Method for obtaining the fundamental and odd harmonic components of AC signals

• US 5,774,366 A
• Filed: 12/16/1996
• Issued: 06/30/1998
• Est. Priority Date: 06/22/1995
• Status: Expired due to Fees

• Current Assignee: Beckwith, Robert W.
• Original Assignee: Beckwith, Robert W.
• Inventors: Beckwith, Robert W.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Shah, Kamini S.
• Application Number:
  US08/767,287
• Time in Patent Office: 561 Days
• Field of Search: 364/483, 364/484, 364/487, 364/485, 364/576, 324/77 R, 324/74, 324/78 D, 324/76.24, 324/76.29, 324/76.47, 324/76.55, 324/76.58, 361/35, 361/36
• US Class Current: 702/64
• CPC Class Codes: G01R 23/16 Spectrum analysis; Fourier analysis

Abstract

A process for sampling half cycles of AC waves and using precomputed stacks of sine values for obtaining fundamental components and odd harmonic phasers of said AC waves.

Claims

1. Devices for obtaining the fundamental and odd harmonic components of alternating current (AC) voltages and currents comprising in combination:

a) analog to digital converter (ADC) means,

b) microprocessor means for inputting signals proportional to said AC voltages and currents to said ADC means,

c) first microprocessor program means for obtaining selected numbers, m, samples of said AC signals from said ADC means at equally spaced increments of signal angle Θ

,

d) microprocessor memory means for storing precomputed stacks of m/2 values of n×

sin Θ

where n=1, 3, 5, -, -, - (m/2-1) with n=1 corresponding to the fundamental component and n=3 to (m/2-1) corresponding to odd orders of harmonics of said signals, and

e) second microprocessor program means for summing products of said samples as they are taken and successive values from said stacks starting with values at the bottom and proceeding to values at the top of said selected stacks and continuing summing said products starting with values at the top and proceeding to values at the bottom of said selected stack

whereby the sums of said products are proportional to real (x) terms of fundamental and harmonic components of said signal corresponding to the stacks elected for each harmonic.

2. Devices as in claim 1 further comprising additional microprocessor program means for summing products of said samples as they are taken and values from said stacks n=3 to (m/2-1) starting with successive values at the top and proceeding to values at the bottom of said selected stacks and continuing summing said products starting with values at the bottom and proceeding to values at the top of said selected stacks

whereby the sums are proportional to imaginary (jy) terms of harmonic components of said signals corresponding to said selected stacks.

3. A system comprising devices communicating with at least one general purpose computer for obtaining the fundamental and odd harmonic components of alternating current (AC) voltages and currents comprising in combination:

a) analog to digital converter (ADC) means in said devices,

b) microprocessor means in said devices for receiving signals proportional to said AC voltages and currents from said ADC means,

c) first microprocessor program means in said devices for obtaining selected numbers, m, of samples of said AC signals from said ADC means at equally spaced increments of signal angle Θ

,

d) second microprocessor program means for communicating said samples to said computer,

e) memory means in said computer for storing precomputed stacks of m/2 values of n×

sin Θ

where n=1, 3, 5, -, -, - (m/2-1) with n=1 corresponding to the fundamental component and n=3 to (m/2-1) corresponding to odd orders of harmonics of said signal, and

f) third program means in said computer for summing products of said samples as they are taken and values from said stacks starting with values at the bottom and proceeding to values at the top of said selected stacks and continuing summing said products starting with values at the top and proceeding to values at the bottom of said selected stack

whereby the sum of said products are proportional to real (x) terms of fundamental and harmonic components of said signal corresponding to the selected stacks.

4. A system as in claim 3 further comprising fourth program means in said computer for summing products of said samples as they are taken and successive values from said stacks n=3 to (m/2-1) starting with values at the top and proceeding to values at the bottom of said selected stacks and continuing summing said products starting with values at the bottom and proceeding to values at the top of said selected stacks

whereby the sums of said products are proportional to imaginary (jy) terms of harmonic components of said signals corresponding to the selected stack.

5. Alternating current (AC) control devices for responding to fundamental components of alternating current (AC) voltages and currents comprising in combination:

a) capacitive burden means having first and second terminals,

b) circuit ground means,

c) AC current transformer means furnishing currents to said first terminal of said capacitive burden means and from second terminal mean of said capacitive burden to said circuit ground mean,

d) resistive burden means having first and second terminals,

e) connective means connecting said AC currents coming from said circuit grounds to first terminals of said resistive burden means and from second terminals of said resistive burdens returning to said transformer,

f) analog to digital converter (ADC) means,

g) first resistor divider means for providing first AC current signals to said ADC means representing voltage drops across said capacitive burdens, and

h) second resistor divider means for providing second AC current signals to said ADC means representing voltage drops across said resistive burdens,

whereby the first signal provides improved response to the fundamental of the AC current.

6. Devices as in claim 5 further comprising microprocessor means for taking digital samples of positive half cycles of said first AC current signals and determining fundamental components of said first AC current signals.

7. Devices as in claim 5 further comprising microprocessor means for taking digital samples of positive half cycles of said second AC current signals and determining odd harmonic components of said second AC current signals.

8. Devices as in claim 7 further comprising in combination:

a) microprocessor means for taking digital samples of positive half cycles of AC voltage signals,

b) first microprocessor program means for determining timing intervals between first samples of said AC voltage signals and first samples of said second AC current signals, and

c) second microprocessor program means for obtaining real and imaginary harmonic phaser components using said first samples of AC voltage signals as harmonic phaser references.

9. Devices as in claim 7 further comprising communications means for sending said digital samples of AC voltage and current signals together with said times between first samples of said voltage signals and first samples of said current signals to external computer means for computation of odd harmonics.

10. A method for determining phase relations between phasers for the fundamental and phasers for odd harmonic components of AC signals having half cycles of selected polarity consisting of the steps of:

a) taking first non-zero samples of said AC signals of first said half cycles,

b) computing harmonic phasers utilizing said samples, and

c) using said first non-zero samples as the time reference for said harmonic phasers computed in subsequent half cycles.

11. A method for determining phasers for the fundamental and odd harmonic components of an AC signal having half cycles of selected polarity consisting of the steps of:

a) taking digital samples of said half cycles of a selected polarity,

b) storing precomputed stacks containing values of the sine function between zero and (n×

90°

) of sine values with each value corresponding to a digital sample taken during said half cycle of selected polarity,

c) multiplying values successively from said stacks first from the bottom to the top and then from the top to the bottom thereby providing sine values by its said corresponding sample to obtain individual products, and

d) summing said products thereby obtaining sums wherein, n equal to one provides said fundamental component and n equal to an odd number greater than one provides a corresponding real term of a phaser for the nth odd harmonic component.

12. A method as in claim 11 further including the step of obtaining said sums of products proportional to the magnitude of the real term of a phaser for the nth component of said signal wherein, n equal to one provides said fundamental component and n equal to an odd number greater than one provides a corresponding odd harmonic components, said stacks containing values of the sine function between zero and (n×

90)°

, utilizing values successively from said stacks first from the bottom to the top and then from the top to the bottom thereby providing sine values each corresponding to an individual sample taken during the full said half cycle of selected polarity.

13. A method as in claim 11 further including the step of obtaining the magnitude of the imaginary term of said phasor by utilizing successive values from said stacks starting first from the top to the bottom and proceeding from the bottom to the top thereby providing cosine values each corresponding to an individual sample taken during the full said half cycle of selected polarity.

14. A method as in claim 11 further including the step of:

a) setting said individual products to zero whenever a digital sample is taken which equals zero, and

b) setting said individual products to zero whenever a digital sample is taken which is non-zero and there are no values left in said stacks

whereby the ratios of volts per hertz across transformers and motors are kept constant.

15. A method as in claim 11 further including the step of comparing an rms measurement of said AC signal with said real component of said AC signal to obtain the total harmonic distortion of said AC signal.

16. A method as in claim 11 further including the step of obtaining the magnitude of the imaginary term of said phaser by multiplying successive value from said stacks starting first from the top to the bottom and proceeding from the bottom to the top thereby providing cosine values each corresponding to an individual sample taken during the full said half cycle of selected polarity.

17. A method as in claim 11 further including the step of:

a) setting said individual products to zero whenever a digital sample is taken which equals zero, and

b) setting said individual products to zero whenever a digital sample is taken which is non-zero and there are no values left in said stacks

whereby the amplitude versus frequency error in determining the phaser fundamental maintains the ratios of volts per hertz of said AC signal constant.

18. A method as in claim 11 further including the step of comparing an rms measurement of said AC signal with said real component of said AC signal to obtain the total harmonic distortion of said AC signal.