It has been found in existing research works that the dc-link dynamics are significant internal dynamics in the type-IV wind turbine system, which can shape system characteristics and influence system stability. If dc-link dynamics are weakly damped, this dynamic behavior may reduce system damping and worsen system stability. Considering that dc-link dynamics are determined by the interaction effects of controllers and different control structures can be adopted to regulate dc-link voltage in the type-IV wind turbine system, analytical models are needed to accurately evaluate and analyze dc-link dynamics under different control structures, which are lacked in existing publications. In this article, the mechanism of dc-link dynamics in the system is described at first. A single-in-single-out indicator function is proposed to model the dc-link dynamics, based on which a linearized state-space model of dc-link dynamics is obtained. Then, the eigenvalue sensitivity matrix is applied to determine the influencing factors of dc-link dynamics and possible causes of weakly damped dc-link dynamics. DC-link dynamics under different control structures are compared. The influenced system characteristics can also be modeled by the proposed model of dc-link dynamics and the system stability with weakly damped dc-link dynamics is also investigated with experiments based on control-hardware-in-loop platform.