Electronic watt-hour meter

• US 5,764,523 A
• Filed: 11/04/1994
• Issued: 06/09/1998
• Est. Priority Date: 01/06/1993
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yoshinaga, Tooru, Takahashi, Katuhiko, Tamai, Shinzou
• Primary Examiner(s): Voeltz, Emanuel Todd
• Assistant Examiner(s): COLE, TONY MITCHELL
• Application Number:
  US08/295,872
• Time in Patent Office: 1,313 Days
• Field of Search: 324/142, 324/141, 324/103 R, 324/107, 324/140 R, 341/143, 364/483, 364/572, 364/575, 364/715.02, 364/724.04, 364/574, 364/464.04, 364/724.01, 364/734, 364/923.1, 364/923.2, 364/481
• US Class Current: 702/61
• CPC Class Codes: G01R 21/133 by using digital technique
• CPC Class Codes: G01R 21/1331 Measuring real or reactive component, measuring apparent energy

Abstract

In a method of calculating an electric power by digitalizing a voltage signal and a current signal of an electronic watt-hour meter and multiplying digitalized signals, precision of an electric power calculation is improved by a circuit arrangement suitable for use in an IC mainly composed of a digital circuit with a small analog scale. A voltage signal and a current signal are inputted into analog to digital conversion means composed of a sigma-delta modulation circuit and the like, respectively, and a moving average of outputs from the analog to digital conversion means is determined by moving average processing means as a low-pass filter and then voltages are multiplied by currents. An analog scale for sigma-delta modification is small. Additionally, the circuit arrangement is reduced by the employment of the low-pass filter due to the use of the moving average. Further, an electric power can be calculated with a high precision.

Claims

1. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, wherein said analog to digital conversion means is a sigma-delta modulation circuit for integrating an analog input value by an integrator and outputting a digital value through a comparator as well as delaying and digital to analog converting said output digital value so that said output digital value is fed back to the input of said integrator and said electronic watt-hour meter comprises switching means for switching a plurality of inputs at a predetermined cycle and successively entering said respective inputs to said sigma-delta modulation circuit and holding means for holding integrated values which are successively integrated by said integrator in synchronism with the switching cycle of said switching means in correspondence with the plurality of said respective inputs, respectively, whereby said integrator successively integrates the plurality of said respective inputs and said holding means successively holds said integrated values, at said predetermined cycle.

2. An electronic watt-hour meter according to claim 1, further comprising thinning-out means for thinning out said quantized AC current and said quantized AC voltage each having been subjected to said moving average processing from the sampled value train thereof at a ratio of 1/n (n≧

1).

3. An electronic watt-hour meter according to claim 1, wherein said first analog to digital conversion means and said second analog to digital conversion means include a sigma-delta modulation circuit.

4. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, wherein said first and second moving average processing means have an output of 8 bits or less.

5. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising first and second integration means for integrating each one cycle of a quantized AC current and a quantized AC voltage, second multiplication means for multiplying outputs from said respective integration means, and subtracting means for subtracting an output from said second multiplication means from an output from said first multiplication means.

6. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising zero-cross detection means for detecting one cycle of a quantized AC current and a quantized AC voltage by the zero-cross point of said AC voltage, first and second integration means for integrating each one cycle of said quantized AC current and said quantized AC voltage based on an output from said zero-cross detection means, second multiplication means for multiplying outputs from said respective integration means, and subtracting means for subtracting an output from said second multiplication means from an output from said first multiplication means.

7. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current;

second analog to digital conversion means for quantizing an AC voltage;

first and second digital low-pass filters for causing said quantized AC current and said quantized AC voltage to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized current and said quantized voltage each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

first multiplication means for multiplying AC currents and AC voltages from said thinning-out means; and

cumulation means for cumulating outputs from said multiplication means, wherein said first and second low-pass filters are filters each having an output of 8 bits or less.

8. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising an offset adjustment means for subtracting an offset electric power value from a quantized electric power value, wherein an offset electric power is calculated from a quantized offset current and a quantized offset voltage determined by entering a reference current and a reference voltage and the calculation result is set as said offset electric power value.

9. An electronic watt-hour meter, comprising:

switching means for successively fetching AC currents and AC voltages of respective multiple-element inputs of multiple-input devices from input AC currents and AC voltage of the corresponding multiple-element inputs at a predetermined cycle;

first analog to digital conversion means and second analog to digital conversion means for successively quantizing AC currents and AC voltages of said respective multiple-element inputs from said switching means;

first and second digital low-pass filters for causing said quantized AC currents and AC voltages of said respective multiple-element inputs to successively pass through a low-pass region;

thinning-out means for thinning out said quantized currents and voltages of said respective multiple-element inputs each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

calculation means for multiplying AC currents and AC voltages which correspond to the multiple-element inputs and are supplied from said thinning-out means and determining sums of the multiplication results; and

cumulation means for cumulating outputs of said sums, further comprising an offset adjustment means for subtracting an offset electric power value from a quantized electric power value, wherein an offset electric power is calculated from a quantized offset current and a quantized offset voltage determined by entering a reference current and a reference voltage at a predetermined cycle and the result of calculation is set as said offset electric power value at each predetermined cycle.

10. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current;

second analog to digital conversion means for quantizing an AC voltage;

first and second digital low-pass filters for causing said quantized AC current and said quantized AC voltage to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized current and said quantized voltage each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

first multiplication means for multiplying AC currents and AC voltages from said thinning-out means; and

cumulation means for cumulating outputs from said multiplication means, further comprising delay means capable of obtaining a desired delay time interposed between said second analog to digital conversion means and said second digital low pass filter, whereby a voltage phase angle is adjusted by delay operation of said delay means.

11. An electronic watt-hour meter according to claim 10, wherein said delay means is a shift register capable of carrying out the desired number of shifts and a phase angle is adjusted by shift operation of said shift register.

12. An electronic watt-hour meter, comprising;

first analog to digital conversion means for quantizing an AC current;

second analog to digital conversion means for quantizing an AC voltage;

first and second digital low-pass filter for causing said quantizing AC current and said quantized AC voltage to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized current and said quantized voltage each having subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

first multiplication means for multiplying AC currents and AC voltage from said thinning-out means; and

cumulation means for cumulating outputs from said multiplication means, further comprising delay means capable of obtaining a desired delay time interposed between said first analog to digital conversion means and said first digital low pass filter, whereby a current phase angle is adjusted by delay operation of said delay means.

13. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising a balance adjustment means for multiplying quantized electric power values of respective 2, 3, . . . n elements by balance adjustment values B2, B3, Bn in a case of multi-element inputs for entering AC currents and AC voltages of n elements, wherein respective balance adjustment values B2=w₁ /w₂, B3=w₁ /w₃, . . . Bn=w₁ /w_n are set as said balance adjustment values, where quantized electric power values which are quantized by applying a reference current and a reference voltage to inputs of respective first, second, third, . . . n elements are represented by w₁, w₂, W₃, . . . w_n.

14. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current;

second analog to digital conversion means for quantizing an AC voltage;

first and second digital low-pass filters for causing said quantized AC current and said quantized AC voltage to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized current and said quantized voltage each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

first multiplication means for multiplying AC currents and AC voltages from said thinning-out means; and

cumulation means for cumulating outputs from said multiplication means, further comprising a potential operation preventing means for resetting a cumulated value of quantized electric power values each time said cumulated value exceeds a preset rated reference value to repeat cumulation as well as measuring a time until said cumulated value of said electric power values exceeds said rated reference value, and not measuring electric power values within said measuring time when said time exceeds a predetermined time.

15. An electronic watt-hour meter according to claim 14, further comprising a third digital low-pass filter for causing a quantized electric power value to pass through a low-pass region and an output having passed through said third digital low-pass filter is inputted into said potential operation preventing means.

16. An electronic watt-hour meter, comprising;

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising a light load adjustment means for adding a predetermined light load adjustment value to a quantized electric power value at least when a light load is applied.

17. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current;

second analog to digital conversion means for quantizing an AC voltage;

first and second digital low-pass filters for causing said quantized AC current and said quantized AC voltage to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized current and said quantized voltage each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m (m;

a number larger than the number of delay means of said first and second digital low-pass filters);

first multiplication means for multiplying AC currents and AC voltages from said thinning-out means; and

cumulation means for cumulating outputs from said multiplication means, further comprising;

a third digital low-pass filter operating at a predetermined clock cycle frequency f and causing a quantized electric power value to pass through a low-pass region;

a first register for storing an output value having passed through said third digital low-pass filter;

a second register for operating at an operating clock frequency f×

n and adding a value of said first register n times and storing a resulting value; and

comparison means for comparing a value output from said second register with a preset rated reference value at the operating clock cycle f×

n and sending an output for calculating an electric energy each time a compared result exceeds said rated reference value.

18. An electronic watt-hour meter, comprising:

first analog to digital conversion means for quantizing an AC current in synchronism with time;

second analog to digital conversion means for quantizing an AC voltage in synchronism with time;

first and second moving average processing means for determining a moving average of each of said quantized AC current and said quantized AC voltage;

first multiplication means for multiplying said AC current and said AC voltage each subjected to said moving average processing; and

cumulation means for cumulating outputs from said multiplication means, further comprising rating adjustment means for outputting an entered electric energy as an electric energy corrected based on a rated reference value, wherein a previously set rated reference value is corrected in accordance with a ratio of a reference electric power value obtained in an actual measurement by inputting a reference current and a reference voltage to a reference electric power value calculated by multiplying said reference current by said reference voltage and the corrected rated reference value is set as said rated reference value.

19. An electronic watt-hour meter, comprising:

switching means for successively switching at a predetermined cycle and outputting respective currents and voltages entered from a first phase, a second phase and a third phase;

first and second analog to digital conversion means for quantizing AC currents and AC voltages of said respective phases output from said switching means, respectively;

first and second digital low-pass filters for causing said quantized AC currents and AC voltages of said respective phases to pass through a low-pass region, respectively;

thinning-out means for thinning out said quantized AC currents and AC voltages of said respective phases each having been subjected to said low-pass filtration from the sampled value train thereof at a ratio of 1/m;

multiplication means for multiplying said AC currents of said respective phases by said AC voltages of said respective phases each output from said thinning means, respectively;

addition means for determining sums of outputs from said multiplication means;

a third low-pass filter for causing said added outputs to pass through a low-pass region;

cumulating means for cumulating outputs from said third digital low-pass filter;

as well as at least one of the following adjustment means;

(1) balance adjustment means including first and second balance adjustment registers for multiplying quantized electric power values of a second phase and a third phase determined from an AC current and an AC voltage of a usual object to be measured by balance adjustment value B1, B2, respectively and setting a value B2=w₀₁ /w₀₂ to said first balance adjustment register and setting a value B3=w₀₁ /w₀₃ to said second balance adjustment register, where an output from said third digital low-pass filter is represented by w₀₁ at the time when a predetermined analog value of the same phase is input as a current·

voltage value of the first phase, said analog value is input as a current·

voltage value of the second phase and an output from said third digital low-pass filter at the time is represented by W₀₂, and said analog value is input as a current·

voltage value of the first phase and an output from said third digital low-pass filter at the time is represented by w₀₃ ;

(2) rating adjustment means including a register for cumulating outputs from said third digital low-pass filter and an F value setting register for setting a value F=(w₀₁ /reference electric power)×

(rated reference value) (where, reference electric power=product in calculation determined by multiplying reference voltage·

reference current, and rated reference value=value in calculation for determining the number of pulses per unit of electric energy (constant), and sending an output for measuring an electric energy each time said cumulated value exceeds said F value as well as resetting said register;

(3) light load adjustment means including a light load adjustment register for adding a set light load adjustment value to an output value from said third digital low-pass filter and setting a value L=(w₀₁ /nm)-w_0n to said light load adjustment register as a light load adjustment value, where an output from said digital low-pass filter is represented by wo@ at the time when a value of 1/n (n≧

1) a current analog value entered in said (1) is entered as a current input of the first phase as well as a value of 1/m (m≧

1) a voltage analog value entered in said (1) is entered as a voltage input of the second phase; and

(4) phase adjustment means including a shift register capable of carrying out the desired number of shifts interposed between said second analog to digital conversion means and said second digital low-pass filter and respective registers P1, P2, P3 for designating the number of shifts of said shift register and carrying out phase adjustment by successively shifting respective phases to values P1, P2, P3 by said shift register in synchronism with said switching means, where an output from said third low-pass filter is represented by w_0P1 at the time when an analog value having the same effective value as that of the analog value of the (1) and a power factor=1 is input as an input of the first phase and a value P1=K(w₀₁ ×

0.5)-w₀₁ (K;

constant) is set to said P1 shift register,

an output from said third low-pass filter is represented by w_0P2 at the time when an analog value having the same effective value as that of the analog value of the (1) and a power factor=1 is input as an input of the second phase and a value P2=K(w₀₁ ×

0.5)-w_0P2 is set to said P1 shift register, and

an output from said third low-pass filter is represented by w_0P3 at the time when an analog value having the same effective value as that of the analog value of the (1) and a power factor=1 is input as an input of the second phase and a value P3=K(w₀₁ ×

0.5)- W!w_0P3 is set to said P1 shift register.