JPH06284784A - Motor control method - Google Patents

Abstract

PURPOSE:To make it possible to perform operation under the state, wherein noises become minimum, by sending vibration/noise information from a sensor into a control circuit, searching the frequency, where the noises of a motor become minimum within the range of the allowance width of the frequency with a target frequency as the center, and performing the operation. CONSTITUTION:As a vibration/noise sensor of an induction motor 7, a vibration pickup 9 is used. When a control circuit 8 performs the control command at a motor rotating frequency of 55Hz, the rotating frequency, where the vibration becomes minimum within the range from 53Hz to 57Hz when the frequency allowance width is + or -2Hz, is found. he operation is performed at this frequency. As a result, the abnormal resonance noise can be prevented in the variable speed operation and in the safe speed operation of the motor. The motor can be operated at the operating frequency, where the motor noises are decreased, all the time. Therefore, the low-noise operation can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable speed control method for an electric motor.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a typical system for controlling a conventional variable speed electric motor.
Conventionally, when continuously controlling the rotation speed of the electric motor 13, a system in which a control circuit 14 operates a power supply 16 for the electric motor to adjust the rotation speed to a target rotation speed is often adopted. The target rotation speed is a value that is set in advance by a microcomputer or the like, or is determined based on information from a sensor or the like. The control circuit 14 controls and supplies the electric motor power so that the rotation speed is reached.

In the conventional case, the target rotational speed has one value in one state. There are cases where the target rotation speed has a range, but in the conventional case, any value within that range will be the target value.

[0004]

In the case of the conventional example of FIG. 4,
The operation system is unrelated in terms of motor noise.
That is, since the electric motor is only controlled so as to reach the predetermined target rotational speed, if the target rotational speed approaches the vibration resonance point of the electric motor, the noise becomes loud. Even with the same type of motor, the vibration resonance point is affected by variations in windings, assembly, and environment, so it is difficult to set the resonance point countermeasure in advance in the control circuit. Further, in general, the noise level of an electric motor changes as the rotation frequency changes.

As an example, FIG. 3 shows a change in motor noise when the power supply frequency of the induction motor is changed from 45 Hz to 61 Hz. In this case, the change in dBA range of 1/3 octave analysis was shown. This change is also seen in each frequency band. That is, the noise level of the electric motor fluctuates due to changes in the rotation frequency.

Such changes occur due to the relationship between vibrations due to the motor rotation frequency and its harmonics and some motor resonance points.

Therefore, if the command value of the target rotation speed of the control circuit becomes close to the rotation frequency at which the electric motor noise becomes maximum, the electric motor noise is operated in a large state.

[0008]

The present invention provides the following driving system in order to solve the above-mentioned disadvantageous driving condition in terms of noise. A sensor that detects vibration or noise is installed around the motor, and the vibration and noise information from that sensor is sent to the control circuit to recognize the noise level. A frequency margin for the target frequency is set in advance in the control circuit, and a frequency at which the motor noise is minimized is searched for within the range of the frequency margin centered on the motor target frequency, and the motor is operated.

[0009]

The noise level of the electric motor generally changes depending on the operating speed. Therefore, if the control circuit has a margin of the target rotation speed of the electric motor, and if the rotation speed at which the noise is minimized is detected within the margin, the control circuit operates even when the target rotation speed of the control circuit is changed. It is possible to realize the operation of the electric motor in which the noise is minimized near the rotation speed. That is,
The variable speed control operation can be realized so that the motor noise is always small.

[0010]

1 and 2 show an example of variable speed control of an electric motor according to an embodiment of the present invention. FIG. 1 shows a general block diagram, and FIG. 2 shows an example of specific connections using an induction motor as an example.

In the case of FIG. 1, the vibration / noise level 6 of the electric motor 1 is judged by the judgment circuit 3, and the electric power source 5 for the electric motor is adjusted by the control circuit 2 so that the vibration level 6 becomes small.

In the case of FIG. 2, the vibration pickup 9 is used as a vibration / noise sensor of the induction motor 7. Here, for example, the control circuit 8 controls the motor rotation frequency 5
If the frequency margin is ± 2 Hz when the control command is given at 5 Hz, the rotation frequency at which the vibration is minimized is found within the range of 53 Hz to 57 Hz, and the operation is performed at that frequency. The frequency of the induction motor −
If the vibration characteristics are as shown in FIG. 3, about 53.
Control with 5Hz as operating frequency.

Although the dBA range is taken as an example of the frequency-vibration characteristic of the electric motor this time, the vibration level of the frequency-vibration characteristic of a certain specific frequency or frequency range varies depending on the operating frequency. Therefore, if a function of frequency analysis of vibration / noise information is added and the electric motor is controlled so that the vibration level is minimized, it is possible to take measures against noise of a specific frequency.

Further, even if the operation is performed at the same frequency, the frequency of the minimum noise changes due to vibration, temperature, etc. Therefore, if the optimum frequency is searched for constantly or at regular intervals, the low noise can be maintained. .

[0015]

As described above, according to the effects of the present invention, the abnormal resonance noise can be prevented in the variable speed operation and the stable speed operation of the electric motor, and the electric motor is operated at the operating frequency such that the noise is always reduced. Therefore, noise reduction operation can be realized as compared with the conventional case. Also, it becomes possible to take measures against noise of a specific frequency.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a variable speed control of an electric motor according to an embodiment of the present invention.

FIG. 2 is a specific connection diagram of electric motor variable speed control according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of an example of frequency-noise characteristics of an electric motor (d
BA range)

FIG. 4 is a configuration block diagram of an example of a conventional variable speed control of an electric motor.

[Explanation of symbols]

 1,13 Electric motor 2,14 Electric motor control circuit 3 Vibration level judgment circuit 4,12,15 Main power supply 5,16 Electric motor power supply 6 Vibration / noise level signal 7 Induction motor 8 Induction motor control circuit 9 Vibration pickup 10 Amplifier 11 Electric power supply Terminal

Claims (3)

[Claims] 1. A system for operating an electric motor by a rotation speed control circuit, wherein vibration or noise of the electric motor is reduced by incorporating vibration or noise information from a sensor attached to the electric motor while the electric motor is operating at a target rotation speed. A method of controlling an electric motor having a control circuit having a function of increasing or decreasing the rotational speed of the electric motor within a set adjustment range. 2. The method of controlling a motor according to claim 1, wherein the vibration or noise information of the motor is subjected to frequency analysis, and countermeasures are taken against vibration and noise of a specific frequency and frequency range. 3. The method of controlling an electric motor according to claim 1, wherein the vibration or noise information of the electric motor is constantly or periodically taken into a control circuit to control the electric motor.