Zian Qin | Searcharxiv

arXiv2025

Online Full ZVS Optimization for Modular Multi-Active Bridge Converter in MV PET

Multi-active bridge (MAB) converters, the core of the state-of-the-art medium-voltage power electronic transformers, can flexibly connect multiple DC ports among distributed DC grids and loads, but suffer from hard switching under conventional single phase-shift control, especially under unbalanced voltage conversion ratios and light load conditions. Although some offline methods manage to improve the efficiency through complex optimization structures, there lacks online optimization methods that are simple but effective due to the strong coupling among ports of the converter. By leveraging the time-domain model of the MAB converter under the multiple phase-shift modulation scheme, this paper simplifies the optimization process and proposes an online optimization method that can achieve full zero-voltage switching (ZVS) operation regardless of the load conditions. The proposed method has simple solutions with only voltage conversion ratios involved and can be implemented within a wide operation range without additional sensors or advanced controllers. A four-port MAB converter is constructed as the prototype. The simulation and experimental results have verified the feasibility and superiority of the proposed online strategy in achieving ZVS operation, dynamic response, and efficiency improvement.

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arXiv2025

Mitigation of Active Power Oscillation in Multi-VSG Grids: An Impedance-Based Perspective

Active power oscillations frequently arise in inverter-dominated power systems with multiple converters operating under Virtual Synchronous Generator control, posing risks to system stability and protection coordination. While various mitigation strategies have been proposed, many rely on prior knowledge of system parameters, offer limited damping performance, or involve complex models that lack physical interpretability, making them difficult to apply in practice. To address these challenges, this paper first introduces a physically intuitive RLC equivalent circuit model to explain the root causes of APOs in both stand-alone and grid-connected modes. By mapping inertia, damping, and feeder impedance to capacitive, resistive, and inductive elements, respectively, the model reveals how mismatches among converters lead to inter-unit oscillations characterized by LC resonance. Building on this insight, we propose two mode-specific mitigation strategies: in SA mode, a graph theory based impedance control ensures proportional reactive power sharing and effectively suppresses APOs; and in GC mode, adaptive inertia and damping control with feedforward filtering is designed to reshape transient power dynamics while preserving frequency stability. The proposed methods are validated through extensive simulations and real-time hardware-in-the-loop experiments, demonstrating their effectiveness in suppressing oscillations and enhancing the robustness of multi-converter power systems.

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