Jiachen Tian

With rapid development of new-typed transportation system such as electric vehicle applications or railway station, this paper proposes a novel efficiency promotion strategy for three-level active neutral-point-clamped dual-active-bridge (ANPC-DAB) DC-DC converters in distributed energy storage systems. A comprehensive soft-switching model incorporating non-ideal factors such as dead time effects, nonlinear junction capacitance C_oss and charge Q_oss variations is established to achieve full zero-voltage-switching (ZVS) for all power switches, including historically problematic active-clamping devices. By deriving precise ZVS boundaries through resonant energy analysis and implementing a wide operating range comprehensive optimization strategy under double-side variable duty modulation (DVDM), the strategy collaboratively minimizes conduction, switching, and copper losses while extending the ZVS operating range. Experimental validation confirms superior efficiency, reduced current stress, and the widest ZVS range compared to existing methods.

With the high penetration of renewable energy sources and power electronic devices in power systems, the continuous expansion of the transmission distance and scale of electric energy transmission has led to an increase in grid-side impedance, thereby endowing the power system with weak grid characteristics. However, limited by the measurement accuracy of the phase-locked loop (PLL), the control strategy of traditional grid-connected inverters cannot satisfy the current quality requirements at the point of common coupling (PCC) under weak grid conditions, and may even trigger system instability and oscillation in extreme cases. To improve the grid-connected current quality of converters under PLL-based weak grid tracking control, this paper establishes a small-signal model of the system to clarify the impacts of the PLL and grid strength on system stability, as well as the propagation path of the PLL phase angle error in grid-connected systems. A current feedforward compensation method based on an optimized PLL structure with the ability to calculate the phase angle error in real time is also proposed. Finally, comparative analysis and experimental results demonstrate that, in contrast to the single oscillation suppression effect of conventional methods, the proposed method can mitigate oscillations induced by both insufficient grid strength and unreasonable PLL bandwidth design, thus having a broader application scope in oscillation suppression and the improvement of PCC current quality.

Due to high power density, simple control scheme, and bidirectional power transmission ability, the dual-active-bridge (DAB) converter has been widely applied in electric vehicle (EV) applications. For conventional phase-shift modulations, a fixed 50% duty ratio of driving signals will lead to a limited zero-voltage-switching (ZVS) range and excessive current level. Meanwhile, root-mean-square (rms) current optimization will also result in a restricted ZVS range. Subsequently, in this article, double asymmetric duty modulation (DADM) is introduced to solve the aforementioned questions. On the one hand, the operation principle, typical mode demonstrations are displayed. Considering the nonlinear characteristics of junction capacitance ${C} _{\mathbf {oss}}$ , ZVS performance under different DADM modes is analyzed in detail, and the corresponding ZVS boundary can be established. Simultaneously, the effect of dead time is also illustrated. On the other hand, for an efficiency promotion strategy, a wide-operating-range multiobjective optimization method based on nondominated sorting genetic algorithm II (NSGA-II) is proposed to optimize rms current and peak current simultaneously under all switches ZVS operations. Meanwhile, current Pareto-optimal curves under numerous operation conditions will be established. Through comprehensive comparisons among existing modulations, peak current and rms current could be reduced by more than 10%. The ZVS range could be extended by more than 33%. As a result, efficiency value could be optimized more than 1.1%, especially at light-load conditions. Finally, a DAB prototype is established, and the effectiveness and correctness of the proposed method can be proved.

With the increasing requirements of higher‐voltage withstanding ability, higher modulation flexibility, lower cost for prototype establishment, wider zero‐voltage‐switching (ZVS) range adjustment ability and bidirectional power transmission ability, a three‐level active neutral‐point‐clamped dual active bridge (ANPC‐DAB) converter is proposed to achieved the aforementioned goals. To achieve efficient power transmission inside the ANPC‐DAB converter, a double‐side variable duty modulation (DVDM) strategy is also proposed. On the one hand, switching states and soft‐switching conditions of the ANPC half‐bridge circuit are discussed in detail. How to realize ZVS turn‐on of clamping switches and non‐clamping switches is also discussed. Meanwhile, typical mode illustrations, power characteristics, and current characteristics under different DVDM operation modes are demonstrated comprehensively. On the other hand, to achieve efficient power transfer inside the ANPC‐DAB converter, based on a genetic algorithm, under a certain transmission power, peak current can be achieved at the lowest. Meanwhile, based on a complete differential algorithm, a wide operating‐range comprehensive optimization strategy is developed to reduce RMS current and extend the ZVS region simultaneously. Through the comprehensive comparisons among existing modulation methods inside the ANPC‐DAB converter, the proposed DVDM strategy can achieve better efficiency performance. In the end, an ANPC‐DAB prototype is established, and the effectiveness and correctness of the proposed method can be proved.

The dual‐active‐bridge (DAB) converter has garnered significant research interest owing to its galvanic isolation, simple circuit topology, and ease of modularisation, making it an effective interface circuit for integrating diverse energy sources. However, conventional DAB operation involves multiple working regions with limited efficiency and narrow soft‐switching ranges. To improve high‐efficiency performance under light‐load conditions, this paper employs triple phase‐shift (TPS) modulation as a case study and introduces a novel multi‐objective optimisation strategy, which is designed to concurrently optimise both the peak and root‐mean‐square (RMS) currents while extending the zero‐voltage‐switching (ZVS) range. Consequently, compared to existing modulation schemes, the proposed strategy effectively reduces overall power losses. It also achieves a noticeable reduction in RMS and peak currents, resulting in superior light‐load efficiency. Furthermore, a significant expansion of the ZVS operating range is realised. Finally, a hardware prototype based on the DAB topology has been built to experimentally validate the effectiveness of the proposed optimisation method.

Film capacitors are used in traction inverters to stabilize the voltage on the battery side. However, excessive hotspot temperatures can lead to premature capacitor failure, significantly reducing the reliability of the entire traction system. Monitoring the temperature rise profile of capacitors is vital for assessing their lifetime. Existing finite element analysis (FEA) and lumped thermal network (LTN) models for capacitors have certain limitations: FEA requires substantial computational resources, while traditional LTN models fail to account for the influence of heat capacity on thermal dynamics, which limits their effectiveness in temperature monitoring. To address this issue, this article develops a second-order LTN, whose parameters are obtained through FEA, to incorporate the effect of heat capacity on the thermal characteristics of capacitors. Subsequently, the proposed LTN is combined with the ripple current profile of an electric vehicle (EV) to efficiently calculate the capacitor’s hotspot temperature. Based on this, the reliability of capacitors is evaluated using cumulative fatigue damage theory. The findings provide insights for planning the scheduled maintenance of capacitors used in traction inverters.

Virtual DC Machine (VDCM) control is a promising approach for providing inertia support in DC microgrids, thus enhancing voltage stability. However, it suffers from a complex model and difficult parameter tuning. For this issue, an improved VDCM (IVDCM) control strategy is proposed, offering several advantages over the conventional VDCM (CVDCM) control. Specifically, compared to CVDCM, the voltage recovery control in IVDCM is moved after the VDCM loop, and a capacitor current feedback is adopted in the current inner loop. The improved control structure enables the IVDCM to provide more inertial power and mitigate the DC bus voltage fluctuations. Furthermore, the small-signal output impedance of the IVDCM can be simplified into a second-order model. The time-domain expressions for the DC output voltage are then derived, and the dynamic performance indices and constraints of the IVDCM are established, defining the feasible region for IVDCM control parameters. Consequently, an intuitive approach for control parameter design is achievable. Simulation and experimental results demonstrate the effectiveness of the proposed IVDCM control strategy and the associated parameter design method.

With the increasing demand and fast advancement of distributed energy storage system, dual-active-bridge (DAB) converter has become a popular interface circuit with simple circuit structure, bidirectional power transmission ability and simple control scheme. To improve efficiency performance of DAB converter, in this paper, an optimized asymmetrical duty modulation scheme (OAS) is proposed to widen soft-switching region and reduce current level. On the one hand, operation principles, power characteristics and current characteristics under different OAS modes are displayed systematically. For soft -switching characteristics modelings under proposed OAS, influences of both dead time t _d and junction capacitance C _oss are taken into consideration. Electrical characteristics for resonant process within dead time t _d are also modeled and analyzed. Meanwhile, based on energy balance principle and relationship between junction capacitance C _oss and drain-to-source voltage V _ds , the minimum current value to achieve zero voltage switching (ZVS) turn-on of switches can be obtained. On the other hand, to obtain better efficiency performance, a integrated optimization method is proposed. Based on the multi-objective particle swarm optimization (MOPSO) algorithm, root mean square (RMS) current value, peak current and soft-switching range can be optimized simultaneously. Through comprehensive comparisons with existing modulation schemes, proposed OAS can achieve lowest peak current, lowest RMS current and widest ZVS range. Finally, a DAB-based prototype is established and effectiveness and correctness of proposed method can be verified.