JPH0454462Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device that detects a phase angle between voltage and current as a DC signal corresponding to the phase angle.

[Conventional technology]

FIG. 4 shows a conventional example of a phase angle detection device. In the figure, 10 is an AC power supply circuit, 11 is its source side, and 12 is its load side. 100
is a phase angle detection device. In the device 100,
20 and 30 are current transformers for isolation. The voltage V of the AC power supply circuit 10 is input to the primary coil 21 of the current transformer 20 via the series resistor 22, and the current A is input to the primary coil 31 of the current transformer 30. 40 is a waveform shaping circuit that shapes the waveform of the voltage V taken out from the secondary coil 23 of the current transformer 20;
50 is a phase circuit that shifts the phase of the current A taken out from the secondary coil 32 of the current transformer 30 by π/2;
60 is a waveform shaping circuit that shapes the output waveform of the phase shift circuit 50. 70 is a phase discrimination circuit that detects whether the phase of the current A is ahead or behind the voltage V, and to one input terminal of the circuit, an alternating current voltage V obtained through the waveform shaping circuit 40 is applied. ,
The other input terminal receives an alternating current A whose phase is shifted by π/2 and whose waveform is shaped by the phase shift circuit 50.
has been added. The phase discrimination circuit 70 discriminates the phases of the voltage V and the current A, and as shown in FIG. When it is ahead, it outputs a (+) polarity DC signal, and when it is behind, it outputs a (-) polarity DC signal. 80 is a scaling circuit with an amplification function. Since the DC output of the phase discrimination circuit 70 is at a low level, this DC output is added to the amplification and scaling circuit 80 and is appropriately amplified and scaled (for example, ±1deg/
±10mV DC output). Therefore, a DC signal corresponding to the phase angle of the voltage V and current A in the AC power supply circuit 10 is amplified to a predetermined level, scaled, and extracted from the output terminal 81 of the circuit 80. Phase angle detection devices with such a configuration have been used in the past, but the operating range on the current A side in the AC power supply circuit 10 is extremely large compared to the operating range on the voltage V side (for example, the operating range on the voltage side input The range is 60-300V while the current side input is 0.5
~10A). By the way, when a current transformer is used as an isolator, a phase angle error occurs. In particular, when a small current transformer (for example, a 13 mm square iron core) is used, the phase angle error becomes large. Moreover,
The value of the phase angle error changes depending on the input level. Therefore, the phase angle error becomes significant in the current-side current transformer 30 whose input level changes are larger than in the voltage-side current transformer 20. The chain line in FIG. 6 is a phase angle characteristic diagram of the device shown in FIG. 4, in which the horizontal axis shows the current [A] and the vertical axis shows the error [deg]. Note that Lead is Lag.
The same trend occurs with the opposite polarity. As shown in the figure, the current transformer 30 causes an error of ±1.5 degrees with an input of 0.5 A. If the change in phase angle is constant even if the input level changes, phase correction is possible, for example, using a capacitor, but if it changes, it becomes difficult.

[Problem that the invention attempts to solve]

This invention was devised to solve these problems, and its purpose is to detect phase angles that have a means of correcting phase changes due to the characteristics of the current transformer for input isolators in response to large changes in input level. The goal is to provide equipment.

[Means for solving problems]

In order to achieve the above object, the present invention has a pair of diodes connected in series with a first resistor and connected in parallel with opposite polarities, and a pair of diodes connected in parallel between the terminals of the pair of diodes. A phase correction circuit including a capacitor and a second resistor is connected between a current input current transformer and a phase discrimination circuit. Examples will be described below.

〔Example〕

FIG. 1 is a connection diagram of an embodiment of a phase angle detection device according to the present invention. In FIG. 1, parts that are the same as those in FIG. 4 are designated by the same reference numerals as in FIG. 1, and further explanation thereof will be omitted. In Figure 1, 9
0 is a phase correction circuit connected between the phase shift circuit 50 and the waveform shaping circuit 60. Phase correction circuit 9
The specific circuit configuration of 0 is shown in FIG. In FIG. 2, 91 is an AC voltage source, 92 is a resistor, 93,
94 is a diode, 95 is a capacitor, and 96 is a resistor. A pair of diodes 93 and 94 connected in parallel with opposite polarities are connected to an AC voltage source 91 via a resistor 92 connected in series to this diode circuit, thereby shaping the waveform of voltage e1. A shaping circuit is configured. A capacitor 95 is connected between the terminals of the pair of diodes 93 and 94.
and a resistor 96 are connected in parallel.
One end 97 of the resistor 96 is connected to the waveform shaping circuit 60 shown in FIG.

In the phase correction circuit 90 having such a configuration, the capacitor 95 performs phase correction, but the phase correction changes depending on the input level. That is, the resistor 92 is
When the current flowing through the resistor 96 is i1 and the current flowing through the resistor 96 is i2, the phase angle between the currents i1 and i2 changes as shown in FIG. 3 by varying the value R of the resistor 96. In Figure 3, the horizontal axis shows the current i
2, the phase angle (deg) of currents i1 and i2 is plotted on the vertical axis.
It has been taken. As shown in FIG. 3, when the value R of the resistor 96 is zero, even if the current i2 increases, i1 and i2
The phase angle between i1 and i2 is zero, but as the value R of the resistor 96 is varied from small to large, the phase angle between i1 and i2 changes in accordance with the current i2 as shown in the figure. If the voltage drop of i2,R is V2, V2 is the voltage drop across diode 9.
Clipped in the forward direction of 3,94. As i2 increases, the clipped voltage gradually becomes a square wave. This means that the fundamental component of V2 has become a constant amount, and the phase angle between i1 and i2 will change as i2 increases. The curve in FIG. 3 shows the relationship of phase angle changes due to clipping. The currents i1 and i2 correspond to the output voltage e1 of the AC voltage source 91, and the voltage e1 is the first
In the figure, it corresponds to the output of the phase shift circuit 50, that is, the magnitude of the current A in the AC power supply circuit 10. Therefore, the value R of resistor 96 and capacitor 9
5, and select the value of capacitance C appropriately, i2 for i1
The phase angle error occurring in the current transformer 30 can be improved by selecting the complementary normal number so that the phase angle of A matches the phase angle error caused by the level change of the input current A of the isolator current transformer 30. The solid line in Fig. 6 is the experimental result of the device shown in Fig. 1 with the addition of the phase correction circuit 90, and the error can be reduced to ±1deg with an input of 0.5A.
I was able to keep it within the range. In addition, resistor 9
By using a variable resistor 6, the phase angle error can be corrected more accurately.

[Effect of idea]

As explained above, according to the present invention, by adding a phase correction circuit that varies depending on the input level, a phase angle detection device can be realized in which the phase angle error is corrected even when a small current transformer is used for isolation. It can be realized.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an embodiment of the phase angle detection device according to the present invention, Fig. 2 is a connection diagram of a phase correction circuit used in the device shown in Fig. 1, and Fig. 3 is an explanation of the characteristics of the circuit shown in Fig. 2. 4 is a connection diagram of a conventional phase angle detection device, FIG. 5 is a waveform diagram for explaining the operation of the phase discrimination circuit used in the devices of FIGS. 1 and 4, and FIG. FIG. 4 is a characteristic explanatory diagram of the circuit shown in FIG. 20, 30...Current transformer, 50...Phase shift circuit, 7
0... Phase discrimination circuit, 90... Phase correction circuit.

Claims (1)

[Scope of utility model registration request] Phase discrimination is performed by a phase discrimination circuit between an alternating current voltage obtained through an isolation current transformer and an alternating current obtained via an isolation current transformer and phase-shifted by π/2. In a device configured to detect the phase angle between voltage and current as a corresponding DC signal, a pair of diodes connected in series to a first resistor and connected in parallel with each other with opposite polarities, and a phase correction circuit comprising a capacitor and a second resistor connected in parallel between the terminals of the pair of diodes, respectively, is connected between the current input current transformer and the phase discrimination circuit. phase angle detection device.