Sergio Bruno

Dynamic Security Corrective Control by UPFCs

This paper deals with the development of a nonlinear programming methodology for evaluating corrective actions to improve the dynamic security of power systems when transient instability is detected. Remedial actions are implemented by exploiting the fast response of unified power flow controllers (UPFCs). The algorithm is implemented and tested on the Italian grid.

Transient security dispatch for the concurrent optimization of plural postulated contingencies

The implementation. of a transient security dispatch (TSD) algorithm for real-time applications is presented. The algorithm, based on the generalized reduced gradient (GRG) method, processes collectively a set of contingencies in order to ensure transient stability for all postulated cases. The massive computation has been decomposed on a cluster of workstations, exploiting the decoupled nature of the GRG method and the benefits of distributed computing. The feasibility of the implementation is shown through tests on a realistic-sized test network.

Unified power flow controllers for security-constrained transmission management

Although flexible ac transmission system (FACTS) devices and unified power flow controllers (UPFCs) have proven to be powerful tools for the exploitation of network capacities, their performances with regard to transient stability have not been deeply explored yet. In this work, we propose a methodology to assess preventive control actions through adjustments of UPFC reference signals. This control action does not imply changes in the generation and load asset defined by day-ahead market laws. The representation of UPFC devices in a power system is given through a nonlinear model. The UPFC model includes electrical equivalent circuits, a local control scheme, and a centralized control scheme. Control actions are evaluated through a nonlinear optimization process. The approach is tested on a detailed representation of the Italian national grid and test results are presented.

Development of applications in WAMS and WACS: an international cooperation experience

This paper focuses on applications in the area of WAMS (wide area measurement systems) and WACS (wide area control systems) development. A main issue is the report of an international cooperation oriented to test new algorithms and methods in this field. A feature of the cooperation has been the planning and carrying out of the common full-scale experiment in power systems aimed to investigate the feasibility in the implementation of new technologies of monitoring and control. The cooperation experience of the full-scale experiment at the Russian Far East Interconnected Power System is described in the paper

Taking the pulse of Power Systems: Monitoring Oscillations by Wavelet Analysis and Wide Area Measurement System

Real-time monitoring of power system dynamics can help in identifying poorly damped modes of oscillation and possible threats to the security of the system. System monitoring can avoid or mitigate the effects of black-outs if equipped with a good man-machine interface. In this paper, a monitoring architecture based on wavelet spectral analysis and WAMS is proposed. The wavelet analysis of real-time trajectories can show the occurring of disturbances on the network, even when the measurements are performed very far from the disturbance. Test results on a representation of the Italian power grid during the black-out in 2003 are presented. Analyses of real data measured by PMUs during an experiment on large scale are also reported

Predictive Dispatch Across Time of Hybrid Isolated Power Systems

The paper proposes a methodology for the optimal dispatch of energy sources in hybrid and isolated energy systems. The proposed approach is based on the formulation and solution of a nonlinear discrete optimization problem aimed at optimizing input and output time trajectories for a set of combined generating and storage technologies. Loads and interruptible loads are among controlled variables, and are modeled according to their interruption costs. The approach is general enough to be applied to any hybrid system configuration and was developed having in mind the complex hybrid system architectures comprising several competing storage technologies (battery, pumping, and hydrogen). Test results are aimed at showing the feasibility of the proposed methodology, comparing optimal trajectories to suboptimal system behavior given by load-following strategies.

Coordination of active and reactive distributed resources in a smart grid

The authors present a methodology for assessing centralized control of active and reactive distributed resources in a smart distribution grid. The methodology is based on three-phase optimal power flow and is able to deal properly with unbalanced conditions and both single-phase and three-phase control resources. Single-phase resources that can be exploited by means of this approach are domestic loads, photovoltaic and distributed micro-generation. The methodology is developed on an open-source simulating environment and tested on the IEEE 123-bus Radial Distribution Feeder test case.

Transmission Grid Control Through TCSC Dynamic Series Compensation

Electromechanical stability of transmission systems has been challenged by many factors such as market re-regulation, high penetration of renewables, operation under stressed conditions. After the implementation of electricity markets, it appeared evident that the transmission grid needs autonomous capacity to control the system during sudden disturbances and new protection schemes to maintain stability. This paper explores the possibility to control dynamically the impedance of transmission lines through Thyristor Controlled Series Capacitor (TCSC). The feasibility and the effectiveness of the approach are demonstrated through numerical tests on a realistic sized network for both voltage and transient stability.

Advanced Monitoring and Control Approaches for Enhancing Power System Security

Enhancements of power system security can be achieved by developing an online environment where control center operators have the capability to monitor in real time the power system dynamic behavior, recognize threats to its integrity, evaluate, and implement suitable control actions. The methodological approaches proposed here are respectively a spectral analysis based on wavelet transform and a response-based wide-area control for improving power system dynamic behavior on the transient timescale. The monitoring technique consists in processing real-time data coming from phasor measurement units by adopting an approach based on wavelet spectral analysis. The final result is a diagram that shows the amplitude of different modes usually associated to different phenomena (electromechanical modes, inter-area oscillations, etc.) and their related dampings. The methodology proposed for control assessment is based on the solution of a dynamic optimization problem whose basic variables are acquired through a wide-area measurement system.

Protection system monitoring for the prevention of cascading events in smart transmission grids

With the diffusion of standardized communication protocols in smart transmission systems, it is expected that digital distance relays will become active elements in monitoring and control architecture. Real-time tuning of distance relays settings will allow to overcome the classical conflict between dependability and security, or to avoid improper operation of such devices in vulnerable conditions and during major blackout events. In this paper, along with the presentation of a monitoring and control architecture that integrates such devices into SCADA/EMS, a system security monitoring function, based on simulated system trajectories and their closeness to distance relay zones, is proposed for system operation and contingency analysis.