JP2016144251A - Control device for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device capable of estimating a rotational speed in reactivation without generating brake torque during low-speed rotations of an induction motor.SOLUTION: The control device comprises: an inverter 20; current detection means 30 which detects a phase current of an induction motor 10; current regulation means 50 which calculates a voltage command value in such a manner that the current detection value is matched with a current command value; magnetic flux estimation means 90 for estimating a secondary magnetic flux by integrating a value that is obtained by subtracting a voltage drop component caused by primary resistance of the motor 10 from an output voltage corresponding value of the inverter 20; differentiation arithmetic means 100 which differentiates output of the magnetic flux estimation means twice; and rotational speed estimation means 150 which estimates a rotational speed on the basis of output of the differentiation arithmetic means. When a DC current is applied to the motor 10 in a free-run state for a short time, the estimation means 150 divides a twice differentiation result of a q-axis component of the secondary magnetic flux outputted from the differentiation arithmetic means 100 with a product of excitation inductance, an inverse of a secondary time constant and the DC current and estimates the rotational speed of the motor 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a so-called sensorless vector control apparatus that controls an induction motor by a power converter without using a speed detector, and more particularly, to rotate an induction motor when restarting an induction motor in a free-run state. The present invention relates to a technique for estimating speed.

Sensorless vector control of induction motors is widely used for applications that require consideration of miniaturization of motors and maintenance of rotary encoders. When restarting an induction motor in a free-run state, it is desirable to estimate the rotational speed first in order to reduce torque shock at the time of restart.
As such a control device for estimating the rotation speed when the induction motor is restarted, for example, a control device described in Patent Document 1 is known.

FIG. 4 is a block diagram showing the configuration of the control device described in Patent Document 1. As shown in FIG.
In FIG. 4, the start related signal generator 1 outputs a power converter start signal S0, a speed estimation signal S1, and a controller start signal S2. The power converter 2 such as an inverter is controlled based on the power converter start signal S0 and the voltage command selected by the switch SW, converts the DC voltage into an AC voltage having a variable voltage and a variable frequency, and supplies the AC voltage to the induction motor 10. .

The pre-excitation current control means 4 outputs a voltage command V _c3 so that the input current i of the induction motor 10 becomes a predetermined DC current, and the secondary voltage calculation means 5 outputs the input voltage v and input current of the induction motor 10. computing the secondary voltage V ₂ of the induction motor 10 on the basis to i. 3a is a current detector, and 3b is a voltage detector.

The first speed estimation means 6 estimates the rotational angular frequency ω and the secondary magnetic flux φ ₂ using the residual magnetic flux of the induction motor 10 and generates and outputs a voltage command V _c2 .
The second speed estimating unit 7, based on the secondary flux vector obtained by integrating the secondary voltage V ₂ times, and calculates the rotational angular frequency ω corresponding to the rotational speed of the induction motor 10.

The initial magnetic flux calculation means 8 uses the rotational angular frequency ω, the secondary time constant T _{2 of the} induction motor 10, the excitation inductance M, the minute time when the speed estimation signal S 1 is “2”, etc., and the secondary magnetic flux φ. ₂ is calculated and output.
The control device 9 generates a voltage command V _c1 based on the rotational angular frequency ω, the secondary magnetic flux φ ₂ and the controller start signal S2.
It should be noted that the switch SW provides a voltage command V _c1 when the speed estimation signal S1 is “0”, V _c2 when the S1 is “1”, and V _c3 when the S1 is “2”. It operates to select and give to the power converter 2.

In this prior art, a direct current is passed through the induction motor 10 in accordance with the voltage command V _c3 from the pre-excitation current control means 4 in the minute time, and a value obtained by subtracting the primary resistance voltage drop from the output voltage v of the power converter 2 is obtained. The secondary magnetic flux Φ is obtained by integration, and the vector locus is drawn on the dq axis plane of the rotating coordinate system. Here, the time change Φ _dq (t) of the secondary magnetic flux when the direct current i _{dx is made} to flow on the d axis is expressed by the secondary time constant T ₂ , the rotational angular frequency ω _re , the direct current i _dx of the induction motor 10. Can be expressed by Equation 1 using the elapsed time t from the start of application of the voltage, the exciting inductance M, and the imaginary operator j.

According to Patent Document 1, Φ _dq (t) draws a circular locus when t is sufficiently shorter than T ₂ , and the rotation angular frequency ω _re that draws the locus coincides with the rotation speed. Therefore, by the action of the speed estimation means 7, within a very short time when the speed estimation signal S1 is “2”, two vectors starting from the center of the circle and ending at the point on the circular locus are obtained. The rotational angular frequency ω _re of the induction motor 10, that is, the rotational speed is estimated based on the fact that the phase difference between the two coincides with ω _re t.

Japanese Patent No. 3535735 (paragraph [0019], FIG. 1 etc.)

  However, when the induction motor 10 is rotating at an extremely low speed, the time until the vector locus of the secondary magnetic flux is obtained becomes long. In the meantime, the conventional technique has a problem that a brake torque proportional to the rotation speed is generated because the time elapses while a direct current is passed through the induction motor 10.

  Therefore, the problem to be solved by the present invention is to provide a control device for an induction motor that can estimate the rotational speed at the time of restart without generating brake torque when the induction motor is in a free-run state at a low speed. There is to do.

In order to solve the above problem, an invention according to claim 1 is a control device that performs variable speed control of an induction motor without using a speed detector.
A power converter for converting a DC voltage into a three-phase AC voltage of variable voltage and variable frequency and supplying the same to the motor;
Current detecting means for detecting the phase current of the motor;
Current adjusting means for calculating a voltage command value so that a current detection value by the current detection means matches a current command value;
Magnetic flux estimating means for estimating a secondary magnetic flux of the motor by integrating a value obtained by subtracting a voltage drop due to a primary resistance of the motor from an output voltage equivalent value of the power converter;
Differential operation means for differentiating the output of the magnetic flux estimation means twice;
Rotation speed estimation means for estimating the rotation speed of the electric motor based on the output of the differential calculation means,
The rotational speed estimation means includes
When a DC current is passed through the motor in a free-run state in accordance with a DC current command value as the current command value for a short time, the second-derivative result of the q-axis component of the secondary magnetic flux output from the differential calculation means is Means for estimating the rotational speed of the motor by dividing by the product of the exciting inductance of the motor, the reciprocal of the secondary time constant, and the direct current.

  According to a second aspect of the present invention, in the induction motor control device according to the first aspect, the rotational speed estimating means determines the second derivative result of the d-axis component of the secondary magnetic flux as the excitation inductance, the direct current, and the like. Means for calculating the reciprocal of the second-order time constant based on the value divided by the product of.

The invention according to claim 3 is a control device that performs variable speed control of an induction motor without using a speed detector.
A power converter that converts a DC voltage into a three-phase AC voltage having a variable voltage and a variable frequency and supplies the three-phase AC voltage to the electric motor;
Current adjusting means for calculating a voltage command value so that a current detection value by the current detection means matches a current command value;
Differential operation means for differentiating the output voltage equivalent value of the power converter once;
Rotation speed estimation means for estimating the rotation speed of the electric motor based on the output of the differential calculation means,
The rotational speed estimation means includes
The result of one-time differentiation of the q-axis component of the output voltage equivalent value output from the differentiation calculation means when a direct current is passed through the motor in the free-run state for a short time according to the direct current command value as the current command value Is divided by the product of the exciting inductance of the motor, the reciprocal of the second-order time constant, and the DC current to estimate the rotational speed of the motor.

  According to a fourth aspect of the present invention, in the control apparatus for an induction motor according to the third aspect, the rotational speed estimating means determines the first derivative result of the d-axis component of the output voltage equivalent value and the excitation inductance of the motor. Means for calculating the reciprocal of the second-order time constant based on a value divided by the product of the direct current is provided.

  According to a fifth aspect of the present invention, in the induction motor control device according to the fourth aspect, the current adjusting means is constituted by a proportional integral adjustment calculating means, and the q-axis component of the integration result by the proportional integral adjustment calculating means is the Differentiating by the differential calculation means to obtain a single differential result of the q-axis component of the output voltage equivalent value, and differentiating the d-axis component of the integration result by the proportional integral adjustment calculation means by the differential calculation means to output the output voltage The result of one-time differentiation of the equivalent d-axis component is obtained.

According to the first aspect of the invention, the initial speed is estimated using the second derivative value of the secondary magnetic flux when a direct current is passed through the induction motor in a free-run state at a low speed for a short time. The time required for the rotational speed estimation calculation can be shortened. Thereby, the brake torque generated when the induction motor is restarted can be reduced.
Further, according to the invention of claim 2, even when the secondary time constant changes due to temperature or the like, the initial speed is estimated after the calculation of the secondary time constant, so that it is not affected by the temperature change. The rotational speed can be estimated.

  According to the inventions according to claims 3 to 5, instead of the magnetic flux estimating means, for example, the output of the integrator constituting the current adjusting means can be used, and the configuration and calculation of the control device for estimating the rotational speed The contents can be simplified.

1 is a block diagram showing a configuration of a control device according to a first embodiment of the present invention. It is explanatory drawing of the 1st differential value and secondary differential value of the secondary magnetic flux in 1st Embodiment. It is a block diagram which shows the structure of the control apparatus which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the control apparatus described in patent document 1. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a control device according to the first embodiment of the present invention. In FIG. 1, addition / subtraction means 150d and 150q are provided from an externally applied d-axis current command value i _d ^* and q-axis current command value i _q ^{* of} a rotating coordinate system, and a three-phase / two-phase conversion means 70 described later. Deviations between the output d-axis current detection value i _d and the q-axis current detection value i _q are calculated. The current adjusting means 50 performs a proportional-integral (PI) adjustment calculation so that these deviations become zero, and outputs a d-axis voltage command value v _d ^* and a q-axis voltage command value v _q ^* .

In this embodiment, since it is assumed that the induction motor 10 is in a free-run state, the d-axis current command value i _d ^* is a predetermined positive DC current command value i _dx ^* , and the q-axis current command value i _q ^* Is given “0”. Further, the current adjusting means 50 sets a gain such that the current detection value follows the current command value with a time constant sufficiently faster than the secondary magnetic flux of the induction motor 10.

In normal operation, the two-phase / three-phase conversion means 60 converts the d-axis voltage command value v _d ^* and the q-axis voltage command value v _q ^* of the rotating coordinate system synchronized with the output frequency of the inverter 20 to each of the fixed coordinate systems. The phase voltage command values v _u ^* , v _v ^* , and v _w ^* are converted and output. In this embodiment, since a direct current flows through the induction motor 10, the output frequency of the inverter 20 is 0 [Hz]. Shall.
The inverter 20 converts the DC voltage into a three-phase AC voltage by PWM (pulse width modulation) control according to the voltage command values v _u ^* , v _v ^* , and v _w ^* , and supplies the three-phase AC voltage to the induction motor 10.

The current detection means 30 detects the current flowing through the induction motor 10 and outputs the three-phase current detection values i _u , i _v , i _w to the first three-phase / two-phase conversion means 70. In addition, the voltage detection means 40 outputs the output voltage detection values v _u , v _v , v _w of the inverter 20 to the second three-phase / two-phase conversion means 80. Here, the detected values of the current and voltage may be converted from three-phase values from two-phase values.
In addition, the output voltage of the inverter 20 may detect an actual voltage using an AC voltage detector, or may be estimated based on a voltage command value.

  The first and second three-phase / two-phase conversion means 70, 80 convert each detected value of the fixed coordinate system into each detected value of the rotating coordinate system synchronized with the output frequency of the inverter 20 in normal operation. However, in the same manner as described above, the frequency is fixed to 0 [Hz].

Next, the magnetic flux estimation means 90 estimates the secondary magnetic flux by performing the calculation of Equation 2. In Equation 2, Φ _d is a d-axis magnetic flux, Φ _q is a q-axis magnetic flux, R _s is a primary resistance of the induction motor 10, and other various amounts are as described above.

Differential operation means 100, using the d-axis magnetic flux [Phi _d and q-axis magnetic flux [Phi _q, calculates the second derivative value of the secondary flux in the following manner.
In other words, when Φ _d and Φ _q are input from the magnetic flux estimating means 90, the differential calculation means 100, with respect to these Φ _d and Φ _q , the value immediately before the calculation cycle T _s and the value input this time Is divided by T _s to perform first differentiation to obtain dΦ _d / dt and dΦ _q / dt. In general, the differential calculation also includes unnecessary high frequency band noise, so that the value after the first differential calculation is preferably passed through an appropriate low-pass filter.

In the upper part of FIG. 2, the waveform of the first derivative value (dΦ _d / dt, dΦ _q / dt) of the secondary magnetic flux obtained in this way and the second derivative value (d ² ) described later, which is the inclination of these waveforms. Φ _d / dt ² , d ² Φ _q / dt ² ).

The timing generation unit 110 in FIG. 1 receives the d-axis current command value i _d ^* (DC current command value i _dx ^* ) from the current adjustment unit 50 at time t ₀ in FIG. slight period Delta] t _on from time _{t 1} that is substantially coincident with the value _{i dx} ^* until time _{t 2, the} outputs oN signal to the differential operation means 100.

Differential operation means 100 calculates the slope of the first derivative value of the average secondary flux in the period Delta] t _on, and outputs this as the second derivative value of the secondary flux. That is, the second-order differential value (d ² Φ _d / dt ² ) of the _d- axis magnetic flux is output to the second-order time constant reciprocal computing means 120, and the second-order differential value (d ² Φ _q / dt ² ) of the q-axis magnetic flux is output. Output to the initial speed calculation means 130.

The secondary time constant reciprocal computing means 120 computes the reciprocal (= R _r / L _r ) of the secondary time constant T _{2 according to} the following Equation 3 and inputs it to the initial speed computing means 130. Note that _Rr is a secondary resistance of the induction motor 10, and _Lr is a secondary inductance.

Further, the initial speed calculation means 130 estimates the initial speed ω _re0 as the rotational speed of the induction motor 10 that starts from the free-run state by the following mathematical formula 4.
The secondary time constant reciprocal computing means 120 and the initial speed computing means 130 constitute a rotational speed estimating means 160 in the claims.

Here, according to the prior art described in Patent Document 1, the secondary magnetic flux draws a locus close to a circle. That is, since the secondary magnetic flux is composed of an exponential function representing a locus, it is a function that can be differentiated multiple times.
For this reason, the following formula 5 is obtained by differentiating the above-described formula 1 twice. However, in this embodiment, instead of the secondary time constant T ₂ in Equation 1, the reciprocal of the secondary time constant T ₂ = 1 / T ₂ = R _r / L _r is used.

つまり、数式３、数式４は、数式６に示される関係を二次時定数の逆数（Ｒ_ｒ／Ｌ_ｒ）及び回転速度ω_ｒｅ０について求めたものであることがわかる。 Further, as described above, Equation 6 is approximately established in a short period (t≈0) after the direct current according to the command value is supplied to the induction motor 10.

That is, it can be seen that Equations 3 and 4 are obtained by _{obtaining the} relationship shown in Equation 6 with respect to the reciprocal of the secondary time constant (R _r / L _r ) and the rotational speed ω _re0 .

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of a control device according to the second embodiment.
In the second embodiment, the voltage detection means 40, the second three-phase / two-phase conversion means 80, the magnetic flux estimation means 90, and the differential calculation means 100 in FIG. 1 are removed, and instead, as shown in FIG. The output of the d-axis integrator and the output of the q-axis integrator derived from the current adjustment means 50 having the PI adjustment calculation function are input to the differentiation calculation means 140, and during the ON signal period Δt _on output from the timing generation means 110, The average slopes of the outputs of the d-axis and q-axis integrators are calculated as differential values, respectively. Other configurations in FIG. 3 are the same as those in FIG. 1, and thus description thereof is omitted to avoid duplication.

The average slope of the d-axis integrator output output from the differential calculation means 140 in FIG. 3 is input to the second-order time constant reciprocal calculation means 120 as a second-order differential value of the d-axis magnetic flux, and the q-axis integrator output The average gradient is input to the initial speed calculation means 130 as a twice differential value of the q-axis magnetic flux.
Here, when a leakage coefficient in the case where a direct current is passed through the induction motor 10 is σ, the voltage equation is expressed by Equation 7.

When the direct current is constant, the result obtained by differentiating Equation 7 is Equation 8.

Therefore, by regarding the voltage gradients dv _d / dt and dv _q / dt as the differential values d ² Φ _d / dt ² and d ² Φ _q / dt ^{2 of the} secondary magnetic flux as shown in Equation 8, The rotation speed estimation means 160 can perform the calculation of Expression 3 by the secondary time constant reciprocal calculation means 120 and the calculation of Expression 4 by the initial speed calculation means 130, and can calculate the rotation speed ω _re0 as in the first embodiment. Can be estimated.
In the second embodiment, unnecessary noise components are not included in the calculation result by using the d and q axis integrator outputs of the current adjusting means 50 for estimating the rotation speed.

10: induction motor 20: inverter 30: current detection means 40: voltage detection means 50: current adjustment means 60: two-phase / three-phase conversion means 70, 80: three-phase / two-phase conversion means 90: magnetic flux estimation means 100: differentiation Calculation means (2nd derivative)
110: Timing generation means 120: Secondary time constant reciprocal calculation means 130: Initial speed calculation means 140: Differential calculation means (one-time differentiation)
160: Rotational speed estimation means

Claims (5)

In a control device for variable speed control of an induction motor without using a speed detector,
A power converter for converting a DC voltage into a three-phase AC voltage of variable voltage and variable frequency and supplying the same to the motor;
Current detecting means for detecting the phase current of the motor;
Current adjusting means for calculating a voltage command value so that a current detection value by the current detection means matches a current command value;
Magnetic flux estimating means for estimating a secondary magnetic flux of the motor by integrating a value obtained by subtracting a voltage drop due to a primary resistance of the motor from an output voltage equivalent value of the power converter;
Differential operation means for differentiating the output of the magnetic flux estimation means twice;
Rotation speed estimation means for estimating the rotation speed of the electric motor based on the output of the differential calculation means;
With
The rotational speed estimation means includes
When a DC current is passed through the motor in a free-run state in accordance with a DC current command value as the current command value for a short time, the second-derivative result of the q-axis component of the secondary magnetic flux output from the differential calculation means is An induction motor control apparatus comprising: means for estimating the rotational speed of the motor by dividing by the product of an exciting inductance of the motor, a reciprocal of a secondary time constant, and the direct current. In the induction motor control device according to claim 1,
The rotational speed estimation means includes
And a means for calculating a reciprocal of the secondary time constant based on a value obtained by dividing a second-order differential result of the d-axis component of the secondary magnetic flux by a product of the exciting inductance and the direct current. Induction motor controller. In a control device for variable speed control of an induction motor without using a speed detector,
A power converter for converting a DC voltage into a three-phase AC voltage of variable voltage and variable frequency and supplying the same to the motor;
Current detecting means for detecting the phase current of the motor;
Current adjusting means for calculating a voltage command value so that a current detection value by the current detection means matches a current command value;
Differential operation means for differentiating the output voltage equivalent value of the power converter once;
Rotation speed estimation means for estimating the rotation speed of the electric motor based on the output of the differential calculation means;
With
The rotational speed estimation means includes
The result of one-time differentiation of the q-axis component of the output voltage equivalent value output from the differentiation calculation means when a direct current is passed through the motor in the free-run state for a short time according to the direct current command value as the current command value Is divided by the product of the exciting inductance of the motor, the reciprocal of the secondary time constant, and the direct current, to estimate the rotational speed of the motor. In the induction motor control device according to claim 3,
The rotational speed estimation means includes
Means for calculating a reciprocal of the second-order time constant based on a value obtained by dividing the result of one-time differentiation of the d-axis component of the output voltage equivalent value by the product of the exciting inductance of the motor and the direct current. A control device for an induction motor as a feature. In the induction motor control device according to claim 4,
The current adjusting means is constituted by proportional integral adjustment calculating means,
The q-axis component of the integration result obtained by the proportional-integral-adjustment calculating means is differentiated by the differential-calculating means to obtain a single-derivative result of the q-axis component of the output voltage equivalent value, and A control apparatus for an induction motor, wherein a d-axis component is differentiated by the differential operation means to obtain a once-differential result of the d-axis component of the output voltage equivalent value.

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