JP7367498B2 - Vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump.

Axial flow vacuum pumps such as turbomolecular pumps rotate a pump rotor at high speed to perform vacuum evacuation. At this time, the pump rotor rotates in only one direction because the diluted gas is exhausted while performing compression work. Therefore, the pump rotor normally accelerates and decelerates between a stationary state and a normal rotation region, and performs steady rotation.

As a motor that rotationally drives the pump rotor, for example, a synchronous motor having a permanent magnet in its rotor is used. Generally, in a vacuum pump, when controlling a synchronous motor by vector control, control is applied in which the excitation current vector component Id is set to Id=0. During acceleration, Iq>0 is set, and during deceleration, Iq<0. During deceleration when Iq<0, the controller receives power from the motor and generates electricity. The generated electric power is consumed by a brake resistor provided in the controller to perform a brake operation on the motor (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2016-145555

Generally, during brake operation, the inverter voltage increases due to power generation, so the q-axis current Iq is controlled while monitoring the inverter voltage so that the inverter voltage does not exceed the rated voltage of the electronic components. However, the inverter voltage may become unstable during Iq control during brake operation, and there is a risk that the Iq control may not be able to respond to the sudden increase in inverter voltage caused by the instability phenomenon, causing the inverter voltage to exceed the rated voltage. Ta.

A vacuum pump according to an aspect of the present invention includes a pump rotor, a motor that rotationally drives the pump rotor, a motor control unit that controls the motor, and a brake resistor that consumes regenerated power generated during braking operation of the motor. The motor control unit sets a voltage command vector during a brake operation such that a ratio between a d-axis component and a q-axis component of the voltage command vector is constant.

According to the present invention, it is possible to prevent overvoltage of the inverter voltage during braking operation.

FIG. 1 is a block diagram showing a schematic configuration of a vacuum pump. FIG. 2 is a block diagram showing the motor drive control system. FIG. 3 is a diagram showing a conventional example of inverter voltage during brake operation. FIG. 4 is a diagram showing an example of inverter voltage during brake operation in this embodiment.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a vacuum pump 1. As shown in FIG. The vacuum pump 1 is a magnetic bearing type turbomolecular pump, and includes a pump body 1A provided with a pump rotor 10, and a controller 1B that drives and controls the pump body 1A.

The pump rotor 10 is fastened to a rotating shaft 11. The rotating shaft 11 is magnetically supported by a magnetic bearing (MB) 12 and rotationally driven by a motor (M) 13. When not energized, the rotating shaft 11 is supported by a protective bearing 14 such as a mechanical bearing. Although not shown, the pump body 1A is provided with a pump stator relative to the pump rotor 10.

AC power from a commercial power source 2 is supplied to the controller 1B. The input AC power is converted into DC power by the AC/DC converter 20. A three-phase inverter 21 is connected to a DC line on the output side of the AC/DC converter 20. The three-phase inverter 21 converts the DC power supplied from the AC/DC converter 20 into AC power, and drives the motor 13. The three-phase inverter 21 is controlled by a motor control unit 221 provided in the control unit 22 so that AC power at a frequency necessary for rotating the motor 13 is output. The motor 13 is a sensorless permanent magnet synchronous motor, and the motor rotor is provided with a permanent magnet.

The DC/DC converter 23 steps down the voltage of the DC power from the DC line and supplies it to the control unit 22 . The control unit 22 is a digital computing unit that controls the magnetic bearing 12 and the motor 13, and includes, for example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output interface (I/O). It consists of a microcomputer equipped with an FPGA (Field Programmable Gate Array), etc.

A bearing control unit 222 provided in the control unit 22 controls the drive of the magnetic bearing 12 provided in the pump body 1A. The magnetic bearing 12 is provided with a displacement sensor (not shown) that detects displacement of the rotating shaft 11. The bearing control unit 222 controls the driving power of the magnetic bearing 12 based on the detection information of the displacement sensor so that the rotating shaft 11 is supported in a desired position in a non-contact manner.

When stopping the rotation of the pump rotor 10, the three-phase inverter 21 is regeneratively controlled and the rotation is decelerated by a regenerative brake. Therefore, a series circuit including a brake resistor 24 and a switch element (transistor, etc.) 25 is provided in parallel to the three-phase inverter 21 in the DC line. On/off of the switch element 25 is controlled by a motor control section 221. During regenerative braking, the switch element 25 is turned on, and the regenerative power is consumed by the brake resistor 24. A diode 26 for preventing backflow of regenerated power is provided in the DC line.

Further, when the power supply from the commercial power supply 2 is stopped due to a power outage or the like, regenerated power is input to the DC/DC converter 23. As a result, the motor control section 221 and the bearing control section 222 are operated by the regenerated power, and the magnetic levitation of the rotating shaft 11 is maintained by the regenerated power. Note that when supplying regenerated power to the motor control section 221 and the bearing control section 222, the switch element 25 is turned off.

FIG. 2 is a diagram showing a motor drive control system regarding the motor 13. The motor drive control system includes a motor control section 221 provided in the control section 22, a current detector 50, a voltage detector 51, etc. that are not shown in FIG. Although not shown, the three-phase inverter 21 includes a plurality of switching elements and a gate drive circuit for turning them on and off. The currents flowing through the U, V, and W phase coils of the motor 13 are detected by the current detectors 50, and the current detection signals as the detection results are sent to the rotational speed/magnetic pole position estimation unit 407 of the motor control unit 221 via the low-pass filter 409. is input. In addition, the voltages at each terminal and the neutral point of the U, V, and W phase coils are detected by a voltage detector 51, and the voltage detection signal as a detection result is sent to the motor control unit 221 through a low-pass filter 410 for the rotational speed and magnetic pole. It is input to the position estimation section 407.

The rotation speed/magnetic pole position estimation unit 407 estimates the rotation speed ω and the magnetic pole position (electrical angle θ) of the motor rotor based on the current detection signal and the voltage detection signal. Note that since the magnetic pole position of the motor rotor is expressed by an electrical angle θ, the magnetic pole position will be referred to as the magnetic pole electrical angle θ below. The calculated rotational speed ω is input to the speed control section 401, the Id/Iq setting section 402, and the equivalent circuit voltage conversion section 403. Further, the calculated magnetic pole electrical angle θ is input to the dq-two-phase voltage converter 404.

The speed control unit 401 performs PI control (proportional control and integral control) or P control (proportional control) based on the difference between the input target rotation speed ωi and the estimated current rotation speed ω, and generates a current command. Outputs I. The Id/Iq setting unit 402 sets the excitation current vector component (hereinafter referred to as q-axis current) Iq and the torque current vector component (hereinafter referred to as d-axis current) Id in the rotating coordinate dq system based on the current command I. do. The d-axis of the rotating coordinate dq system is a coordinate axis whose positive direction is the north pole of the rotating motor rotor. The q-axis is a coordinate axis in a perpendicular direction leading by π/2 [rad] with respect to the d-axis, and its direction is the direction of the back electromotive force during forward rotation.

Generally, in motor control in a turbomolecular pump, the d-axis current Id is controlled such that Id=0. In this embodiment, during acceleration or steady rotation except during brake operation, the equivalent circuit voltage converter 403 converts the rotation sensorless control parameters Ke [V0-pk/(rad/t)], r [Ω], L [mH], find the voltage command vector (Vd, Vq) in the rotating coordinate dq system expressed by the following equations (1) and (2), and convert it to the dq-2 phase voltage converter. 404.
Vd=-ω×L×Iq…(1)
Vq=r×Iq+Ke×ω…(2)

The dq-2 phase voltage conversion unit 404 converts voltage commands Vd, Vq in the rotational coordinate dq system based on the voltage command vector (Vd, Vq) and the magnetic pole electrical angle θ input from the rotational speed/magnetic pole position estimation unit 407. is converted into voltage commands Vα and Vβ of a fixed coordinate αβ system. A two-phase to three-phase voltage converter 405 converts two-phase voltage commands Vα and Vβ into three-phase voltage commands Vu, Vv, and Vw. The PWM signal generation unit 406 generates a PWM control signal for turning on and off (conducting or cutting off) the switching elements provided in the three-phase inverter 21 based on the three-phase voltage commands Vu, Vv, and Vw. The three-phase inverter 21 turns on and off the switching elements based on the PWM control signal input from the PWM signal generation section 406, and applies a drive voltage to the motor 13.

(Explanation of brake operation)
As described above, voltage commands Vd and Vq during acceleration and steady rotation are given by equations (1) and (2). On the other hand, during a brake operation to stop rotation, in this embodiment, voltage commands Vd and Vq as shown in the following equations (3) and (4) are input to the dq-2 phase voltage converter 404, and the 3-phase The inverter 21 is controlled for regeneration. Here, r is the winding resistance of the entire motor wire, Ke is the back electromotive force constant, and the angular frequency of the ω motor.
Vd=0...(3)
Vq=r×Iq+Ke×ω…(4)

When power is generated by the motor 13 under regeneration control, current returns from the motor 13 to the inverter side, and the inverter voltage (voltage on the DC line side of the three-phase inverter 21) increases. Then, when the inverter voltage rises to a predetermined value, the switch element 25 is brought into conduction, allowing current to flow through the brake resistor 24 and consuming power. During braking, if the inverter voltage increases too much due to power generation by the motor 13 and exceeds the rated voltage of the electronic components forming the controller 1B, there is a risk of damaging them. Therefore, the q-axis current Iq is controlled while monitoring the inverter voltage so that the inverter voltage does not rise too much.

The present embodiment is characterized in that the voltage command Vd is set to Vd = 0 as described above, but conventionally, the brake operation is performed by controlling the q-axis current Iq according to equations (1) and (2). is common. The parameters Ke, r, and L in equations (1) and (2) are currently adjusted to the values of the motor 13 of the actual machine. However, the parameters Ke and L have a characteristic that they change depending on the rotational speed ω of the motor 13. Therefore, the values of parameters Ke and L, which are assumed to be constant values in equations (1) and (2), actually change as the q-axis current Iq is controlled, causing the inverter voltage to change unstablely. .

FIG. 3 is a diagram showing an example of the inverter voltage when a brake operation is performed based on equations (1) and (2). Brake operation is started at t=t1. Since the values of the parameters Ke and L change according to the rotational speed ω, the following processes (a) to (d) are repeated, resulting in a voltage waveform as shown in FIG. 3.
(a) In order to increase the inverter voltage, the value |Iq| of the q-axis current Iq=-|Iq| is increased. When |Iq| is small, the voltage command Vd is also small and regeneration efficiency is poor (t=t2).
(b) When |Iq| is further increased to raise the inverter voltage, the voltage command Vd increases and the regeneration efficiency improves (t=t3).
(c) Since the inverter voltage rises rapidly (region A), |Iq| is reduced to prevent overvoltage.
(d) As shown in region B, the inverter voltage decreases.

In FIG. 3, the brake is difficult to apply in the section C where the inverter voltage repeatedly increases and decreases, so the deceleration time becomes longer. Further, if the inverter voltage cannot cope with a sudden increase in the inverter voltage, there is a risk that the inverter voltage will exceed the rated voltage of the electronic components.

On the other hand, when brake control is performed based on equations (3) and (4) as in this embodiment, the inverter voltage changes as shown in FIG. The braking operation is started at t=t1, the inverter voltage begins to increase from approximately t=t11, and becomes stable after t=12. The instability of the inverter voltage in Iq control as shown in Figure 3 is caused by the fact that the electrical angle of the voltage command vector (Vd, Vq) fluctuates due to changes in Ke and L when |Iq| is increased. This is thought to be the cause. In this embodiment, by setting Vd=0 as in equation (3), fluctuations in the electrical angle of the voltage command vector (Vd, Vq) during Iq control are prevented, and stability as shown in FIG. 4 is achieved. It becomes possible to control the inverter voltage to a certain value. As a result, it is possible to prevent overvoltage of the inverter voltage during braking operation, and it is also possible to shorten the deceleration time.

In addition, as a method of preventing fluctuations in the electrical angle of the voltage command vector (Vd, Vq) in Iq control, more generally, the ratio of the d-axis component Vd and the q-axis component Vq of (Vd, Vq) is It may also be set such that Vd/Vq=constant. This means that the following equation (5) using D=constant is used instead of equation (3). Setting the voltage command Vd=0 corresponds to the case where D=0.
Vd=D×(r×Iq+Ke×ω)…(5)

It will be appreciated by those skilled in the art that the exemplary embodiments and variations described above are specific examples of the following aspects.

[1] A vacuum pump according to one embodiment includes a pump rotor, a motor that rotationally drives the pump rotor, a motor control unit that controls the motor, and a brake resistor that consumes regenerative power generated during brake operation of the motor. In the vacuum pump provided, the motor control unit sets a voltage command vector during brake operation so that the ratio of the d-axis component and the q-axis component of the voltage command vector is constant. By setting the ratio of the d-axis component and the q-axis component of the voltage command vector to a constant value, fluctuations in the electrical angle of the voltage command vector (Vd, Vq) during Iq control are prevented, and the inverter voltage is controlled to be stable. becomes possible. As a result, it is possible to prevent overvoltage of the inverter voltage during braking operation, and it is also possible to shorten the deceleration time.

[2] In the vacuum pump according to [1] above, the motor control unit may set the d-axis component of the voltage command vector to Vd=D×(r×Iq+Ke×ω) during brake operation. . Here, Ke is a back electromotive force constant, r is the winding resistance of the entire motor wire, ω is the angular frequency of the motor, and D is a constant. Vq during brake operation is controlled as Vq=r×Iq+Ke×ω, so by setting Vd=D×(r×Iq+Ke×ω), the d-axis component and q-axis component of the voltage command vector can be The ratio of is constant.

[3] In the vacuum pump according to [1] or [2] above, the motor control unit sets the d-axis component of the voltage command vector to zero during a braking operation. When setting the ratio of the d-axis component Vd and the q-axis component Vq of the voltage command vector to a constant value, it is necessary to adjust the two voltage commands Vd and Vq so that "Vd/Vq = constant" is satisfied. , here, since the voltage command Vd is set to Vd=0, control becomes simpler.

[4] In the vacuum pump according to any one of [1] to [3] above, the motor control unit sets the q-axis component of the voltage command vector to Vq=r×Iq+Ke×ω during brake operation. You may also do this.

Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments considered within the technical spirit of the present invention are also included within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1...Vacuum pump, 1A...Pump body, 1B...Controller, 10...Pump rotor, 11...Rotating shaft, 13...Motor, 21...3-phase inverter, 22...Control unit, 24...Brake resistor, 25...Switching element, 221 ...Motor control unit, Id...d-axis current, Iq...q-axis current, Vd, Vq...voltage command

Claims (4)

pump rotor,
a motor that rotationally drives the pump rotor;
a motor control unit that controls the motor;
A brake resistor that consumes regenerated power generated when the motor brakes,
In the vacuum pump, the motor control unit sets a voltage command vector during brake operation in regeneration control so that a ratio of a d-axis component to a q-axis component of the voltage command vector is constant. The vacuum pump according to claim 1,
The motor control unit is a vacuum pump that sets the d-axis component of the voltage command vector to Vd=D×(r×Iq+Ke×ω) during brake operation. Here, Ke is a back electromotive force constant, r is the winding resistance of the entire motor wire, ω is the angular frequency of the motor, and D is a constant. The vacuum pump according to claim 1 or 2,
The motor control unit is a vacuum pump that sets a d-axis component of the voltage command vector to zero during a brake operation. The vacuum pump according to any one of claims 1 to 3,
The motor control unit is a vacuum pump that sets the q-axis component of the voltage command vector to Vq=r×Iq+Ke×ω during brake operation.

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