Electricity: single generator systems – Automatic control of generator or driving means – Power factor or phase relationships
Reexamination Certificate
1999-09-30
2001-09-04
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Power factor or phase relationships
C322S058000
Reexamination Certificate
active
06285168
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a system and method for controlling reactive circulating currents in voltage generators. In particular, the present invention employs a bi-linear transformation technique to facilitate controlling reactive circulating currents.
BACKGROUND OF THE INVENTION
Power generation is a fundamental aspect of the modern technological age. The need for efficient power at affordable prices is found in many areas such as, for example, industrial, commercial, and consumer applications. Power needs are ever increasing as computer users demand more power. As the need for power increases, so does the need for uninterrupted power. Many industrial applications require twenty four hour a day operation, therefore, loss of power can have severe economic consequences. Many commercial applications, such as banking, require round the clock service to customers, and computer power must be maintained to provide such services. Even home consumers have increased needs for continuous power as a result of the home computer revolution.
One way power suppliers provide uninterrupted power is to employ parallel voltage generating systems. By paralleling generators, power can be delivered reliably because one generator can provide power for another when it fails. Technical problems must be overcome, however, because parallel generators may produce large reactive circulating currents flowing between the generators. Reactive circulating currents are therefore undesirable. Reactive currents increase generator power losses and reduce generator efficiency.
Analog systems have historically been employed to control reactive circulating currents. Although analog systems were able to accomplish the task, such systems were subject to drift and frequently required readjustment thereby increasing maintenance expenses and reducing reliability. As a consequence, digital systems have evolved to improve deficiencies of analog systems.
Digital control systems have mitigated the need to manually adjust control systems. Digital systems operate by computing control signals in response to generator feedback. Traditional analog systems rely on analog systems such as amplifiers, capacitors, diodes, and resistors to control necessary parameters to reduce reactive circulating currents. Digital systems, however, rely on control systems to compute the necessary parameters for controlling reactive circulating currents. Several of the determined parameters require complex algebra and trigonometry in conventional control systems. Therefore, fairly rigorous mathematical steps are necessary to determine the parameters. Rigorous mathematical computations produce inefficiencies in control systems by increasing the processing requirements of the controllers. Such inefficiencies contribute to increased power losses in the generators and may ultimately lead to increased costs to consumers.
Consequently, there is a strong need in the art for a system and/or method for controlling reactive circulating currents in voltage generators which mitigate some of the aforementioned problems associated with conventional systems and/or methods.
SUMMARY OF THE INVENTION
The present invention provides a system and method for controlling reactive circulating currents in voltage generators by applying a bi-linear transformation to a complex mathematical surface composed of key variables fed back from a generator. It has been found that control system performance may be improved significantly by reducing complex mathematical processing to a small series of efficient and reliable tasks.
More particularly, it has been found that a geometric analysis of key feedback variables from the voltage generator significantly reduce the trigonometric computations required of the control system. Key feedback variables include the generator voltage, current, and power factor phase angle with respect to the generator voltage and current. By controlling the phase angle, reactive circulating currents may be minimized.
By analyzing the power factor phase angle with respect to current feedback, a three dimensional mathematical surface may be constructed describing a control compensation signal with respect to the power factor phase angle and current. The control compensation signal is produced by a controller to facilitate minimizing reactive circulating currents. By applying a geometric analysis to the three dimensional surface, a two dimensional bi-linear equation is produced which greatly reduces the computations necessary to produce the control compensation signal.
In accordance with one aspect of the present invention, a system for controlling reactive currents in a generator is provided. A control system receives current and voltage feedback from the generator. The control system determines a phase angle based on the current and voltage feedback. The control system determines a compensation signal corresponding to the phase angle and current magnitude. The control system modifying a generator excitation signal based on the compensation signal and a bi-linear transformation technique.
Another aspect of the present invention provides for a system for controlling reactive currents in a generator; including: means for receiving current and voltage feedback from the generator; means for determining a phase angle based on the current and voltage feedback; means for determining a compensation signal corresponding to the phase angle and current magnitude; and means for modifying a generator excitation signal based on the compensation signal and a bi-linear transformation technique.
Yet another aspect of the present invention provides for a method for controlling reactive currents in a generator. Current and voltage feedback are received from the generator. A phase angle based on the current and voltage feedback is determined. A compensation signal corresponding to the phase angle and current magnitude is determined. A generator excitation signal is modified based on the compensation signal and a bi-linear transformation technique.
Another aspect of the present invention provides for a system for controlling reactive currents in a generator, including: a system for receiving current and voltage feedback from the generator; a system for determining a phase angle based on the current and voltage feedback; a system for determining a compensation signal corresponding to the phase angle and current magnitude; a system for modifying a generator excitation signal based on the compensation signal and a bi-linear transformation technique, the bi-linear technique employing at least the following equations:
Z
P
=−[C×X
P
×&thgr;
P
];
wherein:
Z
P
provides the compensation signal which represents (voltage droop magnitude in per units—VCA magnitude in per units);
C is a constant defined by known endpoints of a plane representive of a three-dimensional relationship between a rated, per unit, burden voltage; a power factor phase angle; and voltage droop over the rated, per unit, range;
X
P
is a most recent burden voltage factor (VBR); and
&thgr;
P
is a most recent power factor phase angle computed from the voltage and current feedback.
The system further employs the equation:
C=
(
Z
P1
−Z
P2
)/[(&thgr;
P1
−&thgr;
P2
)×(
X
P5
−X
P6
)];
wherein: Z
P1
and Z
P2
are endpoints of a VDROOP axis within the predetermined range of the plane; &thgr;
P1
and &thgr;
P2
are endpoints of a power factor phase angle axis within the predetermined range of the plane; and X
P5
and X
P6
are endpoints of a VBR axis within the rated, per unit, range of the plane.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel fe
Amin Himanshu S.
Gerasimow Alexander M.
Ponomarenko Nicholas
Rockwell Automation Technologies Inc.
Walbrun William R.
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