JPH10164882A - Method and apparatus for control of induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus, in which a power consumption is reduced, and in which the operation time of a warming-up operation is shortened. SOLUTION: The frequency of a primary current at an induction motor is set to be high to such an extent that a slip becomes a value close to one and that a rotor is not vibrated even when the direction of rotation of a rotating magnetic field is changed alternately. A current instruction is set in such a way that the primary current which is sufficient to positively heat a stator by a copper loss and an iron loss flows. The direction of rotation of the rotating magnetic field is changed in such a way that the rotor is held in a substantially stopped state, and a warming-up operation is executed so as to be shifted to an ordinary operation after the warming-up operation has been finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor for performing a normal operation after a warm-up operation for increasing the temperature of a processing portion of a machine attached to an output shaft of an induction motor without substantially rotating a rotor. The present invention relates to an electric motor control method and apparatus.

[0002]

2. Description of the Related Art In a machine tool or the like that requires high machining accuracy, such as a numerically controlled machine tool, at the stage of starting machining, particularly the machined portion of the machine is sufficiently warm and is thermally saturated. It is necessary. Therefore, conventionally, a dummy operation called a warm-up operation in which an electric motor used as an electric source of a machine tool is rotated for a predetermined time and heat generated from the electric motor is transmitted to a machined portion of the machine has been implemented. In the conventional warm-up operation method, the same normal operation (operation of rotating the rotor) as in the case of performing the machining is performed for a certain period of time to increase the temperature of the machined portion of the machine.

[0003]

As in the prior art, when the rotor of the electric motor is rotated, energy for rotating the rotor is required, and there is a problem that wasteful power is used for the warm-up operation. . In addition, when the warm-up operation is performed using an electric motor having a large heat capacity, it takes time to increase the temperature of the electric motor, and there is a problem that the time required to actually start machining is considerably long. For example, in a self-cooling motor that cools the motor by fixing a fan to the rotor,
The heat capacity of the stator is small due to the forced cooling by the fan. On the other hand, in a so-called fanless motor without a cooling fan, the heat capacity is increased by increasing the thickness of the iron core of the stator by that much to suppress the temperature rise of the motor due to natural heat radiation. I have. Therefore, in such an electric motor having a large heat capacity, it takes a considerable time to raise the temperature of the electric motor (particularly, the stator) to bring the machined portion of the machine tool to heat saturation. For example, even when a continuous rated current is applied, there is a problem that it takes 5 to 6 hours to reach thermal saturation.

An object of the present invention is to provide a control method and apparatus for an induction motor that can reduce unnecessary power consumption and shorten the operation time of a warm-up operation as compared with the related art.

An object of the present invention is to provide a method and apparatus for controlling an induction motor, in which the temperature of the induction motor can be quickly increased without substantially rotating the rotor during the warm-up operation, thereby shortening the warm-up operation time. It is in.

Another object of the present invention is to provide a method and apparatus for controlling an induction motor in which energy required for rotation of the rotor is utilized for raising the temperature of the induction motor without substantially rotating the rotor during warm-up operation. To provide.

Another object of the present invention is to provide a control method and apparatus for an induction motor in which it is easy to determine the completion of a warm-up operation.

Another object of the present invention is to provide a control device for an induction motor capable of performing a warm-up operation using an existing primary current vector calculator.

[0009]

According to the method of the present invention, a rotating magnetic field is created by supplying an alternating current of a predetermined frequency as a primary current to a winding wound on a stator, and the primary current is controlled by using a current feedback loop. The object of the present invention is to improve an induction motor control method in which an induction motor is controlled by performing feedback control on a current according to a current command.

In the present invention, first, even if the slip [(rotational speed of rotating magnetic field-rotating speed of rotor) / rotating speed of rotating magnetic field] is close to 1, and the rotating direction of the rotating magnetic field is alternately changed. The frequency of the primary current is set high enough that the rotor does not vibrate. Ideally, one slip
However, as long as the rotating magnetic field exists, a slight rotational torque is generated in the rotor, and the rotor tends to rotate. Therefore, the “value close to 1” is a slip value in a state where the rotation of the rotor is suppressed, and varies depending on the frequency of the primary current and the reversal timing of the rotating magnetic field. Further, the requirement of “to the extent that the rotor does not vibrate even when the rotating direction of the rotating magnetic field is changed” is a requirement for enabling control to keep the rotor substantially stopped. Considering these points, the preferred frequency of the primary current is about five times or more the rated frequency and less than the response frequency of the current feedback loop in the case of a three-phase induction motor. At a frequency lower than approximately 5 times the rated frequency, it is difficult to control the rotor to be stopped, and at a frequency higher than the response frequency of the current feedback loop, it is difficult for the primary current to flow, thereby increasing the amount of heat generated by the motor. Because it becomes difficult.

In the present invention, the current command is set so that a primary current sufficient to actively heat the stator due to the copper loss and the iron loss flows. As the current value of the primary current increases, the amount of generated heat increases, but the current value is limited by the capacity of the winding. Therefore, it is preferable to set the current command so that the effective value of the primary current is substantially equal to the rated effective value of the primary current of the induction motor.

In the present invention, the warming-up operation is performed by changing the rotating direction of the rotating magnetic field so as to keep the rotor substantially stopped, and after the warming-up operation is completed, the normal operation is started. If the rotation torque is small, a slight rotation of the rotor is detected, and the rotation direction of the rotating magnetic field is alternately reversed, so that the rotor can be kept substantially stopped. The reversal timing of the rotating magnetic field may be determined by detecting the rotating speed of the output shaft of the induction motor and changing the rotating direction of the rotating magnetic field when the rotating speed reaches a predetermined value. The rotation speed can be detected using, for example, an encoder. Here, the "predetermined value" differs depending on the frequency of the primary current, but a value of 50 rpm or less is appropriate. The direction of rotation of the rotating magnetic field can be easily changed by changing the order of excitation of the primary winding.

In the present invention, by increasing the frequency of the primary current and increasing the value of the primary current, the iron loss and the copper loss are increased to cause the stator to generate heat. At that time,
Since the direction of the rotating magnetic field is repeatedly reversed so as not to substantially rotate the rotor, the energy required for the rotation of the rotor can be used for heat generation of the stator. As a result, wasteful power consumption is reduced, the temperature rise of the induction motor is accelerated, and the warm-up operation time can be shortened as compared with the related art.

A control device for an induction motor that implements the method of the present invention includes an inverter circuit for generating a rotating magnetic field by supplying an alternating current of a predetermined frequency as a primary current to a winding wound on a stator, and the inverter circuit. And an inverter drive signal generating circuit for outputting an inverter drive signal.
A primary current vector calculator for inputting a primary current angle signal obtained by time-integrating a torque current command, an excitation current command, and a primary current angular velocity signal with a time integrator, and outputting a primary current command signal; And a current feedback loop that detects a primary current and feeds back a primary current detection signal in order to perform feedback control of the current.

[0015] The apparatus of the present invention comprises: an operation mode determining means;
A warm-up operation signal generating unit and a mode switching unit are provided. The operation mode determination means determines whether to control in the warm-up operation mode or in the normal operation mode. The operating mode determination means determines that the warming-up operation start signal is input and the processing unit of the machine attached to the output shaft of the induction motor is controlled in the warming-up operation mode until the processing unit of the machine is in a heat saturation state. Is configured to determine that control is to be performed in the normal operation mode when is in a heat saturation state. The warm-up operation start signal may be automatically generated when power is turned on to the control device for controlling the electric motor.
It may be generated manually by turning off. Whether the processing part of the machine attached to the output shaft of the induction motor is in a heat-saturated state is determined by measuring the temperature of the processing part with a temperature sensor, and when the temperature of the processing part exceeds a predetermined value, or It can be determined by detecting that the rise has become saturated. However, the heat saturation state of the processing section can be indirectly determined by detecting the heat saturation state of the electric motor that is a heat generation source. This is because the heat from the motor flows to the processing section if the processing section is directly attached to the output shaft of the motor, and the motor is thermally saturated only when the processing section is in a heat-saturated state. It is. Therefore, the temperature of the stator may be detected, and it may be determined from the detected temperature whether or not the processing portion has been in a heat saturated state. If a test is performed in advance, the heat saturation state of the processed part can be determined also by the time of the warm-up operation. When the determination is made based on the time, the operation mode determination means is configured to start counting a predetermined time period when a warm-up operation start signal is input, and to determine that the processing unit has reached a heat saturation state when the counting of the time period is completed. May be configured. Such time counting is realized using a timer.

The warming-up operation signal generating section is configured to output a warming-up torque current command signal, a warming-up exciting current command signal, and a warming-up command signal when the operation mode determining means determines that control is to be performed in the warming-up operation mode. A primary current angular velocity signal. The mode switching unit inputs the torque current command and the excitation current command to the primary current vector calculator and time-integrates the primary current angular velocity signal when the operation mode determination unit determines that the control is performed in the normal operation mode. When the operation mode determination means determines that control is to be performed in the warm-up operation mode, the warm-up torque current command and the warm-up excitation current command are input to the primary current vector calculator. The time integrator is configured to switch so as to input a primary current angular velocity signal for warm-up.

Here, the warming-up operation command generating section has a slip of 1
And a frequency that increases the frequency of the primary current to such an extent that the rotor does not vibrate even if the rotation direction of the rotating magnetic field is alternately changed, and that the rotor is kept substantially stopped. A primary current angular velocity signal generator for warming that generates a primary current angular velocity signal for warming that changes the rotating direction of the rotating magnetic field, and a primary current sufficient to actively heat the stator due to copper loss and iron loss flows And a warming-up current command generating means for generating a warming-up torque current command and a warming-up exciting current command for outputting a current command necessary for the above from the primary current vector calculator. The primary current angular velocity signal for warm-up is integrated by a time integrator and input to a primary current vector calculator as a primary current angle signal. Increasing the frequency of the warm-up primary current angular velocity signal means increasing the frequency of the primary current. A cycle in which the warm-up primary current angle signal outputs 360 ° in electrical angle corresponds to a cycle of the primary current. The warming-up current command generating means includes a warming-up torque current command and a warming-up torque command that cause the primary current vector calculator to output a current command such that the effective value of the primary current is substantially equal to the rated primary current effective value of the induction motor. It is preferable to generate the excitation current command for use.

In order to reverse the direction of rotation of the rotating magnetic field,
The warming-up primary current angular velocity signal generating means is provided when the rotation speed of the rotor of the induction motor reaches a predetermined value when the rotor rotates in one direction and when the rotor rotates in the other direction. A speed polarity discriminating means for detecting that the rotation speed of the rotor has reached a predetermined value is provided. It is configured to change the polarity. Here, “changing the polarity of the warming-up primary current angular velocity signal” means that the angle change of the primary current angle signal obtained by integrating the warming-up primary current angular velocity signal changes while increasing from 0 ° to 360 °, for example. 360
This means changing the warming-up primary current angular velocity signal so as to change while decreasing from ° to 0 °.

The rotation direction of the rotating magnetic field may be changed while detecting the rotation speed of the rotor. However, a test is performed in advance to determine the change period, and the change of the primary current angular velocity signal for warm-up is periodically performed. The warm-up primary current angular velocity signal generating means may be configured to change the polarity.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of a control device used when a three-phase induction motor is controlled using rectangular coordinate vector control according to the control method of the present invention. In this figure, reference numeral 1 denotes a three-phase induction motor (hereinafter referred to as an electric motor or an induction motor);
Reference numeral 3 denotes an encoder that detects the rotation speed of the rotor and outputs a speed detection signal Sv0. Reference numeral 3 denotes a temperature sensor that detects the temperature of the stator and outputs a temperature detection signal St corresponding to the detected temperature. Reference numeral 4 denotes an inverter circuit controlled by pulse width modulation for generating a rotating magnetic field by supplying an alternating current of a predetermined frequency as a primary current to a winding wound on a stator of the electric motor 1. To the inverter circuit 4, a PWM signal (that is, an inverter drive signal) pulse-width modulated for three phases is input from the current amplifier 5. In FIG. 1, PWM signals for three phases are collectively described as one PWM signal. The current amplifier 5 has a primary current command signal i for three phases.
u, iv, iw and the output current (primary current) of each phase of the inverter circuit 4 are detected by a current detector 6 (only one phase is shown in FIG. 1) and fed back via a feedback loop. A current deviation obtained by taking a deviation from the primary current detection signal is input. Then, based on the current deviation, the current amplifier 5 outputs three-phase PWM signals for performing feedback control of the primary current of each phase.

Primary current command signals iu, iv, i for three phases
w is created as follows. First, the speed detection signal Sv0 and the speed command signal Sv1 from the encoder 2 are input to a subtractor, and a speed deviation is obtained. This speed deviation is input to the torque current setting device 7, and the torque current setting device 7 outputs a torque current command signal iT based on the speed deviation. The speed detection signal Sv0 is input to the exciting current setting device 8,
The exciting current setter 8 outputs an exciting current command signal im based on the speed detection signal Sv0. The torque current command signal iT and the excitation current command signal im are input to the slip angular velocity calculator 9, respectively.
Calculates a slip angular velocity signal based on these signals. The speed detection signal Sv0 is output from the rotor angular speed calculator 10
And is converted into a rotor angular velocity signal. The addition signal of the rotor angular velocity signal and the slip angular velocity signal becomes a primary current angular velocity signal iθ. Primary current angular velocity signal iθ
Is time-integrated by a time integrator 11 and input to a primary current vector calculator 12 as a primary current angle signal θ.
The torque current command signal iT and the excitation current command signal im are also input to the primary current vector calculator 12. In this example, the switch circuit S of the mode switching unit 13 described later
These signals are input to the primary current vector calculator 12 via W1 to SW3.

The primary current vector calculator 12 is a rectangular coordinate calculator, and first calculates the following two equations based on the primary current angle signal θ, the torque current command signal iT, and the excitation current command signal im.

Iα = im · cos θ−iT · sin θ iβ = im · sin θ + iT · cos θ Then, based on the above two equations, the three-phase primary current command signals iu, iv, iw are generated by the following three equations.

Iu = 2/3 · iα iv = − ／ · iα + 3 ⁻¹ / ² · iβ iw = − ／ · iα−3 ⁻¹ / ² · iβ Note that the three-phase primary is calculated by a polar coordinate type arithmetic unit. Current command signal iu, i
To calculate v and iw, the following equation may be used.

Iu = | I1 | sin θ iv = | I1 | sin (θ−120 °) iw = | I1 | sin (θ−240 °) where | I1 | = (iT ² + im ² ) ^1/2 .

The above primary current command signals iu, iv, iw
Since the circuit configuration for calculating is well known, detailed description is omitted. Note that the primary current command signals iu, iv,
The circuit for calculating iw, the current amplifier 5, and the current detector 6 constitute an inverter drive signal generation circuit.

In this device, the operation mode determining means 14
Then, the warm-up operation is performed using the warm-up operation signal generation units (15, 16) and the mode switching unit 13. First, the operation mode determining means 14 determines whether to control in the warm-up operation mode or in the normal operation mode. The operation mode determination means 14 determines that the warm-up operation start signal is input, and that the processing section of the machine attached to the output shaft of the induction motor is controlled in the warm-up operation mode until the processing portion of the machine is in a heat saturation state, A mode switching signal S1 and a warm-up operation command signal S2 for instructing the mode switching unit 13 to switch the switches SW1 to SW3 to the B contact are output. And operation mode determining means 1
4, when the processing section is in a heat-saturated state, determines that control is to be performed in the normal operation mode, and outputs a mode switching signal S1 for instructing the mode switching section 13 to switch the switches SW1 to SW3 to the A contact; The output of the warm-up operation command signal S2 is stopped.

Here, the warm-up operation start signal input to the operation mode determining means 14 is automatically output from a warm-up operation start signal generating means (not shown) when the control device is turned on. In this example, it is indirectly determined whether or not a machined portion of a machine directly attached to the output shaft of the induction motor 1 has reached a heat saturation state by detecting a heat saturation state of a stator of the motor 1 which is a heat source. judge. For this purpose, a temperature detection signal St from the temperature sensor 3 is input. The operation mode determining means 14 determines that the stator is in a heat-saturated state when the temperature detection signal St detects a predetermined temperature (saturation temperature) which is confirmed in advance by a test.
Unless the processing section is in a heat-saturated state, the heat from the electric motor 1 flows to the processing section, so that the temperature of the output shaft is not saturated. The motor 1 is thermally saturated only when the processing section is in the heat saturation state, and the temperature of the rotor becomes the saturation temperature. Therefore, by indirectly measuring the saturation temperature of the rotor with the temperature sensor 3 embedded in the stator winding, the thermal saturation state of the processed portion can be indirectly detected. In this case, when manufacturing a machine tool using this electric motor, it is not necessary to consider where to attach the temperature sensor, and the design becomes easy.

Without using the temperature sensor 3, the timer circuit 18
May be used to determine whether or not the processing section has been thermally saturated. When it is determined whether or not the processing section has reached the thermal saturation state based on the time, when the warm-up operation start signal is input, the timer circuit 18 starts counting a predetermined time period, and completes the counting of the time period. When the timer circuit 18 outputs the warm-up time measurement signal, the operation mode determination means 14 may be configured to determine that the processing section has reached the heat saturation state. The timer circuit 18 is unnecessary when detecting the thermal saturation state using the output of the temperature sensor 3.

The warm-up operation signal generating section 17 includes a warm-up current command generating means 15 and a warm-up primary current angular velocity signal generating means 1.
And 6. The warm-up operation signal generation unit 17 outputs the warm-up torque current command signal iT ′, when the operation mode determination unit 14 determines that the control is performed in the warm-up operation mode.
A warm-up excitation current command signal im ′ and a warm-up primary current angular velocity signal iθ ′ are generated.

When the operation mode determining means 14 determines that the control is to be performed in the normal operation mode, that is, when the warm-up operation command signal S2 is not output, the switches SW1 to SW1 are controlled.
SW3 switches to the A contact, and the torque current command signal iT
And the excitation current command signal im is the primary current vector calculator 1
2 and the primary current angular velocity signal iθ is
1 is input. When the operation mode determining means 14 determines that the control is to be performed in the warm-up operation mode, that is, when the warm-up operation command signal S2 is being output, the warm-up current command generation means 15 outputs the warm-up torque current command. Signal iT
′ And the warming-up exciting current command signal im ′ are input to the primary current vector calculator, and the warming-up primary current angular velocity signal generating means 16 receives the warming-up primary current angular velocity signal iθ ′ from the time integrator 11. You.

Here, the warming-up primary current angular velocity signal generating means 16 of the warming-up operation command signal generating section 17 has a slip value close to 1 (slip as close to 1 as possible) and alternates the rotating direction of the rotating magnetic field. (Even if the direction of rotation of the rotating magnetic field is alternately changed to the forward direction and the opposite direction to keep the rotor stopped), the frequency of the primary current is increased to such an extent that the rotor does not vibrate. The rotating direction of the rotating magnetic field is changed so as to have a frequency and keep the rotor substantially stopped (the rotor is stopped by alternately changing the rotating direction of the rotating magnetic field between the forward direction and the reverse direction). It is configured to generate a primary current angular velocity signal iθ ′ for the machine.

If the rotor is completely stopped, the slip will be 1. In the present invention, the slip is made as close to 1 as possible to keep the rotor substantially stationary.
When the frequency of the primary current increases, the rotation speed of the rotating magnetic field increases, and the generated torque decreases. When the slip is 1, the generated torque becomes the smallest. FIG. 2 shows the generated torque T1 when the frequency of the primary current is set to 50 Hz, and 500%.
Hz schematically shows the state of the generated torque T2. As can be seen from this figure, when the frequency of the primary current is increased, the generated torque is considerably reduced.

This will be verified numerically. The generated torque Te of the electric motor can be expressed by the following equation.

Te = α / 2π · f · β where α = m 1 · V ² · (r ² / s) · P β = [r 1 + (r ² / s)] ² + 4π ² · f ² (L 1 +
L2) ² .

In the above equation, f is the primary current frequency [Hz] r1 is the stator winding resistance [Ω] r2 is the secondary resistance primary side conversion value [Ω] s is the slip L1 is the primary leakage inductance [H] L2 is The secondary leakage inductance primary side converted value [H] m1 is the number of phases (3 in the case of three phases) V is the primary primary phase terminal voltage [V] P is the number of poles.

Using the above equation, the primary current frequency f of an 11 kW three-phase induction motor (rated torque 70 N · m) is set to 50
Hz (rated) and 500 Hz, s = 1
(Stop), r1 = r2 = 0.1 [Ω], L1 = L2 = 1
When the generated torque was calculated with × 10 ⁻³ [H], V = 100 [V], and P = 4, the generated torque T1 at a frequency of 50 Hz was about 88 [N · m], and the frequency 500H
The generated torque at the time of z was 0.1 [N · m]. As can be seen from this result, by increasing the primary current frequency,
When the slip approaches 1, the generated torque becomes very small.

However, even if the slip is set to 1, the rotor tends to rotate because the generated torque exists. Therefore, in order to prevent the rotor from rotating with this small torque, when the rotor starts to rotate in one direction,
By changing the phase sequence of the primary current command signal (for example, U → V → W)
By changing the rotation direction of the rotating magnetic field and changing the phase sequence of the primary current command signal (for example, U → W → V) when the rotor starts to rotate in the other direction, Hold the rotor substantially stationary.

In order to reverse the direction of rotation of the rotating magnetic field,
The warm-up primary current angular velocity signal generating means 16 employs the configuration shown in FIG. The warming-up primary current angular velocity signal generating means 16 generates the speed detection signal S output from the encoder 2.
By inputting v0, the rotation speed of the rotor when the rotor of the induction motor 1 is rotating in one direction has reached a predetermined value, and the rotation speed of the rotor when the rotor is rotating in the other direction. Is detected, the speed polarity discriminating means 16a for outputting a speed polarity signal indicating that the rotating direction of the rotating magnetic field is to be changed. Also, based on the determination result of the speed polarity determining means 16a, the polarity of the warming-up primary current angular velocity signal iθ 'is changed so as to change the rotating direction of the rotating magnetic field.
6b and an addition / subtraction switch 16c. The added / subtracted number generator 16b has a frequency of the primary current of 500 Hz, for example.
In this case, the add / subtract signal is output so as to advance by one period of the sine wave in 2 [ms]. Addition / subtraction switch 16
c is the output (speed polarity signal) of the speed polarity determination means 16a.
, And adds or subtracts the polarity of the add / subtract number signal, and outputs the signal as a warm-up primary current angular velocity signal iθ ′. The time integrator 11 is configured to be reset every time the warm-up primary current angular velocity signal iθ ′ corresponding to ± 360 degrees is integrated, and start a new integration. An increase in the frequency of the warm-up primary current angular velocity signal iθ ′ means an increase in the frequency of the primary current. The cycle in which the warm-up primary current angular velocity signal iθ ′ outputs 360 degrees in electrical angle corresponds to the cycle of the primary current. The primary current angle signal θ for warm-up output from the time integrator 11 is input to a sine wave generator 12b of a primary current vector calculator 12, and the sine wave generator 12b outputs a primary current angle signal θ ′ for warm-up. A sine wave is output according to the indicated angle. This sine wave is input to the rectangular coordinate calculator 12a, and is used for the above-described calculation of iα and iβ. The rectangular coordinate calculator 12a performs the above-described rectangular coordinate calculation to obtain the three-phase primary current command signal i.
u, iv, iw are output.

Returning to FIG. 1, warming-up current command generating means 1
5 is a warming-up torque current command signal iT ′ for outputting from the primary current vector calculator a current command necessary to flow a primary current sufficient to actively heat the stator due to copper loss and iron loss; It is configured to generate a warm-up excitation current command signal im ′. Warm-up current command generating means 15
Keeps outputting the warm-up torque current command signal iT 'and the warm-up excitation current command signal im' while the operation mode determining means 14 outputs the warm-up operation command signal S2. The warm-up torque current command signal iT ′ and the warm-up excitation current command signal im ′ are input to the orthogonal coordinate calculator 12a in FIG.
It is preferable that the values of the warm-up torque current command signal iT 'and the warm-up excitation current command signal im' be as large as possible in order to increase the amount of heat generated, but in practice they are limited by the characteristics or performance of the induction motor. . So in this example,
The values of the warming-up torque current command signal iT ′ and the warming-up exciting current command signal im ′ are set to a primary current command such that the effective value of the primary current of each phase is substantially equal to the rated primary current effective value of the induction motor. The output is set so as to be output from the current vector calculator 12. In this case, the temperature of the stator can be increased as quickly as possible without burning out the induction motor.

In the above example, the part included in the area indicated by reference numeral 19 is a part constituting the main part of the present invention,
All this part 19 can be realized by software.

Next, the operation of the above example will be described with reference to FIG. First, when the power supply of the device using the induction motor 1 is turned on and a warm-up operation start signal is input to the operation mode determination means 14, the operation mode determination means 14
1 and the warm-up operation command signal S2 are output. Upon receiving the mode switching signal S1, the mode switching unit 13 switches the switches SW1 to S
Switch W3 to B contact. Further, in response to the warm-up operation command signal S2, the warm-up current command generation means 15 converts the warm-up torque current command signal iT 'and the warm-up excitation current command signal im' through the switches SW1 and SW2 to the primary current vector calculator 13 Output to

Further, in response to the warm-up operation command signal S2, the warm-up primary current angular velocity signal generating means 16 outputs a warm-up primary current angular velocity signal iθ '. Specifically, the add / subtract number generator 16b outputs an add / subtract number signal that advances by one period of the sine wave at 2 [ms]. At this stage, since the rotation direction of the rotor cannot be determined, the speed polarity determining means 16a
Is indeterminate as shown in FIG. 4 (2). In addition, the addition / subtraction switch 16c adds a + polarity (polarity indicating addition) to the addition / subtraction number signal (FIG. 3) and outputs the signal as a warm-up primary current angular velocity signal iθ ′ in order to perform dummy addition for the time being. The warming-up primary current angular velocity signal iθ ′ is integrated by the time integrator 11 and the time integrator 11 outputs the warming-up primary current angle signal θ ′. FIG. 4D conceptually shows data included in the warm-up primary current angle signal θ ′ in the form of a waveform. In this case, as can be seen from FIG. 4 (4), the warm-up primary current angle signal θ ′ increases from 0 ° toward 360 °, is reset when it reaches 360 °, and increases again from 0 ° to 360 °. This change is repeated at a predetermined frequency. This frequency is 500 Hz in this example. The warm-up primary current angle signal θ ′ is input to the primary current vector calculator 12.

The primary current vector calculator 12 generates a warm-up torque current command signal iT ′ and a warm-up excitation current command signal iT.
The above-described orthogonal coordinate calculation is performed based on m ′ and the warm-up primary current angle signal θ ′, and the three-phase primary current command signals iu,
iv and iw are output. FIG. 4 (5) conceptually shows data included in the primary current command signal for one phase. As can be seen from FIG. 4 (5), the primary current command signal changes at 500 Hz similarly to the warm-up primary current angle signal θ ′, and changes the primary current at 500 Hz. At this time, the phase sequence of the three-phase primary current flowing by the three-phase primary current command signals iu, iv, iw is, for example, “U → V → W” as shown in FIG. The magnetic field is rotating in a counterclockwise direction (CCW). As a result, the direction in which the minute torque of the motor is generated is also in the counterclockwise direction. In this state, the slip is almost a value close to 1.

Even if the primary current changes at 500 Hz, a slight torque is generated as described above. Therefore, the rotor tries to rotate with the small torque. The rotation speed of the rotor is detected by the encoder 2 and output as a speed detection signal of FIG. When the rotation speed of the rotor reaches 50 rpm, the speed polarity discriminating means 16a of the warming-up primary current angular velocity signal generating means 16 discriminates that the rotation direction of the rotor is counterclockwise, and indicates the speed polarity signal indicating that. Is output to the addition / subtraction switch 16c. Addition / subtraction switch 16c
When this speed polarity signal is received,-
And outputs it as a warm-up primary current angular velocity signal iθ ′. The time integrator 11 integrates the warming-up primary current angular velocity signal iθ ′ with a negative polarity over time. As a result, FIG.
As shown in (4), the warm-up primary current angle signal θ ′ is
It increases from 0 ° to −360 °, resets when it reaches −360 °, and repeats a change that increases again from 0 ° to −360 ° at a frequency of 500 Hz. As can be seen from FIG. 4 (5), the polarity of the three-phase primary current command signals iu, iv, and iw output from the primary current vector calculator 12 are inverted similarly to the warm-up primary current angle signal θ ′. And changes at 500 Hz. At this time, the phase order of the three-phase primary current flowing by the three-phase primary current command signals iu, iv, iw is reversed as “W → V → U” as shown in FIG. It will rotate clockwise (CW). At this time, a small torque of the electric motor is also generated in the clockwise direction. As a result, the rotor tends to rotate in the opposite direction.

Further, the encoder 2 detects a speed change when the rotation direction of the rotor is about to change, and FIG.
It is output as the speed detection signal of (1). When the rotation speed of the rotor reaches -50 rpm, the speed polarity discriminating means 16a of the primary current angular velocity signal generator 16 for warming-up discriminates that the rotation direction of the rotor is clockwise, and indicates the speed polarity. The signal is output to the addition / subtraction switch 16c.
Upon receiving the speed polarity signal, the addition / subtraction switch 16c adds the + polarity to the addition / subtraction number signal and outputs the signal as the warm-up primary current angular velocity signal iθ ′. The time integrator 11 performs time integration of the warming-up primary current angular velocity signal iθ ′ having a positive polarity. As a result, as shown in FIG. 4 (4), the warm-up primary current angle signal θ ′ increases again from 0 ° toward + 360 °, is reset when it becomes + 360 °, and is again reset from 0 ° to + 360 °.
The change increasing toward 360 ° is repeated at a frequency of 500 Hz. The primary current command signals iu, iv, iw for three phases output from the primary current vector calculator 12 are also shown in FIG.
As can be seen from (5), the warm-up primary current angle signal θ ′
Similarly, the polarity is inverted and changes at 500 Hz. At this time, the phase order of the three-phase primary current flowing by the three-phase primary current command signals iu, iv, iw is reversed as “U → V → W” as shown in FIG. It starts to rotate counterclockwise. At this time, a small torque of the electric motor is also generated in the counterclockwise direction, and as a result, the rotor tends to reverse the rotation direction.

Thereafter, the above operation is repeated, and as a result, the rotor only slightly rotates within the range of ± 50 rpm, and does not substantially rotate. In this way, by increasing the frequency of the primary current and increasing the value of the primary current, the iron loss and the copper loss are increased, causing the stator and the rotor to generate heat and rotating so that the rotor is not substantially rotated. By repeatedly reversing the direction of the magnetic field, the energy required for the rotation of the rotor can be used for heat generation of the stator. As a result, wasteful power consumption can be reduced, and the temperature of the induction motor rises faster.

When the temperature sensor 3 detects a predetermined temperature, the operation mode judging means 14 judges that the stator is in the heat saturation state, and that the device provided with the electric motor 1 is also in the heat saturation state. The output of the command signal S2 is stopped, and a mode switching signal S1 for switching the contacts of the switches SW1 to SW3 from B to A is output to the mode switch 13. As a result, in the primary current vector calculator 12, the torque current command signal iT from the torque current setter 7, the excitation current command signal im from the excitation current setter 8, and the primary current angular velocity signal iθ are calculated by the time integrator 11. The integrated primary current angle signal θ is input. The primary current vector calculator 12 outputs a three-phase primary current command signal for outputting three-phase AC power from the inverter circuit 4, and the motor 1 is operated in the normal operation mode.

Incidentally, when controlling the induction motor of the induction type servo system of several kW to several tens of kW class, the motor must be operated for 4 to 6 hours in order to make the machined part or the output shaft of the machine into the heat saturation state in the continuous rated operation. I need to drive. On the other hand, when the present invention is used, a heat saturation state can be obtained in several tens of minutes.

In the above example, the heat saturation state is detected by measuring the temperature of the stator of the electric motor 1. However, the heat saturation state may be detected by using the timer circuit 18 shown in FIG.
Moreover, you may use both together. If you use both,
The warm-up operation may be stopped in accordance with the earlier result of the temperature detection or the count completion of the timer period, whichever is earlier.

In the above example, the primary current waveform is a sine wave. However, it is needless to say that the primary current waveform may be a rectangular wave to increase heat generation due to harmonic components.

When the present invention is expressed by the concept of a warm-up operation method for an electric machine tool, the following is obtained.

(1) An alternating current of a predetermined frequency is applied as a primary current to a winding wound on a stator to generate a rotating magnetic field, and the primary current is feedback-controlled according to a current command using a current feedback loop. A warm-up operation method for an electric machine tool using an induction motor as a drive source, wherein the slip is close to 1 and the rotor does not vibrate even if the rotating direction of the rotating magnetic field is alternately changed. The frequency of the primary current is set high, the current command is set so that the primary current is sufficient to actively heat the stator due to copper loss and iron loss, and the rotor is substantially stopped. Changing the direction of rotation of the rotating magnetic field so as to maintain the state until the temperature of a processing unit connected to the output shaft of the induction motor becomes equal to or higher than a predetermined temperature. How to warm up a machine tool.

[0054]

According to the present invention, by increasing the frequency of the primary current and increasing the value of the primary current,
Since the stator heat is generated by increasing the iron loss and the copper loss, and furthermore, the direction of the rotating magnetic field is repeatedly reversed so that the rotor is not substantially rotated. Can be used for fever. As a result, there is an advantage that wasteful power consumption can be reduced, the temperature of the induction motor can be increased quickly, and the warm-up operation time can be shortened as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a configuration of a control device used when controlling a three-phase induction motor using rectangular coordinate vector control according to a control method of the present invention.

FIG. 2 shows a generated torque T1 when the frequency of the primary current is 50 Hz and a generated torque T2 when the frequency is 500 Hz.
FIG. 3 is a diagram schematically showing the state of FIG.

FIG. 3 is a block diagram showing an example of a specific configuration of a warm-up primary current angular velocity signal generating means.

FIG. 4 is an operation waveform diagram used for explaining the operation of the example of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction motor 2 Encoder 3 Temperature sensor 4 Inverter circuit 5 Current amplifier 7 Torque current setting unit 8 Excitation current setting unit 9 Slip angular velocity calculator 10 Rotor angular velocity calculator 11 Time integrator 12 Primary current vector calculator 13 Mode switching unit 14 Operation Mode determination means 15 Warm-up current command generation means 16 Warm-up primary current angular velocity signal generation means 17 Warm-up operation signal generation unit

Claims (13)

[Claims] 1. A rotating magnetic field is created by applying an alternating current of a predetermined frequency as a primary current to a winding wound on a stator, and the primary current is feedback-controlled according to a current command using a current feedback loop. A method of controlling an induction motor for controlling an induction motor, wherein the frequency of the primary current is reduced to such an extent that the slip is close to 1 and the rotor does not vibrate even if the rotation direction of the rotating magnetic field is alternately changed. Set high to set the current command to flow the primary current sufficient to actively heat the stator due to copper and iron losses, and to keep the rotor substantially stationary. And performing a warm-up operation by changing the rotation direction of the rotating magnetic field, and then shifting to a normal operation after the warm-up operation is completed. 2. The induction motor control method according to claim 1, wherein the warm-up operation is continued until the stator of the induction motor is in a heat saturation state. 3. The control method for an induction motor according to claim 1, wherein the warming-up operation is continued until a processing portion of a machine attached to an output shaft of the induction motor is in a heat saturation state. . 4. The induction motor according to claim 1, wherein the induction motor is a three-phase induction motor, and a frequency of the primary current is approximately five times or more of a rated frequency and is equal to or less than a response frequency of the current feedback loop. Control method. 5. The control method for an induction motor according to claim 1, wherein the current command is set such that an effective value of the primary current is substantially equal to a rated primary current effective value of the induction motor. . 6. The induction motor according to claim 1, wherein a rotation speed of an output shaft of the induction motor is detected, and the rotation direction of the rotating magnetic field is changed when the rotation speed reaches a predetermined value. Motor control method. 7. An inverter circuit for generating a rotating magnetic field by supplying an alternating current of a predetermined frequency as a primary current to a winding wound on a stator, and an inverter drive signal generating circuit for outputting an inverter drive signal to the inverter circuit. The inverter drive signal generation circuit comprises: a torque current command;
A primary current vector calculator that inputs a primary current angle signal obtained by time-integrating an excitation current command and a primary current angular velocity signal with a time integrator and outputs a primary current command signal, and the primary current for feedback control of the primary current. A current feedback loop for detecting and feeding back a primary current detection signal, wherein the control device determines whether to control in a warm-up operation mode or in a normal operation mode. Means for generating a warm-up torque current command signal, a warm-up excitation current command signal, and a warm-up primary current angular velocity signal when the operation mode determining means determines to control in the warm-up operation mode. A warm-up operation signal generating unit that performs the control when the control unit determines that the control is to be performed in the normal operation mode. The current mode command and the excitation current command are input to the primary current vector calculator, and the primary current angular velocity signal is switched to be input to the time integrator, and the operation mode determination means performs control in the warm-up operation mode. When it is determined, the warm-up torque current command and the warm-up excitation current command are input to the primary current vector calculator, and the warm-up primary current angular velocity signal is input to the time integrator. And a mode switching unit for switching the operation mode, wherein the operation mode determination unit is configured to operate until the warming-up operation start signal is input and the processing unit of the machine attached to the output shaft of the induction motor is in a heat-saturated state. The warm-up operation command generation unit is configured to determine that control is to be performed in the warm-up operation mode, and to determine that control is to be performed in the normal operation mode when the load is in a heat-saturated state. Having a frequency at which the frequency of the primary current is increased to such an extent that the slip is close to 1 and the rotor does not vibrate even if the rotating direction of the rotating magnetic field is alternately changed, and the rotor is substantially The warming-up primary current angular velocity signal generating means for generating the warming-up primary current angular velocity signal that changes the rotating direction of the rotating magnetic field so as to maintain the stopped state, and positively activates the stator by copper loss and iron loss. A warm-up current command that generates the warm-up torque current command and a warm-up excitation current command that cause the primary current vector calculator to output the current command necessary to flow the primary current sufficient for heating. A control device for an induction motor, comprising: a generator. 8. The apparatus according to claim 7, wherein the operation mode determination means is configured to determine whether or not the heat saturation state of the processing portion of the machine is detected by detecting whether or not the stator is in the heat saturation state. Induction motor control device. 9. The operation mode determining means measures a temperature of a processing part of a machine attached to an output shaft of the induction motor with a temperature sensor, and determines whether the processing part is in a heat saturation state from an output of the temperature sensor. The control device for an induction motor according to claim 7, wherein the control device is configured to determine whether or not the control is performed. 10. The operation mode determination means starts counting a predetermined time period when the warm-up operation start signal is input, and determines that the load is in a heat saturated state when the counting of the time period is completed. The control device for an induction motor according to claim 7, wherein the control device is configured as follows. 11. The primary current angular velocity signal generating means for warming-up, the rotation speed of the rotor when the rotor of the induction motor is rotating in one direction reaches a predetermined value, and Comprises speed polarity discriminating means for detecting that the rotation speed of the rotor when rotating in the other direction has reached a predetermined value, based on the judgment result of the speed polarity discriminating means, The control device for an induction motor according to claim 7, wherein a polarity of the warm-up primary current angular velocity signal is changed so as to change a rotation direction. 12. The warm-up primary current angular velocity signal generating means is configured to periodically change the polarity of the warm-up primary current angular velocity signal so as to change the rotation direction of the rotating magnetic field. 8. The control device for an induction motor according to claim 7. 13. The warming-up current command generating means causes the primary current vector calculator to output the current command such that the effective value of the primary current becomes substantially equal to the rated primary current effective value of the induction motor. The control device for an induction motor according to claim 7, wherein the control device is configured to generate the warm-up torque current command and the warm-up excitation current command.