JP2011247472A - Pid control method of absorption type device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PID control method of an absorption type device that stabilizes a brine outlet temperature, even if a brine flow rate is changed from a rated value.SOLUTION: There are defined an input heat quantity as M (%), a flow rate ratio with respect to a rated flow rate of brine as F, a difference between brine temperatures at an inlet and an outlet of an evaporator as e (°C), a proportional zone in the rated flow rate as P(°C), an integrated time in the rated flow rate as Ti(sec), and a differential time in the rated flow rate as Td(sec). Then, the input heat quantity M is PID-controlled by a following expression in which the proportional zone is set as (P/F), the integrated time as (Ti/F), and the differential time as (Td.F). M=(100/(P/F)).e+(1/(Ti/F))∫edt+(Td.F)de/dt.

Description

  The present invention relates to a control method for performing heat input control of an absorption refrigerator or an absorption chiller / heater (in the present application, including both of them) by a PID method.

  When air conditioning is performed by an absorption device, a system called PID control is often used to control the amount of heat input to the regenerator. Generally, this is arithmetically controlled by the parameters of the proportional band P, the integration time Ti, and the differentiation time Td set based on the case where the flow rate of the brine flowing through the heat load device is rated. On the other hand, the flow rate of brine may be reduced below the rated value for the purpose of energy saving. An example of PID control is disclosed in Patent Document 1 below.

JP 2007-263462 A

However, even if the brine flow rate is changed, in the conventional control, the parameters of the PID remain set values based on the rated flow rate value, so that the brine outlet temperature when leaving the evaporator fluctuates up and down greatly. It may rise and fall repeatedly (hunting phenomenon).
Therefore, a problem to be solved is to provide a PID control method for an absorption type device in which the brine outlet temperature is stabilized even if the brine flow rate is changed from the rated value.

In view of the above problems, the first invention
Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
M = (100 / (P _r / F)) · e +
_{(1 / (Ti r / F} )) ∫edt + (Td r · F) de / dt ······ (2)
An absorption-type apparatus characterized in that the heat input M is PID controlled by the above formula where the proportional band is (P _r / F), the integration time is (Ti _r / F), and the differential time is (Td _r · F). A PID control method is provided.

In the second to fourth inventions, unlike the first invention, not all three parameters are replaced as a function of F, but one of P, I, and D is used as a function of F.
That is, PID control is performed using one of the following equations.
M = (100 / (P _r / F)) · e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
_{M = (100 / P r)} · e + (1 / (Ti r / F)) ∫edt + (Td r) de / dt
M = (100 / P _r ) · e + (1 / Ti _r ) ∫edt + (Td _r · F) de / dt

In the fifth invention,
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
(100 / P _r ) e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
An absorption formula characterized by setting the value obtained by multiplying the calculated value by this formula, where the proportional band is P _r , the integration time is Ti _r , and the differential time is Td _r to the flow rate ratio F, the heat input amount (%) of PID control. A device PID control method is provided.

  In 6th invention, it replaces with the said flow rate ratio F of 1st-5th invention, and uses the ratio with respect to the pressure difference at the time of the rated flow of the pressure difference of the evaporator inlet and outlet of a brine flow.

If the brine flow rate is made smaller than the rated value, that is, the flow rate ratio F is made small, it is considered that the brine temperature difference e increases. Small Therefore, if the difference between the brine temperature at the inlet and outlet of the evaporator at the rated flow rate e _r, be replaced with e = e r / _F, e is than the value (1 F than e _r ) Is appropriate in the sense that it expands according to When this substitution is performed, the formula (2) for obtaining the heat input M is the following formula (4).
_{M = (100 / P r)} · e r + (1 / Ti r) ∫e r dt +
(Td _r ) de _r / dt (4)
Although described again in the embodiment, this equation (4) is the same as the equation at the rated flow rate. That is, even when the flow rate ratio F is decreased, the time t in the control equation (2) is obtained by replacing each parameter with P = P _r / F, Ti = Ti _r / F, and Td = Td _r · F. The state of the change is the same as the time change state of the control arithmetic expression at the rated flow rate, and a large hunting phenomenon as in the conventional case when the flow rate ratio F is reduced can be prevented, contributing to stabilization.

  In the second to fourth inventions, some of the terms are the same as those in the formula (2), and thus, a large hunting phenomenon is mitigated according to the same terms, although not as much as the first invention.

In the fifth invention, the output value is made smaller by multiplying the output value by the following formula, that is, the control arithmetic expression for calculating the conventional heat input (%) by the flow rate ratio F, and the recalculated value is used as the heat input. This is a control method. Therefore, it can be operated with a simple correction by simply multiplying the heat input value of the conventional control method by F.
(100 / P _r ) e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
In the sixth invention, since the flow rate depends on the pressure difference, the pressure difference ratio can be used instead of the flow rate ratio.

FIG. 1 is an overall view of an absorption type apparatus according to the present invention in which heat load devices are also displayed. FIG. 2 is a flowchart showing an example of the control method of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. The present invention may be a single-effect absorption device or a double-effect or higher-effect absorption device, but the entire structure will be described with reference to FIG. 1, taking a typical double-effect absorption chiller / heater as an example. To do. It is connected to a heat load device F such as an external indoor air conditioner, thereby enabling cooling and heating.
In the case of cooling, the on-off valves V1, V2, and V3 are closed. The casing is divided into an upper body 11 and a lower body 10. An evaporator 12 is formed on one side of the lower body 10 in the left-right direction, and an absorber 14 is formed on the other side. The upper body 11 is provided with a low temperature regenerator 18 and a condenser 20, and a high temperature regenerator 16 is provided apart from these. The high-temperature regenerator 16 in this example is a gas burner type, but may be an oil burner type. In the following, the role of each of these devices and the flow of refrigerant and absorbent are outlined.

  The evaporator 12 is disposed so that a brine pipe D through which brine (water here) circulates through the heat load device F flows. In the middle of the brine pipe D, a flow meter S1 used for control described later is provided. Instead, the differential pressure between the inlet side and the outlet side of the brine pipe D to the evaporator 12 is measured. In some cases, a pressure sensor is provided across the inlet side and the outlet side. The absorber 14 also passes through a cooling water pipe C1 through which cooling water circulating through a cooling tower (not shown) flows. The cooling water pipe C1 exiting the absorber 14 also passes through the condenser 20, and the cooling water exiting the condenser 20 can be circulated through the cooling tower.

  The refrigerant vapor (water in this example) evaporated by the evaporator 12 is absorbed by the absorber 14 in the absorbing liquid (lithium bromide solution in this example), and the evaporator 12 is maintained in a high vacuum state. The absorbent that has absorbed the refrigerant has a reduced concentration and becomes a diluted absorbent. The dilute absorbent stored in the lower part of the lower body 10 and in the lower part of the absorber 14 is flowed to the dilute absorbent pipe H1 by the absorbent pump P1 and travels to the high temperature regenerator 16. In the middle of this, heat is removed from the concentrated absorbent via the low-temperature heat exchanger N1 with the concentrated absorbent pipe H3 through which the concentrated absorbent flows, which will be described later, and the temperature rises. Thereafter, the dilute absorbing liquid also takes heat from the intermediate absorbing liquid via the high temperature heat exchanger N2 between the intermediate absorbing liquid pipe H2 through which the intermediate absorbing liquid whose concentration has become intermediate by the high temperature regenerator 16 flows. The temperature rises.

  In this way, the diluted absorbent whose temperature is higher than that when it comes out of the absorber 14 flows into the high temperature regenerator 16. Then, it is heated by the gas burner 17. This heating amount is instructed to a driving device 22 such as a stepping motor by a control method to be described later, and the on-off valve 24 of the gas flow path and the air flow path is opened or closed at an appropriate angle. When the diluted absorbent is heated by the burner 17 in the high-temperature regenerator 16, the refrigerant is evaporated and separated. This refrigerant vapor passes through the low-temperature regenerator 18 described above through the refrigerant pipe R1. On the other hand, the intermediate absorption liquid whose intermediate concentration is obtained by evaporating and separating the refrigerant in the high temperature regenerator 16 flows through the intermediate absorption liquid pipe H2 and enters the low temperature regenerator 18.

  The intermediate absorption liquid that has entered the low-temperature regenerator 18 is heated by the heat transfer section of the above-described refrigerant pipe R1 in which the refrigerant vapor flows. The refrigerant vapor further evaporated from the intermediate absorbing liquid by this heat enters the condenser 20. Further, the refrigerant vapor flowing through the refrigerant pipe R1 enters the condenser 20 via the refrigerant pipe tip portion R1 'as vapor or as a refrigerant liquid. The refrigerant vapor in the condenser is cooled by the cooling water flowing through the heat transfer section of the cooling water pipe C1 passing through the inside of the condenser, and returns to the refrigerant liquid.

  This refrigerant liquid flows down to the evaporator 12 through the second refrigerant pipe R2. The refrigerant liquid collected in the lower part of the evaporator 12 is sprayed from the sprayer R3A provided in the upper part of the evaporator 12 through the third refrigerant pipe R3 by the refrigerant pump P2. The sprayed refrigerant liquid takes evaporative heat from the brine flowing through the heat transfer section of the brine pipe D to become refrigerant vapor, and lowers the temperature of the brine. As described above, the refrigerant vapor is absorbed by the absorbent in the absorber 14.

  The above is an explanation of the case where the heat load device F is cooling, but in the case of heating, the on-off valves V1, V2, V3 are opened, the cooling water pump P3 is stopped, and cooling water is supplied to the cooling water pipe C1. The gas burner 17 is ignited without flowing, and the diluted absorbent is heated in the high temperature regenerator. The refrigerant vapor generated by this heating enters the absorber 14 and the evaporator 12 from the middle of the refrigerant pipe R1 mainly through the heating pipe R1 "having a small flow resistance. Thus, through the heat transfer section of the brine pipe D. The brine is heated and the heat load device F can be heated.

  On the other hand, the refrigerant vapor heats the brine in the evaporator 12, loses heat and condenses into a refrigerant liquid. This refrigerant liquid enters the lower part of the absorber 14 through the fourth refrigerant pipe R4, and is mixed with the absorption liquid flowing in through the absorption liquid pipe H2 'by evaporating and separating the refrigerant in the high temperature regenerator 16. And it is sent to the high temperature regenerator 16 by the operation of the absorption liquid pump P1.

A first embodiment of a PID control method for an absorption type device according to the present invention will be described.
Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band is P (° C),
Integration time is Ti (seconds),
The derivative time is Td (seconds),
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow rate is defined as Td _r (seconds).

As a conventional heat input PID control method, there is a typical method of calculating and controlling by the following equation (1).
M = (100 / P) e + (1 / Ti) ∫edt + (Td) de / dt (1)
The three parameters P, Ti, and Td of this equation are determined based on the rated flow rate of the brine. That is, until now, control has been performed by the following equation (1 ′) where P = P _r , Ti = Ti _r , and Td = Td _r .
M = (100 / P _r ) e + (1 / Ti _r ) ｔedt + (Td _r ) de / dt (1 ′)
Here, in the present invention, the three parameters P, Ti, and Td in the formula (1) are replaced with P = P _r / F, Ti = Ti _r / F, and Td = Td _r · F, respectively. Thus, the expression (1) becomes the following expression (2). PID control is performed using this equation (2).
M = (100 / (P _r / F)) e +
(1 / (Ti _r / F)) ∫edt + (Td _r · F) de / dt (2)

Here, if the brine flow rate decreases, the brine temperature difference e is considered to increase. Therefore, it is appropriate to substitute as in the following formula (2).
e = _er / F (3)
Substituting this into equation (2) yields:
_{M = (100 / P r)} e r + (1 / Ti r) ∫e r dt +
(Td _r ) de _r / dt (4)
That is, if the above three parameters are replaced in the PID control equation (1) and further replaced by the equation (3), the equation (4) is obtained. The equation (4) is expressed by the PID control equation (1). Is the same as that at the rated flow rate.

That is, even when the flow rate ratio F is lowered, the PID control equation (2) of the present invention by replacing each PID parameter with P = P _r / F, Ti = Ti _r / F, Td = Td _r · F. It is considered that the state of change with time t is expressed by equation (4). Whether or not the equation (4) is actually obtained depends on the validity of the equation (3), and this validity is as described above. That is, it can be understood that a large hunting phenomenon as in the conventional case when the flow rate ratio F is reduced can be prevented, which contributes to stabilization.

A second method that replaces the first control method will be described.
If only P of the three parameters P, Ti, and Td in the equation (1) is replaced with P = P _r / F, and the others are left as Ti = Ti _r and Td = Td _r , then the equation (1) becomes Equation (2.1) is used to perform PID control.
M = (100 / (P _r / F)) e +
(1 / Ti _r ) ∫edt + (Td _r ) de / dt (2.1)
Moreover, if Formula (3) is substituted into this, it will become the following Formula.
M = (100 / P _r ) _er +
_{(1 / (Ti r · F} )) ∫e r dt + (Td r / F) de r / dt ·· (4.1)
In this equation (4.1), only the first term which is a proportional term is the same as that at the rated flow rate of the PID control equation (1). A large hunting phenomenon as in the conventional case when it is reduced can be prevented by the amount corresponding to the proportional portion, and contributes to stabilization.

A third method instead of the first control method will be described.
If only Ti among the three parameters P, Ti, and Td in the formula (1) is replaced with Ti = Ti _r / F, and the others are left as P = P _r and Td = Td _r , the formula (1) is The PID control is performed using this equation (2.2).
M = (100 / P _r ) e +
(1 / (Ti _r / F)) ∫edt + (Td _r ) de / dt (2.2)
Moreover, if Formula (3) is substituted into this, it will become the following Formula.
M = (100 / (P _r · F)) · e _r +
_{(1 / Ti r) ∫e r} dt + (Td r / F) de r / dt ····· (4.2)
In this equation (4.2), only the second term which is an integral term is the same as that at the rated flow rate of the PID control equation (1). A large hunting phenomenon as in the conventional case in the case of lowering can be prevented by the amount corresponding to the integration part, and contributes to stabilization.

A fourth method instead of the first control method will be described.
If only Td of the three parameters P, Ti, and Td in equation (1) is replaced with Td = Td _r · F, and the others are left as P = P _r and Ti = Ti _r , equation (1) becomes The PID control is performed by this equation (2.3).
M = (100 / P _r ) e +
_{(1 / Ti r) ∫edt +} (Td r · F) de / dt ······ (2.3)
Moreover, if Formula (3) is substituted into this, it will become the following Formula.
M = (100 / (P _r · F)) · e _r +
_{(1 / (Ti r / F} )) ∫e r dt + (Td r) de r / dt ··· (4.3)
In this equation (4.3), only the third term, which is a differential term, is the same as that at the rated flow rate of the PID control equation (1). A large hunting phenomenon as in the conventional case in the case of lowering can be prevented by the amount corresponding to the differential portion, and contributes to stabilization.

Formula (1 ′) M = (100 / P _r ) e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
When the flow rate ratio F is multiplied on both sides, the following equation is obtained.
F · M = (100 / P _r ) F · e +
(1 / Ti _r ) ∫F · edt + (Td _r ) d (F · e) / dt
The left side F · M of the equation (5) means a value obtained by lowering the heat input M (%) calculated by the conventional control to this decrease rate when the flow rate ratio F decreases. If the value of M is the heat input amount according to the control of the present invention, it is considered that the heat input control is appropriate (fifth control method).

On the other hand, this equation can be rewritten as:
F · M = (100 / (P _r / F)) e +
_{(1 / (Ti r / F} )) ∫edt + (Td r · F) de / dt ··· (5)
That is, the right side of equation (5) is the same as the right side of equation (2). The left side of Expression (2) is M, which means control with the right side of Expression (2) as the heat input, and this Expression (5) also has the right side as heat input, which is the same as Expression (2). Calculate heat input. Therefore, the heat input amount by the first control method based on the formula (2) is the same as the heat input amount of the fifth control method, which is F times the heat input amount of the conventional heat input control.

  Further, the brine flowing through the brine pipe D has a strong fluid resistance in the heat transfer section located inside the evaporator 12. This causes a pressure loss in the brine stream. Increasing the flow rate causes a large pressure loss, and the pressure (static pressure) difference between the inlet side and the outlet side of the brine pipe to the evaporator 12 increases. Further, if the flow rate is reduced, the pressure loss is reduced and the pressure difference is reduced. That is, it can be considered that the pressure difference between the inlet side and the outlet side of the brine pipe to the evaporator 12 corresponds to the magnitude of the flow rate. Therefore, if the ratio of the pressure difference when the flow rate is reduced to the pressure difference at the rated flow rate is α, the pressure difference ratio α may be used instead of the flow rate ratio F described above.

The PID control method of the present invention will be briefly described again based on the flowchart of FIG. 2 corresponding to the first control method. In step 30, the proportional band P _{r at} the rated flow rate, the integration time Ti _{r at} the rated flow rate, and the differential time Td _r at the rated flow rate are read. Alternatively, a value stored in advance in a ROM memory or the like is taken out. In step 32, a flow signal from the flow meter S1 or a signal from a pressure sensor (not shown) that measures a pressure difference between the inlet and outlet of the brine is received. In step 34, the flow rate ratio F or the pressure difference ratio α is calculated from these signals.

In step 36, if using the flow rate ratio F, the proportional band P _{= P} r / F, integral time Ti = _Ti r / F, to calculate the PID parameters as derivative time Td = Td _r · F. In step 38, the conventional PID control is performed using the three parameters obtained in step 36. As a result, the heat input M (%) is calculated and output. In this calculation, the calculation load of control can be reduced by performing the control calculation of the brine temperature difference e in the above-described equation (2) using an average value for a predetermined time.

  In step 40, the control valve opening according to the heat input M is calculated, a drive signal is issued to the drive device 22 shown in FIG. 1, and the gas flow passage and the air flow passage opening / closing valve (control valve) 24 are appropriately set. Open or close the angle. In step 42, it is determined whether or not there is an absorption device stop signal. If not, the process returns to step 30, and if it is present, the signal is stopped.

In the second to fourth methods, the calculation formulas of the three parameters in step 36 are different, but the others are the same.
In the fifth method, the three parameters of step 36 are calculated as P = P _r , Ti = Ti _r , Td = Td _r , and the value obtained by multiplying the value of heat input M of the calculation result of step 38 by F is The amount of heat input M sent to step 40 may be used.

  The present invention can be used for PID control of an absorption refrigerator or an absorption chiller / heater.

DESCRIPTION OF SYMBOLS 12 Evaporator 14 Absorber 16 High temperature regenerator 18 Low temperature regenerator 20 Condenser 22 Driving devices, such as a stepping motor 24 On-off valve (control valve)
D brine tube S1 flow meter

Claims (6)

Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
M = (100 / (P _r / F)) · e +
(1 / (Ti _r / F)) ∫edt + (Td _r · F) de / dt
A heat input M is PID controlled by the above equation where the proportional band is (P _r / F), the integration time is (Ti _r / F), and the derivative time is (Td _r · F). PID control method. Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
M = (100 / (P _r / F)) · e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
A PID control method for an absorption type apparatus, wherein the heat input M is PID controlled by the above formula where the proportional band is (P _r / F), the integration time is Ti _r , and the differential time is Td _r . Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
_{M = (100 / P r)} · e + (1 / (Ti r / F)) ∫edt + (Td r) de / dt
A PID control method for an absorption type device, wherein the heat input M is PID-controlled by the above equation where the proportional band is P _r , the integration time is (Ti _r / F), and the derivative time is Td _r . Heat input is M (%),
F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
M = (100 / P _r ) · e + (1 / Ti _r ) ∫edt + (Td _r · F) de / dt
A PID control method for an absorption-type apparatus, wherein the heat input M is PID-controlled by the above formula where the proportional band is P _r , the integration time is Ti _r , and the differentiation time is (Td _r · F). F is the flow rate ratio relative to the rated flow rate of brine.
E (° C), the difference in brine temperature at the inlet and outlet of the evaporator
The proportional band at the rated flow is P _r (° C),
The integration time at the rated flow is Ti _r (seconds),
The differential time at the rated flow is defined as Td _r (seconds)
(100 / P _r ) e + (1 / Ti _r ) ∫edt + (Td _r ) de / dt
The proportional band P _r, the integration time Ti _r, absorption, characterized in that the heat input of the PID control value obtained by multiplying the flow rate ratio F value in the calculated value by the equation where the differentiation time Td _r (%) Device PID control method.   The PID control method for an absorption type apparatus according to any one of claims 1 to 5, wherein the ratio of the pressure difference between the evaporator inlet and outlet of the brine flow to the pressure difference at the rated flow rate is used instead of the flow rate ratio F.

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