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.