JPS6230478Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a speed control device for a DC motor that controls the speed by controlling the phase of electric power supplied from a commercial AC power source.

Conventional devices of this type supply firing pulses to a phase control thyristor from a relaxation oscillator circuit whose output pulse phase changes according to the motor's armature induced voltage to keep the motor's rotational speed constant. It is known what has been done. FIG. 1 shows an example of a conventional speed control device of this type, and in the figure, AC is a commercial alternating current power source. The output of this AC power supply is the diodes D ₁ , D ₂ and the thyristor Q ₁ ,
Q ₂ is input to a single-phase bridge control rectifier circuit 1 , and an armature M of a DC motor is connected between the DC output terminals of the control rectifier circuit 1 . The anodes of diodes D ₃ and D ₄ whose cathodes are commonly connected are connected to both terminals on the input side of the control rectifier circuit 1, and a full-wave rectifier circuit 2 is constituted by the diodes D ₁ to _{D 4} . A semi-fixed resistor VR _1, a variable resistor VR ₂ , and a semi-fixed resistor are connected between the DC output terminals of the full-wave rectifier circuit 2.
VR ₃ are connected in series. The intermediate terminal (slider) of the variable resistor VR ₂ is connected to the anode A of the programmable union transistor (or N-gate thyristor, hereinafter referred to as PUT) _{Q 3} via the resistor R ₁ , and the The cathode K is connected to the positive output terminal of the controlled rectifier circuit ₁ via a resistor R2. An oscillation capacitor (hereinafter also simply referred to as a capacitor) C and a diode _D5 are connected in parallel between the anode A of PUT Q ₃ and the positive output terminal of the control rectifier circuit 1, and the cathode of the diode _D5 is connected to the PUT Q ₃ . It is connected so that it is on the anode A side of the A series circuit of resistors R ₃ and R ₄ forming a voltage dividing circuit is connected between the positive output terminals of the full-wave rectifier circuit 2 and the control rectifier circuit 1, and a diode D is connected between both ends of the resistor R ₄ . ₆ are connected in parallel such that their anodes are on the positive output terminal side of the control rectifier circuit 1. Furthermore, the gate G of PUT Q ₃ is connected to the connection point between resistors R ₃ and R ₄ . Further, the cathode K of PUT Q ₃ is connected to the gates of thyristors Q ₁ and Q ₂ via resistors R ₅ and R ₆ , respectively, and the pulse obtained across the resistor R ₂ is connected to the gates of thyristors Q ₁ and Q ₂ . The voltage is applied between the cathodes. Furthermore, a flywheel diode _D7 is connected in parallel to both ends of the armature M of the motor, with its anode facing the negative output terminal of the control rectifier circuit 1. Among the above configurations, R ₁ ~
R ₄ , D ₅ , D ₆ , C, and Q ₃ constitute a relaxation oscillation circuit 3 surrounded by a chain line in the figure.

In the above speed control device, a full-wave rectifier circuit 2, a semi-fixed resistor VR ₁ , a variable resistor VR ₂ , a resistor
Current flows through R ₁ , capacitor C, and armature M, and capacitor C is charged. This results in
The anode-cathode voltage Va of PUT Q ₃ also increases. On the other hand, if the output voltage of the full-wave rectifier circuit 2 is Vd and the induced voltage of the armature M is Ea, then when PUT Q ₃ is in the cutoff state, the gate-cathode voltage Vg of this PUT Q ₃ is Vg≈(Vd−Ea ) {R ₄ / (R ₃ + R ₄ )} ...(1). Here, the peak point voltage of PUT Q ₃ is Vp,
If the offset voltage is Vt, the voltage across capacitor C increases and the voltage Va between the anode and cathode of PUT Q ₃ becomes Va=Vp=Vg+Vt (2) At the moment the voltage between the anode and cathode of PUT Q ₃ becomes Becomes conductive. This discharges the charge on the capacitor C through the resistor _R2 , and a pulsed voltage is obtained across the resistor _R2 . This pulse signal is supplied as a firing signal between the gate cathode of thyristors Q ₁ and Q ₂ via resistors R ₅ and R ₆ , and a forward voltage is applied between the anode and cathode of thyristors Q ₁ and Q ₂ . The thyristor that is connected becomes conductive. Therefore, the control rectifier circuit 1 from the alternating current power supply AC
Power is supplied to the armature M of the DC motor via the DC motor, and the motor is driven. When the rotational speed of the motor increases and the induced voltage Ea of the armature M increases, the phase in which PUT Q ₃ becomes conductive is delayed and the thyristor
The phase of the ignition signal to Q ₁ and Q ₂ is delayed, and the rotation speed of the motor decreases. Also, when the rotational speed of the motor decreases and the induced voltage Ea of armature M decreases, PUT
The phase in which Q ₃ becomes conductive advances, the phase of the ignition signal to the thyristors Q ₁ and Q ₂ advances, and the rotational speed of the motor increases. In this way, the rotational speed of the motor is kept constant. Ideally, such a control device would provide the same feedback to load fluctuations at any speed setting from high to low, but in this type of device, the amount of feedback varies significantly depending on the speed. On the contrary, at high speeds the feedback is small, at medium speeds it is the largest, and at low speeds the feedback tends to be in the middle. Regarding this situation, the terminal voltage Vm of armature M in Fig. 2
This will be explained in more detail using the waveform diagram. In FIG. 2, a is a waveform chart of Vm in each speed range of high speed, b is medium speed, and c is low speed. In the high-speed region shown in FIG. 5A, there are a section α in which the thyristor is in a non-conducting state and the reverse induced voltage Ea of the motor appears, and a section β in which the thyristor is in a non-conducting state and a power supply voltage is applied. In Figure 1, the charging of capacitor C causes a reverse induced voltage as the load on armature M increases.
As Ea decreases, the thyristor's trigger phase becomes smaller and tries to keep the rotation constant. That is, in the high speed region shown in FIG. 2a, load fluctuations are detected only by changes in the reverse induced voltage Ea. However, in the medium speed and low speed regions shown in FIGS. 2b and 2c, within the period α in which the thyristor is in a non-conducting state, there is a period γ in which current flows to the flywheel diode _D7 . The course of charging the capacitor C is the same as in the high-speed case, but in the section γ there is no reverse induced voltage Ea, so a large charging current flows. As the load increases, the reverse induced voltage Ea decreases and at the same time the period γ increases. Therefore, in the middle and low speed region shown in Figure 2 b and c, load fluctuation detection depends on changes in the reverse induced voltage Ea and the interval γ. This is done by changing the time width. In the low-speed region shown in Fig. 2c, the difference between the time width of section γ and the time width of the section where the reverse induced voltage Ea appears is small, but in the medium-speed region shown in Fig. 2b, this difference is large. , the detected amount of load fluctuation increases.
Therefore, the amount of feedback is greatest at medium speeds. If the feedback is too large, the control system becomes unstable, so in conventional equipment, the circuit constants have to be determined at medium speeds, where the amount of feedback is greatest, and at high speeds, the lack of feedback causes the motor rotation speed to change due to load fluctuations. The disadvantage was that the changes were large. For this reason, there is a method of detecting the motor current Ia and compensating Vm by the internal voltage drop due to the motor winding resistance Ra to keep Ea (=Vm - IaRa) constant, but in this case the circuit is complicated and expensive. However, there is a problem in that the response to sudden changes in load is slow. Furthermore, there is a device that directly connects a speed generator to a motor to control the rotational speed at a constant level, but this device is also very expensive.

The purpose of the present invention is to provide a speed control device for a DC motor that has almost the same amount of feedback in response to load fluctuations from high speed to low speed, and that can reduce fluctuations in rotational speed in response to load fluctuations without impairing the stability of the control system. It's about doing.

The present invention consists of an oscillation capacitor that is charged at a predetermined time constant through the armature of a motor by the output of a rectifier circuit connected to a commercial AC power supply, and a semiconductor that becomes conductive when the terminal voltage of the oscillation capacitor reaches a predetermined value. A DC motor that performs speed control by supplying a pulse signal obtained from an oscillation circuit that includes a switching element as a firing signal to a thyristor in a control rectifier circuit that rectifies the output of a commercial AC power supply and supplies it to the armature of the motor. In the speed control device of By making the charging current of the oscillation capacitor almost equal to the charging current of the oscillation capacitor when induced voltage is generated in the armature, it is possible to make the amount of feedback against load fluctuations almost the same from high speed to low speed. This is what I did.

Therefore, in the present invention, a charging current bypass semiconductor switch that becomes conductive when the current flowing through the flywheel diode reaches a predetermined value is provided in parallel with the oscillation capacitor, so that the current flowing through the flywheel diode reaches a predetermined value. By turning on the charging current shunting semiconductor switch when the current is reached, a part of the charging current of the oscillation capacitor is shunted from the oscillation capacitor.

With the above configuration, the charging current of the oscillation capacitor when current flows through the flywheel diode is limited, and an induced voltage is generated in the armature and the charging current of the oscillation capacitor when current flows through the flywheel diode. Since the charging current amount can be made almost equal to the amount of charging current when the engine is running, the amount of compensation for load fluctuations can be made almost the same from the low speed region to the high speed region, and rotation speed fluctuations can be reduced.

Hereinafter, the present invention will be explained in detail with reference to the drawings and examples. In the following description, the same reference numerals are used for parts equivalent to those in FIG. 1.

FIG. 3 is a wiring diagram showing an embodiment of the speed control device for a DC motor according to the present invention, and the difference from FIG. 1 is that the transistor Q ₄ , the diodes D ₈ , D ₉ ,
The main difference is that a charging current bypass circuit is added using a Zener diode Dz and resistors _R7 and _R8 . i.e. a Zener diode at the intermediate terminal of the variable resistor VR ₂
The cathode of Dz is connected, the anode is resistor R ₇
is connected to the collector of transistor _Q4 as a semiconductor switch for shunting the charging current.
The emitter of the transistor Q ₄ is connected to the positive output terminal of the controlled rectifier circuit 1, and the base is connected to the cathode of the flywheel diode D ₇ via a resistor R ₈ . Furthermore, diodes D ₈ and D ₉ are connected in parallel between the cathode of the flywheel diode D ₇ and the positive output terminal of the control rectifier circuit 1. Furthermore, the anode of diode D ₈ and the cathode of diode D ₉ form a flywheel diode.
Connected to the cathode of D ₇ .

The basic operation of the above embodiment is exactly the same as that shown in FIG. 1, but in this embodiment, when a flywheel current exists, part of the charging current is
I am trying to lower it by flowing it to _Q4 .
That is, when the flywheel current is flowing through the flywheel diode _D7 and the diode _D8 as shown in sections γ in FIG. 2b and c, the diode _D8
There is a forward voltage drop due to the flywheel current. Since this forward voltage drop is typically larger than the base-emitter forward voltage of a small current transistor, by passing this signal through resistor _R8 to the base of transistor _Q4 , transistor _Q4
conducts. Then, the charging current to capacitor C is the full-wave rectifier circuit 2, the semi-fixed resistor VR ₁ , and the variable resistor.
It is bypassed in the path of VR ₂ , Zener diode Dz, resistor R ₇ , transistor Q ₄ and armature M. The Zener diode Dz and the resistor _R7 are used to set the bypassed amount, and in some cases one of these can be omitted or replaced by an element such as a varistor. Also, diode _D9 is for protecting transistor _Q4 . The operation when there is no flywheel current is similar to that in FIG. In this way, when the flywheel current is flowing, the capacitor C
Since the amount of charging current can be made almost equal to the amount of charging current when the induced voltage Ea is generated, the amount of compensation (feedback amount) for load fluctuations can be made almost the same from the low speed region to the high speed region.
Rotational speed fluctuations can be reduced.

In the above explanation, the presence or absence of flywheel current is detected using diode _D8 , but the diode
A resistor may be used in place of _D8 , and a field effect transistor may be used in place of a bipolar transistor for transistor _Q4 . Further, in the above embodiment, a series circuit of semi-fixed resistors VR ₁ , VR ₃ and variable resistor VR ₂ is connected to the output terminal of the full-wave rectifier circuit 2 consisting of diodes D ₁ to D ₄ .
It may be connected between the cathodes of D ₃ and D ₄ and the cathodes of thyristors Q ₁ and Q ₂ . Also thyristor
One thyristor may be used instead of Q ₁ and Q ₂ and this thyristor may be connected in series with the armature M between the DC output terminals of the full-wave rectifier circuit 2.
A relaxation oscillation circuit using a unidirectional transistor may be used instead of PUT.

As described above, according to the speed control device for a DC motor according to the present invention, the oscillation capacitor of the oscillation circuit that generates the pulse that is supplied as a firing signal to the thyristor of the control rectifier circuit is passed through the armature of the DC motor. When using a charging configuration, by providing a semiconductor switch for bypassing the charging current, the charging current of the oscillation capacitor is limited during the period when current flows through the flywheel diode connected in parallel to the armature. It is possible to equally compensate for rotational speed fluctuations due to load fluctuations up to
This has the advantage of being able to reduce fluctuations in rotational speed, especially at high speeds. Moreover, since it can be implemented by adding only a few parts to a conventional device, it can be manufactured at a lower cost than other devices using speed generators or devices using the armature current compensation method, and is highly profitable.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram showing an example of a conventional speed control device for a DC motor, Figures 2a to c are armature voltage waveform diagrams explaining the operation of Figure 1, and Figure 3 is a diagram of a DC motor according to the present invention. FIG. 2 is a wiring diagram showing an example of a speed control device. 1... Control rectifier circuit, 2... Full wave rectifier circuit, 3
...Relaxation oscillator circuit, AC...Commercial AC power supply, D ₁ ~
D ₄ ... Diode, Q ₁ , Q ₂ ... Thyristor, Q ₃
...PUT, VR ₁ , VR ₃ ...Semi-fixed resistor, VR ₂ ...
...Variable resistor, C...Variable resistor, R ₁ ...Resistor, Q ₄ ...Transistor, Dz...Zener diode, _D7 ...Flywheel diode,
D ₈ , D ₉ ... Diode, R ₇ , R ₈ ... Resistor, M
...The armature of a DC motor.

Claims (1)

[Scope of utility model registration request] a control rectifier circuit including a thyristor that controls and rectifies the output of a commercial AC power source and supplies it to the armature of a DC motor; a rectifier circuit that rectifies the output of the AC power source; an oscillation circuit including an oscillation capacitor that is charged with a time constant and a semiconductor switching element that becomes conductive when the terminal voltage of the oscillation capacitor reaches a predetermined value; and a flywheel diode that is connected in parallel to the armature. In a speed control device for a DC motor, wherein a pulse signal obtained from the oscillation circuit is supplied as a firing signal to a thyristor of the control rectifier circuit, the flywheel diode is provided in parallel with the oscillation capacitor. A speed direct current motor characterized by comprising a charging current bypassing semiconductor switch which conducts when the flowing current reaches a predetermined value and bypasses a part of the charging current of the oscillation capacitor from the oscillation capacitor. Control device.