JP2863449B2 - Control method of DC motor by pulse width modulation signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to pulse width modulation (hereinafter referred to as "pulse width modulation").
The present invention relates to a DC motor and a brushless DC motor control method using a signal (hereinafter simply referred to as PWM).

[0002]

2. Description of the Related Art Conventionally, as a method of controlling a DC motor using this kind of PWM signal, as shown in FIG. 5, an H-type bridge circuit composed of four switching elements S1, S2, S3, S4 is used. There is a method of controlling the DC motor M. This method is called upper and lower arm PWM control, and has superior response characteristics compared to PWM control of only the upper-arm switching elements S1 and S2 or only the lower-arm switching elements S3 and S4, and can easily achieve higher output. .

[0003] The speed or output torque of the DC motor M can be controlled by the duty ratio of the PWM signal higher than the electrical time constant of the DC motor M. Here, the speed will be described.

In FIG. 5, in one cycle of the PWM signal, the switching elements S1 and S4 are turned on and off at the same timing, and the switching elements S2 and S3 are turned on and off at the same opposite timing. Since the switching elements S1 and S4 are on and the switching elements S2 and S3 are off during the x period of the PWM signal, current flows from the switching element S1 through the motor M to the switching element S4. The current per unit time of this current is defined as I1. On the other hand, in the y period, a current of I2 per unit time flows through the motor M in the direction opposite to the x period. Accordingly, the current supplied to the motor M by this circuit is the sum of I1 and I2, but since the directions of I1 and I2 are opposite, the current I for generating the forward torque is I = I1−I2.

The ratio between the currents I1 and I2 is determined by the duty ratio of the PWM signal. That is, when the PWM signal duty is 100%, only the switching elements S1 and S4 are ON, so that the motor M has the maximum forward speed, and
When the signal duty is 0%, the switching elements S2, S3
When only the PWM signal duty is 50% since only the switch is on, the current I becomes I = I1 from I1 = I2.
Since -I2 = 0, the motor M stops. Therefore, PWM
The relationship between the signal duty ratio and the speed of the motor M is as shown in FIG.

Next, a conventional method of controlling a DC motor by using a PWM signal will be described with reference to a block diagram of FIG. A pulse of + V and a pulse of -V are formed based on the speed feedback information FG by the pulse generator 1 coupled to the DC motor M, and are selected by the rotation direction information DIR of the pulse generator 1. VC is a speed command voltage. When the rotation direction is the forward direction, the feedback signal of the + V pulse is smoothed by the smoothing filter 2, and when the rotation direction is the reverse direction, the feedback signal of the -V pulse is smoothed to obtain the feedback voltage VF.
Get. As a result, the feedback voltage VF becomes a voltage proportional to the speed of the positive voltage in the positive direction and the negative voltage in the reverse direction.

The difference between the feedback voltage VF and the speed command voltage VC is obtained by the error amplifier 3. That is, the output difference voltage VE is VE = −G (VC−VF)
Becomes Here, G is the amplification degree of the error amplifier 3.
The comparator 4 applies a triangular wave signal 5 to the difference voltage VE.
Compared with the pulse width modulation signal PW shown in FIG.
M1 is output, and the DC motor M is controlled and driven by the signal PWMI.

Therefore, as described above, if VC = VF = 0, VE = 0, and PW
When the M signal duty ratio is 50%, the motor M stops, and V
When C> VF, VE <0, the duty ratio increases, the motor M rotates in the forward direction, and VC <V
At F, VE> 0, the duty ratio decreases, and the motor M rotates in the reverse direction. Therefore, FIG.
6 realizes the relationship shown in FIG. 6 between the PWM signal duty ratio and the speed of the motor M.

[0009]

However, in such a conventional DC motor control method using a PWM signal, the motor M rotates in both forward and reverse directions when the PWM signal duty ratio is 50%. Therefore, the "rotation direction" information is necessary for the feedback information from the motor M. Without this information, the motor M may run out of control, or if the information is coarse, hunting may occur when the duty ratio is around 50%. There was a problem that it occurred.

For this reason, a high-resolution encoder is required, and a complete triangular wave generating circuit 6 comprising an operational amplifier 6a, capacitors 6b and 6c and resistors 6d and 6e as shown in FIG. 9 is required. There is a problem that both the encoder and the operational amplifier 6a are expensive.

[0011] The present invention has been made in view of such a point,
An object of the present invention is to solve the above-mentioned problems and to provide a DC motor control method using a pulse width modulation signal which can control the speed and output torque of the DC motor stably and can be inexpensive.

[0012]

The structure of the present invention for achieving the above object is as follows.

(1) A difference between a signal obtained by smoothing a speed feedback signal from a signal generator coupled to a DC motor and a speed command signal is obtained, and the difference signal is compared with a triangular wave signal by a comparator. Controlling the DC motor with the pulse width modulation signal obtained by
A circuit performs an OR operation on the pulse width modulation signal and a pulse signal having a 50% duty ratio in synchronization with the triangular wave signal and having the same phase.
The speed of the DC motor is controlled.

(2) a signal obtained by smoothing a torque feedback signal from a signal generator coupled to a DC motor;
In a method of controlling the DC motor by taking a difference from the torque command signal, and by using a pulse width modulation signal obtained by comparing the difference signal with a triangular wave signal by a comparator,
An OR circuit performs an OR operation on the pulse width modulation signal and a pulse signal having a 50% duty ratio in synchronization with the triangular wave signal and controlling the torque of the DC motor by the output pulse width modulation signal. It is characterized by doing.

(3) In the above (1) or (2), instead of the triangular wave signal, a capacitor and a resistor are connected in series, and a constant voltage power supply is connected to the resistor side,
50% of both ends of the capacitor by switching element
The incomplete sawtooth signal output from the connection point between the capacitor and the resistor is opened and closed at a duty ratio to be charged and discharged, and the incomplete sawtooth signal is compared by the comparator.

[0016]

According to the present invention, the pulse signal having a duty ratio of 50% is always added (or ORed) to the PWM signal output from the comparator.
When the WM signal duty ratio is around 50%, the DC motor does not run out of control or hunt, and the speed and output torque of the motor can be controlled stably.

Further, in place of the triangular wave signal, an imperfect sawtooth wave signal obtained by opening and closing both ends of the capacitor in a series circuit including a capacitor and a resistor at a duty ratio of 50% using a switching element is used. Control can be performed at low cost.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a DC motor control method using a pulse width modulation (hereinafter simply referred to as PWM) signal according to the present invention.

In FIG. 1, the speed or output torque of the DC motor M can be controlled by the duty ratio of the PWM signal which is higher than the electrical time constant of the DC motor M. Here, the speed will be described. The speed feedback signal FG formed by the + V pulse from the pulse generator 1 coupled to the DC motor M is smoothed by the smoothing filter 2 to obtain a feedback voltage VF. The feedback voltage VF has no information on the rotation direction. The feedback voltage VF is input to one input terminal of the error amplifier 3 and the speed command voltage VC is input to the other input terminal, and the difference between the feedback voltage VF and the speed command voltage VC from the error amplifier 3 is calculated by: That is, the difference voltage VE is output.

The difference voltage VE is input to one input terminal (− side) of the comparator 4 and the triangular wave signal 5 is input to the other input terminal (+ side) to compare the two. The signal PWM1 is output. Next, by the OR circuit 11,
ORing the PWM signal PWM1 with the pulse signal 12 having the same phase and a 50% duty ratio in synchronization with the triangular wave signal 5 and supplying the output PWM signal PWM2 to the DC motor M for driving; Control its speed.

The difference voltage VE between the feedback voltage VF output from the error amplifier 3 and the speed command voltage VC is VE = -G (VC-VF) as in the above equation. For this reason, if VC = VF = 0, VE = 0, the motor M stops at a PWM signal duty ratio of 50%, and if VC> VF, VE <0, and the duty ratio increases to increase the motor M rotates in the forward direction. When VC <VF, VE> 0, and the duty ratio decreases. However, the PWM signal PWM2 output from the OR circuit 11 is
The duty ratio of the PWM signal PWM2 is fixed at 50% by the pulse signal 12 having a 50% duty ratio input to one input terminal of the motor M, and the motor M is stopped.
Therefore, the motor M does not rotate backward or hunt.

FIGS. 2 (a), 2 (b) and 2 (c)
Is a differential voltage VE output from the error amplifier 3 in FIG.
And the PWM signals PWM1 and PWM output from the comparator 4 and the OR circuit 11, respectively.
It is a figure showing the relation with the waveform of M2. 2A shows the case where the difference voltage VE = 0, FIG. 2B shows the case where the difference voltage VE <0, and FIG. 2C shows the case where the difference voltage VE> 0.

The operation described above and FIGS. 2 (a) and 2
2B and FIG. 2C, the triangular wave signal 5 input to the other input terminal (+ side) of the comparator 4
It can be seen that the positive region (upper half) is unnecessary.
Therefore, an incomplete sawtooth wave generating circuit 13 as shown in FIG. 3 can be used instead of the conventional triangular wave generating circuit 6.

The imperfect sawtooth wave generating circuit 13 connects a capacitor 14 and a resistor 15 in series,
A constant voltage power supply -V is connected to the resistor 15 side, and a switching element 16 connected to both ends of the capacitor 14 opens and closes at a 50% duty ratio to charge and discharge the capacitor 14. An incomplete sawtooth signal 18 is generated from a connection point 17 between the resistor and the resistor 15.

FIG. 4 shows the imperfect sawtooth wave generating circuit 1.
3 is a diagram showing the relationship between the switching timing of the switching element 16, the waveform of the incomplete sawtooth signal 18 generated at the connection point 17, and the waveform of the PWM signal PWM 1 output from the comparator 4. Obviously, the imperfect sawtooth signal 15 is suitable for the purpose used as the triangular wave in FIG. Further, the resistor 15 may be replaced with a constant current source.

In this embodiment, the control of the speed of the DC motor by the PWM signal is described. However, the same applies to the torque control of the motor by the signal. In this case, the feedback signal is used as the feedback signal to the DC motor. What is necessary is just to use the torque feedback signal from the pulse generator 1. The same applies to the control of the three-phase brushless DC motor by the PWM signal. In the case of the three-phase brushless DC motor, feedback information FG can be obtained from rotor position information.

The technique of the present invention is not limited to the technique in the above-described embodiment, but may be implemented by means of other modes that perform the same function. Can be changed or added.

[0028]

As is apparent from the above description, according to the present invention, according to claims 1 and 2, a signal obtained by smoothing a speed or torque feedback signal from a signal generator coupled to a DC motor; In a method of controlling the DC motor by taking a difference from a speed or torque command signal and using a pulse width modulation signal obtained by comparing this difference signal with a triangular wave signal by a comparator, Since the pulse width modulation signal is ORed with the pulse signal having a 50% duty ratio in synchronization with the triangular wave signal and having the same phase, the speed or torque of the DC motor is controlled by the output pulse width modulation signal. In addition, the speed or output torque of the DC motor can be controlled stably.

According to a third aspect of the present invention, both ends of the capacitor of a series circuit including a capacitor and a resistor are opened and closed at a duty ratio of 50% by a switching element in place of the triangular wave signal. Since the imperfect sawtooth signal is compared by the comparator, an expensive and high-resolution encoder is not required, and the imperfect sawtooth signal can be used and can be controlled at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a method for controlling a DC motor using a pulse width modulation signal according to the present invention.

FIGS. 2 (a), 2 (b) and 2 (c)
FIG. 2 is a diagram showing a relationship between each positive / negative value of the difference voltage VE output from the error amplifier 3 in FIG. 1 and the waveforms of the PWM signals PWM1 and PWM2 output from the comparator 4 and the OR circuit 11. FIG. 2B shows the case where the difference voltage VE <0, FIG. 2B shows the case where the difference voltage VE <0, and FIG. 2C shows the case where the difference voltage VE> 0.

FIG. 3 is an incomplete sawtooth wave generation circuit diagram.

4 shows the timing of opening and closing of the switching element 16 of the incomplete sawtooth wave generating circuit 13, the incomplete sawtooth signal waveform 18 generated at the connection point 17, and the waveform of the PWM signal PWM1 output from the comparator 4. FIG. It is a figure showing a relation.

FIG. 5 is a circuit diagram illustrating a conventional DC motor control method using a pulse width modulation signal.

6 is a diagram illustrating a relationship between a duty ratio of a pulse width modulation signal and a speed of a motor M in FIG.

FIG. 7 is a configuration diagram showing a conventional DC motor control method using a pulse width modulation signal.

8 (a), 8 (b) and 8 (c)
Each positive / negative value of the difference voltage VE output from the error amplifier 3 in FIG. 7 and the pulse width modulation signal PWM output from the comparator 4
FIG. 8A shows the relationship with the waveform of FIG.
FIG. 8B shows the case where the difference voltage VE <0, and FIG. 8C shows the case where the difference voltage VE> 0.

FIG. 9 is a circuit diagram of a conventional complete triangular wave generation circuit.

[Explanation of symbols]

 Reference Signs List 1 pulse generator 2 smoothing filter 3 error amplifier 4 comparator 5 triangular wave signal 6 complete triangular wave generation circuit 6a operational amplifier 11 OR circuit 12 pulse signal 13 imperfect sawtooth wave generation circuit 14 capacitor 15 resistor 16 switching element 17 connection point 18 non Complete sawtooth signal M DC motor VC Speed command voltage VF Feedback voltage VE Difference voltage PWM1, PWM2 Pulse width modulation signal

Claims (3)

(57) [Claims] 1. A difference between a signal obtained by smoothing a speed feedback signal from a signal generator coupled to a DC motor and a speed command signal, and comparing the difference signal with a triangular wave signal by a comparator. In the method of controlling the DC motor using the obtained pulse width modulation signal, an OR circuit performs an OR operation on the pulse width modulation signal and a pulse signal having a 50% duty ratio in synchronization with the triangular wave signal and having the same phase. And controlling the speed of the DC motor by an output pulse width modulation signal. 2. A difference between a signal obtained by smoothing a torque feedback signal from a signal generator coupled to a DC motor and a torque command signal, and comparing the difference signal with a triangular wave signal by a comparator. In the method of controlling the DC motor using the obtained pulse width modulation signal, an OR circuit performs an OR operation on the pulse width modulation signal and a pulse signal having a 50% duty ratio in synchronization with the triangular wave signal and having the same phase. A method for controlling a DC motor using a pulse width modulation signal, wherein the torque of the DC motor is controlled by an output pulse width modulation signal. 3. In place of the triangular wave signal, a capacitor and a resistor are connected in series, a constant voltage power supply is connected to the resistor side, and both ends of the capacitor are opened and closed with a switching element at a 50% duty ratio. 3. The pulse width modulation according to claim 1, wherein the incomplete sawtooth signal output from a connection point between the capacitor and the resistor is compared by the comparator. 4. Control method of DC motor by signal.