JPH0352591A - Method for controlling current of induction motor - Google Patents

Abstract

PURPOSE:To adjust the gains of a current control system automatically by correcting a required multiplier by the ratio of detecting currents from an inverter to a current amplitude command, correcting the gains of the control system and repeating and gradually converging the correction. CONSTITUTION:When the current amplitude command of a CPU 1 supplying an induction motor with constant currents I is represented by Is, Is' (formula I) to which a required multiplier Kis is multiplied is output actually. When a detecting signal Ifb from an inverter is obtained, formula II is acquired as a more proper multiplier. The multiplier is used as the multiplier of the next current amplitude command. When the arithmetic operation is repeated gradually, Is is converged to the state of formula III, and a multiplier obtained by automatically correcting a multiplier Kis' at that time is acquired.

Description

[Detailed Description of the Invention] A. INDUSTRIAL APPLICATION FIELD The present invention relates to a current control method for an induction motor equipped with a current control loop for an inverter, and more particularly to a current control method for automatically adjusting the gain of a current control system.

B. Summary of the Invention The present invention provides a current control method for an induction motor equipped with a current control loop for an inverter. This invention discloses a technology that reduces the number of adjustment elements, performs automatic gain adjustment, and makes it possible to follow aging of elements.

C. 2. Description of the Related Art A voltage source inverter device equipped with a current control loop is known as a control device for an induction motor.

FIG. 2 is a block diagram showing an example of such a current control device, in which l is a CPU, 2 and 3 are D/A converters, 4 is a gain adjustment circuit, 5 is a multiplier, and 6 is an adder. , 7 is a current control gate generation circuit.

In the above current control device, the D/A converter 2 converts the current amplitude command from the CPU 1 into an analog value, the gain adjustment circuit 4 adjusts the gain, and the multiplier 5 multiplies it by a multiplier based on the sine wave command. An adder 6 matches the detected current signal, and a current control gate generation circuit 7 obtains an inverter gate signal. This gate signal is output as an output current command to the inverter main circuit, and the controlled output current of the inverter is detected again by the adder 6, forming a minor loop of current control, from which the output current of the inverter is detected. It is configured to be automatically controlled.

D. Problems to be Solved by the Invention However, in the above-mentioned current control device, it is necessary to artificially adjust the gain due to the error in the resistance value for determining the gain and the operational characteristics of the elements in the current control minor loop. Further, even if the adjustment is made once, if changes occur over time, the best adjustment value cannot be obtained.

The present invention was created in view of these problems, and
The present invention aims to provide a current control method for an induction motor that can reduce the number of adjustment elements in a current control device, perform automatic gain adjustment, and follow aging of elements.

E. Means for Solving the Problems The means for solving the above problems in the present invention is to detect the output current of the inverter and send this detected current signal to the CPU.
In a method of controlling the current of an induction motor with an inverter equipped with a current control minor loop that obtains an inverter gate signal by comparing output current command signals from a
A method that automatically adjusts the gain of the current control system by multiplying the current amplitude command set in U by an arbitrary multiplier, and then multiplying this multiplier by the ratio of the detected current signal to the current amplitude command signal to change the multiplier. shall be.

F. Effect: In the present invention, the number of amplitude adjustment elements is reduced compared to the conventional method, and the detected current signal is A/D converted and taken into the CPU. In the present invention, this detected current signal is used to automate the adjustment and to correct subtle variations in element characteristics such as aging.

In the current control loop, the output current command output to the inverter is the current amplitude command multiplied by the required multiplier.
By correcting the multiplier according to the ratio between the detected current signal from the inverter and the current amplitude command, the gain of the current control system is corrected, and by repeating the correction and converging, the gain is automatically adjusted to an appropriate value. This is an attempt to make adjustments.

G. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of the current control device of the present invention. In the figure, l is a CPU, 2 and 3 are D/A converters, 5 is a multiplier, 6 is an adder, and 7 is a current control gate generation circuit, which is almost the same as the conventional example except that the gain adjustment circuit 4 is not provided. It has a similar configuration, and an A/D converter 8 is attached thereto. Compared to the conventional example, the number of amplitude adjustment elements is reduced, and the detected current signal is digitally converted by the A/D converter 8 and taken into the CPUI.

The current amplitude command in the CPU to apply a constant current ■ to the induction motor is assumed to be ■9, and the actual current amplitude command 1 s' is determined by multiplying this value by the required K. multiplied by [ s' = I
Output sX K tm. Here, if the detected current signal 1rb is obtained from the inverter, the following equation holds true as a more appropriate multiplier K ts'.

K lm' = K + sX ( I s/ I rb
) This value is processed by a software filter, etc., and used as a multiplier for the next current amplitude command.

By repeating this calculation, it converges to the state of Is''Irb, and the multiplier K im' at this time automatically becomes the corrected multiplier. Through this procedure, the current control system can be automatically adjusted.

As described above, the embodiments of the present invention have the following effects.

(1) Adjustment elements in the t-flow control loop can be reduced.

(2) Since automatic adjustment is possible, it becomes possible to follow changes in the element over time.

H. Effects of the Invention As described above, the present invention provides a current control method for an induction motor that can reduce the number of adjustment elements in a current control device, automatically adjust the gain, and follow changes over time of elements, etc. can do.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. l...CPU, 2.3...D/A converter, 4...
Gain adjustment circuit, 5... Multiplier, 6... Adder, 7
...Current control gate generation circuit, 8...A/D converter. Figure 1: Configuration diagram of an embodiment of the present invention Configuration diagram of a conventional example Snow

Claims (1)

[Claims] (1) In a method of controlling the current of an induction motor with an inverter equipped with a current control minor loop that detects the output current of the inverter and compares this detected current signal with the output current command signal from the CPU to obtain the inverter gate signal, The detected current signal is A/D converted and taken into the CPU, the current amplitude command set by the CPU is multiplied by an arbitrary multiplier, and this multiplier is multiplied by the ratio of the detected current signal to the current amplitude command signal to change the multiplier. 1. A current control method for an induction motor, characterized in that the gain of a current control system is automatically adjusted.