JPH0731200A - Vector controller for induction motor - Google Patents

Abstract

PURPOSE:To provide a vector controller in which the response and stability of control are enhanced through highly accurate high resolution measurement of secondary time constant. CONSTITUTION:In order to apply a constant current to a motor 1 at the time of operating a secondary time constant, a control circuit 11 feeds back the detection value of a current detector 16 and controls the ON/OFF ratio of a switching transistor in the inverter body 12. An operating circuit 14 takes in the primary voltage V1 from a primary voltage detecting circuit 15 for a time interval DELTAT1 and determines a secondary time constant T2 according to a formula. In the formula, T represents an arbitrary time and DELTAT2 represents an integration time.

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 device, and more particularly to a secondary time constant measuring device.

[0002]

2. Description of the Related Art FIG. 5 shows a vector controller. The speed command N and the speed ωn calculated by the speed calculation unit 3 from the speed detector 2 of the induction motor 1 are matched to each other, and the torque calculation unit 4 is calculated by proportional integral (PI) calculation to obtain the torque current command I _T. From this torque current and the excitation current set value I ₀ , the primary current calculation unit 5
Then, the primary current value I ₁ is obtained. On the other hand, the phase calculator 6 calculates the phase angle of the torque current I _T and the exciting current I _{0 by} φ = tan ⁻¹ (I
_T / I ₀ ) and the slip frequency calculation unit 7 determines the torque current I
_T , exciting current I _0, and motor secondary time constant τ ₂

[0003]

Equation 3] _{τ 2 = L 2 / R 2} L 2: secondary self inductance R _2: secondary resistance from the slip frequency _{ωs = (I T / I 0} ) Request (1 / τ _2).

The slip frequency ωs is added to the speed detection value ωn by the adder 8 to obtain the primary angular frequency ω ₀ .

The primary current calculation unit 9 calculates the primary currents Ia, Ib, from the primary current value I ₁ , the phase angle φ and the angular frequency ω ₀ .
Ic is obtained, and this current is used as a current command for the inverter 10, and the inverter 10 supplies the primary current to the electric motor 1.
The calculation of the calculation unit 9 is performed according to the following equation.

[0006]

[Equation 4]

In such a vector controller, the secondary time constant τ ₂ for obtaining the slip frequency ωs is determined by the constants R ₂ and L ₂ of the electric motor 1, but the variation of the secondary resistance R ₂ due to the temperature of the electric motor. Changes in the secondary time constant τ ₂ and eventually the phase of the primary current.

Therefore, in order to obtain the secondary time constant τ ₂ , the applicant of the present application applies a constant current or a constant voltage to the electric motor in a stepwise manner as shown in the waveform diagram of FIG. 6 or 7. A method for obtaining the primary voltage or primary current of three samples every time Δt from an arbitrary time T according to the following equation has been already proposed (Japanese Patent Laid-Open No. 2-106190).

[0009]

[Equation 5]

In this measuring method, the exponential change of voltage or current corresponds to the secondary time constant τ ₂ of the electric motor, and the voltage waveform due to constant current application has an approximate expression as follows:

[0011]

[Equation 6]

[0012] The initial value becomes current i ₁ to i multiplied by primary resistance R ₁ of the motor and the sum of the secondary resistance _{R 2 1 * (R 1 +} R 2), the final value will be i ₁ * R ₁ . Further, the current waveform due to the voltage application has an inverse relationship with the voltage waveform.

[0013]

In the conventional secondary time constant measuring method, the detected value of voltage or current is A / D converted, and the secondary time constant is digitally calculated by the CPU or the like.

Here, when sampling is performed only once for each Δt, the secondary time constant is erroneously measured and set when the sampled value deviates from the true value due to the influence of noise or the like.

This erroneous measurement of the secondary time constant reduces the responsiveness of speed control, which is a characteristic of vector control. Also,
Instable control due to insufficient output voltage and output current of the inverter during operation.

Another problem is that since only three specific samples are detected from the waveform of the measured voltage or current, changes in the primary resistance R ₁ and secondary resistance R ₂ and noise due to slight changes in temperature of the motor. It was difficult to increase the detection resolution in the signal level ratio between and.

It is an object of the present invention to provide a vector control device in which the response and stability of control are improved by measuring the secondary time constant with improved accuracy and resolution.

[0018]

In order to solve the above problems, the present invention provides a constant current or a constant voltage to the electric motor in vector control of the electric motor by obtaining the secondary time constant τ ₂ of the induction motor. Primary voltage v when applied stepwise
₁ or a primary voltage or primary current detection circuit for detecting the primary current i ₁ , and the following formula from the primary voltage or primary current:

[0019]

[Equation 7]

[0020]

[Equation 8]

T: Arbitrary time ΔT ₁ ; Measurement interval ΔT ₂ ; Secondary time constant calculating circuit for calculating the secondary time constant τ ₂ according to the integration time.

Further, the present invention is characterized in that the measurement interval ΔT ₁ and the integration time ΔT ₂ are equally spaced.

[0023]

In order to obtain a change in the primary voltage or a change in the primary current of the motor at the measurement interval ΔT ₁ , the measured values are averaged by integrating each for the integration time ΔT ₂ to reduce the occurrence of errors due to noise. Also, the detection resolution is increased. Further, the calculation is simplified by making the measurement interval and the integration time equal.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention. In the figure, a control circuit 11 corresponds to the arithmetic units 4 to 9 in FIG. 5 described above, and includes an inverter body 12 and a rectifier 13
Are shown corresponding to the inverter 10.

Here, the control circuit 11 receives the secondary time constant τ ₂ as the calculation result of the secondary time constant calculation circuit 14.
The arithmetic circuit 14 receives the primary voltage v ₁ from the primary voltage detection circuit 15 that detects the primary voltage of the induction motor 1 to obtain the secondary time constant.

The control circuit 11 controls the on / off ratio of the switch transistor of the inverter body 12 by using the detection value of the current detector 16 as a feedback in order to apply a constant current to the electric motor 1 in the calculation of the secondary time constant.

In applying this constant current, the arithmetic circuit 14
2, as shown in FIG. 2, the primary voltage v ₁ from the primary voltage detection circuit 15 is taken in only for a time ΔT _{2 at} each measurement interval ΔT ₁ between times t ₁ and t _3, and the secondary time is calculated according to the equation (1). Find the constant τ ₂ .

Therefore, to calculate the secondary time constant τ ₂ , the primary voltage v within a short time from the application of the constant current to the time t ₃ + ΔT _2
It is not necessary to measure the voltage until the steady value i ₁ * R ₁ which is obtained from the detected value of ₁ and requires a relatively long time.

Further, in order to obtain a value corresponding to the average value from a plurality of samples at each time according to the integration time ΔT ₂ ,
The calculation error due to noise can be reduced. Further, the detection resolution can be improved by lengthening the integration time.

The primary voltage detection circuit 15 and the secondary time constant calculation circuit 14 described above are realized by, for example, the circuit configuration shown in FIG. In FIG. 3, the primary voltage of the electric motor 1 is continuously sampled for each integration time ΔT _{2 at} every measurement interval ΔT ₁ by the sample hold circuit 17 through the low frequency filter 16, and these sampling voltages are digitalized by the A / D converter 18, respectively. Convert to a value.

These digital values are measured at time t ₁ ,
t _2, t ₃ are separately inputted as addition data to the adder 19 _1, 19 _2, 19 _3. With this configuration, the adder 19 ₁ stores the integrated value of the _first sample data v ₁ , the adder 19 ₂ stores the integrated value of the second sample data v ₁ , and the adder 19 ₃ Stores the integrated value of the third sample data.

Subtractors 20 and 21 are adders 19 ₁ and 19 ₂ ,
The addition result of 19 ₃ is subtracted, and

[0033]

[Equation 9] V ₁ (t ₁ ) −V ₁ (t ₂ ) V ₁ (t ₂ ) −V ₁ (t ₃ ) are obtained respectively. The divider 22 then subtracts the subtractors 20, 21.
The arithmetic operation result is divided, the logarithmic arithmetic unit 23 performs logarithmic arithmetic operation, and the divider 24 calculates the time ΔT ₁
The secondary time constant τ ₂ is calculated by dividing by and.

In such calculation, the measurement interval ΔT ₁
And by making the integration time ΔT ₂ equally spaced,
Sampling control up to D / D converter 18 and adder 19
_It is possible to simplify the comparison operation of the addition results of ₁ , 19 ₂ and 19 ₃ .

In the embodiment, a constant voltage is applied to the motor to obtain the secondary time constant τ _2, and the primary current i ₁ is measured for each integration time ΔT _{2 at} every measurement interval ΔT ₁ as shown in FIG. However, it can also be obtained according to the above equation (2).

[0036]

As described above, according to the present invention, the change in the primary voltage or the change in the primary current is measured at the measurement interval ΔT ₁ and the integration time Δ is changed.
Since the temperature-corrected quadratic time constant is obtained by obtaining the sample value three times with T ₂ , the following effects are obtained.

(1) The measurement of the steady value of the primary voltage or the primary current is not required, the measurement can be performed in a short time, and the rise of vector control can be accelerated.

(2) When the stop time is included in the middle of the variable speed control of the electric motor, it is possible to readjust the secondary time constant again during the stop period and readjust it.

(3) Since the voltage or current at each measurement time is obtained using a plurality of sample values depending on the integration time, it is possible to reduce the error due to noise, improve the measurement accuracy, and increase the detection resolution.

(4) By improving accuracy and resolution, speed control response can be improved and control can be stabilized.

(5) If the integration time and the measurement interval are made equal, the calculation of the time constant can be simplified, and the secondary time constant measurement and correction during the operation of the electric motor can be facilitated.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention.

FIG. 2 is a voltage measurement mode diagram in the example.

FIG. 3 is a circuit diagram of a secondary time constant calculation circuit in the embodiment.

FIG. 4 is a current measurement mode diagram in an example.

FIG. 5 is a block diagram of a vector control device.

FIG. 6 is a conventional voltage measurement mode diagram.

FIG. 7 is a conventional current measurement mode diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Induction motor 11 Control circuit ... 14 ... Secondary time constant arithmetic circuit 15 ... Primary voltage detection circuit 19 ₁ , 19 ₂ , 19 ₃ ... Adder 23 ... Logarithmic arithmetic unit

Claims (2)

[Claims] 1. A primary voltage v when a constant current or a constant voltage is applied to the electric motor stepwise in obtaining the secondary time constant τ ₂ of the induction motor and performing vector control of the electric motor.
₁ or a primary voltage or primary current detection circuit for detecting the primary current i ₁ , and the following equation from the primary voltage or primary current: [Equation 2] T: Arbitrary time ΔT ₁ ; Measurement interval ΔT ₂ ; Secondary time constant calculation circuit for calculating secondary time constant τ ₂ according to integration time. 2. The vector controller for an induction motor according to claim 1, wherein the measurement interval ΔT ₁ and the integration time ΔT ₂ are equally spaced.