and the recovery speed of DC voltage can be speeded up. The effectiveness of the proposed energy-consuming device and its modulation strategy is verified through theoretical analysis. Besides, a simulation model of the offshore wind power flexible DC transmission system was built on a PSCAD/EMTDC electromagnetic tran-sient simulation platform, and the feasibility of the proposed DC energy-consuming device and corresponding modulation strategy was verified under conditions of different values of surplus power.

To reduce the input current harmonic content of a single-phase PWM rectifier and improve the suppression effect on specific low-frequency harmonics in grid-side current, fuzzy multi-PR control based on PR control is studied, so as to solve the problem of influences due to uncertain factors such as constant parameters under multi-PR control, inability to adapt to variations in parameters in the process of control and system disturbance. Finally, the effectiveness of this method was verified by simulations on MATLAB/Simulink and experiments on an experimental platform. Results show that the proposed control strategy can effectively reduce the total distortion rate of grid-side current, and it can also improve the dynamic and anti-interference performance of the system to a certain extent.

For a wireless power transfer system with one single planar rectangular pad, a metal object detection (MOD) method based on vertically decoupled coil sets is proposed. The detection coils are combined in a reasonable manner to form a detection coil set, which is decoupled from the transmitting and receiving coils simultaneously. When there is no metal object, the induced voltage of the detection coil set will be close to zero and minimally affected by the offset of the receiving coil. When a metal object falls on the top of the transmitting coil, eddy currents will be generated and induced voltage will appear in the detection coil set. The detection accuracy of the proposed method is not significantly affected by the offset of the receiving coil, and there is no need to reset the detection circuit or adjust the threshold for different offset positions. The parameters of the detection coil are optimized by finite element simulations. Based on a 300 W wireless charging system, MOD experiments were conducted, and results show that the proposed method can accurately identify metal objects even in offset situations. This method solves the problem of a planar detection scheme being affected by the offset of the receiving coil, with high detection sensitivity and great engineering application value.

The research on the driving technology for SiC devices has always been a hot issue for scholars both at home and abroad. The existing active drive technology realizes the regulation of switching transient by changing the drive resistance, drive voltage or current. It requires many components, and the drive board is bulky and costly. Therefore, a full-bridge active drive technology based on resonant drive is proposed. By switching on and off the drive switch tube only, different drive circuits are constructed to form different drive currents, thus realizing the switch transient adjustment. First, the 1/4-period full-bridge resonant drive is taken as a reference drive mode for the power tube. Then, a specific design method for active drive switch timing is given by analyzing various stages during the switching on process of the power tube. Finally, through simulations and experimental verification, it is found that the drive mode can reduce 87.0% of current overshoot during the switching on process and 4.2% of voltage overshoot during the switching off process, and it can also achieve flexible speed regulation in a wide range of specific stages.

Aimed at the problems of active power fluctuation and current asymmetry of a Vienna rectifier caused by asymmetric grid, active power fluctuation suppression control (APFSC) and symmetric positive-sequence current control (SPSCC) are introduced. Due to the current limitation of power devices, the use of APFSC will reduce the maximum active power of the Vienna rectifier. In comparison, the use of SPSCC can expand its maximum active power at the cost of significant active power fluctuation. With the comprehensive consideration of disadvantages of the above two methods, an improved power control (IPC) strategy is proposed. When the processing power of the Vienna rectifier is small, keeping the active power without fluctuation is the primary control target. In this case, the effects of IPC and APFSC are the same. The active power fluctuation under IPC is effectively suppressed, while that under SPSCC is large. When the processing power of the Vienna rectifier is large, meeting the power demand is the primary control target, but the active power fluctuation should be reduced as much as possible. Under this circumstance, IPC can meet the active power demand, but APFSC cannot meet the power demand. On the premise of meeting the power demand, the fluctuation of active power under IPC is smaller than that under SPSCC. Finally, experimental results verified the advantage of the proposed control method.

The calculation of high-frequency transformer winding losses is crucial for optimizing the efficiency of CLLC converters. However, there remains a lack of accurate and efficient methods for calculating the winding losses, particularly the winding losses in Litz wire. A mutual-impedance equivalent circuit-based method for calculating the winding losses in Litz wire high-frequency transformers is proposed. First, the analytical approaches for calculating the Litz wire winding losses based on a one-dimensional Dowell model and a two-dimensional Bessel function method are comparatively analyzed. Then, a mutual-impedance equivalent model is established to simplify the calculation of winding losses. A specific case study is given, and the values calculated using the proposed method are compared with the impedance matrix results derived from two-dimensional finite element simulations. Results demonstrate that the relative error between the equivalent series resistances calculated using the proposed method and the results based on the finite element method does not exceed 6%, validating the effectiveness and accuracy of the proposed method. Finally, a high-frequency transformer prototype for the CLLC converter was constructed, and experimental measurements verified the feasibility of the proposed method.

An enhanced extended phase shift modulation strategy for an LCL-type full-half bridge resonant converter is proposed, which can achieve zero voltage switching (ZVS) for all the switches while eliminating the backflow power on the primary side. Meanwhile, the half-bridge structure on the secondary side enhances the cost-effectiveness of the converter under low-power conditions. The steady-state analysis of the converter is performed by using fundamental harmonic approximation, so as to derive a power model and the corresponding ZVS conditions. In addition, simulations are conducted using the software PSIM. Finally, a 300 W experimental prototype was built, and results verified the feasibility of the theory.

A dual-active-bridge DC-DC converter is taken as the research object, and a triple-phase-shift (TPS) control strategy with an optimization objective of reducing the backflow power and inductance peak current is proposed. Through the analysis of characteristics in six operating modes with TPS, the input-side zero-backflow power mode and bilateral zero-backflow power mode with smaller inductance peak current in Boost and Buck modes are obtained, and the constraint of phase-shift ratio and power range in different operating modes are given. The inductance peak current in bilateral zero-backflow power mode is smaller, and the zero switching of the power device can be realized. On this basis, the working point with the smallest inductance peak current at different values of transmission power is further obtained through optimizations using the KKT method. Finally, the proposed TPS optimization method and the inductance peak current optimization method under extended-phase-shift were verified by experiments. Experimental results show that the proposed optimization strategy can eliminate the backflow power, reduce the current stress and improve the conversion efficiency, thus verifying the theoretical analysis.

To solve the problem of uncontrollable area of bus neutral-point potential under high modulation depth of conventional virtual space vector pulse-width modulation (VSVPWM), an optimized VSVPWM algorithm was proposed to realize the rapid balance of neutral-point potential in the whole linear modulation area. A virtual medium vector was reconstructed based on the principle of VSVPWM bus neutral-point potential balancing. To ensure the voltage equalization performance of the reconstructed virtual medium vector while improving the adaptability of the algorithm with respect to the perturbation of system parameters, the fuzzy reasoning for the closed-loop control of neutral-point potential was designed to determine the reconstruction factor for optimizing the VSVPWM. Even in the case of asymmetric DC bus capacitance, the optimized VSVPWM can realize rapid voltage equalization control in the full range of the linear modulation region. The algorithm was further simplified in a 60° coordinate system, so that the number of subsector judgment conditions of reference voltage vector and volt-second equilibrium equations can be reduced from 30 to 5. Experimental results show that the proposed control strategy has good performance, the voltage equalization regulation time is significantly reduced, and the steady-state deviation of DC bus neutral-point potential can be controlled within 1.14%. In addition, the total harmonic distortion of grid-connected current is lower compared with that under the conventional VSVPWM.