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.

Limited by the switching frequency, the frequency-controlled LLC resonant converter is difficult to achieve a wide output voltage range. To solve this problem, an expandable variable-mode interleaved parallel LLC resonant converter is studied. The secondary-side of this converter adopts a voltage doubling rectifier circuit, which can work in a parallel or series mode according to different switch combinations of two half-bridges on the primary-side, and it can adapt to the wide output voltage range of 1-3N times. A fixed-frequency PWM control method is proposed. In the middle region between the parallel and series modes, the fixed switching frequency is taken as the resonant frequency, and the duty cycle of one bridge arm is changed to realize voltage control. PSIM simulation results show that the wide output voltage range of 1-3N times can be realized by expanding 2N resonator cavities. The experimental results of a 100 W prototype demonstrate that the wide output voltage range of 1-3 times can be achieved with two half-bridges and two resonant cavities, and the effectiveness of the proposed converter and its control strategy was verified.

The application of multi-phase interleaved parallel coupled inductors technology can effectively reduce the phase current ripple and improve the dynamic response speed. Aimed at different design objectives, the influencing factors for the steady-state and dynamic performances of direct- and indirect-coupled inductors are analyzed. Subsequently, based on the invariant equivalent dynamic inductance before and after coupling, the direct- and indirect-coupled inductors are designed to enhance the steady-state performance. Similarly, based on the invariant equivalent steady-state inductance before and after coupling, direct- and indirect-coupled inductors are designed to improve the dynamic performance. Finally, the cor-rectness and effectiveness of the theoretical analysis were verified by experimental results, demonstrating that the two different coupling methods can significantly enhance the steady-state and dynamic performances of the converter, respectively.

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.

Resonant converters with a wide input range are much in demand in energy storage and new energy systems. When the voltage gain characteristics of an LLC resonant converter are calculated using the operation mode analysis (OMA) method, it is often assumed in previous studies that the circuit under phase shift control is in discontinuous conduction mode, resulting in significant errors in the gain analysis result of a converter which is in continuous conduction mode. On the basis, an OMA calculation method for an LLC resonant converter with a voltage doubling rectifier is proposed to identify the two modes. First, the criterion for determining whether the converter operates in continuous or discontinuous conduction mode is obtained through the modal analysis. Then, the normalized calculation models of these two modes are derived by OMA, and the calculation results and the criterion are used to verify the actual mode. Finally, a comparison among the calculated, simulated and experimental voltage gain curves under different conditions indicates the effectiveness of the proposed method. This method is more applicable to LLC converters in possible continuous mode, improves the accuracy of the gain analysis and is helpful for parameter design.

New energy vehicles are the main direction for the transformation and development of automobile industry in China, and their safety issues have also attracted the attention from the whole society. To study the safety issues of new energy vehicle power battery, statistics of new energy vehicle accidents which have been publicly disclosed over the past six years are collected in this paper, and the corresponding vehicle models and fire causes are analyzed. The mechanisms of safety accidents such as battery overcharge, overdischarge, internal and external short-circuit faults, extrusion and collision, and thermal runaway are described. The characteristic parameters of battery thermal runaway are summarized. Based on the operating data, the variation in the characteristic parameters of one accident car when it was on fire is analyzed. Finally, some solutions to the existing issues of new energy vehicles are given, and the battery models and intelligent algorithms which are established on the basis of big data are introduced in detail, providing a basis for power battery fault diagnosis in the future.

To address the issue that a dual-active-bridge DC-DC converter will produce large current stress when voltages mismatch and result in a large reduction of its efficiency, a combined dual-phase-shifting (CDPS) control strategy is proposed, which combines dual-internal-phase-shifting (DIPS) and interlaced-dual-phase-shifting (IDPS). First, the working principles of the two control strategies are analyzed, and the mathematical models of transmission power and current stress are established. Second, with the minimum current stress as the objective, the optimal phase-shifting ratios are solved by using the Lagrange multiplied method under the Karush-Kuhn-Tucker condition. Third, the optimization methods under the two control strategies are combined according to different voltage ratios and transmission power. The CDPS control is used to obtain the optimal solution of current stress, which is compared with those obtained under the existing single-phase-shifting and dual- phase-shifting control strategies. Results show that the proposed control strategy can further reduce the current stress and reactive power under the condition of high voltage ratios and improve the efficiency. Finally, an experimental prototype was built to verify the feasibility of the proposed control strategy.

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 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.

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.

Aimed at the time-delay oscillation of a bidirectional H4 bridge converter in a single-phase energy storage inverter, a unified control method for the bidirectional H4 bridge converter is proposed. In this method, a voltage regulator is used to control the power flow of the converter, and a set of bidirectional feasible control parameters are derived based on the power balance theory. At the same time, in order to realize AC current tracking input voltage without static error and increase the stability, the current inner-loop adopts a quasi proportional resonance controller, and a second-order generalized integrator is used to design a phase-locked loop. PSIM simulation and experimental results show that the proposed method can realize seamless switching between the rectification and active inverter modes, and it also has a good effect in the startup and switching between different modes. Therefore, it can realize stable control of the bidirectional AC-DC bridge converter in a single-phase photovoltaic energy storage system and obtain a good dynamic performance.

In an energy storage system, the current-fed dual-active-bridge converter has a large current stress and the corresponding soft-switching range is limited, which limits the converter's efficiency and power density. To solve these problems, combined with the coupled inductor technology, a current-fed dual-active-bridge converter with a low current ripple on the energy storage side and a wide soft-switching range is proposed. Two current-fed full bridges are connected in parallel on the energy storage side, thus effectively reducing the current stress of switches therein. By adjusting the phase shift angle between the two parallel full bridges on the energy storage side, the current ripple is reduced. By reasonably designing the coupling filter inductance, the obtained mutual inductance current is large enough to satisfy the soft-switching conditions for switches. The working principle and steady-state analysis of the converter were given in detail, and a 400 W experimental prototype was designed to verify the superiority and feasibility of the proposed converter.

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.

The accurate estimation of the state-of-charge (SOC) and state-of-health (SOH) of lithium-ion batteries is always a key scientific prob-lem that needs to be solved urgently. In this paper, based on a second-order fractional-order equivalent circuit model, the state space equation of a lithium-ion battery is established, and the discretization expressions of fractional-order differential and integral equations of battery parameters and SOC are derived. Then, a dual fractional-order extended Kalman filter method is studied to estimate the equivalent circuit parameters, SOC and battery capacity simultaneously. In addition, a time weighting sequence method based on estimated SOC and battery capacity is proposed, different discharge currents and cumulative time are monitored, and the available capacity of the battery is calculated online, thus achieving real-time estimation of the SOH of the battery at any discharge depth and any discharge rate. Finally, under the conditions of dynamic stress test, three lithium iron phosphate batteries of the same manufacturer, the same model and different aging degrees were used for experimental verification.

Aimed at the problem that the traditional control methods are difficult to achieve soft-switching in a wide load range due to the limitation of resonant inductor volume and duty cycle loss in phase-shifted full-bridge converters, a hybrid control method based on peak current and Burst mode is proposed. The output voltage is stabilized to a reference value by adjusting the Burst duty cycle, and the phase shift angle is changed to maintain the minimum primary current so as to realize the lagging bridge arm zero voltage switching. A simulation platform was built for the proposed control method, and a 250 W prototype was developed. The hybrid control of a phase-shifted full-bridge converter was realized through a digital signal processor, and the feasibility of the control method was verified by simulation and experimental results.

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 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.

The coupling between the boost control and neutral-point voltage balance control of a quasi-Z-source three-level inverter seriously limits its control performance. To solve this problem, a neutral-point voltage balance control strategy based on a virtual space-vector pulse width modulation method is proposed. The neutral-point voltage balance control is realized through a closed-loop control of the DC-bus capacitor voltage, and the low-frequency fluctuations in the neutral-point voltage are eliminated. Meanwhile, a constant shoot-through boost modulation strategy is employed, which avoids the adverse impact on the neutral-point voltage and guarantees an ample boosting capacity of the quasi-Z-source network. Finally, simulation and experimental results verified the validity of the proposed control strategy.

To address the power quality issues in a multiple grid-connected-converter system (MGCCS) for renewable energy, the series and parallel models of MGCCS are established at first based on the harmonic state space (HSS) method. The HSS models account for high-frequency components during the switching process, with its internal Toeplitz matrix effectively capturing the harmonic coupling within the converters. Based on the series and parallel HSS models of MGCCS, a virtual resistor is introduced to improve the model, and the impact of grid impedance is considered to simulate the multi-converter grid-connected system. In addition, the harmonic stability of this system is investigated by analyzing the eigenvalues of the state matrix. The influences of main circuit and controller parameters on the harmonic instability are analyzed in depth, and the oscillation frequencies in harmonic instability modes are predicted. Simulation results based on MATLAB/Simulink and RT-LAB experimental results validate the accuracy of the improved HSS models and the harmonic stability analysis.

The double-sided LCC compensated inductive power transfer (IPT) system with constant-voltage (CV) output suffers from the problem of low efficiency under light load. To solve this problem, based on the idea of approximate optimal solution, a parameter design method for double-sided LCC compensation topology was proposed. The zero phase angle condition in CV output mode and the loss of a loosely coupled coil were analyzed, and a 6.6 kW prototype was built to verify the proposed method. Experimental results show that the system efficiency can be improved with the proposed compensation parameter design method, especially in the case of light load. The system efficiency can reach 95% under full load of 6.6 kW and 93% under light load of 1.32 kW.

Voltage sag is one of the main power quality problems, and dynamic voltage restorers (DVRs) provide an effective solution. Since the traditional DVRs are unsuitable for medium-voltage applications, a high-voltage direct-connect DVR based on a cascaded H-bridge multilevel converter is introduced. To enhance the response speed and compensation accuracy of the system, a dq-axis decoupling strategy for the AC voltage compensation control of DVR is proposed. Meanwhile, a carrier phase shifted pulse width modulation strategy with voltage offset injection is also employed to balance the DC-side capacitor voltage of the cascaded H-bridge, thus ensuring the safety and stability of the system. Finally, the proposed DVR and the corresponding control algorithm are modeled and simulated by MATLAB/Simulink, demonstrating the effectiveness and feasibility of the approach.

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 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.

As the interface between a new energy power generation system and power grid, inverters play an important role. However, the stable operation of the system may be threatened by the changes in grid impedance in a weak grid environment, interaction between parallel inverters and delay in the control system. Under this background, a novel virtual impedance remodeling strategy based on the passivity theory and traditional proportional voltage feedforward is proposed, which can eliminate the non-passive region below the Nyquist frequency and keep the inverter output impedance phase within [-90°, 90°]. The results of numerical examples show that the proposed scheme can keep a good stability of the inverter parallel system under changes in grid impedance, number of inverters and parameters.

The flying capacitor clamped three-level converter has many advantages, e.g., it can reduce the voltage stress of a switch and the volume of a filter inductor. Under its operation, it is necessary to stabilize the flying capacitor voltage at half of the high-voltage side voltage, so a control strategy of adjusting the duty cycle is often used. However, this method has the problem of coupling control between flying capacitor voltage and output voltage, resulting significant fluctuations of inductance current in the process of flying capacitor voltage regulation. To solve this problem, the advantages of using the phase-shifting control strategy to realize the decoupling control of flying capacitor voltage and output volt-age are analyzed, and the corresponding control characteristics are also studied. Through the establishment of a harmonic model of flying capacitor voltage, the relationship between flying capacitor voltage and phase-shifting angle is given. A low-order harmonic function relationship is constructed, which indicates that the flying capacitor voltage is affected by the switch duty cycle D and phase-shifting angle ∆φ. The effective duty cycle interval of phase-shifting control and the duty cycle that optimizes the performance of phase-shifting control are delimited by combining with a time-domain model. A simulation model was established, and an experimental prototype with 3.6 kW was built. The control strategies of adjusting flying capacitor voltage based on phase-shifting angle and duty cycle are compared to verify the decoupling advantages and control characteristics of phase-shifting control.

To study the conducted common-mode (CM) electromagnetic interference (EMI) characteristics of a single-switch forward converter and reduce its CM noise, the analysis of the transmission mechanism of conducted CM noise in the single-switch forward converter is necessary. On this basis, a CM noise transmission path model is established, and a calculation method is proposed to determine the specific external capacitance to reduce the CM noise. In addition, aimed at the defects of the traditional calculation model of induced charge on the secondary side, an improved calculation model is put forward, and simulation results show that the accuracy of the improved model is higher under ideal conditions. Afterwards, the balanced winding method was used to reduce the CM noise flowing through the transformer, and a prototype of single-switch forward converter power supply was used for experimental verification. Results show that the method of calculating the external capacitance was effective, and the accuracy of charge calculated by the improved calculation model was higher when the windings were close or when the number of turns per unit length was relatively large.

When a three-level bidirectional DC converter is under carrier modulation, the switching between its forward and reverse operations is not smooth and the dynamic response is slow, which will easily cause harmonics in the resonant circuit. To solve these problems, a carrier modulation method for the three-level bidirectional DC converter based on neutral point shift is proposed. The working principle for the bidirectional DC converter is analyzed. Based on the principle of neutral point shift, the phase angle mode of three-phase output voltage from the converter is adjusted. On the basis of constant switching frequency, the neutral point shift voltage with different amplitude modulation ratios is calculated. According to the actual fault state, the shift between adjacent carriers in the same phase unit is rectified, and the carrier phase shift pulse width modulation is used to modulate the carrier of the three-level bidirectional DC converter. Simulation results show that the proposed modulation method can effectively control the output waveform of the three-level bidirectional DC converter. When the converter operates normally, the amplitude modulation ratio is greater than 1.0, the phase voltage is saturated, and the modu- lation signal is overshoot.

Since the traditional algorithm for the space vector modulation (SVM) of a VIENNA rectifier is computationally intensive, complicated and difficult to implement digitally, a fast algorithm for implementing the SVM of the VIENNA rectifier is proposed in this paper. This algorithm does not require coordinate transformation, avoids a large number of root square and trigonometric operations, and only requires simple logic judgment and addition and subtraction operations to quickly determine the duty cycle of a three-phase drive signal, which is easy to implement digitally and saves the time resources of DSP. In addition, a neutral point voltage control strategy is redesigned accordingly. Finally, the effectiveness of the proposed fast algorithm was verified by MATLAB simulations and experiments conducted on a hardware platform.

With the advancement of the construction of photovoltaic, energy storage, DC and flexibility, the problem of harmonics in a low-voltage DC (LVDC) power supply system has received widespread attention. Compared with those of an AC system, the characteristics of a DC system are that the power supply and load are more decentralized, the proportion of power electronic equipment is higher, and the AC-DC coupling effect caused by interface converters is strong. Therefore, the problem of harmonics in the DC system indicates that both the low- and high-frequency harmonic peak-to-peak values may be high, and thus the classic harmonic analysis and control methods for the AC system are not completely applicable. To this end, the main harmonic sources for the LVDC power supply system are analyzed, and the mechanism and characteristics of the DC bus voltage harmonic problem caused by DC sources and load are revealed. Accordingly, a hybrid active power filtering harmonic voltage control technology is proposed for the harmonic sources of a broadband and decentralized DC system, which achieves the control of harmonics in the case of uncertain disturbance location and high- and low-frequency mixing, thus improving the power quality level of the LVDC power supply system. Finally, simulation results prove the effectiveness of the proposed scheme.

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.

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.

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 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.

The switching speed and switching frequency of converters keep increasing, and higher requirements are also imposed on the DC-side decoupling capacitors. To solve the problems of overvoltage spikes and decoupling capacitor losses caused by voltage and current oscillations during the switch-off process, a transient circuit model considering the system's stray parameters is established, and the evolution of overvoltage and decoupling capacitor current oscillation is analyzed. On this basis, a loss model considering the parasitic parameters of the main circuit and the equivalent series resistance of the decoupling capacitor is proposed. The limiting factors for the selection of decoupling capacitors in practical engineering are quantitatively analyzed, and an optimal selection method for the decoupling capacitance and loss limit condition is obtained. Finally, the proposed model and analysis method were verified by simulation and experimental results.

To achieve the target of carbon neutrality, renewable energy power generation represented by photovoltaic (PV) power generation has become an important means. PV power generation systems usually require multiple PV modules to be connected in series to obtain a high output voltage. However, in series-connected PV modules, the mismatch of component characteristics due to partial shading or different degrees of aging of components will cause a serious loss of power generation. Therefore, many technical schemes have been proposed to solve this problem. The PV equalizer has become a promising solution, and it uses a power electronic converter to transfer the mismatched power and change the operating point of the component to obtain the maximum output power. First, the basic concepts and principles of PV equalizers are elaborated, then, the PV-bus, PV-PV and other special types of PV equalizers topologies are introduces in detail. In addition, a comparison and analysis of the paremeters and performance of the existing PV equalizer topologies is performed. Finally, the topological structures of PV equalizers are summarized and evaluated, providing a reference for engineers and practitioners in this field.

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.

Aimed at the problem of eddy current loss, a method for the parameter design and optimization of a wireless power transfer (WPT) system in seawater is proposed to optimize the power transmission efficiency of the system. First, based on the analysis of the electromagnetic field of coils under operation in seawater, the equivalent mutual inductance model of the WPT system in a marine environment is obtained by using the equivalent impedance of eddy current loss. Second, when the positions of the primary- and secondary-side coils are fixed, the corresponding relationship between the equivalent impedance of eddy current loss and the operating frequency of the system and the number of coil turns is established, and the feasibility of the calculation method for the equivalent impedance of eddy current loss is verified by using the coils on both sides of the WPT system. Finally, based on the energy model of an LCC/S-type WPT system in seawater, the particle swarm optimization algorithm is used to optimize the transmission efficiency. A test system was built with the optimized parameters, and results show that when it transmitted 1 kW of power in a simulated marine environment, its overall efficiency can reach 84%.

To reduce the cost and the number of components while ensuring the safe operation of the circuit, a single-phase isolated Δ-source AC-AC converter is proposed. This novel converter can provide a wider range of Buck-Boost output voltage, and the input voltage and output voltage can be in-phase or out-phase. Meanwhile, the surge and harmonic currents are suppressed, and the circuit reliability is improved. The working principle for the proposed circuit is analyzed, the voltage values of main components in each working process are deduced, and the relationship between input voltage and output voltage is formulated, which is further compared with those of other improved AC-AC converters. The theoretical analysis proves the performance of the novel AC-AC converter. A simulation model and an experimental model were built according to the designed parameters for verification, and simulation and experimental results verified the correctness and feasibility of the theoretical analysis.