This paper discusses a recent event in the western American power system when a forced oscillation was observed at a frequency that was close to a well-known 0.38-Hz inter-area electromechanical mode ...frequency of the western system. The event motivates a systematic investigation in this paper on the possibility of resonant interactions between forced oscillations and electromechanical inter-area oscillatory modes in power systems. When the natural oscillatory mode of a power system is poorly damped, and the forced oscillation occurs at a frequency close to system mode frequency at critical locations for the mode, resonance is observed in simulation test cases of the paper. It is shown that the MW oscillations on tie-lines can be as high as 477 MW from a 10-MW forced oscillation in Kundur test system because of resonance. This paper discusses the underlying system conditions and effects as related to resonance in power systems caused by forced oscillations and discusses ways to detect such scenarios using synchrophasors. Simulated data from Kundur two-area test power system as well as measurement data from western American power system are used to study the effect of forced oscillations in power systems.
The letter discusses the oscillation event of November 29, 2005 in the western American power system when a 20 MW forced oscillation in Alberta led to 200 MW oscillations on the California-Oregon ...Inter-tie lines. Using archived synchrophasor data from the event, this letter shows that the large amplitude tie-line oscillations were caused by a resonance between the forced oscillations and the 0.25 Hz inter-area western system mode. Specifically the letter shows that resonance occurred even though the system mode was well-damped during the event because of the oscillation frequency and location of the forced oscillations.
Fast SVD Computations for Synchrophasor Algorithms Tianying Wu; Sarmadi, S. Arash Nezam; Venkatasubramanian, Vaithianathan ...
IEEE transactions on power systems,
2016-March, 2016-3-00, 20160301, Letnik:
31, Številka:
2
Journal Article
Recenzirano
Many singular value decomposition (SVD) problems in power system computations require only a few largest singular values of a large-scale matrix for the analysis. This letter introduces two fast SVD ...approaches recently developed in other domains to power systems for speeding up phasor measurement unit (PMU) based online applications. The first method is a randomized SVD algorithm that accelerates computation by introducing a low-rank approximation of a given matrix through randomness. The second method is the augmented Lanczos bidiagonalization, an iterative Krylov subspace technique that computes sequences of projections of a given matrix onto low-dimensional subspaces. Both approaches are illustrated on SVD evaluation within an ambient oscillation monitoring algorithm, namely stochastic subspace identification (SSI).
Observability of bulk power transmission network by means of minimum number of phasor measurement units (PMUs), with the aid of the network topology, is a great challenge. This paper presents a novel ...equivalent integer linear programming method (EILPM) for the exhaustive search-based PMU placement. The state estimation implemented based on such a placement is completely linear, thereby eliminating drawbacks of the conventional SCADA-based state estimation. Additional constraints for observability preservation following single PMU or line outages can easily be implemented in the proposed EILPM. Furthermore, the limitation of communication channels is dealt with by translation of nonlinear terms into linear ones. Optimal PMU placement is carried out on the IEEE 118-bus test system in different scenarios. The comparison between obtained results of EILPM and those of other methods reveals optimality of the solutions. Moreover, the proposed method is successfully applied on the Iranian National Grid, which demonstrates it can effectively be employed for practical power networks.
This paper presents a novel sectionalizing method for the build-up strategy in power system restoration. Power system restoration is the procedure of restoring power system elements after a partial ...or a complete blackout. Because of its economic and political importance, different strategies have been developed for a secure as well as fast restoration. One of the most practical and economical is the build-up strategy that includes the process of restoring separated parts (islands) in the power system and interconnecting them afterwards. This paper intends to develop a systematic algorithm for sectionalizing a power system considering various constraints such as black-start capability of generators, power supply-demand balance and independence of islands. Moreover, utilizing the Wide Area Measurement System (WAMS), each island will be fully observable in this method which is a crucial requirement for the restoration process. The New England 39 bus power system is used to demonstrate the proposed algorithm and verify the results. The proposed method is also applied to the IEEE 118 bus system as a large-scale power system to prove its capability in practical systems.
This paper proposes a decentralized two-level structure for real-time modal estimation of large power systems using ambient synchrophasor data. It introduces two distributed algorithms that fit the ...structure well, namely, 1) decentralized frequency domain decomposition and 2) decentralized recursive stochastic subspace identification. As opposed to present-day oscillation monitoring methodologies, the bulk of the algorithmic computations is done locally at the substation level in the two-level framework. Substation modal estimates are sent to the control center where they are grouped, analyzed, and combined to extract system modal properties of local and inter-area modes. The framework and the proposed algorithms provide a scalable methodology for handling oscillation monitoring from a large number of substations efficiently. The two-level structure and the two decentralized algorithms are tested using simulated data from standard test systems and from archived real power system synchrophasor data.
Accurate knowledge and estimation of the low-frequency electromechanical oscillations are of vital importance for operational reliability of any power system. Such mode estimation basically can be ...done with two different approaches: using a power system model and by linearizing the equations about operating an equilibrium point or by using measurement based mode estimation methods. Measurement based algorithms for estimating low-frequency electromechanical modes serve as useful practical methods to monitor the modal properties of power system oscillations in real-time. There are two different types of measurement data: ring-down data and ambient data. A ring-down data is from system response to a sudden disturbance in power system. For ambient data, power system is assumed to be operating at its quasi-steady-state condition while the system input is from continuous small random fluctuations in loads and other related small variations which are assumed to be white noise. Stochastic subspace methods are effective algorithms for modal estimation of a system from ambient data. They have a relatively simple order selection technique and they are good choices for handling large data and system dynamic changes. They also are effective methods in estimating mode shapes. The main weakness of the subspace method is that of high computational burden because it requires Singular Value Decomposition (SVD) of a large-dimensional matrix that makes it difficult to implement in real-time applications. Besides these natural electromechanical modes that are excited by load variations, forced oscillations can be introduced into power systems from external mechanisms such as cyclic loads or from mechanical aspects of generators. The existence of forced oscillations may affect the estimation accuracy of the natural modes from some measurement based estimation methods. They can also have a dangerous effect on generators caused by resonance between forced oscillations and local modes. In the first part of this dissertation (chapters 2-3), two new stochastic subspace method are developed and introduced for the power system problem: Recursive Adaptive Stochastic Subspace Identification (RASSI) and Distributed Recursive Stochastic Subspace Identification (DRSSI). In the second part (chapter 4), the concept of resonance in power systems from Forced Oscillations (FO) is discussed and studied.
Measurement based algorithms for estimating low-frequency electromechanical modes serve as useful practical methods to monitor the modal properties of power system oscillations in real-time. This ...paper proposes a Recursive Adaptive Stochastic Subspace Identification (RASSI) algorithm for online monitoring of power system modes using wide-area synchrophasor data. The proposed method gives an online estimation of mode frequency and damping ratio as well as mode shapes using multi-channel measurement data. It exploits both the accuracy of subspace identification and fast computational capability of recursive methods. An adaptive method is proposed to enable fast tracking of modal evolution under poorly damped conditions together with low estimation variance under quasi-steady-state conditions. The algorithms are tested using simulated data from Kundur two-area test power system as well as measured data from real systems.
