Low-frequency oscillation analysis of DC-link voltage-synchronized grid-forming converters: A damping torque perspective

• This paper presents a unified analysis of low-frequency oscillation in DC-Link voltage-synchronized grid-forming (DC-GFM) converters. • The key parameters responsible for generating negative damping torque in various DC-GFM types are analyzed. • The differences in dynamics among various DC-GFM types and the underlying causes of these differences are compared and analyzed. The grid-forming (GFM) converter based on DC voltage synchronization effectively maintains stability on the DC side. However, the addition of a DC voltage control (DVC) loop introduces complexity into the low-frequency oscillation (LFO) characteristics. With numerous DVC loop designs developed to date, understanding LFO characteristics across different configurations has become increasingly challenging, further complicating the development of effective mitigation strategies. This paper provides a unified and comprehensive LFO analysis of various DC-link voltage-synchronized GFM (DC-GFM) converters from the perspective of damping torque. The power angle dynamics of these DC-GFM are formulated and examined through damping and synchronization torques, revealing key parameters that contribute to negative torque. These insights support the design of effective countermeasures for diverse DC-GFM converter types.