JP2823338B2 - Absorption chiller control device - Google Patents

Description

The present invention relates to a control device for an absorption refrigerator that controls an absorption refrigerator by fuzzy control.

(B) Conventional technology Conventionally, in absorption chiller / heaters and refrigerators, the chiller outlet temperature is detected, and based on a deviation from a set value, the absorption chiller / heater,
Proportional control, which controls the heat input to the refrigerator, or PID control, based on the chilled water outlet temperature, was common.

Since these controls uniquely control the heat input to the absorption chiller for a single physical quantity, the chilled water outlet temperature, a skilled operator performs all conditions such as start, stop, and rapid load fluctuations. There was a problem in responsiveness compared to control. To improve this, multiple physical quantities (deviation from the set value of the chilled water outlet temperature, its rate of change over time, etc.) representing the external conditions of the absorption chiller / heater and absorption chiller, A fuzzy rule and membership function are constructed between multiple physical quantities (conditions of high-temperature generator, its rate of change over time, etc.) that represent conditions, the amount of heat input to the absorption chiller / heater, the amount of heat input to the refrigerator, and the amount of circulation of the absorbent. Then, a control method for controlling the absorption refrigerator based on the control method has been proposed.

According to the control method, PID only by chilled water outlet temperature
Compared to the control method, the internal and external states of the absorption chiller / heater and the absorption chiller and their changes can be detected, and these can be judged and controlled in an integrated manner. Good control performance can be obtained.

However, when the operation of the absorption chiller / heater and the absorption chiller is stably controlled (the chilled water outlet temperature can be controlled close to the set value), the set value tracking performance generally referred to in fuzzy control is used. There is a problem. That is, the offset from the set value remains, and the device is easily affected by disturbance.

(C) Problems to be Solved by the Invention An object of the present invention is to improve control performance near a set value, which has a difficulty in the above-described conventional method.

(D) Means for Solving the Problems The present invention has been made in view of such a point,
Control of absorption chillers that form a refrigeration cycle by connecting evaporators, absorbers, generators, condensers, etc., and control the amount of heating of the generator using fuzzy inference based on external conditions including the chilled water outlet temperature In the apparatus, a fuzzy control unit comprising a fuzzy rule and a membership function between the external condition and the heating amount, a proportional value to a deviation between the chilled water outlet temperature and a set value thereof, A differential value, a PID control unit that controls the heating amount using the integral value, and a control by the PID control unit when the deviation is equal to or less than a certain value, and a control by the fuzzy control unit when the deviation is larger than the certain value. As you do,
And a switching device for switching between the two control units.

(E) Operation According to the present invention, control is performed using the fuzzy control unit when the chilled water outlet temperature is more than the set value, and when the chilled water outlet temperature approaches the set value, the PID control unit is used. Since the control is performed, an offset of the chilled water outlet temperature with respect to the set value in the control stable period does not remain, and the responsiveness to the set value of the chilled water outlet temperature is improved.

(F) Example FIG. 1 shows a double-effect absorption refrigerator using water as a refrigerant and an aqueous solution of lithium bromide (LiBr) as an absorbent (solution), wherein 1 is a high-temperature generator equipped with a burner 1B, 2 is a low-temperature generator, 3 is a condenser, 4 is an evaporator, 5 is an absorber, 6 is an absorbent pump, 7, 8 are a low-temperature heat exchanger and a high-temperature heat exchanger, respectively, 10 is a diluted absorbent pipe, 11 Is an intermediate absorption liquid pipe, 12 is a concentrated liquid pipe, 13 is a refrigerant pipe, 14 is a refrigerant liquid flow down pipe, and 15 is a refrigerant liquid circulation pipe, each of which is connected as shown in FIG. A refrigerant pump is provided in the middle of the refrigerant liquid circulation pipe 15.
15P is provided. Reference numeral 16 denotes a fuel supply pipe connected to the burner 1B. A fuel control valve (heating amount control valve) 17 is provided in the fuel supply pipe 16. Reference numeral 20 denotes a cold water pipe, and an evaporator heat exchanger 21 is provided in the middle of the cold water pipe 20. Further, 22 is a cooling water pipe.

23 is a control panel constituting the control device according to the present invention, 24 is a chilled water outlet temperature detector provided in the chilled water pipe 20, and the chilled water temperature detector 24 and the fuel control valve 17 are control panels.
Connected to 23. The control panel 23 is provided with a fuzzy control unit 25, a PID control unit 27, a switching device 28, and a control device 26 for the fuel control valve 17. Among them, the fuzzy control unit
25 includes a fuzzy inference unit and a control rule storage unit. The fuzzy control unit 25 operates the fuel control valve 17
A logical operation is performed on KQ by fuzzy inference, and the obtained operation amount KQ is output to the control device 26.

The control device 26 corrects the opening of the fuel control valve 17 based on the operation amount KQ. Specifically, the control device 26 holds the opening degree information Q of the fuel control valve 17 and adjusts the opening degree of the fuel control valve 17 according to the opening degree information Q. And the amount of operation
Every time KQ _n is received, the previously set opening information Q
new opening information by the _n-1 and the operation amount _{KQ n Q n = Q n-} 1 + KQ n
Set. That is, in this embodiment, the operation amount KQ from the fuzzy control unit 25 or the PID control unit 27 is selectively selected, and the opening of the fuel control valve 17 is changed. The fuzzy control unit 25
A control rule (fuzzy rule) necessary for the fuzzy logic operation to be executed, a condition part, and a conclusion part membership function are stored therein. 30 is an arithmetic unit, 31 is an evaporator 4
This is a chilled water inlet temperature detector provided in the chilled water pipe 20 on the inlet side. 32 is a high temperature generator temperature detector for detecting the temperature of the high temperature generator, and 33 is a cooling water inlet temperature detector for detecting the cooling water inlet temperature. The arithmetic unit 30 is a chilled water outlet temperature detector.
24, cold water inlet temperature detector 31, high temperature generator temperature detector 32,
Then, it takes in the temperature data of the cooling water inlet temperature detector 33, calculates the next data, and sends it to the fuzzy controller 25.

Coil water outlet temperature deviation (eto) eto = current value-target value Chilled water outlet temperature deviation rate of change (dto) dto = current value-previous value Chilled water inlet temperature change rate (dtci) dtci = current value-previous The change rate of the chilled water inlet temperature (dti) dti = present value−previous value The high temperature generator temperature change rate (dtg) dtg = present value−previous value Next, a functional block diagram of the fuzzy controller 25 is shown in FIG. Shown in the figure. In the figure, reference numeral 34 denotes data from the arithmetic unit 30.
eto, dto, dtci, dti, dtg, fuzzy control unit 25
This is a goodness-of-fit calculation unit that calculates the goodness of each control rule from the conditional part membership functions and control rules stored in the unit. Is the degree of conformity. Here, eto, dto, dt
i, dtci, and dtg are defined as shown in FIGS. 3 to 7 using NB, NS, ZR, PS, and PB, respectively. As can be seen, weights of 0.4, 0.5, and 0.5 are applied to dti, dtci, and e to reduce the degree of influence.

The control rules eto, dto, and dtg are as shown in FIG. That is, here, the rule is not defined for the adjacent control rules, and the calculation time of the degree of conformity is shortened. Also, eto and dto are defined as shown in FIG. Here, NZ and PZ, which will be described later, are added to the conclusion part membership function to improve the degree of convergence of the control amount KQ when eto approaches the set value. Fig. 10 is defined for dtci and Fig. 11 is defined for dti.

Reference numeral 35 denotes a correction unit that corrects the conclusion part membership function in the control rule storage device 28 so that the upper part thereof is cut in accordance with the fitness obtained by the fitness calculating unit 34. Note that this conclusion part membership function
The ones in Figure 12 are defined. As can be seen from this figure, NZ and PZ are defined near ZR to improve control.

Reference numeral 36 denotes a logical sum unit that superimposes the respective membership functions corrected by the correction unit 35 to obtain a logical sum, and reference numeral 37 denotes a gravity center calculation unit that calculates the center of gravity of the function generated by the logical sum unit 36. The calculated value is given to the control device 26 as the valve operation amount KQ.

On the other hand, the PID control unit 27 performs PID control based on the chilled water outlet temperature from the chilled water outlet temperature detector 24, and calculates and outputs valve opening information Q by the following equation.

Q = (100 / P) { eTo n + Σ (τ / I) eTo n + D / τ (eTo n -eTo n-1)} + 50 (%) where, P: proportional constant (° C.), I: integral time ( sec) D: derivative time (sec), τ: sampling time (sec),
Sigma: integrated value of the integral term (%), tc: the set temperature, the To: cold water outlet temperature, ETO _n: a eTo _n = To-tc, the scale of PID (steps) P: 0~10 (0.1), I: 0 to 2500 (10) D: 0 to 100 (1.0)

Further, in such a configuration, the switching device 28 controls the chilled water outlet temperature.
When the deviation between To and the set temperature tc is equal to or greater than a predetermined value, the valve control device
The information Q from 26 is transmitted to the fuel control valve 17, and the output of the PID control unit 27 is transmitted to the control valve 17 when the deviation is equal to or less than a predetermined value.

In such a device, during the operation of the absorption refrigerator, the arithmetic unit 30 includes the chilled water outlet temperature detector 24 and the chilled water inlet temperature detector.
31, temperature signals are taken in from the high-temperature generator temperature detector 32 and the cooling water inlet temperature detector 33, for example, every five seconds. Then, from the temperature signal thus obtained, the deviation of the chilled water outlet temperature (eto) and the rate of change of the deviation of the chilled water outlet temperature (dt)
o), the cooling water inlet temperature change rate (dtci), the cold water inlet temperature change rate (dti), and the high temperature generator temperature change rate (dtg) are calculated and sent to the fuzzy controller 25.

The fitness calculation unit 34 in the fuzzy control unit 25 checks the fitness of the condition parts of all the control rules. Then, using the matching degree, the correction unit 35 corrects the membership function of the corresponding conclusion part shown in FIG. That is, the portion above the fitness of each membership function is cut. The logical sum of the membership functions corrected in this way is obtained by the logical sum unit 36, and the center of gravity of the membership function is obtained by the center of gravity calculating unit 37. The output of the center-of-gravity calculation section 37 is output as the operation amount KQ _n of fuel control valve 17.

The valve control device 26 calculates the operation amount KQ _n and the opening degree information Q
calculates a new opening information _{Q n = Q n-1 +} KQ n based on the _n-1. Then, to adjust the fuel control valve 17 in response to the opening information Q _n.

 Such an operation is repeated in the above-described 5-second cycle.

On the other hand, the PID control unit 27 calculates the opening degree information Q at a predetermined cycle according to the above-described formula.

When the switching device 28 detects that the difference between the chilled water outlet temperature To and the set value tc is equal to or higher than a predetermined temperature (for example, 0.2 ° C.), the opening information Q from the valve control device 26 is transmitted to the fuel control valve 17.
Tell When the difference between the chilled water outlet temperature To and the set value tc is equal to or less than a predetermined temperature, the switching device 28 transmits the opening degree information Q from the PID control unit 27 to the fuel control valve 17.

(G) Effect of the Invention As described above, according to the control device of the absorption chiller of the present invention, when the chilled water outlet temperature is more than the set value, the control is performed using the fuzzy controller, and the chilled water outlet temperature is controlled. Control is performed using the PID control unit when the temperature approaches the set value, so that the offset of the chilled water outlet temperature with respect to the set value in the control stable period does not remain, and the ability to follow the set value of the chilled water outlet temperature is improved.

Therefore, it is possible to perform control with responsiveness and stability, and it is possible to perform quick and accurate control.

[Brief description of the drawings]

FIG. 1 is a block diagram of an absorption refrigerator to which the control device of the present invention is applied, FIG. 2 is a functional block diagram of a fuzzy control unit used in the device of the present invention, and FIGS. 8 to 11 are explanatory diagrams of control rules, and FIG. 12 is a characteristic diagram of the membership function of the conclusion part. 1 high temperature generator, 2 low temperature generator, 3 condenser
4 ... Evaporator, 5 ... Absorber, 17 ... Fuel control valve, 23 ...
... Control panel, 24 ... Chilled water outlet temperature detector, 25 ... Fuzzy control unit, 26 ... Control device, 27 ... PID control unit, 28 ... Switching device, 30 ... Computing device, 31 ... Cold water inlet Temperature detector,
32: High temperature generator temperature detector, 33: Cooling water inlet temperature detector.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Eiichi Enomoto 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-62-73054 (JP, A) Hei 4-32668 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F25B 15/00 306

Claims (1)

(57) [Claims] 1. An absorption system in which an evaporator, an absorber, a generator, a condenser, etc. are connected to form a refrigeration cycle, and a heating amount of the generator is controlled by fuzzy inference based on external conditions including a chilled water outlet temperature. In the control device of the type refrigerator, a fuzzy control unit comprising a fuzzy rule and a membership function between the external condition and the heating amount, and a deviation between the chilled water outlet temperature and a set value thereof. A PID control unit for controlling the heating amount using a proportional value, a differential value, and an integral value; and a PID control unit for controlling when the deviation is equal to or less than a certain value. A control device for switching between the two control units so as to perform control by the control unit.