power system dynamics: Stability and control

629 : 24 c

On the nature of power flow equations in security analysis

The power system network is assumed to be in steady-state even during low frequency transients. However, depending on generator dynamics, and toad and control characteristics, the system model and the nature of power flow equations can vary The nature of power flow equations describing the system during a contingency is investigated in detail. It is shown that under some mild assumptions on load-voltage characteristics, the power flow equations can be decoupled in an exact manner. When the generator dynamics are considered, the solutions for the load voltages are exact if load nodes are not directly connected to each othe

Damping of power swings using series facts controllers

The main aim of this paper is to identify optimal control laws and locations of series connected FACTS controllers (like TCSC and SSSC) in a unified framework to damp power swings. A circuit analogy of the electro-mechanical system is used to suggest the control laws and a location index is also proposed. The signals which are used can be synthesized using locally available measurements. The method is validated on a detailed model of a 3-machine and a 10-machine system. (C) 1999 .

Analysis and design of voltage control of static condenser

The static condenser (STATCON) is a shunt connected voltage source converter using self commutating devices like GTOs. The principle of operation is similar to that of a synchronous condenser. This paper is concerned with the application of the STATCON for the reactive power compensation of a long transmission line by regulating the voltage at its midpoint. The design of the voltage controller and the analysis of its dynamic behaviour using eigenvalue analysis and digital simulation is presented. An important observation is that the plant transfer function is generally of the nonminimum phase type. This precludes the use of large gains in a PI controller as there is a risk of instability of an oscillatory mode of frequency between 200-300 rad/s. Eigenvalue analysis using a linearized model was carried out to design a compensator in a cascade with an integral controller to overcome this problem.© IEE

Discrete control of unified power flow controller for stability improvement

The emerging flexible ac transmission system (FACTS) controllers are considered to be suitable for transient stability control due to their speed and flexibility. In this paper, a control strategy is developed to achieve maximal improvement in transient stability and damp the rotor oscillations using unified power flow controller (UPFC). The control strategy involves maximization and minimization of power flowin a line. In general, this involves the solution of a constraine doptimization problem at each step to determine the voltage and current injected by the UPFC. For the special case of a lossless symmetrical line, when the UPFC is located at the midpoint of the line, analytical solution can be derived. The control strategy can be extended to multimachine system and maximizing and minimizing power flow on a critical line can improve transient stability. The control strategy is evaluated by simulation studies

An Integrated Analysis of Voltage and Angle Stability of a Three Node Power System

The paper presents an integrated analysis of power systems, combining both angle and voltage stability. In addition to developing the system model, the case study of a three bus system exhibiting both angle and voltage stability is presented to highlight the factors that distinguish these two forms of stability. In particular, the effects of load and exciter parameters on system stability are discussed

Performance evaluation of unified power flow controller using transient simulation

The unified power flow controller (UPFC) is a power electronic controller which can be used to control active and reactive power flows in a power transmission line the by injection of (variable) voltage in series and reactive current in shunt configuration. In this paper, the authors evaluate the performance of a control strategy for UPFC in which they control real power flow through a power line, while regulating the magnitudes of the voltages at its two ports using transient simulation. The real power reference is modulated in order to improve the damping of power swings in the line. The effectiveness of the UPFC with this control strategy is clearly brought out by the simulation study.© IEE