CN100445561C

CN100445561C - Helical-lobe compressor for refrigerating plant

Info

Publication number: CN100445561C
Application number: CNB2005101185468A
Authority: CN
Inventors: 壶井升
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2005-01-21
Filing date: 2005-10-31
Publication date: 2008-12-24
Anticipated expiration: 2025-10-31
Also published as: JP2006200465A; JP4559241B2; CN1807889A; KR20060085162A; KR100724654B1

Abstract

The screw compressor 1 for a refrigeration device is driven by a motor 21 whose revolution is controlled via an inverter 22 which receives the control signal from a controller 23, and is set in a circulation-flow path I together with a condenser 11, expansion valve 12 and evaporator 13. The revolution of the motor 21 is maintained, increased or reduced correspondingly to a cooling thermal load, and when the revolution becomes lower than the lowest one which is defined as the lower limit of revolution at which there is no further lowering of power consumption, the motor 21 is stopped.

Description

Screw compressor for refrigerating device

Technical Field

The present invention relates to a screw compressor for a refrigeration apparatus driven by a motor controlled by an inverter.

Background

Conventionally, a screw compressor for a refrigerating apparatus is known, which controls the rotational speed of a motor as a driving unit by an inverter.

For example, japanese laid-open patent publication No. 2002-81391 discloses a screw compressor for a refrigerating apparatus, which increases or decreases the rotation speed of a motor as a driving unit so as to avoid overload according to increase or decrease of suction pressure in a one-to-one relationship with a cooling heat load. This screw compressor for a refrigerating apparatus has the effect of improving the durability of the motor and reducing the power consumption in a region where the cooling heat load is proportional to the power consumption.

In the case of the screw compressor for a refrigerating apparatus described in japanese laid-open patent publication No. 2002-81391, the relationship between the cooling heat load ratio, which is the ratio to the maximum value of the cooling heat load, and the power consumption ratio, which is the ratio to the maximum value of the power consumption (horizontal axis: cooling heat load ratio (%), and vertical axis: power consumption ratio (%)) is shown in fig. 7. That is, as the cooling heat load ratio decreases from the maximum value, the rotation speed of the motor decreases, and the power consumption ratio also decreases in proportion to the cooling heat load ratio. However, when the cooling heat load ratio is excessively decreased to about 20% and the rotational speed of the screw rotor in the screw compressor driven by the motor is gradually decreased, the increase in the amount of leakage between the tooth grooves of the screw rotor causes a decrease in the compression efficiency of the coolant gas, so that the power consumption ratio is no longer decreased in proportion to the cooling heat load ratio but is increased. That is, when the cooling heat load ratio is decreased to, for example, about 20% as indicated by point P in fig. 7, the decrease in the power consumption ratio becomes significantly slow as indicated by the broken line, and even if the cooling heat load ratio is further decreased, the power consumption ratio is not decreased much.

Disclosure of Invention

The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a screw compressor for a refrigerating apparatus, which can minimize wasteful power consumption of a motor as a driving unit and improve cooling efficiency, particularly when a cooling heat load ratio is small.

In order to solve the above problem, the present invention provides a screw compressor for a refrigeration apparatus, which is incorporated in a circulation flow path through which a refrigerant of the refrigeration apparatus circulates, the screw compressor including a condenser, an expansion valve, and an evaporator, the screw compressor comprising: a control unit; a converter which receives a control signal from the control unit; and a motor whose rotational speed is controlled via the inverter; wherein,

the control unit receives a suction pressure and a detected temperature, the suction pressure being a pressure at which the compressor is sucked and detected by a pressure sensor, generates and outputs a signal for controlling a rotation speed of the motor so as to be between a maximum rotation speed and a minimum rotation speed set in advance and so as to cancel a difference between the detected temperature and a control temperature, and generates and outputs a control signal for stopping the motor when the control rotation speed is less than the minimum rotation speed, the control temperature being a temperature based on a target temperature set in advance, and the minimum rotation speed being a rotation speed at which a decrease amount of power consumption of the motor does not reach a set amount in a region where a cooling heat load is small.

Further, the control unit includes: a temperature adjusting unit for comparing the detected temperature with the target temperature and outputting a deviation signal; and a controller for generating and outputting a signal for controlling the rotation speed of the motor.

The control temperature based on a preset target temperature is the same as the target temperature.

The control temperature based on a preset target temperature is between an upper limit target temperature higher than the target temperature and a lower limit target temperature lower than the target temperature,

the control signal is generated based on a temperature difference between the detected temperature and the upper limit target temperature and a temperature difference between the detected temperature and the lower limit target temperature.

The minimum rotation speed may be determined as a lower limit of the rotation speed at which a decrease in the motor power consumption is significantly reduced in a region where a cooling heat load is small.

The temperature based on the preset target temperature may be the same as the target temperature.

In addition, the temperature based on the preset target temperature may include an upper limit target temperature greater than the target temperature and a lower limit target temperature less than the target temperature,

the control signal is obtained based on a temperature difference between the detected temperature and the upper limit target temperature and a temperature difference between the detected temperature and the lower limit target temperature.

When the screw compressor for a refrigerating apparatus according to the present invention is configured as described above, wasteful power consumption of the motor as the driving unit can be minimized particularly when the cooling heat load is small, and the effect of improving the cooling efficiency can be obtained.

Drawings

Fig. 1 is a diagram showing an overall configuration of a refrigeration apparatus to which a screw compressor of the present invention is applied.

Fig. 2 is a diagram showing a relationship between a suction pressure of the screw compressor and a control range of a rotation speed of a motor thereof in the refrigeration apparatus shown in fig. 1.

Fig. 3 is a flowchart showing the control content for controlling the screw compressor in the refrigeration apparatus shown in fig. 1.

Fig. 4 is a diagram showing a relationship between a cooling heat duty ratio and power consumption in the refrigeration apparatus shown in fig. 1.

Fig. 5 is a flowchart showing another control content for controlling the screw compressor in the refrigeration apparatus shown in fig. 1.

Fig. 6 is a view showing the entire configuration of another refrigeration apparatus to which the screw compressor of the present invention is applied.

Fig. 7 is a diagram showing a relationship between a cooling heat duty ratio and power consumption in a conventional refrigeration apparatus.

Detailed Description

An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 shows a refrigeration apparatus a to which a screw compressor 1 for a refrigeration apparatus according to the present invention is applied. The refrigeration apparatus a has a refrigerant circulation passage I connected to the screw compressor 1 and provided with a condenser 11, an expansion valve 12, and an evaporator 13.

The screw compressor 1 includes a motor 21 and a control unit for rotating a pair of male and female screw rotors engaged with each other inside the compressor. The motor 21 is operated by electric power supplied through an inverter 22. The control unit includes a temperature controller 25 as a temperature adjusting means and a controller 23, and the inverter 22 is connected to the controller 23 and controls the rotation speed of the motor 21 based on a control signal from the controller 23.

In addition, the screw compressor 1 sucks the refrigerant gas from the evaporator 13, compresses the refrigerant gas, and sends the compressed refrigerant gas to the condenser 11. The coolant gas is condensed by the heat taken off by the condenser 11, becomes coolant liquid, reaches the expansion valve 12, and is reduced in pressure and temperature by the throttling expansion action during the passage through the expansion valve 12, becoming a gas-liquid mixed state. Further, the coolant flows to the evaporator 13, where it absorbs heat from the surroundings, evaporates, and returns to the compressor 11 again, and then repeats the cycle in the same manner as the above-described process.

The evaporator 13 is provided with a temperature sensor 24 for detecting the internal temperature thereof, and a temperature signal indicating the detected temperature t (c) detected by the sensor 24 is output to a temperature regulator 25. The temperature controller 25 compares a target temperature T (c) set to a temperature to be maintained in the evaporator 13 and a detected temperature T (c), and outputs a deviation signal based on the comparison result to the controller 23 as will be described later. Further, in the refrigerant circulation flow path I between the evaporator 13 and the screw compressor 1 for the refrigerating apparatus, a pressure sensor 26 for detecting the refrigerant pressure, that is, the suction pressure of the screw compressor 1 is provided, a pressure signal indicating the suction pressure ps (ata) detected thereby is output to the controller 23, and then a control signal is output from the controller 23 to the inverter 22 based on the deviation signal from the temperature regulator 25 and the pressure signal from the pressure sensor 26, as will be described later, to control the rotation speed of the motor 21. In the controller 23, data indicating the maximum rotation speed and the minimum rotation speed of the motor 21 corresponding to the suction pressure Ps is set in advance. The maximum rotation speed is a function f (Ps) of the suction pressure Ps, the minimum rotation speed is a function g (Ps) of the suction pressure Ps, and fig. 2 (horizontal axis: suction pressure, vertical axis: motor rotation speed) shows an example of the relationship between these and the suction pressure Ps. The hatched area in fig. 2 is a range in which the rotational speed of the motor 21 is controlled by the inverter 22. In fig. 2, the value (2) on the vertical axis corresponds to the point P in fig. 7, which corresponds to a point on the line indicating the minimum rotation speed g (Ps) at each suction pressure Ps, and is about 20% of the value (1). As will be described later, the point P is a starting point at which the decrease in the power consumption ratio of the motor 21 becomes significantly slower than the decrease in the cooling heat duty ratio of the evaporator 13, that is, a point at which the amount of decrease in the power consumption of the motor 21 does not reach the set amount. Therefore, in fig. 2, the minimum rotation speed g (ps) is 20% of the maximum rotation speed f (ps), but the present invention is not limited to this, and the minimum rotation speed g (ps) may be set to a constant value, for example. The controller 23 also sets the reduction range Δ R for the case where the rotation speed R of the motor 21 is reduced.

Next, a control method for the screw compressor 1 used in the refrigeration apparatus a configured as described above will be described with reference to fig. 3.

When the screw compressor 1 is started and the control flow in the controller 23 shown in FIG. 3 is started, first, in step 1(S1), it is determined whether or not the deviation signal from the temperature regulator 25 associated with the detected temperature T indicates that Th ≧ T ≧ T1, and if YES, the determination of step 1 is repeated; if NO, the process proceeds to step 2 (S2). Here, Th and T1 are the upper limit target temperature and the lower limit target temperature set so as to have a certain temperature range in the vicinity of the target temperature T, because when the detected temperature T approaches the target temperature T, a deviation signal for changing the rotation state of the motor 21 is frequently output from the thermostat 25 to the controller 23 in a short time, which should be avoided from the viewpoint of preventing the motor 21 from burning. The upper limit target temperature, the lower limit target temperature and the target temperature T have a relationship of Th > T1.

In step 2, it is determined whether or not the deviation signal from the temperature regulator 25 indicates Th < t, and if YES, the routine proceeds to step 3(S3), and if NO, the routine proceeds to step 4 (S4).

In step 3, since the capacity of the evaporator 13, that is, the cooling capacity of the refrigeration apparatus a is insufficient and it is necessary to increase the capacity, a control signal for setting the rotation speed R of the motor 21 to the maximum rotation speed f (ps) is output to the inverter 22, and the process returns to step 1.

In step 4, since the capacity of the evaporator 13 needs to be reduced, a control signal for reducing the rotation speed R of the motor 21 by the reduction amount Δ R is output to the inverter 22, and the process then proceeds to step 5 (S5).

In step 5, it is determined whether or not the rotation speed R of the motor 21 is R.ltoreq.g (Ps), and if YES, the routine proceeds to step 6(S6), and if NO, the routine returns to step 1.

In step 6, even if the rotation speed R is continuously decreased, the power consumption is not so reduced and the efficiency is not reduced, so that a signal for stopping the motor 21 is output to the inverter 22, and the process proceeds to step 7.

In step 7, it is determined whether or not Th < t, YES in the same manner as in step 2, and the routine proceeds to step 8(S8), and returns to step 6 to maintain the motor 21 in the stopped state in the case of NO.

In step 8, the capacity of the evaporator 13 is insufficient and it is necessary to increase it, and the motor 21 is restarted to return to step 1.

Thereafter, this control flow is repeatedly performed to operate the refrigeration apparatus a. Then, as shown in fig. 4 (horizontal axis: cooling heat load ratio (%), vertical axis: power consumption ratio (%)) corresponding to fig. 7, when the rotation speed of the motor 21 has to be decreased to a point lower than the starting point P at which the decrease in the power consumption ratio of the motor 21 becomes significantly slower with respect to the decrease in the cooling heat load ratio in the evaporator 13, the motor 21 is stopped to minimize the wasteful power consumption, thereby improving the cooling efficiency, and the rotation speed of the motor 21 can be prevented from frequently changing in a short time to avoid burning.

Next, another control method applied to the screw compressor 1 will be described with reference to fig. 5.

When the screw compressor 1 is started and the control flow in the controller 23 shown in fig. 5 is started, first, in step 1(S1), it is determined whether or not the deviation signal from the thermostat 25 indicates the target temperature T, YES, with respect to the detected temperature T, the determination in step 1 is repeated, and in NO, step 2 is performed (S2).

In step 2, it is determined whether or not the deviation signal from the temperature regulator 25 indicates T < T, YES, and the process proceeds to step 3(S3), and the process proceeds to step 5(S5) when NO.

In step 3, since the capacity of the evaporator 13, that is, the refrigerating capacity of the refrigerating apparatus a is insufficient and needs to be increased, a control signal for changing the rotation speed R of the motor 21 to the maximum rotation speed f (ps) is output to the inverter 22, and the process proceeds to step 4 (S4).

In step 4, the timer returns to step 1 after a standby time set in advance for avoiding burnout of the motor 21 due to frequent repeated changes in the rotation speed of the motor 21 has elapsed.

In step 5, the capacity of the evaporator 13 needs to be reduced, and a control signal for reducing the rotation speed R of the motor 21 by the reduction amount Δ R is output to the inverter 22, and then the process proceeds to step 6 (S6).

In step 6, after the standby time elapses by the timer, the process proceeds to step 7 (S7).

In step 7, it is determined whether or not the rotation speed R of the motor 21 is R.ltoreq.g (Ps), YES, the routine proceeds to step 8(S8), and if NO, the routine returns to step 1.

In step 8, even if the rotation speed R is further reduced, the power consumption is not so reduced and the efficiency is low, so that a signal for stopping the motor 21 is output to the inverter 22, and the process proceeds to step 9 (S9). In step 9, after the standby time elapses by the timer, the process proceeds to step 10 (S10).

In step 10, it is determined whether or not T < T, YES in the same manner as in step 2, the routine proceeds to step 11(S11), and in NO, the routine returns to step 8(S8) to maintain the stopped state of the motor 21.

In step 11, since the capacity of the evaporator 13 is insufficient and needs to be increased, the motor 21 is restarted and the process proceeds to step 12 (S12).

In step 12, the process returns to step 1 after the standby time elapses by the timer.

Thereafter, the control flow is repeated to operate the refrigeration apparatus a. Further, as in the case of the above-described control flow, when the rotation speed of the motor 21 has to be decreased to a point lower than the starting point P at which the decrease in the power consumption ratio of the motor 21 becomes significantly slower than the decrease in the cooling heat load ratio in the evaporator 13, the motor 21 is stopped, wasteful power consumption is minimized, cooling efficiency is improved, and frequent repeated driving stop of the motor 21 is avoided.

In the control flow shown in fig. 5, the process returns from step 12 to step 1, but the process may return from step 12 to step 2 as indicated by a broken line in fig. 5. In this case, the rotation speed of the motor 21 is not maintained as it is when step 1 is performed, but is constantly changed and maintained at an appropriate value.

In place of steps 4, 6, 9, and 12, which are kept on standby by a timer, the same steps may be provided before step 1 as shown by the two-dot chain line in fig. 5, and the steps may be returned from

steps

1, 3, 7, and 12. In this case, since there is a limited need to continuously change the rotation speed in a short time, there is no problem in reality.

Further, the judgment in step 1 in FIG. 5 may be made as to whether Th ≧ T ≧ T1, and the judgments in step 2 and step 10 may be made as to whether Th < T.

In the above, as for the evaporator 13, the case where the temperature sensor 24 that detects the internal temperature thereof is provided is shown. This state is suitable when the evaporator 13 is a type that houses a cooling target and cools and freezes the cooling target. However, the temperature sensor 24 is not limited to the form provided inside the evaporator 13.

For example, fig. 6 shows a refrigeration apparatus B to which the screw compressor 1 for a refrigeration apparatus according to the present invention is applied. The refrigeration apparatus B is common to the refrigeration apparatus a described above in many configurations. However, in the refrigeration apparatus B, a cooling target flow path 27 through which the cooling target flows is provided so that the refrigerant passing through the inside of the evaporator 13 and a fluid (water or the like) as the cooling target can exchange heat. The temperature sensor 24 is provided in the vicinity of the outlet of the cooled flow path 27 from the evaporator 13. That is, the temperature sensor 24 is not provided inside the evaporator 13, but is provided in the vicinity thereof. The temperature t (c) detected by the temperature sensor 24 is not the temperature of the atmosphere inside the evaporator 13, but is substantially the temperature itself of the object to be cooled. In this configuration, no extra component that impedes heat exchange between the coolant and the object to be cooled is provided in the evaporator 13, which contributes to the efficiency of heat exchange. It is also more advantageous for maintenance of the temperature sensor 24. This is therefore preferred, especially in the case where the object to be cooled is a liquid. Of course, if the heat exchange between the coolant and the object to be cooled can be sufficiently performed, the temperature sensor 24 may be provided inside the evaporator 13.

In the above embodiment, the deviation signal between the detected temperature of the temperature sensor and the target temperature is output to the controller, but the detected temperature of the temperature sensor may be output to the controller, and the deviation signal may be obtained from the target temperature in the controller.

In the above-described embodiment, when the temperature detected by the temperature sensor is higher than the target temperature (or the upper limit target temperature), the control signal for setting the rotation speed of the motor to the maximum rotation speed is directly output, but the rotation speed of the motor may be increased stepwise toward the maximum rotation speed.

In the above embodiment, the reduction width Δ R in the case of reducing the motor rotation speed is a fixed value, but Δ R may be determined based on the value of the motor rotation speed R at that time.

Claims

1. A screw compressor for a refrigerating apparatus is provided,

the refrigeration system is incorporated in a circulation flow path through which a refrigerant circulates in the refrigeration system including a condenser, an expansion valve, and an evaporator, and is characterized by comprising:

a control unit;

a converter which receives a control signal from the control unit; and

a motor whose rotational speed is controlled via the inverter; wherein,

the control unit receives the suction pressure and the detected temperature, generates and outputs a signal for controlling the rotation speed of the motor so as to be between a preset maximum rotation speed and a preset minimum rotation speed and so as to eliminate a difference between the detected temperature and the control temperature, and generates and outputs a control signal for stopping the motor when the control rotation speed is less than the minimum rotation speed,

the suction pressure is the pressure of the compressor suction detected by the pressure sensor,

the detected temperature is a temperature detected by a temperature sensor provided at or near the evaporator,

the control temperature is a temperature based on a preset target temperature,

the minimum rotational speed is a rotational speed at which the amount of decrease in the power consumption of the motor does not reach a set amount in a region where the cooling heat load is small.

2. The screw compressor for a refrigerating apparatus according to claim 1, wherein the control unit includes:

a temperature adjusting unit for comparing the detected temperature with the target temperature and outputting a deviation signal; and

and a controller for generating and outputting a signal for controlling the rotation speed of the motor.

3. The screw compressor for a refrigerating apparatus according to claim 1,

4. The screw compressor for a refrigerating apparatus according to claim 1,