JPH01267465A - System for sampling ac quantity - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention samples the instantaneous values of various alternating current quantities such as alternating current voltage and alternating current as analog quantities at regular intervals, and converts the analog quantities into digital quantities. The present invention relates to an alternating current amount sampling method for measuring the amplitude and phase of the alternating current amount, or for comparing and determining the measured value and a set value.

(Prior art) In measuring the amplitude and phase of an alternating current amount such as an alternating voltage or an alternating current, or for comparing the measured value and the set value in a digital relay, for example, the instantaneous value of the alternating current amount is measured using an analog method at regular intervals. Usually, the analog quantity is sampled as a quantity, the sampled analog quantity is converted into a digital quantity, and then the measurement and comparative judgment are performed based on the digital quantity.

Here is an example of a sampling method that has traditionally been used to perform such measurements and comparative judgments.

This will be explained with reference to FIGS. 3 and 4.

Figure 3 (A) shows a sampling device and a calculation device used when sampling only a single sampling target, and Figure 3 (B) shows a sampling device and a calculation device used when sampling two sampling targets. This is what is shown.

In the same figure (A), 1 is a sample hold circuit (SH circuit) into which the alternating current amount to be sampled is input, and this SH circuit 1 receives a sampling command from the microcomputer 4, and the Extracts and retains the instantaneous value of AC amount.

The analog signal extracted and held by the SH circuit 1 is input to an analog-to-digital converter (A/D converter) 2, which converts the analog input signal into a digital signal and then converts it into a digital signal. It is stored in the memory 3 as sampling data. This stored sampling data is read into the microcomputer 4, and the microcomputer 4 measures the amplitude, phase, etc. of the alternating current amount, and compares and determines the measured value with the set value.

In addition, in FIG. 3(B), the elements numbered 2 to 4 are the same as in FIG. 3(A), and two SH circuits 1a and 1b are provided in place of the SH circuit 1 in FIG. 3(A). In addition, a multiplexer 5 is provided between the SH circuits 1a and 1b and the A/D converter 2.

In this case, the instantaneous values of the two alternating current amounts to be sampled are input to the SH circuits 1a and lb, respectively. S
The H circuits 1a and 1b receive sampling commands from the microcomputer 4, and extract and hold instantaneous values of each alternating current amount at regular intervals. Each analog signal extracted and held by the SH circuits 1a and 1b is input to the multiplexer 5, and the multiplexer 5 alternately switches the inputs from the SH circuits 1a and 1b based on the signal from the microcomputer 4 to perform A/D conversion. output to device 2. After converting each analog input signal into a digital signal, the A/D converter 2 stores these signals as sampling data in the memory 3, and thereafter, the microcomputer 4 executes calculations in the same manner as described above.

By the way, the sampling interval (electrical angle) θ is θ=2π
/m (1) (m: an integer of 4 or more), and sampling is generally performed with m=12, that is, θ=2π/12 (30@).

FIG. 4(A) shows the case where alternating current is sampled by the device shown in FIG. 3(A), and FIG.
The case where AC voltage and AC current are sampled by the apparatus shown in FIG. 3(B) is shown, respectively.

In FIG. 4(A), the sampling target is an alternating current i +t+=Iasinωt(Im : i <t>
The peak value of ω:i (angular frequency) is input to the SH circuit 1.

This instantaneous value of i+t+ is extracted and held by the SH circuit 1 at intervals of 30' electrical angle. These analog instantaneous value data are output to the A/D converter 2, converted into digital quantities, and then stored in the memory 3.

For example, calculation of the effective value I rms of the alternating current is performed as follows.

If the nth sampling value at the sampling interval 306 of the instantaneous value of the alternating current is in and the n+3rd sampling value is in+3, then in and i n*a have a phase difference of π/2.
Therefore, the peak value In is I m ” (i n2
+ i n+3")"". Therefore, the effective value I
rms becomes (in”+ih◆,z)i/Z.

In FIG. 4(B), the AC voltage to be sampled v (t+= Vmsinωt, i tt)=I
m sin ((11 -φ) (V Peng: V (tt peak value, ■ Feng: 1 (t) peak value.

ω: v(t), i (angular frequency of tt, φ: lagging phase difference of 1(t) with respect to v(t)) are input to the SH circuit 1, and these alternating current amounts ■(i, i (of tt) The instantaneous values are extracted and held by the SH circuits 1a and lb at intervals of 30" electrical angle. Here, the V
The sampling timing of (t) e l (t) is
This is done with a phase difference of approximately 15°. In this way.

Each extracted and held analog instantaneous value data is output to the multiplexer 5, and the multiplexer 5 receives the input v
The instantaneous value data of (t>, i (tt) are alternately output to the A/D converter 2. The instantaneous value data of v(tt, i+1+) are converted into digital quantities by the A/D converter 2. After that, it is stored in the memory 3.

(Problem to be Solved by the Invention) Generally, the sampling data processing time Δt of the sampling device is the sum of the analog-to-digital conversion processing time Δt1 of the A/D converter 2 and the measurement and calculation processing time Δtz of the microcomputer 4. 1 represented by, for example, Figure 4 (
If the sampling period of i (t+ shown in A) is τ', then generally Δt=Δt1+Δtz(τ'), and the conversion process of the A/D converter 2, the measurement of the microcomputer 4, the calculation process, etc. have not yet been completed. There will be no inconvenience such as the next sampling being performed even though the sample has not been sampled.

However, for example, the conversion processing time Δt1 of a 12-bit general-purpose A/D converter, which is generally considered to be easy to apply, is 20 to 40 μS even in the case of a successive approximation type that has a relatively fast conversion time.
It takes a certain length of time.

Therefore, when the frequency of the alternating current amount to be sampled is high, the processing time Δt is Δt;Δt1+Δti)
τ′, and it is theoretically impossible to use the conventional sampling method.

Therefore, if the sampling interval θ (electrical angle) is −constant, then the sampling period (sampling time interval τ′
) must necessarily be shortened.

Further, for example, when outputting to the A/D converter 2 while switching the analog input signals from the SH circuits 1a and lb using the multiplexer 5 shown in the device of FIG. 3(B), the sampling period τ A time interval τ′ that is approximately half of ′
The analog/digital conversion process by the A/D converter 2 and the measurement calculation process by the microcomputer 4 must be performed within /2. Therefore, the sampling period τ′/
2 becomes shorter than Δt, that is.

When Δt>τ'/2, it becomes impossible to employ the conventional sampling method described above.

In this way, with the traditional sampling method.

There are disadvantages in that there are large restrictions on the upper limit frequency of the sampling target, and there are also large restrictions on the number of points to be sampled.

The present invention was proposed to solve the above-mentioned problems, and its purpose is to solve the problem even when the frequency of the alternating current to be sampled is high or when there are many points to be sampled. An object of the present invention is to provide a sampling method for alternating current that allows sampling even if the sampling period is shorter than the processing time of an analog-to-digital converter of an A/D converter or a microcomputer.

(Means for Solving the Problems) In order to achieve the above object, the present invention sets the sampling interval θ (electrical angle) to θ=2π·k+(2π/m) (k: a constant consisting of any natural number, m : a constant consisting of an integer of 4 or more).

(Function) In the present invention, the amount of alternating current to be sampled is 1f
When <t>=As1nωt, sampling of f(t+ is performed at intervals of electrical angle 2π·k+(2π/m).

This time interval (sampling period) τ corresponding to the sampling interval 2π·k+(2π/m) is assumed to be the sampling period equivalent to 2π/m electrical angle as τ′.

τ=(k ports m+1)τ′ It is expressed as

Therefore, if sampling is performed at the sampling period τ,
At the sampling period τ', the alternating current amount f(t) = Asinωt
It is possible to obtain the same sampling results as when sampling is performed.

That is, the sampling value S + t) at one time t is ω S (t) = As1n t − (2
) km+1.

Here, the analog-to-digital conversion process of the alternating current amount, the storage of the sampling data in the memory, and the measurement calculation process in the microcomputer are completed during the above-mentioned sampling period.

(Example) A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows that the apparatus shown in FIG. 3(A) generates an alternating current i + t) = I m5inωt with a sampling period τ.
Sampling time t n when sampling is performed
This shows the relationship between (n = 0, 1, 2, 3, . . .) and the sampling value 5s (tn). here.

I+- is the peak value of i<t>, and ω is the angular frequency of 1(t). Furthermore, the value of m in equation (2) is 12, that is, the sampling interval θ (electrical angle) is 2π+π16, and the value of k in equation (2) is 1.

First, the alternating current i + t) to be sampled is S
It is input to H circuit 1.

The SH circuit 1 receives a sampling period control signal from the microcomputer 4, and based on this signal, the sampling period τ is expressed in electrical angle θ = 2π + π/6 = 13π/
1(t) sampling is performed at a sampling interval of 6.

First, the SH circuit 1 extracts and holds the instantaneous value i (to) = I m5inωto of i <t> at t = t o based on the sampling period control signal of the microcomputer 4.

The sampling value 5i(to) at this time is assumed to be the electrical angle at the time ta.

S1(ta)=Imain'P.

Next, the SH circuit 1 has a sampling interval θ=13/
After 6π elapses, the instantaneous value i( of t+ at t = t 1)
t engineering)=I m5inωt1 is extracted and
Hold.

The sampling value 5Htx) at this time is expressed in electrical angle as S 1(tx ＞= I m5in(13π/ 6 +
IP).

Generally, if the sampling interval is θ=2π·k+(2π/m) and the time interval equivalent to 2π/m is τ', then the sampling period (time interval) τ is.

It is expressed as τ=(mok+1)τ'. This means that, compared to the conventional method of performing sampling with the sampling period τ', the present invention has the following advantages:
This is equivalent to sampling by multiplying the time axis by (m-+1).

Therefore, in the case of this embodiment, since 1 and m=12, τ=(m-+1)τ' = 13τ', so that sampling can be performed by multiplying the time axis by 13 times.

The sampling value at this time is 5ict).

It is expressed as

In equation (3), 12ωta/13 is an advanced phase angle with respect to i<t,>. That is, the sampling interval (2
Sampling at a sampling interval of π+π/6) is equivalent to sampling at a sampling interval of π/6 (m=12).

Since the sampling period τ is set to be longer than the conversion processing time of the A/D converter 2, the A/D converter 2 obtains the instantaneous alternating current value 5i( to), analog
After digital conversion, the data is stored in the memory 3, and the microcomputer 4 ends the measurement calculation process.

Thereafter, sampling of tz, ta, t4, etc. is performed in the same manner.

The nth sampling value 5(n) is 5i(tn)=
It is expressed as lm5in(n (13π/6)+ψ)−(4) or.

In the first embodiment described above, to=1. The case where m=12 has been explained, but if the value of 1m or the size of the frequency to be sampled is different from this example, Δt=Δt+Δt
Any positive integer (that is, a natural number) may be adopted as the value of k so that ti<τ.

Next, a second embodiment of the present invention will be explained with reference to FIG. 2. In this embodiment, the sampling target is v+t+=Vmsinω.
t, 1tt) = In5in(ωt-φ)(φ:v(
In this case, there are two points i (lag phase difference of t>), and in this case, sampling is performed by the apparatus shown in FIG. 3(B).

In this embodiment, as in the first embodiment, the sampling interval θ is 2π+π/6 (m=12), the value of k is 1, and sampling is performed for each of V (t) and i tt).

First, based on the sampling period control signal from the microcomputer 4, the SH circuit 1atlb is set to 'V(t)+
i (Each instantaneous value of t+ is extracted and held at sampling intervals of 13π76 electrical angles.

In this embodiment, the extraction and retention of sampling data by the SH circuit 1a and the extraction and retention of sampling data by the SH circuit 1b are performed with a phase difference of 13π/12 in electrical angle.

Next, the multiplexer 5 selects the instantaneous value of the signal from the SH circuit 1a or 1b to be sampled. The selected instantaneous values of v(t) and 1(t) are alternately outputted to the A/D converter 2 by the multiplexer 5.

In this example, the nth sampling value of
The nth sampling value of v(tn)Pi(t) is 5i
(tn>, then 5v(tn+, S 1(tn) is Sv(tn)=Vmsin(n(13π/6)+ψ)S as in equation (4).
i+tn)=lm5in(n (137C/6)+
9+13π/12-φ).

The A/D converter 2 and the microcomputer 4 perform analog-to-digital conversion of each instantaneous value of V(t+ or i(off) within a time interval corresponding to half the sampling interval (half the sampling period τ). , is stored in the memory 3, and the microcomputer 4 ends the measurement calculation process.

In the second embodiment, the sampling target is two points, voltage and current.
If the value of k is set large so as to exceed , it becomes possible to increase the number of points to be sampled to three or more.

(Effect of the invention) As described above, in the present invention, the sampling period is set to 2π·k.
+(2π/m) (k: a constant made of any natural number; 1m: a constant made of an integer greater than or equal to 4); therefore, when the frequency of the alternating current amount to be sampled is high;

Even when there are many points to be sampled, by making the original sampling period longer than the conversion processing time of the A/D converter, the upper limit frequency of the measurable AC amount can be significantly increased, or the number of points that can be measured with the same device can be increased. This has the effect of greatly expanding the scope of measurement when measuring the peak value and phase of an alternating current amount by sampling, for example, when comparing and determining a measured value and a set value in a digital relay.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the first embodiment of the present invention, Fig. 2 is an explanatory diagram of the second embodiment, and Fig. 3 (A) shows an apparatus used in the first embodiment and the prior art. Block diagram, same figure (
B) is a block diagram showing a device used in the second embodiment and the prior art, and FIGS. 4(A) and 4(B) are explanatory diagrams for explaining the prior art. 1, la, lb,...sample hold circuit 2...
Analog-digital converter 3...Memory 4...Microcomputer 5...Multiplexer Patent applicant, Fuji Electric Co., Ltd.

Claims (1)

[Claims] In a sampling method that samples the instantaneous value of an analog alternating current amount at a constant period, the sampling period is 2π·k+(2π/m) (k: a constant consisting of any natural number, m: an integer of 4 or more) A sampling method for alternating current that is characterized by sampling as a constant consisting of .