JPS58218889A - Speed controller for dc motor - Google Patents

Abstract

PURPOSE:To simplify the structure of the speed controller for DC motor by a method wherein current conducting phase of a semiconductor means is controlled according to the comparison result between the deviation of counter-electromotive force of the motor from a speed setting voltage and a sawtooth voltage. CONSTITUTION:Rectifying diodes 20, 37 take out counter-electromotive force of the motor 4 to apply to a counter-electromotive force detecting resistor 40. A linear amplifier 50 outpus a speed instruction voltage Va according to counter- electromotive force detected by the detecting resistor 40 and the speed setting voltage Vs set by a variable resistor 46. When the sawtooth voltage synchronized with an AC electric power source 2 inputted from a terminal 70 reaches a voltage obtained by adding the speed instruction voltage Va and a correction voltage Vo, a comparator 66 outputs a square wave signal. The square wave signal is applied to the gates of the motor current conducting phase controlling thyristors 10, 12 through a pulse transformer 82.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for a small series-wound motor, and more particularly to an improved speed control device that performs constant speed operation control based on a detected value of rotational electromotive force.

Conventionally, in a speed control device that performs phase control of a small series-wound motor using a phase control method using a thyristor, a device that generates a signal proportional to the rotation speed of the motor, such as a rotary generator directly connected to the rotor of the motor, is used. The output voltage of the rotary generator is supplied to the rotation signal detection amplifier together with the rotation speed setting signal, the rotation speed setting signal and the output voltage of the rotating electric machine are compared, and a signal indicating the difference between the two is provided to the Cyrisk phase control device. There is a known method for stably controlling the energization phase of the cyrisk so that the rotational speed of the motor is maintained at a constant speed determined by a setting signal. However, this control method has a disadvantage in that the cost is increased because a rotary generator or the like is used to extract a signal indicating the rotational speed of the electric motor.

An object of the present invention is to eliminate the above-mentioned drawbacks of conventional speed control devices, and to provide a speed control device for an electric motor that can perform speed control by extracting a signal indicating the speed of the electric motor without using a machine or the like as the rotation source. is to provide.

In order to achieve such an object, the present invention detects the back electromotive force of the electric motor as a signal indicating the rotational speed of the electric motor with a simple configuration, and performs negative feedback control of the rotational speed of the electric motor based on this detected value. It is.

The present invention will now be described in detail with reference to the accompanying drawings.
Figure 1 is a circuit diagram of a typical embodiment of the motor speed control device according to the present invention, and Figures 2 and 6 are time charts showing signal waveforms at various parts to explain the operation of the circuit in Figure 1. It is a chart.

In FIG. 1, reference number 2 is an AC power supply, 3 is a main switch, 4 is a DC motor, 6 is a field winding of the DC motor,
8 is a flywheel diode, 10.12 is a thyristor for controlling the energization phase of the motor current given to the DC motor from the AC power supply, 20° 3T is a rectifier diode for taking out the back electromotive force of the motor 4, and 40 is a back electromotive force. Detection resistor, 46 is variable resistor for motor speed setting, 50 is resistor 4
A linear amplifier 54.56 outputs a speed instruction voltage based on the back electromotive force detected at 0 and the voltage indicating the speed set by the variable resistor 46. A resistor and a capacitor for stabilizing the output, 66 a comparator which inputs a sawtooth wave voltage to its non-reflective input via a terminal 70 and inputs the output voltage of the linear amplifier 50 to its inverting input, 80 a comparator 82 is a pulse transformer whose primary winding is connected to the output of the SBS element and whose secondary winding is connected to the r-) electrode of the thyristor 10.12; 90 is a linear amplifier, comparator and resistor 48°78
The power supply voltage V. . It is a DC power supply that gives

Here, the resistor 18 is for detecting the back electromotive force of the motor, and the resistors 24, 28, 32, 36, and capacitors 22.2
6 has the function of protecting the date electrodes of the thyristors 1°0 and 12, and the resistor 52 and the resistor 44 determine the din of the linear amplifier. Also resistance 72~
78 divides the DC voltage applied through the resistor 78 and applies it to the inverting input of the comparator 66 together with the output voltage of the linear amplifier 50, so that even when the output voltage of the linear amplifier is zero, a small amount of voltage is applied to the inverting input of the comparator. This ensures that the thyristor is energized by applying a predetermined correction divided voltage. Further, the diode 88 is a σ capacitor 56 which absorbs the back electromotive force of the pulse transformer 82, the diode 60 . Switch 62. The DC power supply 64 is a circuit that prevents the si risk from being suddenly turned on at a large energization phase when starting the motor.

The operation of the circuit shown in FIG. 1 will be explained below. , first electric motor 4
The method for detecting the back electromotive force will be described below. Pulse tran・
When the thyristor 10.12 is energized by the output pulse from the switch 82, the output current of the AC power supply 2 is 1, as shown by the solid arrow in the figure.For example, in the positive half cycle, the main switch 3, the thyristor 12, ! A4. Gui, t
-lF2O.

14, and in the negative half cycle, the thyristor 10, the electric motor 4, the diode 20. ．． 16, and flows through the main switch 3, but the diode)'20.
37, so it does not flow to resistance 38.40. Therefore, the full-wave rectified current shown in FIG. 2(a) is supplied to the motor. When the motor rotates due to the energization of the thyristor, a back electromotive force of 1 M is generated between its terminals, and the current generated by the back electromotive force of 9 flows from one end of the motor to the resistor 18, the diode 37, and the resistor. 38.40
to the other end of the motor.

Therefore, when the voltage between the terminals of the motor 4 is controlled by the second
As shown in the figure (b), only the back electromotive force appears during the period (t'1 to t2) when the thyristor 10°12 is cut off, and during the period when the thyristor is energized (t2 to tr5), the AC power supply voltage appears, but since the AC power supply voltage component is blocked by the diode 20.37, the resistor 4
Only a back electromotive force appears between the 0 terminals as shown in FIG. 2 (c), and therefore the back electromotive force is detected by the resistor 401C. It becomes two.

The terminal voltage of the resistor 40 is applied to the linear amplifier 5 via the resistor 44.
00 Å force 50b is applied. On the other hand, to the input 50aK, a speed setting voltage vs, which is set by a resistor 48 and a variable resistor 46, is applied to the DC power supply voltage +VaC via a resistor 42. Therefore, the output voltage of the amplifier 50 becomes a voltage substantially proportional to the speed setting voltage, and also varies depending on the back electromotive force detected by the resistor 40, such that the smaller the back electromotive force is, the lower the value becomes, and the larger the back electromotive force is, the higher the value becomes. Incidentally, the higher the value of the speed setting voltage vs set by the variable resistor 46, the higher the speed rotation of the electric motor is instructed. In addition, a resistor 54" and a capacitor 56 connected in parallel between the amplifier 500A power 50 and the output also slow down the fluctuations in the output when the amplifier input changes rapidly, thus preventing motor disturbances. The output voltage of the amplifier is superimposed on the correction voltage vo applied via the resistor 74 and applied as a speed indication voltage to the inverting input of the comparator 660, and is then transferred from the terminal 70 to the non-inverting input via the resistor 68. It is compared with the applied sawtooth wave voltage (Fig. 6 (b)). The phase of this sawtooth wave voltage is synchronized with each half cycle of the output voltage of the AC power supply 2 (Fig. 6 (a)). Furthermore, if the speed instruction voltage, which is the sum of the output voltage of the amplifier 50 and the correction voltage, is V, then by changing the value of the vI!LiL variable resistor 46, the #i tooth wave voltage can be changed from vo to #i. It changes to the maximum value vm.Now, if the speed instruction voltage slightly higher than vo determined by the variable resistor 46 is Va□, the comparator 66 detects that when the value of the sawtooth wave voltage reaches the speed instruction voltage ■. (Figure 3 (c)),
At that time (time t□), the 8BS element 80 outputs the rectangular wave signal shown in FIG.
As a result, a sharp pulse-like current shown in FIG. 3(e) is caused to flow through the primary winding of the pulse transformer 82 at time t1', which is slightly delayed from time tl. Therefore, a pulse signal is induced in the secondary winding, and the diode 30.34 and the resistor 32.36
is applied as a trigger signal to each of the thyristors 10 and 12 (r-), and energizes each thyristor (Fig.
). Therefore, if the main switch 3 is turned on, the thyristor is energized at a large conduction angle determined by the speed instruction voltage va□, and the motor is operated at high speed.

Next, when the value of the variable resistor 46 is decreased and the value of the speed instruction voltage is increased to v,2, the 8BS element 80 responds to the output rectangular wave from the comparator at time t2, that is, the value of the corresponding power supply voltage. A pulse signal is output at a slow phase of a half cycle, so each thyristor is energized at a small conduction angle, causing the motor to operate at a low speed.

In this way, by changing the value of the variable resistor 46, the speed instruction voltage Va is continuously changed from the minimum value vo to the maximum value V, and the conduction angle of the thyristor is changed from 0 degrees to approximately 180 degrees, thereby controlling the electric motor. The speed can be controlled continuously from low to high speed.

The reason why a slight correction voltage vo is applied to the inverting input of the comparator 660 even when the output voltage of the amplifier 50 is zero is because the phase of the thyristor is 0 degrees (the conduction angle is 180 degrees).
Even if a gate pulse is applied at (degree), conduction does not occur, and energization starts when a gate pulse is applied after delaying to a certain predetermined phase. Therefore, the output voltage of amplifier 50 is This is to ensure that the thyristor is energized by acting so that the conduction angle does not advance to 180 degrees even when is zero.

The speed setting voltage V determined by the resistor 46 in this way,
We will discuss the case where the rotational speed of the motor changes due to changes in load, etc. while the motor is being operated at a speed determined by . Now, if the load increases and the rotational speed decreases, the back electromotive force of the motor decreases and the voltage across the terminals of the resistor 40 decreases, so the output voltage of the amplifier 50 decreases and the speed indicating voltage ratio v6 also decreases. Therefore, the energization phase of the thyristor is advanced, and the rotational speed of the motor is increased to be maintained at the speed determined by the speed stage constant voltage EV. Furthermore, when the load decreases and the rotational speed increases, the back electromotive force increases, so the output voltage of the amplifier 50 increases, and the speed instruction voltage va also increases. Therefore, the energization phase of the thyristor is delayed, and the rotational speed of the motor is reduced and maintained at the original rotational speed.

Therefore, even if the rotational speed of the motor fluctuates due to changes in the load or power supply voltage, it is detected by the back electromotive force and negative feedback control is performed to maintain the rotational speed stably at the speed determined by the speed setting voltage v6. It is possible. Moreover, the present invention does not use the output signal of the rotary generator as a signal indicating the speed of the electric motor, but uses the rotational electromotive force of the electric motor and detects it with a simple configuration. A simple and inexpensive speed control device can be provided.

Next, starting and stopping of the electric motor will be explained. Now, from the DC power supply 64, a current of a predetermined value that instructs to stop is applied to <<-y
Close f62 and compare via resistor T2 1.・,1
When applied to the inverting input of the converter 66, the inverting input voltage becomes
``Since it exceeds the maximum value of the non-inverting input voltage, the comparator does not output and the motor is not driven. When the switch 62 that instructs starting is opened and a signal with a current value of zero is given, the voltage at the inverting input of the comparator is given only to the speed indicating type Eva, and becomes less than the maximum value of the non-inverting input voltage, and the motor is not started. It is driven at a set speed determined by a resistor 46. By the way, when starting the electric motor, the speed setting voltage v determined by the resistor 46 is maintained until the rotational speed of the electric motor reaches the target set rotational speed.
8, the voltage input to the non-inverting input SOa is smaller, so the output voltage of the amplifier 50 is smaller than the speed instruction tlEv.
Since a is also small, there is a risk that the thyristor will be energized in an extremely early phase, causing a large current to flow in the motor and driving it rapidly. To prevent this, a circuit consisting of a resistor 4, a capacitor 56, and a diode 60 is added. Next, the operation of this circuit will be explained.

First, when the motor is stopped, the starting switch 62 is closed and a voltage exceeding the maximum value V of the sawtooth wave voltage applied to the non-inverting input is applied from the DC power supply 64 to the inverting input of the comparator 660 via the resistor 12. If the voltage is left, the output of the comparator 66 will not be obtained, so the thyristors 10 and 12 will remain non-conductive and the motor will continue to be stopped. At this time, the capacitor 56 is
It is charged by a DC power supply 64.

When the starting switch 62 is now opened, the potential at the inverting input of the comparator 660 drops to the voltage v0 given by the resistor 76. 54, the speed instruction voltage V, begins to gradually decrease from the maximum value vm, and the nostar starts energizing at a small conduction angle. Therefore, the electric motor is started slowly and increases to a predetermined rotation speed. In this way, rush rotation of the electric motor is prevented.

Diode 60 is also used to prevent the charge on capacitor 56 from prematurely discharging through resistor 58,52.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a typical embodiment of the speed control device for a DC motor according to the present invention, and FIGS. 2 and 86 are time charts showing signal waveforms of various parts to explain the operation of the device in FIG. 1. be. Explanation of symbols 2... AC power supply, 3... Main switch, 4...
DC motor, 50... linear amplifier, 66... comparator, 80... SBS element, 82... pulse transformer,
90...4 DC power supply representatives Asari and Akira

Claims (1)

[Scope of Claims] (1) A main motor circuit that supplies motor current from an AC power supply to a DC motor via a main switch and a semiconductor means with a control electrode, and a back electromotive force detection means that detects a back electromotive force of the motor. and a means for generating a variable voltage for speed setting of the electric motor, inputting the back electromotive force detected by the detection means and the variable voltage for speed setting, and outputting a voltage corresponding to the two-man power as a speed instruction voltage. a linear amplifier that inputs a sawtooth wave voltage whose phase is synchronized with each half cycle of the output voltage of the AC power source and the speed instruction voltage, and generates a pulse signal when the sawtooth wave voltage reaches the speed instruction voltage. a comparator for outputting an output, a primary winding connected to the output of the comparator and a secondary winding connected to r-) of the semiconductor means; and a pulse transformer that increases the speed indicating voltage when the back electromotive force increases to delay the energization phase of the semiconductor means, and when the back electromotive force decreases, the speed indicating voltage is decreased to delay the energization phase of the semiconductor means. A speed control device for a DC motor, characterized in that the rotational speed of the motor is stably controlled by advancing the energization phase of the means. (2. In claim 1, the back electromotive force detection means includes a first resistor connected in parallel to the electric motor,
A first diode connected in a forward direction with respect to the motor current between one end of the first resistor and the motor in the main motor circuit, a second diode connected in parallel to the first diode, and a second diode connected in parallel to the first diode. The anode of the two nuclear diodes is connected to the cathode of the first diode, and the second resistor is connected to one input of the linear amplifier, so that the voltage between the terminals of the two resistors is connected to the one input of the linear amplifier. A speed control device for an electric motor, characterized in that it exhibits a back electromotive force of . (3) In claim 1, further comprising a capacitor connected between the input and output of the linear amplifier, a diode connected in a forward direction between the output of the amplifier and the capacitor, and a cathode of the diode. and a DC power supply connected to the power supply via an on-off switch, and when the switch is closed, the capacitor is charged and the charged voltage is superimposed on the speed instruction voltage and applied to the comparator. , a speed control device for the capacitor motor by opening the switch.