JP3491676B2 - Measuring instrument for three-phase AC - Google Patents

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 instrument for measuring three-phase alternating current and a three-phase alternating current measuring method, and particularly to a neutral point potential value in the measurement of three-phase three-wire alternating current. The present invention relates to a three-phase alternating current measuring instrument having a function of estimating by a calculation means.

[0002]

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

In FIG. 2, resistors 21, 22 and 23 are Y-connected resistors having the same resistance value 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 the three-phase alternating current.

The voltage input section 31 incorporated in the measuring instrument 1 is
It is connected between the first-phase power supply line 11 of three-phase alternating current and the neutral point a and measures the voltage value of the first phase, 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 voltage value of the first phase and the current value of the first phase obtained here are converted into digital values by the AD converters 32 and 35 and input to the voltage effective 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 the power value based on the instantaneous voltage value and the instantaneous current value input from the AD converters 32 and 35, respectively.

Similarly, the voltage value and the power value of the second phase and the third phase can be obtained by the circuit from the voltage input section 41 to the power calculation section 57.

The secondary operation processing unit 60 uses the voltage effective value and power value for each phase to determine the voltage value, current value, total power value, etc. of each phase of the three-phase power supply, which are required by the user (hereinafter, It is called the representative value of three-phase alternating current). For example, the secondary calculation processing unit 6
0 is an effective value voltage obtained by temporally averaging the voltage effective values measured for each phase by the method described above, and averaging them to obtain a representative voltage value of three-phase alternating current. calculate. Further, the secondary arithmetic processing unit 60 measures, for example, the time T for n cycles of the voltage effective value of the first phase from the voltage effective value measured for each phase by the method described above,
The frequency f was calculated as f = n / T (Hz).

The secondary calculation processing unit 60 displays the representative value of the three-phase alternating current obtained in this way on the display unit 70.

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

[0010]

In the conventional three-phase AC measuring instrument, a three-phase three-wire type AC power source as in the conventional example shown in FIG. 2 is used for the purpose of facilitating the interpretation of measured values. You may 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, in the conventional three-phase AC measuring instrument, the voltage effective value and power value averaged over time are obtained for each phase, and the values are used as a representative value of the three-phase AC as a secondary calculation process. Because I was looking for
There is a problem that the followability to changes in load and power supply is poor.

The present invention solves the above-mentioned problems and provides a three-phase AC measuring instrument with a function of estimating a pseudo-neutral point potential inside the measuring instrument as well as an instantaneous value of a measuring voltage, a measuring current, or the like. An object of the present invention is to provide a measuring instrument for three-phase alternating current capable of obtaining a representative value of three-phase alternating current by using.

[0012]

In order to achieve such an object, according to the invention described in claim 1, a three-phase alternating current for measuring at least a total power value, a frequency value and a voltage value of each phase of the three-phase alternating current. In the measuring instrument for current, from the current measurement circuit that measures the phase current value of each phase, the voltage measurement circuit that measures the interphase voltage value between each phase, from the phase current value of each phase and the interphase voltage value between each phase From the neutral point potential estimation unit that estimates the neutral point potential value using a computing unit, the phase current value of each phase, the interphase voltage value of each phase, and the neutral point potential value, at least the total of three-phase AC It is characterized in that it is provided with a secondary arithmetic processing unit for obtaining an electric power value, a frequency value, and a voltage value of each phase.

As a result, the neutral point potential value of the three-phase three-wire type AC can be obtained by using the phase current value of each phase and the interphase voltage value between each phase, and the representative value of the three-phase AC can be measured. Become.

According to the second aspect of the present invention, this is the inter-phase voltage value V12 of the first phase and the second phase based on the second phase of the three-phase alternating current.
And the interphase voltage value V of the second phase and the third phase based on the second phase
32, it can be realized by estimating the neutral point potential value V02 seen from the second phase using the equation V02 = 1/3 × (V12 + V32).

Further, according to a third aspect, the interphase voltage value V
12, the interphase voltage value V32, and the neutral point potential value V02
Using, 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 third phase voltage value viewed from the neutral point potential value V02. It becomes possible to measure the phase voltage value V30 of the phase using the formula of V10 = V12−V02 V20 = −V02 V30 = V32−V02.

In the invention described in claim 4, the invention described in claim 1
In the invention described above, the secondary operation processing unit may include a phase voltage of the first phase viewed from the neutral point potential value, a phase voltage value of the second phase viewed from the neutral point potential value, and the neutral point. It is characterized in that a combined vector signal is generated from the phase voltage value of the third phase viewed from the potential value, and the magnitude of this combined vector signal is multiplied by a coefficient to obtain the voltage effective value.

As a result, the effective voltage value of the three-phase alternating current can be directly obtained from the scalar quantity of the vector obtained by combining 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 AC.

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

According to the invention of claim 6 ,
In the invention described above, the secondary operation processing unit may include a phase voltage value of the first phase viewed from the neutral point potential value, a phase voltage value of the second phase viewed from the neutral point potential value, and the neutrality. A combined vector signal is generated from the phase voltage value of the third phase viewed from the point potential value,
It is characterized in that the rotational angular velocity of the composite vector signal is multiplied by a coefficient to obtain an instantaneous frequency value.

As a result, the frequency value of the three-phase AC can be obtained by multiplying the rotational angular velocity of the vector obtained by combining the phase voltages of the respective phases by the coefficient. Further, it is possible to obtain the instantaneous frequency value of the three-phase AC by using the instantaneous value for the phase voltage of each phase.

According to the invention of claim 7 , in claim 1,
In the invention described above, the secondary arithmetic processing unit multiplies the instantaneous phase current value and the instantaneous phase voltage value for each phase to obtain the instantaneous power value for each phase, and adds them to obtain the instantaneous value of the three-phase AC. It is characterized in that it is configured to obtain a power value.

As a result, when measuring the instantaneous power of the three-phase alternating current, it is possible to measure the instantaneous power with good responsiveness to changes in the load and the power supply.

[0023]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. The difference between the three-phase AC measuring device of the present invention and the conventional example is that the conventional three-phase AC measuring device 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 measuring device for three-phase alternating current in FIG.
The voltage input section 31 is connected to the first phase and the second phase of the three-phase alternating current and measures the voltage value V12 of the first phase and the second phase with the second phase as a reference. The voltage values V32 of the third phase and the second phase, which are connected to the third phase and the second phase of the alternating current and are based on the second phase, are measured. 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 estimation unit 6.

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

The neutral point potential estimation unit 6 estimates the neutral point potential value V02 seen 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 viewed from the neutral point potential value V02 are respectively V10 = V12-V02 (2) It can be expressed as V20 = -V02 (3) V30 = V32-V02 (4). This corresponds to the voltage value of each phase when the three-phase three-wire type AC is Y-connected and considered as the three-phase four-wire type AC.

In the three-phase AC measuring instrument 5 of the present invention, the neutral point potential estimating section 6 performs the calculation of the above equation (1), inputs this output to the inverter 7, and outputs the output by the adder 8. By adding it to the output of the AD converter 32, the voltage V value 10 of the first phase represented 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 represented by the equation (4) is obtained. The output of the inverter 7 is the second-phase voltage value V20 represented by the equation (3) as it is.

Next, in the three-phase AC measuring instrument 5 of the present invention, the voltage value V10 of the first phase, which is the output of the adder 8 and the output of the inverter 7, which are obtained by the above configuration, are obtained. The voltage value V20 of the two phases and the voltage value V30 of the third phase, which is the output of the adder 9, are respectively calculated by the voltage effective value calculation units 36, 46, 56 and the power calculation unit 37 corresponding to the respective phases, as in the conventional example. Four
Input to 7 and 57 to calculate the voltage effective value and power value of each phase.

The secondary calculation processing unit 60 calculates the representative value of the three-phase AC of the three-phase power supply from the voltage effective value and the power value for each phase as in the conventional example, and displays these values on the display unit 70. indicate.

In this way, the three-phase AC measuring instrument 5 of the present invention uses the three-phase three-wire type AC to the outside without using an external device such as a resistor, and the three-phase values such as the value of each phase and the total power value. It is possible to measure a representative value of alternating current and selectively display it on the display unit 70.

Further, the secondary calculation processing unit 60 and the power calculation unit 3
There are various methods for calculating the representative value of the three-phase alternating current 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 voltage effective value and the frequency value. By using this method, it is possible to construct a voltage measuring device having good responsiveness to voltage fluctuations. (Also, the method of generating a combined vector signal using the voltages of the three-phase alternating current phases described below and multiplying this by a coefficient to obtain the voltage effective value and the frequency value is the three-phase described in FIG. Needless to say, it can be realized by using the AC measuring device 5, but it can be realized by making a slight modification even if the conventional three-phase AC measuring device or the three-phase four-wire measuring device described in FIG. 2 is used. Is possible.)

For example, when the instantaneous vector V0 of the three-phase voltage is expressed on the complex plane using the voltages V10, V20, V30 of each phase obtained by the configuration of FIG. 1, V0 = V10 × (1 + j0) + V20 × ( −1 + j√3) / 2 + V30 × (−1−j√3) / 2 (5). However, j is an imaginary unit.

Here, the instantaneous vector V0 of the above three-phase voltage
The absolute value, that is, the length, corresponds to the total power value of the three-phase alternating current, and can be obtained by obtaining the square root of the sum of squares of the real part and the imaginary part of the above equation (5).

Further, the absolute value of the instantaneous vector V0 of the three-phase voltage obtained here is converted into an effective value by changing the average value of the square of the sine wave.
Convert the average value of the sum of √2 and the three phases to the average value of each phase
To 1/3, i.e. by multiplying the √2 / 3, Y
The voltage effective value of each phase of the connected power supply can be obtained. This value is a constant value irrespective of time when the power source is a distortion-free symmetrical three-phase with constant amplitude and the power source is supplied to a symmetrical three-phase load. Therefore, it is not necessary to use a ripple filter when measuring the voltage of a symmetrical power source with small distortion.

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

[0039] The deflection angle theta of the instantaneous vector V0 of the three-phase voltage, θ = tan ^{- 1} ((the imaginary part of the V0) / (real part of the V0)) can be obtained by (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 source are in a proportional relationship, the instantaneous frequency can be obtained by multiplying this by an appropriate coefficient.

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

In addition to the method of calculating the total power value of three-phase AC described above, there is a method of calculating the total power value of three-phase AC using the instantaneous current value and the instantaneous voltage value of each phase. In the three-phase AC measuring instrument of FIG.
7, 47, 57 and the secondary calculation processing unit 60 are used to multiply the instantaneous current value and the instantaneous voltage value for each phase to obtain the instantaneous power value for each phase, and by adding these, the three-phase AC This is a method of obtaining the total power value.

The total power value of the three-phase alternating current obtained by using this method is a symmetrical three-phase power source having no distortion and constant amplitude, and this power source is supplied to the symmetrical three-phase load. , It becomes a constant value regardless of the power factor of the load. Therefore, it is not necessary to use a ripple filter when measuring the voltage of a symmetrical power source with small distortion. Further, the method for obtaining the total power value of the three-phase alternating current by using the instantaneous current value and the instantaneous voltage value of each phase of the three-phase alternating current described above can be realized by using the three-phase alternating current measuring device 5 described in FIG. Needless to say,
It is also possible to use the conventional three-phase AC measuring instrument or the three-phase four-wire measuring instrument described in FIG.

The above description merely shows specific preferred embodiments for the purpose of explaining and exemplifying the present invention. Therefore, the present invention is not limited to the above-mentioned embodiment, and many modifications are made without departing from the essence thereof.
It also includes deformation.

[0045]

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

According to the invention described in claims 4 to 7, it is possible to realize the measurement of the three-phase alternating current having a good responsiveness to the fluctuation of the load and the power supply. In particular, when measuring an extremely low frequency three-phase AC voltage with an inverter application device or the like, it is not necessary to remove the ripple for each phase, and therefore the measurement becomes easy. Further, according to the three-phase alternating current measuring method of the present invention, it is possible to perform measurement based on the instantaneous voltage. Therefore, for example, when applied to a device that displays voltage values in a graph, voltage fluctuations depending on sudden changes in load, etc. It is also possible to notify the observer.

[Brief description of drawings]

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

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

[Explanation of symbols]

1,5 Three-phase AC measuring instrument 6 Neutral point potential estimation section 7 Inverter 8,9 adder 21,22,23 resistance 31, 41, 51 Voltage input section 32, 42, 52 AD converter 34, 44, 54 Current input section 35, 45, 55 AD converter 36, 46, 56 Effective voltage value calculator 37, 47, 57 Power calculator 60 Secondary calculation processing unit 70 Display

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-34678 (JP, A) JP-A-64-84158 (JP, A) JP-A-9-89949 (JP, A) JP-A-5- 87853 (JP, A) JP 7-98344 (JP, A) Actual development 4-47666 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 21/00-22 / 00 130 G01R 11/00-11/66

Claims (7)

(57) [Claims] 1. A current measuring circuit for measuring a phase current value of each phase in 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 type AC. A voltage measuring circuit for measuring the interphase voltage value between each phase, and a neutral point potential estimation unit for estimating the neutral point potential value from the phase current value of each phase and the interphase voltage value between each phase by using a computing means. A secondary operation processing unit for obtaining at least the total power value, the frequency value, and the voltage value of each phase of the three-phase alternating current from the phase current value of each phase, the interphase voltage value of each phase, and the neutral point potential value. This is a measuring instrument for three-phase alternating current. 2. The neutral point potential estimator is a second phase three-phase alternating current.
The interphase voltage value V12 of the first phase and the second phase based on the phase,
Phase-to-phase voltage value V32 of the second and third phases based on the second phase
3. The three-phase alternating current according to claim 1, wherein the neutral point potential value V02 seen from the second phase is estimated by using the equation V02 = 1/3 × (V12 + V32). Measuring instrument. 3. The neutral point potential estimation unit is configured to have 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 seen from the neutral point potential value V02, the phase voltage value V20 of the second phase seen from the neutral point potential value V02, and the phase voltage value V02 seen from the neutral point potential value V02. The phase voltage value V30 of the three phases is configured to estimate the phase voltage value of each phase using the formula of V10 = V12-V02 V20 = -V02 V30 = V32-V02. The measuring instrument for three-phase alternating current according to. 4. The secondary operation processing unit, the phase voltage value of the first phase viewed from the neutral point potential value, the phase voltage value of the second phase viewed from the neutral point potential value, and the neutrality. Third seen from the point potential value
It generates a composite vector signal from the phase voltage of the phase, according to claim 1, characterized in that it is configured to determine the effective voltage value by multiplying the coefficient to the magnitude of the combined vector signal
Three-phase alternating current for measuring instruments. 5. The three-phase AC measuring instrument according to claim 4, wherein the coefficient is √2 / 3. 6. The secondary operation processing unit, the phase voltage value of the first phase viewed from the neutral point potential value, the phase voltage value of the second phase viewed from the neutral point potential value, and the neutrality. Third seen from the point potential value
The composition vector signal is generated from the phase voltage value of each phase, and the rotational angular velocity of the composition vector signal is multiplied by a coefficient to obtain an instantaneous frequency value . Measuring equipment for three-phase alternating current. 7. The secondary arithmetic processing unit multiplies an instantaneous phase current value and an instantaneous phase voltage value for each phase to obtain an instantaneous power value for each phase, and adds them to obtain an instantaneous three-phase AC. The measuring instrument for three-phase alternating current according to claim 1, which is configured to obtain an electric power value.