JP6223915B2 - Compressor and driving device thereof - Google Patents

Description

  The present invention relates to an apparatus for driving various compressors including an oil-free screw compressor.

  Conventionally, as an apparatus for driving a compressor, for example, one disclosed in Patent Document 1 is known. This device is a device for rotationally driving a screw rotor of a screw compressor, and the screw compressor includes a female rotor and a male rotor that are a pair of screw rotors, and a rotor casing that accommodates them. A screw compressor is provided to rotate one of the female rotor and the male rotor, for example, a male rotor. The apparatus includes an electric motor, and the electric motor rotates the male rotor by electromagnetic force.

  Some of the screw compressors are operated at a high speed of 20,000 rpm or more, such as an oil-free screw compressor. Since this high-speed operation region is a region exceeding the critical speed region where the amplitude of the rotor shaft significantly increases, in order to operate in the high-speed operation region, the critical speed region is set at the time of acceleration of the startup of the screw compressor. Must pass.

  FIG. 10 shows an example of the relationship between the rotor rotational speed and the amplitude of the screw compressor. According to this example, when normal operation is performed in a speed range lower than the critical speed (in this example, 6000 rpm) as in an oil-cooled screw compressor, for example, the critical speed can always be avoided. However, in a compressor such as an oil-free screw compressor in which normal operation is performed in an operation region higher than the critical speed, the critical speed must be passed before the normal operation is reached. The rotation of the screw rotor at or near the critical speed may cause vibration having an amplitude that exceeds the rotor contact limit, that is, an amplitude that causes a pair of screw rotors to contact each other.

  As means for avoiding large vibrations caused by driving in such a dangerous speed range and performing safe driving, Patent Document 1 describes the following measures A and B.

  A. An intermediate bearing is interposed between the screw rotor and the rotor of a built-in type electric motor assembled to the rotating shaft, thereby increasing the natural frequency of the screw rotor and rotor assembly.

  B. When starting up the screw compressor, the acceleration of the screw rotor from the low speed range is sufficiently increased to pass the critical speed range, that is, the rotation speed range where the amplitude of the rotor shaft is remarkably increased in a short time.

JP 2002-122084 A

  As in Measure A, in order to shift the dangerous speed range to a higher speed side than the operating rotation range by installing an intermediate bearing, it is necessary to use a very special and expensive bearing, and a new one is added along with that use. Equipment and maintenance are also required. Therefore, a significant increase in cost is inevitable.

  In order to pass through the dangerous speed range in a short time and reach the high speed operation area as in Measure B, excellent acceleration performance is required for the speed control of the motor, and at the same time, suppression of heat generation in the high speed operation area is required. Is an important issue, and it is difficult to achieve both. Specifically, at high speed rotation of 20,000 rpm or more, significant heat generation is likely to occur in the rotor of the motor due to core iron loss and eddy current loss due to changes in electromagnetic force. Adding a large cooling structure to dissipate the heat results in a significant increase in cost, as in Measure A.

  The problem described above is remarkable in an oil-free screw compressor, but may occur in the same manner when driving other compressors.

The present invention is, such circumstances in view, the which can be safely driven at a high speed side area than the critical speed range without significant increase in the compressor and cost which has a critical speed range drive The purpose is to provide.

  As means for solving the above problems, the present inventors have conceived that PWM control and rectangular wave drive control are used together as a control method of an electric motor for driving a compressor. Since PWM control has harmonic component noise due to its carrier frequency, it can easily generate significant heat when executed in a high-speed region, but it can achieve high-accuracy acceleration control and achieve sufficient acceleration. Moreover, the harmonic component as described above has an advantage that there is no possibility of giving a large excitation force to the screw rotor. On the other hand, in the rectangular wave drive control, it is difficult to obtain high control accuracy particularly in a low speed region, and it is difficult to obtain excellent acceleration. On the other hand, even in the high speed region, the rectangular wave drive control is remarkable due to harmonic component noise such as PWM control. Fever is unlikely to occur.

The present invention has been made from this point of view, a drive compressor and that it is driven at a high speed region with a critical speed range, the drive apparatus, the critical speed at the rising edge of the drive a speed control with excellent acceleration that can pass through in a short time range, the one capable of compatibility between the suppression of heat generation in the high-speed rotation region, provided. That is, to provide the present invention, Ri drive der for driving the compressor and the compressor having a rotor, the drive device includes a motor coupled to the compressor, the motor and its power supply And an inverter that drives the electric motor and a control unit that inputs a control signal to the inverter and controls the driving of the electric motor. The control unit is configured to control the electric motor in an operation region in which the operation speed is lower than a predetermined specific speed in a region higher than a critical speed at which the vibration of the compressor is maximum based on information on the operation speed of the compressor. A control signal for performing PWM control is generated and input to the inverter, and a control signal for performing rectangular wave drive control of the electric motor is generated in the region where the operating speed is equal to or higher than the specific speed. input.

According to the drive device, in the operation region where the operating speed of the compressor is lower than the specific speed, it is possible to obtain high acceleration by executing PWM control capable of highly accurate speed control. By passing through the critical speed in a short time, an increase in compressor vibration can be avoided. Then, in the high-speed operation region where the rotation speed is equal to or higher than the specific speed, the screw is executed by executing the rectangular wave drive control that does not generate the harmonic component noise caused by the carrier frequency like the PWM control. Heat generation of the rotor can be suppressed. The drive device is particularly effective in an embodiment in which the compressor is an oil-free screw compressor having a screw rotor, and the electric motor is connected to the screw compressor so as to rotate the screw rotor.

  The PWM control and the rectangular wave drive control can be executed using a common inverter. Thereby, it is possible to realize both high acceleration and suppression of heat generation at low cost.

  The information regarding the operating speed of the compressor may be a speed command input to the control unit, or an actual rotation speed of the electric motor detected by a magnetic pole position sensor or other detectors.

The drive device further includes a vibration detector for detecting the magnitude of vibration of the compressor, and the control unit has a preset allowable value for the magnitude of vibration detected by the vibration detector. When exceeding, it is preferable to generate a control signal for executing PWM control and input it to the inverter regardless of the information on the rotational speed, that is, to perform control giving priority to suppression of vibration. Thereby, it is possible to control not only the operating speed of the compressor but also the electric motor suitable for the vibration state in the actual machine.

As described above, according to the present invention, which can be safely driven at a high speed region of the high-speed side than the critical speed range without significant increase in the compressor and cost which has a critical speed range drive An apparatus is provided.

It is sectional drawing of the screw compressor which is an example of the compressor driven by the apparatus which concerns on each embodiment of this invention. It is a circuit diagram of the drive device of the compressor concerning a 1st embodiment of the present invention. It is a flowchart which shows the control operation which the control part shown by FIG. 2 performs. It is a graph which shows the example of the waveform of the gate signal for PWM control. It is a graph which shows the relationship between the frequency and noise component in PWM control. It is a graph which shows the example of the waveform of the gate signal for rectangular wave drive control. It is a graph which shows the relationship between the frequency and noise component in rectangular wave drive control. It is a circuit diagram of the drive device of the compressor which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the control operation which the control part shown by FIG. 8 performs. It is a graph which shows the example of the relationship between the rotor rotation speed of a screw compressor, and an amplitude.

  A first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a screw compressor 10 which is a compressor driven by the driving device according to the embodiment. The screw compressor 10 is a so-called oil-free compressor, and includes a male rotor 11 and a female rotor 12, which are a pair of screw rotors that mesh with each other, a rotor casing 14, and an electric motor casing 16.

  The male rotor 11 and the female rotor 12 have rotor shafts 11a and 12a extending in one direction, respectively, and rotor main bodies 11b and 12b provided around the intermediate portions of the rotor shafts 11a and 11b. The male rotor 11 and the female rotor 12 are accommodated in the rotor casing 14 so that the rotor bodies 11b and 12b mesh with each other with an appropriate gap.

  Timing gears 17 and 18 are fixed to end portions (left end portion in FIG. 1) on the same side of the rotor shafts 11a and 12a, respectively. These timing gears 17 and 18 engage with each other to enable synchronous rotation of the male and female rotors 11 and 12. Further, the rotor shaft 11 a of the male rotor 11 is extended to the side opposite to the timing gear 17 as compared with the rotor shaft 12 a of the female rotor 12.

  The rotor casing 14 accommodates the main body portion of the male rotor 11 excluding the extended portion of the rotor shaft 11 a and the entire female rotor 12. Specifically, the rotor casing 14 includes portions of the rotor shafts 11a and 12a between the rotor main bodies 11b and 12b and the timing gears 17 and 18, respectively, on the rotor side bearings (rolling bearings in FIG. 1) 21, 22, while being rotatably held via the rotor main bodies 11 b and 12 b, the portions on the opposite side of the timing gears 17 and 18 are rotated via intermediate bearings (rolling bearings in FIG. 1) 23 and 24, respectively. Hold as possible.

  The electric motor casing 16 is connected to the rotor casing 14 in the axial direction so as to accommodate the extended portion of the rotor shaft 11 a of the male rotor 11. Specifically, the electric motor casing 16 holds the end portion of the extended portion of the rotor shaft 11a via the electric motor side bearing 26 so as to be rotatable.

  The rotor casing 14 has a gas suction port and a discharge port (not shown). The rotor casing 14 and the motor casing 16 are provided with oil supply passages 27, 28, 29 for supplying oil for cooling the rotor side bearings 21, 22, the intermediate bearings 23, 24 and the motor side bearing 26, respectively. Have.

FIG. 2 shows a drive unit of the screw compressor 10 and a compressor controller 30. The drive, drive the screw compressor 10 receives an instruction of the compressor controller 3 0.

  The compressor controller 30 is electrically connected to an operating device including a switch (not shown) and controls the operation of the screw compressor 10 in response to an operation given to the operating device. The compressor controller 30 has a function of outputting a speed command for the rotational speeds of the male and female rotors 11 and 12 as the pair of screw rotors as a main function.

  The drive device includes an electric motor 32, an inverter 40, and an electric motor controller 50.

  The electric motor 32 is a three-phase AC electric motor in this embodiment, and is connected to the AC power source 34 shown in FIG. 2 via the inverter 40, and is one of the male and female rotors 11 and 12 that are the pair of screw rotors. The male rotor 11 is rotated by electromagnetic force. The electric motor 32 according to this embodiment is a so-called built-in motor as shown in FIG. 1 and is built around the extension portion of the rotor shaft 11 a of the male rotor 11 and is built in the electric motor casing 16. ing.

  Specifically, the electric motor 32 includes a rotor 36 fixed around the extended portion of the rotor shaft 11 a and a stator 38 fixed to the electric motor casing 16. The rotor 36 includes a plurality of permanent magnets arranged in the circumferential direction. The stator 38 includes a plurality of stator cores 38a arranged in the circumferential direction and a plurality of exciting coils 38b formed around each stator core 38a. Each stator core 38a is fixed to the inner surface of the electric motor casing 16 so as to be able to face each permanent magnet of the rotor 36 in the radial direction at a position outside the rotor 36 in the radial direction.

  The inverter 40 is interposed between the AC power supply 34 and each excitation coil 38b of the electric motor 32, and operates the electric motor 32 by causing an appropriate current to flow through each excitation coil 38b. That is, the male rotor 11 is driven to rotate by the electric motor 32.

  Specifically, the inverter 40 includes a rectifier circuit 42, a smoothing circuit 43, an inverter circuit 44, and a gate drive circuit 45 as shown in FIG. The rectifier circuit 42 includes a plurality of diodes and converts alternating current supplied from the alternating current power supply 34 into direct current. The smoothing circuit 43 includes a capacitor and smoothes the current converted by the rectifier circuit 42. The inverter circuit 44 includes a plurality of switching devices (for example, IGBTs) provided for each of the U phase, the V phase, and the W phase in the electric motor 32, and the excitation coils 38b corresponding to the respective phases by turning on and off these switching devices. The current flowing through is controlled. The gate drive circuit 45 supplies a gate current to the gate terminal of each switching device corresponding to the gate signal input from the electric motor controller 50, thereby driving the switching device.

  Further, the inverter 40 according to this embodiment is provided with a plurality of detectors. The plurality of detectors include a voltage sensor 46 that detects the voltage across the capacitor in the smoothing circuit 43, a U-phase current sensor 47 that detects a U-phase current and a W-phase current in the inverter circuit 44, and a W-phase, respectively. A current sensor 48. The electric motor 32 is provided with a magnetic pole position sensor 39 for detecting the magnetic pole position. Each of the sensors generates a detection signal that is an information signal about the detection target, and inputs the detection signal to the electric motor controller 50.

  The motor controller 50 corresponds to a control unit according to the present invention, and generates an appropriate gate signal based on a speed command output from the compressor controller 30 and detection signals input from the sensors. Then, the rotational speed of the motor 32 is controlled by inputting the gate signal to the gate drive circuit 45. Specifically, the electric motor controller 50 includes a voltage command unit 52, a control mode command unit 54, and a gate signal generation unit 56.

  The voltage command unit 52 generates a voltage command corresponding to a target output voltage for the inverter 40 based on a speed command output from the compressor controller 30 and a detection signal input from each sensor. .

  Based on the speed command, the control mode command unit 54 determines which control mode should be selected from among a plurality of control modes given in advance for controlling the drive of the electric motor 32 by the inverter 40, and selects the selected mode. A control mode command for the control mode is generated. The plurality of control modes include a PWM (pulse width modulation) control mode and a rectangular wave drive control mode.

  The gate signal generation unit 56 generates a gate signal based on a control mode specified by the control mode command, and obtains a target output voltage specified by the voltage command, and the gate drive circuit 45. Specifically, the gate signal generation unit 56 includes a PWM control unit 56a that generates a gate signal for performing the PWM control, and a rectangular wave drive control unit 56b that generates a gate signal for performing the rectangular wave drive control. And having.

  Next, a specific control operation performed by the motor controller 50 will be described with reference to the flowchart of FIG. 3 and FIGS. This control operation is based on the premise that each of the rotors 11 and 12 of the screw compressor 10 to be driven has the vibration characteristics shown in FIG. 10, and a region near the critical speed (6000 rpm) shown in FIG. In order to safely drive the rotors 11 and 12 while suppressing heat generation at a high rotational speed (20000 rpm) sufficiently higher than the critical speed. Here, the specific numerical value of the critical speed can be measured or predicted when the screw compressor 10 is designed and manufactured, and can be handled as a known value.

  First, the motor controller 50 takes in the speed command output from the compressor controller 30 and the detection signal generated by each sensor (step S1 in FIG. 4).

  The voltage command unit 52 generates a voltage command based on the speed command and the detection signals. Specifically, the voltage command unit 52 calculates the actual rotational speed of the electric motor 32 by time differentiation of the magnetic pole position detected by the magnetic pole position sensor 39 (step S2), and compares this actual rotational speed with the speed command. Based on the above, a torque command is calculated to match the actual rotational speed with the target rotational speed specified by the speed command, that is, to feedback control the rotational speed of the electric motor 32 (step S3). Further, the voltage command unit 52 converts the torque command into a current command that specifies the target current of the motor 32 (step S4), and the actual current (actual current) detected by the U-phase and W-phase current sensors 47 and 48, respectively. Based on the comparison between the U-phase current and the W-phase current) and the current command, the voltage for matching the actual current with the target current specified by the current command, that is, feedback control of the current of the motor 32 A command is calculated (step S5).

  On the other hand, the control mode command unit 54 determines whether or not the specified speed specified by the speed command is equal to or higher than a predetermined specific speed (step S6). This specific speed is set to a speed sufficiently higher than the dangerous speed. Specifically, as shown in FIG. 10, the rotational speed that changes according to the rotor rotational speed (rotational speed) is small enough to avoid contact between the rotors 11 and 12, for example, 10000 rpm, Set to

  In the low speed region where the designated speed is less than the specific speed (NO in step S6), the control mode command unit 54 selects PWM control as the control mode (step S7), and generates a control mode command for designating this. Based on this control mode command, the gate signal generating unit 56 generates a PWM control gate signal for matching the voltage detected by the voltage sensor 46 with the target voltage specified by the voltage command, and the gate drive circuit 45. (Step S8).

  FIG. 4 shows the waveform of the gate signal generated in the PWM control mode. In this PWM control mode, a pulse signal whose pulse width changes in accordance with the amplitude of the target AC voltage is generated as the gate signal. FIG. 4 illustrates a waveform of a pulse signal for obtaining a sinusoidal voltage of 100 Hz and having a carrier frequency of 10 kHz. The PWM control based on such carrier frequency has high control accuracy. Therefore, when the screw compressor 10 starts up, it is possible to increase the rotation speed of the electric motor 32 with excellent acceleration that reliably follows the increase of the target speed. To. That is, it is possible to ensure that the actual rotation speed passes through the critical speed shown in FIG. 10 and the area in the vicinity thereof in a short time.

  On the other hand, the PWM control does not have a frequency characteristic that gives an excitation force to the male rotor 11 in the critical speed and the vicinity thereof, and is excellent in safety in the area. FIG. 5 shows frequency characteristics of noise generated in the PWM control mode. As shown in FIG. 5, the PWM control mode is accompanied by noise including a harmonic component caused by a carrier frequency of 10 kHz, that is, a 10 kHz × n-order harmonic component. There is no fear of giving a serious excitation force.

  While acceleration based on such PWM control proceeds, when the designated speed reaches a high speed region that is equal to or greater than the specific value (YES in step S6), the control mode command unit 54 selects rectangular wave drive control as the control mode. (Step S9), a control mode command designating this is generated. Based on this control mode command, the gate signal generation unit 56 generates a rectangular wave drive control gate signal for matching the voltage detected by the voltage sensor 46 with the target voltage specified by the voltage command, and the gate drive Input to the circuit 45 (step S10).

  FIG. 6 shows the waveform of the gate signal generated in the rectangular wave drive control mode. In this rectangular wave drive control mode, a rectangular wave signal is generated as the gate signal so as to sequentially switch the U phase, the V phase, and the W phase according to the magnetic pole position detected by the magnetic pole position sensor 39. This rectangular wave signal includes a portion where the signal voltage is 0, and the voltage can be controlled by changing the length of this portion.

  FIG. 7 shows frequency characteristics of noise generated in the rectangular wave drive control mode. As shown in FIG. 7, the noise generated in the rectangular wave drive control mode has a relatively low frequency component n times the fundamental frequency (drive frequency) of 100 Hz, and is a carrier frequency as seen in PWM control. Does not contain high frequency components due to Therefore, remarkable heat generation due to the high frequency component does not occur, and a significant temperature rise in the electric motor 32 is avoided.

  As described above, according to this drive device, in the low speed region where the designated speed is less than the specific speed (= dangerous speed + α), although it includes harmonic components that tend to generate heat, it has excellent acceleration performance and the male rotor 11 While the selection of the PWM control that does not give a serious excitation force enables the dangerous speed and the area near it to pass safely and reliably in a short time, while in the high speed area where the specified speed is higher than the specific speed, The selection of the rectangular wave drive control that suppresses harmonic components enables suppression of the temperature rise of the electric motor 32, mutual contact due to thermal expansion of the rotors 11 and 12 due to the temperature rise, and heat reduction of the permanent magnet in the rotor 36. Allows prevention of magnetism.

  Details of the reason for avoiding heat generation by selecting the rectangular wave drive control are as follows. In general, the eddy current loss Pe that causes heat generation is given by the following Steinmetz empirical formula.

Pe = Ke × (t × f × Bm) ² / ρ
Here, Ke is a proportional constant, t is the thickness of a plate that can generate eddy current (in the electric motor 32, the radial thickness of the permanent magnet constituting the rotor 36), f is the frequency, Bm is the maximum magnetic flux density, and ρ is magnetic. Indicates the resistivity of the body. Thus, since the eddy current loss Pe is proportional to the square of the frequency f, selecting a rectangular wave drive control mode that does not involve noise including harmonic components in the high-speed region is extremely effective in suppressing heat generation.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  The drive device according to the second embodiment includes all the components of the drive device according to the first embodiment, and in addition to the vibration level of the rotors 11 and 12 (for example, the speed in the vibration direction, A vibration detector 60 for detecting acceleration and amplitude) is further provided. The vibration detector 60 is composed of, for example, a speed sensor or an acceleration sensor, and is attached to a location where vibration of the rotors 11 and 12 can be detected, for example, the rotor casing 14.

  On the other hand, in addition to the case where the designated speed is less than the specified speed, the control mode command unit 54 of the motor controller 50 is preset with the vibration level detected by the vibration detector 60 even if the designated speed is equal to or higher than the specified speed. If the value is equal to or greater than the specific value, the PWM control mode is selected. Here, the specific value for the vibration level is, for example, “Class III · ZONEB of evaluation criteria of mechanical vibration measured at the rotating part of the non-reciprocating machine” defined in ISO 7919 (long-term continuous operation possible region) Preferably, the specific value is, for example, 4.5 mm / s.

  In the flowchart shown in FIG. 9, the control mode command unit 54 replaces step S6 shown in FIG. 3, that is, whether or not the designated speed is equal to or higher than the specific speed, step S6A, that is, the designated speed is the specific speed. When it is determined whether or not it is above and step S6B, that is, whether or not the detected amplitude is equal to or greater than a specific value, the amplitude is equal to or greater than the specific value even if the specified speed is equal to or greater than the specific speed. (NO in step S6A and YES in step S6B), the PWM control mode is selected (step S7), and only when the specified speed is equal to or higher than the specific speed and the amplitude is less than the specific value (NO in step S6A and step S6B). NO), the rectangular wave drive control mode is selected.

  Specifically, in the second embodiment, in the acceleration operation from the stop state, the PWM control mode is selected as in the first embodiment until the designated speed reaches a specific speed (> dangerous speed). However, when the detected vibration level is higher than the specified value even if the specified speed is higher than the specified speed, the PWM control mode is continuously adopted and the vibration level becomes lower than the specified value. For the first time, the rectangular wave control mode is adopted. The same applies when decelerating, and while the vibration level detected in the high-speed operation region where the specified speed is higher than the specific speed is below the specific value, the rectangular wave drive method is adopted as in the first embodiment. When the vibration level exceeds the specific value, the control mode is switched to the PWM control mode regardless of the designated speed, and the selection of the PWM control mode is continued until the screw compressor stops thereafter.

  Such control mode selection is particularly effective when the critical speed cannot be specified, or when the critical speed may change as the state of the device changes. Even high safety can be guaranteed.

  The present invention is not limited to the embodiment described above. The present invention includes the following embodiments, for example.

1) Information on rotational speed The present invention is characterized in that the control mode is selected based on information on the operating speed of the compressor. The information on the operating speed is a compressor controller as shown in FIG. It is not restricted to the speed command which 30 outputs. For example, the control mode may be selected based on the comparison between the actual rotational speed calculated based on the detection signal of the magnetic pole position sensor 39 shown in FIG. 2 and the specific speed.

2) About drive object The compressor driven by the apparatus which concerns on this invention is not restricted to the said oil free screw compressor. The present invention can also be applied to driving other compressors, for example, oil-cooled screw compressors, and compressors other than screw compressors, for example, turbo compressors.

3) Electric motor The structure and type of the electric motor used in the present invention are not particularly limited. For example, the electric motor according to the present invention is not limited to the built-in type as shown in FIG. 1, and is constructed independently of the rotor casing 14 and the rotor shaft 11a shown in FIG. 1, and coupled to the rotor shaft 11a. It may be connected by.

  Moreover, the site | part of the compressor with which the electric motor which concerns on this invention is connected is not limited. For example, the electric motor may be connected to the rotor shaft of the female rotor instead of the rotor shaft of the male rotor in the screw compressor. Alternatively, it may be connected to a rotary shaft of another type of compressor or an input shaft of a transmission interposed between the compressor and the electric motor.

4) Carrier frequency in PWM control mode In the PWM control mode according to the present invention, the carrier frequency may be fixed at a constant frequency, or may be increased or decreased according to a rotational speed or other factors. For example, a high carrier frequency is set in order to achieve high-precision control in critical speeds where high acceleration is required and in the vicinity, or in low-speed areas where accuracy is difficult to achieve, and in other areas switching loss is low. A relatively low carrier frequency may be set for reduction.

10 Screw compressor 11 Male rotor (screw rotor)
12 Female rotor (screw rotor)
30 Compressor controller 32 Electric motor 34 AC power supply 36 Rotor 38 Stator 39 Magnetic pole position sensor 40 Inverter 50 Electric motor controller (control unit)
52 Voltage command section 54 Control mode command section 56 Gate signal generation section 60 Vibration detector

Claims (4)

A compressor having a rotor ;
And a driving device for driving said compressor,
The driving device includes:
An electric motor coupled to the compressor to rotate the rotor ;
An inverter connected to the electric motor and its power source for driving the electric motor;
And a control unit which inputs a control signal to the inverter controls the driving of the motor, the control unit, based on the information about the operating speed of the compressor, vibrating the operating speed of the compressor In an operating region lower than a predetermined specific speed in a region higher than the maximum critical speed, a control signal for performing PWM control of the electric motor is generated and input to the inverter, and the operating speed is the specific speed. in the above region input to the inverter to generate a control signal for performing rectangular wave drive control of the electric motor, compressor and its drive. A compressor and its drive device according to claim 1, wherein the control unit is performed using the common of the inverter of the PWM control and the rectangular wave drive control, the compressor and its drive. A compressor and its drive device according to claim 1, further comprising a vibration detector for detecting a magnitude of vibration of the compressor, the control unit is detected by the vibration detector vibration If the magnitude of exceeding preset allowable value is input to the inverter to generate a control signal for executing the PWM control regardless of information about the operating speed of the compressor, the driving of the compressor and its apparatus. The compressor according to any one of claims 1 to 3, and a driving device thereof, wherein the compressor is an oil-free screw compressor having a screw rotor, and the electric motor rotates the screw rotor. A compressor connected to the screw compressor and its driving device.

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