Daniel Ruiz-Vega

A comprehensive approach to transient stability control. I. Near optimal preventive control

A general approach to real-time transient stability control is proposed, and two complementary techniques are devised: one for preventive, the other for emergency control. In this paper, the general transient stability control approach is first revisited then applied to real-time preventive control. The technique consists of shifting active power generation. The amount of power and the machines from which to shift it are methodically determined, and various patterns of generation decrease/increase are considered. Further, a standard OPF algorithm is combined with this control technique to get a real-time transient stability-constrained OPF software, able to meet power system security and electricity market requirements. Simulations conducted on the 88-machine EPRI system and the Mexican interconnected power system illustrate the various techniques, highlight their specifics, and assess their performance.

Interpretation and Visualization of Wide-Area PMU Measurements Using Hilbert Analysis

Characterization of the dynamic phenomena that arise when the system is subjected to a perturbation is important in real-time power system monitoring and analysis. This paper discusses the use of Hilbert spectral analysis to visualize and characterize nonlinear oscillations from synchronized wide-area measurements. The method has the potential to be applied for real-time, wide-area monitoring and analysis. As an illustrative example, synchronized phasor measurements of a real event in northern Mexico are used to examine the potential usefulness of nonlinear time series analysis techniques to characterize the time evolution of nonlinear, nonstationary oscillations and to determine the nature and propagation of the system disturbance. The proposed approach is also compared with Prony analysis

Global Transient Stability-Constrained Optimal Power Flow Using an OMIB Reference Trajectory

This paper presents a new approach to transient stability control using global transient stability-constrained optimal power flow (TSC-OPF) methods. Its novelty consists in using the single machine equivalent (SIME) method to perform (and improve) two main important functions of global TSC-OPF approaches: first, SIME is used to efficiently perform the power system transient stability analysis; second, SIME determines a stable one machine infinite bus equivalent rotor angular trajectory that is used as the reference stability constraint, at one specific integration step. In this way, the stability constraint is adjusted by SIME, at each iteration of the TSC-OPF method, in order to accurately reflect power system dynamic behavior. The prowess and main characteristics of the proposed approach are shown by numerical examples.

A comprehensive approach to transient stability control. II. Open loop emergency control

For pt.I see ibid., vol.18, no.4, p.1446-53 (2003). The transient stability-constrained dispatch of an electric power system is a problematic task for the system operator who, under economic pressure, may be reluctant to take expensive preventive actions against very harmful contingencies. The open-loop emergency control (OLEC) technique proposed in this paper aims to relieve such preventive actions by complementing them with emergency ones. This is achieved by combining generation rescheduling, assessed and taken preventively, with generation tripping, assessed preventively but triggered only if the anticipated harmful contingency actually occurs. The relative size of preventive versus emergency control may be modulated so as to furnish a panoply of solutions. Besides, the technique may stabilize simultaneously many contingencies. Simulations conducted on the EPRI 88-machine system illustrate various possibilities of the OLEC technique and compare it with the purely preventive one. Tradeoffs between preventive control and OLEC are also discussed, especially in the context of liberalized electricity markets. It is shown that OLEC is indeed able to provide a good compromise between economics and security, and to realize important savings.

A New Practical Approach to Transient Stability-Constrained Optimal Power Flow

This paper presents a new, significantly improved, approach to formulate a global transient stability-constrained optimal power flow (TSC-OPF), where the sets of dynamic and transient stability constraints to be considered in the optimization process are reduced to one single stability constraint. This constraint is derived from dynamic information provided by the SIngle Machine Equivalent (SIME) method and is only expressed in terms of steady-state variables, which allows us to diminish the length of the time-domain simulation to be included into the global TSC-OPF to a single (initial) time step. In this way, the size of the resulting optimization problem is reduced to one very similar to that of a conventional OPF, overcoming the main drawback of global TSC-OPF techniques (its huge dimension) while maintaining its accuracy and improving its practical application to real power networks. Effectiveness of the proposal is demonstrated by numerical examples on the WSCC three-machine, nine-bus system and the Mexican 46-machine, 190-bus system.

Transient stability-constrained optimal power flow

This paper proposes a new approach able to maximize the interface flow limits in power systems and to find a new operating state that is secure with respect to both, dynamic (transient stability) and static security constraints. It combines the maximum allowable transfer (MAT) method, recently developed for the simultaneous control of a set of contingencies, and an optimal power flow (OPF) method for maximizing the interface power flow. The approach and its performances are illustrated by means of simulations carried out on a real world power system.

E-SIME - A method for transient stability closed-loop emergency control: achievements and prospects

A general response-based technique is presented for closed-loop transient stability emergency control. It relies on E-SIME, derived from the hybrid transient stability method, SIME. E-SIME uses real-time information supposed to be furnished by phasor measurement units to predict the stability status of the power system, and, in view of an imminent instability, to design and trigger appropriate countermeasures, while continuing monitoring in order to check their effectiveness or to apply additional ones. Performance of the method in terms of accuracy and rapidity is scrutinized and illustrated on several real-world power system examples. New technical solutions and algorithms for the accurate estimation and prediction of power system quantities most relevant to the method are discussed. The observations from a recent investigation and conclusions that could prove useful for improving further the method are summarized together with some realistic timing considerations. A natural coupling of the two SIME based emergency control techniques: open-loop emergency control and E-SIME, so as to combine their complementary features is also discussed.

An integrated scheme for on-line static and transient stability constrained ATC calculations

An integrated scheme is proposed for computing on-line power system available transfer capability (ATC) while meeting static and transient stability constraints. The approach is based on the coupling of an OPF program with a method, called MAT (maximum allowable transfer), which relies on SIME (single machine equivalent) and its variants. The way in which this combined approach proceeds is outlined. Basically, the approach takes care of the stability constraints by (generally) decreasing active power on critical machines, then reallocating power generation on noncritical machines so as to ensure maximum allowable power transfer on the considered tie-lines. Stated otherwise, the combined use of the MAT method with the OPF program succeeds in reaching the multifold objective: to guarantee maximum power transfer on the defined tie-lines, and to meet transient stability constraints vis-a-vis all plausible contingencies, together with static constraints. The whole procedure is robust, in the sense that it converges consistently and readily to the solution. It is also compatible with real-time requirements.

Transient stability emergency control combining open-loop and closed-loop techniques

An on-line transient stability emergency control approach is proposed, which couples an open-loop and a closed-loop emergency control technique. The open-loop technique uses on-line transient stability assessment in order to adapt the settings of automatic system protection schemes to the current operating conditions. On the other hand, the closed-loop technique uses measurements in order to design and trigger countermeasures, after the contingency has actually happened, then to continue monitoring in a closed-loop fashion. The approach aims at combining advantages of event-based and measurement-based system protection schemes, namely, speed of action and robustness with respect to uncertainties in system modeling. It can also comply with economic criteria.

On-line transient stability constrained ATC calculations

Transient stability assessment, preventive control measures and dynamic ATC calculations are addressed for a new deregulated EMS system. The combination of time domain analysis, SIME and optimal power flow provide a reliable solution for future transaction requirements and the current operating point.