The aim of this paper is to assess the capability of the emerging synchronized phasor measurement technology in improving the overall stability of the Hydro-Quebec transmission system through supplementary modulation of voltage regulators. Following a thorough singular value and eigenvalue analysis of the system dynamic interactions, five control sites consisting of four generators and one synchronous condenser are chosen to implement new power system stabilizers with a supplementary input from remote phasor measuring units, geographically spread over nine electrically coherent areas. Since the remote feedback loops are built on top of an existing decentralized control system, this design approach results in a decentralized/hierarchical control architecture with significant advantages in terms of reliability and operational flexibility. A systematic control and measurement pairing yielded four dominant natural loops, each associated with a significant open-loop inter-area oscillatory mode at 0.06, 0.4, 0.7 and 0.95 Hz respectively. These PSSs have a speed sensitive local loop operating in the usual way, and a wide-area measurement based global loop which involves a single differential frequency signal between two suitably selected areas. The tuning and coordination technique for these advanced multiple input signals PSSs is described. Their impacts on the system is assessed using both small-signal analysis and nonlinear simulations in a transient stability program. Wide-area stabilizing controllers have a significant potential in improving the dynamic performance of the Hydro-Quebec's existing power system.

Wide-area measurement based stabilizing control of large power systems-a decentralized/hierarchical approach

This paper develops a systematic procedure of designing a centralized damping control system for power grid interarea oscillations putting emphasis on the signal selection and control system structure assignment. Geometric measures of controllability/observability are used to select the most effective stabilizing signals and control locations. Line power flows and currents are found to be the most effective input signals. The synthesis of the controller is defined as a problem of mixed H 2/H infin output-feedback control with regional pole placement and is resolved by the linear matrix inequality (LMI) approach. A tuning process and nonlinear simulations are then used to modify the controller parameters to ensure the performance and robustness of the controller designed with linear techniques. The design process is tested on the New England 39-bus ten-machine system.

Design of Wide-Area Damping Controllers for Interarea Oscillations

The usage of remote signals obtained from a wide-area measurement system (WAMS) introduces time delays to a wide-area damping controller (WADC), which would degrade system damping and even cause system instability. The time-delay margin is defined as the maximum time delay under which a closed-loop system can remain stable. In this paper, the delay margin is introduced as an additional performance index for the synthesis of classical WADCs for flexible ac transmission systems (FACTS) devices to damp inter-area oscillations. The proposed approach includes three parts: a geometric measure approach for selecting feedback remote signals, a residue method for designing phase-compensation parameters, and a Lyapunov stability criterion and linear matrix inequalities (LMI) for calculating the delay margin and determining the gain of the WADC based on a tradeoff between damping performance and delay margin. Three case studies are undertaken based on a four-machine two-area power system for demonstrating the design principle of the proposed approach, a New England ten-machine 39-bus power system and a 16-machine 68-bus power system for verifying the feasibility on larger and more complex power systems. The simulation results verify the effectiveness of the proposed approach on providing a balance between the delay margin and the damping performance.

Wide-Area Damping Controller of FACTS Devices for Inter-Area Oscillations Considering Communication Time Delays

This paper demonstrates a robust damping control design for multiple swing mode damping in a typical power system model using global stabilizing signals. A multiple-input, single-output (MISO) controller is designed for a thyristor-controlled series capacitor (TCSC) to improve the damping of the critical interarea modes. The stabilizing signals are obtained from remote locations based on observability of the critical modes. A H/sub /spl infin// damping control design based on the mixed-sensitivity formulation in a linear matrix inequality (LMI) framework is carried out. It is shown that, with local signal, supplementary damping control through three flexible AC transmission systems (FACTS) devices is necessary to provide damping to the three dominant interarea modes. On the other hand, the use of global signals has been shown to improve the damping of all the critical interarea modes with a single controller for the TCSC only. The damping performance of the centralized controller was examined in the frequency and the time domain for various operating scenarios. The controller was found to be robust against varying power-flow patterns, load characteristics, tie-line strengths, and system nonlinearities, including saturation.

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Robust damping of multiple swing modes employing global stabilizing signals with a TCSC

Conventional power system stabilizers (PSSs) are major local damping controllers acting through generator excitation systems. There are studies that suggest that remote signals could increase damping beyond that attainable by local signals. In this paper, a supervisory level power system stabilizer (SPSS) using wide area measurements is proposed. The robustness of the proposed controller is capable of compensating for the nonlinear dynamic operation of power systems and uncertain disturbances. The coordination of the robust SPSSs and local PSSs is implemented based on the principles of multiagent system theory. This theory is an active branch of applications in distributed artificial intelligence (DAI). The performance of the robust controller as a power system stability agent is studied using a 29-machine 179-bus power system example.

Power system stability agents using robust wide area control

This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid.

Damping controller design for power system oscillations using global signals

This paper proposes a new technique in controlling voltage instability in power systems. This technique coordinates between the reactive power of excitation systems and that of static VAr compensators (SVCs). The method starts with the decomposition of system into several voltage control areas (VCAs). When a reactive power deficiency occurs in certain area, excitation systems respond first to supply the required reactive power by increasing reactive generation of synchronous generators to its upper limit. If more reactive power is needed within the specific area to recover voltage instability, an SVC will be inserted by a switching controller in order to achieve the reactive balance. This controller receives an actuating signal when the terminal voltage is still unsatisfactory. By this technique, it is possible to fully utilize the excitation systems reactive power, and to design economically sized SVCs to recover voltage instability. The application of the proposed technique on the New-England 39 bus system proves its efficiency in controlling voltage instability.

M.E. Aboul-Ela

Papers

Damping controller design for power system oscillations using global signals

Monitoring and control of voltage stability in power systems