JPH053991Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an improvement of an electronic power flow power meter that measures power flow energy with high precision using a microcomputer.

[Technical background of the invention] In recent years, electronic watt-hour meters using microcomputers have been developed, and FIG. 1 is a diagram showing the configuration of the electronic watt-hour meter. That is, this electronic watt-hour meter includes an auxiliary transformer (PT) 1 that obtains a first voltage signal proportional to the load voltage of the power supply line, and an auxiliary transformer (PT) 1 that obtains a second voltage signal that is proportional to the consumed current flowing through the power supply line. Each voltage signal obtained by these transformers 1 and 2 is sampled by subsequent sample and hold sections 3 and 4, and then sent to an A/D conversion circuit 5. , 6 and sent to the microcomputer 7 as a pulse train voltage signal. This microcomputer 7 takes in the voltage signal converted into a pulse train by the A/D conversion circuits 5 and 6, performs multiplication, integration, and arithmetic processing of the frequency division ratio to calculate the amount of electric power.
This amount of power is displayed on the display section 8.

By the way, the above-described power meter has a configuration that is not suitable when applied to a power system where power flow occurs. In other words, power flow means that when power can be supplied between two power systems A and B,
For example, if there is a shortage of power supply in power system B, power will be supplied from power system A, and conversely, if power system A is short of power supply, power will be supplied from power system B. )
It means that the direction of Assuming that power system A is managed by power company A' and power system B is managed by power company B', when power is supplied from power system A to B, power company A' will supply power to power company B'. This means that they are selling power to power company B', and are buying power from power company B′. Therefore, in the watt-hour meter as shown in FIG. 1, when power flow occurs, the phase difference between the load voltage and the consumed current changes, making it impossible to measure the amount of power.

Therefore, conventionally, an electronic power flow watt-hour meter having a configuration as shown in FIG. 3 has been used. This electricity meter detects the phase difference between the first and second voltage signals output from the auxiliary transformer 1 and the auxiliary current transformer 2, and detects the phase difference when the phase difference differs by 180 degrees, that is, the direction of the power flow. A power flow discriminating section 10 is provided which outputs a discriminating signal when the power current discriminating section 10 becomes reversed, and a switching section provided between the auxiliary current transformer and the sample hold section 4 is provided in response to the discriminating signal sent from the power flow discriminating section 10. By switching the switch 11, the second voltage signal output from the auxiliary current transformer 2 is supplied to the inverting section 12 composed of an operational amplifier. This inversion part 1
2 inverts the input voltage signal and supplies it to the sample and hold section 4 . On the other hand, the power flow determination unit 10 outputs a discrimination signal and switches the changeover switch 13 to supply the amount of power determined by the microcomputer 7 to either the electricity sales display 14 or the electricity purchase display 15. and is displayed as electric energy. Therefore, from the display states of the displays 14 and 15, it is determined whether the amount of electric power is sold or purchased from the power company A', for example.

[Problems with Background Art] However, in the conventional power flow watt-hour meter, the inverting unit 12 outputs the output of the auxiliary current transformer 2 as is or inverted depending on the direction of the power flow.
A voltage signal containing the offset voltage of the operational amplifier is output from the switch 11, and it is affected by the switching timing of the changeover switch 11, making it impossible to accurately measure the amount of electric power. On the other hand, a delay circuit is sometimes used to match the phases of the first and second voltage signals when a power flow occurs, but when this delay circuit is used, the influence of errors in this delay circuit can be eliminated. receive. Therefore, the electric energy cannot be measured accurately.

[Purpose of the invention] This invention was made based on the above circumstances,
It is an object of the present invention to provide a highly accurate electronic power flow watt-hour meter that can accurately measure the amount of electric power.

[Summary of the invention] According to the electronic power flow wattmeter of the invention, the power flow discriminator receives the first voltage signal from the auxiliary converter and the second voltage signal from the auxiliary current transformer. It detects a phase difference, determines whether the power flow has reversed based on this phase difference, and outputs a determination signal. Upon receiving this discrimination signal, the phase signal generator outputs a phase signal having a pulse width corresponding to the phase difference between the first voltage signal and the second voltage signal when the current is reversed.

The power calculation unit receives the determination signal, and if the power flow is not reversed, the first voltage signal and the second voltage signal are taken in at any time, and the power is determined based on these voltage signals, and if the power flow is not reversed. If so, the first voltage signal is held for a period corresponding to the pulse width of the phase signal, and the amount of electric power is determined based on the first voltage signal held for this period and the second voltage signal that is taken in from time to time.

[Embodiment of the invention] Hereinafter, an embodiment of the electronic power flow watt-hour meter according to the invention will be described with reference to FIG. 4 and FIGS. 5a and 5b. FIG. 4 is a configuration diagram of an electronic power flow watt-hour meter. An auxiliary transformer (PT) 20, a sample hold section 21, an A/D conversion circuit 22, an auxiliary current transformer 23, a sample hold section 24, and an A/D conversion circuit 25 are the same as those shown in FIG.

The power flow determination unit 26 detects the phase difference between the voltage signal output from the auxiliary transformer 20 and the voltage signal output from the auxiliary current transformer 23, and when this phase difference reaches 180 degrees (π), It determines that the direction of power flow has reversed and outputs a determination signal indicating this reversal.

Now, in the watt-hour meter shown in FIG. 4, the phase of the voltage signal outputted from the A/D conversion circuit 22 and the pulse train outputted from the A/D conversion circuit 25, especially when the direction of power flow is reversed. A phase signal generating section 30 is provided that generates a phase signal for matching the phase of the converted voltage signal. Note that the phase signal S sent out from the phase signal generator 30 is π
It has a pulse width of (180 degrees) and is sent to the microcomputer 31. This microcomputer 31 takes in the voltage signals output from the A/D conversion circuits 22 and 25, performs arithmetic processing of multiplication, integration, and frequency division on these taken-in voltage signals to obtain the electric energy, and also calculates the phase The voltage signal sent out from the A/D conversion circuit 22 and taken in from the time when the signal was taken is held for a period corresponding to the pulse width of the phase signal, and the held voltage signal and the A/D conversion circuit 22 are held for a period corresponding to the pulse width of the phase signal.
It has a function of calculating the amount of electric power by performing the same arithmetic processing as described above on the voltage signal sent out from the conversion circuit 25 and taken in. Naturally, this microcomputer 31 is comprised of a central processing unit (CPU), memory, internal bus, input/output interface, and the like. Then, the power amount signal indicating the power amount determined by the microcomputer 31 is sent to the changeover switch 32 which is switched by the determination signal sent from the power flow determination section 26.
The power selling display 33 or the power purchasing display 3
It is configured to be sent to 4.

Next, the operation of the electricity meter configured as described above will be explained. Note that, as shown in FIG. 2, the case where power is supplied from the power system A to the power system B will be described as a forward direction (power sale), and the opposite direction as a reverse direction (power purchase). When the direction of the power flow is positive, the first voltage signal ev proportional to the load voltage output from the auxiliary transformer 20 is output from the sample hold section 21.
The signal is sampled, momentarily held, and sent to the A/D conversion circuit 22, where it is converted into a pulse train signal and sent to the microcomputer 31. At the same time, a second voltage signal ei proportional to the consumed current output from the auxiliary current transformer 23 is sampled by the sample and hold section 24, converted into a pulse train signal by the A/D conversion circuit 25, and sent to the microcomputer 31. Sent out. The microcomputer 31 takes in the voltage signals of these pulse trains and stores them in its own memory.

At this time, the voltage signal ev output from the auxiliary transformer 20 and the voltage signal ei output from the auxiliary current transformer 23 are in phase as shown in FIG. determines that the direction of power flow is the positive direction. As a result, the phase signal generating section 30 sends out the phase signal S at the "L" level to the microcomputer 31. The microcomputer 31 then calculates the amount of power by performing arithmetic processing such as multiplication, integration, and frequency division on each voltage signal stored in the memory, and transmits the amount of power signal indicating this amount of power via the switch 32. It is sent to the power selling display 33.

Here, assume that power system A is insufficiently supplied with power and power is supplied from power system B.
Then, the auxiliary transformer 20 and the auxiliary current transformer 2
The respective voltage signals ev and ei outputted from 3 are as shown in FIG. 5b. That is, since the direction in which the consumed current flows is reversed, the voltage signal output from C.T23 is inverted. The power flow determining unit 26 detects that the phases of these voltage signals ev and ei are shifted by 180 degrees, and determines that the direction of the power flow is reversed.
Then, the phase signal generating section 30 generates a voltage signal as shown in FIG.
A phase signal S that rises and falls at the zero cross point of ev and ei, that is, a phase signal S having a pulse width of π (180 degrees) is sent to the microcomputer 31. Then, the microcomputer 31 holds the voltage signal taken in from the A/D converter 22 for a period corresponding to the pulse width of the phase signal S, and uses this held voltage signal and the A/D converter that is taken in from time to time. 25
When the phase signal S falls, calculation processing such as multiplication, integration, and frequency division is performed on the voltage signal from the phase signal S to obtain the electric energy. In other words, the voltage signal ev shown in Figure 5b is 180
The electric energy is determined by the delayed voltage signal ev' and the voltage signal ei. Then, the power amount signal sent out from the microcomputer 31 is sent to the power purchase display 34 via the changeover switch 32 which is switched by the discrimination signal sent out from the power flow discrimination section 26.

In this way, in the power meter of the present invention, if the power flow determining section 26 determines that the direction of the power flow is reversed, the phase signal generating section 30 outputs π
A phase signal S having a pulse width of After this holding, the amount of electric power is calculated and determined.
It does not use an inverting section consisting of an operational amplifier as in conventional systems, so it is not affected by the offset voltage of the operational amplifier, and can accurately measure the amount of power with a simple configuration. Without using a delay circuit or a changeover switch for matching the phases of the first and second voltage signals when a power flow occurs, it is possible to eliminate the influence of errors caused by these delay circuits and changeover switches. In addition, when the direction of power flow is reversed, the execution time of the multiplication of each voltage signal, that is, the multiplication by the microcomputer 31, is determined by the A/D conversion circuit 2.
Since the voltage signal from 2 is held and executed at the falling edge of the phase signal S, the execution time can be easily adjusted.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without changing the gist thereof.

[Effects of the invention] According to the invention, it is possible to eliminate the influence of the offset voltage of the operational amplifier constituting the inverting section and the influence of errors caused by delay circuits, changeover switches, etc., and to reduce the amount of power in the power system where power flow occurs. It is possible to provide an electronic power flow watt-hour meter that can accurately measure electricity.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional electronic watt-hour meter, Figure 2
The figure is a schematic diagram for explaining power flow, FIG. 3 is a configuration diagram of a conventional electronic power flow watt-hour meter, and FIG. 4 is an embodiment of an electronic power flow watt-hour meter according to the present invention. The configuration diagram, FIG. 5, is a diagram for explaining the operation of the electricity meter of the present invention. 20...Auxiliary transformer (PT), 21...Sample hold section, 22...A/D conversion circuit, 23...
... Auxiliary current transformer (CT), 24 ... Sample hold section, 25 ... A/D conversion circuit, 26 ... Power flow discrimination section, 30 ... Phase signal generation section, 31 ... Microcomputer, 32 ... Switching Switch, 33...
...Indicator for electricity sales, 34...Indicator for electricity purchase.

Claims (1)

[Claims for Utility Model Registration] An auxiliary transformer that converts into a first voltage signal proportional to the load voltage applied to the power supply line, and an auxiliary transformer that converts the voltage signal into a second voltage signal proportional to the consumed current flowing through the power supply line. a power flow discriminator that detects a phase difference between the first voltage signal and the second voltage signal, determines from this phase difference whether the voltage flow has reversed, and outputs a determination signal thereof; , a phase signal that outputs a phase signal with a pulse width corresponding to the phase difference between the first voltage signal and the second voltage signal when the power flow is reversed in response to the discrimination signal output from the power flow discrimination section; a generating section; if the power flow is not reversed according to the discrimination signal, the first voltage signal and the second voltage signal are acquired at any time to obtain the power based on these voltage signals, and the power is determined from the discrimination signal; If the current is reversed, the first voltage signal is held for a period of the pulse width of the phase signal, and the first voltage signal held for this period is
1. An electronic power flow wattmeter, comprising: a power calculation section that calculates the amount of power based on the voltage signal and the second voltage signal that is taken in from time to time.