Modeling of VSC Connected to Weak Grid for Stability Analysis of DC-Link Voltage Control

In this paper, a small-signal model of voltage source converter (VSC) is developed to investigate the stability of dc-link voltage control. This model contributes to representing the dc-link voltage dynamics characteristics of VSC integrated to weak grid. Effects of grid strength, operating point, and control loops´ interactions on the performance of VSC are taken into consideration. Based on the proposed small-signal model, eigenvalue analysis is employed to study the stability of dc-link voltage control with varying operating conditions. Analysis results show that control loops´ interactions introduce a partial positive feedback to the dc-link voltage control in weak grid. Furthermore, the effect of control loops´ interactions on dc-link voltage control stability reaches largest when the bandwidth of the phase-locked loop is close to that of the dc-link voltage control. Time-domain simulations and experiments were conducted to validate the analysis.