Method for reducing the load imposed on a power source, and apparatus for implementing the method

• US 6,538,343 B1
• Filed: 11/28/2000
• Issued: 03/25/2003
• Est. Priority Date: 11/28/2000
• Status: Expired due to Fees

• Current Assignee: Electric Power Research Institute Incorporated
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Stewart, Robert S.
• Primary Examiner(s): Sircus, Brian
• Assistant Examiner(s): POLK, SHARON A
• Application Number:
  US09/722,661
• Time in Patent Office: 847 Days
• Field of Search: 307/38, 307/39
• US Class Current: 307/38
• CPC Class Codes: H02J 2310/58 The condition being electrical
• CPC Class Codes: H02J 3/14 by switching loads on to, or off from, network, e.g. progressively balanced loading
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

A load reduction system switches from a commercial power distribution system to an onsite power source when a fault in the commercial distribution system is detected, and reduces the drain on the on-site power source by effectively eliminating 240 volt loads such as an electric water heater or stove. This load reduction accomplished by shifting the phase of 120 volt AC power that is applied to a user line by approximately 180°, so that the potential difference between this user line and another user line that receives 120 volt AC power is reduced from 240 volts AC to a small value. Power can still be received by 120 volt loads from the two user lines and a further, neutral, user line. A load reduction system in accordance with the present invention may also be employed with a portable generator, for example, to permit selective removal of 240 volt loads while the generator continues to power 120 volt loads.

Claims

1. A load reduction method for selectively dropping a first load that is connected between a first-leg line and a second-leg line while supplying power to a second load that is connected between a neutral line and one of the first-leg and second-leg lines, said method comprising:

(a) supplying AC power to the first-leg line;

(b) supplying AC power to the second-leg line, the AC power supplied to the second-leg line having a phase angle of about 180°

with respect to the AC power supplied to the first-leg line; and

(c) changing the phase angle of the second-leg line with respect to the first-leg line to about 0°

to drop the first load while continuing to supply power to the second load.

2. The load reduction method of claim 1, wherein the AC power is supplied to the first-leg line at an rms voltage between about 100 volts and about 130 volts and the AC power is supplied to the second leg-line at an rms voltage between about 100 volts and about 130 volts.

3. The load reduction method of claims 2, wherein the AC power is supplied to the first-leg line at an rms voltage of about 120 volts, and wherein the AC power is supplied to the second-leg line at an rms voltage of about 120 volts.

4. The load reduction method of claim 2, wherein the voltage at which AC power is supplied to the first-leg line has a waveform that is approximately sinusoidal, and the voltage at which AC power is supplied to the second-leg line has a waveform that is approximately sinusoidal.

5. A load reduction method for selectively dropping a load that is connected between a first-leg line and a second-leg line while supplying power to another load that is connected between a neutral line and one of the first-leg and second-leg lines, said method comprising:

(a) monitoring a commercial power distribution system to detect a fault in the commercial power distribution system;

(b) supplying AC power from the commercial power distribution system to the first-leg line unless a fault has been detected and supplying AC power derived from an onsite power source to the first-leg line if a fault has been detected;

(c) supplying AC power to the second-leg line, the AC power supplied to the second-leg line having a phase angle of about 180°

with respect to the AC power supplied to the first-leg line; and

(d) changing the phase angle of the second-leg line with respect to the first-leg line to about 0°

to drop the load that is connected between the first-leg and second-leg lines,

wherein step (c) comprises supplying AC power from the commercial power distribution system to the second-leg line unless a fault has been detected and supplying AC power derived from the on-site power source to the second-leg line if a fault has been detected, and

wherein step (d) is conducted when a fault is detected.

6. The load reduction method of claim 5, wherein the on-site power source is a DC power source, and wherein the step of supplying AC power derived from the on-site power source to the first-leg line if a fault has been detected and the step of supplying AC power derived from the on-site power to the second-leg line if a fault has been detected are conducted using at least one inverter, the at least one inverter being connected to the on-site power source.

7. The load reduction method of claim 6, wherein the steps of supplying AC power derived from an on-site power source to the first-leg and second-leg lines if a fault has been detected comprise controlling the at least one inverter in response to a first periodic signal having a predetermined frequency and a second periodic signal having a predetermined frequency that is substantially the same as the predetermined frequency of the first periodic signal.

8. The load reduction method of claim 7, wherein the first and second periodic signals are sinusoidal.

9. The load reduction method of claim 8, wherein the predetermined frequency of the first and secondperiodic signals is about 60 Hz.

10. The load reduction method of claim 8, wherein step (d) comprises shifting the phase of one of the first and second periodic signals with respect to the other of the first and second periodic signals by approximately 180°

after a fault has been detected.

11. The load reduction method of claim 10, wherein the step of shifting the phase is conducted rapidly, in less than about 0.01 second.

12. The load reduction method of claim 11, wherein one of the first and second period signals is generated by a signal source, and wherein the step of shifting the phase comprises, for the other of the first and second periodic signals, switching to the signal source from an inverting amplifier that is connected to the signal source.

13. The load reduction method of claim 10, wherein the shifting of the phase is conducted slowly, taking more than about one second.

14. A load reduction system for selectively dropping a first load that is connected between a first-leg line and a second-leg line while supplying power to a second load that is connected between a neutral line and one of the first-leg and second-leg lines, comprising:

means for supplying AC power to the first-leg line;

means for supplying AC power to the second-leg line, the AC power supplied to the second-leg line having a phase angle of about 180°

with respect to the AC power supplied to the first-leg line; and

means for changing the phase angle to about 0°

to drop the first load while continuing to supply power to the second load.

15. The load reduction system of claim 14, wherein the AC power is supplied to the first-leg line at an rms voltage between about 100 volts and about 130 volts, and the AC power is supplied to the second-leg line at an rms voltage between about 100 volts and about 130 volts.

16. The load reduction system of claim 15, wherein the voltage at which AC power is supplied to the first-leg line has a waveform that is approximately sinusoidal, and the voltage at which AC power is supplied to the second-leg line has a waveform that is also approximately sinusoidal.

17. A load reduction system for selectively dropping a load that is connected between a first-leg line and a second-leg line while supplying power to another load that is connected between a neutral line and one of the first-leg and second-leg lines, comprising:

means for monitoring a commercial power distribution system to detect a fault in the commercial power distribution system;

means for supplying AC power to the first-leg line;

means for supplying AC power to the second-leg line, the AC power supplied to the second-leg line having a phase angle of about 180°

with respect to the AC power supplied to the first-leg line; and

means for changing the phase angle to about 0°

to drop the load that is connected between the first-leg and second-leg lines,

wherein the means for supplying AC power to the first-leg line comprises means for supplying AC power from the commercial power distribution system to the first-leg line unless a fault has been detected and means for supplying AC power derived from an on-site power source to the first-leg line if a fault has been detected,

wherein the means for supplying AC power to the second-leg comprises means for supplying AC power from the commercial power distribution system to the second-leg line unless a fault has been detected and means for supplying AC power derived from the on-site power source to the second-leg line if a fault has been detected, and

wherein the means for changing the phase angle is actuated when a fault is detected.

18. A method for controlling electrical power consumption, comprising:

(a) supplying power to a first load that is connected between a neutral line and a first-leg line that carries an AC voltage,

(b) supplying power to a second load that is connected between the first-leg line and a second-leg line that carries an AC voltage which is about 180°

out of phase with the voltage carried by the first leg line;

(c) changing the phase of the AC voltage carried by the second-leg line to about 0°

to drop the second load without dropping the first load.

19. The method of claim 18, further comprising supplying power to a third load that is connected between the second-leg line and the neutral line, wherein power continues to be supplied to the third load when the phase is changed in step (c).

20. The method of claim 18, wherein step (c) comprises switching an input of a phase locked loop from one of the first-leg and second-leg lines to a local oscillator.