JPH0666844A - Digital estimating operating method for ac input amplitude - Google Patents

Abstract

PURPOSE:To provide an estimated value of amplitude of an AC input signal with less frequency fluctuation error from the sampling value of the AC input signal. CONSTITUTION:Among AC input sampling values, the sampling value just before O-cross point in a O-cross point part ZP is a1, the sampling value just after it is a2, and the sampling value situated ahead by the time interval corresponding to the phase difference 90 deg. of a standard frequency from the sampling point of the value a1 is b1, and the sampling value situated ahead by the time interval corresponding to the phase difference 90 deg. of the standard frequency from the sampling point of the value a2 is b2. The 90 deg. 2-point arithmetic value m2 is determined from the values a2, b2. When the corresponding value Em' of the 90 deg. 2-point arithmetic value of the O-cross point is determined by the linear interpolation of the arithmetic values m1, m2, this value gives an ZC input estimated value close to an AC input true value Em.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a method for sampling an AC input signal, performing A / D conversion, and estimating and calculating the amplitude of the AC input signal from the converted digital data. The present invention relates to a digital estimation calculation method of an AC input amplitude that can obtain accuracy. In the drawings below, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art For example, an AC input signal of 60 Hz has a fixed sampling period corresponding to an electrical angle of 15 ° (in other words, 15/36 of the period 1/60 (sec) of the AC input signal).
0) sampling and A / D conversion, and among the digitally converted sampling values, a sampling value having a time interval of an electrical angle of 90 ° (that is, (1/60) × 1/4 (sec)) is a, When b, the amplitude Em of the AC input signal is

[0003]

## EQU1 ## Em = (a ² + b ² ) ^1/2 (1) For convenience, this calculation method is 90 ° 2.
This is called a point operation method, and the operation value obtained by this operation, that is, the value corresponding to Em in Expression (1) is called a 90 ° 2-point operation value.
However, this method usually causes a large error when the AC input frequency fluctuates.

FIG. 6 shows a sampling value (upper row) when an AC input signal whose frequency has changed to 57 Hz is sampled at the fixed sampling cycle with the reference frequency of 60 Hz, and a 90 ° two-point arithmetic method using this sampling value. The estimated amplitude of the AC input signal obtained by
Shows the relationship between the true value of the two-point calculation value) and the error (lower row). In this case, the sampling value a used in equation (1),
The error greatly changes depending on the phase of b, and the maximum error is about 4%.

However, this error has a characteristic that it is almost "0" when the 90 ° 2-point calculation value for a half cycle is averaged. Conventionally, using the above-mentioned sampling value, the electrical angle of the reference frequency of 30 ° The error was minimized by performing 2-point calculation of 90 ° at 6 points at each time interval and averaging the calculated values. FIG. 7 is a diagram corresponding to FIG. 6, and the lower part of FIG. 7 shows a state of error reduction when the 30 ° 6-point average is applied to the 90 ° 2-point calculated value of FIG. There is an error of 2%.

[0006]

However, as shown in FIG. 7, it takes a long processing time to obtain the calculated values of the six points, and the result fluctuates depending on the time of the calculation, so that the amplitude of the AC input signal can be obtained with high accuracy. If you want to, you still have the problem that there are errors that cannot be ignored. Therefore, an object of the present invention is to provide a digital estimation calculation method of an AC input amplitude that can obtain high accuracy even when the frequency changes.

[0007]

In order to solve the above-mentioned problems, in the digital estimation calculation method according to the first aspect, an AC input signal whose frequency can fluctuate before and after the reference frequency is set to a period ¼n of this reference frequency. (Where n is a predetermined integer of 2 or more) is sampled at a fixed sampling period and A /
A method of D-converting and estimating the amplitude (Em, etc.) of the AC input signal from the digitally converted sampling value, using a sampling value (a1, etc.) immediately before the 0 cross point of the AC input signal. 90 ° 2-point calculated value (m1
Etc.) and the sampling value immediately after the 0 cross point (a2
, Etc.) is used to obtain a value (Em ′, etc.) corresponding to the 90 ° two-point calculated value of this 0 cross point by linear interpolation with the 90 ° two-point calculated value (m2, etc.), and the value is input to the AC input. Estimate the amplitude of the signal.

According to the digital estimation calculation method of claim 2, in the estimation calculation method according to claim 1, the frequency (f, etc.) of the AC input signal is further obtained, and this frequency and the fixed sampling period are used. A value obtained by subjecting the estimated value of the amplitude of the AC input signal to predetermined (formula (6)) correction is again used as the estimated value of the amplitude of the AC input signal (Em ″ or the like).

[0009]

According to the present invention, the point at which the error is smallest (0 cross point) is detected in the calculation algorithm, and the 90 ° two-point calculation is performed using the sampling values immediately before and immediately after that,
By linearly interpolating the two 90 ° two-point calculated values, a value approximately corresponding to the 90 ° two-point calculated value at the 0 cross point is obtained, and this value is used as the estimated value of the amplitude of the AC input signal. This minimizes the error when the frequency changes. If necessary, the frequency at this time is further detected, and the estimated value is corrected by a correction equation using the frequency to obtain an estimated value with less error.

With this method, the 90 ° two-point calculation only needs to be performed twice, and a stable calculation result can be obtained as shown in FIG. 2. Further, by performing frequency error correction, a highly accurate calculation result can be obtained.

[0011]

EXAMPLE In the 90 ° two-point calculation algorithm, the error is minimized when the frequency fluctuates when the AC input instantaneous value is "0" and "maximum" as shown in FIG. Therefore, originally, the error is minimized if the 90 ° 2-point calculation is performed when the input instantaneous value is “0”, but since the sampling is asynchronous with the AC input, the sampling time does not always coincide with the 0 cross point. Absent. Therefore, in the present invention, the "0 cross point" of the input instantaneous value is detected as a point at which the sign of the sampling value is inverted, and the sampling data a1 and a2 at two sampling points immediately before and after the 0 cross point are detected.
90 ° two-point calculation is performed twice using the data b1 and b2 previously sampled at a time interval corresponding to the electrical angle 90 ° of the reference frequency, and the two calculated data By linearly interpolating with, the 90 ° two-point calculated value at the time when the input instantaneous value is “0” is approximately estimated. FIG. 1 is an explanatory diagram of this calculation method. FIG. 1A shows the above sampling data, and FIG. 1B shows the 0 cross point portion (circle area) ZP of FIG.
FIG. Further, FIG. 3C shows a linear interpolation method. Next, the details of the calculation method of the present invention will be described with reference to FIG.

9 using sampling data a1 and b1
The 0 ° 2-point calculation value m1 is expressed by the following equation (2).

[0013]

## EQU2 ## m1 = (a1 ² + b1 ² ) ^1/2 (2) Similarly, 90 ° 2 using the sampling data a2 and b2
The point calculation value m2 is expressed by the following equation (3).

[0014]

## EQU3 ## m2 = (a2 ² + b2 ² ) ^1/2 (3) The two 90 ° two-point calculation values m1 and m2 are linearly interpolated to calculate the 90 ° two-point calculation at the true 0 cross point. When the AC input amplitude estimated value Em 'as a value corresponding to the value is obtained, this value becomes a value extremely close to the true AC input amplitude Em,

[0015]

[Equation 4] Em≈Em ′ = m1 + (m2-m1) · | a1 / (a2-a1) | ... (4) Next, the AC input frequency f is further measured, and the AC input amplitude estimated value Em ′ obtained by the above equation (4) is obtained.
From here, the method of obtaining the AC input amplitude estimated value Em ″ with higher accuracy will be described. The measurement of the input frequency f is performed by detecting the 0 cross point a plurality of times and obtaining the time interval thereof.
It can be performed with high precision.

Ideally, when sampling is performed at a zero cross point and a point having a time interval corresponding to an electrical angle of 90 ° of the reference frequency with respect to this point, when the frequency changes in the 90 ° two-point arithmetic method. The error of can be theoretically calculated. FIG. 3 is an explanatory diagram of this error. FIG. 3A shows a case where the AC input frequency f is the reference frequency of 60 (Hz), and at this time, it corresponds to an electrical angle of 90 ° from the 0 cross point to the reference frequency of 60 Hz. Time interval

[0017]

## EQU00005 ## The value b sampled with t = (1/60) .times.90 / 360 (sec) is shown to exactly match the AC input amplitude Em. On the other hand, FIG. 3B shows a case where the frequency fluctuates to the increasing side with the AC input frequency f = 60 + α (Hz). In this case, since the fixed sampling time t does not change, this time interval t is set from the 0 cross point. The sampled value b has a true AC input amplitude Em because the electrical angle corresponding to the time interval t increases from 90 °.
The value is slightly smaller by ΔE. By the way, formula (1)
The 90 ° two-point calculated value shown in is ideally a = 0 when sampling is performed at the 0 cross point,

[0018]

## EQU6 ## (a ² + b ² ) ^1/2 = | b |, on the other hand, the value of this b is, assuming that the AC input frequency is f, as can be seen from FIG.

[0019]

[Formula 7] b = Em · Sin (2πf · t) = Em · Sin (2πf · (1/60) · 90/36
0) is given. Therefore

[0020]

[Equation 8] Em = b / Sin (2πf · (1/60) · 90/360) (5) On the other hand, the value of b corresponds to Em ′ obtained by the calculation of FIG. Therefore, this equation (5) can be rewritten as the following equation (6).

[0021]

[Equation 9] Em ″ = Em ′ / Sin (2πf · (1/60) · 90/360) (6) However, it is the equation that the left side of the equation (6) is Em ″ instead of Em. This is because the value obtained from the right side of the equation (6) using the relationship of (5) is an estimated value of the amplitude of the AC input signal and is different from the true value Em of the amplitude of the AC input signal.

That is, using this equation (6), the AC input frequency f and the equivalent value E of the 90 ° two-point calculated value at the 0 cross point are obtained.
The amplitude estimation value Em ″ of the AC input signal with a smaller error can be obtained from m ′. In FIG. 4, the input frequency f =
An AC input swing estimated value (here, a correction value) estimated by performing the operation of the present invention on an AC input having a swing Em = 10V at 55 Hz (that is, a frequency variation of -5 Hz with respect to a reference frequency of 60 Hz). Calling). That is, the numbers 1 to 7 in the vertical 1 column at the left end of FIG.
The numerical value in the 1st vertical column is based on the sampling value immediately before the 0-cross point, and the 90 ° 2-point calculated value m1 and its error%. The numerical value in the 3rd vertical 1-column is based on the sampling value immediately after the 0 cross point. The AC input amplitude estimated value E obtained by estimating the 90 ° 2-point calculated value m2 and its error% by the linear approximation (linear interpolation) of the equation (4) from the calculated values m1 and m2 in the fourth vertical one-column numerical value
m ′ and its error% are the AC input amplitude estimated value Em ″ estimated by performing the frequency correction of the equation (6) on the above-mentioned estimated value Em ′ and the error% thereof. Show each.
Here, the error% is the true value of the AC input level Em = 10V
And the detected frequency f is 55.0.
It is 367 Hz.

FIG. 5 shows the same calculation result as in FIG. 4 for an input frequency of 65 Hz (that is, when there is a frequency variation of +5 Hz with respect to a reference frequency of 60 Hz). Thus, the reference frequency 6
Even if there is a variation of about 10% with respect to 0 Hz, the AC input signal amplitude can be estimated with an error of 1% or less by the linear interpolation according to the equation (4) of the present invention, and the estimated value is corrected by the equation (6) frequency correction. It can be seen that this error is reduced by one digit or more by applying.

[0024]

According to the present invention, the amplitude of the AC input signal is estimated by linearly interpolating two 90 ° two-point calculated values obtained from the sampling values immediately before and after the zero crossing point, and further if necessary. Accordingly, since the estimated value is frequency-corrected to estimate the amplitude of the AC input signal, the 90 ° two-point calculation may be performed twice, and a stable calculation result can be obtained. Furthermore, by performing correction with the frequency value, a more accurate calculation result can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a calculation method according to the invention of claim 1.

FIG. 2 is a diagram showing a characteristic example of a frequency fluctuation error based on a calculation according to the invention of claim 1;

FIG. 3 is an explanatory diagram of a frequency correction method according to the invention of claim 2;

FIG. 4 is a diagram showing a specific example of a calculation result of the present invention when the input frequency is reduced.

FIG. 5 is a diagram showing a specific example of a calculation result of the present invention when the input frequency is increased.

FIG. 6 is a diagram showing a characteristic example of a frequency fluctuation error in a 90 ° two-point calculation method.

FIG. 7 is a diagram showing a characteristic example of a frequency fluctuation error by a conventional 30 ° 6-point average calculation method.

[Explanation of symbols]

ZP 0 Cross point part a1 0 Sampling value immediately before cross point a2 0 Sampling value immediately after cross point b1 90 ° of reference frequency with respect to sampling value a1
Sampling value b2 having a time interval corresponding to the phase difference 90 ° of the reference frequency with respect to the sampling value a2
Sampling value m1 having a time interval corresponding to the phase difference 90 ° obtained from sampling values a1 and b1
2-point calculation value m2 90 ° obtained from sampling values a2 and b2
2-point calculation value Em '90 ° 2-point calculation value obtained by linear interpolation from 0 cross point 90 ° 2-point calculation value (= AC input amplitude estimated value) Em "Em' frequency Estimated value of AC input amplitude estimated with correction Em True value of AC input amplitude

Claims (2)

[Claims] 1. An AC input signal whose frequency can fluctuate before and after a reference frequency is set to 1 / 4n (where n
Is a predetermined integer greater than or equal to 2), performs A / D conversion by sampling at a fixed sampling period, and estimates the amplitude of the AC input signal from the digitally converted sampling value. By linearly interpolating the 90 ° 2-point calculation value using the sampling value immediately before the 0-cross point of the signal and the 90 ° 2-point calculation value using the sampling value immediately after the 0-cross point, this 0-cross point A digital estimation calculation method for an AC input amplitude, wherein a value corresponding to a 90 ° two-point calculated value is obtained and the value is used as an estimated value of the amplitude of the AC input signal. 2. The estimation calculation method according to claim 1,
Further, the frequency of the AC input signal is obtained, and a value obtained by applying a predetermined correction to the estimated value of the amplitude of the AC input signal using this frequency and the fixed sampling period is used to estimate the amplitude of the AC input signal again. A method for digitally estimating an AC input amplitude, which is characterized by setting a value.