JPH0724480B2 - Vector control method of induction motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vector control method for an induction motor that can perform stable control using a slip frequency vector control device even if the input voltage fluctuates.

[Conventional technology]

The slip frequency vector control of the induction motor is performed as follows.

That is, the primary current of the electric motor on the secondary magnetic flux coordinate of the induction motor is decomposed into a torque current component and an exciting current component that are orthogonal to each other, and the detected value of the torque current component matches the command value. Also, regarding the exciting current component, each current component is controlled independently so that the detected value matches the command value, but the mutual conversion between the secondary magnetic flux coordinate and the stationary coordinate required at that time is It is performed without detecting the secondary magnetic flux vector.

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

Assuming that the secondary resistance value of the induction motor is R ₂ , the secondary magnetic flux command value is Ψ ₂ ^* , and the torque current is Ti, the slip frequency ωs described above is calculated by the following equation (1).

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

On the other hand, the detected speed value of the electric motor is set as the secondary magnetic flux command value via the magnetic flux calculator, and the exciting current command value is obtained by multiplying the secondary magnetic flux command value by 1 / M. Also, the torque command value is obtained by inputting the deviation between the speed command value of the electric motor and the detected speed value to the speed controller, and this torque command value is divided by the above-mentioned secondary magnetic speed command value to obtain the torque current command. The value is obtained.

Therefore, feedback control for matching the detected torque current value with the torque current command value and feedback control for matching the detected excitation current value with the excitation current command value are performed, and the results are coordinate-converted into a three-phase voltage signal and pulse width modulated. The slip frequency vector control method is to control the induction motor through the PWM inverter (hereinafter abbreviated as PWM).

[Problems to be Solved by the Invention]

By the way, as the torque current Ti used in the equation (1) for calculating the slip frequency ωs, there are a method using a torque current command value and a method using a torque current detection value. The operation using is generally adopted. If the torque current command value still cannot follow the torque current command value in a transient state such as when starting the motor, the maximum slippage frequency that can be output by this motor is generated because the slip frequency is larger than it actually is. This is because there is an advantage such that the acceleration time can be shortened and the slip frequency is not affected by noise and ripple.

However, when the input voltage of this slip frequency type vector control device decreases, the current does not steadily flow according to the torque current command value. Therefore, the secondary magnetic flux coordinate of this induction motor and the secondary magnetic flux coordinate of the control are controlled. Is no longer coincident with each other, and as a result, the control system becomes unstable, and there is a big defect that it is difficult to drive the motor.

Therefore, an object of the present invention is to enable the induction motor to be driven stably by the slip frequency vector control device even when the input voltage of the control device is lowered.

[Means for Solving the Problems]

In order to achieve the above object, the vector control method of the present invention separately provides a torque current component and an excitation current component, which are orthogonal to each other, of the induction motor primary current on the secondary magnetic flux coordinate of the induction motor, respectively. Control to match the detected value with the command value, and to estimate the secondary magnetic flux position of the motor by adding and integrating the motor rotation speed to the slip frequency calculated from the constant of the motor and the torque current or exciting current. ,
In a vector control method for an induction motor equipped with a slip frequency vector controller for converting a secondary magnetic flux coordinate and a stationary coordinate by using this estimated position, an input voltage of the slip frequency vector controller is a predetermined value or more. In this case, the slip frequency is calculated using the torque current command value, and when the input voltage is below the predetermined value, the slip frequency is calculated using the detected torque current value.

[Action]

The present invention normally uses the torque current command value for the slip frequency calculation of the slip frequency type vector control device, but if it is detected that the input voltage of the device is lower than a predetermined value, the torque current By switching the command value to the torque current detection value and calculating the slip frequency, the instability of the motor control system due to the voltage fluctuation is attempted to be eliminated.

〔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, the outline of vector control of the induction motor will be described with reference to FIG. In FIG. 2, the AC power from the AC power supply 1 is converted into a smooth DC by the converter 2 and the smoothing capacitor 3, and this DC is converted into an AC having a desired voltage and frequency by the PWM inverter 4 to induce the induction. Electric motor 5
Variable speed drive. The current of each phase of the electric motor 5 is applied to the current transformer 6
The motor speed is detected by the speed transmitter 7 and input to the microcomputer 20, and the speed command value is set by the speed setter 11, which is also input to the microcomputer 20. Further, in the present invention, the voltage V _DC of the DC intermediate circuit in which the smoothing capacitor 3 is installed is detected by the voltage detector 15, and the voltage set by the voltage setter 16 and the detected voltage have a magnitude relation. The comparator
It is judged in 17 and input to the microcomputer 20.

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

The signal processing contents of the microcomputer 20 shown in FIG. 2 are shown in a circuit diagram in FIG. 1, that is, the embodiment circuit of the present invention.

In the speed control task in FIG. 1, the speed setter 11
The deviation between the speed command value N ^* from the speed transmitter 7 and the speed detection value N from the speed transmitter 7 is given to the speed controller 21 to obtain the torque command value τ ^* . The torque command value τ ^* is divided by the secondary magnetic flux command value Ψ ^* to obtain the torque current command value I _T ^* . The secondary magnetic flux command value Ψ ^* is obtained by converting the speed detection value N to the magnetic flux calculator. Obtained by passing 22. Then, the exciting current command value I _M ^* is obtained by multiplying the secondary magnetic flux command value ψ ^* by 1 / M. When the comparator 17 detects that the DC intermediate circuit voltage V _DC is higher than the set value, the slip frequency calculator 28 is given the torque current command value I _T ^* via the signal switcher 30, and the voltage V DC _{If DC} is lower than the set value, the signal from the comparator 17 causes the torque current detection value I via the signal switcher 30.
_{Since T} is input to the slip frequency calculator 28, the slip frequency calculator 28 uses the secondary magnetic flux command value Ψ ^* and the torque current command value _IT ^* or the detected value _IT to determine the slip frequency ω.
Calculate and output s. This completes the speed control task.

Next, in the current control task, the slip frequency ωs is calculated by the integrator 29.
The secondary magnetic flux estimated position φ ₂ is obtained by adding the value integrated by the above and the value obtained by integrating the speed detection value N by the integrator 27, and using this φ ₂ , the three-phase current detection value Ia of the induction motor 5 is calculated. , Ib, Ic
Is converted by the coordinate converter 31 to detect the torque current value I.
Obtain _T and the exciting current detection value I _M. By inputting the deviation between the detected torque current value _IT and the above-mentioned torque current command value _IT ^* into the torque current controller 25, the torque voltage command value V
_T ^* , the exciting current detection value I _M and the exciting current command value I _M
^* To obtain the excitation voltage command value V _M ^* by giving a deviation between the exciting current regulator 26. Therefore, in the coordinate converter 32, the torque voltage command value V _T ^* and the excitation electric power command value V _M ^* are coordinate-converted using the above-mentioned secondary magnetic flux estimated position φ ₂ to generate a three-phase electric power command value Va ^*. , Vb ^* , 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.

Incidentally, the sliding frequency ω as shown in (1), although calculated by the torque current Ti and secondary magnetic flux command value [psi ^* and the motor secondary resistance value R _2, the secondary magnetic flux command value [psi ^* of Alternatively, the exciting current Mi may be used to perform the calculation by the following equation (2). However, P is a differential operator and α ₂ is a secondary time constant of the electric motor.

In the equation (2), whether the exciting current command value I _M ^* or the exciting current detection value I _M is used as the exciting current Mi,
The characteristics hardly change. Which of the torque current command value I _T ^* and the torque current detection value I _T is selected as the torque current Ti in the equation (2) depends on the present invention described above.

Further, it goes without saying that the voltage of the AC power supply 1 may be used instead of the DC intermediate circuit voltage V _DC as the input voltage, and the present invention can be implemented by detecting the input voltage in the AC power supply 1 as described above. It can be applied to a cycloconverter or a current source inverter instead of the voltage source PWM inverter described in the example.

〔The invention's effect〕

According to the present invention, when the induction motor is controlled by the slip frequency type vector control method, when the current side voltage of the device is normal, the slip frequency is calculated using the torque current command value, and the power supply voltage is equal to or lower than the predetermined value. When the power supply voltage is normal, it is possible to maximize the performance of the motor and to reduce the power supply voltage by providing switching means that calculates the slip frequency using the detected torque current. However, there is an effect that the electric motor can be stably controlled and operated.

[Brief description of drawings]

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 inverter, 5 ... Induction motor, 6 ...
… Converter, 7 …… Speed transmitter, 11 …… Speed setter, 12…
… Carrier generation circuit, 13 …… Pulse width modulation circuit, 15 ……
Voltage detector, 16 ... Voltage setting device, 17 ... Comparator, 20 ...
Microcomputer, 21 ... speed controller, 22 ... magnetic flux calculator, 23 ... divider, 24 ... amplifier, 25 ... torque current controller, 26 ... excitation current controller, 27, 29 ... Integrator, 2
8 …… Slip frequency calculator, 30 …… Signal switch, 31,32…
… Coordinate converter.

Claims (1)

[Claims] Claim: What is claimed is: 1. A torque current component and an exciting current component, which are orthogonal to each other in the primary current of the induction motor on the secondary magnetic flux coordinate of the induction motor, are separately controlled so that their detected values match the command values. Also, the motor rotation speed is added to and integrated with the slip frequency calculated from the constant of the motor and the torque current or the excitation current to estimate the secondary magnetic flux position of the electric motor, and the secondary magnetic flux coordinates and standstill are estimated using this estimated position. In a vector control method of an induction motor having a slip frequency vector controller for conversion with coordinates, when the input voltage of the slip frequency vector controller is a predetermined value or more, the slip frequency is a torque current command value. When the input voltage falls below the predetermined value, the slip frequency is calculated using the detected torque current value. Control method.