An Exact Method to Compute Time Delay Margin for Stability of Time- Delayed Generator Excitation Control System (original) (raw)
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Mathematical Problems in Engineering, 2014
This paper investigates the effect of time delays on the stability of a generator excitation control system compensated with a stabilizing transformer known as rate feedback stabilizer to damp out oscillations. The time delays are due to the use of measurement devices and communication links for data transfer. An analytical method is presented to compute the delay margin for stability. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable. First, without using any approximation, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to the time delay. Then, an expression in terms of system parameters and imaginary root of the c...
Stability Analysis of Time Delayed Generator Excitation Control System using Resultant Theory
Time Delays have become unavoidable in Power System due to the usage of measurement devices and communication links for transferring the control signals. This paper investigates the effect of time delays on the stability of a generator excitation control system with a stabilizing transformer. An analytical method based on frequency domain approach is proposed to compute the delay margin for stability. First, the transcendental characteristic equation is transformed into a polynomial using Rekasius substitution. Then with the help of Resultant theory the lower bound of crossing frequency is determined. After determining the crossing frequency, the delay margin is determined using back transformation formula. The theoretical delay margin values are computed for different sets of controller gains .The theoretical results indicate that the addition of a stabilizing transformer to the AVR system increases the delay margin and improves the damping performance of the system. The theoretical delay margin results are validated using MATLAB/SIMULINK.
TURKISH JOURNAL OF ELECTRICAL ENGINEERING & COMPUTER SCIENCES, 2016
This paper studies the impact of load increase and a power system stabilizer (PSS) on the stability delay margin of a single-machine-infinite-bus system including an automatic voltage regulator. An analytical method is proposed to determine the stability delay margin of the excitation control system. The proposed method first eliminates transcendental terms in the characteristic equation of the excitation system without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. The key result of the elimination process is that the real roots of the new polynomial correspond to the imaginary roots of the transcendental characteristic equation. With the help of the new polynomial, it is also possible to determine the delay dependency of system stability and the root tendency with respect to the time delay. Delay margins are computed for various loading conditions and PSS gains. It is observed that the delay margin generally decreases as the PSS gain and load demand increase, resulting in a less stable system.
Computation of time delay margin for power system small-signal stability
European Transactions on Electrical Power, 2009
With the extensive use of phasor measurement units (PMU) in the wide-area measurement/monitoring systems (WAMS), time delays have become unavoidable in power systems. This paper presents a direct and exact method to compute the delay margin of power systems with single and commensurate time delays. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable for a given operating point. First, without using any approximation or substitution, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. The proposed method is applied to a single-machine-infinite bus (SMIB) power system with an exciter. Delay margins are computed for a wide range of system parameters including generator mechanical power, damping and transient reactance, exciter gain, and transmission line reactance. The results indicate that the delay margin decreases as the mechanical power, exciter gain and line reactance increase while it increases with increasing generator transient reactance Additionally, the relationship between the delay margin and generator damping is found be relatively complex. Finally, the theoretical delay margin results are validated using the time-domain simulations of Matlab.
Oscillation Damping in Momentarily Loss of Excitation Generators Based on Power System Stabilizers
Journal of Kerbala University, 2015
There are many causes that lead the generator to Loss of Excitation (LOE) such as, a short circuit in the field winding, unexpectedly open field breaker or a failure in the excitation system. LOE protection schemes are widely used to detect these faults quickly, but they remain insensitive to the external faults and for other disturbances in the power system. Power System Stabilizer (PSS) is used to measure and damp the power oscillations, which occur by cause of external faults, through the set point of the voltage regulator. In this paper, the Multi-Band and Generic Power System Stabilizers (MB-PSS and GPSS) are been reviewed and examined in case of the generator momentarily loss its excitation, the power system must remain stable via the proposed stabilizer. The case study is based on radial power system are including: a main power station is connected with a substation across the transmission lines and a step-up transformer. The salient-pole synchronous generator is rotated by the Hydraulic Turbine and Governor (HTG) which have auto control when disturbance occurs in the power system. The performance of the power system is demonstrated by using the simulation.
On the Control of Time Delay Power Systems
2013
This paper deals with the control of a power system with time delay in the states. The power system is a seventh order synchronous machine innite bus system. The linearized model of the system belongs to a class of uncertain linear systems with states delays. Two control schemes are proposed for the system. Therst controller uses only the instantaneous states for feedback; the second controller combines the effects of the instantaneous as well as the delayed states. Using Lyapunov theory, it is proven that both control schemes guarantee the exponential stabilization of the power system. Detailed simulation results clearly indicate that the proposed control schemes work well. Keywords: Power system, Delays in the state, Control
Small-Signal Stability Analysis of Delayed Power System Stabilizers
This paper presents a stability analysis of power system stabilizers (PSS) for synchronous generators with inclusion of time delays. The paper shows that a time delay in the PSS feedback loop can improve the small-signal stability of a power system if the regulator gain is properly tuned. The paper provides a proof-of-principle analysis based on the classical model of the synchronous machine as well as a case study based on a detailed transient model of the IEEE 14-bus test system. The paper also provides a discussion on the practical implications that the properties of delayed PSS can have on the control of synchronous machines and of the whole power system.
Control and Configuration of Generator Excitation System as Current Mainstream
An Integral part of generator is Excitation System and new technology of Excitation System has been developed utilizing a power sources. The most important a portion of electric power system is synchronous generator due to it is the source of electrical energy and energy transformation is possible only when generator excitation exists. The generator excitation systems work when generator excitation system operates a dc charge to the generator heads to energize the field of magnetic around them to enable the electricity that should be generated. There are brushless and brush-type exciters and generators are built in exciters or charge can be established from any external source. This paper presents the control and configuration of synchronous generator excitation system as current mainstream technology, which is widely designed for feeding of turbo generator excitation winding with auto-regulated DC in generator operation, control normal and emergency modes. In this paper discuss appended on excitation system models of synchronous generator and emphasis on drawbacks, different possibilities to regulate generator excitation, de-excitation systems and overvoltage Protection with special newly developed nonlinear system regulation. And also append short descriptions of functions, compositions, Structure and Working Principle of Generator Excitation System.
State space formulation and transient stability of the double output asynchronous generator
IEEE Transactions on Energy Conversion, 1993
The double output asynchronous generator state space formulation by using the small displacement procedure valid for both grid connected and for autonomous systems is deduced. The study of the dynamics shows that the transient stability is influenced by disturbances of speed of load and of excitation frequency for any rms value and power factor of the excitation voltage. Because of its linearity the small displacement model in state space form can be used for control design purposes. From the matrices in generalized form, the transfer functions needed for the design of frequency and current controllers are easily computed.
International Journal of Innovation and Applied Studies, 2013
An Integral part of generator is Excitation System and new technology of Excitation System has been developed utilizing a power sources. The most important a portion of electric power system is synchronous generator due to it is the source of electrical energy and energy transformation is possible only when generator excitation exists. The generator excitation systems work when generator excitation system operates a dc charge to the generator heads to energize the field of magnetic around them to enable the electricity that should be generated. There are brushless and brush-type exciters and generators are built in exciters or charge can be established from any external source. This paper presents the control and configuration of synchronous generator excitation system as current mainstream technology, which is widely designed for feeding of turbo generator excitation winding with auto-regulated DC in generator operation, control normal and emergency modes. In this paper discuss appended on excitation system models of synchronous generator and emphasis on drawbacks, different possibilities to regulate generator excitation, de-excitation systems and overvoltage Protection with special newly developed nonlinear system regulation. And also append short descriptions of functions, compositions, Structure and Working Principle of Generator Excitation System.