JPH0654332B2 - Power factor transducer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transducer for converting a power factor into a DC signal corresponding to the power factor.

[Conventional technology]

Assuming that power is P and reactive power is Q, the power factor cosφ is well known. This relationship is shown in FIG. 2 (a). This (1)
It is also known that the equation has a correspondence relationship with the following equation (2).

tanφ = Q / P (2) Equation (2), which is the power ratio, is represented by (b) in FIG.

Although power factor transducers are already known, this type of conventional transducer has an analog indicating instrument connected as an output, which in this case
The formula (2) was calculated, and the scale was converted so that cos φ = (Lag) 0.5 to 1.0 to 0.5 (Lead) on the scale of the indicating instrument.

[Problems to be solved by the invention]

By the way, as shown in FIG. 2 (C), the power factor cosφ is Lead,
There is a case where it is desired to convert to a unified linear DC signal such as 4 to 20 mA including the Lag signal, but in this case, it is directly converted to a linear DC signal from FIG. 2 (A) without scale conversion. It is difficult. The present invention has been made in consideration of such a point, and the progress (Lea) shown in FIGS. 2 (b) to 2 (c) represented by the equation (2) is shown.
d) The purpose of the present invention is to provide a power factor transducer capable of converting into, for example, a unified linear DC signal including a delay signal.

[Means for solving problems]

In order to achieve the above object, the present invention uses a multiplication / division (Q · Y / P) circuit in a circuit that takes a ratio of a power signal P and a reactive power Q (tan φ = Q / P) and uses Y as Q. By setting the / P parameter, it is possible to distinguish the lead and lag power factors, and the power factor is linearly converted into a DC signal. Hereinafter, examples will be described in detail.

〔Example〕

FIG. 1 is a block diagram of an embodiment of a power factor transducer according to the present invention. In the figure, v is a voltage in the AC circuit, and i is a current. PT is a transformer, CT is a current transformer, and PWM is a pulse width modulation circuit.
The voltage input v is taken out via the transformer PT and then applied to a known pulse width modulation circuit PWM to be modulated into a pulse width signal according to its magnitude. R1 to R3 are resistors, C is a 90 ° phase shift capacitor, S1 to S3 are analog switches, and A1 to A3 are amplifiers. Resistor R1
And the capacitor C are connected in series between the secondary windings of the current transformer CT, and the connection point is connected to the reference potential point. The current input i is taken out via the current transformer CT and then the resistor R
1 and capacitor C added to the circuit. As a result, the in-phase component of the current i is taken out from the resistor R1, and its output is applied to the switch S1 via the resistor R2. The switch S1 is driven by the output of the pulse width modulation circuit PWM. Therefore, the in-phase component of the voltage v and the current i is multiplied, and the active power P in the AC circuit is extracted from the output terminal of the switch S1 as is well known. This active power P is applied to the amplifier A1.

On the other hand, the 90 ° phase-shifted portion of the current i is taken out from the capacitor C, and its output is applied to the switch S2 via the resistor R3. The switch S2 is driven by the output of the pulse width modulation circuit PWM. In this case, the 90 ° phase shift of the voltage v and the current i is multiplied, and the reactive power Q ′ in the AC circuit is taken out from the output terminal of the switch S2 and the amplifier A
Added to 2. This reactive power Q'includes a frequency term. The FD is a frequency detection circuit configured by, for example, a mono-multi for detecting the frequency of the AC circuit, the input end thereof is connected to the secondary coil of the transformer PT, and the output end thereof is added to the switch S3 to drive it. Therefore, the reactive power Q'is multiplied by the frequency f, and the reactive power signal Q containing no frequency term is taken out from the output end of the switch S3 and added to the amplifier A3. That is, a signal corresponding to the active power P in the AC circuit is extracted from the amplifier A1, and a signal corresponding to the reactive power Q is extracted from the amplifier A3.

When M, M2 input X, Y, Z respectively, (X
.Y / Z) IC multiplication / division circuit, B
C is an absolute value circuit, FC is a function conversion circuit, and R4 is a variable resistor. The output terminal of the amplifier A1 has multiplication and division circuits M1 and M2.
, And the output end of the amplifier A3 is connected to the X input terminals of the multiplication / division circuits M1 and M2, respectively. The Y input terminal of the multiplication / division circuit M1 is connected to the brush of the variable resistor R4, and a constant voltage V is applied to the Y input terminal of the multiplication / division circuit M2.
P is added. The output terminal of the multiplication / division circuit M1 is connected to the amplifier A4. The output terminal of the multiplication / division circuit M2 is connected to the function conversion circuit FC via the absolute value circuit BC, and the output terminal of the circuit FC is connected to the variable resistor R4. The function conversion circuit FC includes an operational amplifier OP, a Zener diode Dz connected between its input and output terminals, and a variable resistor R5.
It consists of

The multiplication / division circuit M2 is tanned by the active power P applied to its Z input terminal and the reactive power Q applied to its X input terminal.
The calculation of φ = (Q / P) · VP (constant) is performed. That is,
The multiplication / division operation circuit M2 performs the operation of the equation (2) by the input P and Q signals and outputs the signal shown in FIG.

The signal corresponding to this power ratio is applied to the absolute value circuit BC to take its absolute value | Q / P |, and this absolute value output is applied to the function conversion circuit FC. In the function conversion circuit FC, since the Zener diode Dz is connected between the input and output terminals of the operational amplifier OP, as shown in FIG.
The output VC of the function generating circuit FC increases until φ = (Q / P) reaches a predetermined value a, but when the input exceeds the Zener voltage of the Zener diode Dz, VC becomes constant.

The voltage VC having such a functional characteristic is represented by VC = K1 | tanΦ | (3) in the range of −a ≦ Φ ≦ a, and VC = K2 (4) in the case of Φ <−a, Φ> a. Become. Note that K1 and K2 represent coefficients, respectively. The voltage VC represented by such an arithmetic expression is applied to the Y input terminal of the multiplication / division circuit M1. The multiplication / division operation circuit calculates tan φ = (Q / P) from the active power P applied to its Z input terminal and the reactive power Q applied to its X input terminal, and also applies it to the Y input terminal (3 ), The voltage VC shown in the equation (4) is multiplied. As a result, the output voltage Vo ′ of the multiplication / division operation circuit M1 is Vo ′ = (P / Q) · Y (5) In the range of ∴−a ≦ Φ ≦ a, Vo ′ is Vo ′ = tanΦ · K1 | tanΦ | (6), and Φ <-a, Φ> a, Vo ′ = tan Φ · K2 (7) In the multiplication / division operation circuit M1, Y shown in equation (5) is (P / Q) Works as a parameter of (6), (7)
It is represented by a formula. The voltage Vo 'represented by the equations (6) and (7) is applied to the amplifier A4 and becomes the voltage Vo.

Here, the voltage Vo ′ represented by the equations (6) and (7)
Is a value obtained by approximating tan φ of the equation (2) shown in FIG. 2 (b) and converting it into a linear DC signal. That is, the phase angle φ
Is in the range of -35 ° to 0 to 35 ° (0 to a in FIG. 3).
In the range of points), the coefficient k1 is set to 0.402, and this range is squared by 0.402 · tan ² φ as expressed by the equations (6) and (7), and in the range of 35 ° to 65 ° The coefficient k2 is approximated by 0.402 tanφ × 0.700 = 0.281 tanφ.

By selecting the coefficients k1 and k2 as described above, 0.5
It was possible to convert into a power factor signal Vo within ± 1.6 ° in terms of angle between (Lag) and 1.0 to +0.5 (Lead). Figure 4 shows the experimental results (note that
FIG. 4 shows the case where the phase angle φ is only 0 to 70 °), the solid line shows 1-cosφ with respect to the phase angle φ, and the chain line shows the output voltage Vo of the equations (6) and (7). It is a thing.
In this way, the DC voltage Vo obtained by linearly converting the power factor cosφ
Is added to the output circuit OUT.

In the output circuit OUT, A5 is an amplifier, TR is a transistor, R6 to R8 are resistors, Dz1 is a Zener diode, V is a positive voltage source, and t1 and t2 are output terminals. L
Indicates a digital voltmeter or the like. The output circuit OUT converts the output voltage Vo into a unified signal such as 4 to 20 mA, and the resistor R8 and the voltage source V are bias circuits thereof. As described above, in the present invention in which the bias circuit is added to the output circuit, the output terminals t1 and t2 are shown in FIG.
As shown in (c), a unified signal of 4 to 20 mA is taken out.

When only the cosφ linear signal is required in the circuit of FIG. 1, by removing the bias circuit, when the phase angle Φ is positive, Vo = (1-cosΦ), and when Φ is negative, It is output as Vo = (cosΦ-1). In this case, cos φ with respect to the phase angle φ is shown as shown in FIG.

[Effect of the present invention]

As described above, in the present invention, a multiply / divide operation (Vo = Q · Y / P) circuit is used in a circuit that takes a ratio (tan φ = P / Q) of power P and reactive power Q, and Y is Q / P. By setting the parameter of, the power factor signal in the AC circuit including the Lead and Lag signals can be directly converted into a DC signal in proportion thereto. Moreover, since the power factor conversion is performed by the power ratio as described above, the power factor in the power circuit can be adjusted not only in the distorted wave, but also in the single-phase and unbalanced type power circuits. It is possible to obtain a transducer that can be converted into a DC signal.

[Brief description of drawings]

FIG. 1 is a connection diagram of an embodiment of the transducer according to the present invention, and FIGS. 2 to 4 are diagrams for explaining the operation and characteristics of the device of the present invention. M1 ... Multiplication / division circuit, M2 ... Multiplication circuit, FC ... Function generation circuit.

Claims (1)

[Claims] 1. An active power / reactive power conversion circuit for obtaining active power P and reactive power Q in an AC circuit, and this active power
It consists of a division circuit that receives the output of the reactive power conversion circuit and performs the operation of (Q / P), an absolute value circuit that takes the absolute value of the output of this division circuit, a zener diode connected between the operational amplifier and its input / output terminal. A function conversion circuit for function-converting and outputting the output of the division circuit obtained via the absolute value circuit,
A multiplication / division circuit for multiplying / dividing (P / Q) · VC by receiving the outputs P and Q of the active power / reactive power conversion circuit and the output VC of the function conversion circuit, and an output for extracting the output of this multiplication / division circuit Power factor transducer with terminals.