JP2012010499A - Motor drive device for vacuum pump and pump system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive device for a vacuum pump, capable of reducing a harmonic component of motor current.SOLUTION: The motor drive device for a turbo molecular pump that performs exhaust by rotatingly driving a rotor part formed with a rotating blade and a screw rotor as an exhaust function part by a motor includes: an inverter 43 that drives the motor; a DC-DC converter 41 as a DC voltage source having a different plural setting voltages for an inverter input voltage of the inverter 43; and a motor control circuit 44 as voltage switching means that switches a setting voltage of the DC-DC converter 41 according to motor load information. The motor control circuit 44 is configured to PWM control the inverter 43 by setting a duty ratio of a PWM signal so that the rotational speed of the motor is maintained at a predetermined target rotational speed.

Description

  The present invention relates to a motor driving device for a vacuum pump used for a vacuum pump such as a turbo molecular pump, and a pump system including the motor driving device for the vacuum pump.

  In a turbo molecular pump, a rotor on which rotor blades are formed is driven to rotate by a motor, and gas molecules are exhausted by rotating the rotor blades at high speed with respect to fixed blades. Among such turbomolecules, there is known one that rotationally drives a motor by PWM (Pulse Width Modulation) control (see, for example, Patent Document 1).

JP 2007-82370 A

  By the way, in the conventional turbo molecular pump, the inverter input voltage is fixed to the maximum voltage value corresponding to the motor maximum load, and the motor current is controlled by PWM control. Therefore, when the motor load is light, the duty ratio of the PWM signal becomes extremely small, and the ratio of harmonic components of the motor current increases. As a result, there is a problem that the ratio of eddy current loss due to harmonic components increases, leading to an increase in power loss and an increase in rotor temperature.

A first aspect of the present invention is a vacuum pump motor drive device used in a vacuum pump that performs exhaust by rotating a rotor formed with an exhaust function portion with a motor, and an inverter for driving the motor, and an inverter for the inverter DC voltage source having a plurality of different set voltages as input voltage, voltage switching means for switching the set voltage of the DC voltage source according to motor load information, and so that the rotational speed of the motor is maintained at a predetermined target rotational speed And a motor control circuit for setting the duty ratio of the PWM signal and performing PWM control of the inverter.
According to a second aspect of the present invention, in the motor driving device for a vacuum pump according to the first aspect, the plurality of set voltages are provided in association with different motor load regions, respectively, and the motor load region on the higher load side is more It is characterized in that a large set voltage is associated.
According to a third aspect of the present invention, in the motor driving device for a vacuum pump according to the second aspect, the motor load information is based on one of the motor current value and the duty ratio and the set voltage set by the voltage switching means. As a boundary load value between the first motor load region and the second motor load region adjacent to the low load side of the load region, the motor load is larger than the boundary load value. If the motor load is smaller than the boundary load value, switch to the second set voltage associated with the second motor load region. It is a thing.
According to a fourth aspect of the present invention, in the vacuum pump motor driving device according to the first aspect, the apparatus includes a determination unit that determines whether the duty ratio as the motor load information is equal to or less than a predetermined value. When it is determined, the set voltage is switched to a smaller set voltage.
According to a fifth aspect of the present invention, there is provided a pump system comprising: a vacuum pump that performs exhaust by rotating a rotor formed with an exhaust function portion with a motor; and a motor driving device for a vacuum pump according to any one of the first to fourth aspects. It is characterized by that.

  According to the present invention, the harmonic component of the motor current can be reduced.

It is sectional drawing which shows the pump unit 1 of a turbo-molecular pump. It is a block diagram of a motor drive control part. FIG. 4 is a diagram illustrating an inverter 43. It is a figure explaining an excitation sequence. It is a figure which shows the PWM voltage waveform and motor current waveform at the time of PWM control. It is a figure explaining the setting method of a duty ratio. It is a flowchart explaining control of an inverter input voltage and a duty ratio. It is a figure which shows an example of the time change of the duty ratio after a motor drive start, an inverter input voltage, and rotation speed. It is a figure which shows the relationship between a motor load and a duty ratio. It is a figure which shows an example in the case of switching an inverter input voltage in 3 steps.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The turbo molecular pump includes, as a pump system, a pump unit that performs evacuation and a control unit (not shown) that drives and controls the pump unit. FIG. 1 is a cross-sectional view showing a schematic configuration of the pump unit 1. The turbo molecular pump shown in FIG. 1 is a magnetic bearing type pump, and the rotor 30 is supported in a non-contact manner by electromagnets 37 and 38 constituting a 5-axis magnetic bearing. The rotor 30 magnetically levitated by the magnetic bearings is driven to rotate at high speed by the motor 36. For example, a DC brushless motor is used as the motor 36. The rotational speed of the rotor 30 is detected by the rotational speed sensor 23. For example, an inductance type sensor is used as the rotation speed sensor 23.

  The rotor 30 is formed with a plurality of stages of rotating blades 32 and a cylindrical screw rotor 31 as an exhaust function unit. On the other hand, on the fixed side, a plurality of stages of fixed blades 33 arranged alternately with the rotary blades 32 in the axial direction and a screw stator 39 provided on the outer peripheral side of the screw rotor 31 are provided as exhaust function units. . The fixed wings 33 are stacked so as to be sandwiched from above and below in the axial direction by a pair of spacer rings 35 and placed on the base 20. When the pump casing 34 in which the inlet flange 21 is formed is fixed to the base 20, the stacked spacer ring 35 is sandwiched between the base 20 and the pump casing 34, and each fixed blade 33 is positioned.

  The base 20 is provided with an exhaust port 22, and a back pump is connected to the exhaust port 22. By rotating the rotor 30 at a high speed by the motor 36 while magnetically levitating, the gas molecules on the intake port 21 side are exhausted to the exhaust port 22 side.

  The control unit connected to the pump unit includes a magnetic bearing control unit, a motor drive control unit for rotating the motor 36, and the like. FIG. 2 is a block diagram of the motor drive control unit. An external AC 200V power supply is input to a power factor correction circuit 40 including a rectifier. The DC voltage output from the power factor correction circuit 40 is converted into a desired DC voltage by the DC / DC converter 41.

  A voltage value of a DC voltage (hereinafter referred to as an inverter input voltage) input from the DC / DC converter 41 to the inverter 43 is detected by the voltage sensor 42. The detected voltage value is input to the motor control circuit 44. As will be described later, in the present embodiment, the DC / DC converter 41 includes a plurality of set voltages with respect to the inverter input voltage, and these set voltages can be switched by a voltage command from the motor control circuit 44.

  The inverter 43 is provided with a plurality of switching elements for converting the DC voltage from the DC / DC converter 41 into a three-phase AC voltage. On / off of the plurality of switching elements provided in the inverter 43 is controlled by a PWM (Pulse Width Modulation) command from the motor control circuit 44. The motor power is controlled by changing the motor current by changing the duty ratio of the PWM signal output as the current command. The value of the motor current is detected by the current sensor 45. The current value detected by the current sensor 45 and the rotation speed detected by the rotation speed sensor 23 are input to the motor control circuit 44.

  FIG. 3 is a diagram showing the inverter 43. The inverter 43 is provided with a plurality of switching elements Tr1 to Tr6. Power semiconductor elements such as MOSFETs and IGBTs are used for the switching elements Tr1 to Tr6. Reference numeral 361 denotes a motor stator of the motor 36. Based on the rotation information of the rotation speed sensor 23, the switching elements Tr1 to Tr6 are turned on and off at a predetermined timing, thereby supplying current to the U, V, and W phase coils of the motor stator 361 to drive the motor 36 to rotate.

  FIG. 4 shows an excitation sequence when the motor 36 is driven by energization at 120 degrees, and shows the on / off timings of the switching elements Tr1 to Tr6, the U-phase current, the V-phase current, and the W-phase current. Is. The numbers 1 to 12 surrounded by circles indicate the step order. The switching elements Tr1 to Tr6 are turned on by the High signal and turned off by the Low signal. For example, in step 1, switching elements Tr1 and Tr5 in FIG. 3 are turned on, a positive current flows through the U-phase coil, and a negative current flows through the V-phase coil. In the subsequent step 2, switching elements Tr1 and Tr6 are turned on, a positive current flows through the U-phase coil, and a negative current flows through the W-phase coil.

  By turning on and off the switching elements Tr1 to Tr6 according to the procedure shown in FIG. 4, a rotating magnetic field is formed in the motor stator 361, and the motor rotor is rotationally driven by the rotating magnetic field. The rotational speed (that is, the rotational speed) of the motor rotor is made variable by changing the switching cycle. Further, by changing the duty ratio of the PWM signal in the High signal section shown in FIG. 4, the motor current, that is, the motor power is controlled. Increasing the duty ratio increases the motor current, and conversely, decreasing the duty ratio decreases the motor current.

  As described above, the motor rotation speed (that is, the rotation speed) is determined by the switching cycle shown in FIG. 4. If the switching cycle is shortened, the rotation speed is increased. Conversely, if the switching cycle is increased, the rotation speed is decreased. . However, when the motor load increases due to the addition of a gas load or the like, if the motor power at that time is small, the rotational speed determined by the switching cycle cannot be maintained, and the rotational speed of the motor decreases.

  In general, when a turbo molecular pump is used, the motor rotation is set to a constant target rotation speed (usually the rated rotation speed), and is driven to rotate with power sufficient to maintain the target rotation speed. Therefore, when the gas inflow is started from the state where the gas inflow amount is zero and the motor load increases, the motor current is increased to maintain the motor rotation speed at the rated rotation speed. That is, the rated speed is maintained by controlling the duty ratio. When the gas inflow is stopped and the motor is in a no-load state again, the motor speed tends to increase if the motor power remains large.Therefore, control is performed to change the duty ratio so that the motor speed remains constant. The ratio drops.

  In the conventional turbo molecular pump, the inverter input voltage is fixed to a constant value, so that the motor power adjustment described above is performed by changing the duty ratio of the PWM signal. FIG. 5 shows a motor voltage waveform (PWM voltage waveform) and a motor current waveform when PWM control is performed. FIGS. 5A and 5B show the case of no-load rated rotation (low load) where the gas flow rate is zero, and FIGS. 5C and 5D show the case where the motor load is high. In the case of a high load, the duty ratio D is set to a large value so as to increase the motor current, and the PWM voltage waveform at that time is as shown in FIG. In the example shown in FIG. 5C, the duty ratio D is D2 = Δt2 / Δt. FIG. 5D shows a motor current waveform in the case of the PWM voltage waveform shown in FIG.

  On the other hand, during no-load rated rotation, the motor power required to maintain the rotation can be very small. In the conventional turbo molecular pump, the inverter input voltage is set to a voltage that matches the maximum load of the motor. Therefore, the duty ratio D during no-load rated rotation is a small value D1 (= Δt1 / Δt) as shown in FIG. As a result, the ratio of the harmonic component to the non-harmonic component is increased, the iron loss (eddy current loss) is increased in proportion, and there is a problem that a wasteful current due to an increase in rotor temperature flows.

  Therefore, in this embodiment, the output voltage of the DC / DC converter 41, that is, the inverter input voltage is configured to be adjusted not only to the high voltage VH but also to a lower low voltage VL. That is, the voltage can be arbitrarily set between the high voltage VH and the low voltage VL. In accordance with a voltage command from the motor control circuit 44, the inverter input voltage is changed to the high voltage VH when the load is high, and the inverter input voltage is changed to the low voltage VL when the load is low. When changing the voltage between the high voltage VH and the low voltage VL, the voltage is gradually changed so that no overcurrent flows.

  FIG. 6 is a diagram for explaining a duty ratio setting method in the present embodiment. FIGS. 6A and 6B show the PWM voltage waveform and the motor current waveform when the load is high, for example, when the gas load is large. On the other hand, FIGS. 6C and 6D show PWM voltage waveforms and motor current waveforms when the load is low, for example, when the gas load is relatively small or when there is no load. Here, the situation at the time of no-load rated rotation is shown.

  The high voltage VH is set to the same level as the inverter input voltage in the conventional turbo molecular pump. Therefore, as shown in FIG. 6 (a), the duty ratio D at the time of high load becomes large as in the case of the duty ratio D2 in the case shown in FIG. 5 (c).

  On the other hand, the low voltage VL is set such that the duty ratio D during no-load rated rotation is larger than the duty ratio D1 during the conventional no-load rated rotation shown in FIG. When switching from the state shown in FIGS. 5A and 5B to the state shown in FIGS. 6C and 6D, the duty ratio D3 (= Δt3 / Δt) when the low voltage VL is reached The power supplied is approximately the same before and after the inverter input voltage setting is switched, that is, the power in the cases of FIGS. 5A and 5B and the power in the cases of FIGS. 6C and 6D. It is set to be approximately equal. In other words, at no load, when the inverter input voltage is a low voltage VL, the rated speed N0 is maintained at the duty ratio D1, and when the inverter input voltage is a high voltage VH, the rated speed N0 is maintained at the duty ratio D3. Maintained.

  Since the inverter input voltage becomes lower after the voltage is switched, the duty ratio D3 (= Δt3 / ΔT) is larger than the duty ratio D1. For this reason, as shown in FIG. 6D, the motor current waveform rises gently, and the harmonic component included in the motor current is reduced. Since the power before and after the voltage switching is switched so as to be substantially the same, the magnitude of the duty ratio D3 after the switching is determined by the value of the low voltage VL. Therefore, the low voltage VL is set so that the duty ratio D3 is a value that does not cause the influence of the harmonic component.

  FIG. 7 is a flowchart for explaining control of the inverter input voltage and the duty ratio in the present embodiment. The control shown in FIG. 7 starts when the rotor 30 is magnetically levitated and a motor rotation command is input to the motor control circuit 44. In step S110, the inverter input voltage V is set to the high voltage VH, and motor driving is started.

  If the motor drive is started by the process of step S110, the process proceeds to step S120, and acceleration control for increasing the motor speed to the rated speed N0 is started. That is, based on the rotational speed detected by the rotational speed sensor 23, the detected rotational speed is fed back and the duty ratio D of the PWM signal is adjusted so that the motor rotational speed becomes the rated rotational speed N0 that is the target rotational speed. Set.

  For example, when the difference (= N0−N) between the rated rotational speed N0 and the detected rotational speed N is equal to or larger than a predetermined value ΔN, the duty ratio is increased, and when the difference is smaller than −ΔN, the duty ratio is decreased. Let When | diff | <ΔN, that is, when the difference is within the rated speed range, the duty ratio is maintained without being changed. Further, if the initial value D0 in step S110 is set to 1, acceleration is started at the duty ratio D = 1, and if the rotational speed N becomes larger than a predetermined rotational speed N1 (<N0), the difference is as described above. The duty ratio may be controlled according to the above.

  FIG. 8 shows an example of the temporal change of the duty ratio D, the inverter input voltage, and the rotation speed after the motor driving is started. When the rotational drive of the motor is started at time t1, the duty ratio D gradually increases from the initial value D0. In the example shown in FIG. 8, D = 1 at time t2. Thereafter, when the rotational speed N approaches the rated rotational speed N0, the duty ratio D starts to decrease, and finally decreases to a value that can maintain the no-load rated rotational speed (D1 here). At the duty ratio D1, the motor load and the motor supply power are balanced, and the rotation speed (= rated rotation speed N0) becomes constant. In the example shown in FIG. 8, the rotational speed N reaches the rated rotational speed N0 after the duty ratio D becomes D1, but depending on how the duty ratio D is controlled, the rotational speed N once decreases after exceeding the rated rotational speed N0. In some cases, N = N0.

  In step S130 of FIG. 7, it is determined whether or not the rotational speed N detected by the rotational speed sensor 23 has reached the rated rotational speed N0. If it is determined that the rated rotational speed N0, the routine proceeds to step S140 and acceleration control is stopped. To do. In the following step S150, duty ratio control (speed feedback control) is started so that the rotational speed N is maintained at the rated rotational speed N0. That is, if the detected rotational speed N is lower than the rated rotational speed N0, the duty ratio D is increased. Conversely, if the rotational speed N is larger than the rated rotational speed N0, the duty ratio D is decreased. Let

  In step S160, it is determined whether the duty ratio D is equal to or less than a predetermined value D4. Here, the duty ratio D4 is a threshold value for switching the inverter input voltage from the high voltage VH to the low voltage VL, and is set slightly larger than the duty ratio D1 at which the harmonic component of the motor current starts to become a problem. If it is determined in step S160 that the duty ratio D is equal to or less than D4, the process proceeds to step S170, and an operation of switching the inverter input voltage from the high voltage VH to the low voltage VL is started.

  When the inverter input voltage changes, the current value changes and the rotation speed changes. However, as described above, speed feedback control is performed so that the rotation speed N is maintained at the rated rotation speed N0. The duty ratio D is changed so that the rotational speed is restored. Therefore, the switching from the high voltage VH to the low voltage VL in step S170 is gradually changed so that the change in the duty ratio D can follow the change in the rotation speed.

  In the example shown in FIG. 8, when it is determined in step S130 that the rotational speed is the rated rotational speed N0, since the duty ratio D is already D1 and smaller than D4, D ≦ D4 in step S160. And the inverter input voltage is switched to the low voltage VL. The PWM voltage waveform and the motor current waveform before switching are in the states shown in FIGS. 5A and 5B, but when the inverter input voltage finally becomes a low voltage VL, the waveforms shown in FIGS. The state is as shown. As a result, the motor current waveform rises gradually, and the ratio of harmonic components in the motor current decreases. In FIG. 8, the duty ratio D is described so as to change from D1 to D3 at time t3, but actually changes gradually as described above. The same applies to switching at times t6 and t8, which will be described later.

  In step S180 in FIG. 7, it is determined whether or not the duty ratio D is equal to or greater than the value D5 (D3 <D5 ≦ 1). If it is determined that D ≧ D5, the process proceeds to step S190. In step S190, the inverter input voltage is switched from the low voltage VL to the high voltage VH. Also in this case, the inverter input voltage is gradually changed as in step S170. When the process of step S190 is completed, the process returns to step S160.

  In FIG. 8, from time t3 to time t4, the gas load = 0 and the no-load rated rotational state, so the duty ratio D is kept constant at D3 in order to maintain the rated rotational speed N0. Then, when a low gas load state with a relatively small gas inflow amount is reached at time t4, the rotational speed N decreases immediately after that, but the duty of the rotational speed N is maintained at the rated rotational speed N0 by the processing of step S150. The ratio D is changed. That is, as shown in FIG. 8, the duty ratio D increases immediately after time t4, and the duty ratio D becomes constant when the rotational speed N becomes the rated rotational speed N0.

  Further, when the gas flow rate increases at time t5 and a high gas load state is reached, the duty ratio D is increased so that the rotational speed N is maintained at the rated rotational speed N0 again. Thereafter, when the duty ratio D becomes D ≧ D5 at time t6, the inverter input voltage is switched from the low voltage VL to the high voltage VH by the process of step S190 in FIG. Even after switching the inverter input voltage, the duty ratio D is increased so that the rotational speed N becomes the rated rotational speed N0, and the duty ratio is made constant when the rotational speed N becomes the rated rotational speed N0.

  Thereafter, when the gas inflow is stopped at time t7 in FIG. 8 and no load is applied, the duty ratio D is decreased so that the rotational speed N is maintained at the rated rotational speed N0. When the duty ratio D decreases and D ≦ D4 at time t8, the inverter input voltage is switched from the high voltage VH to the low voltage VL by the process of step S170 in FIG. The duty ratio D after switching becomes larger than D3 described above, but thereafter, the duty ratio D continues to decrease so that the rotational speed N becomes the rated rotational speed N0, and becomes the duty ratio D3 at the no-load rated rotational NO. Incidentally, the duty ratio D is constant.

  FIG. 9A is a diagram illustrating a relationship between the motor load and the duty ratio D in the case of the voltage switching described with reference to FIGS. The horizontal axis is the motor load, and the position marked as no load is where the gas load is zero. Line L1 shows the case where the inverter input voltage is the high voltage VH, and line L2 shows the case where the inverter input voltage is the low voltage VL. In the no-load state (no-load rated rotation state), the duty ratio D1 is obtained for the line L1, and the duty ratio D3 is obtained for the line L2.

  When the inverter input voltage is switched from the high voltage VH to the low voltage VL, it is switched when the duty ratio D becomes D4 or less, and when the inverter input voltage is switched from the low voltage VL to the high voltage VH, the duty is switched. It switches when the ratio D becomes D5 or more. That is, the motor load at the time of switching differs between when the motor load decreases and when it increases. For this reason, even if the motor load fluctuates in the vicinity of the switching point, it is possible to avoid the inconvenience of frequently switching between the high voltage VH and the low voltage VL.

  In the example shown in FIG. 9A, the inverter input voltage is switched from the high voltage VH to the low voltage VL at the duty ratio D4 that is slightly larger than the duty ratio D1 in which the harmonic component of the motor current becomes a problem as described above. Thus, the duty ratio D is increased. On the other hand, in the example shown in FIG. 9B, the motor load is divided into a high load and a low load, and the inverter input voltage is switched when the motor load exceeds the boundary. The duty ratio D at the boundary is D6 for the line L1 and D7 for the line L2. Since D6 is larger than D3, the duty ratio D becomes D3 or more regardless of whether the load is high or low, and the generation of harmonic components of the motor current can be further reduced. In the case of FIG. 9B as well, so-called hysteresis in which the motor load varies depending on the switching direction as shown in FIG. 9A may be provided.

  In the above-described example, the case where the inverter input voltage is switched between the high voltage VH and the low voltage VL has been described. However, the same applies to the case where three or more kinds of setting voltages are provided and switching is performed in three or more stages. Can do. FIG. 10 shows an example in which the inverter input voltage is divided into three types V1, V2, and V3 and switched in three stages. Line L11 shows the case of high voltage V1, line L12 shows the case of medium voltage V2, and line L13 shows the case of low voltage V3.

  Here, the low load, the medium load, and the high load are set such that the duty ratio D at the voltages V1, V2, and V3 is equal to the value D8. When the high voltage V1 is switched to the medium voltage V2, the duty ratio D increases from D8 to D9, and when the medium voltage V2 is switched to the low voltage V3, the duty ratio D increases from D8 to D10. In the case of this example, the duty ratio D is set to be not less than D8 which is sufficiently larger than the duty ratio D1 in which the harmonic component of the motor current becomes a problem.

  As described above, in the vacuum pump motor drive device used in the vacuum pump (turbo molecular pump) that exhausts by rotating the rotor 30 formed with the rotor blades 32 and the screw rotor 31 as the exhaust function unit by the motor 36. The inverter 43 for driving the motor 36, the DC / DC converter 41 having a plurality of different set voltages as the inverter input voltage of the inverter 43, and the voltage switching means for switching the set voltage of the DC / DC converter 41 according to the motor load information The motor control circuit 44 sets the duty ratio of the PWM signal so that the rotation speed of the motor 36 is maintained at a predetermined target rotation speed, and performs PWM control of the inverter 43. did. The motor load information includes a combination of the inverter input voltage and the duty ratio D, or a combination of the inverter input voltage and the motor power detected by the current sensor 42. From these pieces of information, the motor load can be estimated. Further, when the gas load information is inputted to the turbo molecular pump controller from the controller on the vacuum device side where the turbo molecular pump is mounted, the inputted gas load information is used as the motor load information. May be.

  As a result, the inverter input voltage can be lowered according to the motor load. Therefore, the harmonic component of the motor current is reduced, eddy current loss can be reduced, and power saving and rotor heat generation can be reduced. Further, it is possible to reduce the occurrence of vibration and noise due to the electromagnetic force of the motor. Note that when the set voltage is switched, the duty ratio is set so that the motor power is approximately equal before and after switching, so that the change in the rotational speed after switching can be substantially prevented.

  When the set voltage (that is, the inverter input voltage) is switched, the duty ratio is set so that the motor power is substantially equal before and after the switching, thereby preventing the rotation speed from changing after the switching.

  Further, like the regions indicated by high load, medium load, and low load in FIG. 10, the plurality of set voltages V1, V2, and V3 are provided in association with different motor load regions, and the motor on the high load side is provided. A larger set voltage is associated with the load region. When the motor load is larger than the boundary load value with respect to the boundary load value between the high load region and the middle load region adjacent to the low load side, the inverter input voltage V1 associated with the high load region is When the motor load is smaller than the boundary load value, the inverter input voltage V2 associated with the medium load region is switched.

  As a result, the duty ratio D is maintained higher than D8 by switching the inverter input voltage from V1 to V2 even in a load situation in which the load decreases and the duty ratio D decreases and falls below the threshold value D8. And the problem of an increase in the harmonic component of the motor current can be prevented.

  Further, as shown in FIG. 9, when it is determined that the duty ratio D as the motor load information is equal to or less than the predetermined value D4, the set voltage may be switched from the voltage value VH to a lower voltage value VL.

  In the description of FIG. 7 described above, the inverter input voltage is switched when the duty ratio D becomes equal to or less than the threshold value D4. However, instead of the duty ratio D as a command value, the motor as a result of the PWM control is changed. You may use for control using an electric current value. That is, when the detected motor current value is equal to or less than the current threshold, the inverter input voltage is switched from VH to VL.

  Each of the embodiments described above may be used alone or in combination. This is because the effects of the respective embodiments can be achieved independently or synergistically. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

  For example, although a magnetic levitation type turbo molecular pump has been described as an example, it can be applied to a turbo molecular pump that is not a magnetic levitation type. In the turbo molecular pump described above, the motor rotation speed is detected by the rotation speed sensor 23, but the present invention can also be applied to a sensorless turbo molecular pump. Furthermore, any vacuum pump other than the turbo molecular pump can be applied as long as it is a vacuum pump that PWM-controls a motor that rotates the rotor at a high speed.

  1: pump unit, 23: rotational speed sensor, 30: rotor, 31: screw rotor, 32: rotary blade, 33: fixed blade, 36: motor, 39: screw stator, 41: DC / DC converter, 42: voltage sensor, 43 : Inverter, 44: Motor control circuit, Tr1 to Tr6: Switching elements

Claims (5)

A motor driving device for a vacuum pump used for a vacuum pump that exhausts by rotating a rotor formed with an exhaust function part with a motor,
An inverter for driving the motor;
DC voltage sources having a plurality of different set voltages as the inverter input voltage of the inverter;
Voltage switching means for switching a set voltage of the DC voltage source according to motor load information;
A motor drive for a vacuum pump, comprising: a motor control circuit that sets a duty ratio of a PWM signal so that the rotation speed of the motor is maintained at a predetermined target rotation speed and performs PWM control of the inverter apparatus. The motor driving device for a vacuum pump according to claim 1,
The plurality of set voltages are provided so as to be associated with different motor load regions, respectively, and a higher set voltage is associated with a motor load region on the higher load side. . The motor driving device for a vacuum pump according to claim 2,
Based on one of the motor current value and the duty ratio and the set voltage set by the voltage switching means, the calculation means for calculating the motor load as the motor load information,
When the motor load is greater than the boundary load value with respect to the boundary load value between the first motor load region and the second motor load region adjacent to the low load side of the load region, the voltage switching means Switching to a first set voltage associated with one motor load region, and switching to a second set voltage associated with the second motor load region when the motor load is smaller than the boundary load value. A motor drive device for a vacuum pump. The motor driving device for a vacuum pump according to claim 1,
Determination means for determining whether the duty ratio as the motor load information is a predetermined value or less;
The motor driving device for a vacuum pump, wherein the voltage switching unit switches the set voltage to a smaller set voltage when the determination unit determines that the voltage is not more than a predetermined value. A vacuum pump that exhausts by rotating a rotor formed with an exhaust function unit with a motor;
A pump system comprising: the vacuum pump motor drive device according to claim 1.

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