A phase compensation method combined with power correction for suppressing sub-synchronous resonance of wind generation under weak grid

Abstract

Since three-phase grid-connected inverters (GCI) play a crucial role as the connection between renewable energy systems and the grid. They are extensively used in wind farms. However, issues related to sub-synchronous resonance (SSR) have been observed in wind farms, which pose a significant threat to the safe and stable operation of large-capacity wind farms and the grid. In this paper, the mechanism and characteristics of the SSR occurring in the GCI system under weak grid are analyzed based on the impedance model. And derives that the origin affecting the stability of the system is the asynchrony of system frames and control frames. Then, a phase compensation method employed in phase-locked loop (PLL) is proposed to suppress SSR, which can introduce a compensation frame to reduce the angle difference with the system frame. The grid strength can be enhanced equivalently. Meanwhile, virtual resistance and virtual reactance will also be introduced through the introduction of reactive power. It will further provide damping to the system, but will limit power transfer capability. Thus, the power needs to be corrected to achieve precise power control by change the value of current reference. By employing the proposed method, the SSR issues of the GCI under weak grid can be effectively solved and achieve precise power control. Finally, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method