JPH07303399A - Velocity sensorless vector controlling method of induction motor - Google Patents

Abstract

PURPOSE:To avoid the instability of a motor actual speed estimated value which is estimated by a speed adaptive secondary magnetic flux observer by switching a motor primary voltage command value to a motor primary applied voltage value and inputting it to the speed adaptive secondary magnetic flux observer when an actual motor speed is in a low speed range. CONSTITUTION:A motor speed discriminator 17 judges whether a motor actual speed estimated value omegar# which is estimated by speed adaptive secondary magnetic flux observers 4, 5 is high or low. A motor primary voltage switch 16 switches the motor primary voltage, which is the input of the same dimension magnetic flux observer 4 of the speed adaptive secondary magnetic flux observers, to motor primary voltage command values V1a*, V1b* when the voltage primary voltage is in a low speed range and inputs them to the speed adaptive secondary magnetic flux observers 4, 5. By this method, the instability of the motor actual speed estimated value omegar# which is estimated by the speed adaptive secondary magnetic flux observers 4, 5 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor vector control system, and more particularly to a speed sensorless vector control system for an induction motor which does not use a speed sensor.

[0002]

2. Description of the Related Art A vector control method has become popular as a high-performance speed control method for an induction motor, and in particular, a speed sensorless vector control method for performing speed control without using a speed sensor is known.

FIG. 2 shows a control system of a conventional speed sensorless vector control system (sliding frequency type vector control method) of an induction motor which estimates the actual speed of the induction motor using a speed adaptive secondary magnetic flux observer. is there.

In FIG. 2, 1 is an induction motor, 2 is a PWM control inverter for controlling the speed of the induction motor 1, and 3 is a motor primary voltage command value V ₁ * (V ₁ for vector control of the motor 1 by the PWM control inverter. a *, V ₁ b *) to obtain a digital current controller, 4 is a primary current i of the induction motor 1.
Same-dimensional magnetic flux observer for estimating ₁ and secondary magnetic flux λ ₂ , 5
Is a speed adaptation mechanism for calculating and estimating an actual speed estimated value ω _r # of the induction motor 1 from the primary current estimated value i ₁ # and the secondary magnetic flux estimated value λ ₂ # estimated by the same-dimensional magnetic flux observer 4. 6 is a speed controller for obtaining the torque axis component primary current command value i ₁ b * of the induction motor 1 by proportional-plus-integral control of the error signal between the speed command value ω _r * and the actual speed estimated value ω _r #, and 7 is the induction motor. A slip calculator that calculates the slip angular frequency command value ω _s * from the primary current command value i ₁ * (i ₁ a *, i ₁ b *) of ₁ , and 8 is the coordinate from the power angular frequency ω ₀ of the induction motor 1 An integrator for calculating the basic phase angle θ ₀ that operates the converters 9 and 10,
10 is a synchronous rotation coordinate (ab axis) system and a stator coordinate (dq
Coordinate converter for performing coordinate conversion with the (axis) system, 11 is the motor 1
Three-phase to two-phase converter for converting the three-phase primary current into the two-phase primary current, 12 converts the two-phase primary voltage command value V ₁ * of the motor ₁ into the three-phase primary voltage command values Vu, Vv, Vw A two-phase to three-phase converter, 13 is an A / D converter that digitally converts the primary current detection value of the induction motor 1, and 14 is a speed command value ω _r * and an estimated actual speed value ω _r # of the induction motor 1. A comparator 15 for comparing the actual speed estimated value ω _r # of the induction motor 1 and the slip angular frequency command value ω _s *
Is an adder for obtaining the power source angular frequency ω ₀ of the induction motor 1. The same-dimensional magnetic flux observer 4 and the speed adaptive mechanism 5 constitute a speed adaptive secondary magnetic flux observer (4, 5) for calculating and estimating the estimated motor actual speed value ω _r #.

First, the estimation of the actual speed (rotational angular frequency ω _r ) of the induction motor 1 will be described with reference to FIG.

The voltage equation of the induction motor 1 is given by the following equation (1) when it is represented by the ab axis for observing various quantities from the synchronous rotation coordinate system rotating at the power source angular frequency (ω ₀ ).

[0007]

[Equation 1]

However, V ₁ a, V ₁ b ... Excitation axis component primary voltage, torque axis component primary voltage (V) i ₁ a, i ₁ b of motor synchronous rotation coordinate (ab axis) system synchronous rotation Excitation axis component primary current of coordinate (ab axis) system, torque axis component primary current (A) λ ₂ a, λ ₂ b ・ ・ ・ Excitation axis component secondary magnetic flux of motor synchronous rotation coordinate (ab axis) system, torque axis component secondary flux (Wb) ω ₀ ‥‥‥‥ motor power supply angular frequency (rad / sec) ω _r ‥‥‥‥ motor speed (rotation angular frequency, rad / sec) ω _s ‥‥‥‥ slip angle Frequency (rad / sec) R ₁ , R ₂・ ・ ・ Motor primary and secondary resistance (Ω) L ₁ , L ₂・ ・ ・ Motor primary and secondary inductance (H) MM ‥‥‥ Motor mutual (excitation) inductance ( H) Lσ ····· Equivalent leakage inductance of motor (H) (Lσ
= (L ₁ L ₂ −M ² ) / L ₂ ) s ······· Time fine molecule (d / dt) And the power source angular frequency (ω ₀ ), the motor speed (ω _r ) and the slip angular frequency (ω _s The relationship of *) and the calculation of the slip angular frequency (ω _s *) are expressed by the following equation (2). ω ₀ = ω _r + ω _s * ω _s * = i ₁ b * / (i ₁ a * ・ τ ₂ ) ‥‥‥‥‥‥‥‥‥‥‥ (2) However, τ ₂ ‥‥‥‥‥‥‥‥‥‥‥ Time constant (τ ₂ = L ₂ /
R ₂ ) Subscript (*) ‥‥‥‥‥ Indicates a command value or set value. Now, i ₁ a * = constant ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ Under the condition of the formula, the primary voltage command value V ₁ * of the synchronous rotation coordinate (ab axis) system
(V ₁ a *, V ₂ b *) is expressed by the following equation (4) which is a constitutive equation of the digital current controller 3.

[0009]

[Equation 2]

When given by, the primary current i ₁ of the synchronous rotation coordinate (a-b axis) system becomes a current value according to the command value i ₁ * (i ₁ a *, i ₁ b *), and the synchronous rotation coordinate System secondary magnetic flux λ
₂ (λ ₂ a, λ ₂ b) is maintained by the following equation (5).

Λ ₂ a = Mi ₁ a * (constant), λ ₂ b = 0 ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (5) As a result, the torque (T) of the induction motor 1 becomes a secondary value. The following equation (6) irrelevant to the magnetic flux λ ₂ (λ ₂ a, λ ₂ b) and the secondary current i ₂ (i ₂ a, i ₂ b): T = M / L ₂ · (λ ₂ a · i ₁ b −λ ₂ b · i ₁ a) = M ² / L ₂ · (i ₁ a · i ₁ b) (6), and the excitation axis component primary current (i ₁ a) and the torque axis component primary current (i ₁ b) The vector control is established, which allows non-interfering control with.

By the way, as is apparent from the equation (2), when the speed sensor is not used, the slip angular frequency ω _s *
Even if is set, since the motor speed ω _r is unknown,
The power source angular frequency ω ₀ cannot be determined, but the secondary magnetic flux λ of the synchronous rotation coordinate system that rotates at the power source angular frequency ω ₀
By controlling the power source angular frequency ω ₀ so that ₂ (λ ₂ a, λ ₂ b) satisfies the above equation (5), vector control that is also current decoupling control is realized. You can That is, by using the speed adaptive secondary magnetic flux observer including the same-dimensional magnetic flux observer 4 and the speed adaptive mechanism 5, the secondary magnetic flux λ ₂ (λ ₂ a, λ ₂ b), and based on the estimated secondary magnetic flux λ ₂ # (λ ₂ a #, λ ₂ b #), the actual motor speed ω _r
By estimating (ω _r #), the above equation (2) (ω ₀ =
Vector control can be realized by obtaining the power source angular frequency ω ₀ from ω _r # + ω _s *) and controlling the digital current controller 3 with the power source angular frequency ω ₀ .

In the conventional speed sensorless vector control system for an induction motor in the vector control system shown in FIG. 2, the actual speed of the induction motor 1 is detected via the A / D converter 13 in order to detect it without using a speed sensor. To detect the primary current (phase current) iu, iv, iw of the induction motor 1 and
Stator coordinates (dq) converted by the two-phase converter 11
(Axis) system primary current detection value i ₁ (i ₁ d, i ₁ q), and the primary current detection value i ₁ (i ₁ d, i ₁ q) and primary voltage command value V ₁ *
(V ₁ d *, V ₁ q *) and the actual velocity estimated value ω _r # are input to the stator coordinate (d−q) by the same-dimensional magnetic flux observer 4.
(Axis) system secondary magnetic flux λ ₂ (λ ₂ d, λ ₂ q) and primary motor current i ₁ (i ₁ d, i ₁ q) are estimated, and the speed adaptation mechanism 5
Then, the estimated error signal (i ₁ −i ₁ #) is obtained by comparing the estimated primary current value i ₁ # (i ₁ d #, i ₁ q #) with the detected primary current value i ₁ (i ₁ d, i ₁ q). ), The actual speed estimated value (ω _r #) is calculated and estimated by the adaptive adjustment law represented by the following equation (7) to detect the speed of the induction motor 1.

Ω _r # = Kp (eid · λ ₂ q # −eiq · λ ₂ d #) + Ki∫ (eid · λ ₂ q # −eiq · λ ₂ d #) dt (7) However, eid = i ₁ d−i ₁ d #: estimation error eiq = i ₁ q−i ₁ q #: estimation error Kp: velocity estimation part proportional gain Ki: velocity estimation part integration gain Note that the same-dimensional magnetic flux observer 4 and velocity adaptation mechanism are used. For the speed sensorless vector control method of the induction motor 1 for estimating the actual speed of the induction motor by the speed adaptive secondary magnetic flux observer consisting of 5 and 5, see, for example, "Journal of the Institute of Electrical Engineers of Japan, Vol. 111, No. 11, 1991". (Kubota, Ozaki, Matsuse, Nakano: "Velocity sensorless direct vector control of induction motor using adaptive secondary magnetic flux observer"). Hereinafter, a conventional speed sensorless vector control method for estimating the actual speed of the induction motor using the speed adaptive secondary magnetic flux observer will be described.

To explain the operation in FIG. 2 (control system), when the motor speed command (ω _r *) is given to the comparator 14, the speed command value (ω _r *) and the actual speed estimated value (ω) are given.
_r #) and the comparison error signal is compared with the speed control unit (A
It is proportional-integral (PI) controlled by the speed controller 6 in SR) and converted into a torque axis component primary current command value (i ₁ b *) of the synchronous rotation coordinate (ab axis) system of the induction motor 1. Next, in the digital current controller 3 in the current controller (ACR), the primary voltage command value V ₁ * of the synchronous rotation coordinate system of the induction motor 1 that controls the PWM control inverter 2 is set.
(V ₁ a *, V ₁ b *) is the primary current command value i ₁ * (i ₁ a *,
i ₁ b *) and the primary current detection value i ₁ (i ₁ a, i ₁ b) are equal (i ₁ a * = i ₁ a, i ₁ b * = i ₁ b) so that the current does not interfere. It is calculated by the above-mentioned expression (4) which is a conditional expression that enables the conversion control.

The primary voltage command value V ₁ * (V ₁ a *, V ₁ b *) of the synchronous rotation coordinate (ab-axis) system is converted by the coordinate converter 10 into the stator coordinate (d-q axis) system. Primary voltage command value V ₁ * (V ₁ d *,
V ₁ q *), and then the number of phases is converted by the two-phase / three-phase number converter 12 into the output voltage control command voltages Vu, Vv, Vw of each phase of the PWM control inverter 2. Converted to the PW
The output voltage of each of the three phases of the M control inverter 2 is controlled.
As a result, the induction motor 1 is speed-controlled according to the desired speed command value (ω _r *). In addition, conversion between the synchronous rotation coordinate system (ab-axis) system rotating at the power source angular frequency ω ₀ of the induction motor 1 and the stator coordinate system (d-q axis) system fixed to the stator of the induction motor 1. unit vector used in the coordinate converter 9 to perform (sin [theta _0, Cos? ₀₎ basic phase angle _{θ 0 (θ 0 = ω 0} t) for producing the slip angle obtained by the above (2) The power supply angular frequency (ω ₀ ) obtained from the frequency command value (ω _s *) and the motor actual speed estimation value (ω _r #) estimated by the speed adaptive secondary magnetic flux observer (4,5)
It can be obtained by integrating with the basic phase angle calculating integrator 8.

[0017]

The conventional speed sensorless vector control system described above uses the motor primary voltage V which is the input of the speed adaptive secondary magnetic flux observer (combining the same-dimensional magnetic flux observer 4 and the speed adaptive mechanism 5). _{As 1} ,
The motor primary voltage command value V ₁ * (V ₁ d *, V ₁ q *) satisfying the condition that the vector control is satisfied is supplied, but the primary voltage command value V ₁ * and the induction motor 1 are actually supplied. Between the applied primary voltage V ₁ m (V ₁ dm, V ₁ qm), a dead band (primary band) for preventing a short circuit of a switching control element (for example, a transistor, not shown) of the PWM control inverter 2 Installation of the voltage V1m) or the voltage across the switching control element during the ON period of the switching control element (the voltage does not become zero but the voltage drop remains)
An error ΔV ₁ has occurred due to the effects (Notes 1 and 2). This error voltage ΔV ₁ is the motor primary voltage command value V ₁ * when the induction motor 1 is in the high speed region (normal speed).
Since (V ₁ a *, V ₁ b *) is high, it is very small with respect to the primary voltage command value V ₁ * and can be ignored. However, in the low speed region, the motor primary voltage command value V ₁ * ( V ₁ a *, V ₁ b *)
Is low, it becomes large with respect to the primary voltage command value V ₁ * (V ₁ a *, V ₁ b *).

Thus, the motor primary voltage command value V ₁ *
When the error ΔV ₁ between (V ₁ a *, V ₁ b *) and the actually applied motor primary applied voltage V ₁ m (V ₁ am, V ₁ bm) increases, the motor primary voltage command value V ₁ * Stator coordinate (d-q axis) system motor primary current estimated value i ₁ # (i ₁ ) which is the estimated output of the same-dimensional magnetic flux observer 4 with (V ₁ a *, V ₁ b *) as input
There is an estimation error in the secondary magnetic flux estimation value λ ₂ # (λ ₂ d #, λ ₂ q #) of the d #, i ₁ q #) and the stator coordinate (d-q axis) system, and these are input. The actual motor speed estimation value (ω _r #), which is the output of the speed adaptation mechanism 5, becomes unstable, and the vector control itself becomes unstable, and the induction motor 1 has a speed according to the speed command (ω _r *). The torque cannot be obtained and the predetermined torque cannot be obtained.

(Note 1) Transactions of the Institute of Electrical Engineers of Japan, Volume D 107, No. 2
1987 (Terashima, Nomura, Adachi, Suda, Nakamura:
Refer to “Comparison of performance of control current source vector control and control voltage source vector control from the practical point of view”).

(Note 2) The motor primary voltage command value V ₁ * is increased by the amount of voltage drop during the ON period of the switching control element (transistor). This effect is not a problem in a region where the motor speed is high (the voltage command value V ₁ * is high), but it significantly appears in a low speed region where the motor primary voltage command value V ₁ * is low.

The present invention has been made in view of the above points, and in the speed sensorless vector control system of the induction motor, the instability of the actual speed estimated value due to the speed adaptive secondary magnetic flux observer is prevented, and the whole speed control range is achieved. The purpose is to obtain stable vector control in.

[0022]

Means for Solving the Problems A motor primary voltage command value, a motor primary current detection value, and a motor actual speed estimated value, which are outputs of a current non-interference control (vector controller), are input to estimate the motor actual speed. In a speed sensorless vector control system of an induction motor using a speed adaptive secondary magnetic flux observer (combining the same dimension magnetic flux observer and a speed adaptive mechanism), the motor primary voltage command value is set in the low speed region of the actual motor speed. The primary applied voltage value of the electric motor is switched to the input of the speed adaptive secondary magnetic flux observer.

[0023]

The actual motor speed estimated by the speed adaptive secondary magnetic flux observer by removing the difference between the motor primary voltage command value in the low speed region and the primary applied voltage actually applied to the motor. Prevent instability of the estimated value.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a control system which is an embodiment of the present invention.

In FIG. 1, 3'is an induction motor 1 actually.
'Primary voltage calculator for calculating a, 10' a primary applied voltage V ₁ applied to the synchronous rotation coordinate axis said primary applied voltages V ₁ '(a-
Coordinate converter for converting from the (b-axis) system to the stator coordinate (d-q-axis) system, 17 is the actual speed estimation of the motor estimated by the speed adaptive secondary magnetic flux observer (same-dimensional magnetic flux observer 4, speed adaptive mechanism 5) A motor speed discriminator for judging whether the value (ω _r #) is high speed or low speed, and 16 is a motor primary voltage switch for switching the motor primary voltage V ₁ which is the input of the same-dimensional magnetic flux observer 4 by the motor speed discriminator 17. is there.

The control system of the present invention in this control system will be described below.

Now, in the low speed region of the induction motor 1,
When the vector control is established, the primary applied voltage V ₁ 'actually applied to the induction motor ₁ (synchronous rotation coordinate ab
V ₁ a on the axis ', V ₁ b') can be obtained by the following theoretical formula (8).

V ₁ a ′ = R ₁ · i ₁ a − ω ₀ L σ · i ₁ b V ₁ b ′ = R ₁ · i ₁ b + ω ₀ L ₁ · i ₁ a ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (8) The above equation (8) is based on the above equation (1) which is the voltage equation of the induction motor, and the following conditions (a), (b) and (c) which are various conditions when the vector control is established. Can be obtained by substituting.

(A) ω ₀ = ω _r + ω _s , ω _s = i ₁ b /
(i ₁ a · τ ₂ ) (b) i ₁ a = constant (c) λ ₂ a = constant, λ ₂ b = 0 Then, the voltage calculator 3 ′ calculates the synchronous rotation coordinates ( a-b axis) primary applied voltage V ₁ '(V ₁
a ', V ₁ b') is calculated, and the coordinate converter 10 'converts the coordinates into a primary applied voltage V ₁ ' (V ₁ d ', V ₁ q') of the stator coordinate (d-q axis) system. To be the input voltage (motor primary voltage) of the same-dimensional magnetic flux observer 4 in the low speed region of the induction motor 1.

On the other hand, in the high speed region of the induction motor 1, the primary applied voltage V ₁ m actually applied to the induction motor ₁
(V ₁ am, V ₁ bm) is the above-mentioned motor primary voltage command value V ₁ * (V ₁ a from the primary applied voltage V ₁ ′ (V ₁ a ′, V ₁ b ′) calculated by the above equation (8). *, V ₁ b *) has less error, so as with the conventional control system (see FIG. 2), the synchronous rotation coordinates (a-b) which are the output of the digital current controller 3 are output.
The primary voltage command value V ₁ * (V ₁ a *, V ₁ b *) of the motor of the axis) system is converted by the coordinate converter 10 into the primary voltage command value V ₁ * (V ₁ of the stator coordinate (d-q axis) system. d *, V ₁ q *) coordinate conversion, and the same-dimensional magnetic flux observer 4 in the high-speed region of the induction motor 1
Input voltage.

Based on the motor secondary flux estimated value λ ₂ (λ ₂ d #, λ ₂ q #) and the motor primary current estimated value i ₁ # (i ₁ d #, i ₁ q #) estimated by the same dimension magnetic flux observer 4. Then, in the speed adaptation mechanism 5, the estimated motor actual speed value (ω _r #) is calculated and estimated by the adaptive adjustment law represented by the equation (7). Then, the electric motor speed discriminator 17 judges whether the estimated actual motor speed (ω _r #) is high or low, and the induction motor 1 is switched by switching the electric motor primary voltage switch 16 according to the high or low.
When the velocity of is in the high velocity region, the stator coordinate (dq
(Axis) system primary voltage command value V ₁ * (V ₁ d *, V ₁ q *) is the same dimension magnetic flux as the motor primary applied voltage V ₁ 'actually applied to the induction motor 1 when in the low speed region. It can be the input voltage of the observer 4. As a result, in the entire speed range of the induction motor ₁ , a voltage equal to the primary voltage V ₁ actually applied to the motor 1 is input as the motor primary voltage of the same-dimensional magnetic flux observer 4 to estimate the motor secondary flux estimation. Since the value λ ₂ (λ ₂ d #, λ ₂ q #) and the motor primary current estimated value i ₁ (i ₁ d #, i ₁ q #) are stable, the estimated actual motor speed value calculated by the speed adaptation mechanism 5 (Ω _r #) is also stable.

[0032]

As described above, according to the present invention, the instability of the motor speed estimated value due to the input voltage error to the observer in the low speed region of the induction motor is transferred to the observer by the voltage calculation by the simple voltage calculator. Since it is possible to eliminate the input voltage error and stabilize the electric motor, stable vector control can be achieved in which a predetermined torque is obtained at a speed according to the speed command (ω _r *).

[Brief description of drawings]

FIG. 1 is a configuration diagram of a control system that is an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional control system

[Explanation of symbols]

 1: Induction motor 2: PWM control inverter 3: Digital current controller 3 ': Primary voltage calculator 4, 5: Speed adaptive secondary magnetic flux observer (same-dimensional magnetic flux observer 4, speed adaptive mechanism 5) 6: Speed controller 7 : Slip calculator 8: Integrator for calculating basic phase angle (θ0) 16: Motor primary voltage selector 17: Motor speed discriminator

Claims (2)

[Claims] 1. An excitation motor component primary voltage command value and a torque shaft component primary voltage command value for an induction motor, an excitation shaft component primary current detection value and a primary torque shaft current detection value for the induction motor, and an actual speed of the induction motor. An induction motor whose speed is controlled based on a speed error signal compared with a speed command value of the induction motor by negatively feeding back an actual speed estimation value of the induction motor estimated by a speed adaptive secondary magnetic flux observer using an estimated value as an input. In the low speed region of the induction motor, in the low speed region of the induction motor, the excitation shaft component primary voltage command value and the torque shaft component primary voltage command value of the induction motor are obtained by calculation. In the induction motor, the voltage value and the torque axis component are applied to the speed adaptive secondary magnetic flux observer instead of the primary applied voltage. Degree sensor-less vector control system. 2. A speed controller for proportionally integrating a speed error signal obtained by comparing a speed command value of an induction motor and an actual speed estimated value to obtain a torque axis component primary current command value of the induction motor, and a speed controller of the induction motor. Input the excitation axis component primary current command value, the torque axis component primary current command value, the excitation axis component primary current detection value and the torque axis component primary current detection value of the induction motor, and input the current non-interference of each axis component primary current. Current controller that outputs the excitation shaft component primary voltage command value and the torque shaft component primary voltage command value of the induction motor by performing the conversion control, and the excitation shaft component primary voltage of the induction motor that is the output of the digital current controller. A power converter that speed-controls the induction motor based on a command value and the torque axis component primary voltage command value, an excitation axis component primary current command value of the induction motor, and the torque axis component primary power. A voltage calculator for calculating the excitation shaft component primary applied voltage value and the torque shaft component primary applied voltage applied to the induction motor based on the flow command value, and the output of the digital current controller in the high speed region of the induction motor. In the excitation shaft component primary voltage command value and the torque shaft component primary voltage command value of the induction motor, the induction shaft component primary applied voltage value of the induction motor that is the output of the voltage calculator in the low speed region of the induction motor. And a primary voltage switch of the motor, which is a switching output of the primary voltage switch of the motor, and an excitation axis component primary voltage command value of the induction motor and a torque axis component primary voltage command value or an excitation shaft. Component primary applied voltage value and torque axis component primary applied voltage value, excitation axis component primary current detection value and primary torque axis current detection value of the induction motor, and The actual speed estimation value of the induction motor is input, and the excitation shaft component primary current and the torque shaft component primary current of the induction motor and the excitation shaft component secondary magnetic flux and the torque shaft component secondary magnetic flux of the induction motor are estimated. Dimensional magnetic flux observer, based on the primary current estimated value of the induction motor, which is the estimated output of the same dimensional magnetic flux observer, secondary magnetic flux estimated value, and excitation axis component primary current detection value and torque axis component primary current detection value, A speed adaptation mechanism that outputs an estimated actual speed value of the induction motor; and a motor primary voltage switcher that determines whether the motor speed is high or low based on the estimated actual speed value of the induction motor that is the output of the speed adaptation mechanism. A speed sensorless vector control system for an induction motor, comprising: an electric motor speed discriminator for switching.