Electricity: single generator systems – Generator control – Combined diverse generator controls
Patent
1999-09-24
2000-10-10
Ponomarenko, Nicholas
Electricity: single generator systems
Generator control
Combined diverse generator controls
322 19, 322 22, 322 58, H02P 910, H02P 944
Patent
active
061305235
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a generator transfer function regulator for use in a generator excitation control system.
Conventional generating systems incorporate automatic voltage regulators the objective of which is to stabilise the generator output. In any generator which is connected to a power system changes in the load represented by that power system result in changes in the generator terminal voltage. A conventional automatic voltage regulator (AVR) control system detects such changes and adjusts the excitation voltage of the generator with a view to maintaining the terminal voltage magnitude close to a predetermined value.
The dynamic characteristics of a generator are strongly influenced by the load on the generator and the operating conditions of the power system to which it is connected. Thus the dynamic characteristics can vary significantly in dependence upon the way in which the generator is used and change with the characteristics of the power network that the generator supplies.
Conventional AVR systems have fixed parameters, that is there is a fixed relationship between the magnitude of the generator voltage output and a control signal which is generated by the AVR for application to an excitation controller of the generator. As a result, the control performance achieved with conventional AVR's varies significantly with system conditions. Although AVR systems can be designed with control parameters that provide a good performance for a chosen set of operating conditions, when different conditions arise the performance of the AVR can be unsatisfactory and in some circumstances unstable.
Theoretical models representing the performance of generators and systems to which those generators are connected have been known for many years. It is known from those models that information about the performance of the generator can be obtained by calculating the direct and quadrature axis voltage and current signals in respect of each phase and the generator rotor angle. The direct and quadrature axis voltage and current signals are not available by direct measurement of the signals appearing at the generator output terminals and must be calculated from the signals which do appear at those terminals. It has been proposed to calculate the direct and quadrature axis components of the current and voltage and by extrapolation of the current components to estimate the required terminal voltage response to compensate for fluctuations in the generator load. The article by M. Saidy and F. M. Hughes: "A first order predictive excitation control of generator terminal voltage", International Journal of Electrical Power and Energy Systems, Volume 16, No. 2, 1994 pages 73-82 describes how to adjust a voltage reference applied to an excitation voltage controller dynamically such that excursions of the generator output are eliminated over a number of steps. This attenuates the demand on the control signal, which is a desirable feature due to the voltage constraints imposed on the field winding, and the lower band width requirement enables a simpler model of the generator to be employed in the predictive algorithm.
It is difficult to design a controller of standard form which can be readily adapted to a particular application and in particular it is not possible to test the performance of such a controller off-line. Furthermore, the retrofitting of sophisticated predictive voltage controllers to generators already fitted with AVR compensators so as to achieve a predictable improvement in generator performance is difficult to achieve.
It is an objective of the present invention to obviate or mitigate the problems outlined above.
According to the present invention, there is provided a generator transfer function regulator comprising a first control loop responsive to variations in the magnitude of the generator output voltage to produce a first generator excitation control signal, a second control loop responsive to the generator rotor angle and the current and voltage of each phase of the generator to produce a seco
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Proceedings of the 29.sup.th IEEE Conference on Decision and Control Dec. 5-7, 1990, IEEE Control Systems Society, vol. 3 of 6.
Ghazizadeh Mohammad Sadegh
Hughes Frank Michael
Browning Clifford W.
Ponomarenko Nicholas
Rolls Royce Power Engineering Plc
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