JPS6323586A - Sepeed controller for induction motor - Google Patents

Abstract

PURPOSE:To improve the reliability of the whole system and widen the range of speed control, by duplicating the feedback control of a rotational speed in case based on an actual rotation and in case based on a theoretical rotational speed. CONSTITUTION:In the range of low rotation, to use the value of the output of a speed detection circuit 5 and control a vector, by generating the output of first control signal to a variable voltage/variable frequency converter 2 from a control circuit 7 and driving the converter 2, the rotational speed of an induction motor 3 is controlled. In the meantime, in the range of high rotation, to provide the input of an input voltage/current detection value to a speed arithmetic circuit 4 and use a theoretical rotational speed found by the operational result of the circuit 4 and control the vector, by generating the output of second control signal to the variable voltage/variable frequency converter 2 from the control circuit 7 and driving the converter 2, the rotational speed of the induction motor 3 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling the rotational speed of an induction motor.

[Prior Art] Fig. 2 is a schematic configuration diagram showing a conventional speed control device for an induction motor. In Fig. 2, an example of vector control of an induction motor without a speed detector is shown. It is shown. In the figure, 1 is a three-phase voltage power supply (AC power supply),
2 is a variable voltage variable frequency converter such as a PWM type inverter, 3 is an induction motor, 4 is a speed calculation circuit, and 5 is a control circuit.

Next, the operation will be explained. First, the input voltage and current of the induction motor 3 are detected, and the rotational speed of the induction motor 3 is calculated in the speed calculation circuit 4. Using this calculation result, the control circuit 5 controls the command to the variable voltage variable frequency converter 2. As a result, the induction motor 3
speed control is performed. Vector control without a speed detector is adopted as the speed control method in this case.

[Problems to be Solved by the Invention] However, in such a conventional speed control device for an induction motor that does not use a speed detector, the speed Ha in the low frequency range
In addition, there was a problem with reliability when control malfunctioned in the high-speed range.

This invention was made to solve the above-mentioned problems, and provides a speed control device for an induction motor that can perform highly reliable speed control over a wide range from high speed to low speed. The purpose is to

[Means for Solving the Problems] A speed control device for an induction motor according to the present invention includes an induction motor connected to a power source via a variable frequency converter, and a speed control device for detecting the actual rotational speed of the induction motor. A detection means and a speed calculation means for calculating a theoretical rotational speed from information input to the induction motor are provided, and the motor receives signals from the speed detection means and the speed calculation means and is based on the signal from the speed detection means. A control means is provided for selectively outputting a first control signal and a second control signal based on the signal from the speed calculation means to the two-part variable frequency converter.

[Function] In the speed control device for an induction motor according to the present invention, the actual rotational speed of the induction motor is detected by the speed detection means, and this detection result is manually input to the control means, and the speed calculation means is input to the induction motor. A theoretical rotational speed is calculated from the information, and the result of this calculation is input to the control means.

The control means outputs a first control signal for vector control to the variable frequency converter based on the detection result from the speed detection means in, for example, a low frequency region (low speed region), and outputs a first control signal for vector control to the variable frequency converter, for example, in a high frequency region (high speed region). Then, a second control signal for vector control is output to the variable frequency converter based on the calculation result from the speed calculation means.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
In the figure, 1 is a three-phase voltage power supply (AC power supply), 2 is a PW
Variable voltage variable frequency converter such as M-type inverter, 3
is an induction motor; 5 is a speed detection circuit; and 6 is a speed detector; these speed detection circuit 5 and speed detector 6 constitute speed detection means for detecting the actual rotational speed of the induction motor 3.

Reference numeral 4 denotes a speed calculation circuit as a speed calculation means for calculating the theoretical rotational speed from input voltage and current information to the induction motor 3. Further, 7 is a control circuit, 8 is a switch, 9 is a comparator, and 10 is an input terminal. Switch 8. Comparator 9. The input terminal 10 receives signals from the speed detection circuit 5 and the speed calculation circuit 4 and selects a first control signal based on the signal from the speed detection circuit 5 and a second control signal based on the signal from the speed calculation circuit 4. It constitutes a control means for outputting to the variable voltage variable frequency converter 2.

The operation will be explained next □. First, the output of the speed detector 6 is input to the speed detection circuit 5, and when this result is lower than a certain frequency (low rotation range), the control circuit 7 is used to perform vector control using the value of the output of the speed detection circuit 5. The rotational speed of the induction motor 3 is controlled by outputting a first control signal from the first control signal to the variable voltage variable frequency converter 2 and driving it.

On the other hand, above the above-mentioned certain frequency (high rotation range),
The input voltage/current detection values are manually inputted to the speed calculation circuit 4, and the second control signal is sent from the control circuit 7 to a variable voltage in order to perform vector control using the theoretical rotation speed obtained from the calculation result in the speed calculation circuit M4. By outputting the signal to the frequency converter 2 and driving it, the rotational speed of the induction motor 3 is controlled.

However, at this time, take the difference Δω1°Δω2 between the output of the speed calculation circuit 4 and the output of the speed detection circuit 5 and the speed command input from the input terminal 10, and calculate the difference Aω(=Δω1− When Δω2) exceeds a certain value, Δω1. Speed control is performed using the smaller speed of Δω2.

In this way, the speed detector 6 is attached to the induction motor 3, and vector control is performed using the detected speed of the speed detector 6 in the low frequency range, and above it (in the high frequency range), the input voltage/current detection value is Since vector control is performed using the estimated theoretical rotational speed, speed control in the low frequency range can be easily performed, and speed control in the high frequency range can also be performed with high reliability.

[Effects of the Invention] As described in Section 2, according to this invention, the feedback control of the rotational speed is performed in two ways, one based on the actual rotational speed and the other based on the theoretical rotational speed, thereby increasing the reliability of the entire system. It also has the effect of widening the speed control range.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a speed control device for an induction motor as an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing a conventional speed control device for an induction motor. In the figure, 1-.- three-phase voltage power supply (AC power supply), 2.
-Variable voltage variable frequency converter, 3-Induction motor, 4.-
- Speed calculation circuit, 5 - Speed detection circuit, 6 - Speed detector, 7 - Control circuit, 8 - Switch, 9.
・−Comparator, 10 ・−・Input terminal. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] Speed detection means for detecting the actual rotational speed of the induction motor, comprising an induction motor connected to a power source via a variable frequency converter; and speed calculation means for calculating the theoretical rotational speed from information input to the induction motor. is provided, and upon receiving the signals from the speed detection means and the speed calculation means, selects a first control signal based on the signal from the speed detection means and a second control signal based on the signal from the speed calculation means. A speed control device for an induction motor, characterized in that it is provided with a control means for outputting an output to the variable frequency converter.