JP2508160B2 - Turbo refrigerator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a turbo refrigerator.

(Prior Art) As a conventional example of a centrifugal chiller, for example, the actual development of Sho 52-59
An example is the device described in Japanese Patent No. 945. In the device, the temperature of the cold water flowing in the evaporator connected to the turbo compressor is detected, and the turbo compression is performed according to the difference (hereinafter referred to as the deviation amount) obtained by subtracting the set temperature from the detected temperature. It is designed to adjust the opening of the vane of the vessel.
That is, by performing the capacity control of the compressor by following the temperature fluctuation of the cold water, the temperature fluctuation width of the cold water is reduced and the energy consumption when maintaining the set temperature is reduced.

(Problems to be Solved by the Invention) By the way, as a calculation formula for calculating the increase / decrease amount of the vane opening from the deviation amount, that is, the operation amount, a time integral term of the deviation amount is added to a proportional term proportional to the deviation amount. By using the added formula, in the operation amount obtained only by the comparison term, for example, when the deviation state on the + side continues, the value by the time integration term increases with the passage of time. The manipulated variable added with the value calculated by the time integral term is obtained as a larger value, so that the change from the + side to the one side, that is, toward the zero deviation state occurs rapidly. As a result, for example, the hunting state can be quickly attenuated after reaching the set temperature, and reachability to the target value and stability can be improved.

However, for example, in the schedule control in which the set temperature is changed stepwise from the state of the set temperature of 5 ° C. to 7 ° C., etc., when the operation amount is determined by the above calculation formula, the time integration is performed. There is a problem that reachability and stability are adversely affected because the effect of the term becomes too large. That is, in the vicinity of the set temperature, that is, in the case where the deviation amount is small, the effect of suppressing the fluctuation is obtained by the time integral term as described above, but when the set temperature is changed, the cold water is cooled to the changed set temperature. Since the large deviation state continues until the temperature reaches, the time integration term becomes extremely large with the passage of time, and as a result, for example, the overshoot amount after reaching the changed set temperature becomes large, The fluctuation range in the subsequent hunting state is large, and the continuation time is long, and the stability and reachability deteriorate.

The present invention has been made in view of the above, and an object thereof is to provide a turbo refrigerator that can improve reachability and stability when changing the set temperature as described above.

(Means for Solving the Problems) Therefore, in the turbo refrigerator according to the present invention, as shown in FIG. 1, the condenser 2 and the evaporator 3 are connected to the turbo compressor 1 and the evaporator 3 is used. Detecting means 5 for detecting a state quantity such as the temperature of water to be cooled, and control means 10 for controlling the opening degree of the vane 6 of the compressor 1 are provided, and the control means 10 detects the detected state quantity and the target reference. And a manipulated variable based on a calculation formula having a time integral term of a product obtained by multiplying the deviation amount by a predetermined integral gain, and at the same time, operating the opening of the vane 6 by the operation. A turbo refrigerator that controls the capacity of the compressor 1 so as to bring the detected state amount closer to the target reference amount by increasing or decreasing according to the amount, and further including a control gain change range with the control unit 10 sandwiching the target reference amount. Change width setting means 11 for setting When the output state quantity is within the control gain change width, the integral gain is set to a constant value, while when the detected state quantity deviates from the control gain change width, the integral gain is reduced to a smaller value with the passage of time. A control gain changing means 12 for changing is provided.

(Operation) In the above turbo chiller, when a large deviation state occurs, for example, when the target reference amount is changed, the detected state quantity deviates from the control gain change range. By this, the operation amount is calculated based on the calculation formula in which the integral gain is changed to a smaller value with the passage of time, and the opening degree of the vane 6 is increased or decreased. Therefore, at the beginning of the lapse of time, the change in the opening of the vane 6 is increased by the contribution of the integral term, and control is performed so as to quickly move toward the target reference amount, while the calculated value of the integral term increases rapidly with the passage of time. By avoiding the above, the rapid change in the opening of the vane 6, which has conventionally caused a large overshoot, is controlled. Then, after the detected state quantity reaches within the control gain change width by continuing the above control, the time integration term having the effect of suppressing the fluctuation for a small deviation amount within this control gain change width. Then, the control is continued. As described above, in the above-mentioned device, when the deviation amount is large, it is possible to reduce the overshoot amount exceeding the target reference amount, for example, while ensuring good reachability to the target reference amount. Since the fluctuation range in the subsequent hunting state can be reduced and the duration thereof can be shortened, it is possible to improve stability and reachability.

(Examples) Next, specific examples of the turbo refrigerator according to the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a schematic configuration diagram of a turbo refrigerator according to an embodiment of the present invention. In FIG. 2, 1 is a turbo compressor, and the compressor 1 includes a condenser 2 and an evaporator 3.
It is installed on Unisiel, which houses and in a can body. A refrigerant circulation path through which the refrigerant circulates is formed between the compressor 1 and the condenser 2 and the evaporator 3 as indicated by solid line arrows in the figure. On the other hand, cooling water circulates in the condenser 2 and cold water circulates in the evaporator 3, and the gas refrigerant flowing from the compressor 1 into the condenser 2 is the inside of the condenser 3. It becomes a liquid refrigerant by heat exchange that radiates heat to the circulating cooling water, and this liquid refrigerant flows into the evaporator 3 after passing through the orifice 4 shown at the lowest position in the figure. Then, a refrigerant circulation cycle is formed in which heat is absorbed from the cold water circulating inside the evaporator 3 to become a gas refrigerant and then returned to the compressor 1. In this refrigerant circulation cycle, the cold water absorbed by the refrigerant in the evaporator 3 is provided to the outside for air conditioning, for example. Further, in the above apparatus, the cold water temperature detector 5 including, for example, a thermistor in the cold water outlet pipe is provided.
Is attached as state quantity detection means, and a suction page 6 is provided at the suction port of the compressor 1, and the temperature detected by the cold water temperature detector 5 is controlled by the control means, that is, the opening control device 10. In response to this, an opening control signal is output to the vane motor 7 that drives the vane 6, whereby the opening of the vane 6 is automatically adjusted to perform capacity control according to the load of the compressor 1. ing.

In the opening degree control device 10, a change width setting section (change width setting means) 11, a control gain changing section (control gain changing means) 12, and a startup control section 13 are further provided,
Hereinafter, these functions will be described together with the specific opening control method of the vane 6.

In the opening control device 10, a target reference amount set in a temperature setter (not shown), that is, a set temperature of cold water
Ts and the detected state quantity detected by the cold water temperature detector 5,
That is, in order to obtain the operation amount of the vane 6, that is, the vane opening increase amount ΔV from the cold water temperature T, first, the calculation formula x = T-Ts of the deviation amount x, and in order to calculate ΔV from the above x, The two formulas are stored respectively.

ΔV = Kp · [x + (1 / Ki) · ∫xdt] to (1) ΔV = Kp · [x + ∫ (1 / Ki (t)) dt] to (2) Ki (t) = Kj × t + 1 where Kp, Ki and Kj are constants, and t is elapsed time. That is, in the above equation (1), the vane opening increase amount Δ is calculated by the sum of the proportional term proportional to the deviation x and the time integral term.
V is calculated, and in the formula (2), the formula x / which is obtained by further dividing the integral function of the time integral term by the function of the elapsed time t
It has been transformed into (Kj × t + 1). As a result, the integral value of the time integral term in the above equation (2) is suppressed to be smaller with the passage of time than the integral value of the time integral term in the equation (1).

On the other hand, the change confirmation setting unit 11 sets the control gain change width with respect to the set temperature Ts in a predetermined temperature width centered on this Ts. FIG. 3 shows the set temperature in the schedule control in which the set temperature is changed stepwise during the elapsed time.
Although Ts is shown by a solid line, the high temperature side change temperature Ts-H is set on the high temperature side and the low temperature side change temperature Ts-1 is set on the low temperature side in a predetermined temperature range across these Ts. If the detected temperature is within the control gain change range, the equation (1) is changed. If the detected temperature deviates from the control gain change range, the equation (2) is changed. Department
12 is selected, and ΔV is calculated based on the selected calculation formula, and the opening degree of the vane 6 is increased or decreased according to the calculation result.

In FIG. 4, the solid line (A) shows the temperature change of the cold water when the set temperature is changed from 5 ° C. to 7 ° C. by the above control, and the calculation formulas (1), (2 The change in the temperature of the cold water when the control is performed only by the equation (1) without changing ()) (hereinafter referred to as the case of the conventional control) is shown by a broken line (B). First, in the case of the conventional control, the deviation amount x is zero when the cold water temperature is maintained at the set temperature 5 ° C. before the set temperature change, and the deviation amount x is x = 5 ° C. when the set temperature is changed. A calculation of -7 ° C is performed, and the state suddenly changes to a large deviation state of x = -2 ° C. The deviation amount x is calculated according to the equation (1) to determine the operation amount, and the vane 6 is subjected to the phenomenon of the opening degree based on the operation amount. After that, the deviation amount x and the manipulated variable ΔV are calculated at predetermined sampling intervals, and the opening degree of the vane 6 is successively decreased. As a result, the compressor 1
In this case, the compression capacity is lowered, that is, the cooling capacity is decreased, and the temperature of the cold water flowing through the evaporator 3 rises while causing some time lag. The absolute value of the deviation amount x also decreases due to such a rise in the cold water temperature, that is, a change approaching the set temperature 7 ° C., and therefore the comparative term in the equation (1) becomes smaller. However, since the time integral term, that is, the cumulative absolute amount to the deviation amount x from the time when the set temperature is changed, increases rapidly with the passage of time, the contribution rate of this time integral term becomes large, and the vane 6 Therefore, a large change in the opening is continued on the decreasing side, and the cold water temperature also rapidly changes. As a result, as shown by point (a) in the figure, the set temperature is 7
As a result, a large overshoot exceeding ℃ occurs, and thereafter, the fluctuation range is large during the hunting phenomenon that fluctuates across the set temperature of 7 ℃, the damping time becomes long and stability and reachability are not sufficiently obtained. Has become. In the above, the coefficient 1 / Ki multiplied by the time integral term of the equation (1) is
It is set in consideration of the ability to follow changes in the cold water temperature due to load fluctuations, etc. when the cold water temperature is substantially maintained at the set temperature. It is designed to work. Therefore, when the deviation amount x continues to have a large value such as when the set temperature is changed, the time integral term is calculated as a very large value, and the overshoot amount becomes large as described above.
The result is that stability and reachability are adversely affected. In addition, FIG. 4 shows the chilled water temperature change curve (C) when the coefficient 1 / Ki is made small and mainly controlled by the comparative term. Since the amount of change is suppressed to a small value, it takes a long time to reach the set temperature, which further reduces the reachability.

Next, a description will be given of the control in which the equations (1) and (2) are switched and used. In this case, the control gain change range is set in a range of, for example, 0.5 ° C. across the set temperature of 7 ° C. after the change. The chilled water temperature of 5 ° C. at the time of changing the set temperature deviates from the above-mentioned control gain change width to the low temperature side. As a result, the control gain changing unit 12 selects the equation (2), and the control based on this equation is started. To be done. In the above embodiment, when the control based on the equation (2) is performed, the deviation amount x whose calculated target temperature is the changed temperature on the deviation side of the detected temperature is calculated, and the operation amount for this deviation amount is calculated. It is designed to do. For example, the deviation amount x at the time of changing the set temperature is given by x = 5 ° C.−6.75 ° C. (low temperature side changing temperature Ts = L). In the control state based on the above equation (2),
At the initial stage of the lapse of time, the contribution ratio of the time integral term is not much different from that in the case of the conventional control. Therefore, as shown in the figure, the chilled water temperature change is substantially the same as that described above. Since the integral function is an expression obtained by dividing the deviation amount x by the elapsed time (t + 1), it does not become a calculated value that rapidly increases with time like the time integral term in the expression (1). Therefore, the changing speed of the opening degree of the vane 6 is suppressed to be smaller. As a result, as shown in the figure, the temperature rise change temperature of the cold water is also suppressed, and the amount of overshoot exceeding the set temperature of 7 ° C. corresponding to the rate of rise change becomes smaller. Further, in the above-described embodiment, the control based on the above equation (2) sets the lower-side change temperature of 6.75 ° C. as the target reaching reference temperature. Therefore, the change rate is suppressed to a small value, and the overshoot amount becomes smaller. It is possible to do. When the chilled water temperature reaches the lower change temperature by the above control, the control is switched to the control based on the equation (1) for the set temperature of 7 ° C. Then, from this switching time point, the integral calculation of the time integral term of the equation (1) is started, and the cumulative integral value at the time of calculation by the equation (2) is cleared. Therefore, the time integral term of the equation (1) has a small deviation value. It acts as a term that gives an integral effect to the change of. As shown in the figure, when the cold water temperature exceeds the set temperature of 7 ° C. and further exceeds the high temperature change temperature of 7.25 ° C., the control switched to the control according to the equation (2) is performed again. As a result, similarly to the above, the effect of the time integration term is suppressed from becoming excessive, and the amount of undershoot that occurs next is suppressed.

When the deviation amount is a small amount within the control gain change range that sandwiches the set temperature by controlling the operation amount calculation formula by switching as described above, this deviation state can be eliminated early. The action of the integral term is maintained, and the action of the time integral term is suppressed from becoming excessive when a large deviation state occurs, for example, when the set temperature is changed,
As a result, for example, the amount of overshoot can be reduced, the fluctuation range in the subsequent hunting state can be reduced, and the duration of hunting can be shortened. Can be improved.

Note that FIG. 5 shows a flow chart of the control by the start-up control unit 13 performed at the time of starting the apparatus, and FIG. 6 shows the change in cold water temperature obtained by this control. As shown in FIG. 6, at the time of start-up, cooling of the water flowing through the evaporator 3 (water temperature To ° C.) is started, and the temperature decrease rate m until the cold water state of the set temperature Ts ° C. becomes substantially constant. , The capacity of the compressor 1 is controlled. This will be described with reference to the flowchart of FIG.
The initial opening of is set at the preset value VO (step
S1), the vane 6 is operated to an opening state corresponding to this VO (step S2). The operation in this opening state is continued for a predetermined sampling time interval Δt (step S3), and in step S4, the water temperature To at the time of starting and the detected water temperature Ti in the first sampling time (i = The value m is obtained by dividing the difference from 1) by the elapsed time i · Δt (i = 1), and then the temperature decrease rate is calculated. And this m
The temperature is compared with an appropriate temperature decrease rate mo stored in advance (step S5), and when m is equal to or higher than mo, it is determined that the temperature is excessively decreased, and in step S6, the increment amount ΔV of the vane opening degree is changed to − vo (vo is a standard increment amount according to a preset Δt) is set, and when m does not reach mo, the value obtained by multiplying vo by vo / m is ΔV in step S7.
Set to. By multiplying this mo / m, the standard incremental amount, that is, the incremental amount based on the correlation amount between the compression capacity change and the refrigerating capacity change in the standard state, which is set in advance, can be used for the actual operating state. Modifications will be made accordingly. After setting ΔV in this manner, the cold water temperature Ti is compared with the high temperature side change temperature Ts-H in step S8, and until reaching Ts-H, the process returns from step S8 to step S2 and the vanes corresponding to ΔV are repeated six times. As the degree is increased or decreased, the processing of steps S3 to S8 is repeated, and the vane opening degree is changed at every sampling time interval Δt.
As shown in the figure, the vanes are gradually opened while giving a substantially constant cooling rate. Then, when the cold water temperature Ti reaches the high temperature side change temperature Ts-H, from step S8, the steady state control is performed, that is, the increase / decrease amount of the vane opening is determined using the equations (1) and (2) according to the deviation amount x. Shift to opening control. In this way, the control is performed based on the standard state that is set in advance, while correcting the difference with the standard state obtained by performing actual operation, that is, while predicting a different load at each startup. By performing the operation, for example, there is no operation with an excessive compression capacity at the time of light load, and control corresponding to the load becomes possible. Also, as a result of suppressing supercooling exceeding the set temperature, stability to the set temperature,
Reachability is also improved.

As described above, in the above-described embodiment, when the large deviation state continues, for example, when the set temperature is changed, the operation amount in which the time integral term is suppressed small is calculated. The amount becomes smaller, and as a result, the subsequent bunching state is rapidly attenuated, so that it is possible to control the stability and reachability to the set temperature. Further, as a result of the change rate of the opening of the vane being suppressed, the load fluctuation on the compressor 1 is also reduced, so that the vibration and noise are also reduced. Further, in the above-mentioned embodiment, the function of the time integral term in the conventionally used equation (1) can be configured by a simple change of dividing by the elapsed time when the deviation amount is large, and a completely independent calculation equation can be obtained. Since it is not necessary to provide it, the cost can be reduced, and the manufacturing cost can be reduced.

The above embodiment is not intended to limit the present invention,
Various modifications are possible within the scope of the present invention. For example, in the above embodiment, an example in which the detected state quantity is configured as the water temperature of cold water is shown, but it is configured as the evaporation temperature or the evaporation pressure of the refrigerant in the evaporator, for example. It is also possible.

(Effects of the Invention) As described above, in the turbo refrigerant machine of the present invention, when there is a large deviation state in which the detected state quantity deviates from the control gain change width, the integral gain in the calculation formula for calculating the manipulated variable from the deviation quantity. Since it becomes smaller with the passage of time, when the large deviation state continues, for example, when the target reference amount is changed, the opening change of the vane of the compressor is increased at the beginning of the passage of time. On the other hand, avoiding a sudden change in the opening with the passage of time, as a result, while ensuring good reachability, the overshoot amount exceeding the target reference amount is suppressed to a small value, and the subsequent hunting state damping is suppressed. Since it is possible to quickly obtain the above, it is possible to prevent the stability and reachability of the control.

[Brief description of drawings]

1 to 6 are explanatory views of a turbo refrigerator according to an embodiment of the present invention, and FIG. 1 is a control function block diagram,
2 is a schematic configuration diagram of a turbo refrigerator, FIG. 3 is an explanatory diagram of a control gain change range, FIG. 4 is a graph showing a change in cold water temperature when a set temperature is changed, and FIG. A flow chart, FIG. 6 is a graph showing a change in cold water temperature at the time of startup. 1 ... turbo compressor, 2 ... condenser, 3 ... evaporator, 5
... Cold water temperature detector (detection means), 6 ... vane, 10 ...
… Opening degree control device (control means), 11 …… change width setting section (change width setting means), 12 …… control gain changing section (control gain changing means).

Claims (1)

(57) [Claims] 1. A detection for connecting a condenser (2) and an evaporator (3) to a turbo compressor (1) and detecting a state quantity such as a temperature of water cooled by the evaporator (3). Means (5)
And a control means (10) for controlling the opening of the vane (6) of the compressor (1), and the deviation given by the difference between the detected state quantity and the target reference quantity by this control means (10). And an operation amount based on a calculation formula having a time integral term of a product of this amount of deviation and a predetermined integration gain, and the opening degree of the vane (6) is increased / decreased according to the operation amount to be detected. A turbo refrigerator that controls the capacity of the compressor (1) so as to bring the state quantity closer to the target reference quantity, and further sets a control gain change width across the target reference quantity in the control means (10). Change width setting means (11)
When the detected state quantity is within the control gain change range, the integral gain is set to a constant value, while when the detected state quantity deviates from the control gain change range, the integral gain becomes smaller with time. A turbo refrigerator having a control gain changing means (12) for changing to.