JPS634434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor control device, and more particularly to an improvement in the frequency feedback method of a chopper type motor speed control device.

[Conventional technology]

Traditionally, a tachometer generator has been commonly used as a rotational speed detector for electric motors, but in recent years, pulse generators have been used to eliminate the drift of rotational speed detectors or to reduce costs. There is a tendency for a frequency feedback method using .

FIG. 1 shows the general configuration of a conventional frequency feedback chopper motor speed control device. In this device, the rotational speed of the electric motor 11 is detected by a pulse generator 12 to obtain pulses with a frequency proportional to the rotational speed, and this pulse signal is converted by an F/V converter 13 into an analog voltage proportional to the frequency. . Then, this analog voltage and the speed command voltage are input to the deviation amplification circuit 14 to obtain an output proportional to the deviation. This output is compared with a sawtooth wave or a triangular wave output from the waveform generation circuit 15 by a comparator 16 to obtain a pulse with a pulse width proportional to the rotation speed of the electric motor 11, that is, a pulse width modulated pulse signal, This pulse drives the chopper transistor 17 on and off to drive the motor 1.
1 is controlled at a constant speed. This is the conventional general tipping method.

[Problem that the invention seeks to solve]

In this conventional method, the frequency of the pulse signal output by the pulse generator 12 is
Since it requires an F/V converter 13 to convert the signal into an analog voltage signal and a sawtooth or triangular waveform generation circuit 15 to perform pulse width modulation, the circuit configuration becomes complicated and expensive, and it is difficult to use a general-purpose electric motor. There was a problem in that it was difficult to apply it to a speed control device.

The present invention has been made in view of these conventional problems, and aims to simplify the circuit and reduce costs.

[Means for solving problems]

To achieve this objective, the motor control device of the present invention includes switches _S1 and _S2 that are turned on and off alternately according to the pulse frequency from a pulse generator that detects the rotational speed of the motor _;
a constant charge switching circuit 9 consisting of a capacitor C ₁ whose one end is connected to the connection point of the switch S ₂ ; a constant voltage source 8 that charges the capacitor C ₁ with a constant charge when the switch S ₁ is turned on; a proportional-integral amplifier 4 which inputs the accumulated charge of the capacitor _C1 when ₂ is turned on; a sawtooth-wave speed feedback voltage V _f outputted from the proportional-integral amplifier 4; and a speed command device connected to the constant voltage source. Speed command voltage from
It is characterized by comprising a comparator 5 that compares the voltage with V _s and a chopper transistor for driving a motor that is turned on and off by the pulse signal output from the comparator 5.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings. FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes an electric motor, the rotational speed of which is detected by a pulse generator 2. 3 is a pulse distribution circuit, which connects the pulse output of pulse generator 2 to an electronic switch.
S ₁ and S ₂ to control these electronic switches S ₁ and S ₂ to be turned on and off alternately. 4 is a proportional-integral amplifier, consisting of an operational amplifier OP ₁ , a resistor R ₁ and a capacitor C ₂ . 5 is a comparator, 6 is a chopper transistor drive circuit for driving the chopper transistor _Tr1 , and 7 is a rectifier. One end of a hold capacitor _C1 is connected to the connection point between the electronic switches _S1 and _S2 ,
Further, a constant voltage source 8 having a voltage _Es is connected to the other end of the electronic switch _S1 . These electronic switches S ₁ and S ₂ , the hold capacitor C ₁ and the constant voltage source 8 form a constant charge switching circuit 9 .

In Fig. 2, the chopper type voltage control circuit has an on-time of transistor Tr ₁ as T ₁ , an on-off period as T , and an input voltage and an output voltage, respectively.
If E _i , _p (average value), then for motor 1, _p =
It is configured to apply a voltage of E _i ·T ₁ /T.
A pulse signal with a frequency proportional to the rotation speed of the electric motor 1 has the waveform shown in FIG. 3a, and this pulse is switched every half cycle by the distribution circuit 3.
Convert S ₁ and S ₂ into signals that alternately turn on and off. At this time, in order to avoid a period in which the switches S ₁ and S ₂ are turned on at the same time, the switches are operated so that there is a period in which they are turned off at the same time for the time t ₁ .

Figure 3b shows the switch pulse of switch _S1 , the third
Figure c shows the switch pulse of switch _S2 . When switch _S1 is turned on (switch _S2 is off),
A charge Q ₁ = E _s C ₁ is accumulated in the capacitor C ₁ (E _s is the terminal voltage of the DC power supply 8), and then the switch
During the period when S ₁ is off and switch S ₂ is on, the charge is added to the summing point of operational amplifier OP ₁ and discharged. Therefore, the capacitor by charging and discharging
The terminal voltage of _C1 is as shown in Figure 3d.

The average value of the current flowing into the addition point of operational amplifier OP _{1 is 1} = E _s C ₁ /T = E _s C ₁ f (f is the repetition frequency)
This average current flows through the feedback resistor R ₁ of the operational amplifier OP ₁ , and therefore the average output voltage of the operational amplifier OP ₁ becomes _f = −E _s C ₁ R ₁ f.

To explain the waveform of the output voltage V _f at this time in more detail, the charge accumulated in the capacitor C ₁ when the switch S ₂ was turned on is transferred to the capacitor C ₂ due to charge invariance; The output voltage changes stepwise by a voltage ΔV _f expressed by the following equation.

E _s C ₁ +ΔV _f C ₂ =0 ∴ΔV _f =−E _s C ₁ /C ₂ This voltage change ΔV _f is discharged through resistor R ₁ until the next time switch S ₂ is turned on. Therefore, the output voltage V _f has a waveform in which the average voltage is −E _s C ₁ R ₁ f and a sawtooth wave is superimposed thereon, as shown in FIG. 3e. This voltage V _f and the command voltage V _s (see Fig. 3 f) are compared by a comparator 5, and when the absolute value of the voltage of the sawtooth wave portion of the waveform of V _f is larger than the command voltage V _s , Transistor Tr ₁
The transistor drive circuit 6 is configured to turn off the current and turn on when the current is small. That is, the duty of the transistor Tr ₁ is controlled so that the command voltage V _s and the output voltage V _f are equal in average value.

Therefore, control is performed so that the relationship V _s =E _s C ₁ R ₁ f is maintained. Here, α
= C ₁ R ₁ f, the previous equation becomes V _s = αE _s , and the command voltage V _s is given by a voltage obtained by dividing the terminal voltage E _s of the DC power supply 8.

Since the pulse frequency f is completely proportional to the rotational speed N of the electric motor 1, if the proportionality constant is K, it is expressed by the relationship f=KN, and therefore α=R ₁ C ₁ KN. The speed command voltage V _s is given by the voltage division ratio α of the terminal voltage E _s and is constant, so the rotation speed N and
It is inversely proportional to R ₁ C ₁ K. Therefore, R ₁ C ₁ is the only major factor causing drift.
As a countermeasure for this, by using a Mylar capacitor with a positive temperature coefficient and a carbon film resistor with a negative temperature coefficient, the temperature characteristics can be compensated simply and with a fairly high degree of accuracy.

Figures 3g and 3h show the output of the comparator 5 and the on/off operation of the transistor Tr _1. The output of the transistor Tr ₁ is smoothed by the LC circuit, and the average value _p = p = 1, as shown in Figure 3i. An output voltage of E _i T ₁ /T is applied to the motor 1.

The principle of controlling the rotational speed of the electric motor will be further explained with reference to FIG. Initially, when the command voltage V _s and the feedback voltage V _f are in equilibrium, the pulse width modulation ratio is controlled to be T ₁ /T, and the motor 1 is driven at a voltage of _p = E _i ·T ₁ /T. It is assumed that

Next, if the command voltage is changed to V′ _s at time t ₀ , the output of comparator 5 changes and transiently T _1t /
The duty ratio of T _t increases, the voltage applied to the electric motor 1 increases, and the rotational speed increases. Eventually, the average value _f of the feedback voltage V _f becomes equal to the command voltage V' _s , and the average value of the output voltage E ₀ (t) also becomes a duty ratio T' of ' ₀ =E _i T' ₁ /T'. ₁ /
Control is performed to give T′. Figure 4a is a waveform diagram showing the relationship between the command voltage input to the comparator 5 and the feedback voltage, and b is a waveform diagram of the transistor Tr ₁ .
c is a waveform diagram showing the on/off operation of the motor 1, and c is a waveform diagram showing changes in the voltage supplied to the motor 1.

In the above description, an example of voltage control of a DC motor was shown, but it goes without saying that the present invention can also be applied to a speed control device using joint control of a VS motor or a speed control device using field control of a DC motor.

〔Effect of the invention〕

As explained above, in the present invention, by using a constant charge switching circuit, a sawtooth waveform voltage superimposed on a DC voltage proportional to the rotational speed of the motor is generated, and a voltage corresponding to that voltage and a reference speed is generated. A pulse signal is obtained by comparing it with a reference voltage using a comparator, and this pulse signal is used to turn on and off the transistors forming the chopper transistor drive circuit. As a result, the functions of a conventional F/V converter and a waveform generation circuit can be combined, and the waveform generation circuit and deviation amplification circuit can therefore be omitted. Therefore, it is possible to simplify the circuit and reduce costs. Further, in the present invention, the speed command voltage is a voltage obtained by dividing the reference voltage of the constant charge switching circuit, or a common power source. This results in
Since the drift of the reference voltage does not appear as a speed drift of the motor, a power supply using a simple Zener diode can be used instead of the conventional complicated low-drift power supply circuit, and costs can be reduced.

Furthermore, in conventional motor control devices, the rotational speed of the motor is detected as a frequency proportional to the rotational speed, and when the motor rotates at high speed, high-speed pulse width modulation is performed to achieve speed control with good response speed. At low speeds, the speed change is 1 of the period frequency.
Since it is detected after a period delay, the responsiveness deteriorates. In contrast, the motor control device of the present invention generates a sawtooth wave with a frequency proportional to the rotational speed of the motor, which improves responsiveness and reduces the switching loss of the chopper transistor. can. This provides better controllability at low speeds than the conventional pulse width modulation method.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of a conventional chopper type motor speed control device, Fig. 2 is a circuit diagram showing the configuration of an embodiment of the present invention, Fig. 3 is an operation waveform diagram of each part, and Fig. 4 is a control operation. FIG. 2 is a waveform diagram for explaining. 1: electric motor, 2: pulse generator, 3: pulse distribution circuit, 4: proportional-integral amplifier, 5: comparator, 6: chopper transistor drive circuit,
7: Rectifier, 8: DC power supply, 9: Constant charge switching circuit.

Claims (1)

[Claims] 1 Switches _S1 and _S2 that are turned on and off alternately according to the pulse frequency from a pulse generator that detects the rotational speed of the motor, and a capacitor _C1 that has one end connected to the connection point of the switches _S1 and _S2 . a constant charge switching circuit 9 consisting of a constant charge switching circuit 9;
A constant voltage source 8 that charges the capacitor C ₁ with a constant charge when the switch S ₁ is on, a proportional-integral amplifier 4 that inputs the accumulated charge of the capacitor C ₁ when the switch S ₂ is on, and a proportional-integral amplifier 4. a comparator 5 that compares the output sawtooth waveform speed feedback voltage V _f with a speed command voltage V _s from a speed command device connected to the constant voltage source; and a pulse signal output from the comparator 5. 1. A motor control device comprising: a chopper transistor for driving a motor that is turned on and off at a certain angle.