JPH0624886Y2 - Proportional-integral amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a proportional-integral amplifier circuit used in a feedback control system.

(Problems with Prior Art) Generally, a proportional-integral amplification circuit for automatic control obtains a control output by matching a detected amount with a set amount and performing a proportional-integral operation, and is often used in a feedback control system. There is. An example of a conventional proportional-plus-integral amplifier circuit is shown in FIG. In FIG. 1, A ₁ is an operational amplifier, and a set amount, for example, a set voltage es, is detected at a first input terminal of the operational amplifier A ₁ via a first resistor Ri ₁ and a detected amount via a second resistor Ri _2. For example, the detection voltage ed is input. Operational amplifier A
_It is assumed that the second input terminal of ₁ is connected to the zero volt line via the third resistor Rg. The variable resistor Rf and the capacitor Cf are connected in series between the first input terminal and the output terminal of the operational amplifier A ₁ . In the circuit configured as described above, the transfer function G ₁ , the loop gain g ₁ , and the time constant T ₁ are respectively expressed by the following equations.

g ₁ = −Rf / Ri ………… (2) T ₁ ＝ Cf ・ Rf (sec) ………… (3) (where Ri ＝ Ri ₁ ＝ Ri ₂ ), where e ₀ is the output voltage and S is Laplace. It is an operator.) The circuit of FIG. 1 is simplified (detection voltage ed is omitted) and expressed as shown in FIG. When a step signal having a magnitude of e ₁ is input to the set voltage es in FIG. 3 as shown in FIG. 4 (a), the waveform of the output voltage e ₀ is shown in FIG. 4 (b).
As shown.

Here, in order to adjust the time constant T ₁ of the proportional-plus-integral amplifier circuit of FIG. ₁ , the capacitance of the capacitor Cf is changed or the variable resistance is changed.
There is a method to change the value of Rf. However, the method of adjusting the time constant T ₁ by changing the capacitance of the capacitor Cf cannot be continuously adjusted, which is very inconvenient. Further, the method of adjusting the time constant T ₁ by changing the value of the variable resistor Rf has a drawback that the loop gain g ₁ changes simultaneously with the time constant T ₁ as shown in the equations (2) and (3). Atsuta As described above, in the proportional-plus-integral amplifier circuit shown in FIG. ₁ , it is difficult to adjust the time constant T ₁ and the loop gain g ₁ separately, so it is difficult to optimally adjust the constants according to the conditions of the circuit used. It was.

(Purpose of the Invention) The present invention has been made in view of the above points, and the time constant and the loop gain can be changed separately without affecting each other, and according to the conditions of the circuit to be used. It is an object of the present invention to provide a proportional-plus-integral amplifier circuit that can be optimally adjusted.

(Summary of the Invention) The present invention includes a resistor for gain adjustment, a second operational amplifier of voltage follower, and a time constant circuit for exclusive use of time constant adjustment in a feedback loop of a proportional-integral amplifier. The feature is that it is provided.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, the same parts as those in FIG. 1 are indicated by the same reference numerals, and the description thereof will be omitted. A time constant circuit 1 is connected to the output terminal of the operational amplifier A _{1 by connecting} a capacitor Cf and a variable resistor Rf ₂ for adjusting the time constant as shown in the figure.
The other end of the variable resistor Rf ₂ is connected to the zero volt line. The common connection point 2 between the capacitor Cf and the variable resistor Rf ₂ is connected to the second input terminal of the second operational amplifier A ₂ of the voltage follower (connecting the first input terminal and the output terminal). A variable resistor Rf ₁ for gain adjustment is connected between the output terminal of the _second operational amplifier A _{2 and} the input terminal of the first operational amplifier A ₁ .

In the circuit configured as described above, the second operational amplifier A ₂ is a voltage follower, so that the input impedance is high, the output impedance is low, and the gain is 1. Therefore, the quantity of electricity input to the second input terminal of the operational amplifier A ₂ (the quantity of electricity at the common connection point 2) appears at the output terminal without changing its size. Therefore, the loop gain g ₂ of this circuit is the variable resistor Rf ₁ for gain adjustment.
Adjust to change. In addition, the time constant T ₂ is the capacitor
Since it is determined by the value of Cf and the variable resistor Rf ₂ for adjusting the time constant, the resistor Rf ₂ may be adjusted. At this time, since the second operational amplifier A ₂ of the voltage follower is connected, the loop gain g ₂ and the time constant T ₂ can be adjusted independently without being influenced by each other. That is, the transfer function G ₂ , the loop gain g ₂ , and the time constant T ₂ are each expressed by the following equation.

g ₂ = −Rf ₁ / Ri ………… (5) T ₂ ＝ Cf ・ Rf ₂ (sec) ………… (6) (where Ri ＝ Ri ₁ ＝ Ri ₂ and e ₀ is the output voltage. ..) The above equation (4) shows that the circuit of FIG. 2 operates similarly to the conventional proportional-plus-integral amplifier circuit. Further, according to the equations (5) and (6), it is understood that the loop gain g ₂ and the time constant T ₂ change independently without affecting each other by changing the resistances Rf ₁ and Rf ₂ respectively. it can.

Here, when the circuit of FIG. 2 is simplified and expressed (the detection voltage ed is omitted), it is shown as in FIG. In FIG. 5, K represents a proportional (P) gain represented by Rf ₁ / Ri, and T represents an integral (I) constant represented by Cf · Rf ₂ . The relationship between the input es and the output e _{0 in} FIG. 5 is e ₀ / es = −K (1 + T _s ) / T _s (7).

A step signal as shown in FIG. 4 (a) is input to the setting es in FIG. 5, and Rf ₁ is changed to obtain a proportional (P) gain (K = Rf).
The output voltage waveform at each gain when ₁ / Ri) is changed is shown in FIG. 6 (a).

Further, a step signal as shown in FIG. 4 (a) is input to the set voltage es in FIG. 5, Rf ₂ is changed, and the integral (I) constant (T
= Rf ₂ · Cf), the output voltage waveform at each integration constant is shown in FIG. 6 (b).

Here, the proportional-integral amplifier circuit of the present invention whose input / output relationship is expressed by the equation (7) is shown on the board gain line as shown in FIG. And the 8th feedback loop
Assuming as shown in the figure, when T ₁ > T ₂ and T = T ₁ are matched, the Bode gain diagram of the closed loop transfer function is shown as in FIG. 9 (provided that K = 1). In FIG. 9, point A is adjusted to T = T ₁ , and K = K independently of T.
If it can be adjusted to ₁ (arbitrary), the stability and response of the feedback system can be easily set to optimum values.

(Effect of the Invention) As described above, according to the present invention, in the proportional-plus-integral amplifier circuit, the time constant and the loop gain can be changed separately without affecting each other. Therefore, optimum adjustment can be performed according to the conditions of the circuit used. Further, since the control output can be obtained similarly to the conventional proportional-plus-integral amplifier circuit, it can be used in a wide range by incorporating it into various circuits having different control purposes.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional proportional-plus-integral amplifier circuit,
FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 4 (a) is a signal waveform diagram showing an example of an input signal, FIG. 4 (b) is an output waveform diagram of the circuit of FIG. 3, and FIG. 5 is a simplified diagram of FIG. Circuit diagram, FIG. 6 (a) is an output waveform diagram when the proportional gain K is changed, FIG. 6 (b) is an output waveform diagram when the integration constant T is changed, and FIG.
9 and 9 are Bode gain diagrams for explaining the effect of the present invention, and FIG. 8 is a block diagram of a feedback loop. 1 ... Time constant circuit, A ₁ , A ₂ ... Operational amplifier, Cf ... Capacitor, Ri ₁ , Ri ₂ , Rg ... Resistor, Rf ₁ ... Gain adjusting variable resistor, Rf ₂ ... Time constant adjusting variable resistor.

Claims (1)

[Scope of utility model registration request] 1. A first operational amplifier to which a detected quantity of electricity and a set quantity of electricity are inputted via a resistor, a capacitor having one end connected to an output terminal of the first operational amplifier, and one end connected to a zero volt line. And a voltage constant follower having the other end connected to the other end of the capacitor and a first variable resistor, and an input terminal connected to a common connection point of the capacitor and the first variable resistor of the time constant circuit. Of the second operational amplifier, and a second variable resistor for gain adjustment connected between the output terminal of the second operational amplifier and the input terminal of the first operational amplifier.