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The increasing penetration of renewables into modern power systems is bringing new oscillatory stability concerns. It is of significance to find all oscillatory modes concerned and evaluate components’ participation into each mode, especially the dominant one. To address this issue, a frequency-domain modal analysis method is developed in this paper. It represents the target system with a networked impedance model and works out the oscillatory modes by locating the zeros of the determinant of the loop impedance matrix or nodal admittance matrix. Loop/nodal participation factors, branch observability, and component sensitivity are derived to give insight into the oscillation, including its origin, oscillation path, and contributive components. The proposed method has been conducted on a simple passive circuit and a practical wind power system that experienced actual subsynchronous resonance incidents. Theoretical results as well as electromagnetic transient simulations have verified its effectiveness. The proposed method has the potential to analyze very large power systems with high penetration of renewables. [ABSTRACT FROM AUTHOR]

With the increasing integration of power electronic converters into the power system, the interactions between converters and their adjacent transmissions bring emerging oscillation issues. A new type of sub- and super-synchronous interactions (S $^2$ SI) between STATCOMs and the weak AC/DC grid were detected in China Southern Grid. As an oscillation incident never reported before, as far as the authors know, its characteristics were quite different from the previous ones. Field measurements as well as simulation studies have revealed that the various factors contributing to the S $^2$ SI include the number of online STATCOMs, the strength of the AC system (in terms of effective short-circuit ratio), the status of series compensation, and the loading level of the HVDC. The mechanism of such oscillation has been clarified and it is caused by the S $^2$ SI between STATCOMs and weak AC grids, where sub- and super-synchronous components are involved in a coupled way. To fully represent such a coupling effect, the concept of sub- and super-synchronous coupled impedance model (IM), or S $^2$ SC-IM, is proposed and developed in order to establish a stability criterion for the S $^2$ SI. Based on the IM-based method as well as the time-domain simulations, the impacts on S $^2$ SI from the various factors are quantitatively analyzed. The results show good consistence among theoretical analysis, electromagnetic simulations, and field measurements. Therefore, the effectiveness of the developed models and the stability criterion has been well verified. [ABSTRACT FROM AUTHOR]

A new type of subsynchronous resonance (SSR), namely, subsynchronous control interaction (SSCI), was recently observed in doubly-fed induction generators (DFIGs) interfaced with series-compensated power networks. In this paper, a more accurate method based on aggregated RLC circuit model is proposed to intuitively explain and quantitatively evaluate this type of SSR. For a practical power system containing multiple DFIGs and fixed series compensation, an improved impedance model (IM) is derived, which incorporates DFIG's full-scale control system. Around the series-resonant frequency, IM can be further represented with an aggregated RLC circuit model. Its equivalent parameters are worked out and then used for the quantitative assessment of potential SSR risk. The proposed method is applied for SSR analysis of a practical wind farm system in North China that experienced actual SSR incidents. The consistence between the obtained results and field measured data verifies its effectiveness very well. Further, its advantage in accuracy over existing impedance-based approaches is validated by both eigenvalue analysis and time-domain simulations. The method is also used to quantitatively investigate the impact on SSR stability from the various factors, including wind speed, number of online DFIGs and their control parameters. [ABSTRACT FROM AUTHOR]

Numerical oscillation is a fatal problem caused by the trapezoidal (TR) algorithm in nodal analysis‐based electromagnetic transient (EMT) programmes. Traditional techniques of suppressing numerical oscillation involve switching among different algorithms or adding damping elements, which would undermine the flexibility and accuracy of the overall algorithm. In this study, a new algorithm based on rational‐fraction approximations to exponential functions is proposed to address the issue. Furthermore, it is combined with TR algorithm to form a hybrid method (HM) for EMT simulation. Analytical as well as numerical analyses have been conducted to compare the HM with other popular methods in terms of stability, accuracy and efficiency. The results from either theoretical analysis or case studies on an RLC circuit and a practical power system have concluded that the proposed HM gains advantages over classical methods in suppressing numerical oscillation without sacrificing accuracy and efficiency. [ABSTRACT FROM AUTHOR]