JP3390797B2 - Motor control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a three-phase AC motor such as a three-phase high frequency motor.

[0002]

2. Description of the Related Art As a control device for a three-phase high frequency electric motor built in a magnetic bearing spindle of a machine tool, a device provided with an inverter is known.

[0003]

When a three-phase high-frequency motor is rotated at a high speed by using the control device as described above, output unevenness in the motor is caused by variations in windings among the three phases of the motor, imbalance of inverter output, etc. Uneven rotation) may occur.

Under the influence of this output unevenness, the rotor of the electric motor may swing around in the radial direction. When such an electric motor is used for a spindle of a machine tool, whirling causes a decrease in machining accuracy. In particular, when a magnetic bearing is used as the bearing of the rotor, whirling may become large, which is an obstacle to maintaining the machining accuracy.

As a countermeasure, it is considered to connect a three-phase transformer between the inverter and the electric motor to balance the output unevenness between the three phases of the electric motor.

Further, when stopping the high frequency motor, generally, the frequency of the inverter output is first gradually lowered to a predetermined frequency so that the inertia energy held by the high frequency motor or the load becomes an induction generator operation. The high-frequency motor converts the electric energy into electric energy and returns it to the inverter, and the resistance in the inverter causes heat conversion to perform regenerative braking to reduce the rotation speed of the high-frequency motor to a predetermined rotation speed. Further, when the inverter detects that the number of rotations has reached a predetermined value, it stops regenerative braking and supplies a direct current to the high-frequency motor to create a static magnetic field, and the rotor cuts off this magnetic flux to rotate. The high-frequency motor is completely stopped in a short time by performing DC braking in which a eddy current is generated in the child to perform braking.

However, when the transformer is connected as described above, the regenerative braking performance during deceleration is deteriorated, and the transformer does not pass a DC voltage. Therefore, the braking does not work particularly in the DC braking region, and the free-run state occurs. However, there is a problem that the time required for braking becomes long.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a control device for an electric motor that can reduce rotational unevenness during rotation and can obtain sufficient braking performance during deceleration.

[0009]

In a motor control device according to the present invention, a three-phase transformer and a switching means are provided between a three-phase AC motor and an inverter for supplying a control current thereto. The switching means connects the electric motor and the inverter through the three-phase transformer without directly connecting them at the time of starting the electric motor and during steady rotation, and connects the electric motor and the inverter directly when decelerating the electric motor. It is characterized by what is done.

For example, the three-phase transformer is provided between the output terminal of the inverter and the input terminal of the electric motor, the switching means is provided in parallel with the three-phase transformer, and the switching means is During start-up and steady rotation of the electric motor, by disconnecting the input / output terminals of the three-phase transformer, the electric motor and the inverter are connected directly via the three-phase transformer, and the electric motor is decelerated. Is configured to directly connect the electric motor and the inverter by short-circuiting the input and output terminals of the three-phase transformer.

Further, for example, the rotating shaft of the electric motor is
It is supported by magnetic bearings in a radial and axial direction in a non-contact manner.

[0012]

When the motor is started and rotating, the motor and the inverter are not directly connected but are connected via the three-phase transformer. Therefore, the control current from the inverter is supplied to the motor through the three-phase transformer, and Since the output unevenness between the three phases is balanced, the rotation unevenness is reduced. Therefore, whirling of the rotor is reduced.

During deceleration of the electric motor, since the electric motor and the inverter are directly connected to each other, regenerative braking in which the regenerative current from the electric motor is directly supplied to the inverter and / or DC braking in which control current from the inverter is directly supplied to the electric motor are performed. It is possible to secure the same braking performance as the conventional one.

A three-phase transformer is provided between the output terminal of the inverter and the input terminal of the electric motor, and switching means is provided in parallel with the three-phase transformer. The switching means is provided during starting of the electric motor and during steady rotation. By disconnecting the input and output terminals of the three-phase transformer, the motor and inverter are not directly connected, but connected via the three-phase transformer.
When the motor and the inverter are directly connected by short-circuiting the input and output terminals of the phase transformer, it is sufficient to disconnect the input and output terminals of the three-phase transformer during starting and steady rotation of the motor. By a simple operation, the electric motor and the inverter are not directly connected but are connected via a three-phase transformer, and the control current from the inverter is supplied to the electric motor via the three-phase transformer. The electric motor and the inverter are directly connected to each other by a simple operation of short-circuiting between the output terminals, the regenerative current from the electric motor is directly supplied to the inverter, and the control current from the inverter is directly supplied to the electric motor.

When the rotating shaft of the electric motor is supported by the magnetic bearings in the radial direction and the axial direction in a non-contact manner, the effect of reducing the output unevenness and the whirling thereof is particularly great.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a magnetic bearing spindle of a machine tool will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of a main part of a magnetic bearing spindle of a machine tool to which a motor control device according to the present invention is applied. FIG. 2 shows a schematic configuration of a main part of a control device for a high frequency electric motor.

In FIG. 1, the main shaft (12) is arranged in the housing (11) of the magnetic bearing spindle in the radial direction (X in the drawing,
Radial electromagnet (13) magnetically and non-contactly supported in the Y direction)
, The axial electromagnet (14) magnetically and non-contactally supported in the axial direction (Z direction in the figure), the radial position sensor (15) for detecting the radial position of the main shaft (12), and the axial position. Axial position sensor to detect (16)
And a stator (17) which is combined with the main shaft (12) to form a three-phase high frequency electric motor (1). The radial control device (18) controls the current supplied to the radial electromagnet (13) based on the output signal of the radial position sensor (15). The axial control device (19) controls the current supplied to the axial electromagnet (14) based on the output signal of the axial position sensor (16). The high frequency motor controller (20) controls the rotation and stop of the spindle (12) based on the spindle control signal from the NC controller (21) that controls the operation of the entire machine tool (rotation and stop of the spindle). .

In the housing (11), in addition to the above structure,
Touchdown bearing (22) that mechanically supports the spindle (12) instead of the magnetic bearing when the spindle (12) is stopped, and a rotation speed sensor that detects the rotation speed of the spindle (12) and outputs it to the control device (20). (23) etc. are provided. A machining tool (24) is fixed to the tip of the main shaft (12) so that the workpiece (25) can be machined.

An example of the structure of the high-frequency motor controller (20) for the magnetic bearing spindle as described above will be described in detail with reference to FIG.

In FIG. 2, a three-phase transformer (3) and a switching means are formed between the stator (17) of the three-phase high frequency motor (1) and the inverter (2) for supplying a control current to the stator (17). A switching device (4) is provided. Transformer (3)
Is connected between the three-phase output terminal (5) of the inverter (2) and the three-phase input terminal (6) of the stator (17) of the electric motor (1). The electric motor (1), the inverter (2) and the transformer (3) themselves are known ones. Although not shown in the figure, the inverter (2) uses a resistor for thermally converting the electric power generated by the electric motor (1) during regenerative braking, and the main shaft (12), that is, the electric motor, based on the output signal of the rotation speed sensor (23). A DC brake is provided which detects that the rotation speed of (1) has dropped to a predetermined value and supplies a DC current to the stator (17) of the electric motor (1). Further, the inverter (2) is connected to the commercial power source via the converter.

The switching device (4) is connected in parallel to the transformer (3) and comprises three switches (7) respectively connected between the corresponding phases of the input side and the output side of the transformer (3). ing. The switches (7) are operated in conjunction with each other and when the switches (7) are turned on (closed), the transformer
Between the input terminal (8) and the output terminal (9) of (3), that is, the output terminal (5) of the inverter (2) and the stator (1) of the motor (1).
The input terminal (6) of 7) is short-circuited and the switch (7) is turned off (open state), so that the input terminal (8) and the output terminal (9) of the transformer (3) are disconnected. Be cut off. switch
(7) is controlled based on the rotation state of the electric motor (1) by a signal from the other part of the control device (20), and is turned off at the start of the electric motor (1) and during the rotation of the electric motor (1). It is switched on during deceleration. For example, the switch (7) is controlled by the spindle stop signal and is switched on after the stop signal is turned on until the spindle actually stops, and is turned off otherwise.

During start-up and rotation of the electric motor (1), the stop signal is off and the switch (7) is off.
Therefore, the input terminal (8) and output terminal (9) of the transformer (3)
Since the motor (1) and the inverter (2) are not directly connected to each other via the transformer (3), the control current from the inverter (2) passes through the transformer (3). Supplied to the electric motor (1). Then, since the output unevenness between the three phases of the electric motor (1) is balanced by the transformer (3), the rotational unevenness is reduced.

During deceleration of the electric motor (1), first, the stop signal is turned on. This turns on the switch (7), short-circuiting the output terminal (5) of the inverter (2) and the input terminal (6) of the motor (1), and the motor (1) and the inverter (1).
(2) is directly connected. Then, as described above, first, regenerative braking is performed in which the output frequency of the inverter (2) is gradually reduced, and then direct current from the inverter (2) is directly supplied to the electric motor (1). Be seen. Therefore, the same braking performance as the conventional one can be ensured, and in particular, the DC braking does not work and the free-running state does not increase the braking time.

The configuration of the switching means is not limited to that of the above embodiment, but can be changed as appropriate.

In the above embodiment, the inverter that performs regenerative braking and DC braking in combination during braking is used, but it is also possible to use an inverter that performs only regenerative braking.
Further, in the above embodiment, the switch (7) is switched by the signal in the control device (20), but this may be performed by a signal from the outside such as the NC control device (21). Alternatively, it may be operated manually.

[0027]

According to the motor control device of the present invention,
As described above, it is possible to reduce uneven rotation during rotation, obtain sufficient braking performance during deceleration, and prevent a long braking time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part of a magnetic bearing spindle of a machine tool to which a motor control device according to the present invention is applied.

FIG. 2 is a schematic configuration diagram of a main part showing an example of a control device for the electric motor of FIG.

[Explanation of symbols]

(1) Three-phase high frequency motor (2) Inverter (3) Three-phase transformer (4) Switching device (switching means) (5) Inverter output terminal (6) High frequency motor stator input terminals (7) Switch (8) 3-phase transformer input terminal (9) Output terminal of 3-phase transformer (20) High frequency motor controller

Continuation of the front page (56) References JP-A-57-170034 (JP, A) JP-A-5-262469 (JP, A) Actual development Sho-59-185998 (JP, U) (58) Fields investigated (Int .Cl. ⁷ , DB name) H02P 3/18 101 H02P 7/63

Claims (3)

(57) [Claims] 1. A three-phase transformer and a switching means are provided between a three-phase AC motor and an inverter for supplying a control current to the three-phase AC motor. The control device for the electric motor is characterized in that the electric motor and the inverter are not directly connected to each other via the three-phase transformer, but the electric motor and the inverter are directly connected to each other when the electric motor is decelerated. . 2. The three-phase transformer is provided between the output terminal of the inverter and the input terminal of the electric motor.
The switching means is provided in parallel with the phase transformer, and the switching means shuts off the input and output terminals of the three-phase transformer during startup and during steady rotation of the electric motor, whereby the electric motor and the inverter. The above 3 without directly connecting
Connection via a phase transformer, and during deceleration of the electric motor, by short-circuiting the input and output terminals of the three-phase transformer,
The control device for the electric motor according to claim 1, wherein the electric motor and the inverter are directly connected. 3. The control device for the electric motor according to claim 1, wherein the rotating shaft of the electric motor is supported by a magnetic bearing in a non-contact manner in the radial direction and the axial direction.