Operation control method for inverter-driven compressor and inverter-driven compressor

Abstract

To provide an operation control method for an inverter drive compressor that can reduce a power consumption when only a small amount of compressed gas is consumed.SOLUTION: An operation control method for an inverter drive compressor comprises: performing operation switching control to switch operation from a loaded operation to an unloaded operation (T3, ...) when supply pressure P in a supply flow passage 52 reaches predetermined unloaded operation start pressure and also switch operation to the loaded operation (T4, ...) when the supply pressure P drops to predetermined target pressure or lower; setting, as stationary control, variable frequency control to vary the output frequency of an inverter between a predetermined lower-limit frequency and an upper-limit frequency so that the supply pressure matches the target pressure; transitioning to constant-frequency control to maintain the output frequency of the inverter at a predetermined pressure increasing frequency which is higher than the lower-limit frequency when the supply pressure P reaches the unloaded operation start pressure; and then transitioning to the variable frequency control when the supply pressure P is at predetermined automatic recovery pressure or lower.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an operation control method for an inverter-driven compressor and an inverter-driven compressor that executes the operation control method, and more specifically to an operation control method that enables a reduction in power (power consumption) in an inverter-driven compressor in which the rotational speed of a motor that is the drive source of the compressor body is controlled by an inverter, and an inverter-driven compressor that executes the operation control method. [Background technology]

[0002] An inverter-driven compressor has an inverter installed between the motor, which is the drive source for the compressor body, and the power supply.This inverter changes the frequency of the AC current input from the power supply to the motor between an upper limit frequency fmax and a lower limit frequency fmin, so that the rotational speed of the motor, and therefore the rotational speed of the compressor body driven by the motor, can be changed between an upper limit rotational speed corresponding to the upper limit frequency fmax and a lower limit rotational speed corresponding to the lower limit frequency fmin.

[0003] In such an inverter-driven compressor, the pressure P of the compressed gas supplied to the consumption side (hereinafter referred to as "supply pressure") is detected by a pressure detection means such as a pressure sensor, and when the supply pressure P exceeds the target pressure Ptarget, the frequency of the AC current output to the motor is reduced, and when the supply pressure P falls below the target pressure Ptarget, the frequency of the AC current output to the motor is increased to change the rotational speed of the compressor body.By performing rotational speed control, it is possible to supply compressed gas at the target pressure Ptarget to the consumption side regardless of changes in the amount of compressed gas consumed.

[0004] In addition to controlling the rotational speed in response to changes in the supply pressure P as described above, inverter-driven compressors have also been proposed that are configured to reduce power consumption by stopping the intake of air into the compressor body and / or transitioning to "unload operation" in which the compressor body is operated with the discharge side open to the atmosphere when the supply pressure P rises above a predetermined unload operation start pressure Punload due to, for example, the cessation of consumption of compressed gas on the consumption side, thereby reducing power consumption.

[0005] However, when such an inverter-driven compressor is installed as production equipment in a factory, for example, and is used as a common source of compressed gas for multiple pneumatic equipment located in various locations within the factory, the piping connecting the inverter-driven compressor and the pneumatic equipment becomes long and complex, and there are many connection points in the piping, making it inevitable that piping leaks will occur due to poor connections in various parts and deterioration of gas seals.

[0006] When such a piping leak occurs, a relatively small amount of compressed gas due to the leak continues to be consumed, so even if all pneumatic equipment connected to the consumption side is stopped and the consumption of compressed gas by the pneumatic equipment is stopped, the supply pressure P does not rise to the no-load operation start pressure Punload, or it takes a long time for the supply pressure P to rise to the no-load operation start pressure Punload.

[0007] Therefore, when only a small amount of compressed gas is consumed due to such piping leaks, etc., the inverter-driven compressor will continue to operate at a low speed at a frequency near the lower limit frequency fmin through rotational speed control, generating a relatively small amount of compressed gas (hereinafter, such low-speed load operation will be referred to as "low-load operation") for a long period of time.

[0008] Although such low-load operation consumes less power per unit time than full-load or high-load operation (hereinafter collectively referred to as "high-load operation"), which is performed at or near the upper limit of the rotational speed, it still consumes more power than no-load operation.

[0009] Furthermore, although the power consumption per unit time is lower during low load operation compared to high load operation, when comparing the power consumption required to generate compressed gas per unit gas volume, efficiency is lower than during high load operation.

[0010] Therefore, if low-load operation is performed for a long period of time without transitioning to no-load operation, the efficiency of compressed gas generation relative to power consumption decreases.

[0011] Therefore, in order to eliminate the decrease in compressed gas generation efficiency that occurs when a relatively small amount of compressed gas continues to be consumed due to such piping leaks, etc., resulting in the failure to transition to no-load operation or the need for a long time to transition to no-load operation, the applicant of the present invention has already proposed an operation control method for an inverter-driven compressor, which is listed below as Patent Document 1.

[0012] In the operation control method of Patent Document 1, as shown in the time chart of Figure 5, when the load rate of the compressed gas [load rate (%) = (air consumption rate / rated discharge air rate) x 100] starts to decrease to less than 100% (T1), and the operation state continues for a certain period of time (t; T2-T5) at or below the reference frequency fref (22 Hz), which is a frequency higher than the lower limit frequency fmin (20 Hz) by a predetermined value, or when the supply pressure P continues for a certain period of time (t'; T4-T5) at or above the reference pressure Pref (0.70 MPa), which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), the aforementioned rotational speed control that changes the inverter output frequency in accordance with changes in the supply pressure P is stopped (T5).

[0013] Then, until the supply pressure P rises to the unload operation start pressure Punload, forced transition control is performed to temporarily (T5-T6) raise the inverter output frequency to a pressure rise frequency frise (40 Hz) which is a predetermined higher frequency than the frequency when the low load operation state is determined (fmin: 20 Hz in the illustrated example) and which is a frequency that can raise the supply pressure to the unload operation start pressure.

[0014] This forced transition control (T5-T6) increases the supply pressure P to the no-load operation start pressure Punload (0.73 MPa), and forcibly transitions the operating state of the compressor body to no-load operation (T6-T7) with the discharge side flow path open to the atmosphere, thereby eliminating a state in which low-load operation, which has poor efficiency in generating compressed gas relative to the power consumption, continues for a long period of time, thereby reducing power consumption (see Figure 2 of Patent Document 1). [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-34535 Summary of the Invention [Problem to be solved by the invention]

[0016] In the operation control method described in Patent Document 1 above, when a predetermined low-load operation continues for a certain period of time (t or t'), the system is forced to switch to no-load operation, thereby preventing low-load operation from continuing for a long period of time, even if a small amount of compressed gas is constantly being consumed due to a pipe leak, etc., thereby reducing power consumption.

[0017] However, in the control method of Patent Document 1, low-load operation is still performed frequently during times when only a relatively small amount of compressed gas is consumed, so there is still room for further reduction in power consumption.

[0018] To explain this point in more detail, in the operation control method described in Patent Document 1, after the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa) and transitions to no-load operation, when the supply pressure P drops to the target pressure Ptarget (0.69 MPa), the no-load operation is terminated and the operation returns to the aforementioned rotational speed control, which changes the inverter output frequency according to the supply pressure P (Claim 1 of Patent Document 1).

[0019] Therefore, even if the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa) (T6), even if all pneumatic equipment connected to the consumption side remains stopped because a small amount of compressed gas is always being consumed due to a pipe leak, etc., the supply pressure P will decrease over time to the target pressure Ptarget (0.69 MPa) (T7), thereby ending no-load operation (T7) and returning to rotational speed control (T7-T5').

[0020] When returning to this rotational speed control (T7), the supply pressure P is close to the target pressure Ptarget (0.69 MPa). Therefore, when the no-load operation ends and the compressor main body resumes generating compressed gas, the supply pressure P immediately rises above the target pressure Ptarget, and therefore the compressor main body will perform the low-load operation described above during rotational speed control (T7-T5').

[0021] Then, when this low-load operation state continues for a predetermined time (t or t'), the aforementioned forced transition control is performed again (T5'-T6'), which causes the system to transition again to no-load operation (T6'-T7').This operation is repeated during the time (T3-T8) when only a relatively small amount of compressed gas is consumed on the consumption side due to leakage from the piping.

[0022] In this way, in the operation control method described in Patent Document 1, when the consumption of compressed gas on the consumption side is only a relatively small amount due to a pipe leak, rotational speed control (T7-T5') always intervenes between the no-load operation (T6-T7) and the no-load operation (T6'-T7') that are performed in between, and this rotational speed control (T7-T5') operates the compressor body at low load for a predetermined period of time.

[0023] Therefore, if the time of low-load operation that takes place between such no-load operation (T6-T7) and no-load operation (T6'-T7') can be shortened, or if low-load operation can be eliminated, the frequency of transitions to no-load operation can be increased, thereby lengthening the total no-load operation time and thereby further reducing power consumption.

[0024] In the above explanation, the problem that occurs when a relatively small amount of compressed gas is continuously consumed due to a pipe leak or the like has been given as an example.

[0025] However, such problems can occur not only when there is a piping leak, but also when a relatively small amount of compressed gas is continuously consumed, such as when only a small portion of multiple pneumatic equipment connected to the consumption side is used for a long period of time, or when pneumatic equipment that constantly consumes a relatively small amount of compressed gas is connected to the consumption side.

[0026] Therefore, the present invention aims to provide an operation control method for an inverter-driven compressor that can further reduce power consumption during times when only a relatively small amount of compressed gas is consumed, and an inverter-driven compressor that executes this operation control method. [Means for solving the problem]

[0027] The means for solving the problems are described below together with the reference numerals used in the description of the embodiment of the invention. These reference numerals are intended to clarify the correspondence between the description of the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

[0028] In order to achieve the above object, the operation control method of the inverter-driven compressor 1 of the present invention includes the following steps: An inverter-driven compressor 1 is provided with a compressor body 2, a motor 3 that drives the compressor body 2, an inverter 4 that changes the AC current input to the motor 3, and an operation switching device 20 that switches the operating state of the compressor body 2 between a load operation that generates compressed gas and a no-load operation that stops the generation of compressed gas, and is capable of frequency control that controls the output frequency of the inverter 4 and operation switching control that switches between the load operation and no-load operation, A check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52, As the pressures to be used as the control standards, a predetermined target pressure Ptarget (for example, 0.69 MPa), a no-load operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa) are set, The load operation is maintained as a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the no-load operation start pressure Punload (0.73 MPa), the operation is switched to the no-load operation (T3-T4, T3'-T4'), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation. The frequency control The inverter 4 includes a variable frequency control that changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and a constant frequency control that maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), The variable frequency control is a steady-state control, and when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is switched to the constant frequency control, and when the supply pressure P falls to or below the automatic return pressure Preturn (0.50 MPa), the variable frequency control is switched to the constant frequency control (see claim 1, Figures 1 and 2).

[0029] Another method for controlling the operation of an inverter-driven compressor according to the present invention includes the steps of: An inverter-driven compressor 1 is provided with a compressor body 2, a motor 3 that drives the compressor body 2, an inverter 4 that changes the AC current input to the motor 3, and an operation switching device 20 that switches the operating state of the compressor body 2 between a load operation that generates compressed gas and a no-load operation that stops the generation of compressed gas, and is capable of frequency control that controls the output frequency of the inverter 4 and operation switching control that switches between the load operation and no-load operation, A check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52, As the pressures to be used as the control standards, a predetermined target pressure Ptarget (for example, 0.69 MPa), a no-load operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa) are set, The load operation is maintained in a steady state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the unload operation start pressure Punload (0.73 MPa), the operation is switched to the unload operation (T6-T7, T6'-T7' in FIG. 3; T7-T8, T7'-T8' in FIG. 4), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation. The frequency control The control system includes a variable frequency control that changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and a constant frequency control that maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz) that is a frequency that is predetermined higher than the lower limit frequency fmin (20 Hz) and can raise the supply pressure P to the no-load operation start pressure Punload (0.73 MPa) or higher, The variable frequency control is a steady-state control, and after it is determined that the compressor body 2 is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure P becomes equal to or lower than the automatic return pressure Preturn (0.50 MPa), the variable frequency control is switched to the constant frequency control (see claim 2, Figures 1, 3 and 4).

[0030] In a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, when the inverter 4 continuously outputs a frequency equal to or lower than the reference frequency fref (for example, 22 Hz), which is a predetermined higher frequency than the lower limit frequency fmin (20 Hz), for a predetermined time t, and / or When the supply pressure P continues for a predetermined time t' and becomes equal to or greater than the reference pressure Pref (for example, 0.70 MPa), which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), The compressor body 2 may be configured to determine that it is in the predetermined low load operating state (see claim 3, FIGS. 1, 3 and 4).

[0031] Similarly, in a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, after the variable frequency control is stopped (T5), the output frequency of the inverter 4 is increased stepwise at predetermined time intervals t'', and the output frequency when the supply pressure P reaches the no-load operation start pressure Punload (0.73 MPa) (T7) is set to the pressure rise frequency frise (30 Hz) to perform the constant frequency control (see claim 4, Figures 1 and 4).

[0032] Furthermore, in any of the above operation control methods, the air flow path 50 on the primary side of the check valve 54 is made into a discharge flow path 51, and the no-load operation is performed as follows: Either blocking the intake port 2a of the compressor body 2, opening the discharge flow path 51 to the atmosphere, or connecting the discharge flow path 51 to the intake port 2a of the compressor body 2, or This may also be achieved by a combination of blocking the intake port 2a of the compressor main body 2 and opening the discharge flow path 51 to the atmosphere, or connecting the discharge flow path 51 to the intake port 2a of the compressor main body 2 (see claim 5, Figure 1).

[0033] Furthermore, the inverter-driven compressor 1 of the present invention is An inverter-driven compressor 1 includes a compressor body 2, a motor 3 that drives the compressor body 2, an inverter 4 that changes the AC current input to the motor 3, an operation switching device 20 that switches the operating state of the compressor body 2 between a load operation that generates compressed gas and a no-load operation that stops the generation of compressed gas, and a frequency control device 30 that controls the output frequency of the inverter 4. A check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52, A memory area 42c is provided for storing a predetermined target pressure Ptarget (for example, 0.69 MPa) that is preset as a pressure to be used as a control reference, a no-load operation start pressure Punload (for example, 0.73 MPa) that is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) that is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa), The operation switching device 20, The load operation is maintained as a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the no-load operation start pressure Punload (0.73 MPa), the operation is switched to the no-load operation (T3-T4, T3'-T4'), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation. The frequency control device 30, It is possible to perform variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and constant frequency control, which maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), The variable frequency control is a steady-state control, and when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is switched to the constant frequency control, and when the supply pressure P falls to or below the automatic return pressure Preturn (0.50 MPa), the variable frequency control is switched to the constant frequency control (see claim 6, Figures 1 and 2).

[0034] Another inverter-driven compressor 1 of the present invention is An inverter-driven compressor 1 includes a compressor body 2, a motor 3 that drives the compressor body 2, an inverter 4 that changes the AC current input to the motor 3, an operation switching device 20 that switches the operating state of the compressor body 2 between a load operation that generates compressed gas and a no-load operation that stops the generation of compressed gas, and a frequency control device 30 that controls the output frequency of the inverter 4. A check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52, A memory area 42c is provided for storing a predetermined target pressure Ptarget (for example, 0.69 MPa) that is preset as a pressure to be used as a control reference, a no-load operation start pressure Punload (for example, 0.73 MPa) that is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) that is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa), The operation switching device 20, The load operation is maintained in a steady state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the unload operation start pressure Punload (0.73 MPa), the operation is switched to the unload operation (T6-T7, T6'-T7' in FIG. 3; T7-T8, T7'-T8' in FIG. 4), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation. The frequency control device 30, It is possible to perform variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and constant frequency control, which maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 30 Hz or 40 Hz) that is a frequency that is predetermined higher than the lower limit frequency fmin (20 Hz) and can raise the supply pressure P to the no-load operation start pressure Punload (0.73 MPa) or higher, The variable frequency control is a steady-state control, and after it is determined that the compressor body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure P becomes equal to or lower than the automatic return pressure Preturn (0.50 MPa), the control is switched to the variable frequency control (see claim 7, Figures 1, 3 and 4).

[0035] In a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, the storage area 42c further stores a judgment reference frequency fref (for example, 22 Hz) which is a predetermined higher frequency than the lower limit frequency fmin (20 Hz), and / or a judgment reference pressure Pref (for example, 0.70 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), The frequency control device 30, The compressor main body 2 may be configured to be determined to be in the predetermined low-load operating state when the inverter outputs a frequency below the judgment reference frequency fref (22 Hz) for a predetermined time t, and / or when the supply pressure P becomes above the judgment reference pressure Pref (0.70 MPa) for a predetermined time t' (see claim 8, Figures 1, 3 and 4).

[0036] Similarly, in a configuration in which the constant frequency control is performed when it is determined that the compressor body 2 is in a predetermined low load operating state, The frequency control device 30, After the variable frequency control is stopped (T5), the output frequency of the inverter 4 may be increased stepwise at predetermined time intervals t'', and the output frequency when the supply pressure P reaches the no-load operation start pressure Punload (0.73 MPa) (T7) may be set to the pressure rise frequency frise (30 Hz) to perform the constant frequency control (see claim 9, Figures 1 and 4).

[0037] In any of the above configurations of the inverter-driven compressor 1, The air flow path 50 on the primary side of the check valve 54 is formed as a discharge flow path 51, The operation switching device 20, The compressor includes an intake control valve 21 that opens and closes the intake port 2a of the compressor body 2, an air release valve (solenoid valve 23 or 23') that opens the discharge flow path 51 to the atmosphere, or a return flow path opening / closing valve (solenoid valve 23'') that opens and closes the return flow path 25 that connects the discharge flow path 51 and the intake port 2a of the compressor body 2, or a combination of the intake control valve 21 and either the air release valve (solenoid valve 23 or 23') or the return flow path opening / closing valve (solenoid valve 23''), The no-load operation may be achieved by either closing the intake control valve 21, opening the air release valve (solenoid valve 23 or 23'), or opening the return flow path opening / closing valve (solenoid valve 23''), or by a combination of closing the intake control valve 21 and opening either the air release valve (solenoid valve 23 or 23') or the return flow path opening / closing valve (solenoid valve 23'') (see claim 10 and Figure 1). [Effects of the Invention]

[0038] In the configuration of the present invention described above, once the system switches to constant frequency control, the output frequency of the inverter 4 is maintained at the pressure rise frequency frise (30 Hz or 40 Hz) until the supply pressure drops below the predetermined automatic return pressure Preturn (0.50 MPa), and during this period, only switching between load operation and no-load operation is performed by the operation switching device 20.

[0039] As a result, in the control method of the present invention, low-load operation does not occur between no-load operations during the time when only a relatively small amount of compressed gas is consumed on the consumption side due to pipe leaks, etc., and therefore, compared to the control method of Patent Document 1, in which low-load operation is always performed for a predetermined period of time between no-load operations, the frequency of transitions to no-load operation, and therefore the total no-load operation time, can be increased, making it possible to further reduce the power consumption of the inverter-driven compressor 1.

[0040] Furthermore, in the operation control method of the present invention, when switching from unloaded operation to loaded operation, the rotational speed of the compressor main body 2 is already increased to a rotational speed corresponding to the pressure rise frequency frise (for example, 30 Hz or 40 Hz). Therefore, compared to the case where the output frequency of the inverter 4 is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (for example, 40 Hz) to increase the rotational speed of the compressor main body 2 each time forced transition control is performed as in the control method of Patent Document 1, the time (see Δ' in Figures 2 to 4) for increasing the supply pressure P to the unloaded operation start pressure Punload (0.73 MPa) can be made shorter compared to the case of Patent Document 1 (see Δ in Figure 5).

[0041] As a result, in this respect too, the control method of the present invention can increase the frequency of transitioning to no-load operation during times when only a relatively small amount of compressed gas is consumed due to pipe leaks, etc., and therefore the total no-load operation time, making it possible to further reduce the power consumption of inverter-driven compressors.

[0042] When the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is stopped and the output frequency of the inverter 4 is raised to a pressure rise frequency frise (30 Hz or 40 Hz) that is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), and the constant frequency control is switched to maintain the pressure rise frequency frise (30 Hz or 40 Hz). In this configuration, the transition conditions for switching from variable frequency control to constant frequency control can be easily determined without counting using a timer, etc.

[0043] On the other hand, in a configuration in which variable frequency control is stopped and a transition to constant frequency control is made when it is determined that the compressor main body 2 is in a predetermined low-load operating state, it is possible to transition to constant frequency control before the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa).Therefore, by setting the pressure rise frequency frise applied during constant frequency control to a frequency that can raise the supply pressure P above the no-load operation start pressure Punload (0.73 MPa), it is possible to force a transition to no-load operation early by transitioning to constant frequency control.

[0044] Furthermore, in a configuration in which the compressor body 2 transitions to constant frequency control when it is determined that it is in a predetermined low-load operating state, a configuration can be adopted in which, after variable frequency control ends, the output frequency of the inverter 4 is increased stepwise at predetermined time intervals, and the output frequency when the supply pressure P reaches the no-load operation start pressure is set to the pressure rise frequency frise.This makes it possible to keep the pressure rise frequency frise during constant frequency control as low as possible (for example, 30 Hz), thereby achieving even further reductions in power consumption. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a schematic explanatory diagram of an inverter-driven compressor according to the present invention; [Figure 2] 3 is a time chart showing the correspondence relationship among the supply pressure, the load factor, the operating state (load operation / unload operation), and the inverter output frequency in the control method (embodiment 1) of the present invention. [Figure 3] 6 is a time chart showing the correspondence between the supply pressure, the load factor, the operating state (load operation / unload operation), and the output frequency of the inverter in another control method (embodiment 2) of the present invention. [Figure 4] 10 is a time chart showing the correspondence between the supply pressure, the load factor, the operating state (load operation / unload operation), and the output frequency of the inverter in yet another control method (embodiment 3) of the present invention. [Figure 5]1 is a time chart showing the correspondence between supply pressure, load factor, blocking / opening of the discharge flow path, and inverter output frequency in a conventional control method (Patent Document 1). DETAILED DESCRIPTION OF THE INVENTION

[0046] The inverter-driven compressor of the present invention will be described below with reference to the accompanying drawings.

[0047] [Overall configuration of inverter-driven compressor] In FIG. 1, reference numeral 1 denotes an inverter-driven compressor for carrying out the operation control method of the present invention.

[0048] This inverter-driven compressor 1 comprises a compressor main body 2, a motor 3 which is the drive source of this compressor main body 2, an inverter 4 which converts the frequency of the AC current from the power source and outputs it to the motor 3, an operation switching device 20 which switches the operating state of the compressor main body 2 between loaded operation and unloaded operation, and a frequency control device 30 which controls the rotation speed of the motor 3 by changing the frequency of the current output by the inverter 4, and is configured so that by driving the compressor main body 2 with the motor 3, the compressor main body 2 draws in the compressed gas, in the illustrated example air, from the intake port 2a and discharges the compressed gas from the discharge port 2b.

[0049] In this embodiment, an oil-cooled screw compressor is used as the compressor main body 2, which injects lubricating oil into the cylinder and compresses and discharges the compressed gas.A receiver tank 51b is provided into which the compressed gas discharged from the compressor main body 2 together with the lubricating oil is introduced, and the compressed gas and lubricating oil are separated within this receiver tank 51b so that the separated compressed gas can be supplied to pneumatic equipment (not shown) provided on the consumption side, and the lubricating oil recovered in the receiver tank 51b can be supplied to the oil supply port 2c of the compressor main body 2 via an oil supply circuit.

[0050] A check valve 54 is provided in the compressed gas flow path (air flow path 50) that runs from the discharge port 2b of the compressor main body 2 to the pneumatic equipment (not shown) provided on the consumption side to prevent backflow of compressed air from the consumption side toward the compressor main body 2.

[0051] In the description of the present invention, the air flow path 50 from the discharge port 2b of the compressor main body 2 to the aforementioned check valve 54 (the air flow path 50 on the primary side of the check valve 54) will be described as the "discharge flow path (51)", and the air flow path 50 from the check valve 54 to the consumption side (the air flow path 50 on the secondary side of the check valve 54) will be described as the "supply flow path (52)".

[0052] Therefore, in the embodiment shown in Figure 1, the receiver tank 51b provided on the primary side of the check valve 54 constitutes part of the discharge flow path 51 defined above, and the aforementioned discharge flow path 51 is formed by this receiver tank 51b and the pipes 51a and 51c connected to the receiver tank 51b.

[0053] [Operation switching device] As described above, the inverter-driven compressor 1 of the present invention is provided with an operation switching device 20 that switches the operating state of the compressor main body 2 between load operation in which compressed gas is generated and no-load operation in which the generation of compressed gas is stopped.

[0054] In the illustrated embodiment, this operation switching device 20 is composed of an intake control valve 21 that opens and closes the intake port 2a of the compressor main body 2, a control flow path 22 one end of which is connected to the discharge flow path 51 (receiver tank 51b), a solenoid valve 23 that opens and closes the control flow path 22, an air discharge flow path 24 that branches off from the control flow path 22 on the secondary side of the solenoid valve 23, a pressure detection means 41 that detects the pressure (supply pressure P) in the supply flow path 52, and an operation switching section 42a of a control device 42 that controls the opening and closing of the solenoid valve 23 based on the detection signal of the pressure detection means 41.

[0055] The other end of the control flow path 22 is connected to the closed valve pressure chamber (not shown) of the intake control valve 21, and the release flow path 24 is connected to the primary side of the intake control valve 21 via an orifice, so that when the solenoid valve 23 opens, the compressed gas in the receiver tank 51b is released into the atmosphere via the release flow path 24 through an air filter provided on the primary side of the intake control valve 21, and operating pressure is introduced into the closed valve pressure chamber of the intake control valve 21, causing the intake control valve 21 to close.

[0056] Therefore, in the configuration of the inverter-driven compressor 1 shown in FIG. 1, the aforementioned solenoid valve 23 functions as an "air release valve" that opens the discharge flow path 51 to the atmosphere.

[0057] Due to the configuration of the operation switching device 20, when the operation switching section 42a of the control device 42 opens the solenoid valve 23, the intake control valve 21 closes, stopping the intake of air into the compressor main body 2, and the compressor main body 2 enters unloaded operation in which it is driven with the discharge flow path 51 (receiver tank 51b) open to the atmosphere and the back pressure reduced, and when the operation switching section 42a of the control device 42 closes the solenoid valve 23, the intake control valve 21 opens, starting the intake of air into the compressor main body 2, and the compressor main body 2 is driven with the discharge flow path 51 (receiver tank 51b) no longer open to the atmosphere, switching to a loaded operation state.

[0058] In the embodiment shown in Figure 1, it has been explained that during no-load operation, both the intake control valve 21 is closed to stop the intake and the discharge flow path 51 (receiver tank 51b) is opened to the atmosphere to reduce the back pressure. However, instead of this configuration, for example, the air discharge flow path 24 in Figure 1 may be omitted, and the load operation and no-load operation may be switched over only by opening and closing the intake control valve 21.

[0059] Furthermore, as shown as variant example 1 in Figure 1, the discharge flow path 51 (receiver tank 51b) may be connected to the intake port 2a of the compressor body 2 via the air release flow path 24' without providing the intake control valve 21, and the discharge flow path 51 may be opened to the atmosphere by opening the air release valve (solenoid valve 23') provided in the air release flow path 24', thereby transitioning to no-load operation.

[0060] Furthermore, as shown as variant example 2 in Figure 1, a return flow path 25 is provided on the secondary side of the solenoid valve 23'', branching off the control flow path 22, and this return flow path 25 is connected to the secondary side of the intake control valve 21, so that during no-load operation with the solenoid valve 23'' open, the intake control valve 21 is closed and the compressed gas in the discharge flow path 51 (receiver tank 51b) is returned to the intake port 2a of the compressor main body 2, thereby achieving no-load operation; in the configuration of variant example 2, the solenoid valve 23'' also functions as a ``return flow path opening / closing valve''.

[0061] The aforementioned control device 42, which is a component of the operation switching device 20 described above, stores in memory area 42c a target pressure Ptarget (0.69 MPa as an example) and an unload operation start pressure Punload (0.73 MPa as an example), which is set as a predetermined pressure higher than this target pressure Ptarget (0.69 MPa), as the pressure to be used as the control standard during operation switching control.

[0062] Then, based on the detection signal received from the pressure detection means 41 which detects the supply pressure P, which is the pressure inside the supply flow path 52, the operation switching unit 42a of the control device 42 executes operation switching control in which, when the supply pressure P rises to the unload operation starting pressure Punload (0.73 MPa) during load operation, the solenoid valves 23, 23', 23'' are opened to transition to unload operation, and when the supply pressure P drops to the target pressure Ptarget (0.69 MPa) during unload operation, the solenoid valves 23, 23', 23'' are closed to return to load operation.

[0063] [Frequency control device] The inverter-driven compressor 1 of the present invention is provided with a frequency control device 30 that controls the rotation speed of the compressor main body 2 by changing the output frequency of the inverter 4 .

[0064] This frequency control device 30 is configured to be able to selectively perform variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (20 Hz) and an upper limit frequency fmax (60 Hz) so that the pressure in the supply flow path 52, and therefore the supply pressure P, which is the pressure of the compressed gas supplied to the consumption side, matches the target pressure Ptarget (0.69 MPa), and constant frequency control, which maintains the output frequency of the inverter 4 constant at a predetermined pressure rise frequency frise (for example, 30 Hz or 40 Hz) without changing it.

[0065] In the embodiment shown in Figure 1, the frequency control device 30 is composed of a pressure detection means 41 that detects the pressure (supply pressure P) in the supply flow path 52, and a frequency control unit 42b of a control device 42 that outputs a control signal to the inverter 4 based on the detection signal of the pressure detection means 41.In the embodiment shown in Figure 1, the pressure detection means 41 and the control device 42 share the same components as the operation switching device 20 described above, thereby reducing the number of parts.

[0066] In order to perform the above-mentioned frequency control, the above-mentioned control device 42 stores the above-mentioned target pressure Ptarget (for example, 0.69 MPa) and the no-load operation start pressure Punload (for example, 0.73 MPa) as reference pressures for frequency control, as well as the automatic return pressure Preturn (for example, 0.50 MPa) in the memory area 42c of the control device 42.

[0067] The frequency control unit 42b of the control device 42 calculates the pressure difference between the supply pressure P detected by the pressure detection means 41 and the target pressure Ptarget until the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), determines the output frequency of the inverter 4 based on this pressure difference using PI or PID calculation processing, generates a corresponding rotation speed command (frequency command), and outputs this as a control signal to the inverter 4, thereby performing "variable frequency control" as steady-state control, which changes the frequency output by the inverter 4 between a predetermined lower limit value fmin and upper limit value fmax, thereby controlling the rotation speed of the compressor main body so that the supply pressure P approaches the target pressure Ptarget.

[0068] As an example, in this variable frequency control, a frequency that is lower than the upper limit frequency fmax (60 Hz) by a predetermined margin and that can make the supply pressure P equal to the target pressure Ptarget (0.69 MPa) when compressed gas is being consumed on the consumption side with the load factor [(consumed air volume / rated discharge air volume) x 100 (%)] at 100% is set as the rated frequency frating (for example, 50 Hz), and when the load factor decreases and the pressure P in the discharge flow path 51 exceeds the target pressure Ptarget, the control device 42 reduces the output frequency of the inverter 4 to a frequency lower than the rated frequency frating (50 Hz) and switches the motor 3 to low-speed operation.

[0069] This reduction in output frequency is set so that the supply pressure P reaches the lower limit fmin (20 Hz) before it reaches the unload operation start pressure Punload (0.73 MPa).

[0070] On the other hand, if the supply pressure P drops below the predetermined target pressure Ptarget (0.69 MPa) when the compressor main body 2 is driven at a rotation speed corresponding to the lower limit frequency fmin (20 Hz) due to an increase in the load factor, the output frequency of the inverter 4 is increased to a frequency higher than the lower limit value fmin (20 Hz), for example, the rated frequency frating (50 Hz). By repeating this operation, the supply pressure P is made to match the target pressure Ptarget.

[0071] Furthermore, when the frequency control unit 42b of the control device 42 determines that the supply pressure P has risen to the unload operation start pressure Punload (0.73 MPa) during variable frequency control, or when it determines that the operating state of the compressor main body 2 has reached a predetermined low-load operating state, it stops the above-mentioned variable frequency control and transitions to "constant frequency control" in which the inverter output frequency is kept constant at a pressure rise frequency frise (for example, 30 Hz or 40 Hz) set as a predetermined higher frequency than the lower limit frequency fmin (for example, 20 Hz) and the motor 3 is driven.

[0072] The frequency control device 30 continues this constant frequency control until the supply pressure P drops to the automatic return pressure Preturn (for example, 0.50 MPa), and when the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa), it stops the constant frequency control and returns to the variable frequency control described above.

[0073] Example 1 Below, the operation of an inverter-driven compressor (Example 1) configured to transition from variable frequency control to constant frequency control when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) will be explained with reference to the time chart in Figure 2.

[0074] The preconditions for the embodiment shown in FIG. 2 are as follows. The rated frequency frating (50Hz) is the frequency at which the supply pressure P can be maintained at the target pressure Ptarget when compressed gas is consumed at a load factor of 100%. The lower limit frequency fmin (20Hz) is the frequency at which the supply pressure P can be maintained at the target pressure Ptarget when compressed gas is consumed at a load factor of 40%. Due to a pipe leak or other reason, compressed gas is being consumed (leaked) at a load factor of 10% when all pneumatic equipment connected to the consumption side is stopped.

[0075] In the inverter-driven compressor 1 configured as described above, when compressed gas is consumed at a load rate of 100%, the supply pressure P does not exceed the target pressure Ptarget and does not rise to the unload operation start pressure Punload, and the frequency control unit 42b of the control device 42 closes the solenoid valve 23, opens the intake control valve 21, and stops the release of compressed gas in the discharge flow path 51 (receiver tank 51b), causing the compressor main body 2 to enter load operation, which is a steady operating state.

[0076] Furthermore, since the supply pressure P has not reached the no-load operation start pressure Punload (0.73 MPa), the frequency control device 30 (frequency control unit 42b of the control device 42) performs "variable frequency control" to change the frequency output by the inverter 4 according to the supply pressure P detected by the pressure detection means 41, and outputs a control signal to the inverter to output the rated frequency frating (50 Hz).

[0077] With variable frequency control being performed in this manner, when the amount of compressed gas consumed by the pneumatic equipment connected to the consumption side decreases and the load rate begins to drop from 100% (T1), the control device 42 as the frequency control device 30 reduces the output frequency of the inverter 4 so that the supply pressure P maintains the target pressure Ptarget (0.69 MPa), and when the load rate drops to 40%, the control device 42 reduces the output frequency of the inverter 4 to the lower limit frequency fmin (20 Hz).

[0078] As mentioned above, in the inverter-driven compressor 1 of this embodiment, the frequency at which the supply pressure P can be maintained at the target pressure Ptarget (0.69 MPa) when the load factor is 40% and compressed gas is being consumed is set to the lower limit frequency fmin (20 Hz).Therefore, when the consumption of compressed gas decreases further and the load factor falls below 40%, the discharge air volume of the compressor main body 2 exceeds the consumption of compressed gas, causing the supply pressure P to exceed the target pressure Ptarget (0.69 MPa) and begin to rise gradually.

[0079] Then, when all pneumatic equipment connected to the consumption side stops completely and the load rate drops to 10%, which corresponds to the consumption amount due to pipe leaks, etc. (T2), the increase in supply pressure P accelerates and then rises to the unload operation start pressure Punload (0.73 MPa) (T3).

[0080] When the operation switching unit 42a of the control device 42 determines based on the detection signal of the pressure detection means 41 that the supply pressure P has reached the unload operation start pressure Punload (0.73 MPa), it opens the solenoid valve 23, introduces compressed gas into the closed valve pressure chamber of the intake control valve 21 via the control flow path 22, stops the intake of the compressor main body 2, and releases the compressed gas in the receiver tank 51b (discharge flow path 51) via the air release flow path 24, thereby transitioning to unload operation (T3).

[0081] Furthermore, when the supply pressure P reaches the no-load operation start pressure Punload (0.73 MPa), the frequency control unit 42b of the control device 42 stops the variable frequency control described above and outputs a control signal to the inverter 4 to output a pressure rise frequency frise (40 Hz), thereby increasing the rotational speed of the compressor main body 2 from the lower limit rotational speed corresponding to the lower limit frequency fmin (20 Hz) to the rotational speed corresponding to the pressure rise frequency frise (40 Hz), and transitioning to "constant frequency control" in which the compressor main body is operated at a constant pressure rise frequency frise (40 Hz) (T3).

[0082] This transition to constant frequency control causes the rotational speed of the compressor main body 2 to increase, but since the compressor main body 2 is in an unloaded operating state in which no compressed gas is generated, the supply pressure P gradually decreases (T3-T4) as compressed gas is consumed at a load rate of 10% due to pipe leaks, etc.

[0083] Then, when the supply pressure P drops to the target pressure Ptarget (0.69 MPa), the operation switching unit 42a of the control device 42 closes the solenoid valve 23, opens the intake control valve 21, and terminates the release of the receiver tank 51b (discharge flow path 51) to the atmosphere via the release flow path 24, returning the compressor body to load operation (T4).

[0084] Once the frequency control unit 42b of the control device 42 stops the variable frequency control and switches to constant frequency control, it will not resume variable frequency control until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa), which is set as a predetermined pressure lower than the target pressure Ptarget (0.69 MPa).

[0085] As a result, the compressor main body 2 transitions to load operation while maintaining a relatively high rotational speed corresponding to the pressure rise frequency frise (40 Hz), and the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) in a relatively short time Δ' (T4-T3'), so the operation switching unit 42a of the control device 42 re-transitions the operating state of the compressor main body to unload operation in a relatively short time (T3').

[0086] Thereafter, the same process is repeated as long as the consumption of compressed gas at a load rate of less than 40%, such as when the consumption of compressed gas on the consumer side is limited to a load rate of 10%, which corresponds to the consumption of a small amount of compressed gas due to a pipe leak, etc.

[0087] Then, if the use of pneumatic equipment connected to the consumption side is resumed, the load rate rises above 10%, which corresponds to consumption due to pipe leaks, etc., and the rate at which the supply pressure P drops accelerates.When the supply pressure P drops to the target pressure Ptarget (0.69 MPa), the operation switching device 20 returns the operating state of the compressor main body 2 to load operation.Furthermore, when the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa), the frequency control device 30 terminates the above-mentioned constant frequency control and returns to variable frequency control, which changes the frequency output to the inverter according to the supply pressure P.

[0088] Thus, according to the operation control method of the present invention, during constant frequency control, the pressure rise frequency frise (40 Hz), which is a predetermined higher frequency than the lower limit frequency fmin (20 Hz), is maintained while transitioning to load operation.

[0089] Therefore, there is no time lag (see TL in Figure 5) until the rotation speed increases, as occurs when the rotation speed is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (40 Hz) each time a forced transition to unload operation occurs, as in the conventional configuration introduced in Patent Document 1.Therefore, compared to the time (Δ in Figure 5) required to increase the supply pressure P to the unload operation start pressure Punload (0.73 MPa) using the method of Patent Document 1, it is possible to increase the supply pressure P to the unload operation start pressure Punload (0.73 MPa) in a short time (Δ' in Figure 2), making it possible to shorten the load operation time during constant frequency control.

[0090] Moreover, once the operation has shifted to constant frequency control, the operation state is simply switched between load operation and no-load operation by the operation switching device 20 (operation switching section 42a of the control device 42), and constant frequency control continues until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa).

[0091] As a result, in the control method of the present invention, during the time (T2-T5) when only a relatively small amount of compressed gas is consumed on the consumption side due to pipe leaks, etc., there is no low-load operation between no-load operations, and transitions to no-load operation occur frequently, so the total time of no-load operation is long, making it possible to further reduce power consumption compared to the conventional control method listed in Patent Document 1.

[0092] Example 2 In the configuration of Example 1 described with reference to the time chart of Figure 2, an example configuration was described in which, when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) during variable frequency control, the variable frequency control is stopped and the system switches to constant frequency control.

[0093] In contrast, the configuration of Example 2, which will be explained with reference to the time chart of Figure 3, is configured to transition from variable frequency control to constant frequency control when it is determined that the compressor main body 2 is in a predetermined low-load operating state, and other operations are the same as those of the inverter-driven compressor explained with reference to Figure 2.

[0094] In addition, among the operating conditions of the inverter-driven compressor assumed in Example 2 shown in Figure 3, the rated frequency frating (50 Hz) is a frequency that can maintain the pressure P in the supply flow path at the target pressure Ptarget (0.69 MPa) when compressed gas is consumed at a load rate of 100%, and the lower limit frequency fmin is a frequency that can maintain the supply pressure P at the target pressure Ptarget (0.69 MPa) when compressed gas is consumed at a load rate of 40%, which are the same as those of the inverter-driven compressor in Example 1.

[0095] However, the explanation of the operation of the inverter-driven compressor 1 in this embodiment (embodiment 2) differs from embodiment 1, which assumed a leak at a load rate of 10%, in that it assumes a case in which all pneumatic equipment connected to the consumption side is stopped and compressed gas leaks at a load rate of 20% occur due to a piping leak on the consumption side, etc.

[0096] In the inverter-driven compressor 1 of Example 2, when variable frequency control is being performed and the amount of compressed gas consumed by the pneumatic equipment connected to the consumption side decreases and the load factor begins to decrease from 100% (T1), the frequency control device 30 (frequency control unit 42b of the control device 42) reduces the output frequency of the inverter 4 so that the supply pressure P maintains the target pressure Ptarget (0.69 MPa), and when the load factor reaches 40%, the output frequency of the inverter 4 is reduced to the lower limit frequency fmin (20 Hz) (T1-T3).

[0097] Furthermore, when the consumption of compressed gas falls below a load rate of 40% (T3), the amount of air discharged from the compressor main body 2 exceeds the consumption of compressed gas, causing the supply pressure P to exceed the target pressure Ptarget (0.69 MPa) and begin to rise gradually.

[0098] Then, when the use of the pneumatic equipment connected to the consumption side is completely stopped, the consumption of compressed gas on the consumption side drops to a load factor of 20%, which is caused by a pipe leak or the like (T4).

[0099] The frequency control device 30 (frequency control unit 42b of the control device 42) compares the output frequency of the inverter 4 with a judgment reference frequency fref (22Hz) that has been set in advance as a predetermined higher frequency than the lower limit frequency fmin (20Hz), and when it counts that the output frequency of the inverter 4 has remained below the judgment reference frequency fref (22Hz) for a predetermined time t (T2-T5), it determines that the compressor main body 2 is in a predetermined low-load operating state, stops variable frequency control, and switches to constant frequency control.

[0100] Alternatively, instead of or in addition to the above judgment criteria, the supply pressure P detected by the pressure detection means 41 can be compared with a judgment reference pressure Pref (0.70 MPa) that is preset as a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and when it is counted that the supply pressure P remains above the judgment reference pressure Pref (0.70 MPa) for a predetermined time t' (T4-T5), it can be determined that the compressor main body 2 is in a predetermined low-load operating state, and variable frequency control can be stopped and a transition to constant frequency control can be made.

[0101] When it is determined in this way that the compressor main body 2 is in a predetermined low-load operating state, the frequency control device 30 (frequency control unit 42b of the control device 42) stops the variable frequency control and outputs a control signal to the inverter 4 to output the pressure rise frequency frise (40 Hz), increasing the rotational speed of the compressor main body from the lower limit rotational speed corresponding to the lower limit frequency fmin (20 Hz) to the rotational speed corresponding to the pressure rise frequency frise (40 Hz), and transitioning to "constant frequency control" in which the compressor main body 2 is operated at a constant pressure rise frequency frise (T5).

[0102] By setting this pressure rise frequency frise (40 Hz) to a frequency corresponding to the rotational speed that can raise the supply pressure P to the unload operation start pressure Punload (0.73 MPa), by switching to constant frequency control, the supply pressure P can be raised to the unload operation start pressure Punload (0.73 MPa) in a short period of time (T5-T6).

[0103] The operation switching device 20 (operation switching section 42a of the control device 42), which determines based on the detection signal of the pressure detection means 41 that the supply pressure P has risen to the unload operation start pressure Punload (0.73 MPa), opens the solenoid valve 23, introduces compressed gas into the closed valve pressure chamber of the intake control valve 21 via the control flow path 22 to block the intake port 2a of the compressor main body 2, and transitions to unload operation in which the compressed gas in the receiver tank 51b (discharge flow path 51) is released via the release flow path 24 (T6).

[0104] By transitioning to constant frequency control, the rotational speed of the compressor main body 2 increases, but since the compressor main body 2 transitions to a state of no-load operation in which compressed gas is not generated, the supply pressure P gradually decreases as compressed gas is consumed due to piping leaks, etc. (T6-T7).

[0105] Then, when the pressure P in the supply flow path drops to the target pressure Ptarget (0.69 MPa), the operation switching device 20 (operation switching section 42a of the control device 42) closes the solenoid valve 23, opens the intake control valve 21, and terminates the release of the receiver tank 51b (discharge flow path 51) to the atmosphere via the release flow path 24, returning the compressor body to load operation (T7).

[0106] Once the frequency control device 30 (frequency control unit 42b of the control device 42) stops variable frequency control and switches to constant frequency control, it will not return to variable frequency control until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa).

[0107] Therefore, during constant frequency control, the compressor body transitions to load operation while maintaining a relatively high rotational speed corresponding to the pressure rise frequency frise (40 Hz), and therefore load operation during constant frequency control (T7-T6') can be completed in a short time (Δ') compared to when the output frequency is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (40 Hz) to increase the rotational speed while increasing the supply pressure P (Δ in the case of T5-T6), as is the case when transitioning to constant frequency control.

[0108] This load operation (T7-T6') causes the supply pressure P to rise to the unload operation start pressure Punload (0.73 MPa) (T7-T6'), and the operation switching device 20 (operation switching section 42a of the control device 42) re-transitions the operating state of the compressor body to unload operation in a relatively short time (T6'-T7').

[0109] Thereafter, if the consumption of compressed gas on the consumer side is only a small amount due to a pipe leak or the like, the same process is repeated.

[0110] Then, when the use of pneumatic equipment connected to the consumption side is resumed, for example, and the load rate begins to rise above 20%, which corresponds to consumption due to pipe leaks, etc. (T9), the rate at which the supply pressure P decreases accelerates, and when the supply pressure P decreases to the target pressure Ptarget (0.69 MPa), the operation switching device 20 (operation switching section 42a of the control device 42) returns the operating state of the compressor main body 2 to load operation, and when the supply pressure P decreases further to the automatic return pressure Preturn (0.50 MPa), the frequency control device 30 (frequency control section 42b of the control device 42) ends the constant frequency control that rotates the compressor main body 2 at a constant rotational speed corresponding to the above-mentioned pressure rise frequency frise (40 Hz), and returns to variable frequency control, which varies the frequency output to the inverter 4 according to the supply pressure P.

[0111] In the control method of Example 1 described with reference to Figure 2, when the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa), variable frequency control is stopped and a transition to constant frequency control is made. In contrast, in this example (Example 2), the control is configured to transition to constant frequency control when the compressor main body 2 is in a predetermined low-load operating state, making it possible to transition from variable frequency control to constant frequency control before the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa).

[0112] As a result, the configuration of this embodiment (embodiment 2) can achieve the effect of shortening the low-load operating time before transitioning to constant frequency control in addition to the effect obtained with the configuration of embodiment 1.

[0113] In other words, if the load rate due to the consumption of compressed gas due to piping leaks, etc. is close to the discharge rate at the lower limit frequency fmin (20 Hz) (discharge rate corresponding to a load rate of 40% in this embodiment), such as from 10% in Example 1 to 20% as assumed in this embodiment, it will take a longer time for the supply pressure P to rise to the no-load operation start pressure Punload (0.73 MPa) even if the use of the pneumatic equipment connected to the consumption side is stopped, and a longer time will be required to switch to constant frequency control.

[0114] In contrast, in the method of this embodiment, when a specified low-load operating state is reached, the system switches to constant frequency control and forcibly switches to no-load operation, thereby making it possible to shorten the low-load operating time before switching to constant frequency control even in such cases.

[0115] Example 3 FIG. 4 shows a time chart according to still another embodiment of the method for controlling an inverter-driven compressor of the present invention.

[0116] In the embodiment (embodiment 2) described with reference to Figure 3, when transitioning from variable frequency control to constant frequency control, a configuration is adopted in which the output frequency of the inverter 4 is directly increased from the output frequency during low load operation (20 Hz, the lower limit frequency fmin in the example of Figure 3) to the pressure rise frequency frise (40 Hz).

[0117] In contrast to this, in the embodiment (embodiment 3) shown in Figure 4, when transitioning from variable frequency control to constant frequency control, the output frequency of the inverter 4 is increased stepwise from the output frequency during low load operation (lower limit frequency fmin of 20 Hz in the example of Figure 4) to, for example, fmin+Δf(T5; as an example, 25 Hz), fmin+2Δf(T6; as an example, 30 Hz), fmin+3Δf(35 Hz), etc. at regular intervals of time t'' (for example, a time arbitrarily selected by the user between 5 and 60 seconds in accordance with the usage state of the inverter-driven compressor 1), so that the frequency when the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa), in the example of Figure 4, frequency fmin+2Δf(T7; as an example, 30 Hz), is set as the pressure rise frequency frise, and the constant frequency control described above is performed; in other respects, this is the same as the control method described with reference to Figure 3.

[0118] In this way, in this embodiment (embodiment 3), the output frequency of the inverter 4 is gradually increased from the output frequency during low load operation (as an example, the lower limit frequency fmin: 20 Hz) and the frequency when the supply pressure P rises to the no-load operation starting pressure Punload (0.73 MPa) is set to the aforementioned pressure rise frequency frise.By doing so, the pressure rise frequency frise applied during constant frequency control is set to as low a frequency as possible depending on the conditions of use, etc., and therefore the rotational speed of the motor 3 during constant frequency control can be kept as low as possible, thereby further reducing power consumption.

[0119] Incidentally, such a gradual increase in output frequency may be performed each time there is a transition from variable frequency control to constant frequency control, but, for example, the output frequency may be increased in stages only when transitioning to constant frequency control the first time, and the output frequency (fmin+2Δf=30Hz in the example of Figure 4) when the no-load operation start pressure Punload (0.73MPa) is reached may be memorized, and when transitioning to constant frequency control from the second time onwards, the output frequency may be directly increased from the output frequency during low-load operation (for example, the lower limit frequency fmin) to the pressure rise frequency frise (fmin+2Δf=30Hz) memorized when transitioning to constant frequency control the first time, and constant frequency control may be performed at this frequency. [Explanation of symbols]

[0120] 1. Inverter-driven compressor 2 Compressor body 2a Inlet (of compressor body) 2b Discharge port (of compressor body) 2c Fuel filler 3 motors 4 inverters 20 Operation switching device 21 Intake control valve 22 Control Channel 23 Solenoid valve (air release valve) 23' Air release valve (solenoid valve) 23'' solenoid valve (circulation flow opening / closing valve) 24,24' Air discharge channel 25 Circulation path 30 Frequency Control Device 41 Pressure detection means (pressure sensor) 42 Control device 42a Operation switching unit (of control device 42) 42b Frequency control section (of control device 42) 42c Memory area (of control device 42) 50 air flow path 51 discharge flow path 51a Pipe line (between the compressor discharge port and the receiver tank) 51b Receiver tank 51c Pipeline (between receiver tank and check valve) 52 supply channel 54 Check valve Punload No-load operation start pressure Ptarget target pressure Preturn Automatic return pressure Pref Criterion pressure fmax upper limit frequency frating rated frequency frise pressure rise frequency fmin Lower limit frequency fref reference frequency

Claims

1. An inverter-driven compressor comprising: a compressor body; a motor that drives the compressor body; an inverter that changes the AC current input to the motor; and an operation switching device that switches the operating state of the compressor body between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and that enables frequency control that controls the output frequency of the inverter and operation switching control that switches between the load operation and no-load operation, a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path; As pressures to be used as control standards, a predetermined target pressure, a no-load operation start pressure which is a predetermined higher pressure than the target pressure, and an automatic return pressure which is a predetermined lower pressure than the target pressure are respectively set; The load operation is maintained in a steady state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation. the frequency control includes variable frequency control that changes the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure equal to the target pressure, and constant frequency control that maintains the output frequency of the inverter constant at a pressure rise frequency that is a predetermined frequency higher than the lower limit frequency, an inverter-driven compressor operation control method comprising: setting the variable frequency control as steady-state control; shifting from the variable frequency control to the constant frequency control when the supply pressure rises to the no-load operation start pressure; and shifting back to the variable frequency control when the supply pressure falls to or below the automatic return pressure.

2. An inverter-driven compressor comprising: a compressor body; a motor that drives the compressor body; an inverter that changes the AC current input to the motor; and an operation switching device that switches the operating state of the compressor body between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and that enables frequency control that controls the output frequency of the inverter and operation switching control that switches between the load operation and no-load operation, a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path; As pressures to be used as control standards, a predetermined target pressure, a no-load operation start pressure which is a predetermined higher pressure than the target pressure, and an automatic return pressure which is a predetermined lower pressure than the target pressure are respectively set; The load operation is maintained as a steady operating state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation. the frequency control includes variable frequency control for varying the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure coincide with the target pressure, and constant frequency control for maintaining the output frequency of the inverter constant at a frequency that is predetermined higher than the lower limit frequency and at a pressure increase frequency that can increase the supply pressure to or above the no-load operation start pressure, an operation control method for an inverter-driven compressor, characterized in that the variable frequency control is a steady-state control, and after it is determined that the compressor main body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure becomes equal to or lower than the automatic return pressure, the operation control method is switched to the variable frequency control.

3. When the inverter outputs a frequency equal to or lower than a reference frequency, which is a predetermined frequency higher than the lower limit frequency, for a predetermined period of time, and / or When the supply pressure continues to be equal to or higher than a reference pressure, which is a predetermined higher pressure than the target pressure, for a predetermined time, 3. The operation control method for an inverter-driven compressor according to claim 2, further comprising determining that the compressor body is in the predetermined low-load operating state.

4. 3. The operation control method for an inverter-driven compressor according to claim 2, wherein after the variable frequency control is stopped, the output frequency of the inverter is increased stepwise at predetermined time intervals, and the output frequency when the supply pressure reaches the no-load operation start pressure is set as the pressure increase frequency, and the constant frequency control is performed.

5. The air flow path on the primary side of the check valve serves as a discharge flow path, The no-load operation is Either closing the intake port of the compressor body, opening the discharge flow path to the atmosphere, or connecting the discharge flow path to the intake port of the compressor body, or 5. The operation control method for an inverter-driven compressor according to claim 1, wherein the operation control is performed by a combination of closing the intake port of the compressor body and either opening the discharge flow path to the atmosphere or connecting the discharge flow path to the intake port of the compressor body.

6. An inverter-driven compressor including a compressor body, a motor that drives the compressor body, an inverter that changes the AC current input to the motor, an operation switching device that switches the operating state of the compressor body between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device that controls the output frequency of the inverter, a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path; a storage area for storing a predetermined target pressure, a no-load operation start pressure that is a predetermined higher pressure than the target pressure, and an automatic return pressure that is a predetermined lower pressure than the target pressure, which are preset as a reference pressure for control; The operation switching device, The load operation is maintained as a steady operating state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the pressure in the supply flow path falls to the target pressure or lower, the operation is switched to the load operation. The frequency control device The inverter is capable of executing variable frequency control, which changes the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure equal to the target pressure, and constant frequency control, which maintains the output frequency of the inverter constant at a pressure rise frequency that is a predetermined frequency higher than the lower limit frequency, an inverter-driven compressor, characterized in that the variable frequency control is a steady-state control, the variable frequency control is switched to the constant frequency control when the supply pressure rises to the no-load operation start pressure, and the variable frequency control is switched to when the supply pressure falls to or below the automatic return pressure.

7. An inverter-driven compressor including a compressor body, a motor that drives the compressor body, an inverter that changes the AC current input to the motor, an operation switching device that switches the operating state of the compressor body between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device that controls the output frequency of the inverter, a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path; a storage area for storing a predetermined target pressure, a no-load operation start pressure that is a predetermined higher pressure than the target pressure, and an automatic return pressure that is a predetermined lower pressure than the target pressure, which are preset as a reference pressure for control; The operation switching device, The load operation is maintained in a steady state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation. The frequency control device variable frequency control is possible in which the output frequency of the inverter is changed between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure coincide with the target pressure, and constant frequency control is possible in which the output frequency of the inverter is maintained constant at a frequency that is predetermined higher than the lower limit frequency and at a pressure increase frequency that is a frequency at which the supply pressure can be increased to or above the no-load operation start pressure, an inverter-driven compressor characterized in that the variable frequency control is a steady-state control, and after it is determined that the compressor main body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure becomes equal to or lower than the automatic return pressure, the compressor switches back to the variable frequency control.

8. The storage area further stores a reference frequency that is a predetermined higher frequency than the lower limit frequency and / or a reference pressure that is a predetermined higher pressure than the target pressure, The frequency control device 8. The inverter-driven compressor according to claim 7, wherein the compressor body is determined to be in the predetermined low-load operating state when the inverter outputs a frequency equal to or lower than the judgment reference frequency for a predetermined period of time, and / or when the supply pressure is equal to or higher than the judgment reference pressure for a predetermined period of time.

9. The frequency control device 8. The inverter-driven compressor according to claim 7, wherein after the variable frequency control is stopped, the output frequency of the inverter is increased stepwise at predetermined time intervals, and the output frequency at which the supply pressure reaches the no-load operation start pressure is set as the pressure increase frequency, and the constant frequency control is performed.

10. The air flow path on the primary side of the check valve serves as a discharge flow path, The operation switching device, The compressor includes one of an intake control valve that opens and closes the intake port of the compressor body, an air release valve that opens the discharge flow path to the atmosphere, or a return flow path opening / closing valve that opens and closes the return flow path that communicates between the discharge flow path and the intake port of the compressor body, or a combination of the intake control valve and either the air release valve or the return flow path opening / closing valve, The inverter-driven compressor according to any one of claims 6 to 9, characterized in that the no-load operation is achieved by closing the intake control valve, opening the air release valve, or opening the return flow path on-off valve, or by a combination of closing the intake control valve and opening either the air release valve or the return flow path on-off valve.

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