JPS63242187A - Controller for motor - Google Patents

Abstract

PURPOSE:To increase the rated speed of a motor and extract the performance of the motor at its maximum, by reducing a limit value when the driving voltage of the motor has exceeded a power source voltage. CONSTITUTION:An subtracter 3 operates a difference between the commanding signal of a rotating speed and the detected signal of the same speed. A torque signal generating circuit 4 generates a torque signal proportional to the exciting current of the coil of a motor 1 based on the difference signal operated by the subtracter 3. A limit circuit 5 reduces the value of a limit when the rotating speed of the motor the has exceeded a given value to limit the output of the torque signal generating circuit 4, i. e. the magnitude of a current. According to this constitution, the maximum torque is reduced but a driving voltage may be kept lower than a power source voltage whereby a rated speed of the motor may be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an improvement of a motor control circuit that performs feedback control of the rotational speed of a motor.

[Prior Art] Generally, when driving a motor such as a DC brushless motor, the maximum rotation speed of the motor is determined by the motor's back electromotive force, the inductance of the motor coil, the resistance of the coil, the maximum current, and the power supply voltage. . This is shown in a vector diagram as shown in FIG. 6. Each symbol in the figure is as follows.

V: Drive voltage [V] N: Number of rotations [rpsl neo-number of teeth L: Inductance of motor coil [H] R: Resistance of motor coil [Ω] K: Back electromotive force of motor coil [V/rps] ■: Excitation current of motor coil [A] In such a motor, if there is an input of rotation speed such that the motor drive voltage V exceeds the power supply voltage, abnormal operation will occur in the servo system, resulting in circuit failure or motor failure. This may cause vibration.

For this reason, as shown in FIG. 7, some motors have set the maximum rotational speed at which the drive voltage exceeds the power supply voltage when the maximum torque Tmaχ is generated as the rated speed.

However, in this case, there is a problem that the rated speed of the motor is limited to the maximum torque Ttaχ, and the performance of the motor cannot be fully exploited.

The present invention has been made to solve these problems, and an object of the present invention is to realize a motor control device that has a high rated speed and can fully bring out the performance of the motor.

[Means for Solving the Propositional Point] The present invention provides a motor control circuit that performs feedback control of the rotational speed of the motor, and includes: a subtracter that takes the difference between a rotational speed command signal and a rotational speed detection signal; a torque signal generation circuit that generates a torque signal proportional to the excitation current of the motor coil based on the difference signal obtained by the motor; The characteristic curve of the command signal and the current limit value has a slope portion having a slope equal to the slope portion of the torque speed curve of the motor.

[Example] The present invention will be explained below using the drawings.

FIG. 1 is a block diagram of an embodiment of a motor control device according to the present invention.

In the figure, 1 is a motor subject to speed series control, and 2 is speed detection means for detecting the rotational speed of the motor 1. As the speed detection means, for example, a combination of an encoder and an F/V converter is used.

3 is a subtracter that takes the difference between the speed input (command signal for motor rotational speed) N and the speed signal detected by the speed detection means 2; 4 is a subtractor that takes the difference signal from the subtractor 3 according to the torque generated by the motor; This is a torque signal generation circuit that outputs a torque signal.

The torque signal generated by this circuit is a signal proportional to the exciting current I.

5 is activated according to the speed input! ! This is a limit circuit that regulates the output range of the torque signal generation circuit 4 by regulating the limit of the current (2). The relationship between the speed human power N and the limit value of the excitation 1i1N flow (2) of this circuit is shown in FIG.

In Figure 2, the limit value is a constant value until the speed input is N.■1
When N+ is exceeded, the limit value decreases linearly as the speed input increases. The slope of the linear portion is equal to the slope of the slope portion of the torque-speed curve of the motor 1. Rotational speed N.

is equal to the rotational speed at which the torque-speed curve of the motor 1 begins to slope.

6 is a commutation control circuit that controls the commutation of the motor 1 based on the output of the limit circuit 5; 7 is a current detection means that detects the excitation current supplied to the coil of the motor 1; 8 is a commutation control circuit 6
This is a current servo circuit that performs feedback control of the excitation current given to the motor 1 based on the difference signal between the output of the motor 1 and the detection signal of the current detection means 7.

Next, the operation of such a device will be explained.

When the rotational speed of the motor 1 exceeds a constant value +1flN+, the limit value of the limit circuit 5 decreases to limit the output of the torque signal generating circuit 4, that is, the magnitude of the current. N in Figure 2
Vector diagrams of the drive voltage at rotational speeds of + and N2 are shown in FIGS. 3 and 4. When the rotational speed is N2, the back electromotive force of the motor and the impedance of the coil increase, but the excitation current ■2 is increased by 1 of the excitation current 1+ shown in Figure 3.
Since the voltage is limited to /2, the drive voltage v2 can be maintained at approximately the same level as in case (1).

By limiting the current in this manner, the drive voltage V is kept below the power supply voltage even if there is an excessive speed input.

[effect] According to the present invention, the following effects can be obtained.

When controlling the motor without installing a torque limit circuit, 1. As shown in FIG. 7, when the maximum torque Ttaχ is generated, the maximum rotation speed at which the drive voltage of the motor exceeds the power supply voltage becomes the rated speed.

On the other hand, if a torque limit circuit is provided as in the motor control device according to the present invention, when the maximum torque T(ax) is generated, the motor is activated. When the rotation speed reaches a point where the lJ voltage exceeds the power supply voltage, the limit circuit lowers the limit value of the excitation current. As a result, as shown in FIG. 5, although the maximum torque is lowered, the drive voltage is kept below the power supply voltage and the rated speed can be increased. For example, when the maximum torque becomes 0.7 Ttaχ, the rated speed becomes approximately 40% higher than in the case shown in FIG. Further, the maximum rotation speed 1 (rotation speed when Tmaχ becomes O) can be approximately twice the rated speed shown in FIG.

In this manner, the motor control device according to the present invention can maximize the performance of the motor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a motor control device according to the present invention, FIG. 2 is a characteristic diagram of the limit circuit shown in FIG. 1, and FIG.
Figure 4 is an explanatory diagram of the operation of the device shown in Figure 1, Figure 5 is a characteristic diagram of the device shown in Figure 1, Figure 6 is a vector diagram of the motor drive voltage, and Figure 7 is a diagram of the conventional motor. FIG. 3 is an explanatory diagram of the operation of the control device. DESCRIPTION OF SYMBOLS 1...Motor, 2...Speed detection means, 3...Subtractor, 4...Torque signal generation circuit, 5...Limit circuit. Fig. 1 Tachibara input N Fig. 5 Fig. 4

Claims (1)

[Claims] In a motor control circuit that performs feedback control of the rotational speed of the motor, a subtracter that takes the difference between a rotational speed command signal and a rotational speed detection signal, and a difference signal obtained by the subtracter is used. a torque signal generation circuit that generates a torque signal proportional to the excitation current of the motor coil; and a torque signal generation circuit that regulates the limit of the excitation current based on a command signal of the rotational speed of the motor, and determines the characteristics of this command signal and the current limit value. A control device for a motor, comprising: a limit circuit in which the curve has a slope portion having a slope equal to a slope portion of a torque-speed curve of the motor.