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.

The design of fractional-order PID control of a Boost converter is studied, and the fractional-order inductor and capacitor models of the system are fitted using the Oustaloup filter approximation algorithm. To solve the problems of insufficient learning capability and weak iterative convergence when a particle swarm optimization (PSO) algorithm is used to adjust the parameters of the fractional-order PID controller, an improved PSO algorithm is proposed, which introduces three strategies of adaptive inertia weight, adaptive learning factor and weighted mutation to improve the diversity of particles and enhance the convergence speed and accuracy. The improved PSO algorithm is applied to the design of a PID control system for a fractional-order Boost converter. Simulation results show that the control system designed using the improved PSO algorithm has a faster dynamic response of output voltage and inductance current, a better anti-interference capability of output voltage and a better tracking and adjusting capability of inductance current when the load changes suddenly.

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.

The actual duty cycle of a single-stage Buck converter is affected by the switching speed and dead time, so it is difficult to meet the wide range of voltage regulation applications. On this basis, a multilevel cascade Buck topology is adopted, and an output voltage cooperative control strategy for multilevel cascade converters is proposed. This control strategy takes into account the operation efficiency, and it adopts a hybrid modulation method combining pulse width modulation and frequency conversion modulation, thus realizing the output voltage control switching at all levels of the converter and covering the full range of output voltage. A switching loss model is established, and the efficiency optimization under hybrid modulation is analyzed. Finally, a simulation model was established to verify the correctness of the modulation and control design, and an 8 kW two-stage prototype with 50-75 V input and 1-40 V/ 200 A output was built to verify the feasibility of the proposed control strategy.

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.

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.

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.

With the large-scale development and utilization of renewable energy sources such as photovoltaics and wind power, inverters based on droop control are widely used in distributed generation systems and microgrids. Sequential impedance modeling is one of the important methods to assess the stability of a multi-inverter parallel system and optimize the control parameters. However, there is currently limited research on the sequential impedance modeling of droop-controlled inverters. Therefore, a detailed investigation was carried out. First, the steady-state operating point of a droop-controlled inverter was determined, and the inverter response was analyzed by introducing positive-and negative-sequence small signal disturbances. Second, the sequential impedance model was derived from the inverter response to characterize the inverter’s impedance properties. Subsequently, the accuracy of the sequential impedance model was verified through PSCAD simulations. Finally, the effects of key parameters such as droop coefficients and the cutoff frequency of a low-pass filter in the power calculation link on the inverter output impedance were analyzed and verified through experiments. Results demonstrate that the proposed sequential impedance model has a good performance in analyzing the droop control stra-tegies, providing valuable insights for further optimization and practical implementation of the strategies.

In power systems, unbalanced and nonlinear loads might lead to voltage and current imbalance and harmonic distortions, which will affect the operation of some critical equipment. To improve the power quality of a system consisting of multiple grid-forming (GFM) converters, it is necessary to reasonably share the load current’s fundamental negative-sequence and harmonic component while reducing the voltage imbalance and harmonics at the point of common coupling (PCC) as much as possible. To solve this problem, a power quality control strategy for GFM converters based on unified unbalanced/harmonic voltage-current droop is proposed in this paper. By establishing a unified droop relationship of fundamental negative-sequence and harmonic component between PCC voltage and output current, unbalanced and harmonic current is shared in accordance with the capacity of each converter while suppressing imbalance and harmonics of PCC voltage. The proposed me-thod can be applied to multiple converters in both the islanded and grid-connected modes without extracting the fundamental negative-sequence or individual harmonic sequences separa-tely. Compared with the existing control methods, this method is simpler and easy to implement in embedded controllers. The design scheme for control parameters based on closed-loop the pole analysis is discussed in detail. Moreover, through a comparison with the existing methods, it is shown that the proposed method has superior dynamic performance and less computation resources. Finally, the effectiveness of the proposed control method was verified by experimental results.

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.

In view of the problem that the traditional LLC resonant converters cannot well meet the requirements of wide voltage gain due to their narrow voltage gain range, a DC-DC converter with a wide input voltage range based on a multi-resonant structure is proposed, which achieves a wide voltage gain in both the under-resonant and over-resonant frequency ranges. The topology of the proposed resonant converter and its working principle are introduced, its fundamental wave equivalent mathematical model is established, and the voltage gain and input impedance characteristics are analyzed in detail. On this basis, the influences of each resonance parameter on the voltage gain, input impedance and working efficiency are analyzed, and the parameter design process of a 500 W converter is given. Finally, an experimental platform with rated power of 500 W was built. Experimental results show that the proposed converter not only had a wide voltage gain in both the under-resonance and over-resonance frequency ranges, but also can transmit the fundamental wave and third-order harmonic power, thus improving its working efficiency. In addition, this converter had good soft-start and short-circuit current limiting capabilities.

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.

To minimize the current stress of a dual active bridge (DAB) converter in its full power range, a global optimization strategy for the current stress under triple phase shift (TPS) control is studied. First, the operation principle and process of the converter under TPS control are analyzed, and a model of the relationship among its output power, current stress and phase-shift ratio is established. On this basis, the TPS control is optimized by seeking the optimal phase shift ratio combination with the goal of global minimization of current stress. In addition, the optimization results are compared with those under the dual phase shift (DPS) control in terms of current stress and reactive power. Finally, verification was performed by carrying out an experiment. The theoretical and experimental results show that the TPS control with the global optimization of current stress further reduces the current stress and reactive power in the full power range.

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.

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 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 four-switch Buck-Boost converter applied to a fuel cell system can theoretically achieve a higher efficiency under the traditional two-mode control. However, in fact, the dynamic performance of the system is poor due to the influence of a voltage gain blind zone in the process of transition between the two modes, which greatly reduces the operation stability of the converter. In high-power applications with large current, the interleaving technology is usually used to reduce the inductor current ripple and increase the power density of the converter. Therefore, the smooth mode transition of a four-phase interleaved four-switch Buck-Boost converter is taken as a control objective. First, the topology of the converter is introduced, and its basic mathematical relationship is obtained. Then, the reason for the voltage gain blind zone of the converter is analyzed using a graphical method, and a control strategy is proposed to eliminate the blind zone and realize the smooth mode transition based on the traditional three-mode control strategy. In the dynamic process, the changes in duty cycle are minimized and the inductor ripple current is also optimized, which improves the efficiency and stability of the converter. Finally, the effectiveness of the proposed control strategy was verified by 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.

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.

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.

The current inner loop of a peak current controlled Boost DC-DC converter needs to detect the IGBT collector current. However, the existing current detection methods need to connect the components to the main circuit of IGBT, which increases the circuit volume and cost and reduces the efficiency of the main circuit. Based on the IGBT smart driver technology with a collector current detection function, a peak current controlled Boost DC-DC converter without current sensors is proposed. First, a smart drive design is given. Based on the relationship between collector current and gate current during the Miller plateau, a three-point method is used to determine the relationship between collector current and gate current during the Miller plateau of the IGBT device, and the collector current is detected by detecting the gate current. Second, a small signal model of leading edge modulated Boost DC-DC converter considering the effects of sample and hold, quantization error and delay is established, and the stability of the converter is analyzed. Finally, a sensorless Boost DC-DC converter prototype based on current detection on the driver side was built, and the effects of current detection and stability control were verified by experimental results.

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.

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.

Different winding schemes for a toroidal inductor can affect its magnetic field leakage, which will intensify the near-filed coupling of an electromagnetic interference (EMI) filter. First, the effect of equivalent radial current and tangential current on magnetic field leakage was studied by using the partial element equivalent circuit method, and it was found that the equivalent current loop composed of tangential current was the main source of axial magnetic field leakage in the toroidal inductor. Then, a winding scheme was proposed, in which a PCB was sandwiched by two magnetic cores to generate reverse current loops above and below the PCB for magnetic field cancellation. In the experimental link, three-dimensional finite element simulation was conducted to demonstrate that the proposed scheme can further reduce the axial magnetic field leakage while maintaining a similar inductance as the traditional scheme. The impedance and insertion loss tests of the EMI filter were conducted, and it was verified that compared with the traditional scheme, the novel scheme can weaken the influence of high-frequency parasitic parameters on the inductor’s impedance characteristic, thereby further optimizing the high-frequency filtering performance of the EMI filter.

Three-level inverters have attracted widespread attention in medium-and high-voltage applications. However, traditional continuous pulse width modulation (CPWM) methods suffer from drawbacks such as high switching losses, significant common-mode voltage (CMV) fluctuations and neutral-point voltage imbalance. To solve these problems, based on the analysis of the generation mechanism for CMV, the suppression conditions for CMV are derived based on discrete pulse width modulation (DPWM), and a modified DPWM modulation strategy is proposed, which can reduce switching losses under DPWM0~DPWM3 modulations while suppressing CMV. In addition, based on the proposed DPWM modulation strategy, the control method for neutral-point voltage is explored, and the multi-objective optimal control of the three-level inverter is realized ultimately. Simulation and experimental results verified the validity of the proposed DPWM control strategy.

The loss calculation accuracy of a three-phase full-bridge inverter will be reduced if the parasitic capacitance and parasitic inductance loss of SiC MOSFET in the switching process and the conduction loss caused by changes in the duty cycle in the conduction process are ignored. To solve the problems, a physical model of SiC MOSFET considering parasitic capacitance and parasitic inductance was proposed. The parasitic capacitance and parasitic inductance were obtained by querying a data sheet and using an oscillation method. The losses of parasitic inductance and parasitic capacitance during the switching process were calculated, the average conduction loss equation under space vector pulse width modulation (SVPWM) was deduced, and the three-phase full-bridge loss was obtained. Finally, experiments were carried out on the control system of a permanent magnet synchronous motor based on SiC MOSFET. The influence of PWM frequency on the three-phase full-bridge loss was analyzed, and the accuracy of parameters for the physical model of SiC MOSFET was verified. Moreover, the loss calculation method based on the physical model of SiC MOSFET can improve the loss calculation accuracy of the inverter.

With the continuous increase in new energy penetration, the impedance interaction between a grid-connected inverter (GCI) and a weak grid is easy to induce small-signal oscillation instability. To solve this problem, the limitations of the existing voltage feedforward impedance reshaping strategy are analyzed in this paper at first. Then, an adaptive voltage feedforward impedance reshaping strategy is proposed. This strategy utilizes simulated anneal-particle swarm optimization algorithm to optimize the feedforward path parameters off-line under sample conditions of different values of output power and grid impedance, and polynomial fitting is used to cover the continuous full operating range. By deploying the fitting relationship in the inverter, the feedforward path parameters can be adjusted adaptively according to real-time power and grid impedance. The proposed adaptive strategy can ensure a better stability margin of GCI under conditions of different values of output power and grid impedance, and the dynamic performance of the system is considered to some degree. Finally, experiments were carried out on an OPAL-RT semi-physical experimental platform to verify the effectiveness of the proposed strategy.

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.

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.

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.

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.

As an energy manager for spacecraft power supply systems, the combined non-isolated three-port converter (TPC) can transfer and transform the electric energy between the three power ports of solar photovoltaic, battery and load, showing advantages of high-power density, high conversion efficiency, easy system construction and easy on-orbit maintenance. The combined non-isolated TPC is stacked with an interleaved bidirectional Buck/Boost converter and a semi-active full-bridge rectifier to realize the single-stage power conversion between any two ports, and the independent power control of the two ports is achieved by the pulse width modulation and phase-shift modulation strategies. The working principle, modulation strategy and control strategy for TPC were analyzed in detail, the corresponding design considerations were proposed, and its performance was further evaluated by experimental results.

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.

With the significant integration of transportation and energy fields, the electrified and “green” energy consumption in transportation is an important technical solution for achieving the targets of carbon peak and carbon neutrality. The use of low-temperature energy as coolants for high-temperature superconductor (HTS) cables can simultaneously transport the electric energy and fuels, which can improve the energy transmission efficiency and reduce the overall costs for large-scale renewable energy transmission. For a 10 km transmission distance, a 1.5 kV/10 kA liquid hydrogen (LH₂) energy pipeline structure for railway transportation is designed. Meanwhile, the effect of the arrangement angle of positive and negative bipolar HTS tapes on their critical currents was investigated by establishing a finite element simulation model of HTS cable. The maximum critical current was about 15 240 A in the parallel arrangement. Finally, the transmission losses of HTS cables and conventional copper cables with the same capacity (i.e., 15 MW/10 km) were compared. Results show that the transmission loss of 1.5 kV HTS cable was only 15% of that of 10 kV conventional AC cable, and it was also slightly lower than that at the 35 kV voltage level. The findings in this research can provide a feasible technical solution for LH₂ HTS energy pipelines to be used for large-capacity combined hydrogen-electricity transmission.