## 1 Introduction
On the other hand, the stability region technique can be applied online to quickly and intuitively judge the system operation status, providing guidance for the reasonable selection of parameters and refreshing controller parameters according to the current operation mode. Considering variable operation modes of renewable power grids, the stability region technique is highly effective for the prevention and control of the SSO issue caused by the mismatch of parameters between the power generation side and grid side controllers or between power generation side controllers and power networks. However, due to the high dimension of the state matrix of whole renewable power systems, the PSR is hard to form rapidly for online evaluation based on the point-wise method because of the time-consuming eigenvalue calculation. At present, there is little research on the establishment of the SSO-oriented dominant control PSR. Aiming at the dilemma of PSR online construction based on point-wise accurate eigenvalue calculation, an estimation method of eigenvalues' distribution range based on Gerschgorin disk theorem (GDT) offers a practicable direction. In the field of control engineering, the sufficient conditions for the dynamic system stability are deduced by combining Lyapunov stability theory and GDT in the literature [13; 14; 15]. This process can avoid eigenvalue calculation and improve analysis efficiency. Reference [16] exerts the above idea into the small signal stability analysis of the power system further, in which the basic disk theorem is used only for the fast verification of parameter adjustment schemes, without proposing the concept of PSR. According to [17], the extended disk theorem is utilized to establish the PSR for harmonic resonance and high-frequency wide band oscillation prevention. Compared with the point-wise eigenvalue calculation method, that the rapidity of constructing harmonic PSR by using the extended disk theorem, and the simplicity without eigenvalues calculations, are highlighted. However, the possibility of the online prevention and control of SSO still needs further investigation and research. Aiming at the prevention and control of the SSO issue in a renewable power grid, and rapid online assessment of the controller parameters' matching degree between power generation and grid under the current operation mode, a novel method to construct controller PSR is proposed in Section 2. Based on GDT, the eigenvalue distribution range of the system state matrix containing controller parameter variables is rapidly estimated, instead of the time-consuming direct calculation of eigenvalues, and then the PSR is deduced according to the small signal stability criterion and corresponding stability constraints on the obtained eigenvalue distribution range. On the basis of PSR, the stability margin evaluation index is proposed to rapidly evaluate the distance between the controller parameter set and the boundary of the PSR, providing guidance for the reasonable selection and online refreshing of the controller parameters under the current operation mode for the prevention and control of SSO, so as to secure the safe and stable operation of the high-proportion renewable power grid. Specifically, the preconditions of the application of the GDT on the PSR construction are discussed in detail, and a construction method for the transition matrix based on the system state matrix is proposed in Section 3. The transition matrix is used for the PSR construction instead of applying the system state matrix directly, to overcome its limitations. Furthermore, to reduce the conservativeness of the PSR, a method for extending the PSR is also given. The efficiency of the proposed method is highlighted by comparing the proposed method and the point-wise eigenvalue calculation of the state matrix from a time-consuming perspective in Section 4, which demonstrates its potential for online application. A Method of Parameter Stability Region Construction and Stability Margin Evaluation Based on Gerschgorin Disk Theorem