Subsynchronous Stability Analysis of DFIG-Based Wind Farm Considering the Error of Current Measuring System

Although many scholars have made a comprehensive explanation of the mechanism of subsynchronous oscillation (SSO), there still exist unexplained events in actual wind farms. Therefore, from the perspective of input signal of current controller, this article proposes an equivalent model of doubly fed induction generators (DFIGs) connected to series-compensated transmission line that considers the influence of the current measuring system. The mathematical model of the current measuring system is established by a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Gamma $ </tex-math></inline-formula>-type circuit and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula>-type circuit equivalent to the electromagnetic current transformer and the power cable, respectively. Then, the oscillation mechanism of DFIGs in critical stability is explained from the perspective of Nyquist criterion. Meanwhile, the impact regulations of the proposed current measuring system on the SSO occurrence in wind farm are verified by PSCAD and compared with field tests. Finally, the transfer characteristics of the proposed model are explored within a wide frequency range, illustrating the necessity to consider the current measuring system when analyzing the stability of SSO.