JP2014079085A - Motor driving device and vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor driving device capable of reducing power loss caused by a ripple current.SOLUTION: A motor driving device generates a sine-wave drive command by a speed control unit 401, an Id and Iq setting unit 402, an equivalent-circuit voltage conversion unit 403, and voltage conversion units 404 and 405, generates a PWM control signal (a PWM drive command) by a PWM signal generating unit 406 on the basis of the sine-wave drive command, and on-off controls a plurality of switching elements SW1 to SW6 on the basis of the PWM control signal. A motor load determination unit 408 calculates a load of a motor M and determines whether the calculated load is a light load. Moreover, when the load is determined less than or equal to a predetermined threshold value, the motor load determination unit 408 controls a switching unit 410 so that the operation that blocks driving currents Iu, Iv, and Iw outputted to the motor M for a predetermined time is repeated.

Description

  The present invention relates to a motor drive device and a 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).

  The turbo molecular pump rotates the rotor at a high speed in order to evacuate as described above, and accelerates by generating a large motor torque to reach the high speed rotation (rated rotation). Also, a large torque is required when a gas load is applied during high-speed rotation. On the other hand, when there is no gas load and a high vacuum is maintained at a predetermined rotational speed (usually the rated rotational speed), the torque is relatively small due to bearing loss and loss associated with permanent magnet rotation of the permanent magnet synchronous motor. Low torque drive that can compete is sufficient.

JP 2001-69784 A

  By the way, when the motor current is controlled by the PWM control, a ripple current is generated by the PWM carrier. When the motor is driven in a sine wave, the current amplitude of the fundamental wave that generates the required torque changes depending on the gas load. However, the amplitude of the ripple current due to the PWM carrier does not change significantly depending on the magnitude of the gas load. Therefore, at the time of low load, the ratio of loss (for example, eddy current loss) due to the ripple current in the power loss increases. Furthermore, since the low load operation time is longer than the gas load operation time, the loss caused by the ripple current cannot be ignored.

A motor drive device according to a first aspect of the present invention includes a sine wave drive command generation unit that generates a sine wave drive command, a PWM drive command generation unit that generates a PWM drive command based on the sine wave drive command, and a PWM drive command An inverter circuit that outputs a driving current generated by turning on and off the plurality of switching elements to the synchronous motor, a load calculation unit that calculates a load of the synchronous motor, and a load A drive current control unit that repeatedly performs an operation of cutting off a drive current input to the synchronous motor for a part period when the load calculated by the calculation unit is equal to or less than a predetermined value.
According to a second aspect of the present invention, in the motor drive device according to the first aspect, the drive current is interrupted in a predetermined section in one cycle of the sine wave drive.
According to a third aspect of the present invention, in the motor drive device according to the first or second aspect, the drive current is cut off by turning off all of the plurality of switching elements to a cut-off state.
The invention according to claim 4 further includes a rotational position computing unit that computes the rotational position of the rotor of the synchronous motor based on information related to the rotation of the synchronous motor in the motor drive device according to claim 2 or 3, The predetermined section is set based on the rotational position calculated by the rotational position calculation unit.
The vacuum pump according to the invention of claim 5 is a rotor having an exhaust function part, a synchronous motor for rotationally driving the rotor, and a motor drive according to any one of claims 1 to 4 for driving the synchronous motor. An apparatus.
A sixth aspect of the present invention is the vacuum pump according to the fifth aspect, further comprising a current detection unit that detects a motor current of the synchronous motor, and the load calculation unit is synchronized based on the motor current value detected by the current detection unit. The motor load is calculated.

  According to the present invention, power loss due to ripple current can be reduced.

FIG. 1 is a diagram illustrating a vacuum pump according to the present embodiment. FIG. 2 is a block diagram showing a schematic configuration of the control unit. FIG. 3 is a diagram illustrating a motor drive control system. FIG. 4 is a block diagram illustrating the sine wave drive control unit 400. FIG. 5 is a diagram illustrating the directions of the d-axis and the q-axis. FIG. 6 is a diagram illustrating the U-phase current (line L1) and the electrical angle θ (line L2). FIG. 7 is a diagram illustrating an example of a phase voltage and a phase current in PWM driving. FIG. 8 is a diagram showing the phase currents Iu, Iv, and Iw with respect to the electrical angle θ, where 0 deg <θ <20 deg, 160 deg <θ <200 deg, 340 deg <θ <360 deg are set as the cut-off section. FIG. 9 is a diagram illustrating another example of the current interrupting configuration.

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

  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 parts, are formed in the pump rotor 4. The pump rotor 4 is fastened to the shaft 5. The rotor unit R is configured by the pump rotor 4 and the shaft 5.

  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 5 is supported in a non-contact manner by magnetic bearings 67, 68 and 69 provided on the base 60. Each magnetic bearing 67, 68, 69 includes an electromagnet and a displacement sensor. The floating position of the shaft 5 is detected by the displacement sensor. Note that the electromagnets constituting the axial magnetic bearing 69 are arranged so as to sandwich the rotor disk 55 provided at the lower end of the shaft 5 in the axial direction. The shaft 5 is rotationally driven by a motor M.

  The motor M is a synchronous motor, and for example, a permanent magnet synchronous 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 5. The motor rotor 11 is provided with a permanent magnet. When the magnetic bearing is not operating, the shaft 5 is supported by emergency mechanical bearings 66a and 66b.

  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 control unit. An AC input from the outside is converted into a DC output (DC voltage) by an AC / DC converter 40 provided in the control unit. The DC voltage output from the AC / DC converter 40 is input to the DC / DC converter 41, and the DC / DC converter 41 generates a DC voltage for the motor M and a DC voltage for the magnetic bearing.

  The DC voltage for the motor M is input to the inverter 43. The DC voltage for the magnetic bearing is input to the DC power supply 42 for the magnetic bearing. The magnetic bearings 67, 68, and 69 constitute a 5-axis magnetic bearing. The magnetic bearings 67 and 68 each have two pairs of electromagnets 46, and the magnetic bearing 69 has a pair of electromagnets 46. The five pairs of electromagnets 46, that is, the ten electromagnets 46, are individually supplied with current from ten excitation amplifiers 45 provided for each of them.

  The control unit 44 is a digital arithmetic unit that controls the motor and the magnetic bearing, and for example, an FPGA (Field Programmable Gate Array) or the like is used. The control unit 44 outputs a PWM control signal for on / off control of a plurality of switching elements included in the inverter 43 to the inverter 43, and each excitation amplifier 45 includes a switching element included in each excitation amplifier 45. PWM control signals for ON / OFF control of the signal are output.

  FIG. 3 is a diagram showing a motor drive control system related to the motor M. As shown in FIG. The motor drive control system includes a sine wave drive control unit 400 and an inverter 43. The inverter 43 includes a plurality of switching elements SW1 to SW6 and a gate drive circuit 430 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. D1 to D6 are free-wheeling diodes. Currents flowing in U, V, and W phase coils provided in the motor stator 10 are detected by current sensors 50U, 50V, and 50W, respectively.

  The sine wave drive control unit 400 generates a PWM control signal for on / off control of the switching elements SW1 to SW6 based on the current values (three-phase currents Iu, Iv, Iw) detected by the current sensors 50U, 50V, 50W. Generate. The gate drive circuit 430 generates a gate drive signal based on the PWM control signal, and turns on / off the switching elements SW1 to SW6. Thereby, a sine wave drive current is supplied to the U, V, and W phase coils.

  In the present embodiment, the rotational speed and the magnetic pole position are estimated based on the motor current detected by the current sensors 50U to 50W. That is, the current sensors 50U to 50W also function as a rotation detection unit that detects information related to the rotation position of the motor rotor 11. In the case of a sensorless motor that does not have a rotation sensor that detects the rotational position of the motor rotor 11 as in the present embodiment, it is common to estimate the rotational speed and magnetic pole position based on the motor current or motor voltage. Is. In the case of a motor having a rotation sensor, the rotation detection unit is a Hall sensor, an inductance sensor, or the like.

  FIG. 4 is a block diagram illustrating the sine wave drive control unit 400. The current sensor 50 corresponds to the current sensors 50U to 50W in FIG. The rotational speed / magnetic pole position estimation unit 407 estimates the rotational speed ω and the magnetic pole position (electrical angle θ) of the motor M based on the three-phase currents Iu, Iv, Iw detected by the current sensor 50.

  The speed control unit 401 performs PI control (proportional control and integral control) based on the difference between the input target rotational speed ω0 and the actual rotational speed ω, and outputs a current command I. Based on the current command I, the Id / Iq setting unit 402 sets the current commands Id and Iq in the dq axis rotation coordinate system. As shown in FIG. 5, the d-axis of the dq-axis rotation coordinate is a coordinate axis with the N pole of the rotating motor rotor 11 as the positive direction. The q-axis is a perpendicular coordinate axis that is advanced 90 degrees with respect to the d-axis, and its direction is the counter electromotive voltage direction.

  The equivalent circuit voltage conversion unit 403 converts the current commands Id and Iq into voltage commands Vd and Vq in the dq axis rotation coordinate system based on the electric equivalent circuit constant of the motor M. Based on the magnetic pole position (electrical angle θ) estimated by the rotation speed / magnetic pole position estimation unit 407, the voltage conversion unit 404 converts the voltage commands Vd and Vq in the dq axis rotational coordinate system to the biaxial fixed coordinate system (α -Β coordinate system) voltage commands Vα and Vβ.

  The electrical angle θ is set to θ = 0 when the magnetic pole N and the phase of the U-phase current coincide with zero. FIG. 6 is a diagram illustrating the U-phase current (line L1) and the electrical angle θ (line L2). In FIG. 6, the horizontal axis indicates time, and the vertical axis indicates the current value (in the case of line L1) and the angle deg (in the case of line L2).

  The voltage converter 405 converts the two-phase voltage commands Vα and Vβ into the three-phase voltage commands Vu, Vv, and Vw. The PWM signal generation unit 406 generates a PWM control signal for turning on / off (conducting or blocking) the six switching elements SW1 to SW6 provided in the inverter 43 based on the three-phase voltage commands Vu, Vv, and Vw. The PWM control signal output from the PWM signal generation unit 406 is input to the inverter 43 via the switching unit 410. The inverter 43 turns on and off the switching elements SW <b> 1 to SW <b> 6 based on the PWM control signal input from the PWM signal generation unit 406 and applies a drive voltage to the motor M.

  FIG. 7 is a diagram illustrating an example of a phase voltage and a phase current in PWM driving. A line L3 indicates a U-phase current, and a line L4 shown above the line L3 indicates a phase voltage applied to the U-phase coil. The phase voltage L4 is a PWM-modulated rectangular wave, and the width (on duty) of the rectangular wave changes sinusoidally. As a result, the U-phase current flowing through the U-phase coil also shows a sinusoidal change. The amplitude of the rectangular wave phase voltage is the voltage value of the DC voltage input to the inverter 43. The fundamental wave amplitude of the U-phase current L3 is A, and a ripple amplitude B is generated corresponding to on / off of the phase voltage L4 (rising and falling of the rectangular wave). This ripple current portion becomes a loss. Although not shown, the same applies to the V phase and the W phase.

  In this embodiment, in order to reduce the loss due to the ripple current, the loss due to the ripple current is performed by repeatedly executing the operation of interrupting the current from the inverter 43 to the motor M for a predetermined time at a light load with a low required torque. Was reduced.

  In the example shown in FIG. 4, the motor load determination unit 408, the off signal generation unit 409, and the switching unit 410 are provided in the sine wave drive control unit 400 to reduce ripple current loss. The motor load determination unit 408 estimates a gas load, that is, a motor load based on the motor current detected by the current sensor 50. Then, the motor load determination unit 408 compares the estimated motor load with a predetermined threshold value and determines whether or not the motor load is a light load. Here, the light load means, for example, a motor load state when the gas load = 0 and the motor rotates at the rated rotation speed. A load slightly larger than the light load is set as a predetermined threshold value. When the motor load determination unit 408 determines that the load is light, when the magnetic pole position (electrical angle θ) estimated by the rotation speed / magnetic pole position estimation unit 407 is within a predetermined electric angle range of one sine wave cycle, The connection is switched from the PWM signal generation unit 406 to the off signal generation unit 409.

  The off signal generator 409 generates a control signal (blocking signal) that turns off (blocks) all the switching elements SW1 to SW6. When switching unit 410 is switched by a signal from motor load determination unit 408, a control signal from off signal generation unit 409 is input to inverter 43, and switching elements SW1 to SW6 are turned off. As a result, all phase currents of the motor M become zero in a predetermined electrical angle range of one sine wave cycle.

  FIG. 8 shows the phase currents Iu, Iv, and Iw with respect to the electrical angle θ, where 0 deg <θ <20 deg, 160 deg <θ <200 deg, and 340 deg <θ <360 deg. In the above-described blocking section, Iu = Iv = Iw = 0. Note that the amplitude of the fundamental wave components of the phase currents Iu, Iv, and Iw increases in order to maintain the torque by an amount corresponding to the cutoff. However, since the ripple amplitude does not substantially change, the loss due to the ripple current is reduced by the amount that the ripple current in the cutoff section is reduced.

  In the example shown in FIG. 4, the control signal input to the inverter 43 is switched by the switching unit 410 from the PWM control signal of the PWM signal generation unit 406 to the cutoff signal of the off signal generation unit 409, thereby generating a cutoff period. did. However, the blocking method is not limited to this. For example, the determination result of the motor load determination unit 408 is input to the PWM signal generation unit 406, and a blocking interval is generated when the PWM signal generation unit 406 generates a PWM control signal. You may do it. Further, as shown in FIG. 9, an output switch (for example, composed of a semiconductor switching element) 52 for interrupting current is provided in the output line (U phase, V phase, W phase) of the inverter 43, and the U phase is set in the interrupting section. You may make it interrupt | block all of an electric current, V phase current, and W phase current.

  Further, the motor load determination unit 408 determines the motor load based on the motor current detected by the current sensor 50, but based on the PWM control signal generated by the PWM signal generation unit 406, whether or not the motor load is a light load. You may make it determine.

  Furthermore, in the example shown in FIG. 8, a predetermined section of one electrical angle cycle is set as a cut-off section, and the current is cut off in the same section of each cycle. However, the method of setting the cut-off section is not limited to this. For example, one cycle may be set as the cut-off section at a rate of once every several cycles.

  As described above, in this embodiment, a sine wave drive command is generated by the speed control unit 401, Id / Iq setting unit 402, equivalent circuit voltage conversion unit 403, and voltage conversion units 404 and 405, and the sine wave drive command is generated. The PWM signal generation unit 406 generates a PWM control signal (PWM drive command) based on the control signal, and turns on / off the plurality of switching elements SW1 to SW6 based on the PWM control signal. The motor load determination unit 408 calculates the load of the motor M and determines whether or not the calculated load is a light load. When the motor load determination unit 408 determines that the load is equal to or less than the predetermined threshold value, the motor load determination unit 408 controls the switching unit 410 so that the operation of cutting off the drive currents Iu, Iv, and Iw output to the motor M for a part of the period is repeated.

  As a result, power loss due to ripple current can be avoided during the cutoff operation, so that the motor loss during light load driving can be reduced by repeatedly executing the cutoff operation.

  As shown in FIG. 8, the cut-off section may be a predetermined section of one cycle of sine wave drive, or may be one of a plurality of cycles. The predetermined section may be variable according to the load of the motor, for example. Further, as a method for shutting off the drive currents Iu, Iv, and Iw, as shown in FIG. 4, a PWM control signal including a shut-off section is input to the inverter 43, and all the switching elements SW1 to SW6 are turned off in the cut-off section. Alternatively, as shown in FIG. 9, all drive currents Iu, Iv, and Iw may be cut off between the inverter 43 and the motor M.

  The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims. For example, in the above-described embodiment, the motor drive device of the magnetic levitation turbo molecular pump has been described as an example. However, the present invention is not limited to this and can be applied to various vacuum pumps that drive the pump rotor with a motor. Further, the present invention is not limited to a vacuum pump, and can be applied to various synchronous motors controlled by sinusoidal driving, rotating in a light load state, and sometimes being used in a heavy load state. it can.

  1: pump unit, 4: pump rotor, 4a: rotating blade, 4b: cylindrical portion, 5: shaft, 10: motor stator, 11: motor rotor, 43: inverter, 44: control unit, 50, 50U to 50W: current sensor 62: fixed blade, 64: screw stator, 400: sine wave drive control unit, 401: speed control unit, 402: Id / Iq setting unit, 403: equivalent circuit voltage conversion unit, 404, 405: voltage conversion unit, 407: Rotation speed / magnetic pole position estimation unit, 408: motor load determination unit, 409: off signal generation unit, 410: switching unit, 430: gate drive circuit, M: motor, R: rotating body unit, SW1 to SW6: switching element

Claims (6)

A sine wave drive command generator for generating a sine wave drive command;
A PWM drive command generator for generating a PWM drive command based on the sine wave drive command;
An inverter circuit that has a plurality of switching elements that are on / off controlled based on the PWM drive command, and that outputs a drive current generated by the on / off of the plurality of switching elements to a synchronous motor;
A load calculation unit for calculating the load of the synchronous motor;
And a drive current control unit configured to repeatedly perform an operation of interrupting the drive current input to the synchronous motor for a part period when the load calculated by the load calculation unit is equal to or less than a predetermined value. The motor drive device according to claim 1,
The drive current control unit is a motor drive device that cuts off the drive current in a predetermined section in one cycle of sinusoidal drive. In the motor drive device according to claim 1 or 2,
The drive current control unit is a motor drive device that cuts off the drive current by turning off all of the plurality of switching elements to a cut-off state. In the motor drive device according to claim 2 or 3,
A rotation position calculation unit that calculates the rotation position of the rotor of the synchronous motor based on information on the rotation of the synchronous motor;
The motor driving device, wherein the predetermined section is set based on a rotational position calculated by the rotational position calculation unit. A rotor formed with an exhaust function part;
A synchronous motor for rotationally driving the rotor;
A vacuum pump comprising: the motor driving device according to claim 1 that drives the synchronous motor. The vacuum pump according to claim 5,
A current detection unit for detecting a motor current of the synchronous motor;
The said load calculating part is a vacuum pump which calculates the load of the said synchronous motor based on the motor electric current value detected by the said electric current detection part.

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