A novel axially segmented design for enhanced thermal management of bridge arm reactors in flexible HVDC under AC-DC composite conditions

As a core passive component of flexible high-voltage direct current (HVDC) transmission systems, bridge arm reactor is pivotal to the operational safety and efficiency of the overall power-conversion chain. Under complex hybrid AC–DC operating conditions, however, encapsulation overheating has intensified and now constitutes a key bottleneck to long-term stable operation and the reliable grid integration of renewable energy. Existing design approaches that primarily tune encapsulation parameters have shown limited efficacy in suppressing temperature rise, and studies on structural optimization remain scarce. To address this gap, this paper introduces a novel axially segmented architecture and develops a three-dimensional finite-element multi-physics model to systematically analyze temperature distributions across operating conditions. Experimental measurements validate the model’s predictions. The results show that, under hybrid AC–DC operation, an axial segmentation ratio of 45% reduces the maximum encapsulation temperature by approximately 7.5% relative to a conventional design and substantially improves temperature-field uniformity. This work offers a practical pathway for thermal management of bridge arm reactors, with significant engineering implications for enhancing the reliability of flexible HVDC systems, enabling large-scale renewable integration, and advancing the sustainable development of clean power systems.