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.

In an energy storage system, the voltage level on the DC bus side is usually higher, while the voltage level on the battery side is lower with a wide variation range. Under this background, a three-level bidirectional full-bridge multi-resonant DC-DC converter topology is proposed, in which a three-level structure is adopted on the high-voltage side to reduce the voltage stress of the switch. The resonant cavity is designed as an LLCLC multi-resonant structure with auxiliary inductance, so that the left and right sides of the equivalent circuit is symmetrical, thus realizing the peer-to-peer driving control of forward and reverse operations and the bidirectional transmission of power. An improved synchronous pulse-frequency-modulation control strategy is adopted, so that the full-range zero-voltage-switch can be realized for switches on the high- and low-voltage side regardless of the forward or reverse operation. Compared with the traditional LLC resonant topologies, the proposed topology can achieve a wider range of voltage gain in a narrower frequency range. Through the optimization design of resonant cavity parameters, the converter can transmit the current fundamental wave and third harmonic power at the same time, thereby improving the energy transmission efficiency. Finally, a 2 kW experimental prototype was built, and experimental results verified the theoretical analysis.

The bi-directional power transmission with a high efficiency and a high power density can be achieved by employing CLLC resonant converters. However, the traditional parameter design method is cumbersome and requires multiple iterations to obtain appropriate circuit parameters. To solve this problem, the working principle and characteristics of a bi-directional CLLC converter are analyzed, and a novel parameter design method is proposed. By considering the full range of soft switching, design index constraints and high-efficiency optimization conditions, the range of design parameters is narrowed and the design steps are optimized, thus effectively reducing the complexity of the converter parameter design process. Based on the demand for a 48~380 V/kW bi-directional DC-DC converter in industrial applications, specific parameter design steps and results were given, and a prototype was developed. The correctness and effectiveness of the proposed parameter design method was verified through experimental testing.

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.

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.

Aimed at the problems of a traditional LLC resonant converter in wide voltage applications such as a wide switching frequency range and a poor voltage regulation performance, a voltage doubling two-phase parallel resonant converter is proposed. There is a parallel double half-bridge LLC structure on the primary side of this converter, and a bidirectional switch is introduced into the full-bridge rectifier network on its secondary side to form a reconfigurable voltage doubling rectifier network. Fixed frequency control is adopted during operation. The lower half-bridge on the primary side changes the input voltage of the resonant tank by changing the duty cycle, while the upper half-bridge works with a fixed duty cycle. The rectifier network on the secondary side realizes full-bridge and voltage doubling hybrid rectification under the bidirectional switch, which can achieve 4 times of voltage gain. At the same time, this converter has a good soft switching performance, its voltage gain is independent of magnetizing inductance and load, and a larger magnetizing inductance can be selected to reduce the switch-off loss and conduction loss. Finally, the feasibility of the proposed converter was verified by simulation and experimental results.

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.

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.

Phase-shifted full-bridge zero-voltage zero-current switching(ZVZCS) converters are favored in high-power DC conversion applications owing to their advantages such as simple structures and high efficiency. However, high-power phase-shifted full-bridge ZVZCS converters still face problems including difficulty in the current reset and severe duty cycle loss. In response to the above issues, a novel phase-shifted full-bridge ZVZCS converter is put forward, which ensures that it can realize zero-current switching over a wide load range by introducing an auxiliary circuit on the primary side to reset the current to zero before the turn-on of lagging-leg switches. At the same time, it can accelerate the commutation speed on the primary side, reduce the duty cycle loss and realize an optimized design of power supply. Based on the analysis of the circuit structure, working principle and characteristics of the proposed converter, a 1 kW experimental prototype was designed to verify its correctness.

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.

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.

The magnetic integrated coupling technology is introduced into a high-gain converter, and a magnetic integrated Boost converter based on diode clamping is proposed. Through the theoretical analysis of the working principle and performance characteristics of the proposed converter, it is shown that this converter can reduce its volume and inductance current ripple based on the advantages of the original converter, such as a high voltage gain and a simple control strategy. In addition, the voltage gain of the novel converter is further improved by using the switched capacitor technology, the voltage stress of the switch and diode is further reduced, and the energy conversion efficiency of the converter is effectively improved. Finally, the findings were verified by simulation and experimental results.

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 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 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.

Harmonic and electromagnetic interference (EMI) filters are two important output filters used to sup-press the harmonic distortion and EMI noise in grid-connected inverters. Harmonic and EMI filters are combined by planar magnetic integration to reduce the volume and weight. Through the selection of an appropriate magnetic core, the common mode and differential mode inductors are integrated into the same core by drawing PCB planar coil. To integrate the discrete capacitors and further realize the planar magnetic integration of EMI filter, the dielectric is inserted into the PCB and the layer connection mode is reasonably planned. A symmetric LCL filter is used to replace the traditional asymmetric structure of magnetic integration. Furthermore, by designing the air gap in the center pillar of the magnetic core and reasonably arranging the planar windings, the inductors of LCL harmonic filter are also integrated into the same magnetic core unit to form an LCL-EMI planar magnetic integrated filter. A gallium nitride single-phase inverter platform was built, and the LCL-EMI filter with planar magnetic integration was experimentally analyzed to verify the feasibility of the planar magnetic integration method.

Compared with the traditional silicon(Si) devices, the gallium nitride(GaN) devices have lower parasitic parameters, a faster switching speed and a smaller on-resistance, which will easily lead to the phenomenon of continuous oscillation during their switching-on process and further result in the circuit instability. Therefore, it is necessary to suppress this phenomenon in practical circuits. Under this background, a negative conductance model of a bridge circuit under the conventional driving scheme is established at first, and the oscillation stability of the circuit is analyzed. Then, by adding optimization to the conventional driving scheme, the corresponding negative conductance model is established. The optimization schemes of series damping represented by changing the resistance and adding ferrite beads and those of parallel low impedance represented by adding RC snubber are selected, respectively. With this model, the influence of adding the driving optimization schemes on the oscillation stability of the circuit can be identified, and the changes in the stability before and after the addition were verified by experimental results, providing a reference for the driving circuit to select its appropriate driving optimization scheme.

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.

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 constant-current power supply system is suitable for remote seabed power supply in a harsh environment owing to its strong anti-failure capability. As all the seabed equipment adopts constant-voltage power supply, a constant-current to constant-voltage conversion device is needed to convert constant-current input into constant-voltage output to provide electric energy for the seabed equipment. To solve the problem that an efficient conversion from constant-current to constant-voltage in a wide load range as well as a high-pressure isolation control, a constant-current to constant-voltage converter topology with cascade of a shunt regulator circuit and a DC transformer is proposed to achieve the efficient conversion from constant-current to constant-voltage in a wide range. Aimed at the output control problem under high-pressure isolation, an indirect control strategy for output voltage based on input-side detection is studied to achieve an accurate control of output voltage without the need of high-cost and large-volume output isolation detection devices. Finally, an experimental prototype with input of 1 A and rated power of 500 W was built to verify the feasibility of the power conversion technology of constant-current to constant-voltage converter.

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.

With the continuous advancement of medical technology, implantable medical devices (IMD) are increasingly applied in clinical practice. Since the traditional battery-powered method will bring additional tissue damage and surgical costs to patients, the use of wireless power transfer (WPT) technology to power IMD will become a trend in the future. However, how to design a high-efficiency IMD-WPT system in a limited space is very challenging. To this end, the performance characteristics of five WPT technologies suitable for IMD are compared. Then, the magnetic resonance WPT technology is taken as an example to introduce the key issues in the design of a magnetic resonance IMD-WPT system. Finally, the application status of part of the magnetic resonance WPT technologies in some typical IMD is combined, and the research direction of IMD-WPT technology in the future is discussed.

With the development of wide band gap devices, SiC MOSFET has been widely applied, and the research on its short-circuit protection has become an important topic to ensure the reliability of power electronic equipment. In view of the short short-circuit withstand time of SiC MOSFET and the difficulty in short-circuit fault protection, a short-circuit detection method for SiC MOSFET based on a planar differential Rogowski coil is proposed, which realizes a rapid identification of short-circuit fault by measuring the drain source current of the circuit and has advantages such as a fast response speed, a strong anti-interference capability and complete isolation from the main circuit. First, the working process of the SiC MOSFET short-circuit detection method based on the planar Rogowski coil is introduced. The partial element equivalent circuit (PEEC) modeling method for planar Rogowski coil is studied in detail, and an equivalent model which can reflect the coil’s high-frequency characteristics is obtained. At the same time, the influence of the geometric structure of the planar Rogowski coil on its performance is analyzed, and an optimal design scheme considering both the high gain and high bandwidth is proposed. Aimed at the problem of low measurement accuracy of the Rogowski coil in an environ- ment with strong electromagnetic interference, a scheme of using the differential coil is put forward to improve the anti-interference performance. Finally, the anti-interference per-formance of the designed planar differential Rogowski coil and the reliability of short-circuit protection method based on this coil were verified by experimental results.

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.

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.

With the scale expansion of a subsea observation network, the stability of its high-power power supply system has attracted attention. First, the impedance models of key parts in the subsea power supply system are established. Considering the characteristics of high power electronic penetration rate, multi-bus cascading and adjacent bus interactive coupling of the subsea DC power supply system, the stability and influencing factors of the system are explored by using the step-by-step analysis method. The analysis result shows that the integral parameter of the controller is the dominant parameter that leads to the instability of the Buck converter, and the proportional parameter of the controller is the dominant parameter that results in the instability of the junction box subsystem. Both an increase in the impedance parameter of the optoelectronic composite cable and a decrease in the inductance parameter are beneficial to improving the system stability. The simulation results based on the PLECS simulation software verify the stability analysis results.

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.

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.

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.

Single-phase charging systems usually face the problem of secondary power pulsation. To solve this problem, a single-phase electric drive reconstructed onboard charger (EDROC) system with low voltage ripple is proposed, in which a Buck/Boost active filter is placed in parallel on the output side of a traditional single-phase EDROC system to absorb or compensate the secondary power pulsation, thereby obviously reducing the output voltage ripple of the charging system. First, the topology, working principle and secondary power pulsation generation mechanism of the single-phase EDROC system are analyzed. Second, a single-phase EDROC system with low voltage ripple is put forward by combing the Buck/Boost active filter. Meanwhile, the topology, working principle, and selection of inductors and capacitors of the Buck/Boost active filter are analyzed in detail. Third, a control strategy for the proposed EDROC system is designed. Finally, a 200 W experimental prototype was designed, and experimental results verified the feasibility of the proposed charger.

Aimed at the problem that the accuracy of photovoltaic array fault diagnosis based on support vector machine (SVM) is not high and it is easily affected by the kernel function and penalty factor parameters, a photovoltaic array fault diagnosis method based on SVM optimized by the seagull optimization algorithm (SOA) is proposed. The SOA is introduced to optimize the parameters of the SVM model, and an SOA-SVM fault diagnosis model based on the optimal parameters is established. MATLAB software is used to build a photovoltaic array simulation model, and the characteristic parameters under different fault types are extracted and further inputted into the SOA-SVM model for fault diagnosis. Experimental results show that the fault diagnosis accuracy of the SVM model optimized by SOA is significantly improved. Compared with the ABC-SVM and PSO-SVM models, the SOA-SVM model converges faster in the optimization process and has a higher fault diagnosis accuracy.

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.

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.

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 the traditional power module automatic layout optimization algorithm, the electrical evaluation is inefficient and takes up a lot of computing time. To solve this problem, lattice Boltzmann method (LBM) is used to replace the traditional evaluation method. Since LBM does not need to solve multiple invertible matrices, it can quickly judge the rationality of electrical interconnection and calculate the voltage/current. With the program of automatic layout design based on the genetic algorithm, an evaluation method of two-dimensional layout is established by using a D2Q4 lattice type, and the accuracy of the evaluation result under the layout scheme is verified by ANSYS Q3D software simulation. A comparative test was conducted in Python 3.10, and results show that LBM reduces the total time of scheme evaluation by 75.4% on average. Moreover, the more the number of loops in the evaluation scheme, the greater the computing advantage of LBM.

For a hybrid cascade H-bridge inverter with a DC-side voltage ratio of 1:1:2, if the hybrid carrier disp-osition modulation strategy is adopted, the problem of output power imbalance in the low-voltage unit will occur al-though there is no current backflow phenomenon and the harmonic performance of output voltage is good. To solve this problem, the power imbalance is analyzed at first. Then, an improved hybrid modulation strategy is proposed, under which the high-voltage unit performs step wave modulation and the low-voltage unit performs PWM, and two low-voltage units adopt different processing methods for the modulation wave. The good harmonic performance of output voltage is kept, the number of triangular carriers is reduced, and the control process is simplified, with a frequency doubling effect. Third, this strategy is optimized, and the switching signal of low-voltage unit is logically calculated, which can solve the power imbalance problem of low-voltage unit in two carrier cycles. Finally, the feasibility was proved by simulation and experimental results.

To solve the difficulty in online life prediction of silicon carbide metal-oxide-semiconductor field-effect transistor (SiC MOSFET) under practical working conditions, a digital implementation method for SiC MOSFET module life prediction based on particle swarm optimization-back propagation (PSO-BP) neural network was proposed. First, the saturation voltage drop of SiC MOSFET was extracted by a saturation voltage drop platform as the temperature-sensitive electric parameter, and a junction temperature prediction scheme based on experimental data was established. Second, a life prediction scheme based on PSO-BP neural network was established by using a power cycling accelerated aging experimental platform to extract the aging characteristic data. Third, the junction temperature prediction scheme and life prediction scheme were transplanted to field programmable gate array to realize the digitization of SiC MOSFET life prediction. Finally, a circuit was designed to verify the proposed method. Experimental results show that the error between the digital junction temperature and real junction temperature was 4.73 ℃, and the percentage of error between the predicted life times and real life times was 4.1%, which proves that the proposed life prediction method is realized digitally and can accurately predict the life times of SiC MOSFET module.