JPH0431401B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention relates to a proportional/integral/derivative control circuit used for combustion control, flow rate control, etc. of a hot water boiler.

(b) Prior art This type of so-called PID control circuit is disclosed in Japanese Patent Application Laid-Open No. 59-24317.
As disclosed in the publication, there are cases in which proportional, differential, and integral circuits are provided separately and the outputs of these circuits are added together in an adder circuit to obtain a PID control signal, and in which a proportional and differential circuit is added to the outputs of the proportional and differential circuits. It is known that a PID control signal is obtained by adding the outputs of an integrating circuit.

(c) Problems to be solved by the invention In the PID control circuit described above, the time constants of the differentiating circuit and the integrating circuit are determined separately, and in order to stabilize the PID control signal, the time constants of both circuits are determined separately. Since the ratio is generally selected to be 1:4, there is a drawback that circuit design becomes complicated. Furthermore, when performing combustion control, the rate of change of the control signal is often limited, and a rate of change signal of the control signal may be required. However, since the PID control circuit does not have a function to generate a change rate signal in its arithmetic circuit section, a separate circuit must be provided to differentiate the control signal and generate a change rate signal, resulting in high costs. It was hot.

This invention was made in view of the above-mentioned fact, and automatically sets the ratio of the time constants of differentiation and integration to 1:
It is an object of the present invention to provide a proportional-integral-derivative (PID) control circuit which can be selected from 4 to 4, and which can also obtain a speed change signal of a control signal without using a separate circuit.

(d) Means for Solving Problems The proportional/integral/derivative control circuit of the present invention includes an operational amplifier circuit whose signal input terminal is connected to a non-inverting input terminal, and an output terminal and an inverting input terminal of this operational amplifier circuit. a first proportional and differential circuit comprising a resistor connected between the first proportional and differential circuit, and a capacitor connected between the inverting input terminal and the reference terminal of the operational amplifier circuit;
a second proportional and differential circuit connected in cascade to the first proportional and differential circuit using the output terminal of the operational amplifier circuit as an input terminal, and having the same configuration as the first proportional and differential circuit; and an integrating circuit connected in cascade to the output terminals of the proportional and differential circuits,
The configuration is such that the output of this integrating circuit is used as a control signal.

(e) Effect When two proportional and differential circuits of the same configuration are connected in series, a change rate signal of the control signal is obtained, and by integrating this signal, a PID control signal is obtained. Therefore, there is no need to provide a separate circuit for generating a change rate signal. Furthermore, the ratio of the time constants of differentiation and integration is naturally 1:4, which facilitates circuit design.

(F) Embodiments Hereinafter, embodiments of the present invention shown in the drawings will be described in detail.

FIG. 1 shows the basic structure of a PID control circuit according to the present invention. In FIG. 1, an operational amplifier circuit 2 having a non-inverting input terminal A connected to a signal input terminal 1, a resistor 3 connected between an output terminal C and an inverting input terminal B of this operational amplifier circuit 2, A first proportional and differential circuit 6 is constituted by a capacitor 5 connected between the inverting input terminal B of the operational amplifier circuit 2 and the reference terminal 4. In addition, the operational amplifier circuit 2
an operational amplifier circuit 7 with a non-inverting input terminal D connected to the output terminal C of the operational amplifier circuit 7; and a resistor 8 connected between the output terminal F and the inverting input terminal E of the operational amplifier circuit 7.
and a capacitor 9 connected between the inverting input terminal E of the operational amplifier circuit 7 and the reference terminal 4. A second proportionality and differentiation circuit 10 is connected in cascade to the first proportionality and differentiation circuit 6. There is. This second proportional/differential circuit 10 has the same circuit configuration as the first proportional/differential circuit 6, and the resistors 3, 8 and capacitors 5, 9 of both circuits have the same circuit constants. Further, an integrating circuit 11 is cascade-connected to the second proportional/differential circuit 10 . This integrating circuit 11 has an operational amplifier circuit 13 having an inverting input terminal H connected to an output terminal F of an operational amplifier circuit 7 via a resistor 12, and an output terminal O of this operational amplifier circuit 13.
A capacitor 14 is connected between the inverting input terminal H and the inverting input terminal H, and the non-inverting input terminal G of the operational amplifier circuit 13 is connected to the reference terminal 4. Further, the output terminal O of the operational amplifier circuit 13 is connected to the signal output terminal 15.

When a voltage (vi) proportional to the deviation between a measured value such as temperature and a set value is applied between the signal input terminal 1 and the reference terminal 4, the first proportional and differential circuit 6 appears at the output terminal C. The output is given by Eq. However, τd=Rd·Cd, t is time.

v _C = vi + τd·dvi/dt... Furthermore, the output appearing at the output terminal F of the second proportional and differentiating circuit 10 that receives this output is expressed by the formula.

v _F =V _C +τd・dv _C /dt=vi+τd・dvi/dt+τd・d
(vi + τd・dvi/dt)/dt = 2τd・dvi/dt+vi+τd ²・d ² vi/dt ² ... Also, the integration circuit 11 which inputs v _F performs inversion integration, and its output is shown by the formula There is. However, τi=RI・Ci.

v _O = -1/τi∫v _F dt = -1/τi (2τd・vi+∫vidt
+τd ²・dvi/dt) =−2τd/vi(vi+1/2τd∫vidt+τd/2・dvi
/dt)...... On the other hand, it is known that in a PID control circuit, when the deviation input is x and the control output is y, the general formula shown in the following equation can be obtained. However, P is a constant of proportionality, T _I
is the integral time constant and T _D is the differential constant.

y=P(x+1/T _I ∫xdt+T _D・dx/dt)... As is clear from the formula and formula, in the one in Figure 1, the integral time constant T _I is 2τd and the differential constant T _D is τd/2. , the ratio of the time constants of differentiation and integration becomes 1:4.
Therefore, by determining the resistance value Rd of the resistors 3 and 8 and the capacitance Cd of the capacitors 5 and 9, the time constant ratio is automatically selected to be 1:4, making circuit design easy. Furthermore, since the output of the second proportionality/differentiation circuit 10 expressed by the equation corresponds to a control change speed signal obtained by differentiating the control signal, the speed change signal of the control signal can be obtained without constructing a separate circuit. Moreover, since the time constant is only half that of the conventional one, the capacitance of the capacitor can be reduced, and an inexpensive one with a small bias current can be used for the operational amplifier circuit, thereby reducing the cost of the circuit.

FIG. 2 shows an example of application of the PID control circuit of the present invention, and parts common to those in FIG. 1 are given the same reference numerals.

In the one in FIG. 2, the second proportional and differential circuit 10
A speed limiter circuit 18 consisting of two Zener diodes 16 and 17 is provided between the and integrating circuit 11, and the absolute value of the change speed signal of the second proportional and differential circuit 10 is set to the Zener voltage Z _D of the Zener diodes 16 and 17. It is set to be limited. Further, the output of the integrating circuit 11 is inverted and amplified by a proportional amplifier circuit 22 consisting of resistors 19 and 20 and an operational amplifier circuit 21. Note that resistors 23, 24 and capacitors 25, 26 are proportional and differential circuits 6, 1.
This is to limit the high frequency components included in the 0 input. Further, the resistor 27 is used to limit the current flowing through the Zener diodes 16 and 17, and is sufficiently smaller than the resistor 12. Further, resistors 28 and 29 are for bias current compensation.

(G) Effects of the invention Since this invention is configured as described above,
The ratio of the time constants of differentiation and integration can be set to 1:4 without complicated circuit design, and the control signal can be stabilized, and furthermore, without the need to construct a separate circuit,
Since it is possible to generate a speed change signal as a control signal, circuit design is facilitated and the circuit can be simplified. In addition, parts can be standardized,
It can also contribute to lowering the cost of circuits, such as by allowing the use of inexpensive circuit elements.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing the principle structure of a proportional/integral/differential control circuit according to the present invention, and FIG. 2 is an electric circuit diagram showing an example of an applied circuit. 1... Signal input terminal, 2, 7... Operational amplifier circuit, 3, 8... Resistor, 4... Reference terminal, 5, 9...
...capacitor, 6,10...proportional and differential circuit,
11...Integrator circuit.

Claims (1)

[Claims] 1. An operational amplifier circuit whose signal input terminal is connected to a non-inverting input terminal, a resistor connected between the output terminal of this operational amplifier circuit and an inverting input terminal, and an inverting input terminal and a reference terminal of the operational amplifier circuit. and a capacitor connected between the first proportional and differential circuit, and the first proportional and differential circuit is cascade-connected to the first proportional and differential circuit with the output terminal of the operational amplifier circuit as an input terminal, and It is characterized by comprising a second proportional and differentiating circuit having the same configuration as the differentiating circuit, and an integrating circuit connected in cascade to the output terminal of the second proportional and differentiating circuit, and using the output of this integrating circuit as a control signal. Proportional/integral/derivative control circuit.