JPH041306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic watt-hour meter that can display the amount of power by determining the direction of power flow.

Electricity supply companies constantly secure supply capacity to meet ever-changing electricity demand and maintain a balance between supply and demand, that is, the amount of power transmitted and the amount of power generated. In order to maintain a balance between supply and demand, an electric power supply company may, for example, receive power transmitted from another electric power supply company. In practice, as the load increases, the amount of power transmitted increases, and when it becomes impossible to maintain a balance with the amount of power generated, power is transmitted from other power supply companies to make up for the power shortage. In this case, the power supply company will buy electricity from other power supply companies. Since the power flow indicating the state of power supply between power supply companies changes from time to time, the power supply companies constantly monitor the state and operate the power system appropriately according to changes in power flow.

Conventionally, the amount of power transmitted and received was measured using the following devices.

One of them is a method of using two ordinary inductive watt-hour meters, which poses the problem of an increase in the area occupied by the increase in the number of watt-hour meters. That is, in one of the watt-hour meters, the rotational direction of the disk is regulated so that, for example, electric power can be measured only during power transmission.

When receiving electricity in the opposite direction, another watt-hour meter is used whose disk rotates in the opposite direction to that of the previous watt-hour meter. Therefore, in other watt-hour meters, the rotation direction of the disk is restricted so that the electric power cannot be measured during power transmission.

Another method is to use only one inductive energy meter. A circuit that detects the direction of power flow, ie, power transmission or power reception, switches the polarity of the voltage detection circuit or current detection circuit.
That is, the detection circuit switches the polarity of an instrument transformer or an instrument current transformer used in a voltage detection circuit or a current detection circuit. With this method,
A power meter can measure the amount of power by simply rotating in one direction, even if the direction of power flow is power transmission or power reception. However, when the polarity of a voltage transformer or voltage current transformer is changed, errors that would not have occurred if the voltage transformer or voltage current transformer were used with normal polarity appear, and the accuracy of power measurement decreases due to this effect.

In an electronic watt-hour meter using a time-sharing multiplier, a DC voltage obtained by integrating the output of the multiplier is guided to a voltage-frequency conversion circuit to output a pulse signal corresponding to the amount of power. Conventional power flow discrimination involves detecting whether the output of an integrator in a voltage-frequency conversion circuit is positive or negative. In this case, if the output voltage is positive, it is determined that power is being transmitted, and if the output voltage is negative, it is determined that the power is being received. If it is in the power receiving state, the input voltage polarity of the integrator is reversed, and a positive amount of power is displayed in the power receiving display field. If the power is being transmitted, the amount of power is displayed directly in the power transmission display field. In such an electronic watt-hour meter, since the direction of power flow is determined according to the output of the integrator, it is easily affected by the offset voltage of the operational amplifier that constitutes the integrator. That is, since an offset voltage appears in the output of the integrator, the accuracy of determining the power flow direction is poor.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems and provide an electronic watt-hour meter that can display the amount of power according to the direction of power flow.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram for explaining the configuration of an electronic watt-hour meter according to the present invention. Power feed line 1
The potential transformer 11 connected to 0 as shown in the figure is
Outputs a voltage signal e _v proportional to the load voltage of the power feed line. Furthermore, an instrument current transformer 12 connected to the power supply line 10 as shown in FIG. 1 outputs a voltage signal e _i proportional to the load current, and a voltage signal e Proportional voltage signal ±e _i
Output. Secondary coil 12b of this current transformer 12
The intermediate terminal of is grounded.

The configuration of the pulse width modulation circuit 13 is as follows. The voltage signal e _v is applied via a resistor 14 to the negative input terminal of an integrating circuit 15 composed of an operational amplifier. The output of this integrating circuit 15 is applied to the positive input terminal of a comparator circuit 16 composed of an operational amplifier. A capacitor 17 is connected between the negative input terminal and the output terminal of the integrating circuit 15 for integrating the input signal. The output of the comparator circuit 16 is applied to the negative input terminal of the integrating circuit 15 via a resistor 18, and
After being inverted by the inverter circuit 19, the resistor 20,
21 and applied to the negative input terminal of the comparator circuit 16. In this example, resistors 20, 21
have the same resistance value. One end of the resistor 20 is connected to the negative input terminal of the comparator circuit 16, and the other end is connected to the output terminal of the inverter circuit 19. resistance 21
One end is grounded, and the other end is connected to one end of the resistor 20. An input terminal of an inverter circuit 22 is connected to an output terminal of the comparator circuit 16.

The structure of the current direction determination circuit 23 is as follows.

The comparator circuit 24 is composed of an operational amplifier, and its positive input terminal is connected to one end of the secondary winding 11b of the potential transformer 11. Comparator circuit 2
The negative input terminal of No. 4 is grounded. Comparator circuit 2
4, the output signal e _v of the potential transformer 11 is converted into a pulse signal according to its phase.

The comparator circuit 25 is composed of an operational amplifier, and its positive input terminal is connected to one end of the secondary winding 12b of the instrument current transformer 12. Its negative input terminal is grounded. The comparator circuit 25 converts the signal e _i into a pulse signal according to its phase.

The output signal of the comparator circuit 24 is input to one end of the AND circuit 26 . The output signal of the comparator circuit 25 is inputted to the other end via the inverter circuit 27 . The AND circuit 26 generates a voltage signal e _i by the voltage signal e _v and the inverter circuit 27.
A pulse signal is output according to the phase difference between the inverted signal and the inverted signal.

One end of the resistor 28 is connected to the output end of the AND circuit 26, and the other end of the resistor 28 is connected to one end of the capacitor 29. The other end of the capacitor 29 is connected to a predetermined negative power supply Vss. The integrating circuit composed of a resistor 28 and a capacitor 29 is an AND circuit 2.
Integrate the output signal of 6.

One end of the resistor 30 is connected to the output end of the comparator circuit 24, and the other end of the resistor 30 is connected to the capacitor 31.
One end of is connected. The other end of the capacitor 31 is connected to a predetermined negative power supply Vss. An integrating circuit constituted by a resistor 30 and a capacitor 31 integrates the output signal of the comparator 24, that is, a pulse having a width corresponding to 180°.

One end of the resistor 32 is connected to one end of the resistor 30,
The other end of resistor 32 is connected to one end of resistor 33.
The other end of the resistor 33 is connected to a predetermined negative power supply Vss. In this embodiment, for convenience of explanation, it is assumed that the resistance values of the resistors 32 and 33 are the same, for example. In this case, the voltage dividing circuit made up of resistors 32 and 33 divides the output voltage of the integrating circuit made up of resistor 30 and capacitor 31 into half. That is, this voltage dividing circuit outputs a voltage obtained by integrating a pulse having a width corresponding to 90°.

The comparator circuit 34 is composed of an operational amplifier, the positive input terminal of which is connected to one end of the resistor 28,
Its negative input terminal is connected to one end of the resistor 32. Comparator circuit 34 generates a pulse signal when the output voltage of the integrating circuit made up of resistor 28 and capacitor 29 becomes larger than the output voltage of the voltage dividing circuit made up of resistors 32 and 33. In this discrimination circuit 23, the comparator 34 outputs a signal if the output voltage obtained by analyzing the output of the AND circuit 26 is larger than the voltage obtained by integrating a pulse corresponding to a 90° width.

Comparator circuits 24 and 25 convert voltage signals e _v and e _i respectively into pulse signals according to their phases. The AND circuit 26 is a comparator circuit 24, 2
It compares the output signals from 5 and outputs a pulse signal. An integrating circuit composed of a resistor 28 and a capacitor 29 integrates the output signal of the AND circuit 26. An integrating circuit made up of a resistor 30 and a capacitor 31 integrates the output signal of the comparator circuit 24. This integrator circuit integrates pulses that correspond to a phase of 180°. A voltage dividing circuit composed of resistors 32 and 33 divides the integrated output into, for example, 1/2.
In other words, the voltage corresponding to the 90° phase is divided.
The comparator circuit 34 compares the divided output voltage with the output voltage of an integrating circuit constituted by a capacitor 28 and a resistor 29 based on the divided output voltage. The comparator circuit 34 outputs a pulse signal when this integrated output voltage is greater than the integrated voltage corresponding to the 90° phase. When the comparator circuit 34 outputs a logic signal "1", the direction of power flow is determined to be in the power receiving state. If the logic signal is "0", it is a power transmission state.

The inversion circuit 35 includes exclusive OR circuits 35a and 3
5b. Exclusive OR circuit 35a, 3
Each one of the input terminals of 5b is connected to the output terminal of the comparator circuit 34. Further, the other input terminal of the exclusive OR circuit 35a is connected to the output terminal of the comparator circuit 16. Exclusive OR circuit 3
The other input terminal of 5b is connected to the output terminal of the inverter circuit 22. As for the pulse width duty cycle signal D, the output signal of the comparator circuit 34 is “0”
As long as , the exclusive OR circuit 35a outputs the polarity as it is. Comparator circuit 34
When the output signal becomes "1", the polarity of the pulse width duty cycle signal D is inverted, and the exclusive OR circuit 35a outputs the signal. The polarity of the pulse width duty cycle signal output from the inverter circuit 22 is similarly inverted, and the exclusive OR circuit 35b outputs the signal D.

Next, the voltage signal ±e _i is input to the multiplier circuit 36 . The multiplication circuit 36 is composed of a plurality of analog switches that are turned on when the logic signal is "1" and turned off when the logic signal is "0". For this analog switch, a semiconductor element such as a J-FET or a MOS-FET is used. Analog switch 36a, 36b
The input terminal of is connected to one end of the secondary winding 12b of the instrument current transformer 12, and the analog switch 36c, 36
The input end of d is connected to the other end of the secondary winding 12b. The analog switches 36a and 36b are driven by the output signal of the exclusive OR circuit 35a, and the analog switches 36b and 36c are driven by the output signal of the exclusive OR circuit 35b. An instantaneous voltage signal e _po is obtained at the connection point between the output ends of the analog switches 36 a and 36 c, and this connection point is connected to the integrating circuit 37 . An instantaneous voltage signal _epp is obtained at the connection point between the output ends of the analog switches 36b and 36d, and this connection point is connected to the integrating circuit 37.

Integrating circuit 37 is composed of resistors 38 and 39 and capacitors 40 and 41. One end of the resistor 38 is
It is connected to the output ends of the analog switches 36a and 36c, and the other end is connected to one end of the capacitor 40. One end of the resistor 39 is connected to the analog switch 36.
b, 36d, and the other end is connected to one end of the capacitor 41. capacitor 40,4
The other ends of 1 are commonly grounded. Integrating circuit 37
At the output terminal of , there are positive and
Voltage signals _pp and _po having negative polarity are output.
The voltage signals _pp , _po are the product of a voltage signal e _v compared to the load voltage of the power supply line and a voltage signal e _i proportional to the load current, ie a direct voltage proportional to the instantaneous power.

These DC voltage signals _pp and _po are input to the voltage-frequency conversion circuit 42. analog switch 43
a and 43b are each connected to the output terminal of the integrating circuit 37. The output terminals of the analog switches 43a and 43b are connected in common, and further connected via a resistor 44 to the negative input terminal of an integrating circuit 45 constituted by an operational amplifier. The positive input terminal of this integrating circuit 45 is grounded. Moreover, the output terminal of the integrating circuit 45 is
It is connected to the positive terminal of a comparator circuit 46 made up of an operational amplifier that outputs a logic signal "1" or "0" every time the integrated output reaches a certain voltage. The output of the integrating circuit 45 is fed back to the negative input terminal via the capacitor 47. Comparator circuit 4
The negative input terminal of 6 is grounded via a resistor 48. The output of the comparator circuit 46 drives analog switches 43a and 43b to open and close them. Switch 43b receives the output of comparator circuit 46 via inverter circuit 49 in order to open and close in the opposite manner to switch 43a. Comparator circuit 4
The output of 6 is connected to the negative input terminal of the comparator circuit 46 via an inverter circuit 50 and a resistor 51.

The output signal of the voltage-frequency conversion circuit 42 is transmitted to the switch 5 controlled by the output signal of the discrimination circuit 23.
2 is displayed on the display device 53 or 54. For example, when transmitting power, the switch 52
2a, and the amount of power is displayed on the display device 53. When power is received, the switch 52 is switched to 52b and the amount of power is displayed on the display device 54.

Next, the operation of the circuit shown in FIG. 1 will be explained.

The output signal e _v of the potential transformer 11 is converted into a pulse width duty cycle signal by a pulse width modulation circuit 13 . This pulse width duty cycle signal D is a logic signal “1” or “0”
The interval is proportional to the magnitude of the signal e _v . The pulse width duty cycle signals D and ^D are expressed by the following formula.

D=e _r −e _v /2e _r =t _a /T…(1) =e _r +e _v /2e _r =t _b /T…(2) However, e _r is the comparator circuit 16 of the pulse width modulation circuit 13 The reference voltage applied to the negative input terminal of t _a
is the interval of the logic signal “1” of the pulse width duty cycle signal D, and t _b is the logic signal “0” of the signal D.
, T indicates the period of the signal D.

The current direction determination circuit 23 compares the outputs of these comparators with two comparators that convert the signals e _v and e _i into pulses, detects the phase value between the signals e _v and e _i , and converts the detected phase value into a pulse. A DC voltage obtained by integrating this pulse is compared with a reference voltage to output a signal indicating the current direction. When the power flow is in transmission state,
The output of the determination circuit 23 is a logic signal "0", and when the power flow is in the receiving state, the output is a logic signal "1".

The discrimination circuit 35 outputs the output signal D of the pulse width modulation circuit 13 as it is in a normal state, that is, during power transmission, based on the output signal of the discrimination circuit 23. When power is received in the opposite direction, the discrimination circuit 35 inverts the polarity of the output signal of the pulse width modulation circuit 13 and outputs it.
That is, during power transmission, as described above, the output signal of the discrimination circuit 23 is "0", and the polarity of the output signal of the pulse width modulation circuit 13 is not changed. When receiving power, the output signal of the discrimination circuit 23 is "1",
The polarity of the output signal of the pulse width modulation circuit 13 is inverted.

The voltage signal ± _{e i} generated from the instrument current transformer 12 and the resistor 12a is input to the multiplier circuit 36.

After passing through the discrimination circuit 23, the pulse width duty cycle signal of the pulse width modulation circuit 13 (when receiving power, the discrimination circuit 23 inverts the polarity of the output signal of the pulse width modulation circuit 13) selects a plurality of analog switches. Turn it on and off. As a result, the multiplier circuit 36 outputs a signal whose pulse width is proportional to the magnitude of the signal e _v and whose amplitude is proportional to the magnitude of the signal e _i .

(b) During power transmission, the analog switches 36a and 3 of the multiplier circuit 36 are activated by the pulse width duty cycle signal D and the "1" signal of D.
6d is turned on, and analog switches 36b and 36c are turned on with the "1" signal. Then, a voltage signal .±.e _i proportional to the load current of the power feed line is introduced by analog switches 36a to 36c to obtain DC voltage signals e _pp and e _po . That is, by controlling the analog switches 36a to 36c on and off using the pulse width duty cycle signal D of the pulse width modulation circuit 13, the voltage signals e _v and e _i
Extract the DC voltage signals e _pp and e _po multiplied by
This can be expressed as a formula as follows.

e _pp = e _i・+(−e _i )・D = e _i・e _r +e _v /2e _r +(−e _i・e _r −e _v /2e _r )=e _i・e _v
/e _r …(3) e _po =e _i・D+(−e _i )・=e _i・e _r −e _v ／2e _r +(−e _i・e _r +e _v /2e _r ) =−e _i・e _v /e _r …(4) The integrating circuit 37 receives the output signal of the multiplier circuit 36
Integrate e _pp and e _po to obtain DC voltage signals e _pp and e _po . If we express these e _pp and e _po as formulas, we get the following.

e _pp = (e _i・e _v / e _r ) …(5) e _po = (−e _i・e _v / e _r ) …(6) As is clear from equations (5) and (6), , _pp ,
e _po are positive and negative DC voltage signals proportional to the instantaneous power composed of e _i and e _v , each having the same absolute value.

The voltage-frequency conversion circuit 42 outputs a pulse having a frequency proportional to the DC output voltage that is the output of the integrating circuit 37. Comparator circuit 46
outputs a logic signal “1” or “0” on the output side according to the integrated output voltage value, and when the signal is “1”, the analog switch 43a is closed and the DC voltage signal _po is introduced into the integrating circuit 45. are doing. Also, when the signal is "0", the analog switch 43b is closed and the DC voltage signal _pp is transferred to the integrating circuit 4.
We are planning to introduce it in 5th. This means that the integral output of the integrating circuit 45 is the DC voltage signal _pp , _po
(instantaneous power), and since the logic signal of the comparator circuit 46 is inverted with the constant voltage value of this integral output to create a pulse frequency, a frequency signal proportional to the power is extracted from the output terminal of the comparator circuit 46. be able to.

The inversion period T _p of the output signal ef of the comparator circuit 46 is as follows.

T _p =t _c +t _d (7) where t _c is the conduction time of the analog switch 43b, and t _d is the conduction time of the analog switch 43a. Therefore, the frequency of the logic signal is: =1/T _p =1/t _c +t _d (8). t _c and t _d are expressed as follows.

t _c = e _p・R ₁・C ₁ / e _pp …(9) t _d = e _p・R ₁・C ₁ /−e _po …(10) However, e _p is connected to the negative input terminal of the comparator circuit 46. The applied reference voltage, R ₁ is the resistance value of the resistor 44, and C ₁ is the capacitance value of the capacitor 47.

Substituting equations (5) and (6) into equations (9) and (10) yields the following.

t _c =e _p・R ₁・C ₁ /e _i・e _v /e _r …(11) t _d =e _p・R ₁・C ₁ /e _i・e _v /e _r …(12) Therefore , the frequency is expressed as:

=e _i・e _v /2e _r・e _p・R ₁・C ₁ …(13) As is clear from this equation (13), e _r・e _p・
Since R ₁ and C ₁ are all constants, they represent _i and _v , that is, the output frequency proportional to power consumption. The switch 52 is set to 52 in accordance with the output signal of the discrimination circuit 23.
The switching power amount is displayed on the display device 53.

(b) When receiving power, the inversion circuit 35 inverts the polarity of the output signal of the pulse width modulation circuit 13, so e _pp and e _po can be expressed as follows.

e _pp =e _i・D+(−e _i )・=−e _i・e _v /e _r …(3)′ e _po =e _i・+(−e _i )・D=e _i・e _v /e _r …(4)′ In this case as well, if you calculate the frequency in the same way as in (a), it can be expressed as follows.

= −e _i・e _v /2e _r・e _p・R ₁・C ₁ …(13)′ In other words, an output frequency proportional to the amount of electric power at the time of power reception is obtained, and the switch is activated according to the output signal of the discrimination circuit 23. 52 is switched to 52b, and the amount of power is displayed on the display device 54.

Although one embodiment is applied to a single-phase two-wire watt-hour meter, it can also be applied to a polyphase watt-hour meter by providing a plurality of potential transformers, current transformers, multiplier circuits, and the like. Since the power amount of a polyphase watt-hour meter is the sum of the power of each phase, let the voltage signals proportional to the load voltage of each feeder line be e _v1 , e _v2 ~ e _vo , and the load current of each feeder line The proportional voltage signals are e _i1 , e _i2
〜e _io and the proportionality constants are K ₁ and K ₂ 〜K _o , then the electric energy P _{p is} : P _p =K ₁ e _v1・e _i1 +K ₂ e _v2・e _i2 ＋…＋K _o e _vo e _io
...(14) Therefore, if the outputs of the respective multiplier circuits subjected to signal processing are combined and added in the same manner as in the first embodiment, the power P _p that satisfies equation (14) can be obtained.

FIG. 2 is a circuit diagram of a second embodiment of the present invention in which the present invention is applied to a polyphase power meter. In addition,
Circuits that are the same as those in FIG. 1 are given the same reference numerals, and detailed configurations and explanations will be omitted. The second embodiment is based on the instrument transformer 11 and the pulse width modulation circuit 1 of the first embodiment.
3. A plurality of instrument current transformers 12, inverting circuits 35, and multiplication circuits 36 are provided, and each multiplication circuit 3
6 is taken out from an integrating circuit 37 and sent to a voltage-frequency converter 42.

In this second embodiment, two sets of potential transformers 11
and instrument current transformer 12 detect voltage and line current between phases, respectively. In this embodiment, the signals input to the discrimination circuit 23 are voltage signals based on line current and voltage signals based on phase-to-phase voltage. In order to match the phase of the line current and phase-to-phase voltage when determining the power flow direction, in this embodiment, the phase shift circuit 55 is connected to the secondary winding of the instrument current transformer 12 on the side that detects the line current. It is provided between one end and one input end of the discrimination circuit 23. Depending on the direction of the tidal flow, a phase shift difference occurs between the voltage signal based on the line current passing through the phase shift circuit 55 and the phase-to-phase voltage, and the discrimination circuit 23 detects the tidal flow direction. In addition, the phase shift circuit 5
For example, a filter circuit composed of well-known resistors and capacitors is used as the filter circuit 5.

With such a configuration, the second embodiment also provides the same effects as the first embodiment.

As described above, according to the present invention, the direction of power flow is determined by detecting the phase difference between the load voltage and load current waveforms of the power supply line,
The amount of power transmitted and received is distinguished and displayed on the display device. Therefore, there is no fear of an increase in the area occupied by the use of two ordinary induction type watt-hour meters. Further, there is no influence of errors caused by changing the polarity of the voltage transformer or current transformer used in the voltage detection circuit or current detection circuit of the power feed line. Furthermore, in a comparator made up of an operational amplifier, the offset voltage is applied in phase with the voltage for comparison, so no error occurs. Therefore, since the power flow direction is not determined by an integrator configured with an operational amplifier, it is not affected by the offset voltage of the operational amplifier, and it is possible to display the amount of power during power transmission and reception by accurately determining the power flow direction. becomes.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of an electronic watt-hour meter according to the invention, and FIG. 2 is a block diagram in which the invention is applied to a multi-phase electronic watt-hour meter. 11... Instrument transformer, 12... Instrument current transformer, 13... Pulse width modulation circuit, 23... Discrimination circuit, 35... Inverting circuit, 36... Multiplier circuit, 37
...Integrator circuit, 42...Voltage-frequency conversion circuit,
52... Switch, 53, 54... Display device, 5
5...Phase shift circuit.

Claims (1)

[Claims] 1. A first means for outputting a voltage signal proportional to the load voltage of the power supply line, and a second means for outputting a voltage signal proportional to the load current of the power supply line,
a pulse width modulation circuit that outputs a pulse signal having a pulse width that corresponds to the voltage signal output from the first means; and a pulse width that corresponds to the phase of the voltage signal output from the first and second means. The direction of the power flow is determined by comparing the pulse signals according to the phase difference between these pulse signals and the pulse signal according to the phase of the voltage signal from the first means. a discrimination circuit; an inversion circuit that inverts the polarity of the output signal of the pulse width modulation circuit according to the output signal of the discrimination circuit;
A multiplication circuit that is switch-controlled by a pulse signal output from the inverting circuit to obtain a multiplication value of each voltage signal output from the first means and second means and output it as a pulse signal; an integrating circuit that integrates an output pulse signal and outputs a DC voltage signal; a voltage-frequency conversion circuit that outputs a pulse signal having a frequency proportional to the voltage level of the DC voltage signal output from the integrating circuit; and means for displaying the output signal of the voltage-frequency conversion circuit according to the direction of power flow according to the output signal of the discrimination circuit.