JPS59169390A - Controller of ac motor - Google Patents

Abstract

PURPOSE:To reduce the irregularity of rotating speed of an AC motor at the time of driving at extremely low speed and torque by modulating the control signal by a signal of high frequency signal generating means having duty variable means to vary the rotating speed and generated torque of the motor. CONSTITUTION:A motor M is connected to a bridge circuit of switching elements 1-4 controlled by transistors 5, 6, and normal/reverse rotation thyristors 7, 8 controlled by firing circuits 9, 10 are provided. The deviation between the actual speed and the target speed is produced from a variable resistor 11, control signals P1, P2 are obtained through a V/F converter 13, applied to gate circuits 18, 19 together with the output of a high frequency oscillator 15 which can vary the duty ratio by a variable gain amplifier 16, thereby controlling the transistors 5, 6. Accordingly, the duty ratio can be reduced while holding the pulse width of the control signal P to the maximum limit, and the irregular rotation can be reduced at the extremely low speed and torque time.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a control device that simultaneously controls the rotation speed and torque of a single-phase or three-phase AC motor.

(Problems to be solved) The applicant has filed Japanese Patent Application No. 57-21893;
According to No. 231245, etc., a transistor switch is provided in a circuit leading from a single-phase or three-phase AC power supply to an AC motor load, and the switch is controlled on and off using a control signal that can change continuously, thereby controlling the rotational direction of an AC motor. We are proposing a technology that continuously controls rotational speed and torque. This technology uses general-purpose AC motors that have been manufactured and used for power as control motors for servos, etc., and can not only rotate at the original high speed, but also continuously from extremely low speed rotation to stopping. It has the advantage of being controllable.

However, especially when the motor is driven at extremely low speed and low torque, the off-time of the current applied to the motor becomes long, resulting in a drawback that rotational speed unevenness becomes large when the moment of inertia of the motor load is small.

<Purpose of the Invention> Therefore, the present invention has the objective of achieving
The purpose of the present invention is to provide an improved control device that does not take too long a motor current off time and can suppress unevenness in motor rotational speed.

<Configuration of the Invention> The AC motor control device of the present invention includes a high-frequency signal generating means that outputs a square wave with a frequency sufficiently higher than the commercial AC frequency, and a duty ratio of the high-frequency square wave that is continuously changed. control signal ordering means for outputting a polyphase square wave whose frequency changes; means for modulating the control signal with the high frequency signal; and an AC switch connected between the commercial AC power supply terminal and the AC motor. and circuit means for controlling each alternating current switch element on and off by the modulated signal, and changing the rotational speed of the electric motor by changing the frequency of the control signal,
It is characterized by being configured to change the torque generated by the electric motor by changing the duty ratio.

<Example 1> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of the present invention. A commercial AC power source is connected to terminals R and S. Motor M that operates the controlled object
For example, the rotation direction can be switched between forward and reverse, such as a capacitor-advanced single-phase AC motor, and when connecting the terminal UW to the AC power source, it rotates clockwise, and the terminal VW is connected to the AC power source. When doing so, rotate counterclockwise. The four AC switch elements 1, 2, and 3.4 form a bridge circuit, and the control input lines 1a and 3a of the first and third AC switch elements 1.3 on opposite sides of the bridge are commonly connected. The control input lines 2a and 4a of the second and fourth AC switch elements 2.4 forming the other opposite sides of the bridge are connected in common and are controlled on and off by the transistor 6. This yellowtail
To explain the Noji circuit in detail, a first AC switching element 1 is connected between one of the power input terminals R and one of the power output terminals W, and a second AC switch element 1 is connected between one of the power output terminals R and the other power output terminal X.
A third AC switch element 2 is connected between the other power input terminal S and the other power output terminal X, and a fourth AC switch element 3 is connected between the other power input terminal S and the power output terminal W.
AC switch elements 4 are connected to each other. The AC switching element 1.2.3 or 4 is, for example, as shown in the circuit diagram in FIG.
The collector and emitter electrodes of the terminal are connected, and the base electrode is led out as the control terminal C.

A clockwise terminal U of the motor M is connected to a power output terminal X via a bidirectional thyristor 7, and a counterclockwise terminal V
is connected to the power output terminal X via the bidirectional thyristor 8. Thyristor 7 or 8 is connected to ignition circuit 9 or 10
one of them is turned off.

On the other hand, the current values representing the position, speed, etc. of the controlled object are detected by the detector (
(not shown), and the deviation from the target value is detected and introduced to the input terminal IN. In the figure, a variable resistor 11 schematically represents a deviation detector, and a symbol representing a deviation is converted into a voltage of +5V to -5V and inputted. This feedback input signal is amplified by an absolute value amplifier 12 and then converted by a V/F converter (voltage-frequency converter) 13 into a pulse train with a frequency proportional to the input voltage. The control signal generating bridge 14 is a sequential opening/closing circuit consisting of a combination of a counter and a logic gate, and generates two-phase control signals pl and p2. The high frequency oscillator 15 is
It outputs a sine wave with a frequency about 10 to 100 times higher than the commercial AC frequency. The variable gain amplifier 16 amplifies its sine wave output and can automatically and continuously reduce its gain depending on the magnitude of the input signal. The slicing circuit 17 slices the output of the variable gain amplifier 16 at a predetermined level to extract a substantially square waveform.

The duty ratio of the square wave output at this time changes depending on the gain of the amplifier 16. The gate circuits 18 and 19 are AND gates that pass the control signals Pi and P2 only when the square wave output K is at Hi level, and generate control signals P1' and P2' modulated with a high frequency signal. The pulse train P of
The transistor 5 is on/off controlled by i', and the transistor 6 is on/off controlled by the second pulse train P2'. The comparator 20 determines whether the voltage of the feedback input signal is positive or negative, and when it is positive, the output is, for example, Hi (high) level and the clockwise ignition circuit 9 is driven. When it is negative, the output is at Lo (low) level, which is inverted to l (i level) by the NOT circuit 21, and the counterclockwise ignition circuit 10 is driven.

Next, the effect will be explained. When the feed bank input signal is a positive voltage and the ignition circuit 9 is driven, the bidirectional thyristor 7 is turned off, the thyristor 8 is turned off, and the motor M is driven to rotate clockwise.

Conversely, when the state of the controlled object changes and the feedback signal becomes a negative voltage, the ignition circuit 10 is driven, the thyristor 7 is turned off, the thyristor 8 is turned on, and the motor M is driven to rotate counterclockwise. .

When the variable resistor 11 is exactly at the midpoint, the controlled object matches the target value. When the state of the controlled object shifts from the target value, the output voltage of the absolute value amplifier 12 increases in proportion to it, and the pulse frequency that is the output of the V/F converter 13 increases. The waveforms of the control pulse signals Pi and P2 are as follows:
As shown in FIG. 3, they are square waves with a phase difference of 180 degrees, and do not become H level at the same time.

Since the slicing circuit 17 slices a predetermined level, for example between 5V and 6V, to drive the output transistor, the duty ratio of the square wave output changes in accordance with a change in the gain of the amplifier 16 in the previous stage. As a result, the modulated control signal pl
As shown in FIG. 3, the waveforms of ', P2' have a total pulse width equal to that of the control signal PI.

The duty ratio is the same as P2, and as the duty ratio decreases, the drive time of transistors 5 and 6 decreases. When the transistor 5 is on, the AC switching elements 1 and 3 are on, while the other set of AC switching elements 2 and 4 are off. Next, when transistor 6 is on, AC switch elements 2 and 4 are on, and at that time (8) the other set of AC switch elements 1 and 3 are off. Through such on/off operations, the motor M is supplied with an alternating current defined by the on/off operations of the transistors 5 and 6. Therefore, the motor M is rotated by the rotating magnetic field caused by the frequency of the on/off operation of the transistor 5.6, regardless of the frequency of the commercial AC power source.

At this time, the rotational speed of the motor M is controlled to be reduced as the feedbank signal approaches the target value. Further, the torque of the motor M becomes smaller as the duty ratio of the high frequency square wave output decreases.

When the commercial AC frequency is Fl and the frequency of the control pulse signal is f, the output frequency F2 applied to the motor M from the power output terminal is F 2 = f − F 1−−−−−−−(11) .Therefore, when F+ = 60Hz and f = 60Hz, F2
= 0, and the rotation of the motor M stops. At this time, the voltage of the feedback signal is e=0. When e≠0, F2≠0, and the motor M has a frequency F determined by equation 11.
2, and rotates in the hour hand direction or counterclockwise direction depending on whether the voltage e is positive or negative. FIG. 4 shows a voltage waveform applied to the power output terminal WX when f<Fl. In the figure, the solid sine wave line indicates the current in the motor terminal W-X direction, and the dotted line indicates the current in the X-W direction. Note that in the fourth example, modulation by a high-frequency square wave is omitted by vertical stripes.

As a modified embodiment of the duty variable means of the present invention, the gain of the amplifier 16 may be held constant and the slice level of the slice circuit 17 may be varied.

Further, the gain may be configured to be manually changed independently of the magnitude of the input signal.

(Embodiment 2) Fig. 5 shows a circuit configuration diagram in which the present invention is implemented in a chopping control circuit of a three-phase induction motor.The same parts as in the embodiment shown in Fig. 1 are denoted by the same numbers. The different parts will be explained below.

A commercial AC power source is connected to terminals R, S, and T, and a three-phase induction motor M is connected to terminals U, V, and W. The first switch circuit 31, the second switch circuit 32, and the third switch circuit 33 each have three power supply side terminals A, B, C and 3.
Motor side terminals.

E, F, and control input terminals, and its internal configuration is as follows:
As shown in the figure, AC switch elements 34, 35.3 are connected between terminals A and D, between terminals B and E, and between terminals C and F, respectively.
6 are connected, and each AC switch element is controlled on/off simultaneously by one control pulse signal Pi' (i=1.2°3). The AC switching element includes, for example, four diodes D+, D2 . The collector and emitter electrodes of a power transistor Q are connected between the DC output terminals of a full-wave rectifier circuit consisting of Da and D4, and the base electrode is led out as a control terminal. Each transistor Q+, Q2. On/off control is performed all at once by a transistor drive circuit 37 operated by the base signal Pi' of Q3.

Returning to FIG. 5, the control signal generator 14' generates a phase-directional control signal Pl' having a frequency proportional to the output pulse frequency of the V/F converter 13 and corresponding to the output of the comparator 20.
+ P2. Output pa. This control signal is applied to the high frequency square wave output as in the single phase embodiment described above.
The torque of the three-phase AC mok M is controlled by varying the duty ratio of the high frequency square wave modulated by the D gate circuit 22°23.24.

<Effects of the Invention> According to the present invention, the actual duty ratio can be reduced while maintaining the overall pulse width of the control signal Pi to the maximum limit, so that the motor current can be reduced even in extremely low speed and low torque driving. The off time is not too long, and uneven rotation of the motor can be suppressed. Furthermore, since there is no need to step down the power supply input voltage using a resistive element or transformer, torque can be reduced while maintaining high efficiency and miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing specific examples of AC switch elements 1 to 4 in FIG. 1, and FIGS. 3 and 4 are circuit diagrams showing the above embodiments. FIG. Fig. 5 is a circuit diagram showing a second embodiment of the present invention, Fig. 6 is a circuit diagram showing a specific example of the switch circuit in Fig. 5, and Fig. 7 is an explanation of the operation of the embodiment shown in Fig. 5. It is a diagram. R, S, T--Commercial power input terminal U, V, W, X--Power output terminal M--AC motor 14, 14''-11 Control signal generator 18, 19, 2
2, 23, 24 - AND gate (modulation means) 15 - Oscillator 16 - Amplifier 17 - Slice circuit Patent applicant M-System Giken Co., Ltd. Patent attorney Nishi 1) Shin

Claims (1)

[Claims] A high frequency signal generating means for outputting a square wave having a frequency sufficiently higher than the commercial AC frequency, a duty variable means for the square wave high frequency, a control signal generating means for outputting a polyphase square wave whose frequency changes, means for modulating the control signal with the high frequency signal; an AC switching element connected between the commercial AC power supply terminal and the AC motor; and circuit means for controlling on/off of each AC switching element using the modulated signal. and configured to change the rotation speed of the electric motor by changing the frequency of the control signal, and change the generated torque of the electric motor by changing the duty ratio,