To improve the capability of microgrid in coping with new energy output and load uncertainty, an optimal control strategy for microgrid considering flexible resources is proposed. According to the source-storage-load characteristics of various flexible resources, a two-layer optimal scheduling model for microgrid is established. In the user layer, user-side flexibility resources are introduced, with an optimization goal of minimizing the difference between user costs and net load and decision variables of electric vehicles and output power of translatable loads. In the source-storage layer model, flexible resources are added to the energy storage and power generation sides, with an optimization goal of minimizing the microgrid operators’ cost and load loss rate and decision variables of gas turbines, main network tie-line and output power of energy storage unit. A case study based on scenario-reduced seasonal typical daily data is simulated, and the improved MOEA/D(multi-objective evolutionary algorithm based on decomposition) algorithm is used to solve the two-layer optimal scheduling model. Results show that the average annual user cost is reduced by 6.85%, the average annual total cost of operators is reduced by 14.68%, and the average annual load loss rate is reduced by 6.65%. The results verified the correctness and effectiveness of the proposed method.

The dual-active-bridge (DAB) converter is a key device in a bidirectional power transmission system. In this paper, its fundamental operation principle and topologies are reviewed at first. Then, four basic modulation strategies for the DAB converter are introduced, including single-phase-shifted, dual-phase-shifted, extended-phase-shifted and triple-phase-shifted strategies. Moreover, the modeling and optimization methods based on these four modulation strategies are compared and analyzed. Finally, some problems faced by practical applications and the corresponding solutions are discussed. Along with the development of DC power distribution, energy storage and distributed energy resources, DAB converters will have broad application prospects.

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.

Silicon carbide metal-oxide-semiconductor field effect transistor (SiC MOSFET) has attracted attention from the industry owing to its excellent characteristics such as high voltage, high frequency and low conduction loss. However, compared with the silicon-based IGBT, the problem of gate oxide reliability caused by the high defect density at the SiC/SiO2 gate oxide interface has become a key bottleneck restricting the large-scale applications of SiC MOSFET devices. By sorting out and analyzing the research results of the gate oxide reliability of SiC MOSFET at home and abroad in recent years, the causes of the gate oxide reliability problems at present were elaborated upon, and various commonly-used gate oxide reliability evaluation methods were summarized and compared. Finally, the gate oxide reliability of SiC MOSFET under extreme operating conditions and the development status of technologies for improving its performance were discussed.

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.

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.

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.

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.

Electric vehicle fast charging piles are prone to overheating of power devices under high-power operation, causing potential safety hazards. However, the existing cooling strategy adopts a rule-based forced air cooling method, and the cooling fan rotates at a high speed and generates large environmental noise. To protect the thermal safety of core components in the module while optimizing the cooling regulation strategy, an optimal thermal management method for electric vehicle fast charging module based on data-driven model predictive control (MPC) is proposed. This method adopts a data-driven method to construct a prediction model of module temperature distribution based on the long short-term memory neural network, and it combines MPC to control the fan speed, thus optimizing the thermal management strategy for the fast charging module and reducing the fan noise. Through experimental tests, it was verified that this method can effectively reduce the average fan speed by 1 293 rpm and reduce the average noise by 4.99 dB while ensuring that the key components are not overheated, which ensures the thermal safety of core components and the durability of the cooling fan.

In view of the recent situation in which power sources gradually reach their service terms in China, an evaluation method based on improved fuzzy analytical hierarchy process (FAHP) and entropy weight method (EWM) is proposed. First, an appropriate hierarchical structure is constructed based on the analytic hierarchy process to form a judgment matrix. Then, FAHP is used to process the judgment matrix between various layers, and the importance-oriented weight vector is obtained. At the same time, the Delphi survey method is used to form an evaluation matrix for the last sub criterion layer and the target layer. After normalization, EWM is used to obtain the value-oriented weight vector. The two weight vectors are synthesized to form a comprehensive weight vector. Finally, the final weight vector of the scheme layer to the target layer is formed, and the best scheme is given. The result of an example shows that the proposed evaluation method has strong flexibility and wide applicability. In addition, it also has a clear and reasonable process, as well as intuitive and accurate results.