JPH0255592A - Vector control method for induction motor - Google Patents

Abstract

PURPOSE:To control a motor stably upon droppage of source voltage by operating a slip frequency based on a torque current command value or a detected torque current value corresponding to whether the source voltage is normal or dropped. CONSTITUTION:When a comparator 17 detects that a DC intermediate circuit voltage VDC is higher than a set value, a torque current command value I is fed to a slip frequency operating unit 28 through a signal switcher 30. It the DC intermediate circuit voltage VDC is lower than the set value, a detected torque current value IT is fed through the signal switcher 30 to the slip frequency operating unit 28 based on a signal fed from the comparator 17. The slip frequency operating unit 28 operates a slip frequency based on a secondary flux command value PSI* and the torque current command value IT or the detected value IT and outputs the operated slip frequency omegaS.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vector control method for an induction motor that uses a slip frequency type vector control device to perform stable control even when input voltage fluctuates.

[Prior Art] Slip frequency type filter control of an induction motor is performed as follows.

That is, the primary current of the induction motor at the secondary magnetic flux coordinate "2" is decomposed into a torque current component and an excitation current component that are orthogonal to each other, and the detected value of the torque current component matches the command value. In addition, each current component is controlled independently so that the detected value of the excitation current component matches the command value, but mutual conversion between the secondary magnetic flux coordinate and the stationary coordinate is required at this time. is performed without detecting the secondary magnetic flux vector.

Therefore, the slip frequency is calculated using the constant of this induction motor and the above torque current or excitation current, and the rotation speed of the motor is added to this calculation result to determine the rotation speed of the secondary magnetic flux. By integrating this secondary magnetic flux rotation speed, the estimated position of the secondary magnetic flux can be obtained, and this is used for coordinate transformation.

If the secondary resistance value of the induction motor is R2, the secondary magnetic flux command value is ψ2, and the torque current is Ti, then the above-mentioned slip frequency ω
S is calculated using the following equation (1).

ψ2 By using the estimated secondary magnetic flux position obtained as described above, the actual value of the three-phase current flowing through the induction motor can be coordinate-transformed to obtain the detected torque current value and the detected excitation current value.

On the other hand, the speed detection value of the electric motor is set as a secondary magnetic flux command value via a magnetic flux calculator, and the exciting current command value is obtained by multiplying this secondary magnetic flux command value by 1/M.

In addition, the torque command value is obtained by inputting the deviation between the speed command value and the detected speed value of the motor into the speed controller, and the torque current command value is obtained by dividing this torque command value by the secondary magnetic flux command value mentioned above. is obtained.

Therefore, we performed feedbank control to match the detected torque current value to the torque current command value, and feedhack control to match the detected excitation current value to the excitation current command value, and converted the coordinates of the results into three-phase voltage signals. The shear frequency type vector control method uses pulse width modulation (hereinafter abbreviated as PWM) to control an induction motor via a PWM inverter.

[Problem to be solved by the invention]

By the way, as the torque current Ti used in equation (1) for calculating the above-mentioned slip frequency ωS, there are two methods: a method using a torque current command value and a method using a detected torque current value. Calculation using is generally adopted. This occurs in a transient state such as when starting a motor, and if the detected torque current value is still unable to follow the torque current command value, a slip frequency higher than the actual one is produced, so the maximum output that this motor can output is This is because the acceleration time can be shortened, and the slip frequency is not affected by noise and ripples, as the torque is generated each time.

However, when the input voltage of this slip frequency type vector control device decreases, the current according to the torque current command value does not flow steadily, so the secondary magnetic flux coordinate of this induction motor and the secondary magnetic flux coordinate of control As a result, the control system becomes unstable, which poses a major drawback in that it becomes difficult to drive the electric motor.

SUMMARY OF THE INVENTION An object of the present invention is to enable stable driving of an induction motor using a slip frequency vector control device even when the input voltage of the control device decreases.

[Means for Solving the Problems] In order to achieve the above object, the vector control method of the present invention provides an induction motor 1 on the secondary magnetic flux coordinates of the induction motor.
The mutually orthogonal torque current component and excitation current component of the next current are controlled separately so that their detected values match the command value, and the values are calculated from the constant of the motor and the torque current or excitation current. A guidance system equipped with a slip frequency type vector control device that estimates the motor secondary magnetic flux position by adding and integrating the motor rotation speed to the slip frequency, and uses this estimated position to convert the secondary magnetic flux coordinates and stationary coordinates. In the vector control method for an electric motor, when the input voltage of the slip frequency type vector control device is equal to or higher than a predetermined value, the slip frequency is calculated using a torque current command value, and when the input voltage falls below the predetermined value. Assume that the slip frequency is calculated using the detected torque current value.

[Operation] This invention normally uses a torque current command value for slip frequency calculation of a slip frequency type vector control device, but if it is detected that the input voltage of the device has decreased below a predetermined value, The present invention attempts to eliminate instability in the motor control system caused by voltage fluctuations by switching the torque current command value to the torque current detection value and calculating the slip frequency.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an overall circuit diagram to which the embodiment circuit shown in FIG. 1 is applied.

First, an outline of vector control of an induction motor will be explained with reference to Figure 2. In FIG. 2, AC power from an AC power source 1 is converted into smooth DC by a converter 2 and a smoothing capacitor 3, and then this DC is transferred to a PWM inverter 4.
The AC current is converted into AC with a desired voltage and frequency, and the induction motor 5 is driven at variable speed. Each phase current of this motor 5 is detected by a current transformer 6, the motor speed is detected by a speed transmitter 7 and inputted to a microcomputer 20, and a speed command value is set by a speed setting device 11. is also input to the microcomputer 20.

Furthermore, in the present invention, the voltage VDC of the DC intermediate circuit in which the smoothing capacitor 3 is installed is detected by the voltage detector 15, and the magnitude relationship between the voltage set by the voltage setting device 16 and this detected voltage is determined. It is determined by the comparator 17 and inputted to the microcomputer 20.

The microcomputer 20 processes these input signals and outputs the three-phase voltage command value to be applied to the induction motor 5 to the pulse width modulation circuit 13, but the high frequency triangular wave from the carrier generation circuit 12 also has a pulse width. Since the signal is given to the modulation circuit 13 and used to control the PWM inverter 4, the induction motor 5 is operated at a value according to the speed command value output by the speed setter 11. .

FIG. 1 is a circuit diagram showing the signal processing contents of the microcomputer 20 shown in FIG. 2, that is, a circuit according to an embodiment of the present invention.

In the speed control task in FIG.
The deviation between the speed command value N9 from 1 and the speed detection value N from the speed transmitter 7 is given to the speed regulator 21 to obtain the torque command value τ.
Get 9. This torque command value τ” is converted to the secondary magnetic flux command value ψ9
The torque current command value 1% is obtained by dividing by , and this secondary magnetic flux command value ψ9 is obtained by passing the speed detection value N through the magnetic flux calculator 22. Then, by multiplying this secondary magnetic flux command value ψ2 by 1/M, the exciting current command value I
Find r. Also, DC intermediate circuit voltage■. If the comparator 17 detects that , is higher than the set value, the signal switch 30
The torque current command (
! If the voltage vnc is lower than the set value, the torque current detection value IT is input to the slip frequency calculator 28 via the signal switch 30 according to the signal from the comparator 17. ! ! The calculator 28 outputs the secondary magnetic flux command value ψ9 and the torque current command value ITl) or the detected value ■.

The shear frequency ωS is calculated and output.

The speed control task is now complete.

Next, in the current control task, the slip frequency ωS is calculated using the integrator 2
The estimated secondary magnetic flux position φ2 is obtained by adding the value integrated in step 9 and the value integrated in the speed detection value N by the integrator 27,
Using this φ2, the three-phase current detection value 1a of the induction motor 5 is
The coordinates of Tb and lc are converted by the coordinate converter 31 to obtain the detected torque current value I7 and the detected exciting current value 1. and seek.

This torque current detection value ■7 and the aforementioned torque current command value I
By manually inputting the deviation from T to the torque current regulator 25, the torque voltage command value 1 is set, and by inputting the deviation between the excitation current detection value IM and the excitation current command value IM* to the excitation current regulator 26, the excitation is set. Obtain voltage command value ■1. Therefore, in the coordinate converter 32, the torque voltage command value ``V'' and the excitation voltage command value ``M' are coordinate-transformed using the above-mentioned secondary magnetic flux estimated position φ2, thereby converting the three-phase voltage command value Va''V.
b"Vc'", and the above is the current control task.

FIG. 3 is a diagram showing the flow of the speed control task in the embodiment circuit shown in FIG. 1, and FIG. 4 is a diagram showing the flow of the current control task in the embodiment circuit shown in FIG.

As shown in (1) 2, the slip frequency ωS is calculated using the torque current Ti, the secondary magnetic flux command value ψ9, and the motor secondary resistance value R2, but the secondary magnetic flux command value ψ"
It is also possible to use the excitation current Mi instead of , and to calculate by the following equation (2). However, P is a differential operator, and α2 is a second-order time constant of the electric motor.

α·Mi In this equation (2), the characteristics hardly change whether the exciting current command value r5 is used as the exciting current M1 or the exciting current detected value IH is used. Also, as the torque current Ti in this equation (2), the torque current command value T r
Which of I and the current detection value IT is selected depends on the present invention described above.

Furthermore, it goes without saying that there is no problem in using the AC type #1 voltage instead of the DC intermediate circuit voltage VOC as the input voltage. Instead of the voltage-source PWM inverter described above, the present invention can also be applied to a cycloconverter or a current-source inverter.

[Effects of the Invention] According to the present invention, when an induction motor is controlled by the slip frequency type vector control method, when the voltage on the power supply side of the device is normal, the slip frequency is calculated using the torque current command value, and the slip frequency is calculated using the torque current command value. By providing a switching means that calculates the slip frequency using the detected torque current value when the voltage falls below a predetermined value, the ability of the motor can be maximized when the power supply voltage is normal, and Even when the power supply voltage decreases, the electric motor can be controlled and operated stably.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an overall circuit diagram to which the embodiment circuit shown in FIG. 1 is applied.
FIG. 3 is a diagram showing the flow of the speed control task in the embodiment circuit shown in FIG. 1, and FIG. 4 is a diagram showing the flow of the current control task in the embodiment circuit shown in FIG. 1... AC power supply, 2... converter, 3... smoothing capacitor, 4... PWM impark, 5... induction motor, 6... current transformer, 7... speed transmitter , 11・
・・Speed setting device, 12・・Carrier generation circuit, 13・
...Pulse width modulation circuit, 15...Voltage detector, 16.
... Voltage setting device, 17... Comparator, 20... Microcomputer, 21... Speed regulator, 22... Magnetic flux calculator, 23... Divider, 24... Amplifier, 25
...torque current regulator, 26...excitation current regulator,
27.29... Integrator, 28... Slip frequency calculator, 30... Signal switching step

Claims (1)

[Claims] 1) Control the mutually orthogonal torque current component and excitation current component of the induction motor primary current on the secondary magnetic flux coordinates of the induction motor so that their detected values match the command value, and The motor rotation speed is added and integrated to the slip frequency calculated from the motor constant and the torque current or excitation current to estimate the motor secondary magnetic flux position, and this estimated position is used to calculate the relationship between the secondary magnetic flux coordinate and the stationary coordinate. In a vector control method for an induction motor equipped with a slip frequency vector control device that performs conversion, when the input voltage of the slip frequency vector control device is equal to or higher than a predetermined value, the slip frequency is calculated using a torque current command value. A vector control method for an induction motor, characterized in that when the input voltage is less than the predetermined value, the torque current detection value is used to calculate the slip frequency.