JPH0295188A - Method of controlling speed of dc motor - Google Patents

Abstract

PURPOSE:To inhibit speed hunting resulting from the overshoot of speed by reducing currents only up to a value corresponding to motor voltage when the speed of a DC motor operated by a power conversion means, the direction of power of which is in one direction, is controlled by a speed control loop having a current control minor loop. CONSTITUTION:A DC motor 3 is operated by DC power output from a thyristor converter 2 as a power conversion means, a speed control loop having a current control minor loop is formed for controlling the speed of the DC motor 3, and a voltage detector 21, a cosine converter 22 and a second limiter 23 are installed. The cosine converter 22 generates the phase angle of ignition corresponding to motor voltage, gives it to the second limiter 23 and limits an ignition-angle limiting value alphamax to a value corresponding to the motor voltage. Accordingly, currents can be brought so as not to be reduced up to zero, thus inhibiting the overshoot of speed, then eliminating speed hunting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a speed control method for a DC motor driven by a power conversion means with a unidirectional power supply.

[Conventional technology]

FIG. 2 is a control block diagram showing a conventional example of speed control of a DC motor driven by a power converting means with one direction of power.

In FIG. 2, a Zirrisk converter 2 as a power conversion means converts AC power from an AC power source (not shown) into DC power and supplies it to a DC motor 3.
A load 4 coupled to this DC motor 3 is driven, and the speed of this DC motor 3 is controlled as follows.

That is, the speed setter 11 sets the desired speed command value N'''. On the other hand, the speed detector 12 coupled to the DC motor 3 detects the actual speed value N of the DC motor a3. , when the deviation between the speed command value N'' and the actual speed value N is input to the speed regulator 13, this speed regulator 13 outputs the current command value I4 in order to make the manual deviation zero, and these speeds The setting device 11, the speed detector 12, and the speed regulator 13 form a speed control loop.

The current control minor loop inside this speed control loop is formed by the speed regulator 13, the current detector 14, and the current regulator 15. The deviation from the actual current value I detected by the controller 14 is given to the current regulator 15, and the current regulator 5 outputs a control signal that makes the input deviation zero, that is, the firing angle signal α of the Cyrisk converter 2. .

This firing angle signal α is input to the firing pulse generator 17 via the firing angle limiter 16, and generates a pulse for controlling the phase of the Cyrisk converter 2 at a desired value, so that the current flowing through the DC motor 3 is adjusted to maintain the speed of this electric motor 3 at the speed command value N9.

[Problem to be solved by the invention]

As described above, the DC motor 3 operates while maintaining its speed at the speed command value N'', but due to external disturbances such as load fluctuations, the actual speed value N of the DC motor 3 changes.
becomes higher than the speed command value N8, the speed regulator 13 outputs a speed reduction command and attempts to make the current command value I'' zero, so the firing angle signal α output by the current regulator 15 is , its maximum value is set to α,X.

At this time, the motor speed is in an uncontrolled state, and the speed decreases toward the speed command value N" with a deceleration corresponding to the torque of the load 4. Eventually, the actual speed value N of the motor 3 changes to the speed When the current command value N" becomes lower than the command value N", the speed regulator I3 outputs a command to increase the current command value I9, and the actual speed value N changes from decreasing to increasing. Therefore, the actual speed value N exceeds the speed command value N". The operation of shooting and lowering the actual speed value N is repeated.In other words, this has a major drawback of causing speed hunting.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to stably control the speed of a DC motor driven by a power converter having one direction of power without causing hunting.

[Means to solve the problem]

In order to achieve the above object, the speed control method of the present invention controls the speed of a DC motor driven by a power conversion means that converts AC into DC using a speed control loop that includes a current control minor loop. In the method, a voltage of the DC motor is detected, and a lower limit value of this signal when the current control minor lube outputs a current reduction signal is changed in accordance with the motor voltage.

[Effect]

In a conventional device that drives a DC motor using a power conversion means with a single power direction, when the actual speed value exceeds the speed command value, the firing angle α is maximized to reduce the current to zero. In order to output the signal, the motor speed decreases to the speed command value in an uncontrolled state, which causes hunting in the speed. Therefore, in the present invention, in reducing the actual speed value to the speed command value, The firing angle α is
Since the current is limited to a value corresponding to the motor voltage at that point in time, and the current is not narrowed down to zero, speed overshoot is suppressed, and speed hunting is therefore eliminated.

〔Example〕

FIG. 1 is a control block diagram showing an embodiment of the present invention.

In FIG. 1, a DC motor 3 is operated by DC power outputted from a SIRISK converter 2 as a power conversion means, and this DC motor 3 drives a load 4 and controls the speed of this DC motor 3. For this purpose, a speed setter 11 forming a speed control loop with a current control minor loop
, speed detector 12, speed regulator 13, current detector 14,
It is equipped with a current regulator 15, a firing angle limiter 16, and a firing pulse generator 17, and the names, uses, and functions of these are the same as those of the conventional example circuit already described in FIG. Descriptions of these will be omitted.

In the present invention, a voltage detector 21 and a cosine converter 22
A second limiter 23 is also installed. That is, since the motor voltage is proportional to the motor speed, the voltage detector 21 detects the motor voltage as the actual speed value N.
However, it is detected indirectly.

The cosine converter 22 creates a firing phase angle equivalent to this voltage from the motor voltage and supplies it to the second limit 23, thereby changing the firing angle limit values α, □ to values corresponding to this motor voltage. Restrict.

When the actual motor speed value N rises above the speed command value N'' due to load fluctuations, the speed regulator 13 outputs a current reduction command, and in accordance with this, the output of the current regulator 15, which is the output of the Cyrisk converter 2, is increased. The firing angle α is adjusted to reduce the current.
Move in the direction of l1aX.

According to the invention, this firing angle α does not move up to αIIIMX and the voltage detector 21, the cosine converter 22 and the second
Due to the action of the rimming 23, the firing angle corresponds to the motor voltage, so that the current regulator 15 is prevented from outputting a command to reduce the current excessively.

(Effects of the Invention) According to the present invention, when the speed of a DC motor operated by a power conversion means with one power direction is controlled by a speed control loop having a current control minor loop, When restoring the motor speed that has increased due to load fluctuations, etc., the actual speed value is However, in the present invention, the current is reduced only to a value corresponding to the motor voltage to prevent the speed from going into an uncontrolled state, resulting in speed hunting. The effect of suppressing speed hunting caused by overshoe 1- can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows a control block 1', J7, showing an embodiment of the present invention.
FIG. 2 is a control block diagram showing a conventional example of speed control of a DC motor driven by a power conversion means with one direction of power.

Claims (1)

[Claims] 1) In a method of controlling the speed of a DC motor driven by a power conversion means for converting AC to DC using a speed control loop including a current control minor loop, the voltage of the DC motor is detected and the current control is performed. A method for controlling the speed of a DC motor, characterized in that the lower limit value of the current reduction signal when the minor loop outputs this signal is changed in accordance with the motor voltage.