JPH0419799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current vector control device for an induction motor driven by a current source inverter.

[Conventional technology]

Conventionally, this type of induction motor control device has been designed to control the inductance value between the primary and secondary windings of the induction motor,
Based on the self-inductance value of the secondary winding and the resistance value of the secondary winding, the instantaneous reference value (magnitude and phase) of the primary current to be supplied to the induction motor is calculated from the torse command value and magnetic flux command value, and the frequency The conversion device controls the induction motor by controlling the primary current of the induction motor according to the reference value.

FIG. 3 is a block diagram showing the conventional induction motor control device mentioned above, and FIG. 4 is a time chart thereof.

The input of AC power supply 1 is converted into DC by forward converter 2 . The DC output is supplied to an inverter 3 via a DC reactor 3, and is converted by the inverter 3 into an AC output of a desired frequency to drive an induction motor 5. A torque current command I ₂ ^* is output from a speed regulator 7 that performs speed control using a speed detection value N of a speed detector 6 directly connected to the induction motor 6 and a speed command value N ^* . On the other hand, the magnetic flux command 8 outputs a magnetic flux command φ ^* corresponding to the detected speed value N, and the output is multiplied by _K1 by the amplifier 9 to output an excitation current command I _n ^* . converting the torque current command I ₂ ^* and the excitation current command I _n ^* into a primary current command I ₁ ^* by a root function generator 12;
Current control is performed by the current regulator 15 based on this output and the primary current detection value _I1 of the current detector 18, and the output is outputted to the gate signal generator 16 to perform phase control of the forward converter 2.

A slip frequency calculator 10 converts the torque current command I ₂ ^* and the magnetic flux command φ ^* into a slip frequency f _S . An output frequency f 1 obtained by adding the output and the rotational frequency f _r obtained by multiplying the speed detection value N by K ₃ by the amplifier 11 is output to the integrator ₁₄ , and this output is used as the torque current command I ₂ ^* and the excitation. It is added to the current phase θ (the angle formed by the primary current command I ₁ ^* and the excitation current command I _n ^* ) converted by the arctangent function unit 13 from the current command I _n ^* . The output is sent to the gate signal generator 17, and the inverse converter 4 controls the frequency and phase of the primary current.

[Problem that the invention seeks to solve]

In the conventional control device described above, if the actual current flows according to the primary current command, the torque or output generated by the induction motor can have a fast response, but as shown in Fig. 4, the load at time t ₀ If there is a sudden change in the current phase θ, even though the actual current (primary current detection value I ₁ ) has not reached the primary current command I ₁ ^* due to various inductances of the DC reactor 3 and induction motor 5. As a result, the excitation current I _n decreases, and as a result, the magnetic flux φ of the motor 5 also changes, causing the torque T to no longer be produced and vibrations to occur.

[Means for solving problems]

The induction motor control device of the present invention compares the deviation between the induction motor's primary current command I ₁ ^* and the primary current detection value I ₁ or its equivalent value with a set value x, and determines whether the deviation exceeds the set value x. a deviation level detector that outputs a constant amount y (however, 0<y<x) and a switching signal, and a value obtained by adding the above-mentioned constant amount y to the primary current detection value _I1.
From I' and excitation current command I _n ^* , current phase θ = cos ^-1 (I _n
^* /I′) and the current phase θ output from the arctangent function unit.
and a phase angle switch that outputs the current phase θ determined by the inverse cosine function generator when the switching signal is output.

[Effect]

In a current source thyristor inverter, there is a delay in the actual current following the current command due to the presence of a DC reactor, etc. The present invention controls the current phase in accordance with the rise of the detected current on the premise that there is a delay in the actual current.

That is, in the present invention, since the current phase is controlled so as not to change the excitation current component under the same conditions as above, no change in the magnetic flux of the motor occurs, and therefore, high-speed torque response is possible and no vibration occurs.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the control device for an induction motor according to the present invention, and FIG. 2 is a time chart thereof.

This embodiment has a configuration in which a deviation level detector 20, a phase angle switch 21, and an arc cosine function unit 19 are added to the conventional device shown in FIG.

_The deviation level _detector 20 ^detects a certain amount _y ⁽ ₀ <
y<x), and the phase angle switch 21
Outputs a switching signal to. The inverse cosine function unit 19 converts the current phase θ using the value I ₁ ' obtained by adding the above-mentioned constant amount y to the detected primary current value I ₁ and the excitation current command I _n ^* , that is, θ=cos ^-1 (I _n ^* /I ₁ ′) …(1) is found. The phase angle switch 21 normally selects the output θ of the arctangent function unit 13, and when the deviation ΔI between the primary current command I ₁ ^* and the detected primary current value I ₁ is equal to or higher than the comparison level x, it selects I' ₁ and excitation. Inverse cosine function unit 1 from current command value Im ^*
9, select the converted current phase θ.

Next, the operation of this embodiment will be explained with reference to the time chart of FIG.

Assuming that the load suddenly changes at time t ₀ ,
The primary current detection value _I1 has not reached the primary current command I ^* . At this time, primary current command I ^* primary current detection value
Since the deviation ΔI of I ₁ is larger than the comparison level x, a constant amount y is output, and the phase angle switch 21 is switched from the arctangent function unit 13 to the arc cosine function unit 19. Then, the arc cosine function unit 19 calculates the current phase θ from equation (1), and the current phase θ smoothly changes from θ ₁ ^* to θ ₂ ^* as shown in the figure. Therefore,
The excitation current I _n is approximately constant, the magnetic flux φ of the motor 5 is also approximately constant, and the torque T increases as shown in the figure.

Note that the deviation input to the deviation level detector 20 is not limited to this embodiment, and may be the deviation between the output current of the inverter 4 and the primary current command I ₁ ^* .

〔Effect of the invention〕

As explained above, the present invention calculates the current phase from the detected value when the difference between the primary current command and the detected value becomes large, and adjusts the current phase to the change in the actual current magnitude. This has the effect of providing high torque responsiveness and stability in transient characteristics such as command changes and command changes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the induction motor control device of the present invention, FIG. 2 is a time chart thereof, FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is a time chart thereof. 1... AC power supply, 2... Forward converter (converter), 3... DC reactor, 4... Inverse converter (inverter), 5... Induction motor, 6... Speed detector, 7... Speed adjustment device, 8...magnetic flux command device,
9, 11... Amplifier, 10... Slip frequency calculator, 12... Root function unit, 13... Arctangent function unit, 14... Integrator, 15... Current regulator, 1
6, 17... Gate signal generator, 18... Current detector, 19... Inverse cosine function unit, 20... Deviation level detector, 21... Phase angle switch.

Claims (1)

[Claims] 1. Based on signals that respectively command the excitation current component and torque current component of the primary current of the induction motor,
In an induction motor control device that controls the magnitude and phase of the output current of a power conversion device that supplies variable frequency alternating current to the induction motor, the induction motor's primary current command I ₁ ^* and primary current detection value I ₁ or its a deviation level detector that compares the deviation of an equivalent value with a set value x, and outputs a certain amount y (however, 0<y<x) and a switching signal when the deviation exceeds the set value x; From the value I′, which is the sum of the current detection value I ₁ and the above-mentioned constant amount y, and the exciting current command I _n ^* , the current phase θ=
cos ^-1 (I _n ^* /I′) and the current phase θ output from the arctangent function unit.
and a phase angle switch that outputs the current phase θ determined by the arc cosine function generator when the switching signal is output.