JPH0634678A - Polyphase wattmeter - Google Patents

Abstract

PURPOSE:To obtain a polyphase wattmeter which can measure the power of multiple phases. CONSTITUTION:The title wattmeter is provided with a plurality of sample/hold circuits 21v-2ni for simulteously sampling the voltage waveform and the current waveform which are added via input terminals P1v-Pni which are provided for each input channel, switcher 4 and 8 for switching and taking out the output voltage of the sample/hold circuits 21v-2ni, A/D converters 6 and 10 for introducing the output of the switcher 4 and 8 and then converting to a digital signal, and an operation means 22 for calculating the power of each phase and the total of power of each phase based on the digital signal value. Further, it is also provided with a first phase calculator 31 for introducing the digital signal which is output by the A/D converter 22 and then calculating the phase difference between the voltage and current for each phase based on the digital signal value and a second phase calculator 33 for calculating the phase difference between voltages at each phase based on the digital signal value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyphase power meter for measuring polyphase power using a digital sampling system.

[0002]

2. Description of the Related Art In recent years, as a result of an increase in equipment (harmonic generation sources) for extracting electric power in a pulsed manner, the power line has come to contain many harmonics. For example, many companies that are specific customers include a power conversion device as a power facility. In recent power converters, the principle of extracting power in a pulsed manner using a thyristor or the like is increasing, and therefore a large amount of high frequency is discharged to the power line.

In addition, even in a general household, television,
Since many devices such as room air conditioners that generate harmonics have become widespread, harmonics are flowing out to the power line.

As a countermeasure for suppressing the harmonics on the power line, a method is known in which the transformer section of the power converter, which is a harmonic generation source, is multi-phased to suppress the amount of harmonic generation itself. There is. Most of the power converters used by specific customers are based on a 6-phase rectifier circuit. This is multi-phased according to 12-phase, 18-phase, ... 6m phase (m is an integer: 1, 2, ...) And converter capacity to reduce 6m ± first-order harmonics.

[0005]

Therefore, single-phase and three-phase are predominant at present, but future power lines will be
It is considered to be polymorphic. On the other hand, looking at the wattmeters that measure electric power, like the single-phase wattmeter and the three-phase wattmeter, they are divided into single-phase and three-phase types, respectively, and are specially configured.
There is no multi-phase power meter that can easily measure various multi-phase power such as 6-phase, 12-phase, ...

An object of the present invention is to provide a polyphase power meter capable of measuring multiphase power using a digital sampling system.

[0007]

According to the present invention, in each of the input terminals, a device for measuring the power value of the polyphase alternating current by introducing the respective voltage waveform and current waveform constituting the polyphase alternating current into each input channel. A plurality of sample and hold circuits that are provided for each of the sample and hold circuits that simultaneously sample the voltage waveform and the current waveform applied via the input terminal, and a switch that sequentially extracts and outputs the output voltage of each sample and hold circuit;
An AD converter that introduces the output of the switching device, converts the digital signal into a digital signal, and introduces the digital signal output by the AD converter, and based on the digital signal value, the active power of each phase and each phase Introducing a calculation means for calculating the total sum of active power of, and a digital signal output from the AD converter,
A first phase calculator that calculates a phase difference between voltage and current for each phase based on the digital signal value and a digital signal output from the AD converter are introduced, and each phase is based on the digital signal value. Second for calculating the phase difference between the voltages at
And a phase calculator of.

[0008]

In the present invention, the instantaneous value of the voltage and current of each phase applied to each input terminal at the same time is obtained as a digital value by the operation of the sample and hold circuit, the switching device and the AD converter. The calculating means obtains the instantaneous power value V _K · i _K from the voltage V _K and the current i _{K for} each phase, which are digital values, and further calculates the average value of the instantaneous power values to calculate the active power for each phase. Ask for. Further, it is also possible to obtain the total sum of active power of each phase.

The first phase calculator calculates the phase difference between the voltage and the current for each phase based on the digital signal value. That is, the power factor for each phase is calculated. The second phase calculator is
The phase difference between the voltages in each phase is calculated based on the digital signal value. Therefore, the symmetry of each phase can be known.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a configuration example of a polyphase power meter according to the present invention, and FIG. 2 is a voltage / current vector diagram in the case of 6 phases. In FIG. 1, input terminals P _{1V to} P _ni have respective voltage waveforms V _{1 to} V _n and current waveform i ₁ forming a polyphase alternating current.
~i _n is added. That is, FIG. 1 is an example in the case of measuring n-phase AC power.

2_1V~ 2_niIs a sample and hold circuit
(Hereinafter referred to as S / H circuit), and each
Input terminal P_1V~ P_niIt is provided for each. Each S / H
Circuit 2 _1V~ 2_niIs connected via the isolators 14 and 16.
A timing signal is added from the troll circuit 20,
Voltage wave being applied in synchronization with this timing signal
Shape V₁~ V_nAnd current waveform i₁~ I_nSimultaneously sample
It is a thing. That is, each time a timing signal is added,
Voltage waveform V at that time₁~ V_nAnd current waveform i ₁~ I_n
The instantaneous analog value of
It

Numerals 4 and 8 are switching devices, and an isolator 14,
According to the command signal applied from the control circuit 20 via 16, the output voltage of each S / H circuit _21V to _2ni is switched in order and taken out to the next stage. Reference numerals 6 and 10 denote AD converters, which are voltage waveforms V ₁ introduced through the switches 4 and 8.
˜V _n and the instantaneous analog values of the current waveforms i _{1 to} i _n are converted into digital signals.

Numerals 12, 14, 16 and 18 are isolators which electrically insulate the input circuit side and the digital signal processing circuit (20, 22, 24) side from each other to protect the digital signal processing circuit. is there. As the isolator, for example, a pulse transformer or a photo coupler is used. Reference numeral 20 is a control circuit for controlling the AD converters 6 and 10 and the switches 4 and 8 via the isolators 14 and 16 as described above.

Reference numeral 22 denotes an arithmetic unit, which receives digital signals from the AD converters 6 and 10 and performs arithmetic operations on the digital signals to calculate active power of each phase, sum of active power of each phase, voltage and current of each phase. And the phase difference between the voltages in each phase. In order to obtain these measured values, the calculator 22 has an effective value calculator 25, a power calculator 27, a total power calculator 29, a first phase calculator 31, and a second phase calculator 33. Is equipped with. The memory 23 temporarily stores the data from the AD converters 6 and 10 and the data obtained by the effective value calculator 25 and the like.

Reference numeral 24 is an MSU for controlling the entire apparatus of FIG.

The operation of the apparatus of FIG. 1 configured as described above will be described with reference to FIG. Since it is easier to understand in a concrete manner, it is assumed here that the six-phase power is measured. That is, this is the case where n = 6 in FIG. Further, FIG. 2 is a vector diagram of 6 phases,
V ₁ , V ₂ , V ₃ , ... Are neutral point potentials, i ₁ , i ₂ , i ₃ ,.
Is the line current, V ₁₂ , V ₂₃ , V ₃₄ , ... Is the line voltage, i
₁₂ , i ₂₃ , i ₃₄ , ... Represent ring load currents.

The voltage V ₁ and the current i ₁ of the first phase are input to the input terminal P
It is added to _1V and P _1i , and sampled and held by the S / H circuits 2 _1V and 2 _1i . Similarly, the voltages V ₂ , V ₃ , ... And the currents i ₂ , i ₃ ,.
/ H circuits are sampled and held by 2 _2V , 2 _2i , ....

Each S / H circuit 2_1V, 2_1i, 2_2V, ...
From the control circuit 20 via the isolators 14 and 16
The timing signal is added
A sampling operation is performed when the voltage is applied. Control times
Path 20 is for all S / H circuits 2 _1V, 2_1i, 2_2V, 2_2i、…
Timing signals such that the sample operations are performed at the same time
Is output. The switches 4 and 8 are the S / H circuit 2_1V, 2_1i，
Two_2V, 2_2iThe output voltage of ...
Add to converters 6, 10. In addition, which S /
The control circuit 20 controls whether to select the H circuit.
U

The AD converters 6 and 10 convert the analog signals introduced from the switches 4 and 8 into digital signals. Therefore, at a certain time t1, the digital values of the instantaneous values of the voltage and current of each phase sampled at the same time are A
Obtained from D converters 6 and 10. When the sampling data at time t1 are all converted to digital signals, the next timing signals are added to the S / H circuits 2 _1V , 2 _1i , 2 _2V , ... The operation is repeated.

As described above, in the device of FIG. 1, at a certain time t1, the voltages V ₁ , V ₂ , V ₃ , ... And the currents i ₁ , i ₂ ,
The instantaneous values of i ₃ , ... Are sampled all at once, and at time t1
The same operation is repeated at subsequent times t2, t3, ....

The computing unit 22 receives the digital signals D _V and D _i of the instantaneous voltage value and the instantaneous current value of each phase from the AD converters 6 and 10 via the isolators 12 and 18, and calculates them. , Active power of each phase, sum of active power of each phase, phase difference between voltage and current for each phase, and phase difference between voltages in each phase are calculated. Below, RMS value calculator 2 built in calculator 22
5, the operation of the power calculator 27, the total power calculator 29, the first phase calculator 31, and the second phase calculator 33 will be described.

The effective value calculator 25 comprises a multiplier, an averaging means and a square root calculator. For example, if the same instantaneous voltage V _k is applied to the two input terminals of the multiplier, V _K
You get ² . Since this V _K ² is added to the averaging means, A = (1 / M) · Σ _K V _K ² is obtained as its output A. Since the square root calculator squares the signal A, the next signal B can be obtained.

B = {(1 / M) Σ _K V _K ² } ^1/2 Σ _K is a symbol indicating the addition and sum calculation when K = 1 to M is changed. This signal B means the effective value of the introduced voltage V _K.

The power calculator 27 can be composed of a multiplier and an averaging means. The multiplier of this power calculator 27 uses the instantaneous voltage value V for each phase sampled at the same time.
_The instantaneous electric power value V _K · i _K is obtained by multiplying _K by the instantaneous current value i _K. The averaging means calculates the average value of the instantaneous power values to obtain the active power P _n for each phase. For example, the first phase will be described. The instantaneous power value V ₁₁ · i ₁₁ is obtained by multiplying the instantaneous voltage value V ₁₁ of the first phase and the instantaneous current value i ₁₁ based on the sampling at time t1. Next, the instantaneous power value V ₁₂ · i ₁₂ is obtained by multiplying the instantaneous voltage value V ₁₂ of the first phase and the instantaneous current value i ₁₂ based on the sampling at time t2. In this way one after another
By obtaining the instantaneous power value of the phase and performing the calculation of equation (1), the average value of the instantaneous power values, that is, the active power value P of the first phase
You can get _one .

P ₁ = (1 / j) Σ _m V _1m · i _1m (1) Σ _m is a symbol indicating the addition and sum operation when changing from m = _{1 to} j. The calculation of the equation (1) is a so-called arithmetic average calculation, but can be executed by a known calculation technique.

Thereafter, in the same manner, the power calculator 27 is
The active power P ₂ of the phase, the active power P ₃ of the _third phase, the active power P ₄ of the fourth phase _, ... Can be obtained. Total power calculator 29
Can introduce the above-mentioned P ₁ , P ₂ , P ₃ , ... And perform the operation of the equation (2) to obtain the total active power P _T (total power) of each phase. P _T = P ₁ + P ₂ + P ₃ + P ₄ + ... (2)

The first phase calculator 31 introduces the effective value data of the voltage and current of each phase obtained by the effective value calculator 25 and the active power data P _n obtained by the power calculator 27, A calculation is added to this to calculate the phase difference between the voltage and the current for each phase.
That is, the phase angle of cosφ ₁ , cosφ ₂ , cosφ ₃ , ... (Power factor of each phase) in FIG. 2 is calculated. The operation is as follows. Due to the above-described function, the effective value calculator 25 has effective values V _1e , V _2e , V _3e , ..., V _6e of voltages for each phase and effective values i _1e , i _2e , i _3e , ..., i of currents. Calculate _6e . Also,
The power calculator 27 calculates the active powers P ₁ , P ₂ , ..., P ₆ for each phase as described above.

The first phase calculator 31 performs the following equation to calculate cosφ ₁ , cosφ ₂ , cosφ ₃ , ... In FIG.
To calculate. cosφ ₁ = P ₁ / (V _1e · i _1e ) (3) cosφ ₂ = P ₂ / (V _2e · i _2e ) (4) _：: Note that the symmetry and asymmetry of the power supply and the load in FIG. Although the vector diagram changes, the effective values V _e and i _e of the voltage and current for each phase
And the effective power P _{n of} each phase are obtained, and the expressions (3) and (4) are obtained.
The required phase angle can be calculated by calculating the equation.

The second phase calculator 33 is the first phase calculator.
By performing the same calculation as in 31, the phase difference between the voltages in each phase, that is, the phase angle of θ ₁ , θ ₂ , ... In FIG. 2 is calculated. The reason why the phase angles of θ ₁ , θ ₂ , ... Are obtained by performing the same calculation as that of the first phase calculator 31 will be described. The first phase calculator 31 to determine the phase angle phi ₁ of the two vectors for example in FIG. 2 V ₁ and i _1, firstly, V ₁
And the effective values V _1e and i _1e of i ₁ are obtained. Furthermore, P shown in equation (1)
_{Get one} . Then, cosφ ₁ is obtained by performing the calculation of the equation (3).

The second phase calculator 33, the case of obtaining the phase angle theta ₁ of the two vectors V ₁ and V ₂ in FIG. 2, also vector V ₁ the vector V ₁ in the first phase calculator 33 described above As a result, the effective value V _1e is obtained. By replacing the vector i ₁ in the first phase calculator 33 described above with the vector V ₂ , an effective value V _2e is obtained. P ₁ = (1 / j) Σ _{m in the} above-mentioned first phase calculator 33
Instead of the V _1m · i _1m, and _{G 1 = (1 / j)} Σ m V 1m · V 2m, obtain G _1. From the above obtained V _1e , V _2e and G ₁ , the operation of the equation (5) is performed to obtain cos θ ₁ .

Cos θ ₁ = G ₁ / (V _1e · V _2e ) (5) Hereinafter, cos θ ₂ , cos θ ₃ , ... Can be calculated in the same manner.

Although FIG. 1 illustrates an example in which two switching devices and two AD converters are provided, one switching device and one AD converter may be provided.

[0033]

As described above, according to the present invention, it is possible to easily measure arbitrary multiphase power.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a polyphase power meter according to the present invention.

[Fig. 2] Voltage / current vector diagram for 6-phase

[Explanation of symbols] 2 _1V , 2 _1i , 2 _2V , ... Sample and hold circuit 4, 8 Switching device 6, 10 AD converter 12, 14, 16, 18 Isolator 20 Control circuit 22 Operation unit 23 Memory 25 Effective value operation Unit 27 Power calculator 31 First phase calculator 33 Second phase calculator

Claims (1)

[Claims] Claim: What is claimed is: 1. In a device for measuring the power value of a polyphase alternating current by introducing each voltage waveform and current waveform constituting the polyphase alternating current into each input channel, the device is provided for each input terminal, A plurality of sample and hold circuits that simultaneously sample the voltage waveform and the current waveform applied via the switch, a switcher that sequentially switches and extracts the output voltage of each sample and hold circuit, and introduces the output of this switcher, An AD converter that converts this into a digital signal, and a digital signal output by this AD converter are introduced, and the active power of each phase and the sum of the active power of each phase are calculated based on this digital signal value. Means for introducing a digital signal output from the AD converter, and calculating a phase difference between voltage and current for each phase based on the digital signal value; Introducing a digital signal D converter output, a second phase calculator for calculating a phase difference between the voltage between the phases on the basis of the digital signal values, a multi-phase power meter equipped with a capital.