The dual-active-bridge (DAB) converter serves as a crucial galvanic isolating solution to provide dc grid-forming for dc elements in low-voltage direct-current (LVdc) systems. Key performance metrics such as efficiency, current stress, power density, and cost of DAB converter are chiefly subject to the optimal design of magnetic components and modulation strategies. However, existing DAB converter designs yield compromised solutions that optimize a limited subset of these metrics. This article develops a comprehensive analytical framework to characterize DAB converter operation across three key dimensions: 1) zero-voltage switching (ZVS) range; 2) power rating utilization; and 3) reactive power. To achieve a well-balanced design, a holistic optimization methodology is proposed, integrating multiobjective particle swarm optimization (MOPSO) with triple phase-shift control. By optimally selecting the transformer turns ratio and product of switching frequency and series inductance, the proposed MOPSO approach can collectively or selectively improve these performance aspects, enabling tailored DAB converter designs to meet diverse performance objectives. Experimental validation on a 1-kW DAB converter prototype demonstrates enhanced ZVS capability, improved utilization of converter rating, reduced reactive power, and achieves a peak efficiency over 95.9%.

The grid-forming (GFM) converter is the trend and a promising solution for low-inertia and weak grids. Traditional GFM converters employ a current limit strategy to prevent the risk of overcurrent. However, the current limit strategy will lead to unstable issues when larger disturbances occur, such as large frequency and voltage drops. Furthermore, unlike high-voltage transmission grids, the resistive feature is more pronounced in low-voltage distribution grids, which can lead to an overvoltage issue. Therefore, this paper proposes an improved voltage regulation method for the GFM converter, where a Lyapunov-based grid-impedance estimator is developed to obtain the grid inductance and resistance, enabling the proposed method to adapt to different X/R ratios. The proposed method can alleviate overvoltage problems in GFM converters under low X/R ratio conditions. The simulation results are given to prove the effectiveness of the proposed method.

Off-grid power delivery from photovoltaic (PV) systems to electrolyzers serves as a key pathway toward sustainable green hydrogen production, with the PV output voltage adapted to the electrolyzer operating voltage by dc/dc converters. However, a systematic understanding of the performance trade-offs between different converter architectures and their associated control strategies is still lacking, particularly for ensuring robust operation under intermittent solar conditions. This paper presents a systematic comparative study of single- and dual-stage dc/dc converter architectures for standalone PV-electrolyzer (PVEC) systems. The study investigates the fundamental control trade-offs, comparing the single-stage's rigid electrolyzer-following operation with the dual-stage's superior flexibility in providing direct electrolyzer current regulation. To enhance operational resilience, two distinct low power ride-through (LPRT) strategies are proposed and analyzed for the dual-stage configuration, ensuring stable power delivery during significant solar power reductions. The feasibility and performance of the proposed architectures and control strategies are validated through both 5 kW system simulations and experiments on a 200 W GaN-based hardware prototype. The results demonstrate that while the single-stage architecture is viable for small-scale systems, the dual-stage configuration's enhanced control flexibility and scalability are essential for large-scale, storage-ready PVEC applications.

This paper proposes a Newton-Raphson with search-loop (NR-SL) islanded power flow (IPF) algorithm to solve the PF problem for islanded ac microgrids. The slack bus voltage magnitude in the conventional NR algorithm can be adjusted through the integration of outer search loop also adapting the system frequency. The proposed IPF algorithm also allows for any bus (droop bus, PQ bus, and PV bus) to be a slack bus, since the objective function in the search loop is formulated from the power balance equation at the selected bus. Different derivative-free search approaches, including binary search, golden-section search, and quadratic interpolation search, are independently applied to derive the accurate deviations in system frequency and slack bus voltage magnitude from their initial assumptions. Their convergence behaviour and computational efficiency are then evaluated to identify the most robust approach. Simulation results of a 6-bus ac microgrid demonstrate the accuracy of the proposed NR-SL IPF algorithm, with the quadratic interpolation search achieving the fewest iterations despite being less robust than binary and golden-section search methods.