JPH06335273A - AC motor controller - Google Patents

Abstract

(57) [Summary] [Purpose] To keep the AC motor in a braking state with a compact, simple and inexpensive structure. [Configuration] A control means 4 is connected to the inverter circuit 2, and a voltage waveform output from the inverter circuit 2 is controlled by the control means 4. When the stop command for the fan motor 1 is input to the control means 4, the control means 4 first causes the inverter circuit 2 to output the braking DC voltage, thereby stopping the rotation of the fan motor 1. Next, the fan motor 1 is held in the braking state by outputting the braking state maintaining DC voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor control device for driving and controlling an AC motor.

[0002]

2. Description of the Related Art For example, a fan device for rotating a fan by a fan motor composed of an AC electric motor is provided with a control device for driving and controlling the fan motor. This control device includes an inverter circuit having a plurality of switching elements and control means for controlling a voltage waveform output from the inverter circuit, and rotates the fan motor by an AC voltage output from the inverter circuit. Is configured to control.

By the way, in the fan device, even when the fan motor is not operating, the fan motor may rotate when the fan receives an external force such as wind. In this case, if the fan motor is started while the fan motor is rotating in the reverse direction, an overcurrent will flow in the inverter circuit. Therefore, conventionally, the fan motor is provided with a mechanical braking device, and the braking device holds the fan motor in a braking state.

[0004]

However, since the conventional mechanical braking device is provided, the size of the device is increased, and the structure is complicated and expensive. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for an AC electric motor, which is compact and can hold the AC electric motor in a braking state with a simple and inexpensive structure.

[0005]

The present invention comprises an inverter circuit having a plurality of switching elements and a control means for controlling a voltage waveform output from the inverter circuit, and an AC voltage output from the inverter circuit. In the control device of the AC motor for controlling the driving of the AC motor by the control means, when the AC motor is stopped, the inverter circuit outputs the DC voltage for braking the AC motor and then outputs the DC voltage for maintaining the braking state. It is characterized in that it is configured to perform (claim 1).

In this case, the control means may be configured so that the braking DC voltage is output after the rotational speed of the AC motor is attenuated by the inverter circuit (claim 2).

Further, rotation detecting means for detecting the rotation and the rotation speed of the AC electric motor is provided, and when the rotation detecting means detects the rotation while the AC electric motor is kept in the braking state, the braking state is determined according to the rotation speed. The control means may be configured to change the value of the holding DC voltage (claim 3).

[0008]

According to the above means, when the alternating current motor is stopped, when the braking DC voltage is first output from the inverter circuit, the direct current braking acts on the alternating current motor to stop the rotation, and then the braking state is maintained. When the DC voltage for use is output, the AC motor is held in the braking state. In this case, since the series of operations is performed by the control means for controlling the voltage waveform output from the inverter circuit, the braking device having a mechanical structure can be eliminated, and as a result, the structure can be downsized, simplified, and costly. Can be down.

According to the second aspect of the invention, since the braking DC voltage is output after the rotational speed of the AC motor is attenuated, only a small braking DC voltage is output for a short time. Thus, the AC motor can be stopped.

According to the third aspect of the present invention, the rotation of the AC motor during the braking state is detected, and when the AC motor is rotating, the DC voltage for holding the braking state is determined according to the rotation speed. Since the value of is changed, it is possible to prevent the AC motor from rotating even though the braking state maintaining DC voltage is output. Moreover, the AC motor can be kept in a braking state with a voltage value as small as possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, in FIG. 1, a fan motor 1 formed of a three-phase AC motor has a configuration in which one terminal is commonly connected to A,
It has B and C phase coils 1a, 1b and 1c and is connected to the AC output terminal of the inverter circuit 2. The inverter circuit 2 is a bridge connection of transistors 2Ua, 2Ub and 2Va, 2Vb and 2Wa, 2Wb which are three pairs of switching elements capable of self-extinguishing.
The DC input terminals of the transistors 2Ua to 2Wb are connected to the positive terminal of the DC power supply 3a and the negative terminal of the DC power supply 3b,
The negative terminal of the DC power supply 3a and the positive terminal of the DC power supply 3b are grounded.

A control means 4 is connected to the inverter circuit 2. The control means 4 is mainly composed of a microcomputer, and is provided with a command generator 4a for generating a voltage command K, a frequency command fin, and a phase command θ, and a signal generator 4b to which each command is given. There is.

In this case, the signal generator 4b is configured to calculate a drive signal based on each of the given commands and output the drive signal to the inverter circuit 2. Each of the transistors 2Ua-2Wb is On / off control is performed based on the drive signal output from the signal generator 4b. As a result, the coils 1a of the A, B and C phases of the fan motor 1 are
A pulse width modulation signal (PWM signal) having a phase shift of 120 degrees is supplied to 1b and 1c, and the fan motor 1 is driven. 2 (a) shows the PWM signal supplied to the A-phase coil 1a of the fan motor 1.
(B) shows the voltage waveform.

The power lines 1d and 1e of the fan motor 1 are
As shown in FIG. 1, the resistor 5a, the two diodes 5b,
A detection circuit 5 as a rotation detection means composed of an operational amplifier 5c is connected, and the detection circuit 5 detects the residual voltage of the fan motor 1. That is, since the pulse voltage is applied from the inverter circuit 2 to the fan motor 1, the control means 4 extracts the detection signal from the detection circuit 5 aiming at the moment when the pulse voltage is not applied, so that the fan motor 1 The residual voltage of is detected.

Next, the operation of the above configuration will be described. When a stop command for the fan motor 1 is input to the control means 4 from a state in which the fan motor 1 is normally operated based on a sinusoidal voltage waveform under PWM control, the control means 4 first causes the command generation unit 4a to output the command. Generated frequency command fin
The value of the voltage command K is gradually decreased, and the value of the phase θ is slowly increased. Then, the signal generator 4
The drive signal from a changes according to each of the above-mentioned commands, and the PWM signal applied to the fan motor 1 becomes
As shown in b, it gradually becomes narrow and intermittent. Then, as shown in (a) and (b) of FIG. 2B, the frequency thereof gradually decreases, and the rotation speed of the fan motor 1 decreases.

Next, the control means 4, when the frequency becomes sufficiently small, as shown in (c) of FIG.
The values of the frequency command fin, the voltage command K, and the phase θ output from the command generation unit 4b are adjusted so that the PWM signal having a constant width is output to the fan motor 1 at a constant cycle. As a result, the fan motor 1 is supplied with the braking DC voltage having the voltage value V1 as shown in FIG. 2B. Then, by continuing the above operation for t1 time, the control means 4 supplies the braking DC voltage having the voltage value V1 to the fan motor 1 for t1 time to stop the rotation of the fan motor 1.

In this case, since the braking DC voltage V1 is output after the rotation speed of the fan motor 1 is attenuated, the fan motor 1 is operated by simply outputting the braking DC voltage having a small voltage value V1 for a short time. It can be stopped. As a result, it is possible to prevent the fan motor 1 from being suddenly braked, and to heat the fan motor 1 and reduce the power consumption.

After that, the control means 4 decreases the value of the voltage command K from the command generator 4a. Then, a narrower PWM signal is output to the fan motor 1 at a constant cycle as shown in D of FIG. 2A, and the fan motor 1 is output to the fan motor 1 as shown in D of FIG. , DC voltage for braking V1
A DC voltage for maintaining the braking state having a smaller value V2 is supplied. Then, the control means 4 keeps the fan motor 1 in the braking state by continuing this operation.

Therefore, the fan motor 1 by an external force such as wind
Can be prevented, and as a result, overcurrent can be prevented from occurring when the fan motor 1 is restarted. Moreover, since the series of operations described above is performed by the control means 4 that controls the voltage waveform output from the inverter circuit 2, the mechanical braking device can be eliminated, and as a result, the configuration can be made compact, simple, and cost can be reduced. Can be planned.

While the control means 4 outputs the braking state maintaining DC voltage from the inverter circuit 2 as shown in FIG. 3 (a) which is an enlarged view of FIG. As described above, the detection signal from the detection circuit 5 is taken aiming at the period t2 in which the pulse voltage is not applied, and it is determined whether or not the polarity is constant. When the polarity is constant, the control means 4 determines that the fan motor 1 is in the braking state, and causes the inverter circuit 2 to continue outputting the braking state maintaining DC voltage V2.

On the contrary, when the polarity of the residual voltage is changing, the control means 4 judges that the fan motor 1 is in the rotating state and counts the number of changes of the polarity per unit time. In this case, if the count value is large, the rotation speed of the fan motor 1 is also large, so the control means 4
Increases the value of the voltage command K, that is, the braking holding DC voltage V2 in proportion to the magnitude of the count value, and controls the fan motor 1 to be held in the braking state.

Therefore, it is possible to prevent the fan motor 1 from rotating even though the DC voltage V2 for maintaining the braking state is output. Moreover, since the value of the DC voltage for maintaining the braking state is changed according to the rotation speed of the fan motor 1, the fan motor 1 can be maintained in the braking state with a voltage value as small as possible, and as a result, the heating and consumption of the fan motor 1 are performed. The amount of electric power can be reduced. Although the detection circuit 5 is used as the rotation detection means in the above embodiment, for example, a rotary encoder or the like may be used.

[0023]

As is apparent from the above description, according to the control device for an AC electric motor of the present invention, the AC electric motor can be held in the braking state by the control means for controlling the voltage waveform output from the inverter circuit. Therefore, the braking device having a mechanical structure for holding the AC motor in the braking state can be eliminated, and as a result, the structure can be downsized, simplified, and the cost can be reduced.

In particular, according to the second aspect of the invention, since the braking DC voltage is output after the rotational speed of the AC motor is attenuated, only a small braking DC voltage is output for a short time. Thus, the AC motor can be stopped. As a result, it is possible to prevent the AC motor from being suddenly braked, and to heat the AC motor and reduce the power consumption.

According to the third aspect of the invention, the rotation of the AC motor during the braking state is detected, and when the AC motor is rotating, the DC voltage for maintaining the braking state is determined according to the rotation speed. Since the value of is changed, it is possible to prevent the AC motor from rotating even though the braking state maintaining DC voltage is output. Moreover, since the AC motor can be kept in the braking state with a voltage value as small as possible, heating of the AC motor and reduction of power consumption can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of an electrical configuration showing an embodiment of the present invention.

FIG. 2A is a PW applied to phase A of a fan motor.
The figure which shows the M signal, (b) the figure which shows the voltage waveform which is impressed in phase A of the fan motor

FIG. 3A is a diagram showing a PWM signal in a braking holding state, and FIG. 3B is a diagram showing a timing of detecting a residual voltage.

[Explanation of symbols]

Reference numeral 1 is a fan motor (AC electric motor), 2 is an inverter circuit, 2Ua to 2Wb are transistors (switching elements), 4 is control means, and 5 is a detection circuit (rotation detection means).

Claims (3)

[Claims] 1. An inverter circuit having a plurality of switching elements, and a control means for controlling a voltage waveform output from the inverter circuit, wherein the AC motor is driven and controlled by the AC voltage output from the inverter circuit. In the above, the control means is configured such that, when the AC motor is stopped, the inverter circuit outputs a DC voltage for braking the AC motor and then outputs a DC voltage for holding a braking state. Control device. 2. The control device for an AC electric motor according to claim 1, wherein the control means outputs the braking DC voltage after the rotational speed of the AC electric motor is attenuated by the inverter circuit. . 3. The rotation detecting means for detecting the rotation and the rotation speed of the AC electric motor, wherein the control means sets the rotation speed to the rotation speed when the rotation detecting means detects the rotation while the braking state of the AC electric motor is maintained. 3. The control device for an AC electric motor according to claim 1, wherein the control device is configured to change the value of the braking state holding DC voltage in accordance with the braking state holding DC voltage.