JP2000329803A - Instrument and method for measuring three-phase alternating current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring instrument for a three-phase alternating current having a function for estimating a pseudo neutral potential therein, capable of computing a central value of a three-phase alternating current by use of instantaneous values of a measured voltage and a measured current, etc. SOLUTION: This measuring instrument 5 for a three-phase alternating current includes a current measuring circuit for measuring currents of each phase by measuring power and frequency of a three-phase alternating current with the use of a digital value by A-D conversion of a sampled instantaneous value of an input signal, a voltage measuring circuit for measuring a voltage between the phases, A-D converters 32, 35, 45, 52, 55 for outputting instantaneous digital values by A-D conversion of the instantaneous measured values outputted from the current-and voltage-measuring circuits, a neutral potential estimation portion 6 for estimating a neutral potential by computation from the instantaneous digital values, and a secondary computation processing portion 60 for determining instantaneous power and frequency, etc., from the instantaneous digital values and the neutral potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase alternating current measuring device and a three-phase alternating current measuring method for measuring three-phase alternating current. The present invention relates to a three-phase AC measuring instrument having a function of estimating by a calculating means.

[0002]

2. Description of the Related Art In a conventional measuring device for three-phase alternating current, a neutral point potential cannot be obtained for a measuring object wired in a three-phase three-wire system. Is used to make a Y connection, and a pseudo three-phase four-wire circuit is configured to perform measurement. FIG. 2 is a connection diagram of a resistor connected for such a purpose and a conventional three-phase AC measuring instrument.

In FIG. 2, resistors 21, 22, and 23 are resistors having the same magnitude and connected in a Y-connection outside the three-phase AC measuring instrument. By connecting the three resistors in this way, the common connection point a can be treated as a neutral point of three-phase alternating current.

[0004] The voltage input unit 31 incorporated in the measuring instrument 1
The voltage input of the first phase is connected between the first-phase power supply line 11 of the three-phase alternating current and the neutral point a, and the current input unit 34 is connected in series to the first-phase power supply line 11. The current value of the first phase is measured. The obtained first-phase voltage value and first-phase current value are converted into digital values by AD converters 32 and 35 and input to the effective voltage value calculation unit 36 and the power calculation unit 37. The voltage value and the power value obtained here are instantaneous values for each input.

A voltage effective value calculating section 36 and a power calculating section 37
Calculates the first phase voltage effective value and power value based on the instantaneous voltage value and instantaneous current value input from the AD converters 32 and 35, respectively.

Similarly, voltage values and power values of the second and third phases can be obtained by circuits from the voltage input unit 41 to the power calculation unit 57.

[0007] The secondary arithmetic processing unit 60 calculates a voltage value, a current value, a total power value, and the like of each phase of the three-phase power supply from the voltage effective value and the power value for each phase (hereinafter, referred to as a value required by the user). Calculate the representative value of three-phase alternating current.) For example, the secondary operation processing unit 6
0 uses the voltage effective value measured for each phase by the method described above to obtain a time-averaged effective value voltage, and averages these values to obtain a representative voltage value of three-phase AC. calculate. Further, the secondary arithmetic processing unit 60 measures, for example, a time T for n cycles of the effective voltage value of the first phase from the effective voltage value measured for each phase by the method described above,
The frequency f was calculated as f = n / T (Hz).

[0008] The secondary arithmetic processing unit 60 displays the representative value of the three-phase alternating current obtained on the display unit 70.

In this way, the conventional three-phase AC measuring instrument can selectively display the representative value of the three-phase AC on the display unit 70.

[0010]

In a conventional three-phase AC measuring instrument, a three-phase three-wire AC power supply as in the conventional example shown in FIG. There are times when you want to perform measurement as a wire type AC power supply. In this case, there is a problem that an additional component such as a resistor is required to create a pseudo neutral point outside the measuring instrument. In addition, a conventional three-phase AC measuring instrument obtains a time-averaged voltage effective value or power value for each phase, and uses that value as a secondary calculation process to represent the representative value of the three-phase AC. Was seeking
There is a problem that the ability to follow changes in load and power supply is poor.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem. A three-phase AC measuring instrument has a function of estimating a pseudo neutral point potential inside the measuring instrument, and has a function of measuring instantaneous values of a measuring voltage, a measuring current, and the like. It is an object of the present invention to provide a three-phase alternating current measuring device capable of obtaining a representative value of three-phase alternating current using the same.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, a three-phase AC for measuring at least a total power value, a frequency value, and a voltage value of each phase of the three-phase AC is measured. In the measuring instrument, a current measuring circuit for measuring the phase current value of each phase, a voltage measuring circuit for measuring the inter-phase voltage value between each phase, and the phase current value of each phase and the inter-phase voltage value of each phase. A neutral point potential estimating unit for estimating a neutral point potential value by using arithmetic means; and a phase current value of each phase, an inter-phase voltage value of each phase, and the neutral point potential value, and at least a total of three-phase alternating current. It is characterized by including a secondary arithmetic processing unit for obtaining a power value, a frequency value, and a voltage value of each phase.

This makes it possible to determine the neutral point potential value of the three-phase three-wire AC using the phase current value of each phase and the inter-phase voltage value between each phase, and measure the representative value of the three-phase AC. Become.

This is because the interphase voltage value V12 between the first phase and the second phase with respect to the second phase of the three-phase alternating current is defined as in claim 2.
And the inter-phase voltage value V between the second phase and the third phase based on the second phase
32, the neutral point potential value V02 viewed from the second phase can be realized by estimating the neutral point potential value V02 using an equation of V02 = 1/3 × (V12 + V32).

Further, the inter-phase voltage value V
12, the inter-phase voltage value V32 and the neutral point potential value V02
, The first phase voltage value V10 viewed from the neutral point potential value V02, the second phase phase voltage value V20 viewed from the neutral point potential value V02, and the third phase voltage value V02 viewed from the neutral point potential value V02. The phase voltage value V30 of the phase can be measured using the following equation: V10 = V12−V02 V20 = −V02 V30 = V32−V02.

According to a fourth aspect of the present invention, there is provided a three-phase AC measuring method for measuring a three-phase AC voltage effective value using a neutral point potential value and a phase voltage value of each phase viewed from the neutral point potential value. In the above, the phase voltage of the first phase and V10 viewed from the neutral point potential value V02, the phase voltage value of the second phase V20 viewed from the neutral point potential value V02, and the second phase voltage viewed from the neutral point potential value V02. Generating a composite vector signal from the three-phase voltage values V30;
The magnitude of the combined vector signal is multiplied by a coefficient to obtain a voltage effective value.

Thus, the effective voltage value of the three-phase alternating current can be directly obtained from the scalar quantity of the vector obtained by synthesizing the phase voltages of the respective phases. Further, by using the instantaneous value for the phase voltage of each phase, it is possible to obtain the instantaneous voltage effective value of the three-phase alternating current.

This can be realized by multiplying the scalar amount of the vector obtained by synthesizing the phase effective voltage of each phase with the effective voltage value of the three-phase alternating current by √2 / 3.

In the three-phase alternating current measuring method for measuring the frequency value of three-phase alternating current by using a neutral point potential value and a phase voltage of each phase viewed from the neutral potential value,
The phase voltage value V1 of the first phase viewed from the neutral point potential value V02
0, a phase voltage value V20 of the second phase viewed from the neutral point potential value V02, and a phase voltage value V30 of the third phase viewed from the neutral point potential value V02, to generate a synthesized vector signal. The instantaneous frequency value is obtained by multiplying the rotation angular velocity of the signal by a coefficient.

Thus, the frequency value of the three-phase alternating current can be obtained by multiplying the rotation angular velocity of the vector obtained by synthesizing the phase voltages of the respective phases by a coefficient. Further, by using an instantaneous value for the phase voltage of each phase, an instantaneous frequency value of three-phase alternating current can be obtained.

According to the present invention, the three-phase instantaneous power value is measured by using the neutral point potential value and the phase voltage value and the phase current value of each phase viewed from the neutral potential value. In the AC measurement method, the instantaneous phase current value and the instantaneous phase voltage value of each phase are multiplied to obtain an instantaneous power value of each phase, and these are added to obtain an instantaneous power value of three-phase AC. Characterized by

Thus, when measuring the instantaneous power of the three-phase AC, it is possible to perform the instantaneous power measurement with good responsiveness to the fluctuation of the load and the power supply.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. The three-phase alternating current measuring device of the present invention is different from the conventional example in that the conventional three-phase alternating current measuring device shown in FIG. The operation performed by the three-phase AC measuring instrument having such a configuration will be described in detail with reference to the configuration diagram shown in FIG.

In the three-phase AC measuring instrument shown in FIG.
The voltage input unit 31 is connected to the first phase and the second phase of the three-phase alternating current, and measures the voltage values V12 of the first phase and the second phase with reference to the second phase. A voltage value V32 of the third and second phases connected to the third and second phases of the alternating current is measured with reference to the second phase. The voltage values V12 and V3 obtained here
2 is converted into a digital value by the AD converters 32 and 52 and input to the neutral point potential estimating unit 6.

The current input sections 34, 44 and 54 are connected in series to the power supply lines of each phase, and measure the current value of each phase. The current values of the respective phases obtained here are converted into AD converters 35 and 4
It is converted into a digital value by 5 and 55 and the power calculation unit 37
Is input to The voltage value and current value obtained here are instantaneous values for each input.

The neutral point potential estimating unit 6 estimates the neutral point potential value V02 as viewed from the second phase as V02 = 1/3 × (V12 + V32) (1) using the voltage values V12 and V32. .

The first-phase voltage value V10, the second-phase voltage value V20, and the third-phase voltage value V30, as viewed from the neutral point potential value V02, are as follows: V10 = V12-V02 (2) V20 = −V02 (3) V30 = V32−V02 (4) This corresponds to the voltage value of each phase when the three-phase three-wire AC is Y-connected and considered as a three-phase four-wire AC.

In the three-phase AC measuring instrument 5 of the present invention, the calculation of the above equation (1) is performed by the neutral point potential estimating section 6, the output is inputted to the inverter 7, and the output is outputted by the adder 8. By adding to the output of the AD converter 32, the voltage V value 10 of the first phase expressed by the above equation (2) is obtained.

Similarly, by adding the output of the inverter 7 to the output of the AD converter 52 by the adder 9,
The voltage V30 of the third phase expressed by the above equation (4) is obtained. The output of the inverter 7 is the voltage value V20 of the second phase expressed by the above equation (3).

Next, the measuring device 5 for three-phase AC of the present invention uses the voltage V10 of the first phase, which is the output of the adder 8, and the voltage V10, which is the output of the inverter 7, obtained by the above configuration. The two-phase voltage value V20 and the third-phase voltage value V30, which is the output of the adder 9, are respectively converted to the effective voltage value calculation units 36, 46, 56 and the power calculation unit 37 corresponding to each phase, similarly to the conventional example. , 4
7 and 57 to calculate the effective voltage value and electric power value of each phase.

The secondary arithmetic processing unit 60 calculates the representative values of the three-phase alternating current of the three-phase power source from the effective voltage value and the electric power value of each phase as in the conventional example, and displays these values on the display unit 70. indicate.

As described above, the three-phase AC measuring instrument 5 of the present invention can convert three-phase three-wire AC into three-phase AC values without using external devices such as resistors. It is possible to measure a representative value of the alternating current and selectively display the measured value on the display unit 70.

The secondary operation processing unit 60 and the power calculation unit 3
There are various methods for calculating a representative value of three-phase alternating current performed using 7, 47, 57, and the like.

For example, it is possible to generate a combined vector signal using the voltages of the respective phases and multiply this by a coefficient to obtain the effective voltage value and the frequency value. By using this method, it is possible to configure a voltage measuring device having good responsiveness to voltage fluctuation. (Also, a method of generating a combined vector signal using voltages of the three-phase alternating current phases described below and multiplying the resultant by a coefficient to obtain a voltage effective value and a frequency value is described in FIG. Needless to say, it can be realized by using the AC measuring instrument 5, but it can be realized by using the conventional three-phase AC measuring instrument or the three-phase four-wire measuring instrument described with reference to FIG. Is possible.)

For example, when the instantaneous vector V0 of the three-phase voltage is represented on a complex plane using the voltages V10, V20, and V30 of the respective phases obtained by the configuration shown in FIG. −1 + j√3) / 2 + V30 × (−1−j√3) / 2 (5) Here, j = imaginary unit.

Here, the instantaneous vector V0 of the three-phase voltage is obtained.
Is the total power value of the three-phase alternating current, and can be obtained by calculating the square root of the sum of squares of the real part and the imaginary part of the above equation (5).

By multiplying the absolute value of the instantaneous vector V0 of the three-phase voltage obtained above by √ / 2/3, Y
The effective voltage value of each phase of the connection power supply can be obtained. This value is constant regardless of time if the power supply is a symmetrical three-phase with no distortion and a constant amplitude and this power supply is supplied to a symmetrical three-phase load. Therefore, when measuring the voltage of a symmetric power supply with small distortion, it is not necessary to use a ripple filter.

Further, the frequency of the three-phase alternating current can be obtained by obtaining the argument θ of the instantaneous vector V0 of the three-phase voltage obtained by the above equation (5). The method will be described below.

The argument θ of the instantaneous vector V0 of the three-phase voltage can be obtained by θ = tan ^{− 1} ((imaginary part of V0) / (real part of V0)) (6) Furthermore, the angular frequency omega can be obtained by _{ω = (θ (t) -θ} (t- Δ t)) / Δt (7). However, θ _(t): deflection angle theta of the current vector V0 _(t- Δ _t): angle of deviation Delta] t time past vector V0 Delta] t: a measurement cycle.

Here, since the angular frequency ω obtained by the above equation (7) and the frequency of the three-phase power supply are in a proportional relationship, it is possible to obtain the instantaneous frequency by multiplying this by an appropriate coefficient.

In the above equation (5), (1 + j0), (−1 + j√3) / 2 and (−1−
Although j√3) / 2 is used, the same effect as the above equation (5) can be obtained by using three vectors having the same absolute value and an angle of every 120 degrees.

In addition to the method of calculating the total power value of the three-phase AC described above, there is a method of calculating the total power value of the three-phase AC using the instantaneous current value and instantaneous voltage value of each phase. This is because in the three-phase AC measuring device of FIG.
The instantaneous current value and the instantaneous voltage value are multiplied for each phase by using 7, 47, 57 and the secondary arithmetic processing unit 60 to obtain the instantaneous power value for each phase. This is a method for obtaining the total power value.

The total power value of the three-phase alternating current obtained by using this method is as follows if the power supply is a symmetrical three-phase power supply having no distortion and a constant amplitude, and this power supply is supplied to a symmetrical three-phase load. , Is constant regardless of the power factor of the load. Therefore, when measuring the voltage of a symmetric power supply with small distortion, it is not necessary to use a ripple filter. Further, the above-described method of calculating the total power value of the three-phase AC using the instantaneous current value and instantaneous voltage value of each phase of the three-phase AC can be realized using the three-phase AC measuring device 5 described in FIG. Needless to say,
The present invention can also be realized by using a conventional three-phase AC measuring device or a three-phase four-wire measuring device described with reference to FIG.

It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

[0045]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. Claims 1 to 3
According to the invention described in (3), when measuring the voltage or power of three-phase alternating current, even if a neutral point potential cannot be obtained, a pseudo three-phase four-wire measurement without using an external circuit such as a resistor. Is possible only with a measuring instrument. In addition, this function can be easily realized by using the hardware of the conventional three-phase AC measuring instrument almost as it is, and adding only a few circuits and modifying the software.

According to the inventions described in claims 4 to 7, it becomes possible to realize a three-phase alternating current measurement with good responsiveness to changes in load and power supply. In particular, when measuring an extremely low frequency three-phase AC voltage with an inverter-applied device or the like, it is not necessary to remove a ripple for each phase, so that the measurement is facilitated. In addition, according to the three-phase alternating current measurement method of the present invention, measurement based on instantaneous voltage is possible. For example, if the present invention is applied to a device that displays a voltage value as a graph, voltage fluctuation depending on a sudden change in load, etc. To the observer.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a three-phase AC measuring instrument according to the present invention. .

FIG. 2 is a configuration diagram illustrating an example of a conventional three-phase AC measuring instrument.

[Explanation of symbols]

 1,5 Three-phase AC measuring device 6 Neutral point potential estimating unit 7 Inverter 8,9 Adder 21,22,23 Resistance 31,41,51 Voltage input unit 32,42,52 AD converter 34,44, 54 current input unit 35, 45, 55 AD converter 36, 46, 56 voltage effective value calculation unit 37, 47, 57 power calculation unit 60 secondary calculation processing unit 70 display unit

Claims (7)

[Claims] 1. A three-phase AC measuring device for measuring at least a total power value, a frequency value, and a voltage value of each phase of a three-phase three-wire AC, a current measuring circuit for measuring a phase current value of each phase, A voltage measurement circuit for measuring the inter-phase voltage value between the respective phases, and a neutral point potential estimating unit for estimating the neutral point potential value from the phase current value of each phase and the inter-phase voltage value between the phases using arithmetic means. A secondary operation processing unit for obtaining at least a total power value, a frequency value, and a voltage value of each phase of the three-phase alternating current from the phase current value of each phase, the inter-phase voltage value of each phase, and the neutral point potential value. A three-phase alternating current measuring device. 2. The method according to claim 1, wherein the neutral point potential estimating unit is configured to output a three-phase AC
An inter-phase voltage value V12 of the first phase and the second phase based on the phase;
Inter-phase voltage value V32 between the second phase and the third phase based on the second phase
The three-phase alternating current according to claim 1, wherein the neutral point potential value V02 viewed from the second phase is estimated using an equation of V02 = 1/3 x (V12 + V32). Measuring instrument. 3. The neutral point potential estimating section includes: the interphase voltage value V12, the interphase voltage value V32, and the neutral point potential value V0.
2, the phase voltage value V10 of the first phase viewed from the neutral point potential value V02, the phase voltage value V20 of the second phase viewed from the neutral point potential value V02, and the phase voltage value V20 viewed from the neutral point potential value V02. 2. The method according to claim 1, wherein the three phase voltage values V30 are estimated using the following equation: V10 = V12-V02 V20 = -V02 V30 = V32-V02. The measuring device for three-phase alternating current described in 3. 4. A three-phase AC measuring method for measuring a three-phase AC voltage effective value using a neutral point potential value and a phase voltage value of each phase viewed from the neutral point potential value, Phase voltage value V1 of the first phase viewed from value V02
0, a phase voltage value V20 of the second phase viewed from the neutral point potential value V02, and a phase voltage value V30 of the third phase viewed from the neutral point potential value V02, to generate a synthesized vector signal. A three-phase AC measurement method characterized in that the magnitude of the signal is multiplied by a coefficient to obtain an effective voltage value. 5. The three-phase alternating current measurement method according to claim 4, wherein the coefficient is √2 / 3. 6. A three-phase alternating current measuring method for measuring a three-phase alternating current frequency value using a neutral point potential value and a phase voltage of each phase viewed from the neutral potential value, the method comprising: The phase voltage value V1 of the first phase viewed
0, a phase voltage value V20 of the second phase viewed from the neutral point potential value V02, and a phase voltage value V30 of the third phase viewed from the neutral point potential value V02, to generate a synthesized vector signal. A three-phase AC measurement method, characterized in that an instantaneous frequency value is obtained by multiplying a rotation angular velocity of a signal by a coefficient. 7. A three-phase AC measuring method for measuring an instantaneous power value of three-phase AC using a neutral point potential value and a phase voltage value and a phase current value of each phase viewed from the neutral potential value. The instantaneous power value of each phase is multiplied by the instantaneous phase current value and the instantaneous phase voltage value of each phase, and the instantaneous power value of each phase is added to obtain the instantaneous power value of three-phase AC. Phase alternating current measurement method.