JPS6152950B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reactive watt-hour meter with improved frequency characteristics. Generally, the instantaneous value and effective value of the load voltage of one phase are ev and V, the instantaneous value and effective value of the current consumption are ei and I, the angular frequency of the load voltage and current consumption is ω, and the load voltage The difference between the instantaneous values ev, ei and the effective values V, I is ev=√2Vsin ωt ……(1) ei=√2Isin(ωt−) ……(2 ) holds true, and the reactive power Q of this phase
is expressed as Q=VIsin...(3). In conventional reactive energy meters, a phase shifter is used to calculate equation (1).
Shift the phase angle of the instantaneous value ev shown by (π/2) to obtain ev'=√2Vsin(ωt-π/2)...(4), and change this ev' and the instantaneous value shown by equation (2). By multiplying by ei, we obtain ev′×ei=VIsin −VIcos(2ωt−π/2−) (5), and by integrating this, we obtain equation (3) Q=VIsin. When a filter or the like is used as the phase shifter to shift the phase, the amplitude of the signal passing through the phase shifter varies depending on the frequency component. For example, if the phase of the instantaneous value ev is shifted by π/2 using a filter that operates as an integrating circuit, then The maximum amplitude is given by the angular frequency ω.

[Formula] is subject to the constraint of 1/ω. Since there are restrictions on the frequency characteristics due to the phase shifter, it has been difficult to measure the amount of reactive power with high accuracy. The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a reactive energy meter with improved frequency characteristics. Embodiments of the present invention will be described below based on the drawings. FIG. 1 is a block diagram simply showing the structure of a first embodiment of the present invention. Potential transformer 1 converts the load voltage of the power supply line into a voltage signal proportional to its level.
This is to convert it to ev. The angular frequency detector 2 detects the angular frequency ω of the voltage signal ev sent from the transformer 1. An angular frequency-to-voltage converter (hereinafter referred to as ω/V converter) 3 converts the angular frequency signal sent from the angular frequency detection circuit 2 into a voltage signal corresponding to this signal. The phase shifter 4 shifts the phase of the voltage signal ev sent out from the transformer 1 by (π/2). The current transformer 5 converts the current consumption of the power supply line into a voltage signal ei proportional to its level.
The first multiplier 6 multiplies the signal ei sent from the current transformer 5 and the signal sent from the phase shifter 4. The second multiplier 7 multiplies the voltage signal sent from the first multiplier by the voltage signal sent from the ω/V converter 3 to remove frequency fluctuation components. The integrator 8 integrates the voltage signal sent from the second multiplier 7 to obtain reactive power. The display unit 9 obtains the amount of reactive power based on the signal sent from the integrator 8, and displays the amount of reactive power on a display (not shown). FIG. 2 is a circuit diagram of the angular frequency detector 2 and the ω/V converter 3. The angular frequency detector 2 is formed by a comparator circuit 10, and the ω/V converter 3 includes a monostable multivibrator 11 that sends out a one-shot pulse with a pulse width determined by a resistor _R1 and a capacitor _C1 ; Resistor R ₂ and capacitor
The monostable multivibrator 1 consists of C ₂ and
1, and an integrating circuit 12 that integrates the signal sent from 1. Then, when a sine wave voltage signal ev as shown in FIG. 3a, sent from the transformer 1, is supplied to the positive input terminal of the comparator circuit 10, the voltage signal ev shown in FIG.
A rectangular wave signal as shown in FIG. 1 is sent to the monostable multivibrator 11. Then, this monostable multivibrator 11 is driven by the rise of the rectangular wave signal and sends out a one-shot pulse signal as shown in FIG. 3c to the integrating circuit 12. Therefore, the number of pulses of the one-shot pulse signal is proportional to the frequency of the input sine wave. The one-shot pulse signal eg having such frequency information is integrated by the integrating circuit 12 to produce a voltage signal e proportional to the number of pulses, as shown in FIG. 3d.
converted to ω. Therefore, the voltage signal eω will be proportional to the angular frequency of the voltage signal ev. The operation of this embodiment having such a configuration will be explained.
The load voltage and current consumption of the power supply line are converted into voltage signals ev and ei proportional to their respective levels by a voltage transformer 1 and a current transformer 5, respectively. Note that, assuming the phase difference between the load voltage and the current consumption, ev and ei are respectively expressed by formulas (1) and (2) ev=√2Vsinωt...(1) ei=√2Isin(ωt-)...(2) The same is true. Then, when ev is passed through the phase shifter 3, the resulting voltage signal ev′ is, where k is the constant of the phase shifter 3. becomes. This voltage signal ev' is multiplied by the voltage signal ei in the first multiplier 6, and the second signal is ev'ei=2kVI/ω sin(ωt-π/2) sin(ωt-)...(8) is sent to the multiplier 7. As is clear from equation (8), the maximum amplitude of ev′ei varies depending on the value of ω. On the other hand, the voltage signal sent from the transformer 1
The angular frequency ω of ev is detected by the angular frequency detector 2, and the ω/V converter 3 sends a voltage signal eω proportional to the angular frequency ω to the second multiplier 7. Note that the voltage signal eω is set so that eω=k′ω (9) where k′ is a proportionality constant. Then, in the second multiplier 7, the voltage signal ev'ei and eω are multiplied to obtain ev'eieω=2kk'VIsin (ωt-π/2) sin(ωt-) (10). As is clear from equation (10), power VI is not affected by angular frequency ω. Equation (10) can be transformed as ev′eieω=kk′VI {sin−cos(2ωt−π/2−)} (11). When the signal sent from the second multiplier circuit 7, which can be transformed in this way, is integrated by the integrator circuit 8, the reactive power Q is obtained as Q=kk′VIsin...(12), and as is clear from equation (12) This reactive power Q is not affected by the angular frequency ω. Therefore, reactive power with good frequency characteristics can be obtained. The signal indicating the reactive power obtained in this way is sent to the display section 9, the amount of reactive power is obtained, and the amount of reactive power is displayed on a display (not shown). In this way, in this embodiment, the influence of the angular frequency ω on the reactive power caused by the voltage signal ev sent from the potential transformer 1 passing through the phase shifter 4 is reduced to this angular frequency ω. A proportional voltage signal is obtained and removed by multiplying this voltage signal with the voltage signal representing the reactive power. Therefore, according to this embodiment, since it is not affected by the angular frequency ω of the voltage signal ev, a highly accurate amount of reactive power can be obtained. FIG. 4 is a block diagram simply showing the configuration of a second embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. In the first embodiment, ev in equation (1) is (π/
The reactive power was obtained by shifting the phase by 2), but in the second embodiment, ei in equation (2) was shifted by (π/2) to obtain ei'=√2sin(ωt-+π/2)... …(13) is obtained, and this is multiplied by ev in equation (1) to obtain ev×ei′=VIsin− VIcos(2ωt−+π/2) …(14), and this equation (14) is integrated. By doing so, the reactive power Q is obtained as Q=VIsin. Therefore, the configuration of the second embodiment differs from the configuration of the first embodiment in that the multiplier 14 converts the voltage signal ei sent from the potential current transformer 5 into a phase shifter 15 (π/2 ) is multiplied by the voltage signal ev sent from the potential transformer 1 to obtain a voltage signal, and this voltage signal is divided by the voltage signal sent from the ω/V converter 16. The point is that the angular frequency component is removed by dividing by . Note that the phase shifter 15 mainly uses a differentiating circuit, and the voltage signal ei sent from the instrument current transformer 5 is expressed by equation (2): ei=√2Isin(ωt-)...(2) Then, ei′ transferred by (π/2) is ei′=√2VRCd{sin(ωt−)}/dt =√2VRCωcos(ωt−) =−√2VRCωsin(ωt−+π/2) ……(1 5 ) becomes. The operation of the second embodiment having such a configuration will be briefly described. Voltage signal sent from instrument transformer 1
Let ev be expressed by equation (1) ev=√2Vsinωt...(1), and the voltage signal ei sent from the instrument current transformer 5
Let ei=√2Isin(ωt-)...(2) shown in equation (2). When this ei is passed through the phase shifter 15, ei'=√2kIωsin(ωt-+π/2)...(16) (k is the constant of the phase shifter 15),
A multiplier 14 multiplies ev and ei'. As a result, ev・ei′ becomes ev・ei′=2kIVωsinωtsin (ωt−+π/2) …(17), and from equation (17), the maximum amplitude of ev・ei′ is influenced by ω. it is obvious. This ev・
The divider 16 divides ei′ into eω sent from the ω/V converter 3, that is, eω=k′ω (however,
k' is a constant of the ω/V converter 3) to obtain evei'/eω=2kIV/k' sinωtsin(ωh−+π/2) (18). When the voltage signal thus obtained is integrated by the integrator 8, the reactive power Q is obtained as follows: Q=k/k'VIsin (19). As is clear from equation (19), this reactive power Q is not affected by the angular frequency ω, so that reactive power with good frequency characteristics can be obtained. In this way, the second embodiment can also achieve the same effects as the first embodiment. Note that the present invention is not limited to the first and second embodiments described above. For example, in the first and second embodiments, the angular frequency ω was detected from the voltage signal ev sent from the potential transformer 1;
The angular frequency ω may be detected from the voltage signal ei sent from the instrument current transformer 5. Of course, various other modifications can be made without departing from the gist of the present invention. As described above, the present invention uses a signal proportional to the angular frequency to eliminate the influence of the angular frequency on the reactive power, which occurs when a signal proportional to the load voltage or current consumption is phase-shifted. Therefore, according to the present invention, it is possible to provide a reactive energy meter with improved frequency characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the configuration of the first embodiment of the present invention, FIG. 2 is a circuit diagram of the angular frequency detector and ω/V converter shown in FIG. 1, and FIGS.
b, c, and d are waveform diagrams for explaining the operation of the circuit diagram shown in FIG. 2, and FIG. 4 is a schematic block diagram showing the configuration of a second embodiment of the present invention. 1... Instrument transformer, 2... Angular frequency detector,
3...ω/V converter, 4... Phase shifter, 5... Instrument current transformer, 6... First multiplier, 7... Second multiplier, 8... Integrator, 10 ...Comparator, 11...
Monostable multivibrator, 12...integrator circuit,
16...Divider.

Claims (1)

[Claims] 1 Convert the load voltage and current consumption of the power supply line into voltage signals proportional to their respective levels, shift the phase of one of these voltage signals, and then multiply it with the other voltage signal in a multiplier circuit to obtain the voltage signal. A reactive energy meter that obtains reactive energy by integrating this voltage signal includes a frequency detection circuit that detects the frequency of the voltage signal and sends out a voltage signal according to this frequency, and a frequency detection circuit that detects the frequency of the voltage signal and sends out a voltage signal according to this frequency. and a circuit for removing a frequency fluctuation component of the voltage signal sent from the multiplication circuit using the voltage signal.