JPH05244791A - Speed controller for ac motor - Google Patents

Abstract

PURPOSE:To simplify a circuit and to improve response to a speed command by speed-controlling an AC motor in response to a speed command signal by a DC positive and negative power source obtained by double-voltage rectifying an AC power source voltage through a thyristor and an exciting sequencer for turning ON, OFF a switching element. CONSTITUTION:A feedback loop for speed-controlling a motor is formed of a motor is formed of a DC positive/negative power source circuit 10 obtained by a voltage donbler from the voltage of an AC power source E, that is, by thyristors SCR1, SCR2; two switching elements QA, QB per one phase winding of an AC motor M; a speed control amplifier 12 which inputs a command speed signal; an exciting sequencer 13; and a speed detector D. Further, it has a V/f calculator 15 for varying output voltages V1, V2 of the power source circuit in proportion to the command speed signal (f), and an ignition controller 16 for igniting the thyristors QA, QB at predetermined ignition phase angles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for an AC electric motor, and more particularly to a DC positive / negative two power supply obtained by rectifying an AC power supply voltage through a thyristor and a switching element ON or OFF. An excitation sequencer and a device for controlling the speed of the electric motor according to a command speed signal.

[0002]

2. Description of the Related Art Conventionally, as a speed control device for an AC electric motor of this type, there is one that performs variable frequency control by an inverter as shown in the circuit diagram of FIG. In the figure, this control device uses a full-bridge two-phase inverter drive composed of switching transistors Q ₁ , Q ₂ ... Q ₈ for converting a DC voltage obtained by a full-wave rectifier CR and a smoothing capacitor C into a voltage of an AC power source E. the gates of the transistors Q _1, Q ₂ ......... Q ₈ of the circuit 1, PWM
(Pulse width modulation) PWM by gate circuit 2
While controlling, the AC motor, for example, the two-phase induction motor M was driven in the rotation direction and the frequency (speed) based on the operation command given to the PWM gate circuit 2.

In order to make the direction of the current flowing through each winding of the two-phase induction motor M reversible, the inverter drive circuit 1 has four transistors Q _1, ... Q ₄ and Q ₅ , for each phase winding. ...... with Q _8, it has been performed a so-called bipolar driving of a single power supply method.

[0004]

However, in such a speed control device using the inverter of the conventional two-phase induction motor M, PWM control is performed to make the drive voltage, the current direction and the frequency (speed) variable. Therefore, four switching elements (switching transistors in FIG. 4) were required for each phase winding of the electric motor, and eight switching elements in total were required.

Therefore, there are problems that the drive circuit structure becomes complicated, chopping noise and loss peculiar to the PWM control increase, and the speed response of the electric motor is poor.

The present invention has been made in view of the above points.
An object of the present invention is to solve the above problems, to provide a speed control device for an AC electric motor, which has a simplified drive circuit configuration and has a good response to a command speed.

[0007]

The structure of the present invention for attaining the above object comprises a DC positive / negative two power supply circuit obtained by rectifying an AC power supply voltage by a thyristor, and two per phase winding of an AC motor. Switching elements, an excitation sequencer that turns on or off the switching elements according to a predetermined excitation sequence according to a command speed signal to drive each phase winding of the electric motor in a bipolar manner, and an excitation sequencer that is coupled to the electric motor. A speed detector that detects the speed of the electric motor,
A speed control amplifier that outputs a sequencer signal according to the commanded speed signal to the excitation sequencer and negatively feeds back the speed signal of the electric motor from the speed detector is provided.

At the same time, in order to change the output voltage V of the zero-cross detection circuit for detecting the zero-cross timing of the AC power supply voltage and the DC positive / negative two power supply circuit in proportion to the command speed signal f, the thyristor is ignited. A V / f arithmetic circuit for calculating and transmitting a signal for determining a phase,
From the firing phase signal from the / f arithmetic circuit and the zero-cross signal of the AC power supply voltage from the zero-cross detection circuit,
A firing control circuit for firing the thyristor at the determined firing phase angle.

[0009]

[Operation] Since the present invention is configured as described above,
Each switching element is turned on by the speed control amplifier and the excitation sequencer according to the command speed signal from the DC positive / negative two power supplies in which the AC power supply voltage is doubled and rectified by the thyristor.
Alternatively, it is turned OFF to drive each phase winding of the AC motor in a bipolar manner, and the actual speed signal of the motor is detected and negatively fed back to the input side of the speed control amplifier. Therefore, a feedback loop for speed control is provided. Can be formed and the speed of the electric motor can be controlled in response to the command speed signal.

Further, the thyristor is controlled in proportion to the commanded speed signal to change the output voltage of the DC positive / negative dual power supply circuit. That is, since the ratio of the DC output voltage V to the command speed signal f is made constant, the speed of the AC motor can be controlled also from this aspect.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be illustratively described in detail below with reference to the drawings. FIG. 1 is a configuration circuit diagram in the case of a two-phase induction motor showing an embodiment of a speed control device for an AC motor of the present invention. In the figure, the voltage of the AC power supply E is represented by thyristors SCR ₁ and SCR ₂ and capacitors C ₁ and
And voltage doubler rectified by C _2, and the DC positive and negative second power supply circuit 10 to the DC voltage V _1, V ₂ is obtained, four switching transistors Q _A for driving the two-phase induction motor M, Q _B, Q
_An inverter drive circuit 11 composed of _C and Q _D is shown.

By connecting the neutral point N of the DC positive / negative dual power supply circuit 10 and the common connection point P of the two-phase windings of the two-phase induction motor M to each phase winding of the motor M, The inverter drive circuit 11 enables the half-bridge bipolar drive.

Next, referring to FIG. 1, the speed control amplifier 1
2 inputs a command speed signal f (for example, an analog signal) to the electric motor M, and outputs a predetermined sequence signal including a command frequency signal to the excitation sequencer 13.

The excitation sequencer 13 receives the sequence signals from the speed control amplifier 12 to switch the switching transistors Q _A ,
The gates of Q _B , Q _C , and Q _D are driven, and the transistors Q 1 and Q 2 are driven in accordance with a predetermined excitation sequence.
_A, Q _B, Q _C, the Q _D is ON or OFF, outputs a rectangular wave voltage to the motor M from the driving circuit 11.

Now, focusing on the α-phase winding of the electric motor M, the transistor Q _A is ON and the transistor Q _B is OF.
In the case of F, one of the positive and negative DC power supply circuits 10 (the output voltage V
₁ ) is supplied with current, and on the contrary, transistor Q _A is OF
When F and the transistor Q _B are ON, the power supply circuit 10
The other side (output voltage V ₂ ) supplies current in the opposite direction,
The two switching transistors Q _A and Q _B can drive the one-phase winding of the electric motor M in a bipolar manner.

By the way, the speed control amplifier 12 generates a sequence signal for the two-phase induction motor M including a command frequency (command speed) signal in accordance with the command speed signal f to the excitation sequencer 13. . Therefore, the excitation sequencer 13 causes the drive circuit 11 to operate as shown in FIG.
Two-phase rectangular wave voltages having a phase difference of 90 ° as shown in (3) are supplied to the α-phase winding and the β-phase winding of the electric motor M to drive the electric motor M.

Further, a speed detector D for detecting the actual speed of the electric motor M is coupled to the electric motor M, and a speed signal from the speed detector D is input to the speed control amplifier 12. Negative feedback to the side to form a speed control loop.

On the other hand, in FIG. 1, the zero-cross detection circuit 14 is a circuit for detecting the zero-cross timing of the voltage of the AC power source E and generating a zero-cross pulse signal. This is a circuit for calculating and outputting a pulse signal for determining the firing phase of the thyristors SCR ₁ and SCR ₂ in order to change the output voltage V of the DC positive / negative dual power supply circuit 10 in proportion to the signal f.

The firing control circuit 16 compares the firing phase pulse signal from the V / f calculation circuit 15 with the zero cross pulse signal from the zero cross detection circuit 14 to determine the determined firing phase angle. The thyristor S at the timing
This is a circuit for firing CR ₁ and SCR ₂ .

FIG. 3 shows the signal waveform and timing of each of these circuits. FIG. 3 (a) shows the voltage of the AC power source E, FIG. 3 (b) shows the zero-cross pulse signal of the zero-cross detection circuit 14, and FIG. 3 (c). Is a firing pulse signal to the gates of thyristors SCR ₁ and SCR ₂ and (d) is a thyristor SC.
The waveforms of the currents flowing through R ₁ and SCR ₂ and the DC output voltages V ₁ and V ₂ .

Normally, in the speed control by the frequency of the AC electric motor, particularly the induction motor, it is necessary to apply the voltage V proportional to the command speed signal f to the electric motor M.

Therefore, the DC output voltages V ₁ and V _{2 of the} DC positive / negative dual power supply circuit 10 are proportional to the command speed signal f.
In order to change the
A phase pulse signal for determining the firing phase of the thyristors SCR ₁ and SCR ₂ of the power supply circuit 10 is calculated and output. Then, the thyristor firing control circuit 16 compares this phase pulse signal with the zero-cross pulse signal from the zero-cross detection circuit 14, and the thyristors SCR ₁ , S
The firing pulse signals G ₁ and G ₂ are output to each gate of CR ₂ .

By the firing pulse signals G ₁ and G ₂ , the thyristors SCR ₁ and SCR ₂ are respectively fired at the determined predetermined firing phase angles, and their DC output voltages V ₁ and V ₂ are changed. I am making it. That is, each of the circuits 1
An output voltage having a constant ratio of the DC output voltage V to the command speed signal f is applied to the electric motor M by the motors 4, 15.

As described above, in the present embodiment, the case of the two-phase induction motor is shown as an example of the AC motor, but it is also applicable to the polyphase induction motor and the multiphase stepping motor. In this case, the sequence signal and the excitation sequence of the speed control amplifier and the excitation sequencer can be implemented simply by appropriately changing them.

The circuit of the control system shown in FIG. 1 can be controlled by software with a one-chip microcomputer. According to this embodiment, the inverter drive circuit 1
No. 1 does not perform PWM control as in the related art, so that the circuit configuration can be simplified. Moreover, the switching loss peculiar to the PWM control is also reduced, and noise is not generated.

The technique of the present invention is not limited to the technique in the above-described embodiment, and means of another aspect having a similar function may be used, and the technique of the present invention is various within the scope of the above configuration. Can be changed or added.

[0027]

As is apparent from the above description, according to the speed control device for an AC electric motor of the present invention, a command from a DC positive / negative two power source obtained by rectifying an AC power source voltage by voltage doubling by a thyristor as a rectifying element. Depending on the speed signal, the speed control amplifier and the excitation sequencer turn on or off two switching elements for each phase winding of the motor,
Since each phase winding of the electric motor is driven in a bipolar manner, the actual speed of the electric motor is detected, and the speed signal is negatively fed back to the input side of the speed control amplifier, so that the number of switching elements is reduced by half, Responsiveness to the commanded speed of the electric motor is extremely improved.

At the same time, since the thyristor is controlled in proportion to the commanded speed to change the DC positive / negative power supply voltage to control the speed of the electric motor, power loss can be reduced more than before. It plays.

[Brief description of drawings]

FIG. 1 is a configuration circuit diagram in the case of a two-phase induction motor showing an embodiment of a speed control device for an AC electric motor of the present invention.

FIG. 2 is a waveform diagram of a two-phase rectangular wave voltage having a phase difference of 90 ° output from the inverter drive circuit 11 of FIG.

FIG. 3 is a diagram showing a signal waveform and timing of each circuit.

FIG. 4 is a configuration circuit diagram of a conventional AC motor speed control device.

[Explanation of symbols]

10 DC positive and negative second power supply circuit 12 the speed control amplifier 13 energized sequencer 14 zero-cross detecting circuit 15 V / f arithmetic circuit 16 firing control circuit D speed detector E AC power supply f command speed signal M two-phase induction motor Q _A, Q _B, Q _C , Q _D Switching transistor SCR ₁ , SCR ₂ Thyristor V ₁ , V ₂ DC output voltage

Claims (1)

[Claims] 1. A DC positive / negative dual power supply circuit obtained by rectifying an AC power supply voltage by voltage doubling by a thyristor, two switching elements per phase winding of an AC motor, and the switching elements according to a command speed signal. An excitation sequencer that turns on or off according to a predetermined excitation sequence to drive each phase winding of the electric motor in a bipolar manner, a speed detector that is coupled to the electric motor to detect the speed of the electric motor, and the command speed signal A sequence signal corresponding to the excitation sequencer is output, and a speed control amplifier in which the speed signal of the electric motor from the speed detector is negatively fed back is provided, and zero-cross detection is performed to detect a zero-cross timing of the AC power supply voltage. Circuit, and for changing the output voltage V of the DC positive / negative dual power supply circuit in proportion to the command speed signal f Calculating a signal for determining the ignition phase point of said thyristor,
The thyristor is operated at the determined firing phase angle from the V / f operation circuit to be sent, the ignition phase signal from the V / f operation circuit, and the zero-cross signal of the AC power supply voltage from the zero-cross detection circuit. A speed control device for an AC motor, comprising: a firing control circuit for firing.