JPH09215386A - Power controller of ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a zero-crossing point by utilizing a microcomputer even if an exclusive zero-crossing circuit is not used. SOLUTION: A controller has a full-wave rectifier 2 which rectifies a commercial power supply voltage, a voltage converter 5 which transforms the rectified power supply voltage into a voltage of several volts, an A/D converter 7a which converts the voltage transformed by the voltage converter 5 into a digital value with a certain time interval and a microcomputer 7 which processes the output of the A/D converter 7a to perform various control. The controller detects a zero-crossing point at which the output of the A/D converter 7a is zero and the state of the output is transferred from a descending direction to an ascending direction and, if the zero-output of the A/D converter 7a is continued, detects a time for which the zero-output is continued.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Using a 3-pole bidirectional thyristor,
The present invention relates to a power control circuit that controls the speed of an AC motor by controlling the power supplied to the AC motor.

[0002]

2. Description of the Related Art As a conventional method for controlling the rotation speed of an AC motor, a phase control method is well known in which electric power supplied to the AC motor is controlled by using a three-pole bidirectional thyristor. When this phase control is performed with high accuracy, the zero-cross point, that is, the point where the AC voltage changes from positive to negative (or negative to positive) is detected with high accuracy. Then, the three-pole bidirectional thyristor is turned on with reference to the zero-cross point. Thereby, the phase control can be performed with high accuracy.

[0003]

However, in order to control the phase as described above, that is, to control the rotation speed of the AC motor with high accuracy, it is necessary to use a dedicated zero-cross detection circuit.

[0004]

Therefore, according to the present invention, a full-wave rectification circuit for rectifying a commercial power supply and a voltage conversion for transforming a power supply voltage rectified by the full-wave rectification circuit into a voltage of about several volts. A circuit, an A / D converter that converts the voltage transformed by the voltage conversion circuit into a digital value at predetermined time intervals, and an icon that calculates the output value of the A / D converter and performs various controls are provided. A zero-cross point at which the output value of the / D converter is 0 and the output value of the converter shifts from the descending direction to the ascending direction, and when the output value of the converter is 0, the time when the output value of 0 continues is detected. A power control circuit is provided.

[0005]

[Function] The commercial power supply is rectified by the full-wave rectification circuit. Then, the rectified voltage is transformed into a voltage of several V which can be detected by the microcomputer by the voltage conversion circuit. Then, this voltage is input to the A / D converter to convert the analog value into a digital value at predetermined intervals. Then, this digitally converted voltage value, so-called output value is obtained. Then, the microcomputer detects a point where the output value is in the vicinity of 0 V and the voltage waveform changes from the falling direction to the rising direction to obtain the zero cross point. Further, the microcomputer detects the time when the output value is continuously 0V, and obtains the stop time of the power supply voltage supplied to the AC motor.

[0006]

Embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a power control circuit according to the present invention. FIG. 2 is a block diagram illustrating the configuration of the circuit that drives the AC motor according to the present invention. FIG.
3 is a graph of a voltage waveform supplied to an AC motor.

In FIG. 1, a power control circuit 1 is insulated from a full-wave rectifier circuit 2 that generates a control power supply Vcc for a microcomputer, a smoothing circuit 3, a control power supply circuit 4, and a voltage conversion circuit 5 that detects a zero-cross point. It is composed of a circuit 6 and a highly versatile microcomputer 7 having an A / D converter 7a built therein.

Commercial power supply AC100V (or AC200
V) is supplied to the power control circuit 1, the power supply voltage of the commercial power supply is rectified by the full-wave rectification circuit 2. Then, the rectified voltage is supplied to the smoothing circuit 3 and the voltage conversion circuit 5. The voltage supplied to the smoothing circuit 3 is smoothed by the smoothing circuit 3 to remove ripples, and becomes a DC voltage. Then, the control power supply circuit 4 transforms the control power supply Vcc required by the microcomputer 7, for example, DC 5V, and inputs the voltage to the microcomputer.

On the other hand, the voltage supplied to the voltage conversion circuit 5 is transformed by the voltage conversion circuit 5 into several V (about 5 V if the microcomputer control power supply Vcc is 5 V). For example,
By transforming the rectified commercial power source by dividing the voltage with a resistor, the voltage can be transformed with a simple configuration without phase shift. Then, this transformed voltage is input to the A / D converter 7a inside the microcomputer 7 through the insulating circuit 6. The insulating circuit 6 is a circuit for preventing noise generated in the commercial power source from entering the microcomputer, and is composed of a photocoupler, a noise filter, or the like.

A / A provided inside the microcomputer 7
The voltage input to the D converter 7a is digitally converted at a predetermined interval to obtain an output value. Then, the microcomputer determines the point where the output value is near 0V and the voltage waveform changes from the falling direction to the rising direction. As a result, the zero-cross point can be detected.

Further, the torque of the AC motor can be controlled by detecting the value of the current flowing through the AC motor with a current detection circuit or the like (not shown) and inputting this current value to the microcomputer 7.

In FIG. 2, by connecting the AC motor 8 to a commercial power source, it can be driven at a rotation speed corresponding to the frequency of the commercial power source. Further, the three-pole bidirectional thyristor 9 is connected in series to one power supply line of the commercial power supply.
Then, the microcomputer 7 mounted on the power control circuit 1 is connected to the gate of the 3-pole bidirectional thyristor 9, and the ON signal output from the microcomputer 7 is input to the gate of the 3-pole bidirectional thyristor 9. It is possible to control the three-pole bidirectional thyristor 9. That is, the commercial power supply supplied to the AC motor is limited by turning it on and off to control the speed of the AC motor 8.

As shown in the graph of FIG. 3, the AC motor 8
By detecting the zero-cross point A of the commercial power supply supplied to the microcomputer 7 as described above, it becomes easy to turn on the three-pole bidirectional thyristor 9 at the point B with reference to the zero-cross point A. That is, highly accurate phase control can be performed.

From the above, according to the present invention, it is not necessary to separately provide a dedicated zero-cross circuit, and a voltage conversion circuit which can be simply and inexpensively constructed by a resistor and the like is used for torque control or power supply voltage detection. The zero cross point can be detected by a software program using the A / D converter built in the microcomputer.

Further, since the output value can be detected by the microcomputer 7, the maximum value of the output value (the point where the output value shifts from the rising direction to the falling direction) is detected by the microcomputer 7 and the maximum output value It is also possible to measure the change and measure a change in the commercial power supply (such as a voltage drop). Therefore, even if a voltage drop occurs, the microcomputer 7 can output an error signal and perform processing such as operation stop of the AC motor.

Further, by detecting the time when the output value is 0V by the microcomputer 7, it is possible to measure the stop time of the power supplied to the AC motor. Therefore, for example, in a bolt fastening machine for an electric power tool, it is necessary to perform torque control for fastening bolts and nuts at a constant torque for a certain time. Therefore, if the power supplied to the bolt fastening machine stops momentarily while fastening the bolts and nuts (for example, when trying to change the hand holding the bolt fastening machine, the In case of separation, etc.), torque control should be continued from the middle. When the power supplied to the bolt fastening machine is stopped during the time until the next bolt / nut is fastened, the torque control is performed from the beginning. In this way, it is possible to select whether to continue the torque control from the middle or to perform the torque control from the beginning depending on the stop time of the power supplied to the bolt fastening machine.

[0017]

According to the present invention, by using a microcomputer, it is possible to detect a zero-cross point without using a dedicated zero-cross circuit and to manage the state of the power supplied to the AC motor. Therefore, it is possible to easily detect the voltage drop, the power supply stop time, and the like.

[0018]

[Brief description of drawings]

FIG. 1 is a block diagram of a power control circuit according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a circuit that drives an AC motor according to the present invention.

FIG. 3 is a graph of a voltage waveform supplied to the AC motor.

[Explanation of symbols]

 1 ... Power control circuit 2 ... Full wave rectification circuit 3 ... Smoothing circuit 4 ... Control power supply circuit 5 ... Voltage conversion circuit 6 ... Insulation circuit 6 7 ... Microcomputer 7a ... A / D converter 8 ... AC motor 9 ... 3-pole bidirectional thyristor

Claims (1)

[Claims] 1. A full-wave rectifier circuit for rectifying a commercial power source in a power control circuit for controlling the speed of an AC motor by controlling the electric power supplied to the AC motor using a three-pole bidirectional thyristor, A voltage conversion circuit that transforms the power supply voltage rectified by this full-wave rectification circuit into a voltage of approximately several V, and an A / D converter that converts the voltage transformed by this voltage conversion circuit into a digital value at predetermined time intervals. A zero-cross point at which the output value of the A / D converter shifts from the descending direction to the ascending direction when the output value of the A / D converter is 0, and the output value of the A / D converter An electric power control circuit for an AC motor, which detects the time when the output value 0 continues when 0 continues.