JP3322088B2 - Induction motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor driven at a variable speed by a PWM inverter, and more particularly to a control device for improving the torque characteristics of the induction motor in a low speed range.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a conventional example of a control device for an induction motor driven at a variable speed by a PWM inverter of this kind. In FIG. 6, the control device 10 inputs a frequency command value (f ^* ) commanded from the external frequency command device 1 to the fv converter 11 to input a q-axis voltage value (V
q ′), and converts the frequency command value (f ^* ) into the integration calculator 1
2, the rotation angle (θ) is calculated, and the current detector 13,
U-phase induction motor 2 connected to the output of the PWM inverter 20 by 14, the current detection value of the W-phase (i _U, i _W) is detected and the current detection value (i _U, i _W) and the rotation angle (theta ) Is input to the coordinate transformation calculator 15 to calculate the q-axis current (iq), and the frequency command value (f ^* ), the q-axis current (iq), and the preset d-axis current value of the induction motor 2 ( id ^* ), the primary resistance value (r ₁ ) and the leakage inductance (lσ) are input to the compensation amount calculator 16 to calculate the q-axis voltage compensation amount (ΔVq) and the d-axis voltage compensation amount (ΔVd). q-axis voltage value (V
q ′) and the q-axis voltage compensation amount (ΔVq).
To calculate a q-axis voltage command value (Vq), a d-axis voltage compensation amount (ΔVd) and a preset d-axis voltage (Vd ′)
Is input to the adder 18 and the d-axis voltage command value (Vd)
, And input the q-axis voltage command value (Vq) and the d-axis voltage command value (Vd) to the polar coordinate conversion calculator 19 to obtain the voltage command absolute value (| V ^* |), the phase angle (δ ^* ), Is calculated, and the voltage command absolute value (| V ^* |) and the phase angle (δ ^* ) are input to the PWM inverter 20 to obtain the voltage command value ( _VU ^* ,
V _V ^*, a configuration for supplying an output voltage based on V _W ^*) to the induction motor 2.

The operation of the control device 10 will be described below using the voltage equation of the induction motor. First, a voltage equation (steady state) using the dq coordinate axes is expressed by Equation (1),
It is represented by (2).

[0004]

## EQU1 ## v _1d = r ₁ · i _1d -ω ₁ · lσ · i _1q + ω ₁ · φ _2q (1)

[0005]

V _1q = r ₁ · i _1q + ω ₁ · lσ · i _1d + ω ₁ · φ _2d (2) The symbols in the equations (1) and (2) are as follows. r ₁ : primary resistance value of the induction motor lσ: leakage inductance of the induction motor ω ₁ : primary angular frequency of the induction motor φ _2d : secondary magnetic flux d-axis component of the induction motor φ _2q : secondary magnetic flux q-axis component of the induction motor i _1d : primary current d-axis component of the induction motor (excitation current component) i _1q : primary current q-axis component of the induction motor (torque current component) v _1d : primary voltage d-axis component of the induction motor v _1q : primary voltage of the induction motor q-axis component Here, when the induction motor magnetic flux axis for control is placed on the same axis as the secondary magnetic flux d-axis component (φ _2d ), φ _2d is constant, φ _2q = 0, and equations (1) and (2) ) Is transformed into equations (3) and (4).

[0006]

[Expression 3] v _1d = r ₁ · i _1d -ω ₁ · lσ · i _1q (3)

[0007]

V _1q = r ₁ · i _1q + ω ₁ · lσ · i _1d + ω ₁ · φ _2d (4) Therefore, the polar coordinate conversion calculator is used as the voltage (output voltage of the PWM inverter 20) applied to the induction motor 2. The q-axis voltage command value (Vq) and the d-axis voltage command value (V
d) is given by equations (5) and (6).

[0008]

Vd = r ₁ · id ^* −2πf ^* · lσ · iq (5)

[0009]

Vq = r ₁ · iq + 2πf ^* · lσ · id ^* + 2πf ^* · φ _2d (6) That is, the d-axis voltage compensation amount (ΔVd) and q-axis voltage compensation amount (ΔVd) of the output of the compensation amount calculator 16 ΔVq) is given by the equation (7),
(8).

[0010]

ΔVd = r ₁ · id ^* −2πf ^* · lσ · iq (7)

[0011]

ΔVq = r ₁ iq + 2πf ^* · lσ · id ^* (8) Further, φ _2d of the third term on the right side of the equation (6) is constant, so that the output of the fv converter 11 Corresponds to the q-axis voltage value (Vq ′). Therefore, the output of the adder 17 is given by the following equation
It becomes.

[0012]

Vq = Vq ′ + ΔVq (9) Further, the d-axis voltage (Vd ′) is zero (φ _2q =
0), the output of the adder 18 is given by the equation (10)
It becomes.

[0013]

Vd = ΔVd (10)

[0014]

In the conventional control device 10 for an induction motor 2 shown in FIG . 6 , as the drive torque of the induction motor 2 increases, the torque of the induction motor 2 output from the coordinate transformation calculator 15 increases. Q-axis current (i
q) increases, and as a result, the q-axis voltage compensation amount (ΔV) of the output of the compensation amount calculator 16 performing the calculation of the equation (8).
q) also increases, and this increase further increases the q-axis current (iq) and diverges, possibly causing the induction motor 2 to be overexcited.

When the induction motor 2 is generating braking torque, the polarity of the q-axis current (iq) output from the coordinate transformation calculator 15 becomes negative, and the q-axis output from the compensation amount calculator 16 becomes negative. When the voltage compensation amount (ΔVq) decreases, and particularly when the induction motor 2 is operated in a low speed region, the equation (8) is used.
Since the value of the second term on the right-hand side is also small, the q-axis voltage command value (Vq) of the output of the adder 17 becomes a very small value, and the inverter 20 cannot output a sufficient voltage.

An object of the present invention is to provide a control device for an induction motor that solves the above problems.

[0017]

The first aspect of the present invention relates to an external device.
Frequency command value (f^*) To fv converter
Input and convert to q-axis voltage value (Vq '), frequency command value
(F^*) Is input to the integration calculator to calculate the rotation angle (θ)
Connected to the output of the PWM inverter by the current detector.
The detected current value of each phase of the induction motor (i_U, I_W)
The current detection value (i_U, I_W) And rotation angle (θ)
Input to the target conversion calculator to calculate the q-axis current (iq),
Wave number command value (f^*) And the current detection value (i_U, I_W) And PW
M inverter voltage command value (V_U ^*, V_W ^*)
Primary resistance value of the induction motor (r₁) And the torque act
Input to a calculator to calculate the torque (τ) generated by the induction motor
And input the generated torque (τ) to the torque compensation amount calculator.
q-axis voltage torque compensation amount (Vτ ^*) And calculate the frequency finger
Quotation (f^*), Q-axis current (iq), and torque compensation amount (Vτ)
^*) And a preset d-axis current value (i
d^*) And the primary resistance value (r ₁) And pre-set guidance
Motor leakage inductance (lσ) and apparent resistance
Value (k_b) Is input to the compensation amount calculator to calculate the q-axis voltage compensation amount.
(ΔVq) and the d-axis voltage compensation amount (ΔVd), and
The axis voltage value (Vq ′) and the q-axis voltage compensation amount (ΔVq)
1 to the q-axis voltage command value (Vq)
And the d-axis voltage compensation amount (ΔVd) and a preset d-axis
The voltage (Vd ') is input to the second addition arithmetic unit, and the d-axis
The pressure command value (Vd) is calculated, and the q-axis voltage command value (Vq) is calculated.
The d-axis voltage command value (Vd) is input to the polar coordinate conversion calculator.
Voltage command absolute value (| V^*|) And the phase angle (δ^*) And act
And the voltage command absolute value (| V^*|) And the phase angle (δ^*)When
Is input to the PWM inverter, and the voltage command value (V
_U ^*, V_V ^*, V_W ^*) Output voltage based on induction motor
Means.

According to a second aspect, in the first aspect,
A first limit value calculator for limiting a lower limit value of the q-axis voltage command value (Vq) when an output of the torque calculator is negative. In a third aspect based on the first aspect, the second limit value calculator that limits the lower limit of the voltage command absolute value (| V ^* |) when the output of the torque calculator is negative. Prepare.

According to a fourth aspect, in the first aspect,
A polarity discriminator for discriminating the polarity of the output of the torque calculator, and a first limit setting device for limiting a lower limit value of the q-axis voltage compensation amount (ΔVq) when the polarity discriminator determines that the polarity is positive. A second limit setting unit that limits the lower limit of the q-axis voltage compensation amount (ΔVq) when the polarity discriminator determines that the polarity is negative.

According to a fifth aspect based on the first aspect,
A comparator for detecting that the phase angle (δ ^* ) has exceeded a predetermined value; and a q-axis voltage compensation amount (ΔVq) and a d-axis voltage compensation amount (ΔVd) when the comparator operates. And a hold circuit for holding each value at the immediately preceding value. In the first to fifth aspects of the present invention, the torque calculator calculates the generated torque (τ) of the induction motor, and inputs the generated torque (τ) to the torque compensation amount calculator to input the torque compensation amount (Vτ) of the q-axis voltage. ^* ) To calculate a frequency command value (f ^* ), a q-axis current (iq), a torque compensation amount (Vτ ^* ), a preset d-axis current value (id ^* ) of the induction motor, and the primary resistance ( r
₁ ), a preset leakage inductance (lσ) of the induction motor and an apparent resistance value (k _b ) are inputted to a compensation amount calculator, and a q-axis voltage compensation amount (ΔVq) and a d-axis voltage compensation amount ( ΔVd), the compensation amount calculator of the present invention performs the calculation represented by the expression (11) in contrast to the calculation of the expression (8) in the conventional compensation amount calculator. .

[0021]

ΔVq = (r ₁ −k _b ) iq + Vτ ^* + 2πf ^* · lσ · id ^* (11) In the first term on the right side of the equation (11), the apparent resistance is calculated from the primary resistance value (r ₁ ). Since the value obtained by subtracting the value (k _b ) is multiplied by the q-axis current (iq), the aforementioned q-axis current (iq)
Is suppressed, and the induction motor is prevented from being overexcited. Further, the second term on the right side of the equation (11) compensates for the apparent resistance value (k _b ) of the first term on the right side.

Further, according to the second or fourth invention, in addition to the above-described operation, the lower limit of the q-axis voltage command value (Vq) is limited by the polarity of the output (τ) of the torque calculator, or By limiting the lower limit of the command absolute value (| V ^* |),
Particularly, the output voltage of the inverter is ensured when the induction motor is operated in a low speed range. Further, in the fifth invention, in addition to the above-described operation, when the phase angle (δ ^* ) exceeds a predetermined value, the q-axis voltage compensation amount (ΔVq) and the d-axis voltage compensation amount (ΔVd) are respectively set. By holding the value at the immediately preceding value, the output voltage of the inverter is ensured particularly when the induction motor is operated in the low speed range.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiments of the present invention described below, those having the same functions as those of the conventional example shown in FIG. This will be mainly described. FIG. 1 is a block diagram of a control device for an induction motor according to a first embodiment of the present invention. The control device 30 includes a torque calculator 31, a torque compensation calculator 32, and a compensation calculator 33. Have.

A frequency command value (f)
^* ), Current detection values (i _U , i _W ) and PWM inverter 2
Voltage command value of _{^{0 (V U *, V W}} *) and enter the preset primary resistance value of the induction motor 2 is (r _1), generation of the induction motor 2 by using a technique known vector arithmetic The torque (τ) is calculated. The torque compensation amount computing unit 32 computes a torque compensation amount (Vτ ^* ) of the q-axis voltage from the generated torque (τ) of the induction motor 2 obtained by the torque computing unit 31, and the compensation amount is a q-axis voltage command value ( Vq) is several percent of the rated value.

The compensation amount calculator 33 calculates a frequency command value (f ^* ), a q-axis current (iq), and a torque compensation amount (Vτ ^* ).
D-axis current value of the induction motor 2 (id ^* )
And the primary resistance value (r ₁ ), the leakage inductance (lσ), and the apparent resistance value (k _b ), the equations (7) and (11) are calculated, and the q-axis voltage compensation amount (ΔVq) and d It outputs the shaft voltage compensation amount (ΔVd).

The q-axis voltage compensation amount (ΔVq) in the compensation amount calculator 33 is a value of 15 to 20% of the rated value of the q-axis voltage command value (Vq), and the d-axis voltage compensation amount (ΔVd) is -5 to -10 with respect to the rated value of the d-axis voltage command value (Vd)
%, And the apparent resistance value (k _b ) is about 50% of the primary resistance value (r ₁ ) of the induction motor 2. FIG.
FIG. 5 is a block diagram of an induction motor control device according to a second embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals.

The control device 40 shown in FIG.
1, a torque compensation amount calculator 32, a compensation amount calculator 33, a limit value calculator 41, and a limiter 41a. The limit value calculator 41 sets a value for limiting the lower limit of the q-axis voltage command value (Vq) when the output (τ) of the torque calculator 31 is negative, that is, when the induction motor 2 is generating braking torque. Output and this lower limit (about -2% of rated q-axis voltage command value)
The q-axis voltage command value (Vq) is limited by the limiter 41a so as not to be less than the above, the output voltage of the PWM inverter 20 is secured, and the torque characteristics of the induction motor 2 in the low speed region are improved.

FIG. 3 is a block diagram of an induction motor control device according to a third embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals. The control device 50 shown in FIG. 3 includes a torque calculator 31, a torque compensation calculator 32, a compensation calculator 33, a limit calculator 51, and a limiter 51a. The limit value calculator 51 has a negative output (τ) of the torque calculator 31, that is, the induction motor 2.
Outputs a value that limits the lower limit of the voltage command absolute value (| V ^* |) of the output of the polar coordinate conversion calculator 19 when the braking torque is generated. The voltage command absolute value (| V ^* |) is limited by the limiter 51a so as not to be less than about 2%), the output voltage of the PWM inverter 20 is secured, and the torque characteristic of the induction motor 2 in the low speed region is improved. ing.

FIG. 4 is a block diagram of a control device for an induction motor according to a fourth embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals. The control device 60 in FIG. 4 includes a torque calculator 31, a torque compensation calculator 32, a compensation calculator 33, a polarity discriminator 61, a changeover switch 61a, and limit setting devices 62 and 63.

The polarity discriminator 61 discriminates the polarity of the output (.tau.) Of the torque calculator 31. When the output (.tau.) Has a negative polarity, that is, when the induction motor 2 is generating a braking torque, the change is set by the switch 61a. The q-axis voltage compensation amount (ΔVq) of the output of the compensation amount calculator 33 is limited so that the output (τ) does not have a positive That is, when the induction motor 2 is generating a driving torque, the output of the compensation amount calculator 33 is controlled by the changeover switch 61a so that the value does not become lower than the value of the limit setter 63 (about 0% of the rated q-axis voltage command value). By limiting the q-axis voltage compensation amount (ΔVq), the output voltage of the PWM inverter 20 is secured, and the torque characteristics of the induction motor 2 in the low speed region are improved.

FIG. 5 is a block diagram of a control device for an induction motor according to a fifth embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals. The control device 70 in FIG. 5 includes a torque calculator 31, a torque compensation calculator 32, a compensation calculator 33, a comparator 71, and a hold circuit 72. The comparator 71 is a polar coordinate conversion calculator 1
9 has a predetermined phase angle (δ ^* ) of 0 ° with respect to the d-axis.
Or 90 ° on the basis of the q-axis), the hold circuit 72 operates to hold the q-axis voltage compensation amount (ΔVq) and the d-axis voltage compensation amount (ΔVq) of the output of the compensation amount calculator 33. ΔVd), the q-axis voltage compensation amount (ΔVq) and the d-axis voltage compensation amount (ΔV
By outputting d), the output voltage of the PWM inverter 20 is secured, and the torque characteristics of the induction motor 2 in the low speed region are improved.

[0032]

According to the present invention, by introducing an apparent resistance value (k _b ) into the calculation of the compensation amount calculator, q
Preventing over-excitation of the induction motor divergence axis current and due to the divergence, the resistance value of the apparent torque compensation amount calculator (k _b)
To compensate for the shortage of the q-axis voltage, and to limit the lower limits of the various control amounts, thereby securing the minimum value of the output voltage of the inverter. Therefore, the torque characteristics of the induction motor particularly in the low speed region are improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an induction motor control device according to a first embodiment of the present invention;

FIG. 2 is a block diagram of an induction motor control device according to a second embodiment of the present invention;

FIG. 3 is a block diagram of an induction motor control device according to a third embodiment of the present invention;

FIG. 4 is a block diagram of a control device for an induction motor according to a fourth embodiment of the present invention;

FIG. 5 is a block diagram of an induction motor control device according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram of a control device for an induction motor showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frequency commander 2 Induction motor 10 Controller 11 fv converter 12 Integral calculator 13 Current detector 14 Current detector 15 Coordinate conversion calculator 16 Compensation amount calculator 17 Addition calculator 18 Addition calculator 19 Polar coordinate conversion calculation Device 20 PWM inverter 30 controller 31 torque calculator 32 torque compensation calculator 33 compensation calculator 40 controller 41 limit value calculator 41a limiter 50 control device 51 limit value calculator 51a limiter 60 control device 61 polarity discriminator 61a Changeover switch 62 Limit setting device 63 Limit setting device 70 Control device 71 Comparator 72 Hold circuit

Claims (5)

(57) [Claims] A frequency command value (f ^* ) externally commanded.
Is input to an fv converter to convert it to a q-axis voltage value (Vq ′). A frequency command value (f ^* ) is input to an integration calculator to calculate a rotation angle (θ). each phase current detection value of the induction motor connected to the output of the PWM inverter (i _U, i _W) is detected and the current detection value (i _U, i _W) and the rotational angle (theta) and the coordinate transform operator to type calculates a q-axis current (iq), the frequency command value (f ^*) and current detection value (i _U, i _W) and P
Voltage command value of the WM inverter _{^{(V U *, V W *}} ) and a preset primary resistance value of the induction motor to be (r ₁₎ and is input to the torque calculator calculates a torque generated by the induction motor (tau) of , The generated torque (τ) is input to the torque compensation amount calculator to calculate the torque compensation amount (Vτ ^* ) of the q-axis voltage, and the frequency command value (f ^* ), the q-axis current (iq), and the torque compensation amount ( Vτ ^* ), a preset d-axis current value (id ^* ) of the induction motor, the primary resistance value (r ₁ ), a preset leakage inductance (lσ) of the induction motor, and an apparent resistance value (k _b ) Is input to the compensation amount calculator to calculate the q-axis voltage compensation amount (ΔVq) and the d-axis voltage compensation amount (ΔVd). The q-axis voltage value (Vq ′) and the q-axis voltage compensation amount (ΔVq) Are input to a first addition calculator to calculate a q-axis voltage command value (Vq), and a d-axis voltage compensation amount (ΔV ) And a preset d-axis voltage (Vd ′) are input to a second addition calculator to calculate a d-axis voltage command value (Vd), and a q-axis voltage command value (Vq) and a d-axis voltage command The value (Vd) is input to the polar coordinate conversion calculator, and the voltage command absolute value (| V
^* |) And the phase angle (δ ^* ), and the voltage command absolute value (| V ^* |) and the phase angle (δ ^* ) are calculated by PW
The voltage command value (V _U ^* ,
A control device for an induction motor, which supplies an output voltage based on V _V ^* , V _W ^* ) to the induction motor. 2. The control device for an induction motor according to claim 1, wherein a first limit value for limiting a lower limit value of the q-axis voltage command value (Vq) when an output of the torque calculator has a negative polarity. A control device for an induction motor, comprising a computing unit. 3. The control device for an induction motor according to claim 1, wherein a lower limit value of the voltage command absolute value (| V ^* |) is limited when an output of the torque calculator has a negative polarity. A control device for an induction motor, comprising a limit value calculator. 4. The control device for an induction motor according to claim 1, wherein: a polarity discriminator for discriminating the polarity of the output of the torque calculator; and the q-axis voltage when the polarity discriminator determines that the polarity is positive. A first limit setting device that limits a lower limit value of the compensation amount (ΔVq); and a second limitation device that limits a lower limit value of the q-axis voltage compensation amount (ΔVq) when the polarity discriminator determines that the polarity is negative. A control device for an induction motor, comprising: a setting device. 5. The control device for an induction motor according to claim 1, wherein the comparator detects that the phase angle (δ ^* ) exceeds a predetermined value; Shaft voltage compensation amount (ΔV
q) and a holding circuit for holding the d-axis voltage compensation amount (ΔVd) at the immediately preceding value, respectively.