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Time delays are inevitable in the power systems with wide-area control signals, which may compromise the control pe-rformance and thus jeopardize the stability of the power systems. To analyze the impacts of system parameters on critical oscillation modes of a time-delayed power system (TDPS), a new method for eigenvalue trajectory tracking of TDPS is proposed in this paper based on the continuation theory of invariant subspaces. When small changes are imposed on system parameters, such as parameters of wide-area damping controllers (WADCs) and time delays, the invariant subspaces are continuously predicted and corrected, followed by the eigenvalues and eigenvectors. In the process, the predictor and corrector are computed by solving linear equations sparsely and in blocks, which is highly scalable and computationally efficient for large-scale power system applications. The 16-generator 68-bus test system and two real-world power grids in China are used to test and demonstrate the proposed method. The results show that the proposed method can accurately and efficiently track eigenvalue trajectories for TDPS, especially for large-scale power grids. In addition, the sensitivities of eigenvalues and eigenvectors with respect to WADCs’ parameters and time delays are obtained as by-products of the approach. [ABSTRACT FROM AUTHOR]

Recently, sustained power oscillation at subsynchronous frequency was captured in direct-drive permanent magnetic synchronous generator (PMSG) based wind farms in Xinjiang Uygur Autonomous Region, China. This new type of subsynchronous interaction (SSI) detected in practical systems has never been reported and analyzed before. Therefore, its mechanism and characteristics are not yet clearly clarified. In this paper, a simplified but representative system model with multiple PMSGs interfaced with AC networks is established first based on the actual system and the PMSG model provided by the manufacturer. Then, small-signal eigenanalysis, time-domain simulation, and impedance model analysis are carried out to investigate the interactive dynamics between them. The results show that such interaction between direct-drive PMSG wind farms and weak ac grids characterized by low short-circuit ratio would cause negative-resistance effect for the SSI mode, leading to unstable oscillation. In such cases, the controller of PMSG would saturate soon, resulting in sustained power oscillation in the system. If unfortunately the oscillation frequency matches the torsional mode of any nearby turbogenerator, severe torsional vibration would be excited on the shaft of the latter. The analysis results are finally validated with field measurements of an actual SSI event. To address the problem, a supplementary subsynchronous damping control loop is attached to the controllers of PMSGs to reshape the impedance and thus to stabilize the SSI. [ABSTRACT FROM PUBLISHER]

In this study, a locally weighted linear regression (LWLR) method is proposed to predict damping ratio of a dominant mode online. The LWLR method, which is nonparametric and data-oriented, is essentially proposed for nonlinear data fitting; therefore, it can track the nonlinear power system operations and help damping ratio prediction in real power systems, which is hardly achieved by the conventional linear regression. To successfully implement this method, the measurement of weighting value and the choice of weighting function as well as its parameter setting, related to prediction accuracy and numerical conditions, are extensively discussed. Simulations are carried out in a two-area four-machine system and a large complex system, China Southern Grid. Both results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The Shangdu power plant has four 600-MW turbine-generators connected to the North-China Grid through two 500-kV transmissions, which are compensated with 45% fixed series capacitors. Extensive studies conducted on the system model indicate that the system suffers from multimodal subsynchronous resonance (SSR). To solve the problem, a countermeasure is developed by combining the supplementary excitation damping control (SEDC) and the torsional stress relay (TSR). In this paper, the characteristics of the SSR problem are investigated. Then the developed SEDC is presented. To validate the effectiveness of the proposed SEDC as well as the results of model studies, field tests were conducted under various operating conditions. The tests fully exposed the realistic threat of SSR in the system. Meanwhile, it is demonstrated that the developed SEDC can improve torsional damping significantly, and thus solve the multimodal SSR problem effectively. This is the first time in China that practical SEDCs have been developed and their ability to mitigate multimodal SSR has been verified in a real series-compensated system. [ABSTRACT FROM AUTHOR]

The rockfall process is characterized by bounces of a block on the ground. The coefficient of restitution (COR), which indicates the degree of rockfall energy dissipation, has a significant effect on the rockfall trajectory. The 3-dimensional Distinct Element Code (3DEC) is an effective tool to study the rockfall trajectory, and the damping can reflect the COR in numerical modeling. However, the relationship between damping and COR is not understood. A field test is numerically modelled to investigate the correspondence between damping and COR. A series of damping–COR correspondences are obtained and compared with the field test and its previous numerical simulation to verify the rationality of the correspondences. Then, the damping–COR correspondence is adopted in a typical rockslide in Yunnan province, China. The numerical results show that the proposed method is in good agreement with practical engineering. This study provides a new method for predicting rockfall trajectory. [ABSTRACT FROM AUTHOR]

Di Wang Tower located in Shenzhen has a height of approximately 325 m and was the tallest building in Mainland China when it was built several years ago. The aspect ratio between the building’s height and transverse width is about 9, which has largely exceeded the criteria in the current design codes and standards in China. This super tall building may be susceptible to severe vibration induced by strong winds. This paper describes some results obtained from the full-scale measurements of wind effects on Di Wang Tower under typhoon condition. The field data, such as wind speed, wind direction and acceleration responses were simultaneously and continuously measured from this building during the passage of Typhoon Sally in 1996. Detailed analysis of the field data was conducted to investigate the typhoon effects on the super tall building. The characteristics of the typhoon-generated wind and the structural responses of the building are presented and discussed in detail. Dynamic characteristics of the building are reported, and comparisons with those from the analysis of the three-dimensional finite element model of Di Wang Tower are made. The serviceability of this super tall building under typhoon conditions is assessed based on the field measurements. The damping ratios of the building during the typhoon are evaluated, and the amplitude-dependent characteristics of damping that were obtained using the random decrement technique are presented on the basis of the field measurements. Furthermore, the full-scale measurements are compared with the wind tunnel test results to verify the reliability of wind tunnel experimental techniques. [Copyright &y& Elsevier]