JP5115687B2 - Vector control device for induction motor - Google Patents

Description

  The present invention relates to a vector control apparatus that controls torque and speed of an induction motor by speed sensorless vector control.

FIG. 4 is a block diagram of a so-called speed sensorless vector control apparatus 100 that controls the torque / speed of the induction motor using the speed estimation value without having a speed detector.
In the figure, the three-phase AC voltage of the AC power supply 12 is converted into a three-phase AC voltage having a predetermined magnitude and frequency by an inverter 13 and supplied to the induction motor 17. Thereby, the electric motor 17 generates a desired torque to drive the load 18.

The speed setter 1 sets a speed ω _r # at which the induction motor 17 should be operated. The speed command calculation circuit 2 calculates and outputs a speed command value ω _r ^* that changes according to a predetermined acceleration and finally matches the speed set value ω _r #.
The speed adjuster 3 outputs the torque command value τ ^* by an adjustment operation that makes the deviation between the speed command value ω _r ^* and the speed estimated value ω _r ^ output from the speed estimation calculator 33 described later zero. . The magnetic flux command calculation circuit 4 calculates a secondary magnetic flux command value φ ₂ ^* from the estimated speed value ω _r ^.

Further, a current command value of a component parallel to the secondary magnetic flux φ ₂ of the motor primary current (hereinafter referred to as M-axis) according to the following formulas 1 and 2 using the torque command value τ ^* and the secondary magnetic flux command value φ ₂ ^*. i _M ^* and a current command value i _T ^{* of} a component perpendicular to the secondary magnetic flux φ ₂ (hereinafter referred to as T axis) are calculated. Here, the arithmetic circuit 7 calculates Equation 1, and the arithmetic circuit 5 calculates Equation 2.

[Formula 1]
i _M ^* = (1 / L _m ) × φ ₂ ^*
(L _m : motor excitation inductance)
[Formula 2]
i _T ^* = τ ^* / φ ₂ ^*

Coordinate converter 11 is for converting the phase current detected by the current detector 14 to the M-axis current detection value i _M and T-axis current detection value i _T, U-phase windings of the motor 17 and the secondary _Assuming that the angle formed by the magnetic flux φ ₂ is ψ ₂ , i _T and i _M are respectively calculated by Equations 3 and 4.

[Formula 3]
i _T = cos φ ₂ × i _u + cos (φ ₂ −120 °) × i _v + cos (φ ₂ + 120 °) × i _w
[Formula 4]
i _M = sinφ ₂ × i _u + sin (φ ₂ −120 °) × i _v + sin (φ ₂ + 120 °) × i _w

The T-axis current regulator 8 outputs the T-axis voltage command value v _T ^* by an adjustment operation that makes the deviation between the T-axis current command value i _T ^* and the T-axis current detection value i _T zero. The M-axis current regulator 9 outputs the M-axis voltage command value v _M ^* by an adjustment operation that makes the deviation between the M-axis current command value i _M ^* and the M-axis current detection value i _M zero.
The coordinate converter 10 performs coordinate conversion of the T-axis voltage command value v _T ^* and the M-axis voltage command value v _M ^* using the angle ψ ₂ , and the three-phase voltage command values V _u ^* and V _u according to Equations 5-7. Calculates and outputs _v ^* and _Vw ^* .

[Formula 5]
^{_{V u * = cosψ 2 × v}} M * + sinψ 2 × v T *
[Formula 6]
^{_{V v * = cos (ψ 2}} -120 °) × v M * + sin (ψ 2 -120 °) × v T *
[Formula 7]
^{_{V w * = cos (ψ 2}} + 120 °) × v M * + sin (ψ 2 + 120 °) × v T *

The inverter 13 outputs a three-phase AC voltage having a predetermined magnitude and frequency based on the three-phase voltage command values V _u ^* , V _v ^* , and V _w ^* and supplies the three-phase AC voltage to the electric motor 17.

On the other hand, the slip frequency calculator 6 calculates the slip frequency ω _sl by the following formula 8. Further, the frequency converter 20 performs the calculation of Equation 9, and converts the motor primary angular velocity estimated value ω ₁ ^ into the motor primary frequency estimated value ω ^.

[Formula 8]
^{_{ω sl = R 2 × I T}} * / φ 2 *
_{(R 2:} motor secondary time constant)
[Formula 9]
ω ^ = ω ₁ ^ × P / 120
(P: Number of motor poles)

The frequency estimated value ω ^ is integrated by the integrator 15 and the angle ψ ₂ is calculated.
Here, the magnetic flux command calculation circuit 4, until the speed estimated value omega _{r ^} reach base speed omega _b outputs a secondary magnetic flux command value φ ₂ ^* 100%, the speed estimation at the base rotational speed omega _b above A secondary magnetic flux command value φ ₂ ^* that decreases in inverse proportion to the value ω _r ^ is output.

Further, the coordinate converter 31 converts the phase voltage (the terminal voltage of the electric motor 17, that is, the output voltage of the inverter 13) detected by the voltage detector 30 into the M-axis voltage detection value v _M and the T-axis voltage detection value v _T. Therefore, v _T and v _M are calculated by Equations 10 and 11.

[Formula 10]
v _T = cos ψ ₂ × v _u + cos (ψ ₂ −120 °) × v _v + cos (ψ ₂ + 120 °) × v _w
[Formula 11]
v _M = sinφ ₂ × v _u + sin (φ ₂ −120 °) × v _v + sin (φ ₂ + 120 °) × v _w

The induced voltage calculator 32 uses the above i _T , i _M , v _T , v _M , and the primary angular velocity estimated value ω ₁ ^ calculated by the velocity estimation calculator 33, and the induced voltage is calculated according to the following equations 12 and 13. An M-axis (magnetization axis) component e _M and a T-axis (torque axis) component e _T are calculated.

[Formula 12]
e _T = v _T −R ₁ · i _T −L _σ · (d / dt) i _T −jω ₁ ^ · L _σ · i _M
[Formula 13]
e _M = v _M −R ₁ · i _M −L _σ · (d / dt) i _M + jω ₁ ^ · L _σ · i _T
However, the primary resistance R ₁ is an induction motor 17, L _sigma is leakage inductance, j is an imaginary unit.

The speed estimation calculator 33 calculates the primary angular velocity estimated value ω ₁ ^ and the motor speed estimated value ω _r ^ according to the following formulas 14 and 15 using the ω _sl and e _T.

[Formula 14]
_{ω 1 ^ = e T / e} Trate
[Formula 15]
ω _r ^ = ω ₁ ^ -ω _sl
However, _eTrate is an induced voltage at the rated speed of the induction motor 17, that is, an induced voltage coefficient.

Here, FIG. 5 shows in detail the circuit configuration between the voltage detector 30 and the coordinate converter 31 (not shown in FIG. 4), and an analog signal output from the voltage detector 30. The detected voltage values v _u and v _w are converted into digital signals by the A / D converters 51 _u and 51 _w and taken into the coordinate converter 31 via the multipliers 52 _u and 52 _w .
The multipliers 52 _u and 52 _w are for multiplying the output signals of the A / D converters 51 _u and 51 _{w by} the normalized gain, and the normalized gain is a voltage detection value after A / D conversion. These are gains for setting v _u and v _w to a predetermined data amount corresponding to the coordinate converter 31.

  Note that a speed sensorless vector control device as shown in FIG.

Japanese Patent Laid-Open No. 10-56800 (paragraphs [0003] to [0006], FIG. 1, FIG. 17, etc.)

As described above, the speed estimation calculator 33 calculates the estimated speed value ω _r ^ using the T-axis induced voltage e _T, and the calculation of e _T is performed by v _T , v _M , in other words, by the voltage detector 30. The detected voltage values v _u , v _v and v _w are indispensable.
However, an actual voltage detector has a limit of detectable data width, that is, full scale (FS). For example, if the voltage detector is F.D. S = 400V, detection resolution is 0.001P. In the case of U, this voltage detector cannot detect a voltage of less than 0.4 V (= 400 V × 0.001).

On the other hand, the induced voltage e _T of the electric motor 17 has a relationship as shown in Expression 16.
[Formula 16]
e _T = φ ₂ ^* × ω ₁
However, ω ₁ is the primary angular velocity of the motor, and the secondary magnetic flux command value φ ₂ ^* is controlled to be constant.

Thus, e _T also becomes a small value when the motor speed is low.
If the electric motor is operated at a low speed so that the terminal voltage of the electric motor 17 is less than 0.4V, the calculation results of the above-described mathematical formulas 14 and 15 have a large error with respect to the true value. This means that an error occurs between the estimated speed value ω _r ^ and the actual motor speed ω _r .

In the speed sensorless vector control device as shown in FIG. 4, the speed is controlled using the estimated motor speed value ω _r ^ which is the calculation result of Formula 15 as the state detection value, so that the motor is operated at a low speed as described above. If the terminal voltage detection value is not accurate, the actual motor speed ω _r cannot be controlled to follow the speed setting value ω _r #.
In particular, when the electric motor 17 is operated at a low speed, the motor 17 may be reversely rotated by matching the inaccurate estimated speed value ω _r ^ with the speed command value ω _r ^* , and the load 18 of the electric motor 17 is in the reverse rotation state. Is an emergency stop condition, there is a risk of causing a serious accident such as the equipment being shut down.

  Therefore, the problem to be solved by the present invention is to provide a vector control device that controls the induction motor to the low speed side without a speed sensor, and that enables a desired torque / speed control without causing an abnormal situation such as reverse rotation of the motor. It is to provide.

In order to solve the above problems, the invention described in claim 1 divides the primary current of the induction motor into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and the currents of these components are in accordance with the command values. In this way, the induction motor vector control device controls the torque and speed of the electric motor by controlling the power converter, and the means for calculating the induced voltage from the terminal voltage detection value and the electric constant of the electric motor In a speed sensorless vector control device comprising: means for estimating the speed of the electric motor using an induced voltage; and means for controlling the speed using the estimated speed as a state detection value.
A voltage detector for detecting a terminal voltage of the motor, the first voltage detector having a normal resolution and a second voltage detector with a high resolution,
Switch means for A / D converting the output of the first voltage detector during high-speed operation of the motor, and switching to A / D-convert the output of the second voltage detector during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
During low speed operation of the motor, multiplied by a value of the terminal voltage detected value and the A / D conversion through the switch means by the second voltage detector, and a normalized gain of high resolution corresponding to switching by the switches The value is used for the calculation of the induced voltage.

According to the second aspect of the present invention, the primary current of the induction motor is separated into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and the power converter is controlled so that the current of each component is in accordance with the command value. An induction motor vector control device for controlling the torque and speed of the motor, wherein the motor uses the induced voltage calculated by means for calculating the induced voltage from a terminal voltage detection value and an electrical constant of the motor. In a speed sensorless vector control device comprising: means for estimating the speed of: and means for controlling the speed using the estimated speed as a state detection value;
A voltage detector for detecting a terminal voltage of the electric motor;
A first integrating A / D converter corresponding to a normal resolution having a long sampling period , and a second integrating A / D converter corresponding to a high resolution having a sampling period shorter than that of the A / D converter ;
Switch means for selecting a long sampling period during high-speed operation of the motor and switching to select a short sampling period during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
During low-speed operation of the electric motor, a value obtained by A / D converting the terminal voltage detection value by the voltage detector by the second integration type A / D converter in which a short sampling period is selected by the switch means, and the switch and the normalized gain of the high resolution corresponding to switching, the value obtained by multiplying those used for the operation of the induced voltage.

The invention described in claim 3 divides the primary current of the induction motor into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and controls the power converter so that the current of each component is in accordance with the command value. An induction motor vector control device for controlling the torque and speed of the motor, wherein the motor uses the induced voltage calculated by means for calculating the induced voltage from a terminal voltage detection value and an electrical constant of the motor. In a speed sensorless vector control device comprising: means for estimating the speed of: and means for controlling the speed using the estimated speed as a state detection value;
A voltage detector for detecting a terminal voltage of the electric motor;
A first ΔΣ modulation type A / D converter corresponding to a normal resolution having a low basic clock frequency used for pulse density modulation , and a second ΔΣ corresponding to a high resolution having a higher basic clock frequency than the A / D converter. A modulation method A / D converter ;
Switch means for selecting a low clock frequency during high-speed operation of the motor and switching to select a high clock frequency during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
Wherein at the time of low speed operation of the motor, and a value of the terminal voltage detection value by the voltage detector by the second ΔΣ modulation type A / D converter a high clock frequency by said switching means is selected and converted A / D, the switch it is to use the normalized gain of the high resolution corresponding to switching by the value obtained by multiplying the calculation of the induced voltage.

  According to the present invention, it is possible to improve the speed estimation resolution at the time of low-speed operation of the electric motor, and these abnormal situations can be detected even in the low-speed operation region in which the conventional controller has caused an abnormal reverse operation of the electric motor. It is possible to provide a vector control device that can prevent the torque and speed of the induction motor and prevent it.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a circuit configuration diagram showing a main part of the first embodiment of the present invention, which is an improvement of the circuit configuration between the voltage detector 30 and the coordinate converter 31 in FIG. 5 described above.

In this embodiment, the voltage detector for detecting the terminal voltage of the electric motor 17 has high resolution (for example, 10 times that of the first voltage detector 30) in addition to the first voltage detector 30 having normal resolution. A second voltage detector 40 is provided. The voltage detection values v _u and v _w detected by these voltage detectors 30 and 40 are input to the switching terminal side of the switches 53 _u and 53 _w constituting the switch means 53 and are output terminals of the switches 53 _u and 53 _w . _Are connected to A / D converters 51 _u and 51 _w , respectively.

In addition, a normalization gain 1 (corresponding to normal resolution) or a normalization gain 2 (corresponding to high resolution) is switched by a switch 54 in the multipliers 52 _u and 52 _w on the output side of the A / D converters 51 _u and 51 _w. Can be input.
Reference numeral 41 denotes a comparator that determines whether or not the induction motor 17 is in the low speed operation region from the speed command value ω _r ^* output from the speed command calculation circuit 2 and outputs the output according to the determination result. The switches 53 _u , 53 _w and 54 operate so as to be switched simultaneously at the same time.

In the above configuration, for example, when the speed command value ω _r ^* is less than 10% of the rated speed, the comparator 41 determines that the operation is at a low speed, and the switch 53 _u , 53 _w is switched to the second voltage detector with high resolution based on the output. In addition to switching to the 40 side, the switch 54 is switched to the normalized gain 2 (corresponding to high resolution) side.
As an example of the resolution setting, the full scale of the first voltage detector 30 having the normal resolution is 400 V, and the detection resolution is 0.001 P.V. U corresponds to the normal speed range of the electric motor 17 (the electric motor speed is 0 to 1500 rpm), the full scale of the high-resolution second voltage detector 40 is 40 V, and the detection resolution is also 0.001 P.s. U only needs to correspond to the low speed region (0 to 150 rpm) of the electric motor 17.
As described above, when the second voltage detector 40 whose substantial resolution is 10 times that of the first voltage detector 30 is used in combination, in the low speed operation region, the speed estimation resolution is equivalent to 10 times that of the prior art. Improvement is possible.

According to this embodiment, in the low-speed operation region of the electric motor 17, the terminal voltage detection values v _u and v _w by the high-resolution second voltage detector 40 are A / D converted and taken into the coordinate converter 31. Therefore, even if the voltage detection values v _u and v _w are small, these can be detected accurately. Then, the coordinate converter 31 and the induced voltage calculator 32 obtain the T-axis induced voltage e _T by the equations 10 and 12, etc., and the speed estimation calculator 33 obtains the estimated speed value ω _r ^ by the equations 14 and 15 with high accuracy. It becomes possible to calculate to.
Therefore, the estimated speed value ω _r ^ substantially coincides with the actual motor speed ω _r , and the motor speed ω _r can be controlled in accordance with the speed command value ω _r ^{* so} that an abnormal situation such as an unexpected reverse phenomenon of the motor 17 occurs. Can be prevented.

Here, if the normalized gains 1 and 2 in FIG. 1 are set to values corresponding to the respective resolutions, even if the voltage detectors 30 and 40 are switched, the physical quantities and coordinate conversion of the voltage detection values v _u and v _w are performed. The relationship with the amount of data input to the device 31 can be kept constant.

Next, FIG. 2 is a circuit configuration diagram showing the main part of the second embodiment of the present invention.
In the figure, 56 _u and 56 _w are so-called integral type A / D converters, which are configured as a simple integral type or a double integral type. The A / D converters 56 _u and 56 _w receive voltage detection values v _u and v _{w from the} voltage detector 30 having a normal resolution, respectively, and the configuration after the A / D converters 56 _u and 56 _w. Is similar to FIG.

Further, 55 is a switch for switching the A / D converter 56 _u, 56 _w sampled periodic cycle is long high sampling cycle (normally resolution support) or cycle is shorter low sampling period (high resolution corresponding), this The switches 55 and 54 are switched simultaneously at the same time by the output of the comparator 41 that determines whether or not the induction motor 17 is in the low speed operation region based on the speed command value ω _r ^* .

Also in this embodiment, for example, when the speed command value ω _r ^* is less than 10% of the rated speed, the comparator 41 determines that the operation is at a low speed, and the switch 55 is set to the low sampling period (high resolution compatible) side by the output. At the same time, the switch 54 is switched to the normalized gain 2 (corresponding to high resolution) side.
In this case, if the low sampling period is set to 1/2 of the high sampling period and the switch 55 is switched to the low sampling period side during low-speed operation, the speed estimation resolution can be doubled compared to the conventional technique. At the same time, the switch 54 is switched to the normalized gain 2 side (having 1/2 the size of the normalized gain 1), whereby the physical quantities of the voltage detection values v _u and v _w and the coordinate converter 31 are changed. The relationship with the amount of input data can be kept constant.
Therefore, also in the present embodiment, the estimated speed value ω _r ^ substantially coincides with the actual motor speed ω _r , and the motor speed ω _r can be controlled according to the speed command value ω _r ^* , so that the motor 17 is not expected. Occurrence of a reverse phenomenon or the like can be prevented.

Next, FIG. 3 is a circuit configuration diagram showing the main part of the third embodiment of the present invention.
Basics This embodiment differs from the Figure 2, that using the A / D converter of the so-called ΔΣ modulation system as the A / D converter ₅₇ u, 57 _w, give these A / D converter ₅₇ u, 57 _w As a clock, a low clock having a low frequency (corresponding to a normal resolution) and a high clock having a high frequency (corresponding to a high resolution) can be switched by a switch 55, and other configurations are the same as those in FIG.

Here, the ΔΣ modulation type A / D converter means that an analog input signal is modulated by modulating an analog input signal into a 1-bit pulse density signal (digital signal) and measuring it with a counter via an oversampler. Is converted into a digital signal.
In this ΔΣ modulation type A / D converter, the higher the frequency of the basic clock used for the modulation processing, the greater the weight of the input analog data amount and the higher the resolution of one count of the modulated data, and the voltage detection value. This can be detected even when v _u and v _w are small.

Therefore, as described above, for example, when the speed command value ω _r ^* is less than 10% of the rated speed, the comparator 41 determines that the operation is at a low speed, and switches the switch 55 to the high clock (corresponding to high resolution) side based on the output. If the switch 54 is switched to the normalized gain 2 (high resolution compatible) side, the speed estimation resolution can be improved, and the physical quantities of the voltage detection values v _u and v _{w and} the data input to the coordinate converter 31 The relationship with the quantity can be kept constant.
Therefore, also in the present embodiment, the motor speed ω _r can be controlled according to the speed command value ω _r ^{*, so} that an unexpected reverse phenomenon or the like of the motor 17 can be prevented.

It is a circuit block diagram which shows the principal part of 1st Embodiment of this invention. It is a circuit block diagram which shows the principal part of 2nd Embodiment of this invention. It is a circuit block diagram which shows the principal part of 3rd Embodiment of this invention. It is a block diagram which shows a prior art. FIG. 5 is a partial circuit configuration diagram in FIG. 4.

Explanation of symbols

1: Speed setter 2: Speed command calculation circuit 3: Speed controller 4: Magnetic flux command calculation circuit 5, 7: Calculator 6: Slip frequency calculator 8: T-axis current controller 9: M-axis current controller 10, 11, 31: Coordinate converter 12: AC power supply 13: Inverter 14: Current detector 15: Integrator 17: Induction motor 18: Load 20: Frequency converter 30, 40: Voltage detector 32: Induced voltage calculator 33: Speed estimation calculator 40: Voltage detector 41: Comparator _51u , _51w , _56u , _56w , _57u , _57w , A / D converter _52u , _52w : Multiplier 53: Switch means _53u , 53 _w , 54, 55: switch 100: control device

Claims (3)

The primary current of the induction motor is separated into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and the power converter is controlled so that the current of each component is in accordance with the command value. A vector control device for an induction motor to be controlled, comprising: means for calculating an induced voltage from a detected terminal voltage value of the motor and an electric constant; means for estimating the speed of the motor using the calculated induced voltage; A speed sensorless vector control device comprising: means for controlling the speed using the detected speed as a state detection value;
A voltage detector for detecting a terminal voltage of the motor, the first voltage detector having a normal resolution and a second voltage detector with a high resolution,
Switch means for A / D converting the output of the first voltage detector during high-speed operation of the motor, and switching to A / D-convert the output of the second voltage detector during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
During low speed operation of the motor, multiplied by a value of the terminal voltage detected value and the A / D conversion through the switch means by the second voltage detector, and a normalized gain of high resolution corresponding to switching by the switches A vector control device for an induction motor, wherein a value is used for calculation of the induced voltage. The primary current of the induction motor is separated into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and the power converter is controlled so that the current of each component is in accordance with the command value. A vector control device for an induction motor to be controlled, comprising: means for calculating an induced voltage from a detected terminal voltage value of the motor and an electric constant; means for estimating the speed of the motor using the calculated induced voltage; A speed sensorless vector control device comprising: means for controlling the speed using the detected speed as a state detection value;
A voltage detector for detecting a terminal voltage of the electric motor;
A first integrating A / D converter corresponding to a normal resolution having a long sampling period , and a second integrating A / D converter corresponding to a high resolution having a sampling period shorter than that of the A / D converter ;
Switch means for selecting a long sampling period during high-speed operation of the motor and switching to select a short sampling period during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
During low-speed operation of the electric motor, a value obtained by A / D converting the terminal voltage detection value by the voltage detector by the second integration type A / D converter in which a short sampling period is selected by the switch means, and the switch A vector control device for an induction motor, wherein a value obtained by multiplying a switched high-resolution standardized gain is used for the calculation of the induced voltage. The primary current of the induction motor is separated into a component parallel to the secondary magnetic flux and a component perpendicular to the secondary magnetic flux, and the power converter is controlled so that the current of each component is in accordance with the command value. A vector control device for an induction motor to be controlled, comprising: means for calculating an induced voltage from a detected terminal voltage value of the motor and an electric constant; means for estimating the speed of the motor using the calculated induced voltage; A speed sensorless vector control device comprising: means for controlling the speed using the detected speed as a state detection value;
A voltage detector for detecting a terminal voltage of the electric motor;
A first ΔΣ modulation type A / D converter corresponding to a normal resolution having a low basic clock frequency used for pulse density modulation , and a second ΔΣ corresponding to a high resolution having a higher basic clock frequency than the A / D converter. A modulation method A / D converter ;
Switch means for selecting a low clock frequency during high-speed operation of the motor and switching to select a high clock frequency during low-speed operation of the motor;
A switch that switches between a normalization gain corresponding to a normal resolution and a normalization gain corresponding to a high resolution in conjunction with the switch means ,
Wherein at the time of low speed operation of the motor, and a value of the terminal voltage detection value by the voltage detector by the second ΔΣ modulation type A / D converter a high clock frequency by said switching means is selected and converted A / D, the switch vector controller for an induction motor and the normalized gain of the high resolution corresponding, a value obtained by multiplying is characterized by using the calculation of the induced voltage switched by.

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