JPS6247255B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electronic apparent watt-hour meter.

Conventionally, two methods have been considered for measuring the apparent power amount. One is to receive two signals from an active energy meter and a reactive energy meter, calculate √ ² + ² from active power P and reactive power Q,
Another method for determining the apparent power is the method shown in FIG. In FIG. 1, 1 is an instrument transformer that takes out a signal proportional to the load voltage, and 2 is a current transformer that takes out a signal proportional to the consumed current. As a result, a signal proportional to the load voltage and current consumption is extracted. These signals are then converted into DC signals through rectifier circuits 3 and 4. After that, each DC signal is multiplied by the multiplier 5,
The apparent electric energy is obtained by integrating by the integrating section 6.

These two methods are generally known, but the former method has the disadvantage that the system becomes slightly larger and requires an active watt-hour meter and a reactive watt-hour meter. In addition, the latter has the disadvantage that highly accurate measurement cannot be performed because the characteristics of the rectifier circuit (characteristics of diodes, etc.) directly become the characteristics of the apparent watt-hour meter.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electronic apparent power meter that has a simple configuration and can measure apparent power with high accuracy.

An embodiment of the present invention will be described below with reference to the drawings. First, before explaining one embodiment of the present invention, the principle of the electronic watt-hour meter according to the present invention will be explained. FIG. 2 shows a general configuration of an electronic watt-hour meter, and 10 is an instrument transformer that detects a signal proportional to the load voltage of a power supply line. Reference numeral 11 denotes a pulse width modulation circuit that performs pulse width modulation using the signal from the voltage transformer 10 to obtain a pulse width duty cycle. On the other hand, 12 is a current transformer that detects a signal proportional to the current consumption of the power supply line, and this output is converted into a voltage signal by a resistor 13 and guided to a time division multiplier circuit 14. This time division multiplication circuit 14 is composed of a plurality of analog switches (not shown), and by selectively controlling these analog switches according to the pulse width duty cycle, a voltage signal proportional to the current consumption is generated. It is used to perform time-sharing multiplication. Then, the multiplication result is integrated by the integrating circuit 15 to obtain a voltage output, which is converted to a pulse output by the voltage-pulse frequency conversion circuit 16, and the frequency dividing circuit 1
7 and is then displayed on a display circuit 18.

By the way, the pulse width modulation circuit 11 of the electronic watt-hour meter having such a configuration is actually configured as shown in FIG. A1 is an operational amplifier constituting an integrator, and A2 is a comparator that receives an integrated output and generates a logical output by comparing it with a comparison voltage e _h generated by hysteresis. Here, the output of the comparator A2 is configured to have an amplitude of + _er when the logic is "1" and _-er when the logic is "0".

Next, its operation will be explained. _First , if _the output of comparator A2 is set to logic "1" at e _r = 0, then the negative input terminal voltage e _{h of} comparator _A2 will be _-er /2. Furthermore, since the voltage +e _r is introduced into the integrator via the resistor R ₂ , the output of the operational amplifier A1 exhibits an integral slope in the negative direction. Then, the output voltage e _k of operational amplifier A1
When the value reaches _−er /2 and e _k ≦e _h , the comparator A2 is inverted to logic “0”. Then, this time, the negative input terminal voltage e _k of comparator A2 is +
e _r / ₂ , and _-er
is introduced, and the output of operational amplifier A1 exhibits an integral slope in the positive direction. Then, when e _k reaches +e _r /2 and e _k ≧e _h , comparator A2 rotates normally.

In this way, this pulse width modulation circuit repeats self-oscillation. This is shown in Figures 4a-c. Figure a shows the output state of the comparator A2, Figure b shows the negative input terminal voltage e _h of the comparator A2, and Figure c shows the output e _k of the operational amplifier A1.

Now, if the time interval in which the output of the comparator A2 is logic "1" is t _a and the time interval in which the output is logic "0" is t _b , the operational amplifier output e _k is expressed as e _k (t _a )=-(1/ R ₁ C ₁ ∫ ^tap _{e vdt +} 1/R ₂ C ₁ ∫ ^tap _{e rdt} ) = -e _rHere , if R ₁ = R ₂ , then _ta = e _r R ₁ C ₁ / e _r +e _v e _k (t _b )=-(1/R ₁ C ₁ ∫ ^tb _p e _vdt -1/R ₂ C ₁ ∫ ^tb _p e _rdt ) t _b = e _r R ₁ C ₁ / e _r -e _v . . Here, the pulse width duty cycle is D=t _a /t _a +t _b = _er − e _v / _2er …(1) =t _b /t _a +t _b = _er + e _v /2er _… ( 2) becomes. This is the principle of a pulse width modulation circuit.

An embodiment of the present invention will be described below based on the principle of the electronic watt-hour meter as described above. First, the state of multiplication for determining the effective power and the apparent power will be explained using FIG. 5. Active power is the product of e _v and e _i , and when considered instantaneously, it is the product of point A and point B at time _t1 . In addition, the apparent power is obtained by multiplying e _v by shifting the phase by the phase difference between e _v and e _i , and the present invention
An apparent watt-hour meter is constructed by using the pulse-width modulation time-division multiplication watt-hour meter as described above and calculating the product of point A and point C at time _t1 .

FIG. 6 shows the configuration of an electronic apparent watt-hour meter according to an embodiment of the present invention, and the same parts as those in FIG. 2 are given the same reference numerals and the explanation thereof will be omitted. In FIG. 6, 20 is a delay circuit composed of multistage random shift registers, 21 and 22 are pulse signal conversion circuits that convert alternating current signals into pulses, and 2
Reference numeral 3 denotes a clock pulse generation circuit for supplying pulse width modulated output pulses to the delay circuit 20.

In such a configuration, the pulse width modulation circuit 1
1 is not immediately introduced into the time division multiplication circuit 14 as shown in FIG. 2, but is first introduced into the delay circuit 20. As mentioned above, this delay circuit 20 is composed of a multi-stage random shift register,
The pulse width modulated output pulses from the clock pulse generation circuit 23 are introduced and stored and delayed while being shifted one after another. The AC signal is converted into a pulse signal by the pulse conversion circuits 21 and 22, and the converted pulse signal is sent to the delay circuit 2.
Send to 0. This detects the current phase difference and
The input/output points of the random shift register constituting the delay circuit 20 are determined. In other words, the voltage signal e
The pulse width modulated output pulse is held for the time period from the rise of the pulse synchronized with _v to the rise of the pulse synchronized with the current signal e _i . These pulse width modulated output pulses are successively introduced into a random shift register constituting the delay circuit 20, stored and shifted, and then transferred to the pulse conversion circuit 20.
1 and 22, and is output after being delayed. And time division multiplication circuit 1
4 and multiplication is performed. That is, multiplication is performed by the delay circuit 20 so that the voltage signal and the current signal are always in the same phase. The result of this multiplication will represent the apparent power.

As explained above, according to the present invention, a voltage signal proportional to the load voltage of a power supply line is converted into a pulse width duty cycle by a pulse width modulation circuit, and a signal proportional to the current consumption of the power supply line is converted into a voltage signal proportional to the current consumption of the power supply line. An electronic system that converts the voltage signal into a voltage signal by a converter, selectively controls the pulse width duty cycle, and inputs the voltage signal proportional to the current consumption into a time division multiplication circuit to perform time division multiplication. In the electricity meter, a delay circuit is provided between the pulse width modulation circuit and the time division multiplication circuit, and the pulse width duty cycle is sequentially sent to the delay circuit to generate a voltage signal proportional to the load voltage and current consumption. After detecting each zero point of the voltage signal proportional to Therefore, it is possible to provide an electronic apparent power meter that can measure apparent power with high accuracy without complicating the configuration.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional apparent watt-hour meter, Figure 2 is a configuration diagram of an electronic watt-hour meter for explaining the principle of the present invention, and Figure 3 is the configuration of the pulse width modulation circuit shown in Figure 2. 4 is an explanatory diagram of the operation of the pulse width modulation circuit, FIG. 5 is an apparent power waveform diagram for explaining an embodiment of the present invention, and FIG. 6 is a configuration of an apparent watt-hour meter according to this embodiment. It is a diagram. 10... Instrument transformer, 11... Pulse width modulation circuit, 12... Current transformer, 14... Time division multiplication circuit,
20...Delay circuit.

Claims (1)

[Claims] 1 A voltage signal proportional to the load voltage of the feeder line is converted to a pulse width duty cycle by a pulse width modulation circuit, and a signal proportional to the current consumption of the feeder line is converted to a voltage signal by a current transformer. ,
In an electronic watt-hour meter that performs time-division multiplication by selectively controlling the pulse width duty cycle and inputting a voltage signal proportional to the current consumption into a time-division multiplication circuit, the pulse width modulation circuit and A delay circuit is provided between the time division multiplier circuit and the pulse width duty cycle is sequentially sent to the delay circuit to detect the respective zero points of the voltage signal proportional to the load voltage and the voltage signal proportional to the consumption current. After holding and delaying the above pulse width duty cycle by the phase difference between the two,
An electronic apparent power meter characterized in that the time-division multiplication circuit performs time-division multiplication to obtain apparent power.