JP5519447B2 - Turbo refrigerator - Google Patents

Description

  The present invention relates to a turbo refrigerator. In particular, the present invention relates to a turbo chiller that can save energy by maintaining a turbo compressor in a highly efficient operation state according to a load.

  Conventionally, an evaporator for producing cold water, a condenser for radiating heat taken into the system to the cooling water, and a vapor compression refrigerator having a compressor as a booster necessary for constituting the system as a basic component. is there. In such a refrigerator, the guide vane is fully opened, and the inverter control for controlling the refrigeration capacity (refrigeration output) by the rotational speed control by the inverter and the guide vane control for controlling the refrigeration capacity by increasing or decreasing the guide vane opening are used in combination. Was. This is because, in general, the degree of efficiency reduction is smaller when the rotational speed is reduced and suppressed than when the vane opening is lowered and the refrigeration capacity (compressed refrigerant vapor amount) is suppressed. That is, it is preferable in terms of efficiency to reduce the rotation speed as much as possible and open the guide vanes as much as possible. For this reason, the vane opening is increased by reducing the rotational speed as much as possible within the range where surging can be avoided, thereby improving the efficiency of the refrigerator.

  In such a refrigerator, the inverter control and the guide vane control are switched depending on the situation. Specifically, so-called mode switching is performed by increasing or decreasing the load, and the control target is switched (for example, see Patent Document 1).

Japanese Patent Laying-Open No. 2006-234320 (paragraphs 0014, 0024, FIG. 7, etc.)

  When the mode is switched as in a conventional refrigerator, if the transition condition at the time of switching is inappropriate, the two modes are frequently moved back and forth, and the control becomes unstable. In addition, since the response speed of the refrigerator and various constants change at the moment of switching, and the behavior of the refrigerator changes, there is still a problem that it is likely to cause control instability.

  In general, the rotational speed control has high responsiveness and high resolution. On the other hand, since guide vane control requires mechanical operation, it has poor response and low resolution. In other words, when control is performed by mode switching, the behavior (responsiveness and followability) in each mode is different even though they are the same refrigerator, and there is a problem that usability on the demand side is deteriorated. .

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a turbo chiller that has both high efficiency and control stability, is responsive, and is easy to use.

  In order to solve the above-described problem, the turbo refrigerator according to the first aspect of the present invention generates a refrigerant gas by evaporating the refrigerant liquid, for example, as shown in FIG. An evaporator 10 that performs suction; the impeller 23 that sucks and compresses the refrigerant gas; and a turbo compressor 20 that is provided at the entrance of the impeller 23 and has a guide vane 25 whose opening degree is variable; A condenser 30 that takes heat from the compressed refrigerant gas and condenses the refrigerant gas; a variable speed drive 21 that drives the turbo compressor 20; a variable speed drive 21 that corresponds to the refrigeration load that is processed by the evaporator 10 A first control unit 71 (see, for example, FIG. 2) that controls the refrigerating capacity by adjusting the rotational speed of the guide vane 25; The second to control to SETSP And a control unit 72 (e.g., see FIG. 2).

  If comprised like this aspect, it will be equipped with the 1st control part which adjusts the revolving speed of a variable speed drive machine according to refrigeration load, and controls the refrigerating capacity, and adjusts the opening of a guide vane and makes a variable speed drive machine Since the second control unit for controlling the rotational speed of the motor to a predetermined set rotational speed is provided, the refrigeration capacity is controlled by the rotational speed, and the rotational speed is controlled by the opening and closing of the guide vane. Therefore, the adjustment of the opening degree of the guide vane can be involved in the refrigeration capacity control through the adjustment of the rotation speed without being directly related to the refrigeration capacity control. In this way, without any switching mechanism that switches the control of the refrigeration capacity between the rotational speed control and the guide vane control, that is, while effectively using both control units, the transition of the control related to the control of the refrigeration capacity between the two controls. Can be done smoothly. Therefore, it is possible to provide a turbo chiller that achieves both high efficiency and control stability, is responsive, and is easy to use.

  The turbo chiller according to the second aspect of the present invention is the turbo chiller according to the first aspect. For example, as shown in FIG. 2, the operating condition PL of the evaporator 10 and the operating condition PH of the condenser 30 The set rotational speed calculator 73 is provided for calculating the theoretical rotational speed from the above and determining the set rotational speed SETSP based on the calculated theoretical rotational speed.

  With this configuration, the theoretical rotational speed, for example, the minimum rotational speed at the surging limit, is calculated from the operating conditions of the evaporator and the condenser, and the target rotational speed is calculated based on the calculated theoretical rotational speed. A certain rotational speed can be determined. By adjusting the opening degree of the guide vane, the rotational speed can be controlled to the set rotational speed determined in this way, so that the turbo compressor can be operated at the target rotational speed even when the load is reduced. .

  For example, as shown in FIG. 2, the turbo chiller according to the third aspect of the present invention is the turbo chiller according to the second aspect. It is preferable to add the opening degree GV of the guide vane.

  With this configuration, since the guide vane opening is added to the calculation condition of the theoretical rotation speed, the change can be added to the theoretical rotation speed that can be changed by the guide vane opening. It is possible to obtain a theoretical rotational speed in accordance with. Therefore, it is possible to avoid giving an excessive margin to the set rotational speed.

  For example, as shown in FIG. 8, the turbo refrigerator according to the fourth aspect of the present invention is configured so that the opening degree GV of the guide vane 25 is set in the closing direction in any one of the first to third aspects. It is preferable that the operating speed is faster than the operating speed in the opening direction (twice in the example of FIG. 8).

  When configured as in this aspect, the speed at which the opening degree of the guide vane is operated in the closing direction is faster than the speed at which the guide vane is operated in the opening direction. When this occurs, a decrease in rotational speed can be suppressed.

  The turbo chiller according to the fifth aspect of the present invention includes, for example, as illustrated in FIGS. 8 to 10, in any one of the first to fourth aspects, the second control unit 72 includes: The opening degree GV of the guide vane 25 is controlled by time proportional control.

  If comprised like this aspect, since the 2nd control part 72 controls the opening degree GV of a guide vane by time proportional control, it opens and closes a guide vane using the vane motor etc. which open and close at a fixed speed, for example. It is possible to perform simple control that adjusts the speed according to time (the operation amount is proportional to the operation time).

  In the turbo chiller according to the sixth aspect of the present invention, in the fifth aspect, the second control unit 72 changes the proportionality constant of the time proportional control according to the opening degree of the guide vane 25. Also good.

  If comprised like this aspect, since the 2nd control part changes the proportionality constant of the time proportional control with the opening degree of the guide vane, even if there is a range where response sensitivity is blunt by the opening degree of the guide vane The response sensitivity can be kept high.

  According to the present invention, it is possible to provide a turbo chiller that achieves both high efficiency and control stability, is responsive, and is easy to use.

1 is an overall schematic diagram showing the configuration of a turbo refrigerator according to a first embodiment of the present invention. It is a block diagram which shows the control means which has a 1st control part and a 2nd control part. It is a figure which shows the performance of the turbo refrigerator at the time of performing capacity | capacitance control only by a guide vane. It is a figure which shows the characteristic at the time of changing the rotational speed of a turbo compressor and controlling the capacity | capacitance of a turbo refrigerator (relationship between cooling water inlet temperature and refrigerating capacity ratio). It is a figure which shows the relationship between a cooling water inlet temperature and the rotational speed (inverter frequency) of a turbo compressor, and the relationship between a cooling water inlet temperature and the work of a surging limit. It is a control block diagram which shows the actual example of the control apparatus of 1st embodiment. It is a control block diagram which shows the example of the control apparatus of 2nd embodiment. It is a figure which shows an example of the internal flow of a guide vane opening / closing calculator. It is a figure which shows the modification of the internal flow of the guide vane opening / closing calculator of FIG. It is a figure which shows an example of the internal flow of the guide vane opening / closing calculator in the case of time proportional control. It is a diagram explaining the behavior when the load of the centrifugal chiller according to the embodiment of the present invention increases rapidly on the time axis. It is a diagram explaining the behavior when the load of the centrifugal chiller according to the embodiment of the present invention is suddenly reduced on the time axis. It is a diagram explaining the behavior when the load of the centrifugal chiller according to the embodiment of the present invention is further greatly increased on the time axis.

  Embodiments of the present invention will be described below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same or similar reference numerals, and redundant description is omitted.

  A first embodiment of the present invention will be described with reference to an overall schematic configuration diagram showing a turbo refrigerator 101 according to an embodiment of the present invention in FIG. The refrigerator shown in this figure is a turbo refrigerator, that is, a vapor compression refrigerator using a turbo compressor (centrifugal compressor). The turbo refrigerator 101 generates refrigerant gas by evaporating the refrigerant liquid, and cools the cold water that is the medium to be cooled by the latent heat of evaporation, and sucks and compresses the refrigerant gas generated in the evaporator 10. And a turbo compressor 20 that pressurizes and compresses the refrigerant gas from the evaporator 10 to the condenser 30. The condenser 30 takes heat from the compressed refrigerant gas, condenses it, and releases the condensed heat to the cooling water. Between the condenser 30 and the evaporator 10, a throttling mechanism (decompression device) 40 that decompresses the refrigerant liquid from the condenser 30 to the pressure of the evaporator 10 is provided.

  Further, the motor 21 as a variable speed drive for driving the turbo compressor 20, the motor start panel 60 used for starting / stopping the motor 21, and the frequency of the power supplied from the commercial power source 75 are freely controlled. An inverter 80 supplied to the electric motor 21; a control means 70a for controlling the operation of the turbo refrigerator 101 by outputting a speed command signal C1 indicating the frequency of the power supplied to the electric motor 21 to the inverter 80; and an evaporator A chilled water temperature detector 13 for detecting the chilled water outlet temperature TL 10, a chilled water temperature detector 14 for detecting the chilled water inlet temperature TH of the condenser 30, and a refrigerant pressure (low pressure side pressure) PL in the evaporator 10. And a high-pressure side pressure detector P2 for detecting the pressure (high-pressure side pressure) PH of the refrigerant in the condenser 30. The cold water temperature detector 13 is installed in the cold water outlet pipe 11 of the evaporator 10.

  The electric motor 21 is driven by a power source whose frequency is converted by a frequency converter (switching inverter, hereinafter referred to as “inverter”) 80, thereby acting as a variable speed driving machine. The rotational speed of the rotating body including the turbo compressor 20, the speed increaser, and the electric motor 21 can be arbitrarily changed at a speed equal to or lower than the maximum rotational speed determined by the dangerous rotational speed of the main shaft. The maximum rotation speed limit may be set in the control means 70a or the inverter 80.

  The turbo compressor 20 incorporates a centrifugal single-stage or multi-stage impeller 23 in the casing (single stage in the figure), a guide vane 25 is installed on the suction side thereof, and the motor 21 and the impeller 23 are connected to each other. A speed increasing device comprising a gear mechanism or the like is installed between them. The suction side of the centrifugal impeller 23 faces in the axial direction, and sucks refrigerant gas in the axial direction.

  When the refrigeration load is the design value and the corresponding refrigeration capacity is the design value, the refrigerant gas flows in the axial direction. When viewed from a speed triangle (representing a relative speed with respect to the impeller 23) (not shown) representing the relationship between the impeller 23 and the flow of the refrigerant gas, the refrigerant gas inflow direction and the inlet angle of the impeller 23 coincide with each other. Is minimized. However, when the refrigeration load is reduced to a partial load, the refrigeration capacity is reduced as a result of the control, and the volume flow rate of the refrigerant gas flowing in the axial direction is reduced. As a result, a deviation occurs between the inflow direction and the entrance angle of the impeller 23. As a result, the efficiency of the turbo compressor is reduced, and the head generation capability is also reduced. When the guide vane 25 is provided, the refrigerant gas inflow direction is adjusted by opening and closing the guide vane 25. As a result, the inflow direction of the refrigerant gas to the impeller 23 on the speed triangle can be made coincident with the entrance angle of the impeller 23, and a reduction in efficiency can be suppressed. In addition, the head is hardly reduced. Thus, in the control by the guide vane 25, at least in the range where the opening degree is not so small, the volume flow rate of the refrigerant gas to be sucked can be adjusted without causing the generated head to be lowered. Therefore, the freezing capacity can be increased or decreased while suppressing the surging phenomenon described later.

  However, when the guide vane opening is reduced, the suction gas is diluted, and it becomes close to damper control for adjusting the mass flow rate of the inflowing refrigerant gas. In other words, the turbo compressor 20 is designed so that the predetermined suction capacity and work can be obtained with the suction guide vane 25 fully open, so that if the suction guide vane 25 operates in a direction in which the suction capacity decreases. Naturally, the efficiency of the turbo compressor 20 is reduced as compared with the operation in the designed state, and as a result, the effect of the energy saving operation of the turbo refrigerator 101 is reduced.

  Further, when the opening degree GV of the guide vane 25 is small, the head is reduced corresponding to the pressure loss due to the damper, so the effect of suppressing the surging phenomenon is reduced. This problem can be dealt with by correcting the set rotational speed described later.

  The discharge pipe of the turbo compressor 20 is connected to the condenser 30, and the suction pipe of the turbo compressor 20 is connected to the evaporator 10. Note that the low pressure side pressure detector P1 may be installed on the suction side (suction pipe) of the turbo compressor 20 instead of being installed in the evaporator 10 to detect the suction pressure. The high pressure side pressure detector P2 may be installed on the discharge side (discharge pipe) of the turbo compressor 20 instead of being installed in the condenser 30 to detect the discharge pressure.

  Next, refrigeration capacity control based on the rotation speed SP will be described. In the performance curve (HV curve) (not shown) showing the relationship between the head H generated by the turbo compressor 20 and the volume flow rate of the suction gas of the impeller 23, the head H is 2 of the rotational speed SP of the impeller 23. The volume V is proportional to the rotation speed SP. On the other hand, the turbo refrigerator 101 has a necessary head determined by the evaporation temperature (or evaporation pressure) of the evaporator 10 and the condensation temperature (or condensation pressure) of the condenser 30. Therefore, a surging phenomenon occurs when the head H generated by the turbo compressor 20 becomes less than the required head. The rotational speed of the turbo compressor 20 cannot be lowered below the rotational speed corresponding to the head H. Here, this rotational speed is referred to as “minimum rotational speed”.

  The control means 70a includes a chilled water outlet temperature signal S1 representing the chilled water outlet temperature TL detected by the chilled water temperature detector 13, a low pressure side pressure signal S7 representing the low pressure side pressure PL detected by the low pressure side pressure detector P1, and a high pressure. The high pressure side pressure signal S8 indicating the high pressure side pressure PH detected by the side pressure detector P2 and the guide vane opening signal S3 indicating the guide vane opening GV are input, and a speed command is sent to the inverter 80 based on these detection signals. A signal (inverter rotation speed adjustment signal) C1 is output, and a guide vane opening adjustment signal C2 for opening and closing the guide vane 25 is output. Details of the control means 70a will be described later.

  In the set rotational speed calculator described later, the set rotation is based on the low pressure side pressure signal S7 (PL) as the operating condition of the evaporator 10 and the high pressure side pressure signal S8 (PH) as the operating condition of the condenser 30. The speed SETSP is calculated, but instead, the cooling water outlet temperature signal S1 representing the cold water outlet temperature TL as the operating condition of the evaporator 10 and the cooling as the operating condition of the condenser 30 detected by the cooling water temperature detector 14 are detected. It may be based on a cooling water inlet temperature signal S2 representing the water inlet temperature TH. Details will be described later.

  In the turbo chiller 101 configured as described above, the refrigerant is repeatedly evaporated, pressurized and compressed, condensed, and decompressed by the evaporator 10, the turbo compressor 20, the condenser 30, and the decompression device 40, thereby constituting a refrigeration cycle. Is done. In the embodiment of the present invention, the control means 70a of the turbo chiller 101 monitors the load, and increases or decreases the rotational speed SP of the turbo compressor according to the increase or decrease of the load. This is referred to herein as “load control”.

  In the turbo refrigerator 101 of the present embodiment, the control means 70a receives the cold water outlet temperature TL from the cold water temperature detector 13. In this embodiment, since the cold water temperature detector 13 is provided in the cold water outlet pipe 11, S1 is a signal indicating the cold water outlet temperature TL. On the other hand, the cold water outlet set temperature SETTL is set in the control means 70a. A speed command signal C1 for adjusting the rotational speed SP of the turbo compressor 20 is output from the control means 70a to the inverter 80. The cold water outlet temperature TL reflects the increase or decrease of the refrigeration load most directly. That is, when the centrifugal chiller 101 is stably operated, the chilled water outlet temperature TL increases as the refrigeration load increases. This is controlled by the load control so that it becomes the set temperature SETTL.

  Further, as described above, the control means 70a receives the pressure signal S7 (PL) from the pressure detector P1 installed in the evaporator 10, and the pressure signal S8 (PH) from the pressure detector P2 installed in the condenser 30. The guide vane opening signal S3 (GV) is received from the guide vane opening detector 15 installed in the guide vane 25. And the guide vane opening degree adjustment signal C2 which adjusts the opening degree GV of the guide vane 25 is output. Furthermore, the control means 70a receives the rotational speed signal S4 (SP).

  With reference to the block diagram of FIG. 2, the configuration and operation of the control means 70a will be described in detail. The control means 70a has an inverter control device 71 as a first control unit. The inverter control device 71 receives the cold water outlet temperature signal S1 (TL). A cold water outlet temperature set value SETTL is set. The cold water outlet temperature set value SETTL may be given as the signal S6 or may be given artificially from a setting dial, a keyboard, or the like. A speed command signal C <b> 1 is output from the inverter control device 71 toward the inverter 80.

  The inverter control device 71 may be any of a proportional control device (P), a proportional integration control device (PI), or a proportional integration differentiation device (PID). When it is a proportional control device, it becomes a simple control device. Some offset remains, but it is not a problem with air conditioning. Typically, a proportional integral control device is used. At this time, no offset remains, and control can be performed so that the chilled water outlet temperature TL matches the chilled water outlet set temperature SETTL. In the case of a proportional-integral-derivative device, when the change in the refrigeration load is sudden, the change can be anticipated and controlled, so that a quick response is possible.

  The control means 70a further includes a guide vane control device 72 as a second control unit. The guide vane control device 72 is inputted with the rotational speed SP of the electric motor 21 (signal is S4) and eventually the rotational speed of the turbo compressor 20. The rotational speed of the electric motor 21 and the rotational speed of the turbo compressor 20 are in a completely corresponding relationship with only a difference in the speed increasing ratio of the speed increasing machine, which is a constant. Therefore, adjusting the rotational speed of the electric motor 21 is synonymous with adjusting the rotational speed of the turbo compressor 20. Furthermore, the frequency of the inverter 80 may be used. This is because it substantially corresponds to the rotational speed of the electric motor 21. Hereinafter, the term “rotational speed” simply refers to the rotational speed of the turbo compressor 20 (rotational speed of the impeller 23), the rotational speed of the electric motor 21, and the frequency of the inverter. Further, instead of the rotation speed, the speed ratio (rotation speed / minimum rotation speed) may be described as appropriate.

  The guide vane control device 72 is supplied with a set rotation speed signal S5 representing the set rotation speed SETSP calculated by the set rotation speed calculator 73. The set rotational speed calculator 73 receives a low pressure side pressure signal S7 (PL), a high pressure side pressure signal S8 (PH), and a guide vane opening signal S3 (GV). The set rotation speed calculator 73 receives the low pressure side pressure signal S7 and the high pressure side pressure signal S8, calculates the minimum rotation speed, and calculates the set rotation speed SETSP. Further, the set rotational speed SETSP is corrected using the guide vane opening signal S3 (GV).

  FIG. 3 is a diagram illustrating the performance of the turbo refrigerator 101 when the refrigerating capacity is controlled only by the guide vanes 25 without performing the rotational speed control. This performance curve itself is the same as that of the prior art. The behavior of the guide vane 25 of the turbo chiller 101 constituting this embodiment is shown for understanding first. This figure is a refrigeration capacity ratio / performance coefficient curve with the parameter being the cooling water (inlet) temperature TH. The refrigeration capacity ratio on the horizontal axis indicates the refrigeration capacity as a ratio, assuming that the designed refrigeration capacity is 1.0. The vertical axis represents the coefficient of performance (COP), that is, the refrigeration capacity obtained for the input power. This figure shows how the coefficient of performance changes depending on the coolant temperature TH.

  When attention is paid when the refrigerating capacity ratio is 1.0, the coefficient of performance is about 6.1 when the cooling water temperature is 32 ° C., and at this time, the guide vane 25 is fully opened. When the refrigerating capacity ratio decreases, the guide vane 25 operates in the closing direction. The operating point moves to the left in the figure. As can be seen from the figure, there is almost no decrease in the coefficient of performance until the refrigeration capacity ratio is about 0.85.

  When the cooling water temperature is 20 ° C., the coefficient of performance shows about 7.9. It is in a state such as an interim period. At this time, the guide vane 25 is already closed to some extent even if the refrigerating capacity ratio is 1.0. When the refrigerating capacity ratio decreases, the guide vane 25 further operates in the closing direction. As can be seen from the figure, when the refrigeration capacity ratio starts moving from 1.0 to the left in the figure, the coefficient of performance starts to decrease immediately.

  With reference to FIG. 4, the surging phenomenon peculiar to the turbo compressor 20, that is, the centrifugal compressor will be described. This performance curve itself is not different from the prior art. This is also shown in order to understand the surging limit when the rotational speed of the turbo chiller constituting this embodiment is controlled. This figure shows characteristics (relationship between the cooling water inlet temperature TH and the refrigeration capacity ratio) when the parameter is the rotation speed ratio and the refrigeration capacity of the turbo chiller 101 is controlled by changing the rotation speed SP of the turbo compressor 20. FIG. Here, the rotation speed ratio is a percentage (%) of the rotation speed of the compressor with respect to the rated rotation speed, and is approximately 100% when the cooling water temperature is about 32 ° C. and the refrigeration capacity ratio is 1.0.

  As can be seen from this figure, if the cooling water temperature TH decreases, the rotational speed of the turbo compressor 20 can be decreased to perform the refrigeration capacity control operation, but it also shows that there is a limit value. For example, when the cooling water temperature is 32 ° C., the rotation speed is about 100% and the freezing capacity ratio is 1.0. When the rotation speed is lowered to 91.5%, the refrigerating capacity ratio becomes about 0.71. However, the surging limit line is reached here. That is, if the load decreases under the condition where the cooling water inlet temperature is 32 ° C., the refrigeration capacity ratio can be reduced to about 0.71, by reducing the rotational speed SP of the turbo compressor 20, but here the surging The limit line is reached and the turbo compressor 20 enters an area where stable operation is impossible. This limit rotation speed is the minimum rotation speed when the cooling water temperature is 32 ° C. In the prior art, the mode is switched using the minimum rotation speed as a guide, and guide vane control is started. In the present embodiment, the transition to guide vane control is smoothly performed without causing control instability due to mode switching.

  With reference to the diagram of FIG. 5, a method for obtaining the surging limit line and thus the “minimum rotation speed” in a certain state will be described. This figure is a diagram showing the relationship between the cooling water inlet temperature and the rotational speed (inverter frequency)% of the turbo compressor 20 and the relationship between the cooling water inlet temperature and the surging limit work when the guide vane 25 is fully open. .

In the embodiment of the present invention, the set rotational speed signal SETSP of the guide vane control device 72 as the second control unit is calculated and determined by the set rotational speed calculator 73 based on the limit rotational speed (minimum rotational speed). . In the present embodiment, the limiting rotational speed that is the boundary is, first of all, the pressure in the evaporator 10 (or the suction pressure of the turbo compressor 20) (the pressure signal is S7 (PL)), and the pressure in the condenser 30. The pressure (or the discharge pressure of the turbo compressor 20) (the pressure signal is S8 (PH)) is determined only by two points of information. In other words, if the work of the turbo compressor 20 is displayed by isothermal work, the work Wc is set such that the pressure on the low pressure side and the pressure on the high pressure side are PL and PH, respectively.
Wc = PL × V1 × Log (PH / PL) Equation (1)
It becomes. Here, V1 is the specific volume of the turbo compressor suction, and the value of PL × V1 hardly changes during operation except when the turbo refrigerator 101 is started. That is, PL × V1 can be set as a constant if the specifications of the turbo refrigerator 101 are determined, and the limit work of the turbo compressor 20 can be calculated by detecting the pressures PL and PH at two points on the low pressure side and the high pressure side. .

  Accordingly, it can be seen that the recommended rotation speed of the turbo compressor 101 and the corresponding surging limit line can be simply determined by the temperature of the cooling water (in this example, the cooling water inlet temperature TH). The linear relationship shown in FIG. 5 can be easily derived from the rotational speed SP on the surging limit line in FIG. 4 showing the capacity control characteristics and the operating state of the turbo compressor 20 at this position, in addition to the pressures PL and PH. If the coolant temperature TH is detected, this indicates that the stable operation region of the turbo chiller 101 can be determined.

  Returning to FIG. 2, the control by the control means 70a will be described. From the above, as a technique for controlling the refrigeration capacity by determining the increase or decrease of the refrigeration load in the turbo chiller 101, the chilled water temperature detector 13 detects the chilled water outlet temperature TL, and the control means 70a uses the chilled water outlet temperature signal S1. To the inverter control device 71. The rotational speed SP is adjusted so that the temperature TL becomes the target value SETTL.

  Here, the case where the inverter control device 71 is proportional-integral (PI) control will be described. In this case, if there is a deviation between TL and SETTL, if the deviation is positive, it means that the refrigeration capacity (refrigeration output) is insufficient compared to the refrigeration load, so a speed command for increasing the rotational speed SP. The signal C1 is sent to the inverter 80. Conversely, when the deviation is negative, it means that the refrigeration capacity is excessive compared to the refrigeration load, and therefore, a speed command signal C1 for decreasing the rotational speed SP is sent to the inverter 80. It stabilizes when the deviation becomes zero. In this way, the chilled water outlet temperature TL, and thus the refrigeration capacity, is controlled by adjusting the rotational speed and adjusting the suction capacity of the turbo compressor 20. In particular, when the present turbo chiller is for an air conditioner, when the temperature TH of the cooling water decreases during an intermediate period or the like, the refrigeration capacity is controlled by reducing the rotational speed of the turbo compressor 20. Note that in a refrigerator, the magnitude of the load is often determined by the cold water temperature, and particularly by the cold water outlet temperature.

  On the other hand, as described above, in the operation in which the refrigerating capacity is controlled by lowering the rotational speed of the turbo compressor 20, there is a limit value of the minimum rotational speed for avoiding surging.

  The description will be continued with reference to FIG. As a control means for avoiding surging of the turbo compressor 20, the turbo refrigerator 101 according to the embodiment of the present invention includes a guide vane control device 72 that is a second control unit. The guide vane control device 72 adjusts the opening degree GV of the guide vane 25 so that the rotational speed SP of the electric motor 21 and thus the turbo compressor 20 is not reduced below the minimum rotational speed.

  The guide vane control device 72 is a guide vane that is a control signal so that the rotation speed SP (rotation speed signal S4) becomes a set rotation speed signal S5 (SETSP) indicating the set rotation speed calculated by the set rotation speed calculator 73. An opening adjustment signal C2 is transmitted to the guide vane 25 (guide vane driving machine). That is, the control signal C2 is a control signal for opening the guide vane 25 when the deviation between SP and SETSP is positive, and is a signal for closing the guide vane 25 when the deviation is negative. As described above, the guide vane control device 72 does not directly control the freezing capacity. However, since the output characteristics of the refrigerator change by opening and closing the guide vanes, the inverter rotational speed increases or decreases as a result.

  Here, when the guide vane controller 72 controls the rotational speed SP to be the set rotational speed SETSP, the guide vane control device 72 is controlled so as to coincide with the set rotational speed SETSP, and within a predetermined range sandwiching the set rotational speed SETSP. Control is also included. This is typically the case for proportional control. Alternatively, the control is within a dead zone described later.

  The relationship between the guide vane control device 72 and the inverter control device 71 will be further described. If the refrigeration capacity (refrigeration output) and the refrigeration load coincide with each other at a certain rotational speed SP, but the rotational speed SP is lower than the set rotational speed SETSP, the guide vane control device 72 operates and the vane opening GV. Lower. Then, since the refrigerating capacity of the turbo refrigerator becomes smaller than the refrigerating load at the same rotation speed, the “load control” works in the direction in which the inverter control device 71 increases the rotation speed SP. As a result, the rotational speed SP and thus the speed ratio increase. Therefore, by manipulating the vane opening degree GV, the speed ratio can be controlled after all. This control can be called “vane following control”.

  The set rotational speed calculator 73 receives the low pressure side pressure signal S7 (PL) and the high pressure side pressure signal S8 (PH) as described above with reference to FIG. 5, and obtains the minimum rotational speed. Although the minimum rotational speed can be substantially determined by the low-pressure side pressure PL and the high-pressure side pressure PH, as described above, it slightly increases as the guide vane 25 moves from the fully open direction to the closed direction. Therefore, it is preferable to correct the minimum rotational speed by receiving the guide vane opening signal S3 (GV).

  The set rotational speed SETSP is a value obtained by giving a margin to the obtained minimum rotational speed. The margin depends on the characteristics of the turbo compressor and the inverter control device, but is typically 0.01% to 10%, preferably 0.1% to 2.0%, more preferably 0.5% to 1 0.0% or less is recommended. If the margin is too small, there is a high possibility that the minimum rotational speed is reached and surging occurs, and the range in which the rotational speed is controlled by operating the guide vane 25 in the closing direction becomes narrow. If the margin is too large, the range in which the turbo compressor can be operated with high efficiency is reduced accordingly. In terms of the speed ratio, the set rotational speed SETSP is, for example, 1.010 times the minimum rotational speed when a margin of 1.0% is provided.

  When the correction calculator 73-4 (see FIG. 6) is not provided and the minimum rotation speed is not corrected by the guide vane opening signal S3 (GV), the minimum guide vane opening that can be used is obtained. A value obtained by multiplying the minimum rotation speed by 1.010 may be used as the set rotation speed value. Although the margin when the guide vane is fully opened is somewhat too large, the calculation can be simplified.

  In this system, when the rotation speed SP is sufficiently higher than the set rotation speed SETSP, the inverter control device 71 performs the refrigerating capacity control. The guide vane control device 72 is also in operation, but the rotational speed SP is sufficiently higher than the set rotational speed SETSP, which means that the deviation between the rotational speed SP and the set rotational speed SETSP continues to be positive, A control signal C2 in the direction to open the guide vane 25 is continuously output. Therefore, the guide vane 25 is fully opened, which is substantially the same as that only the rotational speed control is working, and the state in which the refrigerating capacity is controlled by the rotational speed control unit 71 continues. Referring to FIG. 4, for example, the cooling water temperature is 20 ° C. and the refrigerating capacity ratio is between 1.0 and about 0.6. During this time, it can be seen that the rotational speed is between about 82% and about 68%. The surging limit line is reached when the rotational speed SP decreases to about 68%.

  In the present embodiment, since the set rotational speed SETSP is 1.010 times the minimum rotational speed, the guide vane control device 72 starts to work when the rotational speed reaches 68 × 1.01 = about 69%. When the rotational speed ratio falls below 69%, the deviation between the rotational speed SP and the set rotational speed SETSP becomes negative. Therefore, the guide vane control device 72 closes the control signal C2 for increasing the rotational speed SP, that is, the guide vane 25. A guide vane opening adjustment signal C2 that moves in the direction is output. In this way, when the guide vane 25 is slightly closed, the rotational speed SP is returned to the set rotational speed SETSP and stabilized. Since it is controlled in this way, the rotation speed SP does not reach the minimum rotation speed, and the surging phenomenon can be avoided.

  In the present embodiment, the response speed of the guide vane control device 72 is set slower than the response speed of the inverter control device 71. In other words, the time constant of the guide vane control device 72 is set longer than the time constant of the inverter control device 71. Therefore, even when the rotation speed ratio is around 69%, the inverter control device 71 first responds quickly to a change in the refrigeration load or a change in the cooling water temperature, and the refrigerating capacity is adjusted by adjusting the rotation speed SP. Be controlled.

  In general, the fluctuation of the refrigeration load or the fluctuation of the cooling water temperature occurs gently. Therefore, even if the response speed of the guide vane control device 72 is not so fast, the rotation speed does not reach the minimum rotation speed. However, when the refrigeration load fluctuates rapidly, the rotational speed SP may decrease too much and reach the minimum rotational speed. In order to make it easier to avoid this, it is preferable that the speed at which the opening degree of the guide vane 25 is operated in the closing direction is faster than the speed at which the guide vane 25 is operated in the opening direction. When operating the opening degree of the guide vane 25 in the opening direction, there is no problem in control even if it is somewhat delayed. Operation with a low coefficient of performance is only somewhat longer. Furthermore, it is preferable to limit the lower limit in order to prevent the rotation speed from decreasing beyond the minimum rotation speed. This will be described later.

  In this way, for example, when the load increases rapidly, first, the rotational speed SP increases and the output of the turbo chiller 101 increases. If the response speed of the rotational speed control is made faster than that of the vane opening control, the rotational speed control can quickly catch up with the rapidly increased load. That is, the control is stabilized. On the other hand, the speed ratio increases due to the increase in the rotational speed SP. In response to this, the vane opening GV slowly rises. Thereby, since the output of the turbo refrigerator 101 increases, the rotational speed SP gradually decreases. As a result, the speed ratio decreases and eventually stabilizes again at the target value (set rotational speed).

  Here, as described above, it is generally more efficient that the rotational speed SP is as small as possible and the vane opening GV is as large as possible. That is, according to the control of the present embodiment, the rotational speed SP is temporarily high and the vane opening degree GV is temporarily reduced compared to the optimum point, so that the efficiency is lowered. However, in practice, the temporary decrease in efficiency due to this control is negligibly small, and the state immediately changes to an optimum state, so that there is almost no decrease in energy saving. On the other hand, since the load fluctuation is immediately followed by the operation of the rotational speed SP, the followability to the load is greatly improved. Thereby, both energy saving and follow-up properties can be achieved.

  In the centrifugal chiller 101 of the present embodiment, unlike the conventional centrifugal chiller, the rotational speed SP is adjusted by adjusting the rotational speed SP by adjusting the rotational speed SP and the opening degree GV of the guide vane 25 to adjust the rotational speed SP. Both the guide vane control to be controlled are always active, and the mode is not switched between the two controls. Therefore, it is possible to suppress the phenomenon of frequently going back and forth between the two modes, which is likely to occur along with the mode switching, and stable control becomes possible. Since there is no mode switching, there is no problem with the change in the response speed of the centrifugal chiller and various constants that tend to occur at that moment, and there is no concern about changes in the behavior of the turbo chiller.

  In the above embodiment, the setting rotational speed calculator 73 has been described with the low pressure side pressure signal S7 (PL) and the high pressure side pressure signal S8 (PH) being input. The signal and the condensation temperature signal of the condenser 30 may be input. Further, the cold water outlet temperature signal S1 (TL) and the cooling water inlet temperature signal S2 (TH) may be input, respectively. Strictly speaking, the surging limit slightly deviates from the actual limit at the cold water outlet temperature TL and the cooling water inlet temperature TH, but the detection of the evaporation pressure / condensation pressure or the evaporation temperature / condensation temperature of the evaporator 10 and the condenser 30 is detected. The device can be omitted, and the device becomes simple. In this case, the chilled water outlet temperature detector 13 used for detecting the refrigeration capacity can also be used for the set rotational speed calculation.

  The minimum rotation speed is preferably calculated by the evaporation pressure of the evaporator 10 and the condensation pressure of the condenser 30. Specifically, the minimum rotation speed corresponding to several pressure differences depends on the characteristics of the refrigerant in advance. The speed may be calculated and stored in the storage unit of the control means 70a, and the minimum rotation speed at the calculated pressure ratio may be extracted from the storage unit and calculated. Note that, as described above, the minimum rotational speed may be corrected by the vane opening degree GV at this time. That is, surging is likely to occur when the vane opening degree GV is small, so the minimum rotation speed may be increased in advance according to the vane opening degree GV.

  Here, for the vane follow-up control, it is better to use a control method that slows the operation to some extent. Specifically, the integral constant is reduced, the control cycle is increased, or the vane is intentionally driven by a slow motor. This is because, in the conventional control, the control of the vane opening GV is mainly intended to follow the load, and if the operation is made too slow, the chilled water outlet temperature or the like deviates greatly from the set value. According to the embodiment, since the load following is performed rapidly by the rotational speed control, no major problem occurs even if the tracking is somewhat slow. Rather, the control is more stable when the control result (speed ratio) by the load control is averaged over a certain period of time, for example, so as to make it a first order delay.

  By the way, a high-level control method such as so-called PID control may be used for the vane follow-up control. However, since the operation amount is normally applied to the upper limit of the value range, the integral term becomes an unnecessarily large value. Can cause unexpected behavior. Rather, the control method may be simple, only gradual increase or decrease, or it is particularly preferable to use time proportional control described later.

  In the case of gradual increase / decrease, the guide vane control device 72 confirms the speed ratio at regular intervals (several seconds to several minutes are good), and if the speed ratio is equal to or greater than the target range, the vane opening GV is increased. For example, the vane opening GV is reduced. At this time, the speed (increase amount) in the opening direction and the speed (decrease amount) in the closing direction of the vane opening GV are not necessarily the same, and the speed in the closing direction of the vane is increased as described above. It is preferable to reduce the speed in the opening direction.

  Next, time proportional control will be described. In the time proportional control, the difference between the target value and the current value is calculated at regular intervals (usually several seconds to several minutes, and the optimum value varies depending on the characteristics of the apparatus). Then, the guide vane 25 is moved in a direction based on the difference for a time proportional to the difference. Specifically, when the actual speed ratio is 1.015 with respect to the target value 1.010, the motor for operating the guide vane 25 is opened in the opening direction with respect to the speed ratio difference of 0.005. For example, drive for 5 seconds. At this time, when the actual speed ratio is 1.020, the difference in speed ratio is 0.010, so the driving is performed for 10 seconds. Though this is a kind of integral control in concept, it is well matched with the vane follow-up control of the turbo refrigerator in the present invention.

  The control constant in the time proportional control is normally a constant value, but the change (sensitivity) of the freezing capacity with respect to the same change in opening degree is different between the case where the vane opening degree GV is high and the case where the vane opening degree GV is low. When the constant is changed, the followability is further improved. For example, when the vane opening is 60% or more, the speed ratio difference is 0.005, while the driving time is 5 seconds, and when it is less than 60%, it is 1 second.

  In the above embodiment, the guide vane control device 72 has been described on the assumption that the set rotational speed SETSP is 1.010 times the minimum rotational speed, and this is used as a set value to adjust the rotational speed SP. Normally, this may be done, but if the response of the guide vane control device 72 does not catch up and the rotational speed SP falls below the minimum rotational speed, the turbo compressor will surging.

  Therefore, as a first configuration, it is preferable to limit the rotation speed SP in the inverter control device 71 so that the rotation speed SP does not fall below the minimum rotation speed. When the minimum rotation speed is reached, a limit is set as a lower limit rotation speed at a value immediately before reaching the minimum rotation speed (for example, 1.001 times the minimum rotation speed). That is, the speed command signal C1 is set such that the rotational speed SP does not decrease even if the refrigeration capacity is smaller than the refrigeration load.

  Now, a case where the load is reduced in the embodiment in which the limit is set to 1.001 times the minimum rotation speed will be described. As described repeatedly, the efficiency is improved when the rotational speed SP is as low as possible and the vane opening degree GV is increased. When the target value of the speed ratio is set to 1.010 times the minimum rotational speed and the speed ratio is stable at this target value, the rotational speed SP immediately decreases to the minimum when the load decreases rapidly. Decreases in the direction of rotation speed. Even in that case, the speed ratio stops at the limit value of 1.001.

  No matter how much the refrigeration load is reduced (originally, it is in a state where the speed ratio is to be set to 0.990 (a state in which the difference in speed ratio is to be set to 1.010−0.990 = 0.020)) The state where the ratio difference is small (0.010) continues. Therefore, when viewed from the guide vane control device 72, since the deviation is small, the guide vane opening degree adjustment signal C2 (in the closing direction) does not increase, and the opening degree GV does not decrease easily. In this case, there is a concern that the state where the refrigeration capacity is excessive continues, the cold water outlet temperature TL is excessively lowered, and the control becomes unstable. In order to prevent this, as described above, it is preferable that the decrease amount (decrease speed) of the vane opening degree GV is larger than the increase amount (increase speed). By doing so, the vane opening degree GV decreases relatively quickly even when the rotational speed SP is not lowered, and this effect can be reduced.

  As a second configuration, the guide vane opening GV may be gradually decreased at a constant speed when the speed ratio becomes a certain value or less. Specifically, for example, when the speed ratio is reduced to 1.001, the guide vane opening GV is continuously reduced at a constant speed regardless of the time proportional control regardless of the actual difference. If it does in this way, refrigeration capacity will fall rapidly by the guide vane opening degree GV falling, and will follow the fall of load.

  As described above, both the first configuration and the second configuration tend to temporarily close the guide vane opening GV too much. However, in the embodiment of the present invention, the load control works again due to the decrease in the refrigeration capacity, and the rotation speed SP increases to compensate for the decrease in the refrigeration capacity. If it carries out like this, it will be in the same state as "when the load increases rapidly" mentioned above, and the turbo refrigerator 101 will finally be stabilized again by the same control.

  Generally, in a refrigerator, there is a problem that the cold water temperature is too low. That is, there is a concern about unnecessary light load stoppage due to a decrease in the cold water outlet temperature and freezing of the cold water. In conventional control, mode switching is not in time when the load suddenly decreases, or vane control is used at low loads, so the response is originally slow, so there is a limit in response, and light load stops due to sudden change in load There were many things. According to the embodiment of the present invention, when the load suddenly decreases, (1) the vane opening degree GV is immediately greatly reduced to immediately respond to the decrease in the load, and (2) the rotation speed SP is temporarily compensated for, (3) The operation is such that the efficiency is recovered by gradually increasing the vane opening GV, and the possibility of a light load stop is reduced. In this operation, since the guide vane opening GV is temporarily closed too much, the efficiency is temporarily lowered, but the efficiency is slightly reduced, and the energy required for stopping and restarting due to the light load stop is large. Increasing the avoidance ability contributes to energy saving.

  Control of the turbo chiller 101 of the first embodiment will be described with reference to the control block diagram of FIG. The control means 70b is an example in which the control means 70a is specifically developed. In practice, the control means 70b and the arithmetic units constituting the control means 70b may be virtually provided in the programmable controller using a logic circuit or a description language. Here, the control means 70b monitors the cold water outlet temperature TL using a PID calculator, and adjusts the rotational speed SP of the turbo compressor 101 so as to keep it constant.

  In the present embodiment, the inverter control device 71 includes a PID calculator 71-1. Specifically, PID calculation is continuously performed here to determine the “command rotation speed” so that the cold water outlet temperature TL becomes the target temperature SETTL. This is sent to the inverter 80 as a speed command signal C1. The PID calculator 71-1 calculates the rotational speed SP so that the chilled water outlet temperature TL is equal to or higher than the separately calculated minimum rotational speed and becomes the target value SETTL.

  In addition, as long as it is quantity which represents the increase / decrease in the load on the facility side, such as a cold water inlet temperature instead of the cold water outlet temperature TL, a state signal on the facility side from the outside, it may be controlled by anything. However, if the cold water outlet temperature TL is used, the increase or decrease in the load on the facility side can be detected most significantly. Moreover, the temperature detector 13 installed in the cold water outlet pipe 11 can be easily and reliably detected, which is convenient. The calculation is not PID control, and any calculation method of P control (proportional control) and PI control (proportional integral control) may be used as long as the calculation method is used for load control of the turbo chiller 101. The characteristics and effects of each control method are as described above.

  Here, the minimum rotation speed is calculated as follows. First, the evaporator pressure PL and the condenser pressure PH of the turbo chiller 101 are taken in, and the ratio (PH / PL) is calculated by the PH / PL calculator 73-1. Based on this ratio, the minimum rotation speed calculator 73-2 temporarily calculates the minimum rotation speed with reference to the calculation table 73-3 calculated in advance. Based on the guide vane opening GV, the correction calculator 73-4 multiplies the coefficient according to the opening GV when the guide vane 25 has a low opening to determine the final minimum rotational speed. The minimum rotation speed signal S5a is sent to the target speed calculator 72-3.

  The minimum rotation speed signal S5a is also sent to the PID calculator 71-1. This is to put a limit corresponding to the minimum rotation speed on the speed command signal C1. By applying the limit, the turbo compressor 20 can be prevented from entering the surging state.

  In another embodiment of the present invention, not limited to this method, a method of determining the minimum rotational speed based on the cooling water inlet temperature TH, a method of calculating based on an enthalpy difference at the inlet / outlet of the turbo compressor 20, etc., a turbo compressor You may calculate by the method of determining by 20 map calculations.

  Note that the minimum rotational speed is set to a value higher than the actual surging rotational speed by multiplying the speed of the surging limit line (see FIG. 5) calculated from PH / PL by a predetermined margin as described above. For example, it is 1.001 times the calculated value. Such a margin may be multiplied in the calculation process, or may be given by storing data with a margin in the calculation table 73-3.

  The above PID calculation corresponds to the aforementioned “load control”. The speed command signal C1 calculated here is transmitted to the inverter 80. At the same time, referring to this speed command signal C1, the vane opening / closing calculator 72-1 calculates the driving of the guide vane 25. Here, the command rotational speed is used, but actually, the actual rotational speed SP (signal S4) of the electric motor 21 is preferably used. However, since the inverter 80 has a fast response and the command rotational speed is reflected almost immediately on the rotational speed SP of the electric motor 21, the vane opening / closing calculator 72-1 can use the speed command signal C1. Since the speed command signal C1 exists in the control means 70b, it is convenient because it is not necessary to input the actual rotational speed SP of the electric motor 21 to the control means 70b anew.

  In the present embodiment, as described above, the difference or ratio between the calculated minimum rotational speed and the actual rotational speed SP (value determined by increasing or decreasing by load control) is calculated. Note that taking the difference and taking the ratio differ only in the arithmetic expression and the value, and there is no substantial difference. The case of taking the ratio will be described later as a modified example.

  The turbo refrigerator 101 controls the suction vane opening degree GV so that the rotational speed SP becomes a target value (here, the minimum rotational speed is 1.010). In practice, the centrifugal chiller 101 monitors the rotational speed SP, and decreases the vane opening GV if the rotational speed decreases, and increases the vane opening GV if the rotational speed SP increases. That is, when the vane opening degree GV is increased, the refrigeration capacity of the turbo chiller 101 is increased at the same rotational speed, so that the chilled water outlet temperature TL is lowered, and “load control” is performed in a direction of decreasing the rotational speed SP. As a result, the rotational speed SP decreases.

  On the other hand, a signal S5 representing a set rotational speed SETSP that is a target value of the rotational speed SP is input to the vane opening / closing calculator 72-1. The set rotation speed SETSP is calculated by the target speed calculator 72-3 based on the minimum rotation speed calculated via the correction calculator 73-4. In the present embodiment, the target speed calculator 72-3 multiplies the minimum rotational speed by a predetermined coefficient, for example, 1.010 to obtain the set rotational speed SETSP.

  Further, the proportional speed (signal S3a) calculated by receiving the vane opening signal S3 (GV) by the proportional speed calculator 72-4 is input to the vane opening / closing calculator 72-1. The vane opening / closing calculator 72-1 transmits a guide vane opening degree adjustment signal C2 to the guide vane motor M so that the received rotational speed SP becomes the set rotational speed SETSP. The guide vane opening adjustment signal C2 is transmitted for a time corresponding to the proportional speed signal S3a. In this way, the control unit 72 controls the opening degree GV of the guide vane 25 by time proportional control.

  In this embodiment, since a vane motor that opens and closes at a constant speed is used, simple control that adjusts the opening and closing speed of the guide vane 25 with time is possible. The control unit 72 changes the proportionality constant of the time proportional control according to the opening degree of the guide vane 25. That is, the sensitivity of changes in the refrigeration capacity is dull with respect to the vane opening width, and the opening / closing speed is relatively increased in a large opening range.

  With reference to FIG. 7, the control apparatus concerning 2nd embodiment of this invention is demonstrated. This embodiment is a modification of the embodiment of FIG. The difference is that in this modification, a rotation speed ratio is used instead of the rotation speed. Explanation of similar parts is omitted as appropriate.

  A signal S5a representing the corrected minimum rotation speed output from the correction calculator 73-4 is input to the speed ratio calculator 72-2. A speed command signal C1 is also input to the speed ratio calculator 72-2. The speed ratio calculator 72-2 calculates a “speed ratio” that is a ratio between the “command rotational speed” and the “minimum rotational speed”. Then, the speed ratio signal S4-1 is input to the vane opening / closing calculator 72-1. Referring to this, the vane opening / closing calculator 72-1 calculates the driving of the guide vane 25.

  In this case, the speed ratio SETSP ′ serving as a target value is a constant set for each apparatus, and ideally a value larger than 1 and as close as possible to 1 is desirable. Actually, since the response speed varies depending on the model of the centrifugal chiller, an optimum value is appropriately obtained through experiments or the like and stored in the storage unit of the control means 70a. The signal S5b '(SETSP') is input to the vane opening / closing calculator 72-1. The calculation in the vane opening / closing calculator 72-1 is the same as that in FIG. Take the ratio between the minimum rotation speed and the rotation speed and control the vane so that it becomes the set value, and set the target rotation speed by multiplying the minimum rotation speed by a constant, and the rotation speed matches this. Thus, controlling the vane is mathematically equivalent.

  In the present embodiment, as described above, the ratio between the calculated minimum rotational speed and the actual rotational speed SP (value determined by increasing / decreasing by load control) is calculated. Note that, as described above, taking the difference and taking the ratio are different from each other only in the arithmetic expression and the value, and there is no substantial difference. Therefore, the speed ratio has been referred to as needed, but the following description will be mainly based on the ratio of the rotational speed rather than the rotational speed SP itself. This ratio is called “speed ratio”.

  The operation of the vane opening / closing calculator 72-1 will be described with reference to a simplified internal flowchart in the vane opening / closing calculator 72-1 (see FIG. 7) in FIG. The vane opening / closing calculator 72-1 has a first reference value F1 and a second reference value F2 therein. The first reference value F1 and the second reference value F2 are values that sandwich a set rotational speed ratio (a ratio of SETSP to the minimum rotational speed). The vane opening / closing calculator 72-1 confirms the speed ratio F at regular intervals, and if the speed ratio F is greater than a first reference value (for example, 1.015), it is defined by a “proportional time” separately calculated. An open signal is sent to the guide vane 25 for a predetermined time. (At this time, if the guide vane opening GV is already 100%, the guide vane 25 will not be opened any more even if an open signal is received, and the inverter control device 71 keeps the speed ratio F exceeding the first reference value. The point that the load control by the adjustment of the rotational speed SP is continued is as described above.) Also, if it is smaller than the second reference value (for example, 1.005), the time defined by the “proportional time” Then, a close signal is sent to the guide vane 25. At this time, the opening time and the closing time may be the same, but the closing operation may be strengthened by setting the closing time to a constant multiple (for example, twice) of the “proportional time”. In this example, it is doubled.

  Specific steps are followed in the flowchart of FIG. 8 to 10, the rotational speed ratio (also simply referred to as speed ratio) is displayed as F, and the reference value of the rotational speed ratio is displayed as a combination of F and a number. In FIG. 8, first, when control is started (started), it is determined whether a fixed time has passed (ST1). If it has not elapsed (No), it waits for a certain time to elapse. If it has elapsed (Yes), it is determined whether or not the speed ratio F is greater than the first reference value F1 (ST2). If it is determined in step ST2 that it is larger (Yes), an open signal is sent to the guide vane 25 (ST3), and the passage of a fixed time is again waited. When it is determined in the step ST2 that it is as follows (No), it is determined whether or not F is smaller than the second reference value F2 (ST4). If it is determined in step ST4 that the time is smaller (Yes), an open signal of proportional time × 2 is sent to the vane (ST5), and it is determined again that a fixed time has elapsed. If it is determined in step ST4 that it is the above (No), the process waits again for a predetermined time.

  Next, an example in which the method of FIG. 8 is improved will be described with reference to FIG. In this method, the vane opening / closing calculator 72-1 has a first reference value F1, a second reference value F2, and a third reference value F3 therein. The third reference value F3 is a value slightly higher than the minimum rotation speed (minimum rotation speed ratio), for example, 5 to 35% of the difference between the set rotation speed (speed ratio) and the minimum rotation speed (minimum rotation speed ratio) ( Preferably, the value is higher than the minimum rotational speed (minimum rotational speed ratio) by 10 to 30%, more preferably 15 to 25%, typically 20%. A value 20% higher than the difference is 1.002 when the set rotational speed ratio is 1.010.

  The vane opening / closing calculator 72-1 confirms the speed ratio at regular intervals, and if the speed ratio is equal to or greater than a first reference value F1 (eg, 1.015), it is defined by a “proportional time” separately calculated. An opening signal is sent to the guide vane 25 for the time. If the second reference value F2 (for example, 1.005) or less, a closing signal is sent to the guide vane 25 for a time defined by “proportional time”. Further, when the value is equal to or less than the third reference value (for example, 1.002), a closing signal is sent to the guide vane 25 for a time that is a constant multiple (for example, five times) of “proportional time”. Thus, by making it a constant multiple greater than 1, it is possible to increase the closing speed of the guide vane 25 and to suppress the rotation speed SP from reaching the minimum rotation speed, that is, the surging limit speed. The third reference value is 1.000 or more and is preferably as small as possible. This is because the guide vane 25 is preferably as open as possible from the viewpoint of the efficiency of the turbo compressor.

  Next, specific steps are followed in the flowchart of FIG. The description of the same steps as in FIG. 8 will be omitted as appropriate. It is determined whether the speed ratio F is smaller than the third reference value F3 when the result of the determination step (ST1) is Yes or not (ST6). When it is determined that the time is smaller (Yes) in step ST6, a close signal of proportional time × 5 is sent to the guide vane 25 (ST7), and the passage of a fixed time is again waited (ST1). When it is determined in step ST6 that the speed ratio F is greater than or equal to the third reference value F3 (No), the process proceeds to determination step ST2. When it is determined in step ST2 that the speed ratio F is larger than the first reference value F1 (Yes), the process proceeds to step ST3. When it is determined in step 2 that the speed ratio F is equal to or less than the first reference value F1 (No), the process proceeds to step ST4. When it is determined in step 4 that the speed ratio F is smaller than the second reference value F2 (Yes), a proportional time closing signal is sent to the guide vane 25 (ST8), and the passage of a fixed time is again waited. When it is determined in step ST4 that the speed ratio F is greater than or equal to the second reference value F2 (No), the process waits again for a certain period of time.

The case where this control is based on the time proportional control described above will be described with reference to the internal calculation flowchart of the vane opening degree calculation device 72 of FIG. In this case, the vane opening / closing calculator 72-1 has a target value F0 which is a set rotational speed ratio and a closing reference value FS inside. The vane opening / closing calculator 72-1 also confirms the speed ratio F every specified time (ST1). The vane opening / closing calculator 72-1 determines whether or not the speed ratio F is smaller than the closing reference value FS (ST9). If the speed ratio F is smaller (Yes), the motor driving direction is closed and the driving time is set to the proportional time. (ST10 in FIG. 10 is proportional time × 0.1. In ST11, as described below, drive time M = | F−F0 | × proportional time. Is, for example, | F−F0 | = | 1.015−1.010 | = 0.005, so that the driving time M of ST10 is 0.1 / 0.005 = 20 times the driving time M of ST11. Here, when FS is about 0.005, this constant is suitably about 0.02 to 0.10). In ST9, when the speed ratio F is not smaller than the closed reference value FS (No), the driving time M is determined by the following equation.
Driving time M = proportional time S × | speed ratio F−target value F0 |
When the determined driving time M is shorter than a predetermined time, for example, 0.5 seconds (Yes), the guide vane 25 is not opened and closed, and the process returns to the step (ST1) for determining whether a certain time has elapsed. . When the determined drive time M is not shorter than a predetermined time, for example, 0.5 seconds (No), it is determined whether or not the speed ratio F is smaller than the target value F0 (ST13). If it is small (Yes), a closing signal is sent to the guide vane 25 for the drive time M (ST14), and the process returns to the step (ST1) for determining the passage of a fixed time. When the speed ratio F is not smaller than the target value F0 in step ST13 (No), an open signal is sent to the guide vane 25 for the driving time M (ST16). The predetermined time of M, which is a criterion for determining whether to open and close the guide vane 25, is 0.5 seconds, but is not limited thereto.

  If the driving time is short (in the above example, about 0.5 seconds or less), or if the difference is expected to be small and the operation time is expected to be short, the driving may not be performed. be called.

  Here, the proportional time is calculated from the vane opening GV. In general, when the vane opening degree GV is large, the actual change in the freezing capacity is small with respect to the change in the vane opening degree GV. Conversely, when the vane opening degree GV is small, the change in the freezing capacity is large. Therefore, it is fundamental to increase the proportional time when the vane opening degree GV is large, and decrease the proportional time when the vane opening degree GV is small. However, simply, two proportional times may be set and switched between a case where it is larger and a case where it is smaller than the predetermined vane opening degree GV. Other than that, there are various methods such as calculating with a polynomial, performing a table operation, storing a characteristic diagram and following it. With this configuration, since the proportional time is increased in a portion where the sensitivity of the change in the freezing capacity is low with respect to the change in the opening degree of the guide vane 25, the response sensitivity is averaged regardless of the opening degree of the guide vane 25. It is convenient to be able to. In particular, when the guide vane 25 is fully open, the refrigeration load decreases rapidly, and there is an advantage that the responsiveness can be maintained high when the rotational speed is lower than the set rotational speed. However, it can be operated even at a constant constant.

  With reference to FIG. 11 and subsequent figures, an outline of how the element moves in the case of the above control will be described. Here, in order to simplify the explanation, it is assumed that the minimum rotation speed that is originally expected to fluctuate is constant and does not change. In this case, the upper and lower rotational speeds may be considered as the upper and lower speed ratios. In the following drawings, the load is represented as LOAD, the cold water outlet temperature is represented as TL, the rotation speed is represented as SP, and the guide vane opening is represented as GV. In both cases, the horizontal axis represents time, the target value is expressed as Target, the minimum value is expressed as min, and the maximum value is expressed as MAX. Here, the target value of the chilled water outlet temperature TL is SETTL, and the target value of the rotational speed SP is SETSP, but in the figure, all are displayed as Target.

  With reference to FIG. 11, the case where the load LOAD increases rapidly in a stable operation state (CASE 1) will be described. In this example, it is assumed that the rotational speed SP is stable at Target in the intermediate period, and the guide vane 25 is operated in a closed state to some extent. In this case, when the load LOAD increases rapidly, the output of the turbo chiller 101 is insufficient with respect to the load LOAD, so that the chilled water outlet temperature TL starts to increase. This is detected by the load control, and the rotational speed SP increases. As a result, the cold water outlet temperature TL stops rising at a certain point and gradually decreases. On the other hand, when the speed ratio increases due to the increase in the rotational speed SP, the guide vane opening GV gradually increases so as to return it to the Target. The characteristics of this increase vary depending on the vane opening / closing calculator 72-1, but generally increase monotonously.

  Now, the cold water outlet temperature TL is stabilized near the target value Target by load control. In this state, since the rotational speed SP is still high and the speed ratio is larger than the target (Target (SETSP)), the increase in the vane opening degree GV continues. For this reason, the freezing capacity gradually increases. Here, the chilled water outlet temperature TL is lower than the target temperature Target due to the increase of the freezing capacity, but the rotational speed SP is lowered by the rotational speed control and works to maintain the temperature, so the chilled water outlet temperature TL is almost the target value or slightly It is in a state below As a result, the rotational speed gradually decreases and finally settles to the target speed ratio, and at this point, the increase in the vane opening degree GV also stops. This stabilizes again.

  Next, with reference to FIG. 12, a case where the load LOAD suddenly decreases in a stable operation state (CASE 2) will be described. Also in this example, it is assumed that the rotational speed SP is stable at Target in the intermediate period, and the guide vane 25 is operated in a closed state to some extent. In this case, when the load LOAD suddenly decreases, first, the output of the centrifugal chiller becomes excessive with respect to the load LOAD, so the cold water outlet temperature TL starts to decrease. Similar to CASE 1, this is detected by the load control and the rotational speed SP decreases, but when the load LOAD fluctuates greatly, the rotational speed SP reaches the minimum rotational speed min and stops decreasing.

  Here, the rotation speed SP stops decreasing, but the vane opening / closing calculator 72-1 has a small speed ratio, so that the guide vane opening degree GV works to decrease, and the chilled water outlet temperature TL stops decreasing at a certain point in time. To rise. At this time, as described above, the vane opening / closing calculator 72-1 may lower the opening degree GV relatively quickly based on the speed ratio.

  Now, by this control, the chilled water outlet temperature TL starts to increase and reaches the target temperature Target, but the overshoot (overshoot) occurs somewhat due to the effect of lowering the vane opening GV in a state where the rotational speed SP has stopped decreasing. . At this time, the rotational speed SP starts to increase due to the load control, but thereafter, the rotational speed SP and the vane opening GV change on the same principle as when the load is rapidly increased, and finally become stable.

  Referring to FIG. 13, the case where the load LOAD increases greatly and rapidly (CASE 3) in a stable operation state after CASE 2 will be described. In this case as well, the vane opening GV increases as in CASE 1, but reaches the maximum opening in the final phase and stops rising there. In this case, the decrease in the rotational speed SP stops and the speed ratio does not reach the target value, but the turbo chiller is stably operated by the load control while the guide vane opening GV is fully opened. Controlling the speed ratio to the target value Target is a convenient means for controlling the guide vane opening degree GV and is not the purpose, so there is no problem in not reaching the target value.

  In the present invention, the turbo refrigerator is a concept including a turbo heat pump, that is, a turbo compression heat pump. In the heat pump, the hot water obtained by the condenser is the output. Further, the medium to be cooled is read as a heat source fluid.

  The turbo chiller of the present invention appropriately controls the rotational speed and the opening degree of the guide vane without switching the control method according to the operating state of the turbo chiller, and has high stability and followability and is easy to use. Used as a machine.

DESCRIPTION OF SYMBOLS 10 Evaporator 11 Chilled water outlet piping 13 Chilled water temperature detector 14 Cooling water temperature detector 15 Guide vane opening degree detector 20 Turbo compressor 21 Electric motor 23 Impeller 25 Guide vane 30 Condenser 40 Throttle mechanism 60 Electric motor starting board 70a Control means 70b Control means 71 Inverter control device (first control unit)
71-1 PID computing unit 72 guide vane control device (second control unit)
72-1 Vane Open / Close Calculator 72-2 Speed Ratio Calculator 72-3 Target Speed Calculator 72-4 Proportional Speed Calculator 73 Set Speed Calculator 73-1 PH / PL Calculator 73-2 Minimum Speed Calculator 73-3 Calculation table 73-4 Correction calculator 75 Commercial power supply 80 Inverter 101 Turbo refrigerator C1 Speed command signal (Inverter rotation speed adjustment signal)
C2 Guide vane opening adjustment signal S1 Chilled water outlet temperature signal S2 Cooling water inlet temperature signal S3 Guide vane opening signal S4 Rotational speed signal S5 Set rotational speed signal S6 Chilled water outlet temperature set value signal S7 Low pressure side pressure signal (evaporation pressure signal)
S8 High pressure side pressure signal (condensation pressure signal)
TL Cold water outlet temperature TH Cooling water inlet temperature GV Guide vane opening SP Rotational speed SETSP Set rotational speed SETTL Cold water outlet preset temperature PL Low pressure side (evaporation pressure)
PH High side pressure (condensation pressure)
P1 Low pressure side pressure detector (evaporation pressure detector)
P2 High pressure side pressure detector (Condensation pressure detector)

Claims (5)

An evaporator that evaporates the refrigerant liquid to generate refrigerant gas and cools the medium to be cooled with latent heat of vaporization;
An impeller that sucks and compresses the refrigerant gas; and a turbo compressor that is provided at an inlet of the impeller and has a guide vane having a variable opening degree;
A condenser that removes heat from the refrigerant gas compressed by the turbo compressor and condenses the refrigerant gas;
A variable speed drive for driving the turbo compressor;
A first control unit that controls a refrigerating capacity by adjusting a rotation speed of the variable speed drive according to a refrigeration load processed by the evaporator;
A second controller that adjusts the opening of the guide vane to control the rotational speed of the variable speed drive to a predetermined rotational speed ;
The operating conditions of the evaporator and the calculated from the operating condition of the condenser theoretical rotational speed, based on the theory rotational speed that is the calculated, defining said set rotation speed, Ru with the setting rotational speed calculator;
Turbo refrigerator. The turbo chiller according to claim 1, wherein the set rotational speed calculator adds the opening degree of the guide vane to the condition for calculating the theoretical rotational speed. The turbo refrigerator according to claim 1 or 2 , wherein a speed at which the opening degree of the guide vane is operated in the closing direction is faster than a speed at which the guide vane is operated in the opening direction. The turbo chiller according to any one of claims 1 to 3 , wherein the second control unit controls the opening degree of the guide vane by time proportional control. The turbo chiller according to claim 4 , wherein the second control unit changes a proportional constant of the time proportional control according to an opening degree of the guide vane.

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