Electricity: single generator systems – Automatic control of generator or driving means – Power factor or phase relationships
Reexamination Certificate
1999-09-30
2001-04-17
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Power factor or phase relationships
C322S022000, C322S025000, C290S00400D
Reexamination Certificate
active
06218813
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 connected in a cross current configuration. In a cross current configuration, at least two controllers reduce reactive circulating currents simultaneously by sampling a portion of at least two generators reactive current. The sampled currents from each generator is combined and coupled to each controller. The sampled currents are then converted to voltages and fed back to each controller. Reactive currents are minimized when each controller simultaneously increases or decreases the respective generator excitation voltages to reduce the fed back voltages. The generator excitation voltages are increased or decreased based on the voltages from the cross current feed back and the reactive phase angle with respect to the line voltages of the generators.
The present invention minimizes reactive currents in a cross current configured system by applying a bi-linear transformation to a complex mathematical surface composed of key variables fed back from the generators. 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 line voltage, cross current feedback, and the reactive phase angle with respect to the generator line voltage and cross current feedback.
By analyzing the reactive phase angle with respect to cross current feedback, a three dimensional mathematical surface may be constructed describing a control compensation signal with respect to the reactive 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.
One aspect of the present invention provides for a cross current control system for controlling reactive currents in a generator. A control system receives voltage feedback from a first generator of a plurality of generators and cross current feedback from at least a second generator of the plurality of generators. The control system determines a phase angle based on the voltage feedback from the first generator and cross current feedback from the at least a second generator. The control system determines a compensation signal corresponding to the phase angle and cross current feedback. The control system modifies a generator excitation signal for the first generator based on the respective compensation signal and a bi-linear transformation technique.
Another aspect of the present invention provides for a cross current compensation system for controlling reactive currents in a generator; including: means for receiving voltage feedback from a first generator of a plurality of generators and cross current feedback from at least a second generator of the plurality of generators; means for determining a phase angle based on the voltage feedback from the first generator and cross current feedback from the at least a second generator; means for determining a compensation signal corresponding to the phase angle and cross current feedback; and means for modifying a generator excitation signal for the first generator based on the respective compensation signal and a bi-linear transformation technique.
Another aspect of the present invention provides for a method for controlling reactive currents in a generator; including the steps of: receiving voltage feedback from a first generator of a plurality of generators and cross current feedback from at least a second generator of the plurality of generators; determining a phase angle based on the voltage feedback from the first generator and cross current feedback from the at least a second generator; determining a compensation signal corresponding to the phase angle and cross current feedback; and modifying a generator excitation signal for the first generator based on the respective compensation signal and a bi-linear transformation technique.
Another aspect of the present invention provides for a cross current compensation system for controlling reactive currents in a generator; including: a system for receiving voltage feedback from a first generator of a plurality of generators and cross current feedback from at least a second generator of the plurality of generators; a system for determining a phase angle based on the voltage feedback from the first generator and cross current feedback from the at least a second generator;
Amin Himanshu S.
Gerasimow A. M.
Horn John J.
Ponomarenko Nicholas
Rockwell Technologies LLC
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