JP2015061372A - Motor drive device and vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive device capable of surely starting a motor without using a complicated method for detecting a magnetic pole position in the vicinity of rotation stop.SOLUTION: A motor drive device comprises: an inverter which drives a permanent magnet type synchronous motor; a reverse voltage detection unit which detects reverse voltage of the permanent magnet type synchronous motor; an estimation unit which estimates a magnetic pole position of a motor rotor and a rotational frequency on the basis of the reverse voltage detected by the reverse voltage detection unit; and a control unit which makes the motor stator generate rotating magnetic field on the basis of the estimation results of the estimation unit and controls driving of the permanent magnet type synchronous motor in a sensorless synchronous manner. The control unit makes the motor stator generate rotating magnetic field of a prescribed frequency and asynchronously drive the motor until a prescribed time elapses after the motor is started, and controls synchronous driving of the motor after the prescribed time has elapsed.

Description

  The present invention relates to a motor drive device that drives and controls a permanent magnet type synchronous motor, and a vacuum pump including the motor drive device.

  An axial flow type vacuum pump such as a turbo molecular pump rotates a rotor having moving blades at a high speed by a motor in order to evacuate. Since such a vacuum pump exhausts while performing compression work on the rare gas, the rotor is rotated only in one direction, and acceleration and deceleration operations are performed in a stationary to normal rotation region.

  In such a vacuum pump, a DC brushless motor that does not use a magnetic pole position sensor may be used for cost reduction or the like. In that case, a method of detecting a target (having a step) provided on the rotor by using one inductance type gap sensor is known. However, it is difficult to detect position information using only the rotation sensor.

  For this reason, a countermeasure is usually taken by devising a control sequence when the motor is driven (particularly, at the time of starting at which the possibility of reverse rotation is relatively high) (see, for example, Patent Document 1). However, the method of dealing with the problem by devising the control sequence has a drawback that it takes a long time to start up the rotor in the forward direction.

  By the way, apart from the method using the inductance gap sensor as described above for the rotation sensor, rotation sensorless control has been proposed for improving reliability and reducing cost. Further, a DC brushless motor is applied from the viewpoint of energy saving, and sinusoidal driving is often used as a driving method. In such a vacuum pump, the magnetic pole position and the rotation speed are estimated based on the back electromotive force accompanying the rotation of the permanent magnet attached to the motor rotor.

Japanese Patent No. 469891

  However, since the counter electromotive voltage is a voltage proportional to the rotation speed, the voltage value is weak in the low speed rotation region as in the motor start. On the other hand, the output voltage of the three-phase inverter is generally set to a voltage value equal to or higher than the counter electromotive voltage at rated rotation (for example, several tens of volts in the case of a turbo molecular pump).

  Therefore, for example, in a vacuum pump with a rated rotational speed of 1000 rps, the back electromotive voltage value at 1 rps immediately after the start of starting is 1/1000 of the back electromotive voltage value at the rated time, and is about several tens of mV. It is very difficult to accurately extract such a weak counter electromotive voltage from a PWM output voltage that repeatedly turns on and off at several tens of volts or more.

A motor driving device according to a preferred embodiment of the present invention includes an inverter for driving a permanent magnet type synchronous motor, a counter electromotive voltage detection unit for detecting a counter electromotive voltage of the permanent magnet type synchronous motor, and a counter electromotive voltage detection unit. Sensorless synchronization of the permanent magnet type synchronous motor by generating a rotating magnetic field in the motor stator based on the estimation result of the estimation unit and the estimation unit estimating the magnetic pole position and rotation frequency of the motor rotor based on the back electromotive voltage detected in A control unit that controls driving, and the control unit generates a rotating magnetic field of a predetermined frequency by a motor stator until a predetermined time elapses from the start of the motor, performs asynchronous driving, and performs synchronous driving control after a predetermined time elapses. To do.
In a more preferred embodiment, the predetermined frequency is set to a constant frequency in the frequency range of the rotation frequency estimated by the estimation unit when the inverter is driven.
In a further preferred embodiment, the frequency range includes a first range having a low frequency and a second range having a high frequency, which are different from each other in motor drive control system, and the predetermined frequency is set to a constant frequency in the second range. A motor drive device.
In a further preferred embodiment, the control unit includes a determination unit that determines whether or not the rotational frequency estimated by the estimation unit is equal to a predetermined frequency, and the control unit determines that the determination unit becomes equal after the start of the motor, Even before the lapse of a predetermined time, generation of a rotating magnetic field having a predetermined frequency is stopped and synchronous drive control is started.
A vacuum pump according to a preferred embodiment of the present invention includes a pump rotor having an exhaust function unit, a permanent magnet type synchronous motor that rotationally drives the pump rotor, and the motor driving device that drives the permanent magnet type synchronous motor, Is provided.

  According to the present invention, it is possible to reliably start the motor without using a complicated magnetic pole position detection method in the vicinity of rotation stop.

FIG. 1 is a diagram showing a configuration of a pump unit 1 in the vacuum pump of the present embodiment. FIG. 2 is a block diagram showing a schematic configuration of the motor control system. FIG. 3 is a diagram for explaining the inverter 100. FIG. 4 is a diagram for explaining a rotation starting method in the present embodiment. FIG. 5 is a diagram illustrating an example of open section setting. FIG. 6 is a diagram illustrating a current flowing in one phase of the motor M. FIG. 7 is a diagram for explaining restart when an instantaneous power failure occurs. FIG. 8 is a flowchart for explaining the starting operation. FIG. 9 is a diagram for explaining another example of the rotation starting method.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a vacuum pump according to the present embodiment. The vacuum pump shown in FIG. 1 is a magnetic levitation turbo molecular pump, and FIG. 1 shows the configuration of a pump unit 1 of the turbo molecular pump. The turbo molecular pump includes a pump unit 1 shown in FIG. 1 and a control unit (not shown) that drives the pump unit 1.

  The pump unit 1 has a turbo pump stage composed of the rotary blade 4a and the fixed blade 62, and a drag pump stage (thread groove pump) composed of the cylindrical portion 4b and the screw stator 64. Here, a screw groove is formed on the screw stator 64 side, but a screw groove may be formed on the cylindrical portion 4b side. The rotary blade 4a and the cylindrical part 4b, which are the rotation side exhaust function part, are formed in the pump rotor 4. The pump rotor 4 is fastened to the shaft 30a. The rotor unit R is constituted by the pump rotor 4 and the shaft 30a.

  By forming a plurality of turbine blades over one circumference of the outer periphery of the pump rotor 4, one stage of rotary blades is configured. The pump rotor 4 is formed with a plurality of stages of rotary blades in the axial direction. The plurality of stages of fixed blades 62 are alternately arranged with the rotary blades 4a in the axial direction. Each fixed wing 62 is placed on the base 60 via the spacer ring 63. When the fixing flange 61c of the pump casing 61 is fixed to the base 60 with a bolt, the stacked spacer ring 63 is sandwiched between the base 60 and the locking portion 61b of the pump casing 61, and the fixed blade 62 is positioned.

  The shaft 30 a is supported in a non-contact manner by radial magnetic bearings 37 and 38 and an axial magnetic bearing 39 provided on the base 60. Each magnetic bearing 37, 38, 39 includes an electromagnet and a displacement sensor. The floating position of the shaft 30a is detected by the displacement sensor. The electromagnet constituting the axial magnetic bearing 39 is arranged so as to sandwich the rotor disk 55 provided at the lower end of the shaft 30a in the axial direction. The shaft 30a is rotated by a motor M.

  The motor M is a permanent magnet type synchronous motor, and for example, a DC brushless motor is used. The motor M includes a motor stator 10 disposed on the base 60 and a motor rotor 11 provided on the shaft 30a. The motor rotor 11 is provided with a permanent magnet. When the magnetic bearing is not operating, the shaft 30a is supported by emergency mechanical bearings 26a and 26b.

  An exhaust port 65 is provided at the exhaust port 60 a of the base 60, and a back pump is connected to the exhaust port 65. By rotating the rotating body unit R at a high speed by the motor M while magnetically levitating, the gas molecules on the intake port 61a side are exhausted to the exhaust port 65 side.

  FIG. 2 is a block diagram showing a schematic configuration of the motor control system. Here, the motor stator 10 side that generates the rotating magnetic field constitutes an armature, and the motor rotor 11 side provided with the rotor magnet (permanent magnet) 110 constitutes a field. The motor stator 10 is provided with a U-phase coil 10U, a V-phase coil 10V, and a W-phase coil 10W, while the motor rotor 11 is provided with a rotor magnet 110 for generating a field. Excitation current is supplied from the inverter 100 to each of the coils 10U to 10W.

  Currents flowing through the U, V, and W phase coils 10U to 10W of the motor stator 10 are detected by the current detection unit 101, and the detection result is input to the control unit 102 via the signal amplification gain setting unit 104. Further, the voltage of each terminal and neutral point of the U, V, W phase coils 10U to 10W is detected by the voltage detection unit 103, and the detection result is input to the control unit 102 via the signal amplification gain setting unit 104.

  FIG. 3 is a diagram for explaining the inverter 100. The inverter 100 includes a plurality of switching elements SW1 to SW6 and a gate drive circuit 1000 for driving the switching elements SW1 to SW6 on and off. Power semiconductor elements such as MOSFETs and IGBTs are used for the switching elements SW1 to SW6. Note that freewheeling diodes D1 to D6 are connected in parallel to each of the switching elements SW1 to SW6.

  The control unit 102 generates a PWM control signal for on / off control of the switching elements SW1 to SW6 based on the input current detection signal and voltage detection signal. The gate drive circuit 1000 generates a gate drive signal based on the PWM control signal, and turns on / off the switching elements SW1 to SW6. Thereby, sinusoidally modulated and PWM voltages are applied to the U, V and W phase coils, respectively.

  In the present embodiment, control unit 102 controls inverter 100 based on the detection results of current detection unit 101 and voltage detection unit 103. The gate drive circuit 1000 of the inverter 100 controls the excitation current supplied to the coils 10U to 10W by driving the switching element on and off based on a command from the control unit 102. As a result, a rotating magnetic field that rotates counterclockwise is generated, and the motor rotor 11 having the rotor magnet 110 is rotationally driven. In the example shown in FIG. 2, the motor rotor 11 is driven to rotate counterclockwise.

  In order to increase (accelerate) the number of rotations of the motor rotor 11, the frequency of the rotating magnetic field generated by the motor stator 10 is matched with the rotating frequency of the motor rotor 11, and the phase of the rotating magnetic field is rotated with respect to the rotor rotation. The motor stator 10 is excited so as to proceed to step. Conversely, in order to decrease (decelerate) the rotational speed of the motor rotor 11, the frequency of the rotating magnetic field of the motor stator 10 is matched with the rotational frequency of the motor rotor 11, and the phase of the rotating magnetic field is delayed with respect to the rotor rotation. Thus, the motor stator 10 is excited.

  Further, in order to rotate the motor rotor 11 in a stopped state, the motor stator 10 is excited so that a magnetic field that advances in the rotation direction from the magnetic field of the rotor magnet 110 is generated. Thus, in the operation of the brushless motor, it is important to accurately detect the direction of the magnetic field of the motor rotor 11, that is, the magnetic pole position of the rotor magnet 110. The motor M in the present embodiment is a sensorless DC brushless motor that does not use a magnetic pole position detection sensor. However, in a DC brushless motor with a sensor, the magnetic pole position is generally detected using a Hall element. I have to.

  On the other hand, in the sensorless motor M in the present embodiment, the control unit 102 estimates the magnetic pole position and the rotation frequency based on the counter electromotive voltage detected by the voltage detection unit 103. An AC voltage (back electromotive voltage) corresponding to the magnetic pole position of the field is generated at the coil end of the motor stator 10, but when the motor rotor 11 is rotating at a speed close to the rated speed, the rated voltage is A counter electromotive voltage with a voltage value close to is generated. Therefore, the magnetic pole position of the motor rotor 11 can be detected relatively easily using this counter electromotive voltage. However, since the back electromotive force also decreases as the rotational speed of the motor rotor 11 decreases, it is difficult to accurately detect the magnetic pole position in the low rotational speed region.

  For example, in the case of a vacuum pump with a rated rotational speed of 1000 rps, the back electromotive voltage value at 1 rps immediately after the start of startup is 1/1000 of the back electromotive voltage value at the rated time, and is about several tens of mV. It is very difficult to accurately extract such a weak counter electromotive voltage from a PWM output voltage that repeatedly turns on and off at several tens of volts or more.

  In this way, at the start of rotation, since the drive is started with the rotor magnetic pole position unknown, there may be a reverse rotation. For this reason, various driving methods have been proposed in the past, but there is a drawback that the control becomes complicated. According to the control method of the present embodiment described below, it is possible to reliably start rotation in a desired rotation direction (forward rotation direction) with a simpler control method than before.

  FIG. 4 is a diagram for explaining a rotation starting method in the present embodiment. In FIG. 4, the vertical axis indicates the rotation frequency of the motor rotor 11 or the excitation frequency of the inverter 100, and the horizontal axis indicates time. First, the operation mode at the start will be described. As described above, since accurate magnetic pole position detection is difficult in the low rotation region of the motor rotor 11, control is generally performed in a plurality of stages according to the rotation frequency.

  In the example shown in FIG. 4, the control is divided into three stages, and the operation mode 1 (rated to f1), the operation mode 2 (f1 to f2), and the operation mode 3 (f2 to 0) are controlled as the rotation speed decreases from the rated rotation. I try to switch. As specific numerical examples of the frequencies f1 and f2, f1 = 44 Hz (= rps), f2 = 8 Hz, and rating = 1000 Hz are set.

  First, an outline of the operation modes 1 to 3 will be described. The operation mode 1 is an operation mode in a rotation region where the back electromotive voltage is sufficiently large and the magnetic pole position can be accurately estimated from the back electromotive voltage. In this operation mode 1, general sensorless rotation control for performing motor control based on the estimated magnetic pole position is performed. That is, the frequency f1 indicates a substantially lower limit value of the rotation frequency at which the normal magnetic pole position can be estimated by the counter electromotive voltage. Note that the magnetic pole position estimation is not discriminated so as to be strictly detectable / impossible at the frequency f1, and can be estimated even at a frequency slightly lower than f1, but it is inferior in reliability. .

  The output voltage of the inverter 100 is repeatedly turned on and off with the amplitude of the power supply voltage (for example, several tens of volts or more) by repeatedly turning on and off the switching element, and the back electromotive voltage is superimposed on the output voltage. On the other hand, in the region where the rotation frequency of the motor rotor 11 is lower than f1, the counter electromotive voltage becomes small, and it becomes difficult to detect the counter electromotive voltage superimposed on the inverter output voltage. Moreover, even if it is detected, it is not reliable. Therefore, in the operation modes 2 and 3 of the present embodiment, the counter electromotive voltage measurement operation different from the operation mode 1 is performed, and the rotation control of the motor rotor 11 is performed based on the measurement result.

  When the rotation frequency is lower than f1, the control unit 102 turns off all the three-phase high-side and low-side switching elements SW1 to SW6 of the inverter 100 shown in FIG. Disconnect the connection. When the connection between the inverter 100 and the motor M is cut off, the motor phase current does not flow, so that only a weak counter electromotive voltage generated in the motor M is detected by the voltage detection unit 103.

  FIG. 5 is a diagram illustrating an example of open section setting. In FIG. 5A, the horizontal axis indicates time, and the vertical axis indicates a voltage application state by the inverter 100. The state indicated as “PWM drive application” in the voltage application state indicates a normal state in which the switching elements SW1 to SW6 are driven on / off (PWM drive). On the other hand, the state indicated as “blocking” indicates a state in which all of the switching elements SW1 to SW6 are turned off. In the open section indicated by the reference symbol T2, a cut-off state is established. On the other hand, in the PWM voltage application section in the (T1-T2) period, a normal PWM drive application state is set. Tpwm is a carrier cycle in PWM control.

  FIG. 5B is a diagram schematically showing phase voltages detected in the PWM voltage application section and the open section. In the PWM voltage application interval, a voltage in which the counter electromotive voltage is superimposed on the PWM modulation rectangular wave voltage applied by the inverter 100 is detected, but only the counter electromotive voltage that changes in a sine wave shape is detected in the open interval T2. The Therefore, voltage detection is performed in this open section T2. The black circle in FIG. 5B indicates the detection timing. The voltage detection in the open section T2 may be performed at least one point. Further, although depending on the arithmetic processing capability in the control unit 102, a plurality of points may be detected and averaged within the same open section T2.

  FIG. 6 is a diagram illustrating a current flowing in one phase of the motor M when the command of FIG. 5A is output. The phase current becomes zero in the open section T2, and the current flows only in the PWM voltage application section (T1-T2).

  By performing such control, it becomes possible to detect a weak counter electromotive voltage in a rotation region lower than the rotation frequency f1, and to perform magnetic pole position calculation.

  Since the counter electromotive voltage detected in the open section described above is proportional to the rotation frequency, it is extremely small in the vicinity of a stationary state where the rotation frequency is very low, and the detection accuracy is essentially poor. Therefore, it is necessary to set the amplification degree high at the detected analog signal stage. On the other hand, in the second half of the rotation frequency range of 0 to f1, where the signal level is not as weak as that in the vicinity of the stationary state, it is not appropriate to increase the amplification degree due to the restrictions on the dynamic range of the AD converter and amplifier.

  The signal amplification gain setting unit 104 shown in FIG. 2 includes an amplification unit and an amplification gain switching unit, and switches the amplification gain according to the rotation frequency at the rotation frequency 0 to f1. Here, the amplification gain is switched in two steps between the frequency range f2 to f1 of the operation mode 2 and the frequency range 0 to f2 of the operation mode 3, and the amplification degree is increased in the operation mode 3 where the back electromotive voltage is weak. If the frequency exceeds f2, the amplification degree is lowered to enter the operation mode 2. Of course, even if the degree of amplification is increased at such a low rotational frequency, it is very difficult to estimate the magnetic pole position in a very low speed state where the rotational frequency is 0 to several Hz. In FIG. 4, the rotation frequency 0 to f0 corresponds to the region where it is difficult to estimate the magnetic pole position.

  Next, a procedure for accelerating from motor start to rated rotation will be described. First, at the time of start-up, a rotating magnetic field is generated at a constant excitation frequency f1, as indicated by a line L21, regardless of the rotational frequency of the motor rotor 11 and the magnetic pole position. The excitation frequency f1 at this time is set to a high frequency that the motor rotor 11 cannot follow in synchronization with the rotation of the magnetic field. In the present embodiment, the lowest frequency f1 is set as the excitation frequency at the start in the frequency range of the operation mode 1 in which the counter electromotive voltage can be reliably detected even when the inverter is driven. Here, since the excitation frequency at the start is the frequency in the operation mode 1, the control in the operation mode 1 is also adopted for the control of the magnetic pole position estimation at the start.

  By the way, when the rotating magnetic field having the frequency f1 is generated, it becomes difficult for the stopped motor rotor 11 to follow the magnetic field. However, an eddy current EC is induced in the metal portion of the motor rotor 11 due to a change in magnetic flux caused by the rotation of the magnetic field with respect to the motor rotor 11. As a result, the motor rotor 11 starts to rotate in the rotation direction of the stator magnetic field on the same principle as the rotor of the induction motor. Line L11 shows the rotational frequency of the motor rotor 11 after starting. In this case, since the rotation is started by the rotational torque generated by the action of the generated eddy current and the rotating magnetic field, the motor rotor 11 does not reversely rotate at the start.

  Next, when a predetermined time t1 has elapsed since the generation of the rotating magnetic field was started at a constant excitation frequency f1, the excitation frequency is reduced to the rotation frequency of the motor rotor 11, and the drive control (synchronous drive) in the operation mode 3 is performed. Start. Line L22 shows the change in excitation frequency after shifting to operation mode 3. The predetermined time t1 at this time is set to a time until the motor rotor 11 becomes a frequency higher than the rotational frequency f0 when a rotating magnetic field having a constant frequency f1 is generated. Therefore, when the predetermined time t1 has elapsed, the magnetic pole position of the motor rotor 11 can be estimated by the magnetic pole position estimation method in the operation mode 3. The predetermined time t1 is determined in advance by actual measurement or the like.

  After that, when the rotation frequency reaches f2, the operation mode 2 (line L23) is shifted to, and the operation mode 1 (line L24) is shifted when (rotation frequency) = f1. When the motor rotor 11 reaches the rated rotational speed, the excitation frequency is kept constant (line L25). That is, after the predetermined time t1 has elapsed, conventional drive control is executed. Lines L12, L13, L14 and line L15 indicate changes in the rotation frequency of the motor rotor 11 during operation mode 3, operation mode 2, operation mode 1, and rated rotation. In addition, since it is difficult to estimate the magnetic pole position in the rotation frequency range 0 to f0 of the operation mode 3, the rotation frequency (line L12) in this range is not displayed.

  When the motor rotor 11 is decelerated from the rated rotation state to the stop state, the motor rotor 11 may be controlled in the order of operation mode 1 → operation mode 2 → operation mode 3, and driving at a constant frequency f1 is omitted.

  In FIG. 4, the start from the stop state has been described. For example, when the stop operation is started and restarted in a short time, such as after an instantaneous power failure, as shown in FIG. It becomes control. When the rotation of the motor rotor 11 at the time of restart is (rotation frequency) ≧ f1, if a rotating magnetic field is generated at a frequency lower than the rotation frequency of the motor rotor 11, regenerative electric power is generated, which may return to the inverter 100 There is. By the way, when the rotational frequency is f1 or more, the magnetic pole position (that is, the rotational frequency) can be accurately estimated from the counter electromotive voltage as described above. Therefore, when the rotational frequency estimated at the start of activation is higher than the frequency f1, the excitation frequency is raised from the frequency f1 to the estimated rotational frequency, and control is performed so that synchronous driving is performed in the operation mode 1.

  On the other hand, when the rotation of the motor rotor 11 at the time of restart is (rotational frequency) <f1, it is difficult to estimate the magnetic pole position of the motor rotor 11 by the position estimation method in the operation mode 1. However, since (excitation frequency f1)> (rotational frequency), regenerative power is not generated. Therefore, as in the case shown in FIG. 4, a rotating magnetic field is generated at a constant excitation frequency f1 for a predetermined time t1, and when the predetermined time t1 has elapsed, the excitation frequency is set to the rotation frequency estimated at that time. Change to the same frequency and start synchronous drive in the operation mode at that frequency.

  FIG. 8 is a flowchart showing the above-described procedure. In step S1, the rotational frequency of the motor rotor 11 is estimated. 4 and 7, the magnetic pole position is estimated by the estimation method in the operation mode 1, and the rotation frequency is calculated from the estimation result. In the case shown in FIG. 4, since the rotational frequency is too small to estimate the rotational frequency by the operation mode 1 estimation method, it is recognized that the rotational frequency is smaller than f1.

  In step S2, it is determined whether or not the estimated rotation frequency is lower than the excitation frequency f1. In the case shown in FIG. 4, since the rotation frequency is determined to be smaller than f1 in step S1, it is determined as yes in step S2, and the process proceeds to step S3. On the other hand, in the case shown in FIG. 7, since (rotational frequency)> f1, it is determined to be no in step S2, and the process proceeds to step S5. Further, as shown in FIG. 4, even in the case of starting in the state of (rotational frequency) <f1, if the rotational frequency becomes equal to the frequency f1 before the predetermined time t1, it is determined as no in step S2 and the process proceeds to step S5.

  In step S3, a rotating magnetic field is generated at a constant excitation frequency f1. In step S4, it is determined whether or not a predetermined time t1 has elapsed from the start of generation of the rotating magnetic field. If it has elapsed, the process proceeds to step S5, and synchronous driving in the normal operation mode is started. On the other hand, if it is determined in step S4 that the predetermined time t1 has not elapsed, the process returns to step S1. Then, the processing from step S1 to step S4 is repeatedly executed until the rotational frequency of the motor rotor 11 becomes f1 or more or until the predetermined time t1 elapses.

  As described above, in order to avoid the generation of regenerative electric power at the time of starting, the constant excitation frequency at the time of starting is set, and the excitation frequency of the rotor at the start of starting is the lowest rotation frequency f1 to which a method of operating at the rated speed can be applied. It is preferable to set the same. Of course, if the rotational frequency can be accurately estimated even when the excitation frequency at startup is lower than f1, the constant excitation frequency at startup may be set to a value lower than f1 (however, within an estimable range). I do not care.

  In the present embodiment, the magnetic pole position can be accurately obtained by generating the open section in the operation mode 2, so that it is theoretically possible to set the frequency f2 to the above-described constant excitation frequency. However, when the rotational frequency at the same time as the restart is close to the frequency at the rated rotation, the open time becomes very short, and it becomes difficult to accurately obtain the back electromotive voltage due to the transient phenomenon. Therefore, in order to prevent the generation of regenerative power, it is not desirable to set the frequency of the operation mode 2 to the above constant excitation frequency.

  As described above, in the present embodiment, when a permanent magnet type synchronous motor is driven, a rotating magnetic field having a frequency that the motor rotor 11 cannot follow synchronously until a predetermined time t1 has elapsed since the start of the motor, that is, a predetermined magnetic field. The motor stator 10 generates a rotating magnetic field having a frequency f1 to perform asynchronous driving, and synchronous driving control is performed after a predetermined time t1 has elapsed. An eddy current EC is generated in the motor rotor 11 by generating a rotating magnetic field having a constant frequency f1 that cannot be followed by the motor rotor 11. As a result, the motor rotor 11 starts to rotate in the same direction as the rotating magnetic field. When synchronous driving is performed after a predetermined time t1 has elapsed, the motor rotor 11 has already been rotated in the direction of the rotating magnetic field (forward rotation direction), so that it can be reliably driven synchronously without reverse rotation.

  Further, by continuing a rotating magnetic field having a constant frequency for a predetermined time, it is not necessary to detect the magnetic pole position in the rotational frequency range 0 to f0 where it is difficult to detect the magnetic pole position.

  Furthermore, the predetermined frequency is set to a constant frequency within the frequency range of the rotational frequency estimated when the inverter is driven, preferably to a constant frequency f1. By setting in such a manner, it is possible to avoid the generation of regenerative power even when the rotational frequency at the time of starting the motor is higher than the predetermined frequency f1. Instead of setting everything between 0 and the predetermined time t1 to the constant frequency f1, the excitation frequency may be lowered halfway as indicated by a two-dot chain line L211 in FIG.

  In addition, when the section of the operation mode 1 in which the magnetic pole position can be reliably detected as shown in FIG. 4 is further divided into two operation modes 1A and 1B as shown in FIG. 9, the predetermined frequency is set to the operation mode 1A. May be set to a frequency in the frequency range, or may be set to a frequency in the frequency range of the operation mode 1B. For example, as the amplitude gain is changed in the operation modes 2 and 3, the gain is changed in the operation modes 1A and 1B.

  Further, the control unit 102 stops the generation of the rotating magnetic field having the predetermined frequency f1 even before the predetermined time t1 has elapsed when the rotational frequency estimated after the start of the motor becomes equal to the predetermined frequency. Start synchronous drive. By controlling in this way, it is possible to appropriately shift from the control for generating the rotating magnetic field of the predetermined frequency f1 to the synchronous driving.

  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, in the embodiment, a magnetic levitation turbo molecular pump has been described as an example. However, the present invention is not limited to a turbo molecular pump and can be similarly applied to a vacuum pump such as a drag pump. Since the torque generated when a rotating magnetic field having a constant frequency is generated is small, the present invention is suitable for application to a magnetic levitation vacuum pump having a small starting torque.

  1: pump unit, 4: pump rotor, 4a: rotating blade, 4b: cylindrical part, 10: motor stator, 11: motor rotor, 100: inverter, 101: current detection part, 102: control part, 103: voltage detection part, 110: Rotor magnet, M: Motor

Claims (5)

An inverter for driving a permanent magnet type synchronous motor;
A counter electromotive voltage detector for detecting a counter electromotive voltage of the permanent magnet type synchronous motor;
An estimation unit that estimates the magnetic pole position and the rotation frequency of the motor rotor based on the back electromotive voltage detected by the back electromotive voltage detection unit;
A control unit for generating a rotating magnetic field in the motor stator based on the estimation result of the estimation unit and controlling the permanent magnet type synchronous motor with sensorless synchronous drive,
The control unit causes the motor stator to generate a rotating magnetic field having a predetermined frequency until a predetermined time has elapsed from the start of the motor to perform asynchronous driving, and performs the synchronous driving control after the predetermined time has elapsed. . The motor drive device according to claim 1,
The motor driving apparatus, wherein the predetermined frequency is set to a constant frequency in a frequency range of a rotation frequency estimated by the estimation unit when the inverter is driven. In the motor drive device according to claim 2,
The frequency range is composed of a first range having a low frequency and a second range having a high frequency, which are different from each other in motor drive control system.
The motor driving apparatus, wherein the predetermined frequency is set to a constant frequency in the second range. In the motor drive unit according to any one of claims 1 to 3,
A determination unit that determines whether or not the rotation frequency estimated by the estimation unit is equal to the predetermined frequency;
When the control unit determines that the determination unit has become equal after the start of motor activation, the motor stops generation of the rotating magnetic field of the predetermined frequency and starts the synchronous drive control even before the predetermined time has elapsed. Drive device. A pump rotor formed with an exhaust function part;
A permanent magnet synchronous motor for rotationally driving the pump rotor;
A vacuum pump comprising: the motor drive device according to claim 1 that drives the permanent magnet type synchronous motor.

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