Recently, an emerging subsynchronous resonance (SSR) issue was observed in series-compensated systems com-prising multiple wind farms. However, only simplified single- machine-infinite-bus system models were adopted to investigate the characteristics of this issue in the previous work. As a result, it is unable to reflect the impact on SSR from some critical factors, such as the network topology, the spatial distribution of wind farms, the diversity of wind turbine generators, and the distrib-uted wind speed. To fill in this gap, this paper proposes an im-pedance network model (INM) based SSR stability analysis method. The impedance models of each wind farm and transmis-sion line are established, and then interconnected according to system topology to form the whole INM. Such INM is further aggregated into lumped impedance. By analyzing the imped-ance-frequency features of the latter, a new stability criterion is developed to quantify the stability of SSR. The application of the criterion is demonstrated on a practical power system containing multiple wind farms. Both field measurements and time-domain simulations have been presented to validate its effectiveness and accuracy. The proposed method is of great potential in analyzing the SSR issue for very large-scale wind power systems.

In the past decade, several subsynchronous control interaction (SSCI) incidents have been reported in various large-scale grid-interfaced doubly-fed induction generator (DFIG) based wind farms. The unstable SSCI endangers the safe and reliable operation of the wind farms. The DFIG's converter controls play a crucial role in such interactions; therefore, several SSCI mitigation schemes have been reported, which modify the DFIG's converter control in such a way that the interaction is stabilized. However, the effectiveness of such converter control modifications has not been verified through laboratory or field experiments. This paper considers a practical rotor-side subsynchronous damping controller (RSDC) and fills the gap by first validating the RSDC's performance through controller hardware-in-the-loop (CHIL) simulations, and then implementing it in a real-world DFIG connected to a series compensated line. The RSDC fundamentally reshapes the effective impedance of the DFIG to stabilize the unstable SSCI. The CHIL simulations, as well as the field tests, successfully validated the RSDC's ability to suppress the SSCI. The results enhance the practical confidence of the damping control strategy based on RSC's converter control modification.

It has become a great challenge to mitigate the unstable subsynchronous control interaction (SSCI) in practical series compensated wind power systems, mainly because of the system-wide influential factors, such as the constantly changing wind speed, number of in-service wind turbines, and operating conditions. In an effort to address the challenge, this work proposes a simple yet practical grid-side subsynchronous damping controller (GSDC), which consists of a subsynchronous damping controller (SDC) supplemented to a subsynchronous current generator (SCG). The GSDC utilizes bus voltages and line currents as feedback signals and injects currents at the subsynchronous frequency into the system to provide active damping. The parameters of the SDC and SCG can be optimized for any system facing SSCI issues. In this study, a GSDC is developed and optimized over an EMT model of a realistic system. The proposed scheme has demonstrated its effectiveness and robustness through controller-hardware-in-the-loop (CHIL) tests for mitigating SSCI over a wide range of operating conditions. This work has paved the way for the commissioning of a practical GSDC in a real-world system that has experienced unstable SSCI incidents.

Unstable subsynchronous control interaction (SSCI) between wind farms (WFs) and series-compensated grid has posed a big threat to the safety of equipment and the stability of system. Many studies have been conducted on their analysis and control. However, very little research has been done on the protection. To fill the gap, this paper proposes a system-wide protection against unstable SSCI in wind power systems with fixed series compensations (FSCs). The protection is composed of a central-ized protection coordinator (CPC) and several distributed pro-tection relays (DPRs). Local DPRs measure the subsynchronous impedances of WFs in real time. These impedances are next collected by the CPC to calculate the sensitivities of tripping for each WF. The sensitivities are then used to determine the can-didate WFs and the number of WTGs to trip at those WFs, so as to stabilize the SSCI. The effectiveness of the proposed pro-tection is verified with detailed electromagnetic simulations on a wind power system that had experienced actual SSCI incidents.

Doubly‐fed induction generators (DFIGs) connected to series‐compensated transmission system is facing the risk of sub‐synchronous resonance (SSR). In recent years, SSR events have occurred many times in the area with large‐scale wind power plants in Guyuan, Zhangjiakou. Previous studies have shown that DFIGs exhibit negative damping at sub‐synchronous frequencies, thus leading to the SSR phenomenon. The permanent magnet synchronous generator (PMSG) is decoupled from the grid by a full‐power converter, so it does not participate in the SSR process. In this study, the impact of PMSG on SSR will be analysed based on the impedance characteristics. The results show that PMSG enhances system damping in some frequency bands and deteriorates the system damping in other frequency bands.

The interaction between controllers of doubly fed induction generators and fixed series compensation would induce sub‐synchronous resonance (SSR) problem. The literatures are mainly based on the practical cases in Texas and North China, and no other case has been reported so far. Recently, the grid structure of the case in North China has been changed and the characteristics of SSR phenomena are different from the past. This brings up some new problems and the damping ratio under different grid structures need to be investigated. This particular case was analysed in detail in this study. The impact on SSR from different structures of power grid is the combined result of multiple factors. This study is aimed to find out the key factors and how the factors affect SSR phenomenon.