# US 2014/0195182 A1 · Novel digital signal processing method for measurement of ac voltage with power converters at light load operation

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- Number: US 2014/0195182 A1
- Document ID: US20140195182A1
- Status: Published application
- Kind: A1
- Application number: 13/737,739
- Filed: 2013-01-09
- Published: 2014-07-10
- Earliest claimed: 2013-01-09
- Assignees: Flextronics AP, LLC
- Inventors: Zhen Z. Ye; Xiangping Xu
- Web page: https://patentgrep.com/patent/US20140195182A1

## CPC

- G01R 19/02: Measuring effective values, i.e. root-mean-square values
- G01R 19/16576: {comparing DC or AC voltage with one threshold (G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

An observation is made that the peak voltage value for a rectified AC voltage signal is substantially the same from cycle to cycle. Using this observation, a method of measuring an AC voltage is used to determine a more accurate RMS voltage value under light load conditions. The method includes rectifying the AC voltage signal to form a rectified signal, sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal, searching the sampled values for each half-cycle to determine a local minimum value for each half-cycle, searching the sampled values following the local minimum value to determine a local maximum value for each half-cycle, and calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.

## Claims

### Claim 1

A method of measuring an AC voltage signal under light load conditions, the method comprising:
a. rectifying the AC voltage signal to form a rectified signal;
b. sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal;
c. searching the sampled values for each half-cycle to determine a local minimum value for each half-cycle;
d. searching the sampled values following the local minimum value to determine a local maximum value for each half-cycle; and
e. calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.

### Claim 2 (depends on 1)

The method of claim 1 further comprising:
a. setting a sensing voltage threshold value;
b. comparing the sampled values to the sensing voltage threshold value; and
c. if one of the sampled value is equal to or less than the sensing voltage threshold value, then searching sampled values following the one sampled value to determine the local minimum value for each half-cycle.

### Claim 3 (depends on 2)

The method of claim 2 wherein setting the sensing voltage threshold value comprises passing the rectified signal through a low-pass filter and setting the sensing voltage threshold value as an output of the filter.

### Claim 4 (depends on 1)

The method of claim 1 further comprising scaling the rectified signal prior to sampling.

### Claim 5 (depends on 4)

The method of claim 4 wherein calculating the root mean square value comprises re-scaling the local maximum value.

### Claim 6 (depends on 1)

The method of claim 1 further comprising filtering the determined local maximum value for noise prior to calculating the root means square value.

### Claim 7 (depends on 6)

The method of claim 6 wherein filtering the determined local maximum value comprises averaging the local maximum value of a current half-cycle with one or more filtered local maximum values from one or more preceding half-cycles.

### Claim 8 (depends on 6)

The method of claim 6 wherein calculating the root mean square comprises applying a linear interpolation function to the filtered local maximum value.

### Claim 9 (depends on 1)

The method of claim 1 wherein calculating the root mean square comprises applying a linear interpolation function to the local maximum value.

### Claim 10

A method of measuring an AC voltage signal under light load conditions, the method comprising:
a. rectifying the AC voltage signal to form a rectified signal;
b. sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal;
c. searching the sampled values to determine a local maximum value for each half-cycle; and
d. calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.

### Claim 11 (depends on 10)

The method of claim 10 further comprising:
a. setting a sensing voltage threshold value;
b. comparing the sampled values to the sensing voltage threshold value; and
c. if one of the sampled value is equal to or less than the sensing voltage threshold value, then searching sampled values following the one sampled value to determine the local maximum value for each half-cycle.

### Claim 12 (depends on 11)

The method of claim 11 wherein setting the sensing voltage threshold value comprises passing the rectified signal through a low-pass filter and setting the sensing voltage threshold value as an output of the filter.

### Claim 13 (depends on 10)

The method of claim 10 further comprising:
a. setting a sensing voltage threshold value;
b. comparing the sampled values to the sensing voltage threshold value; and
c. if one of the sampled value is equal to or greater than the sensing voltage threshold value, then searching sampled values following the one sampled value to determine the local maximum value for each half-cycle.

### Claim 14 (depends on 13)

The method of claim 13 wherein setting the sensing voltage threshold value comprises passing the rectified signal through a low-pass filter and setting the sensing voltage threshold value as an output of the filter.

### Claim 15 (depends on 10)

The method of claim 10 further comprising scaling the rectified signal prior to sampling.

### Claim 16 (depends on 15)

The method of claim 15 wherein calculating the root mean square value comprises re-scaling the local maximum value.

### Claim 17 (depends on 10)

The method of claim 10 further comprising filtering the determined local maximum value for noise prior to calculating the root means square value.

### Claim 18 (depends on 17)

The method of claim 17 wherein filtering the determined local maximum value comprises averaging the local maximum value of a current half-cycle with one or more filtered local maximum values from one or more preceding half-cycles.

### Claim 19 (depends on 17)

The method of claim 17 wherein calculating the root mean square comprises applying a linear interpolation function to the filtered local maximum value.

### Claim 20 (depends on 10)

The method of claim 10 wherein calculating the root mean square comprises applying a linear interpolation function to the local maximum value.

### Claim 21

An apparatus for measuring an AC voltage signal under light load conditions, the apparatus comprising:
a. means for rectifying the AC voltage signal to form a rectified signal;
b. means for sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal;
c. means for searching the sampled values for each half-cycle to determine a local minimum value for each half-cycle;
d. means for searching the sampled values following the local minimum value to determine a local maximum value for each half-cycle; and
e. means for calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.

### Claim 22 (depends on 21)

The apparatus of claim 21 further comprising:
a. means for setting a sensing voltage threshold value;
b. means for comparing the sampled values to the sensing voltage threshold value; and
c. means for means for searching the sampled values following the local minimum value searches sampled values following the one sampled value to determine the local minimum value for each half-cycle if one of the sampled value is equal to or less than the sensing voltage threshold value.

### Claim 23 (depends on 22)

The apparatus of claim 22 wherein the means for setting the sensing voltage threshold value comprises means for passing the rectified signal through a low-pass filter and means for setting the sensing voltage threshold value as an output of the filter.

### Claim 24 (depends on 21)

The apparatus of claim 21 further comprising means for scaling the rectified signal prior to sampling.

### Claim 25 (depends on 24)

The apparatus of claim 24 wherein the means for calculating the root mean square value comprises means for re-scaling the local maximum value.

### Claim 26 (depends on 21)

The apparatus of claim 21 further comprising means for filtering the determined local maximum value for noise prior to calculating the root means square value.

### Claim 27 (depends on 26)

The apparatus of claim 26 wherein the means for filtering the determined local maximum value comprises means for averaging the local maximum value of a current half-cycle with one or more filtered local maximum values from one or more preceding half-cycles.

### Claim 28 (depends on 26)

The apparatus of claim 26 wherein the means for calculating the root mean square comprises means for applying a linear interpolation function to the filtered local maximum value.

### Claim 29 (depends on 21)

The apparatus of claim 21 wherein the means for calculating the root mean square comprises means for applying a linear interpolation function to the local maximum value.