Decentralized excitation control for an electrical power utility system

• US 5,483,147 A
• Filed: 03/23/1993
• Issued: 01/09/1996
• Est. Priority Date: 07/10/1992
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Ilic, Marija D., Chapman, Jeffrey W.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/035,917
• Time in Patent Office: 1,022 Days
• Field of Search: 322/19, 322/20, 322/22, 322/23, 322/25, 322/32, 322/58, 307/87
• US Class Current: 322/25
• CPC Class Codes: H02P 9/102 for limiting effects of transients
• CPC Class Codes: H02P 9/105 for increasing the stability
• CPC Class Codes: H02P 9/30 using semiconductor devices

Abstract

A power utility system includes a generator driven by a prime mover in response to a mechanical input power and an excitation to provide an electrical output power. The excitation of the generator is controlled in response to an estimated equilibrium rotor angle. The estimation of the rotor angle is based on purely local measurements. This estimated rotor angle is used in conjunction with a feedback linearizing controller to provide field excitation control of the generator. The rotor angle reference signal is also used to provide a rotor angle error signal to a power system stabilizer which is modified to operate on the basis of an angle error rather than a speed or frequency error.

Claims

1. An excitation controller, for an electrical power utility system which includes a generator for providing an output electrical power to a transmission line in response to input mechanical power and an excitation, the controller comprising:

means for receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line, an estimate of the input mechanical power and a desired generator terminal voltage;

means for estimating equilibrium rotor angle according to the estimate of the voltage magnitude and phase, with respect to the time reference signal, at the distal point on the transmission line, the estimate of the input mechanical power and the desired generator terminal voltage and for providing a signal indicative of the equilibrium rotor angle; and

means for controlling the excitation provided to the generator according to the signal indicative of the estimated equilibrium rotor angle.

2. In an electrical power utility system which includes a generator for providing an output electrical power to a transmission line in response to input mechanical power and an excitation, the improvement comprising:

means for receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line, an estimate of the input mechanical power and a desired generator terminal voltage;

means for estimating an equilibrium rotor angle according to the estimate of the voltage magnitude and phase, with respect to the time reference signal, at the distal point on the transmission line, the estimate of the input mechanical power and the desired generator terminal voltage and for providing a signal indicative of the equilibrium rotor angle; and

means for controlling the excitation provided to the generator according to the signal indicative of the estimated equilibrium rotor angle.

3. An excitation controller, for an electrical power utility system which includes a generator for providing an output electrical power to a transmission line in response to input mechanical power and an excitation, the controller comprising:

means for estimating a voltage magnitude and phase at a distal point of the transmission line according to a measurement of the voltage magnitude and phase and current at a local end of the transmission line;

means, responsive to the estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line, an estimate of the input mechanical power and a desired generator terminal voltage, for estimating an equilibrium rotor angle and for providing a signal indicative thereof; and

means, responsive to the signal indicative of the estimated equilibrium rotor angle, for controlling the excitation provided to the generator.

4. An excitation controller, for an electrical power utility system which includes a generator for providing an output electrical power to a transmission line in response to input mechanical power and an excitation, the controller comprising:

means, responsive to an estimation of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line, the input mechanical power and a desired generator terminal voltage, for estimating an equilibrium rotor angle and for providing a signal indicative thereof; and

means, responsive to the signal indicative of the estimated equilibrium rotor angle, for controlling the excitation provided to the generator,

wherein the estimate of the voltage magnitude and phase at the distal point on the transmission line is provided by;

means for measuring the voltage magnitude and phase at the distal point of the transmission line;

means, connected to the means for measuring, for transmitting a measurement of the voltage magnitude and phase to the means for estimating an equilibrium rotor angle; and

means, responsive to the means for transmitting, for synchronizing the transmitted measurements with the means for estimating.

5. The excitation controller of claim 4 wherein the means for synchronizing includes means for receiving a synchronizing signal from a satellite.

6. A control system for an electrical power system including a generator having a rotor and which provides electrical output power at a voltage magnitude and phase, with respect to a time reference signal, to a transmission line responsive to an excitation controlled by the excitation controller and mechanical input power, the control system comprising:

an equilibrium rotor angle estimator having a first input receiving an estimate of the mechanical input power and a second input receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line and an output providing a signal indicative of an equilibrium generator rotor angle according to the estimate of the input mechanical power, the estimate of voltage magnitude and phase and a desired generator terminal voltage;

a controller having an input connected to the output of the equilibrium rotor angle estimator and an output providing the excitation to the generator according to the equilibrium rotor angle.

7. The control system of claim 6 wherein the controller is a feedback linearizing controller.

8. The control system of claim 6 wherein the controller is a power system stabilizer.

32. The control system of claim 6 wherein the computer includes means for storing a desired local terminal voltage, means for determining a desired phase angle for the desired local terminal voltage, and means, responsive to the means for storing and means for determining, for estimating the equilibrium rotor angle.

33. The control system of claim 6 wherein the desired local terminal voltage is specified by an operator based on desired reactive power output.

9. A control system for a an electrical power system including a generator having a rotor and which provides electrical output power at a voltage magnitude and phase, with respect to a time reference signal, to a transmission line responsive to an excitation controlled by the excitation controller and mechanical input power, the control system comprising:

an equilibrium rotor angle estimator having a first input receiving an estimate of the mechanical input power and a second input receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line and an output providing a signal indicative of an equilibrium rotor angle;

a position encoder providing an output signal indicative of an angular position of the rotor;

means for determining an angle of the rotor according to the output signal of the position encoder and the time reference signal, and providing an output signal indicative of the angle; and

means for comparing the determined rotor angle to the estimated equilibrium rotor angle to generate a signal indicative of a rotor angle error; and

a power system stabilizer having an input connected to the output of the means for comparing and an output providing the excitation to the generator according to the rotor angle error.

10. A controller for an electrical power generator having a rotor, comprising:

a computer which periodically determines an estimated equilibrium rotor angle and provides a signal indicative of said angle,

a sensor for periodically measuring a rotor angle and providing as an output a signal indicative thereof;

means, responsive to the signals from the computer and the sensor, for periodically generating a signal indicative of a rotor angle error;

a power system stabilizer, connected to the means for generating and responsive thereto to provide periodically a signal indicative of voltage correction term; and

an exciter which receives a desired generator terminal voltage, a measure of an actual generator terminal voltage and the voltage correction term from the power system stabilizer to provide periodically a field excitation to the electrical power generator responsive thereto.

11. The system of claim 10 wherein the computer includes means for storing a desired local terminal voltage, means for determining a desired phase angle for the desired local terminal voltage, and means, responsive to the means for storing and means for determining, for estimating the equilibrium rotor angle.

12. The system of claim 11 wherein the desired local terminal voltage is specified by an operator based one desired reactive power output.

13. An excitation controller for an electrical power generator which provides electrical output power to a transmission line in response to input mechanical power and an excitation, comprising:

means for periodically receiving a equilibrium rotor angle reference signal according to a time reference signal; and

means, responsive to the means for receiving, for periodically generating a signal indicative of a desired excitation control as a function of the equilibrium rotor angle and for providing the signal to control an exciter which provides the excitation for the generator.

14. A method for controlling excitation of a generator having a rotor which provides output electrical power to a transmission line in response to input mechanical power and an excitation, comprising the steps of:

periodically estimating an equilibrium rotor angle according to status information of the generator and the transmission line, sampled according to a time reference signal; and

controlling the excitation provided to the generator according to the estimated equilibrium rotor angle.

20. The method of claim 14 further comprising the step of estimating the voltage magnitude and phase with respect to a time reference signal, at a distal point of the transmission line and wherein the step of estimating the equilibrium rotor angle involves using the estimated voltage magnitude and phase.

21. The method of claim 20 wherein the step of estimating the voltage magnitude and phase includes using a measurement of the voltage magnitude and phase, with respect to a time reference signal, and current at a local end of the transmission line.

22. The method of claim 20 wherein the step of estimating the voltage magnitude and phase at the distal point on the transmission line includes the steps of:

measuring the voltage magnitude and phase at the distal point on the transmission line;

transmitting the measurement of the voltage magnitude and phase to a local point on the transmission line; and

synchronizing use of the transmitted measurements with the steps of estimating the equilibrium rotor angle.

23. The method of claim 22 wherein the step of synchronizing includes the step of receiving a synchronizing signal from a satellite.

24. The method of claim 14 wherein the step of controlling includes using a feedback linearizing controller.

25. The method of claim 14 wherein the step of controlling includes using a power system stabilizer.

26. The method of claim 25 further comprising the steps of:

providing a time reference signal;

using a position encoder to provide an output signal indicative of an angular position of the rotor;

determining an angle of the rotor on the basis of the output signal of the position encoder and the time reference signal; and

comparing the determined rotor angle to the estimated equilibrium rotor angle to generate a signal, indicative of a rotor angle error, which is supplied to the power system stabilizer.

27. The method of claim 14 further comprising the steps of providing a desired local terminal voltage;

and

determining a desired phase angle for the desired local terminal voltage, and

wherein the step of estimating the equilibrium rotor angle includes using the desired local terminal voltage and the desired phase angle.

28. The method of claim 27 wherein the desired local terminal voltage is specified by an operator based on desired reactive power output.

15. An electrical power generating system including at least first and second generating stations connected by a transmission grid, wherein the first generating station has a first generator and first excitation controller for controlling the first generator and the second generating station has a second generator and second excitation controller for controlling the second generator, wherein each generator provides output electrical power to a transmission line in the transmission grid in response to input mechanical power and an excitation, characterized in that each excitation controller comprises:

means for receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal provided for the generator controlled by the excitation controller and independently of other generators, at a distal point on the transmission line, an estimate of the input mechanical power and a desired generator terminal voltage;

means for estimating an equilibrium rotor angle for the generator controlled by the excitation controller according to the estimate of the voltage magnitude and phase, with respect to the time reference signal provided for the generator controlled by the excitation controller and independently of other generators, at the distal point on the transmission line, the estimate of the input mechanical power and the desired generator terminal voltage, and for providing a signal indicative of the equilibrium rotor angle; and

means for controlling the excitation provided to the generator according to the signal indicative of the estimated equilibrium rotor angle.

16. For use with a generator having a controller which affects generator output voltage, a method for determining an equilibrium rotor angle, comprising the steps of:

measuring variables from which an input mechanical power to the generator may be determined;

measuring variables from which an output electrical power of the generator may be determined;

providing a predetermined reference voltage for the generator output voltage; and

evaluating a function of the input mechanical power, the output electrical power and the predetermined reference voltage to provide an estimate of the equilibrium rotor angle.

17. An equilibrium rotor angle estimator for use with a generator having a rotor and which provides an output electrical power at a voltage to a transmission line in response to input mechanical power, comprising:

means, responsive to a measure of voltage magnitude and phase, with respect to a time reference signal, and on the transmission line, a desired generator output voltage, and a measure of the input mechanical power, for determining a desired phase angle for the output voltage of the generator; and

means responsive to the means for determining to provide an output signal indicative of an equilibrium generator rotor angle.

18. A method for determining a desired phase angle for a local terminal voltage for a generator in an electrical power system, including the steps of:

measuring variables from which an input mechanical power of the generator may be determined;

measuring variables from which an output electrical power of the generator may be determined;

providing a predetermined reference voltage for the generator output voltage; and

evaluating a function of the input mechanical power, the output electrical power and the predetermined reference voltage to estimate the desired phase angle for the generator output voltage.

19. A method for determining an equilibrium rotor angle for a generator which provides an output electrical power at a terminal voltage in response to an input mechanical power, comprising the steps of:

providing a predetermined reference voltage for the generator output voltage;

determining a transient reactance of the generator;

determining a desired phase angle for the generator output voltage;

determining an estimate of an input mechanical power of the generator; and

evaluating a function of the basis of the transient reactance, the input mechanical power, the desired phase angle and the predetermined reference voltage to estimate the equilibrium rotor angle.

29. A control system for an electrical power system including a generator having a rotor and which provides electrical output power at a voltage magnitude and phase, with respect to a time reference signal, to a transmission line responsive to an excitation controlled by the excitation controller and mechanical input power, the control system comprising:

an equilibrium rotor angle estimator having a first input receiving an estimate of the mechanical input power and a second input receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line and an output providing a signal indicative of an equilibrium generator rotor angle;

a controller having an input connected to the output of the equilibrium rotor angle estimator and an output providing the excitation to the generator; and

wherein the estimate of a voltage magnitude and phase at the distal point of the transmission line is obtained using means for estimating the voltage magnitude and phase at the distal point responsive to a measurement of the voltage magnitude and phase, with respect to a time reference signal, and current at a local end of the transmission line.

30. A control system for an electrical power system including a generator having a rotor and which provides electrical output power at a voltage magnitude and phase, with respect to a time reference signal, to a transmission line responsive to an excitation controlled by the excitation controller and mechanical input power, the control system comprising:

an equilibrium rotor angle estimator having a first input receiving an estimate of the mechanical input power and a second input receiving an estimate of the voltage magnitude and phase, with respect to a time reference signal, at a distal point on the transmission line and an output providing a signal indicative of an equilibrium generator rotor angle;

a controller having an input connected to the output of the equilibrium rotor angle estimator and an output providing the excitation to the generator,

wherein the estimate of the voltage magnitude and phase at the distal point on the transmission line is provided by;

means for measuring the voltage magnitude and phase with respect to a time reference signal at the distal point of the transmission line;

means, connected to the means for measuring, for transmitting a measurement of the voltage magnitude and phase to the means for estimating an equilibrium rotor angle; and

means, responsive to the means for transmitting, for synchronizing the transmitted measurements with the means for estimating.

31. The control system of claim 30 wherein the means for synchronizing includes means for receiving a synchronizing signal from a satellite.

34. For use with a generator having a controller which affects generator output voltage, a system for determining an equilibrium rotor angle, comprising:

means for measuring variables from which an input mechanical power to the generator may be determined;

means for measuring variables from which an output electrical power of the generator may be determined;

means for providing a predetermined reference voltage for the generator output voltage; and

means for evaluating a function of the input mechanical power, the output electrical power and the predetermined reference voltage to provide an estimate of the equilibrium rotor angle.

35. A system for determining a desired phase angle for a local terminal voltage for a generator in an electrical power system, including:

means for measuring variables from which an input mechanical power of the generator may be determined;

means for measuring variables from which an output electrical power of the generator may be determined;

means for providing a predetermined reference voltage for the generator output voltage; and

means for evaluating a function of the input mechanical power, the output electrical power and the predetermined reference voltage to estimate the desired phase angle for the generator output voltage.

36. A system for determining an equilibrium rotor angle for a generator which provides an output electrical power at a terminal voltage in response to an input mechanical power, comprising:

means for providing a predetermined reference voltage for the generator output voltage;

means for determining a transient reactance of the generator;

means for determining a desired phase angle for the generator output voltage;

means for determining an estimate of an input mechanical power of the generator; and

means for evaluating a function of the basis of the transient reactance, the input mechanical power, the desired phase angle and the predetermined reference voltage to estimate the equilibrium rotor angle.