JPS6335943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an electronic reactive energy meter with improved frequency characteristics.

[Technical background of the invention and its problems]

As shown in Fig. 1, a conventional electronic reactive energy meter generates a signal e _v proportional to the load voltage of the power supply line and a signal proportional to the current consumption of the power supply line by a voltage transformer 1 and a current transformer 2, respectively. After converting to ±e _i ,
The phase shift circuit 3 obtains a signal e _v ′ by shifting the phase of the signal e _v by π/2, and further introduces the signal e _v ′ and the signal ±e _i into the subsequent pulse width modulation time division multiplication circuit 4. Multiply. In this case, the phase shift circuit 3 is a resistor as shown in Figure 2.
It consists of an integrating circuit consisting of R ₁ , a capacitor C ₁ and an operational amplifier A1, and when a signal e _v is input, the following processing is performed to obtain a signal e _v '.

e _v = sinωt ……(1) e _v ′=−1/R ₁ C ₁ ∫sinωtdt=1/ωR ₁ C ₁ cos
ωt=-1/ωR ₁ C ₁ sin (ωt-π/2)...(2) Therefore, based on the above equation, the phase shift circuit 3 can shift the phase of the signal e _v by π/2. , ω. Therefore, in order to compensate for the influence of frequency, a frequency-voltage conversion circuit 5 that converts the frequency of the signal e _v into a voltage and a pulse width modulation time division multiplication circuit 6 are provided. 5 and the output of the multiplication circuit 4 to obtain a corrected multiplication signal, which is then converted into a pulse frequency by the voltage-frequency conversion circuit 7.

Specifically, the frequency-voltage conversion circuit 5 generates a pulse with a peak value b and a pulse width a for each period of the signal e _v as shown in FIG. Obtain the integral value S shown in .

S=a·b/T=a·b·=kω (3) As is clear from this equation, this integral value S is a voltage value proportional to the frequency. Therefore, the multiplication circuit 6 uses kω to perform correction. However, T is a period, k is a constant, and ω is an angular frequency.

Next, the pulse width modulation time division multiplication circuits 4 and 6 will be explained with reference to FIG. When e _v '=0 in these circuits 4 and 6, comparator A3
Assuming that the output of is a logic signal of "1", the voltage on the inverting input terminal side of comparator A3 is _-er /2 (where -er _is the voltage when it is "1"). At this time, resistor R, capacitor C and operational amplifier A2
The input terminal of the integrating circuit consists of e _r
is added, an integral output having a negative integral slope is obtained from the operational amplifier A2. When this integrated output reaches _-er /2, the comparator A3 is inverted and becomes a logic signal of "0". As a result, the inverting input terminal side of comparator A3 is
e _r /2 (where e _r is the voltage when it is "0") is applied, and - e _r is applied to the input terminal of the operational amplifier A2, so the operational amplifier A2 outputs an integral with a positive integral slope. I get the output. When this integrated output reaches e _r /2, the comparator A3 is inverted and becomes a logic signal of "1". That is, e _v =0
When , self-excited oscillations occur repeatedly.

Next, when e _v is other than zero, the time interval in which the output of comparator A3 is “1” is t _{a and} the time interval in which the output of comparator A3 is “0” is
When t _b is assumed, the integral output e _k in each interval _ta and t _b is as follows.

e _k (t _a )=-1/RC(∫ ^ta _p e _v ′dt＋∫ ^ta _p e _r dt
)=−t _a /RC(e _v ′+e _r )=−e _r ……(4) e _k (t _b )=−1/RC(∫ ^tb _p e _v ′dt−∫ ^tb _p e _r dt
)=t _b /RC(e _v ′−e _r )=e _r ……(5) Here, the time interval t _a , t _b is t _a = e _r RC/e _r +e _v ′ ……(6 ) t _b = e _r RC/e _r −e _v ′ ...(7). From the above equation, the duty cycle signal D, which is the ratio of changes in t _{a and} t _b due to e _v ′, is: D=t _a /t _a +t _b = e _r −e _v ′/2e _r ……(8) =t _b /t _a +t _b =e _r +e _v ′/2e _r ...(9). Therefore, as mentioned above, operational amplifier A2,
Once the duty cycle signal D is obtained by the comparator A3, etc., the signal D is used to drive the analog switches S12 and S13, and the signal obtained by inverting the signal D by the inverter X1 is used to drive the analog switch S11. , S14, a signal ±e _i proportional to the current consumption is taken in, and the subsequent low-pass filters LF1 and LF2 are
Integrate by e _pp = e _i () + (-e _i ) D = e _v ′e _i / e _r ...(10) e _po = e _i (D) + (-e _i ) D = e _v ′e _i /e _r ...(11) Obtain the multiplication value. Considering the multiplication value, if there is a relationship of e _v ′≦e _r and e _i ≦e _r , the multiplication value will be lower than the voltage _{e r} applied to the operational amplifier A2. Therefore, when two stages of multiplication circuits 4 and 6 are connected in series for frequency compensation of phase shift circuit 3, the multiplication value to be supplied to voltage-frequency conversion circuit 7 becomes even lower. As a result, the voltage-frequency conversion resolution of the voltage-frequency conversion circuit 7 becomes unreasonable, resulting in poor linearity and a narrow dynamic lens.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electronic reactive energy meter with excellent characteristics that eliminates the influence of the frequency of the phase shift circuit and widens the dynamic range of the voltage-frequency conversion circuit. be.

[Summary of the invention]

The present invention is based on the CR of an integrating circuit that configures a phase shift circuit according to the frequency of a signal proportional to the load voltage of a power supply line.
The gain is automatically adjusted by changing the time constant, and a multiplication value is obtained by multiplying the output of the phase shift circuit that has adjusted the gain by a signal proportional to the current consumption of the feeder line, and this multiplication value is used as the pulse frequency. This is an electronic reactive energy meter that converts

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 5 and 6. Note that FIG. 5 shows the overall configuration of the watt-hour meter, and FIG. 6 shows the configuration of the phase shift circuit. This electronic reactive energy meter uses an instrument transformer 1 that converts the signal into a signal proportional to the load voltage of the power supply line.
1, a frequency-voltage conversion circuit 12 that converts the output frequency of the voltage transformer 11 into voltage, and a frequency-voltage conversion circuit 12 that converts the output frequency of the voltage transformer 11 into voltage, and the output of the voltage transformer 11 is converted to A phase shift circuit 13 that shifts the phase by /2, and a pulse width modulation time division that multiplies the output of this phase shift circuit 13 by a signal ±e _i obtained by a current transformer 14 and proportional to the consumption current of the feeder line. It is composed of a multiplication circuit 15 and a voltage-frequency conversion circuit 16.

The phase shift circuit 13 includes a reference voltage generating section 13 that generates a plurality of reference voltages using a reference power supply E and a plurality of voltage dividing resistors R _p , R _p1 to _{R p} n as shown in FIG.
1, a plurality of comparators A51 to A5n that individually compare each output of the reference voltage generation section 131 and the output of the frequency-voltage conversion circuit 12, and a plurality of resistors _R21 to _R2o having a common input terminal side. and are selectively closed by the outputs of the comparators A51 to A5n provided corresponding to these resistors R ₂₁ to R _2o , respectively, to connect the output e _v of the voltage transformer 11 to the inverting input terminal of the operational amplifier A4. Multiple switches that lead to
It consists of S ₂₁ to S _2o . This operational amplifier A4
The non-inverting input terminal of is grounded. In addition, resistance
An integrating circuit is configured by one of the resistors _R21 to _R2o , the capacitor _C2 , and the operational amplifier A4. Comparators A51 to A5n are frequency -
The output level of the voltage conversion circuit 12 is determined, and one of the switches S ₂₁ to _{S 2o} is selectively closed based on the result of this determination. Therefore, the switch S ₂₁ ~ S _2o
By selectively closing , a Miller integrating circuit for integrating the output of the potential transformer 11 is constructed.

Next, the operation of the electricity meter configured as above will be explained. First, the instrument transformer 11 and the current transformer 14 convert the signal into a signal proportional to the load voltage and current consumption, respectively, and the signal obtained by converting the instrument converter 11 is sent to the phase shift circuit 13 shown in FIG. supplied to On the other hand, the signal obtained by conversion by the current transformer 14 is supplied to a pulse width modulation time division multiplication circuit 15. Further, the output of the instrument transformer 11 is converted into a voltage signal according to the frequency of the transformer output by a frequency-voltage conversion circuit 12, and this voltage signal is further applied to the non-inverting input terminals of comparators A51 to A5n shown in FIG. supplied to This comparator A
51 to A5n compare the output of the frequency-voltage conversion circuit 12 with each reference voltage, and depending on the magnitude of the voltage, output a signal from one of the comparators A51 to A5n to select one of the switches. Close. Closing that switch couples the corresponding resistor to capacitor C, which performs an integrating operation by operational amplifier A4. In other words, the resistance R ₂₁ to R _2o is A×
Since 1/ω _o is selected, it is possible to obtain an output e _v ′ with a phase shift of π/2 with respect to the input by the integral operation shown in the following equation. A represents gain.

e _v ′=−1/ωR ₂₁ 〜 _2o C ₂ sin(ωt−π/2)
=-1/AC ₂ sin (ωt-π/2)...(12) Therefore, as is clear from the above equation, the phase shift circuit 1
3, a signal e _v ' which is not affected by frequency can be extracted. In other words, this phase shift circuit 13 changes the time constant of C ₂ R by selecting the resistor and changes the gain by the amount that the output level changes depending on the frequency, so that the output level is always constant and only the phase is changed by π/ A signal shifted by 2 is obtained.

In the above embodiment, one of the resistors R ₂₁ to R _2o is selected by selectively closing the switches S ₂₁ to _{S 2o} , but for example, as shown in FIG.
The configuration may be such that C ₂₁ to _{C 2o} are selected by switches S ₂₁ to _{S 2o} . In this case, if C ₂₁ ~ _2o is chosen as A×1/ω, e _v ′=1/ωR ₂ C ₂₁ ~ _2o sin(ωt−π/2) =−1/AR ₂ sin(ωt−π/2 ), a signal e _v ' that is not affected by frequency can be extracted from the phase shift circuit 13.

〔Effect of the invention〕

As detailed above, according to the present invention, the gain of the operational amplifier is adjusted by changing the CR time constant to compensate for the decrease in output level due to frequency, so that a signal with a phase shift of π/2 is always obtained at a constant level. Therefore, we have developed an electronic reactive energy meter that can improve the voltage-frequency conversion resolution of the voltage-frequency conversion circuit, widen the dynamic range by improving linearity, and improve the accuracy of voltage-frequency conversion. Can be provided.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the overall configuration of a conventional electronic reactive energy meter, Figure 2 is a configuration diagram of the phase shift circuit in Figure 1, and Figure 3 is the operation of the frequency-voltage conversion circuit in Figure 1. FIG. 4 is a block diagram of the pulse width modulation time division multiplier circuit of FIG. 1, and FIG. 5 is a block diagram of the overall configuration of an embodiment of the electronic reactive energy meter according to the present invention. , FIG. 6 is a block diagram showing the phase shift circuit of FIG. 5, and FIG. 7 is a block diagram showing another example of the phase shift circuit. 11... Instrument transformer, 12... Frequency-voltage conversion circuit, 13... Phase shift circuit, 14... Current transformer,
15...Pulse width modulation time division multiplication circuit, 16...
Voltage-frequency conversion circuit.

Claims (1)

[Claims] 1. A signal proportional to the load voltage of the power supply line is shifted in phase by (π/2) using a phase shift circuit, and a signal proportional to the current consumption of the power supply line is multiplied by a pulse width modulation time division multiplication circuit, An electronic reactive energy meter that obtains reactive energy by converting this multiplied signal into a pulse frequency, comprising a frequency-voltage conversion circuit that converts the frequency of a signal proportional to the load voltage of the feeder line into a voltage, The phase circuit includes a reference voltage generation section that generates a plurality of reference voltages using a reference power supply and a plurality of voltage dividing resistors, and a reference voltage generation section that generates each reference voltage and the output voltage of the frequency-voltage conversion circuit. Multiple comparators that are compared individually, multiple switches that are selectively controlled to open and close by the outputs of these comparators, and resistors or capacitors connected to each of these switches, each with a different CR time constant when each of the switches is closed. It is characterized by comprising operational amplifiers forming each integrating circuit, and changing the gain of the load voltage according to the frequency fluctuation of the load voltage to always maintain a constant level of output and shifting the phase by (π/2). Electronic reactive energy meter.