Active power line conditioner utilizing harmonic frequency injection for improved peak voltage regulation

• US 5,349,517 A
• Filed: 08/19/1993
• Issued: 09/20/1994
• Est. Priority Date: 08/19/1993
• Status: Expired due to Term

• Current Assignee: S&C Electric Company
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Brennen, Michael B.
• Primary Examiner(s): Voeltz, Emanuel T.
• Application Number:
  US08/108,269
• Time in Patent Office: 397 Days
• Field of Search: 363/39, 363/40, 363/45, 363/46, 363/97, 363/98, 363/71, 323/207
• US Class Current: 363/40
• CPC Class Codes: H02J 3/01 Arrangements for reducing harmonics or ripples
• CPC Class Codes: H02J 3/1814 wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/40 Arrangements for reducing harmonics

Abstract

The present invention provides an active power line conditioner (APLC) which has improved peak voltage regulation capability when compared with similarly-sized devices constructed according to current teachings. The invention utilizes a control function which, when the AC input voltage is not within a given sinusoidal regulation range of the APLC, superimposes selected harmonics of the fundamental frequency on the reference voltage signal used to control voltage regulation action. This causes the AC output voltage of the APLC to have a nonsinusoidal, but peaking waveform shape. The magnitude of the harmonics are preferably controlled to increase as the amount by which the AC input voltage falls outside the linear regulation range of the active power-line conditioner. In presently preferred embodiments, the chosen harmonic frequency is preferably an odd harmonic of the fundamental frequency, with third or fifth harmonics believed to be particularly useful. To Lessen the potential for unwanted zero crossings of the AC output voltage, means may be provided to modulate the harmonic reference with an envelope frequency equal to twice the fundamental frequency.

Claims

1. An improved active power line conditioner of the type for electrical connection interposing an electrical energy source and an electrical load to regulate AC output voltage supplied to said electrical load when AC input voltage remains within a preselected sinusoidal regulation range, said active power line conditioner including control means for controlling at least one inverter including a DC energy storage element, wherein the improvement comprises:

said control means further having harmonic means for regulating said AC output voltage to have at least one harmonic frequency component superimposed on a fundamental frequency component thereof when said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

2. The active power line conditioner of claim 1 wherein said at least one harmonic frequency component is at least one odd harmonic frequency component selected from a group consisting of a third harmonic component and a fifth harmonic component.

3. The active power line conditioner of claim 2 wherein said harmonic means is operative to produce a harmonic reference signal when said variations of AC input voltage supplied by said electrical energy source are not within said sinusoidal regulation range of said active power line conditioner, said harmonic reference signal having an amplitude proportional to an amount by which said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

4. The active power line conditioner of claim 3 wherein said harmonic means is further operative to modulate an amplitude of said harmonic reference signal at an envelope frequency twice a fundamental frequency of said AC input voltage.

5. The active power line conditioner of claim 1 wherein said harmonic means comprises:

means for determining an average value of said AC input voltage;

threshold means for determining whether said average value of said AC input voltage is not within said sinusoidal regulation range;

means for producing a harmonic reference having a selected harmonic frequency of a fundamental frequency of said AC input voltage;

means for superimposing said harmonic reference on a fundamental frequency reference when said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

6. The active power line conditioner of claim 5 wherein said harmonic means further comprises:

means for scaling said fundamental frequency reference in inverse proportion to an amount by which said AC input voltage is not within said sinusoidal regulation range; and

means for scaling said harmonic reference in proportion to said amount by which said AC input voltage is not within said sinusoidal regulation range.

7. The active power line conditioner of claim 6 wherein said harmonic means further comprises amplitude modulation means for varying said harmonic reference at a frequency twice a frequency of said fundamental frequency reference.

8. An active power line conditioner for electrical connection interposing an electrical energy source and an electrical load, said active power line conditioner comprising:

series inverter means for electrical coupling to said electrical energy source to selectively provide an AC regulation voltage in series with an AC input voltage supplied by said electrical energy source;

parallel inverter means for electrical coupling across said electrical load to selectively source and sink electrical current;

a DC energy storage element electrically connected between said series inverter means and said parallel inverter means;

control means for controlling said series inverter means and said parallel inverter means to regulate an AC output voltage across said electrical load during variations of said AC input voltage;

said control means operative to maintain DC energy in said electrical energy storage element at a nominal DC energy level when said variations of said AC input voltage are within a sinusoidal regulation range of said active power line conditioner; and

said control means further having harmonic means for regulating said AC output voltage to have at lease one harmonic frequency component superimposed on a fundamental frequency component thereof when said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

9. The active power line conditioner of claim 8 wherein said harmonic means comprises:

means for determining an average value of said AC input voltage;

threshold means for determining whether said average value of said AC input voltage is not within said sinusoidal regulation range;

means for producing a harmonic reference having a selected harmonic frequency of a fundamental frequency of said AC input voltage;

means for superimposing said harmonic reference on a fundamental frequency reference when said AC input voltage is not within a sinusoidal regulation range of said active power line conditioner.

10. The active Dower line conditioner of claim 9 wherein said harmonic means further comprises:

means for scaling said fundamental frequency reference in inverse proportion to an amount by which said AC input voltage is not within said sinusoidal regulation range; and

means for scaling said harmonic reference in proportion to said amount by which said AC input voltage is not within said sinusoidal regulation range.

11. The active power line conditioner of claim 10 wherein said harmonic means further comprises amplitude modulation means for varying said harmonic reference at a frequency twice a frequency of said fundamental frequency reference.

12. The active power line conditioner of claim 8 wherein said harmonic means further comprises means for boosting an energy level in said DC energy storage element when said AC input voltage is not within said sinusoidal regulation range.

13. An active power line conditioner to selectively condition electrical energy supplied from an electrical energy source to an electrical load, said active power line conditioner comprising:

an inductive winding serially connectable between said electrical energy source and said electrical load;

a parallel inverter generally electrically connectable across said electrical load, said parallel inverter including a DC energy storage element;

control means for controlling said parallel inverter to effect the selected conditioning of electrical energy delivered from the electrical energy source to the electrical load; and

said control means further having harmonic means for regulating said AC output voltage to have at least one harmonic frequency component superimposed on a fundamental frequency component thereof when said AC input voltage is not within a sinusoidal regulation range of said active power line conditioner.

14. The active power line conditioner of claim 13 wherein said harmonic means comprises:

means for determining an average value of said AC input voltage;

threshold means for determining whether said average value of said AC input voltage is not within said sinusoidal regulation range;

means for producing a harmonic reference having a selected harmonic frequency of a fundamental frequency of said AC input voltage;

means for superimposing said harmonic reference on a fundamental frequency reference when said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

15. The active power line conditioner of claim 14 wherein said harmonic means further comprises:

means for scaling said fundamental frequency reference in inverse proportion to an amount by which said AC input voltage is not within said sinusoidal regulation range; and

means for scaling said harmonic reference in proportion to said amount by which said AC input voltage is not within said sinusoidal regulation range of said active power line conditioner.

16. The active power line conditioner of claim 15 wherein said harmonic means further comprises amplitude modulation means for varying said harmonic reference at a frequency twice a frequency of said fundamental frequency reference.