An attempt is made in This work to present critical literature review and an up-to-date and exhaustive bibliography on the AGC of power systems. Various control aspects concerning the AGC problem have been highlighted. AGC schemes based on parameters, such as linear and nonlinear power system models, classical and optimal control, and centralized, decentralized, and multilevel control, are discussed. AGC strategies based on digital, self-tuning control, adaptive, VSS systems, and intelligent/soft computing control have been included. Finally, the investigations on AGC systems incorporating BES/SMES, wind turbines, FACTS devices, and PV systems have also been discussed.

Recent philosophies of automatic generation control strategies in power systems

An energy-based method to locate oscillation sources in power systems is proposed. The energy is identical to the transient energy. The amount of energy is consistent with the oscillation amplitude, and then the component producing energy has negative contribution to the damping and is considered as the oscillation source. The consistency of energy dissipation with damping torque of a generator is proved. A method to compute energy flow in the network based on wide area measurement system data and independent of energy functions is proposed. The energy dissipation or production of a component in the system can be obtained from the net energy flow. The components producing energy are oscillation sources and emergency control actions should be taken on them. The method is validated by simulations and actual oscillation incidents analyses.

An energy-based method for location of power system oscillation source

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.

Inter-Area Resonance in Power Systems From Forced Oscillations

The deployment of a synchrophasor-based wide-area measurement system (WAMS) in a power grid largely improves the observability of power system dynamics and the operator’s real-time situational awareness for potential stability issues. The WAMS in many power grids has successfully captured system oscillation events, e.g. poorly damped natural oscillations and forced oscillations, from time to time. To identify the root cause of an observed oscillation event for further mitigation actions, many methods have been proposed to locate the source of oscillation based on different ideas and principles. However, most methods proposed so far for locating the oscillation source in a power grid are not reliable enough for practical applications. This paper presents a comprehensive review of existing location methods, which basically fall into four major categories, plus a few other methods. Their advantages and disadvantages are discussed in detail. Some trends and challenges on the problem of oscillation source location are pointed out along with potential future research directions. Finally, a practical, general scheme for oscillation source location using available location methods is suggested and analyzed.

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Location methods of oscillation sources in power systems: a survey

Rotational Inertia is an integral part of any electric power system. Due to the increased use of power electronics—both to connect Renewable Energy Sources (RES) and as drives for electric motors—inertia levels are generally reduced and become time dependent. The same power electronic technologies can also be used to actively provide inertia to the power system, raising the question what effect changes in inertia has on power system stability, and how to best place devices providing virtual inertia. We propose an optimization program that answers these question, and analytically derive the sensitivities of transient frequency overshoot and damping ratio to inertia and damping. An example shows how damping ratio can be improved while transient frequency limits are respected.

Effects of rotational Inertia on power system damping and frequency transients

The origin of forced, low frequency oscillations introduced in power systems by low-speed diesel generators is investigated. The linear models of a multimachine power system are presented for both interconnected and autonomous systems. Particular emphasis is given to the calculation of the electromechanical oscillation frequencies. A three-machine test system exhibiting a very strong resonance is analysed. The method of analysis is based upon the computation of the frequency response of a multivariable system. Finally, the electromechanical oscillation analysis and the frequency response computation are applied to the electric power system of the island of Crete, where a number of large low-speed diesel engine driven generators have recently been installed.<
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Analysis of forced oscillations in a multimachine power system

Dynamic stability problems are usually overcome through the application of Power System Stabilizers. This paper presents an alternative approach for power system stabilization based upon the tuning of the existing generator controllers, both governors and A.V.R.'s. The sensitivities of the eigenvalues to the controller parameters are evaluated and an optimization technique is developed to maximize the dynamic stability. Application of the parameter optimization method on a realistic model of the Hellenic Interconnected System has proved an efficient way to stabilize a number of unstable oscillatory modes by relatively small parameter variations. The results are tested with a nonlinear simulation program and the achieved stabilization, as shown by the rotor angle swings, is found to be significant.

Power System Stabilization via Parameter Optimization - Application to the Hellenic Interconnected System

A flexible automatic generation control (AGC) algorithm is described that has been developed for the Hellenic interconnected system. The algorithm includes the three well-known load frequency control (LFC) types (flat frequency, flat tie-line, and tie-line bias) and introduces four operating modes that depend on the magnitude of the measured area control error (ACE). These modes are the steady-state operating mode, the normal operating mode, and two distinct emergency modes. The LFC stability margins are calculated for the case of slow-acting, flat frequency control. The effects of integral feedback are also considered and analyzed. An approximate economic dispatch algorithm is presented that makes use of a predetermined table of the economic loading of units. Simulation results are reported that demonstrate satisfactory operation of the AGC system. Detailed transient stability program simulations demonstrate that a number of ACE measurements per measuring period are necessary to avoid dangerous false emergencies. >

B. C. Papadias

Papers

Analysis of forced oscillations in a multimachine power system

Power System Stabilization via Parameter Optimization - Application to the Hellenic Interconnected System

A flexible AGC algorithm for the Hellenic interconnected system

A general Lyapunov function for transient stability studies of multimachine power systems