JPH11118230A - Air-conditioning fan motor rotation speed control device - Google Patents

Abstract

(57) Abstract: An object of the present invention is to reduce electromagnetic noise generated from a motor when a fan of an air conditioner is rotated. In a rotation speed control device for an air conditioning fan motor driven by varying the rotation speed, a switching device drive circuit having two switching devices, which are IGBTs or power MOSFETs, and two switching devices. A bridge circuit 3 for flowing a current in a certain direction, and driving the air-conditioning fan motor 1.
The WM signal is set to the duty of the target rotation speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation speed control device for controlling a fan motor for air conditioning with low noise.

[0002]

2. Description of the Related Art In a driving circuit of a fan motor for air conditioning, a transistor is used as a switching element for chopping a waveform of a power supply voltage and a switching element for absorbing a back electromotive force generated when switching is OFF. Therefore, the electromagnetic noise generated by the switching cannot be made in the non-audible region, causing annoying sounds.

[0003]

In the above prior art, there is a problem in that electromagnetic noise is generated due to the low carrier frequency of the switching transistor, and the current flowing through the motor is not sinusoidal but discontinuous. .

[0004] An object of the present invention is to reduce electromagnetic noise generated from a motor in order to improve such problems.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a rotation speed control device for an air-conditioning fan motor driven by changing the rotation speed, wherein two switching elements, which are IGBTs or power MOSFETs, are provided. And a bridge circuit for flowing a current in a certain direction to the two switching elements, and setting a PWM signal for driving an air-conditioning fan motor to a duty of a target rotation speed. It is.

[0006] Thus, since the IGBT or the power MOSFET is used as the switching element for switching, the generation of electromagnetic noise can be reduced by setting the carrier frequency of the switching element higher than that of the transistor and in a non-audible range. it can.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to 2, 3, 4, and 5.

FIG. 1 is a motor control circuit diagram showing an outline of the present invention. A motor 1, a switching element 2, a diode bridge 3, a switching element driving circuit 4, a snubber circuit 5, a power supply 6, a current sensor 8, a microcomputer 9, DC power supply circuit 10, surge absorbing capacitor 11,
It is composed of a snubber circuit 12 and the like. The motor 1 is a single-phase induction motor, and the power supply 6 for driving the motor 1 is an AC power supply.

FIG. 2 shows signals output from the microcomputer and voltages applied to the motor. The waveform of the PWM signal 7 for turning on and off the switching element 2 of the chopper section from the microcomputer 9 is shown in FIG. 7A, and the waveform of the PWM signal 7 for turning on and off the switching element 2 of the flywheel section from the microcomputer 9 is shown in FIG. As a result, the voltage applied to the motor 1 is (c), and the averaged voltage V for chopping the sinusoidal waveform is applied to the motor 1.

FIG. 3 shows signals output from the microcomputer and voltages applied to the motor, similarly to FIG.
A waveform obtained by increasing the duty of the PWM signal 7 for turning on and off the switching element 2 of the chopper unit from the microcomputer 9 is shown in FIG. 4D, and the waveform of the PWM signal 7 for turning on and off the switching element 2 of the flywheel unit from the microcomputer 9 is shown in FIG. The waveform is shown in (e), and as a result, the voltage applied to the motor 1 is (f), and the averaged voltage V1 for chopping the sine wave is applied to the motor 1.

FIG. 4 shows a dead time when two switching elements are switched. FIG. 5 shows noise value data of the motor. Hereinafter, the operation will be described with reference to FIG. In order to rotate the motor 1, it is necessary to turn on the switching element 2 of the chopper.
The switching element 2 is repeatedly turned on and off except that the motor 1 is rotated at full speed. In order to turn on / off the switching element 2 of the chopper section, an on / off signal is output from the microcomputer 9 to the switching element 2 via the switching element drive circuit 4. Similarly to the switching element 2 of the chopper section, the switching element 2 of the flywheel section outputs an on / off signal from the microcomputer 9 to the switching element 2 via the switching element drive circuit 4. The reciprocal relationship between the on-off signals from the microcomputer 9 to the chopper section and the flywheel section outputs signals that are mutually inverted. At this time-
A dead time is provided so that the ON-ON timing does not occur in the OFF signal. Switching element 2
Requires a DC voltage, and supplies a DC voltage from the power supply 6 to the microcomputer 9 via the DC power supply 10. Further, a snubber circuit 5 and a capacitor 11 for absorbing a surge voltage generated at the time of switching of the switching element 2 are added. Further, a snubber circuit 12 for absorbing the back electromotive force during the dead time period is added.

Next, an embodiment in which an IGBT is used as a switching element will be described. First, as one embodiment, in an air conditioner using a circuit for driving a single-phase induction motor, two switching elements are 6 to 20 kHz.
Switching is performed at frequencies up to and including noise noise generated from the fan motor in a non-audible range.

Next, the control of this embodiment will be described. In the above operation, when the rotational speed of the motor 1 is not constant but variable, it is possible to change the PWM duty of the on / off signal output from the microcomputer to the switching element 2 of the chopper unit. . IGB is used as a switching element for changing the rotation speed of the motor 1.
Use T.

By using an IGBT for the switching element, switching can be performed at a high frequency unlike a conventional bipolar transistor. The switching frequency of the IGBT can be set in the range of 6 to 20 kHz, but is set to 20 kHz which is a non-audible region in order to set the switching frequency for noise reduction. This makes it possible to reduce electromagnetic noise generated from the motor 1 when the motor 1 is driven to rotate by switching the commercial power supply, thereby making it possible to take measures against the noise. FIG. 5 shows the noise data in this system, and even the peak value is 20 db.
The following is a measure against noise.

Next, another embodiment will be described. In the air conditioner using the single-phase induction motor driving circuit, when one of the two switching elements is ON, the other is OFF and alternately ON.
Repeat -OFF. A dead time is provided at the time of switching between two switching elements.
s or less. Also, a snubber circuit is provided in parallel with the motor to absorb the back electromotive force generated during the dead time,
Attenuates the back electromotive force generated instantaneously during the dead time,
Make it less than the rating of the switching element. Further, a switching element in which a resistor and a capacitor are connected in series between the collector and the emitter or between the drain and the source is provided to attenuate the waveform vibration. Furthermore, a surge absorbing capacitor is provided between the phases of the power supply to absorb a surge voltage due to an inrush current, and a switching waveform is made into a rectangular wave.

A dead time is provided for the PWM duty signal output from the microcomputer to the chopper section and the flywheel section. The dead time is provided so that the IGBT does not turn on and off. However, if you take too much, the chopper and flywheel
Since the back electromotive force generated when the GBT is off increases, the dead time is set to 1 μs or less, although it depends on the turn-on and turn-off times of the IGBT. During this dead time period, the back electromotive force is generated in the motor because both IGBTs are off. A snubber circuit 12 is provided to absorb the surge voltage generated during this short time. As a result, it is possible to suppress the generation of the back electromotive force. Also,
A resistor and a capacitor are provided in parallel with the IGBT. Resistors are 10-20 ohms and capacitors are 1000-2
000 pF. By providing the IGBT in parallel with the IGBT, the oscillation of the switching voltage waveform is suppressed, and a rectangular wave is formed. Furthermore, a surge voltage occurs when the switched voltage waveform rises due to an inrush current when the IGBT is turned on, and a surge voltage higher than the rated voltage of the IGBT is generated at the rising edge of the waveform, which may destroy the IGBT. Provide a surge absorbing capacitor between the power supply voltage phases to prevent this. The constant of the capacitor is 0.1 μF to 0.47 μF. By providing these circuit components, the switching voltage waveform can be made a rectangular wave, and the IGBT can be prevented from being broken. In the above embodiment, the power MOS is used for the switching element.
An FET may be used.

[0017]

According to the present invention, the electromagnetic noise generated by the fan motor can be reduced by switching the two switching elements when controlling the rotation speed of the fan motor.

[Brief description of the drawings]

FIG. 1 is a block diagram of a motor control circuit showing an outline of the present invention.

FIG. 2 shows a PWM duty waveform and a motor applied voltage in the present invention.

FIG. 3 shows a PWM duty waveform and a motor applied voltage in the present invention.

FIG. 4 is a dead time diagram at the time of switching of a switching element according to the present invention.

FIG. 5 is a noise data diagram of an air conditioner using the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Single-phase induction motor, 2 ... Switching element, 3 ... Diode bridge, 4 ... Switching element drive circuit, 5 ...
Snubber circuit, 6: commercial power supply, 7: PWM signal, 8: current transformer, 9: microcomputer, 10: DC power supply circuit, 11: capacitor for absorbing surge, 12: snubber circuit.

Claims (1)

[Claims] 1. An apparatus for controlling the number of revolutions of an air-conditioning fan motor driven by varying the number of revolutions, comprising: a switching element drive circuit having two switching elements, which are IGBTs or power MOSFETs; A bridge circuit for flowing a current in a predetermined direction through the motor, wherein a PWM signal for driving the air conditioning fan motor is set to a duty of a target number of rotations. .