A series resonant DAB converter (SRDAB) is taken as the research object in this paper, and an efficiency optimization strategy for reducing the power return is proposed to improve the converter's operation efficiency under the phase shift modulation strategy. First, a mathematical model of the transmission efficiency of SRDAB is established under phase shift modulation, the mathematical expression for power return during its operation is derived, and the parameters that affect the power return are obtained. Second, the mathematical expressions for the transient and on-state losses generated during the operation of the converter are formulated, a mathematical model for its operation efficiency is constructed, and the relationship of its efficiency with the phase shift ratio and the ratio of switching frequency to resonant frequency is obtained, thus optimizing the two key parameters to further improve the operation efficiency. Finally, the correctness and effectiveness of the proposed efficiency optimization strategy were verified by performing simulations and building experimental circuits.

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.

With the rapid development of microprocessors, more and more attention is paid to the advantages of digital control of microprocessor power supplies as the output capacitor and its equivalent series resistance (ESR) are gradually reduced, and sufficient stability is required for these digital multi-phase Buck controllers. Digital constant on-time multi-phase controllers are studied. First, the stability conditions of the system are derived through a digital compensation ramp (i.e., a ramp with a fixed slope in one switching cycle), the total inductor current information and the charge changes at both ends of the output capacitor. Then, the requirements for the slope are obtained using the stability conditions, where the effects of analog-to-digital converter (ADC) sampling delay and circuit propagation delay are considered. Conclusions can be drawn by classifying and analyzing the overlapped and non-overlapped duty cycles. Based on SIMPLIS simulations and by designing and changing the minimum compensation slope and the actual slope parameters, it is found that the simulation results are consistent with the theoretical analysis results, showing the accuracy of stability analysis for the digital multi-phase Buck converter.

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 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.

A multi-objective optimal control method based on extended phase shift (EPS) is proposed for a dual active bridge (DAB) converter in order to simultaneously reduce the backflow power and improve its dynamic performance. First, the output power and backflow power characteristics of EPS in each mode are comprehensively analyzed, mathematical models are developed, and the optimal combination of the backflow power shift angles is solved according to the Karush-Kuhn-Tucker (KKT) condition. Second, a virtual voltage compensation scheme is used to improve the dynamic performance of the system by rapidly changing the transmission power at that moment. Finally, the proposed scheme was compared with the traditional single phase shift and EPS schemes through experiments, thereby verifying its effectiveness and advantage.

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.

Harmonic pollution is one of the key problems restricting the grid connection of new energy sources. There are many factors that lead to an increase in current harmonics of grid-connected inverters, including the harmonic voltage of the grid and the sampling error of voltage and current signals in the grid-connected inverter system. On the basis, the principle of voltage sampling error and current sampling error of the grid-connected inverter system affecting the 2nd-order harmonic current of the inverter is analyzed, and a 2nd-order harmonic current suppression method based on high-precision harmonic sampling and 2nd-order harmonic current three-phase double-frequency rotation dq feedback is studied. In addition, a model of the 2nd-order harmonic current suppression loop is established, a design method for the parameters of the 2nd-order harmonic current suppression loop is given, and the expression of suppression effect is deduced. Finally, the proposed method was verified by experimental results of a 100 kW prototype.

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.

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.

To reduce the calculation amount in the model predictive current control (MPCC) algorithm for a three-level inverter model, eliminate the weighting factor, achieve a fixed switching frequency and improve the steady-state performance of the system, a three-vector fixed frequency MPCC algorithm based on vector set selection is proposed. First, through the analysis of the relationship between current and voltage, the control of current under the rotational coordinate system is converted into the control of voltage under the stationary coordinate system by using the beat-free idea, and the candidate vector set is selected according to the sector where the reference voltage is located, thus reducing the calculation amount. Second, to achieve the midpoint potential control, according to the different effects of different switching vectors of a neutral point clamped (NPC) three-level inverter on the neutral point and the principle of switching smoothness, different candidate vector sets are reasonably selected, and the switching vector action time is obtained by using the principle of volt-second balance. Afterwards, the optimal switching sequence is selected according to the evaluation function. Finally, the traditional MPCC and the proposed algorithm are compared, and experimental results show that the proposed algorithm has advantages such as small calculation amount, fixed switching frequency and low current harmonic content.

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%.

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.

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 solve the problem of large leakage current in a photovoltaic (PV) grid-connected inverter, a low-leakage current HERIC transformerless single-phase PV grid-connected inverter topology is proposed. This inverter topology only needs eight power switching tubes, four of which constitute four quasi-bidirectional voltage switching units. The four quasi-bidirectional voltage switching units are divided into two groups, and they alternate conduction with grid frequency to realize continuous current, thus reducing the loss of switching tubes and effectively suppressing the common-mode leakage current. Finally, the proposed topology was verified by simulation and experimental results.

In a grid-connected system of non-isolated photovoltaic (PV) inverters, the electromagnetic interference causes the problem of leakage current. Aimed at this problem, an improved model predictive control strategy is proposed for a three-level inverter. First, a mathematical model of the grid-connected inverter system is established to analyze the generation mechanism of leakage current and its relationship with the common-mode voltage. Second, the common-mode voltage variation rate is controlled to improve the model predictive direct power control algorithm, thereby optimizing the optimization result to achieve the suppression of leakage current. Finally, the conventional strategy and the proposed improved model predictive control strategy are compared and analyzed through simulations in terms of output power, harmonic distortion of grid-connected current, DC-side neutral point potential balance and leakage current amplitude. Results show that the proposed strategy performs well in all the above four aspects, and its leakage current suppression effect can reach 99.5% compared with the conventional model predictive control strategy.

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.

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.

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 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.

A lightweight modular multilevel converter-type fuel cells (MMC-FCs) system based on the partial power conversion (PPC) of FCs is proposed, so as to realize the power control of the FC system which is incorporated into a hybrid medium- and low-voltage network. The MMC-FCs on the AC side based on the synchronous switching network of a high-frequency link (HFL) can realize the coupling cancellation of the sub-module (SM) fundamental frequency and double-frequency ripple power, and reduce the demand of SM capacitance by [2(1-m²/4)^3/2f_SM]/ [(1+2m²)πf_F] times. As a result, the volumes of SMs are reduced, and the lightweight of SMs are realized by improving the power density. The FC system uses partial power control to incorporate the DC low-voltage bus, which reduces the partial power capacity and loss of the FC converter. Meanwhile, the FC converter is reused with the AC HFL square wave power signal to reduce the power conversion stages, thus further improving the lightweight of the system. The structure of MMC-FCs, SM filtering principle, FC PPC mechanism, SM capacitance, FC PPC voltage and other parameters are analyzed and designed in detail. Finally, through an evaluation on volume and losses, the effectiveness of the proposed MMC-FCs scheme was verified by simulation and experimental results.

In a high-voltage flexible DC power transmission system, the modular multilevel converter (MMC) has unique advantages. Compared with those of the ordinary MMC, the output voltage levels of a hybrid-leg MMC (HL-MMC) consisting of submodules (SMs) and IGBT are doubled, the harmonic content of output voltage is reduced, and the DC bus voltage utilization is also doubled under the condition of the same number of SMs. The series-connected HL-MMC (SC-HL-MMC) is composed of three single-phase HL-MMCs, and its number of SMs is reduced by 2/3 under the condition of the same DC bus voltage. To be equipped with a DC short-circuit fault-tolerant capability, a hybrid SC-HL-MMC consisting of half bridge SMs (HBSMs) and full bridge SMs (FBSMs) is applied, and the scheme of optimal ratio between FBSMs and HBSMs is analyzed to satisfy the short-circuit fault ride-through requirement. To verify the performance of the proposed topology, a simulation model is built. Simulation results show that the stable three-phase output voltage from the SC-HL-MMC contains less harmonic under the rated operation condition, and it can block the short-circuit current rapidly under the DC short-circuit fault condition, thereby verify the validity of this topology.

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 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.

Load resonance soft-switching can effectively reduce the switching loss of single-phase grid-connected inverters, which is a research hotspot in high-frequency inverter applications. However, the traditional PI control strategy based on linear models is easy to be unstable under large signal disturbance, and the system output waveform is poor. Since the passivity-based control strategy based on the nonlinear theory can effectively improve the output and stability of the system, a passivity-based control strategy for a load resonant soft-switching inverter based on an Euler-Lagrange model is proposed. A single-phase full-bridge grid-connected inverter in unipolar BCM (boundary conduction mode) modulation mode is modeled in detail, and a passivity-based controller based on the damping injection method is designed. To verify the effectiveness of the proposed control strategy, a simulation model of the resonant soft-switching inverter is built, and this strategy is compared with the traditional PI control strategy under steady-state and transient conditions.

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 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.

Under the traditional phase disposition (PD) modulation strategy, there is a power imbalance problem among the units in a cascaded H-bridge inverter. Aimed at this problem, the control principle of freedom degrees is analyzed, and a novel power equalization modulation strategy is proposed. On the basis of ensuring the output power equalization and voltage harmonic characteristics, the power equalization time is shortened, and the complexity in digital control is reduced. On the one hand, the freedom degrees of triangular carriers are recombined based on the PD modulation method to distribute them evenly in different carrier layers. Then, by fully utilizing the switching redundancy state at each output level, the power equalization is achieved within a carrier cycle to shorten the time needed for achieving the equalization. On the other hand, the complexity in digital control is reduced by restructuring the vertical freedom degree of the modulated wave. Finally, the theoretical analysis and feasibility were verified by simulation and experimental 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.

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.

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.

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 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 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.

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.

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.