JPH06123749A - AC measuring device - Google Patents

Abstract

(57) [Summary] [Purpose] The objective is to enable measurement of a power system whose frequency fluctuates even if the sampling time width ωT of the measurement value is fixed. [Structure] The measured values (voltage values) measured at a predetermined sampling time are sequentially distributed through a distribution path 3, and a temporary storage area 4
10 to 10 are temporarily stored, and the frequency calculation unit 11 calculates the frequency using the measurement values stored in the temporary storage areas 4, 7, and 10. Then, using the calculated frequency, the frequency correction coefficient calculation unit 12 calculates the frequency correction coefficient, and the voltage calculation unit 13 calculates the voltage using the frequency correction coefficient and the two measured values of the temporary storage areas 4 and 5. To calculate

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC measuring device for measuring AC electric values such as AC electric voltage and current.

[0002]

2. Description of the Related Art FIG. 2 is a configuration diagram showing a configuration of a voltage measuring device which is an example of a conventional AC measuring device. In FIG. 2, 1 measures (samples) a voltage value at a certain time in a power system. The measuring device 2 is a control unit that sets the timing at which the measuring device 1 measures every 30 electrical degrees, and 13d is the measuring device 1
Is a voltage calculation unit that calculates the voltage of the power system by the following Equation 1 using the sampled measurement values.

K | V | ² = v ² _m + v ² _m-1 −2v _m · v _m−1 · cos ωT (1) where | V |: voltage amplitude ωT: sampling interval v _m : time Measured value (voltage value) at the time of m v _m-1 : Measured value one sample interval before time m k: sin ² ωT

Here, the sampling interval is an electrical angle of 30.
It shows the case of °, voltage value at time m and time m
The calculation result is obtained by using the measured value (voltage value) at the time when the electrical angle is further separated by 30 °.

The operation of the voltage calculator 13d will be described with reference to FIG. FIG. 3 shows, for example, the fourth article in the literature (“Electrical Joint Research, Vol.
Fig. 1-2 is a diagram for explaining an algorithm regarding the voltage value calculation amplitude value calculation method shown in the product form D) of Table 1-2. Expression 1 is shown in the table in the above document as an amplitude value calculation method for obtaining a voltage. Since the power system to be measured is AC electricity, its voltage value changes with time as shown in FIG. 3, and the measured value v sampled at a certain time t.
(T) is given by Equation 2 below.

V (t) = Vp · sin (ωt) (2)

Therefore, the measured values at the time points m and ma are given by the following equation. _{v m = Vp · sin (ωt} ) ··· (3) v ma = Vp · sin (ωt-aωT) ··· (4) where, Vp: amplitude value of the voltage .omega.T: sampling interval a: a = 1, 2, 3, ...

Substituting the equation 3 and the equation 4 when a = 1 into the right side of the equation 1, the following is obtained.

V ² _m + v ² _m-1 −2v _m · v _m−1 · cos ωT = Vp ² · sin ² (ωt) + Vp ² · sin (ωt−ωT) −2Vp · sin (ωt) · Vp · sin (Ωt−ωT) · cosωT = Vp ² {1-cosωT · cos (2ωt−ωT) −cosωT−cos (2ωt−ωT)} = Vp ² · sin ² ωt (5)

Here, Vp is the amplitude value of the voltage, and therefore the left side of Expression 1 is derived. Here, if the square root of the obtained result is taken, since the sampling interval ωT is 30 ° in electrical angle, 0.5 times the amplitude value Vp (sin
A voltage of 30 ° = 0.5) will be calculated,
If this result is multiplied by 0.5, the voltage value can be obtained from the measurement result.

[0011]

Since the conventional voltage measuring device is constructed as described above, the frequency of the power system whose voltage is to be measured is always constant, and the sampling time width ωT is accurate. It is constructed on the premise of. Therefore, cos ωT and sin ωT in Equation 5 are
Is treated as a fixed constant, and if there is a frequency fluctuation in the power system where the voltage is to be measured, the voltage calculation result will show a large error unless the sampling time width ωT of the measured value is changed accordingly. Therefore, there is a problem that the calculated voltage is different from the actual voltage.

The present invention has been made to solve the above problems, and enables measurement of a power system whose frequency fluctuates even if the sampling time width ωT of the measured value is fixed. The purpose is to

[0013]

An AC measuring device of the present invention is a control means for controlling the operation of measuring means for measuring AC electric values such as voltage, current, active power, reactive power, etc. at predetermined intervals, and for controlling the operation of the detecting means. Means, a storage means for temporarily storing a plurality of values measured by the detection means, a frequency calculation means for calculating a frequency of AC electricity using three of the plurality of values stored by the storage means, and a frequency calculation means. It is characterized in that it has a frequency correction coefficient calculating means for calculating a frequency correction coefficient by the frequency calculated by and a measurement value calculating means for obtaining an AC electric value using the frequency correction coefficient.

[0014]

Since the frequency of the alternating current electricity to be measured can be obtained from the measured values obtained by sampling at fixed intervals, accurate voltage and current can be calculated using this.

[0015]

【Example】

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. Figure 1
FIG. 1 is a configuration diagram showing a configuration of a voltage measuring device which is an embodiment of the present invention. In the figure, 3 is a distribution path for sequentially distributing measured values (voltage values) measured at every electrical angle of 30 °, 4
Reference numeral 10 denotes a temporary storage area for the measured values distributed by the distribution path 3, 11 denotes a frequency calculation unit for calculating the frequency of the power system to be measured using the measured values stored in the temporary storage areas 4, 7, and 10. , 12 is a frequency correction coefficient calculation unit for calculating a frequency correction coefficient using the frequency calculated by the frequency calculation unit 11, and 13 is a measurement value stored in the temporary storage areas 4 and 5 and a measurement value frequency correction coefficient. 2 is the same as that of FIG. 2.

Next, the operation will be described. First, the distribution path 3 has a series of measured values ... V _m-3 , v _m-2 , v _m-1 , v _m ...
Is always constant sampling time width ωT (electrical angle 30 °)
It flows every time and is sequentially stored in the temporary storage areas 4 to 10. For example now, when those respectively v _m in the temporary storage area _{4~10, v m-1, v} m-2, v m-3, v m-4, v m-5, v m-6 is stored , When the latest measured value v _{m + 1} appears in the distribution path 3, v _m-6 is displayed in the temporary storage area 10.
V _m-5 that had been cleared and was stored in the temporary storage area 9
To store. At the same time, the same processing is performed in the other temporary storage areas 4 to 9, the data v _m is cleared in the temporary storage area 4, and the latest data v _{m + 1} is stored. On the other hand, the frequency calculation unit 11 calculates the voltage frequency f of the electric power system by using the measured values stored in the temporary storage areas 4, 7, and 10 according to Equation 6 below.

[0017] ^{f = 5 / 9cos -1 (v} m + v m-6 / v m-3) ··· (6)

When the denominator in the equation 6 becomes zero in this processing, another processing such as discarding the calculation result is performed. Next, the frequency correction coefficient calculation unit 12
Using the voltage frequency f calculated in 1
Then, the frequency correction coefficient is calculated according to equation (8).

Sin ωT = sin (2πfT) (7) cos ωT = cos (2πfT) (8) where T: sampling time

Then, the voltage calculation unit 13 uses the measured values stored in the temporary storage areas 4 and 5 and the frequency correction coefficient calculated by the frequency correction coefficient calculation unit 12 to calculate Vp ² by the following equation 9. Is calculated, and the square root is calculated to calculate the voltage Vp of the power system.

Vp ² = v ² _m + v ² _m−1 −2v _m · v _m−1 · cos ωT / sin ² ωT (9)

(Embodiment 2) In the above embodiment, the frequency of the AC electric power to be measured is calculated by the frequency calculating means, the frequency correction coefficient is calculated using this, and the AC electric power to be measured is calculated using these. However, the current is not limited to this, and the current may be calculated. In this embodiment 2, the measuring device 1 of Figure 1 is a measuring instrument 1a for measuring the current i _m, the voltage calculation unit 13 may be replaced with current calculation unit 13a. Then, similarly to the first embodiment, the frequency calculation unit 11 calculates the current frequency f of the power system by the following equation (10).

F = 5/9 cos ^-1 (i _m + i _m-6 / i _m-3 ) (10)

Then, in the frequency correction coefficient calculation unit 12,
Calculate the frequency correction coefficient from the obtained frequency, then
In the current calculation unit 13a, the frequency f and the frequency correction coefficient sin
The electric current of the power system is calculated by the following equation 11 using ωT and cos ωT.

Ip ² = i ² _m + i ² _m−1 −2i _m · i _m−1 · cos ωT / sin ² ωT (9)

Further, in the above embodiment, the voltage and current of the AC electricity to be measured is obtained, but the present invention is not limited to this, and the active power and reactive power of the AC electricity may be obtained.

[0027]

As described above, according to the present invention, the frequency of AC electricity is obtained by measuring the electric value such as voltage or current in AC electricity at a predetermined interval, and the frequency correction coefficient derived therefrom is calculated. Since the electric value is used,
Even if the measurement interval (sampling electrical angle) is fixed, there is an effect that a highly accurate and stable electrical value of AC electricity with frequency fluctuation can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a voltage measuring device that is Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a voltage measuring device which is a conventional AC measuring device.

FIG. 3 is a waveform diagram for explaining the operation of the voltage calculator 13d in FIG.

[Explanation of reference numerals] 1 measuring instrument 2 control unit 3 distribution path 4 to 10 temporary storage area 11 frequency calculation unit 12 frequency correction coefficient calculation unit 13 voltage calculation unit

Claims (1)

[Claims] 1. An alternating current measuring device for measuring alternating current electricity at predetermined intervals to calculate the alternating current electricity value, a measuring means for measuring the alternating current electricity at predetermined intervals, and a control for controlling the operation of the detecting means. Means, storage means for temporarily storing the plurality of values measured by the detection means, and frequency calculation means for calculating the frequency of the AC electricity using three values among the plurality of values stored by the storage means. An AC measurement comprising: a frequency correction coefficient calculation means for calculating a frequency correction coefficient by the frequency calculated by the frequency calculation means; and a measurement value calculation means for calculating the AC electric value using the frequency correction coefficient. apparatus.