Closed loop power factor control for power supply systems

• US 4,590,416 A
• Filed: 11/09/1984
• Issued: 05/20/1986
• Est. Priority Date: 08/08/1983
• Status: Expired due to Fees

• Current Assignee: Integrated Power Systems Corporation
• Original Assignee: Rig Efficiency, Inc.
• Inventors: Porche, Michael N., Beauregard, Louis G.
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): Jennings, Derek S.
• Application Number:
  US06/670,163
• Time in Patent Office: 557 Days
• Field of Search: 307/83, 307/84, 307/87, 323/205, 323/212, 323/215, 322/20, 322/37, 318/729
• US Class Current: 323/205
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• CPC Class Codes: H02J 3/1885 using rotating means, e.g. synchronous generators
• CPC Class Codes: H03L 7/07 using several loops, e.g. for redundant clock signal generation
• CPC Class Codes: Y02E 40/30 Reactive power compensation
• CPC Class Codes: Y10S 174/17 in an electric power conversion, regulation, or protection system

Abstract

A power factor controller for alternating current/direct current drilling rigs is provided which utilizes a uniquely controlled, unloaded, over-excited generator to provide reactive power to maintain the rig'"'"'s power factor within prescribed limits during peak demand operations.

Claims

1. A method of controlling the system power factor of an alternating current power supply system having one or more engine-generator sets, comprising the steps of:

sensing the instantaneous system power factor;

comparing the sensed instantaneous power factor to a prescribed power factor;

forming a power factor control signal indicative of the difference between the sensed power factor and the prescribed power factor;

providing a field excitation signal to an unloaded, over-excited generator operated in the motor mode in proportion to said power factor control signal to cause the over-excited generator to generate the requisite reactive power to correct the system'"'"'s power factor to the prescribed power factor; and

coupling the output of the over-excited generator to the power system.

2. The method of claim 1, further including the step of:

limiting the field excitation signal to prescribed limits.

3. The method of claim 1, further including the steps of:

sensing the instantaneous output of the reactive power generator;

adjusting the prescribed limits for the field excitation signal in response to the sensed output of the over-exicted generator.

4. A method for controlling the system power factor of an alternating current power supply system having a plurality of engine-generator sets, comprising the steps of:

sensing the instantaneous power factor of each engine-generator set;

comparing the sensed power factor from each engine-generator set to a prescribed power factor;

forming a power factor control signal for each engine-generator set indicative of the difference between the sensed instantaneous power factors and the prescribed power factor;

providing a field excitation signal to a reactive power generator proportionate to the power factor control signal which is indicative of the largest differential between sensed power factor and prescribed power factor;

coupling the output of the reactive power generator to the power system;

whereby the system'"'"'s power factor is corrected by providing reactive power to the system which is required to correct the individual engine-generator set operating at the worst power factor.

5. The method of claim 4, further including the step of:

limiting the field excitation signal to prescribed limits.

6. The method of claim 5, further including the steps of:

sensing the instantaneous output of the reactive power generator;

adjusting the prescribed limits for the field excitation signal in response to the sensed output of the reactive power generator.

7. An apparatus for controlling the system power factor of an alternating current power system having one or more engine-generator sets, comprising:

means for sensing the instantaneous system power factor;

means for setting a prescribed system power factor;

means for forming a power factor control signal indicative of the difference between the sensed power factor and the prescribed power factor;

means for generating reactive power in response to the power factor control signal, said generating means comprising an unloaded, over-excited generator operated in the motor mode provided with field excitation current proportional to the power factor control signal; and

means for providing the generated reactive power to the system to maintain the power factor within the prescribed limits.

8. The apparatus of claim 7, wherein said sensing means comprises:

means for providing a system current signal in phase with system current;

means for providing a system voltage signal in phase with system voltage; and

transducer means for determining the cosine of the phase angle between said system current signal and said system voltage signal.

9. The apparatus of claim 7, wherein said means for forming a power factor control signal comprises:

means for forming a signal indicative of the sensed system power factor;

means for forming a signal indicative of the prescribed system power factor; and

means for comparing the sensed power factor signal to the desired power factor signal.

10. The apparatus of claim 9, wherein said comparing means comprises a difference amplifier, said difference amplifier being adapted to receive the system power factor signal and the desired power factor signal as inputs, and to provide as an output a power factor control signal proportionate to the difference between the system power factor signal and the desired power factor signal.

11. The apparatus of claim 7, further comprising:

means for limiting the field excitation current to prescribed limits.

12. The apparatus of claim 11, further comprising:

means for sensing the instantaneous voltage output of said generator;

means for adjusting the prescribed limits for excitation current in response to the sensed output of said generator.

13. The apparatus of claim 11, wherein said current limiting means comprises:

means for prescribing a minimum excitation current for said generator.

14. The apparatus of claim 13, wherein the power factor control signal is an analogue direct current voltage signal suitable for application to the field winding of said generator, and wherein said minimum current prescribing means comprises:

means for setting a prescribed minimum excitation voltage for the field windings of said generator;

means for comparing the power factor control signal to the prescribed minimum excitation voltage; and

,

means for providing the greater of the power factor control signal or the prescribed minimum excitation voltage as the excitation voltage for said generator.

15. The apparatus of claim 14, wherein said minimum voltage prescribing means comprises:

an adjustable step down voltage transformer connected to the power system for providing an alternating current output voltage equivalent to the prescribed minimum excitation voltage;

a rectifier bridge circuit connected to said voltage transformer for rectifying the alternating current voltage output to provide a direct current voltage output equivalent to the prescribed minimun excitation voltage.

16. The apparatus of claim 15 wherein said comparing means comprising:

a rectifier comparator circuit adapted to receive the minimum excitation voltage as a first input voltage and to receive the power factor control signal as a second input voltage and to provide the greater of said first input voltage or said second input voltage as an output to the field winding of said generator.

17. The apparatus of claim 13 further comprising:

means for prescribing a maximum excitation current for said generator.

18. The apparatus of claim 17 wherein the power factor control signal is an analogue direct current voltage signal and wherein said maximum current prescribing means comprises:

a transistor having its collector-emitter circuit connected in series with the field winding of said generator;

a biasing circuit for said transistor adapted to receive said power factor control signal as an input, said biasing circuit being further adapted to provide input biasing voltage to said first transistor in proportion to the power factor control signal to place said first transistor in a conducting state when the power factor control signal is within prescribed maximum limits; and

voltage regulator means, connected to the base-emitter circuit of said transistor for limiting the maximum bias voltage applied to said transistor to that level necessary to prevent the collector-emitter current of said transistor from exceeding the prescribed maximum generator excitation current.

19. An apparatus for controlling the system power factor of an alternating current power supply system having a plurality of engine-generator circuits, comprising:

means for sensing the instantaneous power factors of each of the engine-generator sets;

means for setting a prescribed power factor for each of the engine-generator sets;

means for forming a power factor control signal for each of the engine-generator sets indicative of the difference between the sensed power factor and the prescribed power factor for the particular engine-generator set;

means for selecting the power factor signal indicative of the largest differential between sensed power factor and prescribed power factor;

means for generating reactive power in response to the selected power factor control signal; and

means for providing the generated reactive power to the power system to correct the power factor.

20. A method of controlling the system power factor of an alternating current power supply system having one or more engine-generator sets, comprising the steps of:

sensing instantaneous power factors of one or more engine-generator sets;

deriving a composite power factor by vectorially summing the sensed instantaneous individual power factors;

comparing the composite instantaneous power factor to a prescribed power factor;

forming a power factor control signal indicative of the difference between the sensed composite power factor and the prescribed power factor;

providing a field excitation signal to a reactive power generator in proportion to the power factor control signal to cause the reactive power generator to generate the requisite reactive power to correct the system'"'"'s power factor to the prescribed power factor; and

coupling the output of the reactive power generator to the power system.