Automatic power factor correction system

• US 20020180408A1
• Filed: 06/04/2002
• Published: 12/05/2002
• Est. Priority Date: 06/05/2001
• Status: Active Grant

• Current Assignee: Gail A. Mcdaniel, Timothy J. Mcdaniel, William D. Mcdaniel
• Original Assignee: Gail A. Mcdaniel, Timothy J. Mcdaniel, William D. Mcdaniel
• Inventors: McDaniel, William D., McDaniel, Gail A., McDaniel, Timothy J.
• Granted Patent: US 6,700,358 B2
• Time in Patent Office: Days
• US Class Current: 323/211
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power
• CPC Class Codes: H02J 3/1828 with stepwise control, the possibility of switching in or out the entire compensating arrangement not being considered as stepwise control
• CPC Class Codes: H02J 3/1871 Methods for planning installation of shunt reactive power compensators
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

An automatic power factor correction system, for an electrical power installation drawing varying levels of reactive power, measures an electrical parameter of the power drawn by a load of a power installation which is capable of indicating a level of reactive power drawn by the load and couples a combination of capacitors to the power line to compensate for the level of reactive power indicated by the electrical parameter measured. In particular, the system measures the phase angle of the power drawn and calculates a combination of capacitors to connect to the power line to compensate for a measured level of reactive power.

Claims

1. A power factor correction apparatus for power factor correcting an electrical installation including a power line having coupled thereto a load drawing AC electrical power including a potentially variable level of reactive power, said apparatus comprising:

(a) power sensor circuitry coupled to said power line and operative to detect an electrical parameter of electrical power drawn by said load which indicates a phase relationship of voltage and current of said power;

(b) a plurality of reactance elements;

(c) switching circuitry controllable to couple said reactance elements to said power line individually or in selected combinations; and

(d) a controller interfaced to said power sensor circuitry and said switching circuitry and operative, in response to a level of said phase relationship indicated by said electrical parameter, to cause said switching circuitry to couple an appropriate combination of said reactance elements to said power line to thereby minimize said phase relationship indicated by said electrical parameter.

2. An apparatus as set forth in claim 1 wherein:

(a) said power sensor detects respective zero crossing points of said voltage and current of said power; and

(b) said controller detects a sequence of said respective zero crossing points and measures a time interval therebetween to thereby determine said phase relationship.

3. An apparatus as set forth in claim 1 wherein said reactance elements include:

(a) a plurality of capacitors.

4. An apparatus as set forth in claim 1 wherein said reactance elements include:

(a) a set of capacitors of capacitance values varying in powers of two from a minimum capacitance value to a maximum capacitance value.

5. An apparatus as set forth in claim 1 wherein said reactance elements include:

(a) a plurality of capacitors, each capacitor having a capacitance value which is a multiple of a base capacitance value; and

(b) said base capacitance value is that capacitance value which results in a reactance which draws substantially one ampere at a nominal line frequency and line voltage of said power line.

6. An apparatus as set forth in claim 1 wherein:

(a) said controller includes a digital port formed by a specific plurality of port terminals;

(b) said switching circuitry includes latching elements which couple each of said reactance elements to specific ones of said port terminals; and

(c) said controller causes selected ones of said reactance elements to be coupled to said power line by writing to said port a multiple bit binary word having a bit content corresponding to said selected ones of said reactance elements.

7. A method for power factor correcting an electrical power installation including a power line having coupled thereto a load drawing AC electrical power including a potentially variable level of reactive power, said method comprising the steps of:

(a) measuring a phase value substantially proportional to an electrical phase angle between voltage and current of said electrical power drawn by said load by detecting a sequence of respective zero crossing points of said voltage and current, measuring a time interval between said zero crossing points, and scaling said time interval to said phase angle;

(b) automatically calculating a compensating reactance value to minimize said electrical phase angle of said electrical power; and

(c) automatically controlling coupling to said power line a combination of capacitors to result in a reactance value substantially comparable to said compensating reactance value.

8. A method as set forth in claim 7 wherein said coupling step includes the step of:

(a) coupling one or more of a set of capacitors to said power line, said set of capacitors having capacitance values varying in powers of two from a minimum capacitance value to a maximum capacitance value.

9. A method as set forth in claim 7 wherein said coupling step includes the step of:

(a) coupling one or more of a set of capacitors to said power line, each capacitor having a capacitance value which is a multiple of a base capacitance value, and said base capacitance value being that capacitance value which results in a reactance which draws substantially one ampere at a selected nominal line frequency and a selected nominal line voltage of said power line.

10. A method as set forth in claim 7 and including the steps of:

(a) providing a controller including a digital port formed by a specific plurality of port terminals and switching circuitry including latching elements which couple each of said capacitors to specific ones of said port terminals; and

(b) said controller effecting coupling of said appropriate combination of said capacitors to said power line by writing to said port a multiple bit binary word having a bit content corresponding to said appropriate combination of said capacitors.

11. A method for power factor correcting an electrical power installation including a power line having coupled thereto a load drawing AC electrical power including a potentially variable level of reactive power, said method comprising the steps of:

(a) measuring a phase value substantially proportional to an electrical phase angle between voltage and current of said electrical power drawn by said load by the steps of;

(1) detecting a sequence of respective zero crossing points of said voltage and current;

(2) measuring a time interval between said zero crossing points; and

(3) scaling said time interval to said phase angle;

(b) automatically calculating a compensating reactance value to minimize said electrical phase angle of said electrical power;

(c) providing a plurality of capacitors;

(d) providing a controller including a digital port formed by a specific plurality of port terminals and switching circuitry including latching elements which couple said capacitors to specific ones of said port terminals; and

(e) said controller automatically controlling coupling to said power line a combination of capacitors to result in a reactance value substantially comparable to said compensating reactance value by writing to said port a multiple bit binary word having a bit content corresponding to said appropriate combination of said capacitors.

12. A method as set forth in claim 11 wherein said coupling step includes the step of:

(a) coupling one or more of a set of capacitors to said power line, said set of capacitors having capacitance values varying in powers of two from a minimum capacitance value to a maximum capacitance value.

13. A method as set forth in claim 11 wherein said coupling step includes the step of:

(a) coupling one or more of a set of capacitors to said power line, each capacitor having a capacitance value which is a multiple of a base capacitance value, and said base capacitance value being that capacitance value which results in a reactance which draws a selected unit of current at a selected nominal line frequency and a selected nominal line voltage of said power line.

14. A method as set forth in claim 11 wherein said coupling step includes the step of:

(a) coupling one or more of a set of capacitors to said power line, each capacitor having a capacitance value which is a multiple of a base capacitance value, and said base capacitance value being that capacitance value which results in a reactance which draws substantially one ampere at a selected nominal line frequency and a selected nominal line voltage of said power line.