JP2003111498A - Controller without speed sensor for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain safety of controlling even in a low-speed regenerative state and to prevent stepping-out. SOLUTION: A speed correcting value arithmetic means obtains a speed estimating value fr ' corresponding to a slip frequency fs ' at a boundary line (4), when a slip frequency fs obtained by a slip frequency arithmetic means is larger than the slip frequency fs corresponding to the sped estimated value fr estimated by a magnetic flux speed estimating means at the line (4); and adds the difference between the fr ' and the fr to the previous time speed correcting amount Fcmp as this time speed correcting amount Fcmp .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed sensorless control device for an induction motor, which controls speed without using a sensor for speed detection, and more particularly, to reduce instability during low speed regeneration to cause step out. The present invention relates to a speed sensorless control device for an induction motor, which is to be prevented.

[0002]

2. Description of the Related Art When an induction motor is driven by speed control that does not use a sensor for speed detection, that is, speed sensorless control, the influence of voltage error increases in a low speed regenerative state where the output frequency is near zero. , The operation of the induction motor tends to be unstable. Further, in such speed sensorless control, there is a region in which control is impossible due to low speed regeneration in principle. In this region, the operation of the induction motor is likely to be unstable, and there are cases where the control cannot be continued due to step out.

In order to solve the above-mentioned problems, in the past,
The slip frequency command is set to 0 to prevent the primary frequency from decreasing. However, it is not possible to completely avoid the above-mentioned unstable region only by setting the slip frequency command to 0. Japanese Patent Laid-Open No. 10-033000 proposes a method of setting a reference value of a primary frequency and compensating a torque command when the primary frequency falls below the reference value. A method has also been proposed in which the slip frequency command is multiplied by a negative gain to increase the frequency.

[0004]

As described above, in the conventional speed sensorless control, in order to stabilize the operation of the induction motor in the low speed regeneration state, the slip frequency command is set to 0 so that the primary frequency does not decrease. The torque command is compensated when the primary frequency falls below the reference value, feedback calculation of the output voltage command by the estimated primary magnetic flux is performed, or the slip frequency command is multiplied by a negative gain to determine the frequency. I was raising it.

However, the instability phenomenon cannot be solved only by setting the slip frequency to zero. Further, the method of compensating the torque command based on the reference value of the primary frequency and the method of multiplying the slip frequency by a negative gain are methods applicable only to the slip frequency vector control device, and the phase of the magnetic flux estimation value It cannot be applied to the direct type magnetic flux vector control method that outputs a voltage with reference to.

Also in the slip frequency type vector control device, when the above method is used, the output of the integrator of the speed control means is canceled, and the control device is operated between the normal state and the low speed regenerative state. Since the switching process is required, the configuration of the control device becomes complicated and a shock may occur at the time of switching.

The present invention can be applied to any control method such as a direct type magnetic flux vector control method and a slip frequency type vector control method without complicating the configuration of the control device.
An object of the present invention is to provide a speed sensorless control device for an induction motor, which is capable of maintaining control stability and preventing step-out in a low speed regeneration state.

[0008]

In order to solve the above problems, the present invention is based on a speed estimating means for estimating the speed of an induction motor and a deviation between a speed command input from a host device and a speed estimated value. Speed control means for performing speed control to calculate a torque current command, and magnetic flux control means for calculating a magnetic flux current command based on a magnetic flux command input from a host device,
A slip frequency calculating means for obtaining a slip frequency based on the magnetic flux command and the torque current command,
In a speed sensorless control device for an induction motor, a region sandwiched by two boundary lines among regions including the second quadrant, the fourth quadrant, and the vicinity of the origin on a plane having the estimated speed value and the slip frequency as coordinate axes. Is an unstable region, and the coordinate points on the plane determined by the speed estimated value estimated by the speed estimating means and the slip frequency calculated by the slip frequency calculating means are in the unstable area. Is a speed correction amount calculation means for calculating and outputting a correction amount of the speed command so that the coordinate point is outside the unstable region, and a correction amount output from the speed correction amount calculation means for the speed command. It is characterized by comprising an adding means for adding.

In the speed sensorless control device for an induction motor of the present invention, the speed command is corrected so that the relationship between the estimated speed value and the slip frequency is outside the unstable region. In the speed sensorless control device of the present invention, the unstable state in the low-speed regenerative state can be eliminated only by correcting the speed command input from the higher-order device. It is possible to maintain control stability and prevent step-out in a low-speed regenerative state without complicating the configuration of the device.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a speed sensorless control device for an induction motor according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a speed sensorless control device for an induction motor according to this embodiment. As shown in FIG. 1, this speed sensorless control device includes a magnetic flux speed estimation means 1, a speed control means 2, a slip frequency calculation means 3, a magnetic flux control means 4, and a voltage feed forward (FF) calculation means 5. , Current control means 6
, Voltage conversion means 7, voltage output device 8, current component conversion means 9, speed correction amount calculation means 10, and adder 11
And a subtractor 12.

The magnetic flux velocity estimating means 1 is an induction motor (M).
The current detection values of each phase of 13 are input, and the current detection values, the magnetic flux direction axis (d axis) and the torque direction axis (q
(Axis) voltage commands V _d , V _q and the motor constant value of the induction motor 13, the speed and magnetic flux of the induction motor 13 are estimated, and the estimated speed is output as a speed estimation value F _r , and is also estimated. The magnetic pole position θφ is obtained from the generated magnetic flux and output. The adder 11 outputs a value obtained by adding the speed command correction amount F _cmp to the speed command F _ref input from a host device (not shown) as a speed command F _ref ′. The subtractor 12 outputs a value obtained by subtracting the estimated speed value F _r from the speed command F _ref ′ as a speed deviation ΔF _r . The speed control means 2 determines the speed deviation Δ
Speed control is performed based on F _r , and a torque current command I _{q *} is calculated and output. The slip frequency calculating means 3 calculates and outputs the slip frequency Fs from the torque current command I _{q *} , the magnetic flux command Φ _ref input from the host device (not shown), and the predetermined motor rated slip frequency.

The magnetic flux control means 4 calculates and outputs the magnetic flux current command I _{d *} based on the magnetic flux command Φ _ref . The voltage FF calculation means 5 uses the torque current command I _{q *} and the magnetic flux current command I _{d *.}
, The magnetic flux command Φ _ref , the estimated speed value F _r, and the slip frequency F _s , the output frequency ω is calculated, and the d-axis and q-axis feedforward voltages V _{d *} and V _{q *} are given in (1) below. It is obtained and output according to the equation (2).

V _{q *} = ω × Φ _ref + R × (I _{q *} ) + ω × L × (I _{d *} ) ... (1) V _{d *} = R × (I _{d *} ) + ω × L × (I _{q *} ) (2) The current component conversion means 9 determines the three-phase current detection value of the induction motor (M) 13 as the torque component current I _q and the magnetic flux component current I _d based on the magnetic pole position θφ. Convert to. Current control means 6
Performs current control based on the torque current command I _{q *} , the magnetic flux current command I _{d *} , the torque component current I _q , the magnetic flux component current I _d, and the feedforward voltages V _{q *} and V _{d *.} , D
Axis and q axis voltage commands V _d and V _q are obtained and output. The voltage converting means 7 converts the voltage commands V _d and V _q into voltage commands for each phase of the induction motor 13 and outputs the voltage commands. The voltage output device 8 applies a voltage according to the voltage command of each phase to the induction motor 13.

The speed correction amount calculation means 10 calculates the estimated speed value F
Of the region including the second quadrant, the fourth quadrant, and the vicinity of the origin on the plane having _r and the slip frequency F _s as the coordinate axes, the region sandwiched by the two boundary lines is defined as an unstable region, and the magnetic flux velocity estimating means 1 If the coordinate point on the plane determined by the estimated speed estimation value F _r and the slip frequency F _s calculated by the slip frequency calculating means 3 is within the unstable region, the coordinate point is outside the unstable region. Then, the correction amount F _cmp of the speed command F _ref is _calculated and output. Specifically, when the coordinate point is in the unstable region, the speed correction amount calculation means 10 selects any one of the boundary lines, and the slip frequency at the boundary line is selected. Estimated velocity value corresponding to F _s and magnetic flux velocity estimation means 1
The difference between the estimated speed value F _r and the estimated speed value F _r is added to the previous speed command correction amount F _cmp , and the value is output as the current speed command correction amount F _cmp . Output speed correction amount F
_cmp is the speed command F _ref by the adder 11 as described above.
Is added to.

The speed sensorless control device for an induction motor of the present embodiment differs from the conventional speed sensorless control device in that it is provided with a speed correction amount calculation means 10 and an adder 11. The speed sensorless control device of the present embodiment is a direct type magnetic flux vector type control device and estimates the magnetic flux to calculate the phase of the induction motor. Therefore, in the speed sensorless control device of the present embodiment, since there is no so-called output frequency command, the torque command is compensated when the primary frequency falls below its reference value, as described in the conventional technique, The method of multiplying the slip frequency command by a negative gain to raise the output frequency cannot be applied, but instead, the speed correction amount calculation means 10
The speed command input to the speed control means 2 is corrected by the speed correction amount Fcmp obtained by

A method of calculating the speed correction amount F _cmp in the speed correction amount calculation means 10 will be described. FIG. 2 is a graph showing an example of an unstable region defined in the speed sensorless control device of the present embodiment. In the graph shown in FIG. 2, the horizontal axis represents the estimated speed value F _r and the vertical axis represents the slip frequency F _s . The speed correction amount calculation means 10 sets the regions of the second quadrant and the fourth quadrant surrounded by the straight lines represented by the following equations (3) and (4) as unstable regions.

F _s = −F _r (3) F _s = − ((K ₁ × R ₂ ) / (R ₁ + R ₂ )) × F _r (4) Here, K ₁ is , The coefficient of the unstable region (K ₁ > 0),
R ₁ is a primary resistance of the induction motor 13, and R ₂ is a secondary resistance of the induction motor 13.

These straight lines serve as two boundary lines of the unstable region. In the speed sensorless control device of the present embodiment,
If the relationship between the slip frequency F _s and the estimated speed value F _r remains in the unstable region for a long time, the operation of the induction motor may become unstable and step out may occur. Formulas (3) and (4)
As shown in, the unstable region is determined by the primary resistance R ₁ and the secondary resistance R ₂ of the induction motor 13. Induction motor 13
In order to further stabilize the operation of, it is desirable to set a value such that K ₁ <1.

The speed correction amount calculation means 10 has a speed command F
_The slip frequency f _s calculated by the slip frequency calculation means 3 when _ref is constant and a regenerative load is applied.
But if larger than the slip frequency f _s' corresponding to the estimated velocity estimated value f _r by the magnetic flux speed estimating unit 1 in the formula (4), the speed estimation corresponding to the slip frequency f _s in the formula (4) The value f _r 'is obtained and the following equation (5) is obtained.
_Is calculated to obtain the speed correction amount F _cmp .

F_cmp= F_cmp+ F_r’-F_r... (5) Note that F on the right side of equation (5)_cmpIs the previous speed correction
Is the amount. Estimated speed value F_rControl by performing the previous correction
As a result, the one obtained by the magnetic flux velocity estimation means 1
Therefore, the estimated speed value F_rF_rTo reach
Speed correction amount F_{cm p}Is the previous speed correction amount F_cmpAdd to
Need to ask.

However, as described above, in equation (4), K ₁
If you set <1, if the slip frequency F _s is large,
That is, when the load is high, the corrected speed command F
_{The ref} value may become too large. The operation of the induction motor 13 is less likely to become unstable when the output frequency is increased to some extent. Therefore, in the speed sensorless control device of the present embodiment, when the speed is low, the speed by the speed correction amount calculation means 10 is focused. It is desirable to correct the command F _ref . In other words, as the boundary line of the unstable region, the absolute value of the speed estimation value corresponding to the same slip frequency than the straight line in the low speed region shown in the following formula (6) is not the straight line shown in the formula (4). It is more desirable to use a large quadratic function.

F _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r (F _r ≧ 0) F _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r (F _r <0) (6) where K ₂ is a coefficient (K ₂ > 0) in the unstable region.
FIG. 3 shows the unstable region defined by the equations (3) and (6). The coefficient K ₂ is preferably set to a value such that the unstable region shown in FIG. 2 is completely included in the low speed region. By doing so, the speed sensorless control device of the present embodiment can ensure a more stable operation of the induction motor 13. However, the speed estimation value f
_In order to obtain _r ', the calculation of the square root is required, which increases the amount of calculation. Therefore, in the speed correction amount calculation means 10, instead of the equation (6), the estimated speed value F
The slope K _s of the tangent line at the intersection with the equation (4) in _r is calculated using the following equation (7).

K _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × 2 (F _r ≧ 0) K _s = ((K ₂ × R ₂ ) / (R ₁ + R) ₂ )) × F _r × 2 (F _r <0) ··· (7) Then, the slope of the tangent to the difference between the slip frequency (fs ′ in FIG. 3) obtained by the equation (6) and the slip frequency f _s. K _s
By multiplying by the reciprocal of
Then, the speed correction amount F _cmp is obtained.

[0024] _{F cmp = F cmp + 1 /} K s × (f s' -f s) ··· (8) In the speed sensorless control apparatus of the present embodiment, F
_{Since cmp} is the amount obtained by the integral calculation, even if the tangent slope K _s is simply set to a constant value, the relationship between the estimated speed value F _r and the slip frequency F _s is controlled to be outside the unstable region. be able to.

Further, in the speed sensorless control device of the present embodiment, the unstable region may be widened due to fluctuations in the parameters of the induction motor 13 due to factors such as temperature and the effects of errors. In order to deal with this, in the speed sensorless control device of the present embodiment, the unstable region may have a margin width f _m (f _m > 0). In this case, assuming that the two boundary lines in the unstable region are straight lines based on the equations (3) and (4), the two boundary lines are the slip frequency F
_{When s} is positive, it becomes as shown in the following expressions (9) and (10), and when slip frequency F _s is negative, it becomes as shown in expressions (11) and (12). .

F _s = −F _r −f _m (F _r ≧ 0) (9) F _s = − ((K ₁ × R ₂ ) / (R ₁ + R ₂ )) × F _r + f _m (F _r ≧ _{0) (10) F s =} -F r + f m (F r <0) (11) F s = - ((K 1 × R 2) / (R 1 + R 2)) × F r -f m (F _r <0) (12) The unstable region determined by the equations (9) to (12) is shown in FIG.

Further, one of the two boundary lines of the unstable region is a quadratic curve based on the equation (6), and the margin width f _m
If the slip frequency F _s is positive, the quadratic curve becomes as shown in the following expression (13), and if the slip frequency F _s is negative, the expression ( 1
As shown in 4).

[0028] _{F s = - ((K 2} × R 2) / (R 1 + R 2)) × F r × F r + f m (F r ≧ 0) (1 3) F s = ((K 2 × R _{2) / (R 1 + R} 2)) × F r × F r -f m (F r <0) (14) equation (9), is surrounded by a boundary line (11), (13), (14) The unstable region is shown in FIG.

In the speed sensorless control device of this embodiment, the value of the margin width f _m may be changed according to the fluctuation of the speed estimated value F _r . For example, when the absolute value of the estimated speed value F _r increases, _fm is reduced to make the estimated speed value F _r
When the absolute value of is decreased, f _m may be increased to have a hysteresis characteristic in the unstable region, whereby more stable control adapted to a non-linear system may be realized.

FIG. 6 is a graph showing the torque-speed characteristics when the speed command F _ref is not corrected by the speed correction amount calculator 10, and FIG. 7 is a graph showing the speed command F by the speed correction amount calculator 10. It is a graph which shows a torque-speed characteristic when _ref is amended. As shown in FIG.
It can be seen that when the speed command is not corrected by the speed correction amount calculation means 10, the operation becomes unstable as the load increases, and finally the step is lost. On the other hand, as shown in FIG. 7, when the speed command F _ref is corrected by the speed correction amount calculation means 10, even if the load becomes large, it is stabilized without causing step-out. Recognize. Whether or not it is in the unstable region is determined based on the relationship between the slip frequency F _s and the estimated speed value F _r . Therefore, the increase in the speed of the induction motor 13 is changed by changing the magnetic flux command Φ _ref . It can be adjusted to some extent.

Further, FIG. 7 shows the characteristics when the speed command F _ref is constant, but during acceleration / deceleration, the size of the speed command F _ref changes, so that it is less likely to become unstable. further,
When the induction motor 13 is driven while switching the forward and reverse of the rotation direction, it may be better to operate at a speed as close as possible to the speed command F _ref . In order to meet such a demand, during the acceleration / deceleration, the formula (4) or the formula (1
0) and (12) as boundary lines, and during constant speed operation, if formula (6) or expressions (13) and (14) are used as boundary lines, smooth forward / reverse switching operation and stable constant speed operation are performed. Is possible.

Further, it is unstable in the forward / reverse switching operation.
Occasionally, the area must be passed. like this
In this case, speed correction is performed from the two boundary lines of the unstable area.
Quantity F _cmpIt is necessary to select the boundary line for obtaining.
For example, let the unstable region be the region shown in FIG.
Machine 13 is rotating normally and slip frequency F_sIs positive
In this case, the estimated speed value F_rAnd slip frequency F_sRelationship with
It does not affect the unstable region, but the induction motor 13 is reduced.
When it starts to rotate in reverse, it contacts the formula (11) and becomes unstable region.
It comes to approach. At this time, the speed correction amount F_cmp
Is calculated based on the equation (11), and the speed command F_refBut
If it goes further to the negative side, the speed correction amount F
_cmpIs calculated using equation (12). This
By doing so, it is possible to smoothly pass through the unstable area.
it can. In addition, at the moment when decelerating and contacting the formula (11),
Even if (12) is used, the same effect can be obtained.

When the induction motor 13 is reversely rotated and the slip frequency F _s is positive, when the induction motor 13 is decelerated,
It comes into contact with Expression (12). In this case, the formula (1
2) is used to determine the speed correction amount F _cmp . Induction motor 1
When the stop command of 3 is input, the slip frequency F
_{When s} is small to some extent, the time required for the unstable region is also short, and therefore step-out or the like does not occur even if speed correction by the speed correction amount calculation means 10 is not performed. In such cases,
The induction motor 13 can be stopped without performing the speed correction by the speed correction amount calculation means 10. On the other hand, when the slip frequency F _s is large, there is a risk of step-out if the operation is continued as is.
Using 1), the speed correction amount F _cmp is obtained, the unstable region is quickly passed, and a smooth stop is performed. In the case of switching to the forward rotation direction instead of stopping, when the sign of the speed command F _ref is switched, the speed correction amount F is calculated using the equation (11).
_{Find cmp} and quickly pass through the unstable region.

As described above, in the speed sensorless control device of this embodiment, it is possible to cope with all operating states by appropriately changing the correction method of the speed command F _ref according to the operating state of the induction motor 13. Become.

[0035]

As described above, in the speed sensorless control device for an induction motor according to the present invention, the speed command is corrected so that the relationship between the estimated speed value and the slip frequency is outside the unstable region. There is. In the speed sensorless control device of the present invention, it is possible to eliminate the unstable state in the low-speed regenerative state by only correcting the speed command input from the host device, so regardless of the method of vector control,
Further, without complicating the configuration of the control device, it is possible to maintain control stability and prevent step-out in the low speed regeneration state. Therefore, the present invention can be applied to a hoisting / unwinding crane, which has not been used due to unstable operation during low-speed regeneration.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a speed sensorless control device for an induction motor according to an embodiment of the present invention.

FIG. 2 is a graph showing an unstable region defined in the speed sensorless control device according to the embodiment of the present invention.

FIG. 3 is a graph showing an unstable region defined in the speed sensorless control device according to the embodiment of the present invention.

FIG. 4 is a graph showing an unstable region defined in the speed sensorless control device according to the embodiment of the present invention.

FIG. 5 is a graph showing an unstable region defined in the speed sensorless control device according to the embodiment of the present invention.

FIG. 6 is a graph showing torque-speed characteristics when a speed command is not corrected by a speed correction amount calculation means.

FIG. 7 is a graph showing torque-speed characteristics when a speed command is corrected by a speed correction amount calculation means.

[Explanation of symbols]

1 Magnetic flux velocity estimation means 2 Speed control means 3 Slip frequency calculation means 4 Magnetic flux control means 5 Voltage feed forward (FF) calculation means 6 Current control means 7 Voltage conversion means 8 voltage output device 9 Current component conversion means 10 Speed correction amount calculation means 11 adder 12 Subtractor 13 Induction motor (M)

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Claims (15)

[Claims] 1. A speed estimation means for estimating a speed of an induction motor, and a speed control means for performing a speed control based on a deviation between a speed command input from a host device and a speed estimated value to calculate a torque current command. A magnetic flux control unit that calculates a magnetic flux current command based on a magnetic flux command that is input from a host device; and a slip frequency calculation unit that determines a slip frequency based on the magnetic flux command and the torque current command.
In a speed sensorless control device for an induction motor, a region sandwiched by two boundary lines is defined among regions of the second quadrant, the fourth quadrant, and the vicinity of the origin on a plane having the estimated speed value and the slip frequency as coordinate axes. In the case of an unstable region, when the coordinate points on the plane determined by the speed estimation value estimated by the speed estimating means and the slip frequency calculated by the slip frequency calculating means are in the unstable area, , A speed correction amount calculation means for calculating and outputting a correction amount of the speed command so that the coordinate point is outside the unstable region, and a correction amount output from the speed correction amount calculation means is added to the speed command. A speed sensorless control device for an induction motor, comprising: 2. The speed correction amount calculation means is characterized in that the coordinate point on the plane determined by the speed estimation value estimated by the speed estimation means and the slip frequency calculated by the slip frequency calculation means is the coordinate point on the plane. When it is within the stable region, one boundary line is selected from the boundary lines, and the speed estimation value corresponding to the slip frequency at the boundary line and the speed estimation value estimated by the speed estimating means are selected. The value added to the correction amount of the previous speed command is output as the correction amount of the current speed command,
The speed sensorless control device for an induction motor according to claim 1. 3. The speed estimation value estimated by the speed estimating means is set to F _r and the slip frequency calculated by the slip frequency calculating means is defined as F _{r at} each of the boundaries.
when the _s, F _s = a straight line represented by -F _r contained, the speed sensorless control apparatus for an induction motor according to claim 1 or 2 wherein. 4. On each of the boundaries, K ₁ is a coefficient of an unstable region (K ₁ > 0), R ₁ is a primary resistance of the induction motor, and R ₂ is a secondary resistance of the induction motor. The speed sensorless control of the induction motor according to claim 3, wherein a straight line represented by F _s = − ((K ₁ × R ₂ ) / (R ₁ + R ₂ )) × F _r is included. apparatus. 5. On each of the boundaries, K ₂ is a coefficient of an unstable region (K ₂ > 0), R ₁ is a primary resistance of the induction motor, and R ₂ is a secondary resistance of the induction motor. Then, F _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r
(F _r ≧ 0) F _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r
5. A quadratic curve represented by (F _r <0) is included.
The speed sensorless control device for the induction motor described. 6. The speed correction amount calculation means selects a boundary line having a large absolute value of a speed estimated value corresponding to the same slip frequency from among the boundary lines.
6. The speed sensorless control device for an induction motor according to any one of 1 to 5. 7. The speed correction amount calculation means, when the speed command is changing, F _s = −F _r F _s = − ((K ₁ × R ₂ ) / (R ₁ + R ₂ ). ) × F _r , one boundary line is selected from among the boundary lines, and when the speed command does not change, F _s = −F _r F _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r
(F _r ≧ 0) F _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r
Select one boundary line from among the boundary lines represented by (F _r <0),
The speed sensorless control device for an induction motor according to claim 5. 8. The estimated speed value estimated by the speed estimating means is F _r , and the slip frequency calculated by the slip frequency calculating means is F _r for each boundary line.
_s and the margin width is f _m , a straight line represented by F _s = −F _r −f _m (F _r ≧ 0) F _s = −F _r + f _m (F _r <0) is included. The speed sensorless control device for an induction motor according to claim 1 or 2. 9. On each of the boundaries, K ₁ is a coefficient of an unstable region (K ₁ > 0), R ₁ is a primary resistance of the induction motor, and R ₂ is a secondary resistance of the induction motor. when _{a, F s = - ((K} 1 × R 2) / (R 1 + R 2)) × F r + f m
_{(F r ≧ 0) F s} = - ((K 1 × R 2) / (R 1 + R 2)) × F r -f m
9. The speed sensorless control device for an induction motor according to claim 8, wherein a straight line represented by (F _r <0) is included. 10. On each of the boundaries, K ₁ is a coefficient of an unstable region (K ₁ > 0), R ₁ is a primary resistance of the induction motor, and R ₂ is a secondary resistance of the induction motor. And K ₂ is a coefficient (K ₂ > 0) in the unstable region, F _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r +
f _m (F _r ≧ 0) F _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r −f _m
10. A quadratic curve represented by (F _r <0) is included.
The speed sensorless control device for the induction motor described. 11. The speed correction amount calculation means selects a boundary line having a large absolute value of a speed estimated value corresponding to the same slip frequency, from among the boundary lines.
11. The speed sensorless control device for an induction motor according to any one of 1 to 10. 12. The speed correction amount calculation means, when the speed command is changing, F _s = −F _r −f _m (F _r ≧ 0) F _s = −F _r + f _m (F _{r <0) F s = -} ((K 1 × R 2) / (R 1 + R 2)) × F r + f m
_{(F r ≧ 0) F s} = - ((K 1 × R 2) / (R 1 + R 2)) × F r -f m
When one boundary line is selected from among the boundary lines represented by (F _r <0) and the speed command does not change, F _s = −F _r −f _m (F _r ≧ 0 ) F _s = -F _r + f _m (F _r <0) F _s =-((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r +
f _m (F _r ≧ 0) F _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × F _r −f _m
The speed sensorless control device for an induction motor according to claim 10, wherein one boundary line is selected from among the boundary lines represented by (F _r <0). 13. The speed correction amount calculation means narrows the margin width when the absolute value of the speed estimated value increases, and narrows the margin width when the absolute value of the speed estimated value decreases. The speed sensorless control device for an induction motor according to any one of claims 8 to 12, which is widened. 14. The speed correction amount calculation means, when the selected boundary line is the quadratic curve, sets a slope of a tangent line of the speed estimation value of the quadratic curve to K _s, and K _s = − ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × 2
(F _r ≧ 0) K _s = ((K ₂ × R ₂ ) / (R ₁ + R ₂ )) × F _r × 2 (F
The slope of the tangent line is obtained by _r <0, and the value obtained by multiplying the difference between the slip frequency corresponding to the estimated speed value on the quadratic curve and the slip frequency by the reciprocal of the slope of the tangent line is used as the speed command of the previous speed command. The speed sensorless control device for an induction motor according to claim 5 or 10, wherein the correction amount of the current speed command is added to the correction amount. 15. The speed correction amount calculation means, when the selected boundary line is the quadratic curve, sets a slope of a tangent line of the speed estimation value in the quadratic curve to a constant value, and the quadratic curve The value obtained by multiplying the difference between the slip frequency corresponding to the estimated speed value and the slip frequency by the reciprocal of the slope of the tangent line is added to the correction amount of the previous speed command to obtain the correction amount of the current speed command. The speed sensorless control device for an induction motor according to claim 5 or 10.