US-12620921-B2 - Motor rotational speed control system and method having duty cycle variable modulation mechanism

US12620921B2US 12620921 B2US12620921 B2US 12620921B2US-12620921-B2

Abstract

A motor rotational speed control system and method having a duty cycle variable modulation mechanism is provided. The motor rotational speed control system is performed by the motor rotational speed control system including a motor rotational speed detector and a motor driver. When a rotational speed of a motor detected by the motor rotational speed detector is larger than or equal to a set rotational speed, the motor driver modulates duty cycles of a plurality of waveforms of an on-time signal, and modulates a duty cycle difference between the duty cycle of each of the plurality of waveforms and the duty cycle of a previous one or every other one of the plurality of waveforms in the on-time signal. The motor driver, according to the on-time signal, drives the motor such that the rotational speed of the motor is limited to be smaller than the set rotational speed.

Inventors

Kun-Min Chen
Shih-Hai Chien

Assignees

ANPEC ELECTRONICS CORPORATION

Dates

Publication Date: 20260505
Application Date: 20240311
Priority Date: 20231219

Claims (17)

1 . A motor rotational speed control system having a duty cycle variable modulation mechanism, comprising: a rotational speed detector connected to a motor, and configured to detect a rotational speed of the motor; and a motor driver connected to the rotational speed detector and the motor; wherein, when the rotational speed of the motor that is detected by the rotational speed detector is larger than or equal to a set rotational speed, the motor driver, according to the rotational speed of the motor, modulates duty cycles of a plurality of waveforms that are sequentially generated in an on-time signal, and modulates a duty cycle difference between the duty cycle of each of the plurality of waveforms and the duty cycle of a previous one or every other one of the plurality of waveforms in the on-time signal; wherein the motor driver, according to the on-time signal that is modulated, drives the motor such that the rotational speed of the motor is limited to be smaller than the set rotational speed; wherein, when a current rotational speed of the motor is not larger than a rotational speed limit value, the motor driver maintains the duty cycle difference between the duty cycles of each subsequent two of the plurality of waveforms of the on-time signal to be equal to an initial duty cycle difference.
2 . The motor rotational speed control system according to claim 1 , wherein the motor driver, according to a target duty cycle command instructing a target duty cycle, modulates the duty cycle difference of the on-time signal to be equal to the initial duty cycle difference, and modulates the duty cycle of a latest one of the plurality of waveforms of the on-time signal to be equal to the target duty cycle.
3 . The motor rotational speed control system according to claim 2 , wherein, when the motor driver drives the motor according to one of the plurality of waveforms of the on-time signal, the motor driver determines a relationship between the current rotational speed of the motor and the rotational speed limit value, and accordingly determines whether to modulate the duty cycle differences between subsequent ones of the plurality of waveforms of the on-time signal.
4 . The motor rotational speed control system according to claim 1 , wherein, when the current rotational speed of the motor is larger than or equal to the rotational speed limit value, the motor driver sets the duty cycle difference between the duty cycles of each subsequent two of the plurality of waveforms of the on-time signal to be equal to a duty cycle modulation difference, and the duty cycle modulation difference is smaller than the initial duty cycle difference.
5 . The motor rotational speed control system according to claim 4 , wherein, when the motor driver drives the motor according to the on-time signal having the duty cycle difference being equal to the duty cycle modulation difference, the rotational speed detector detects the rotational speed of the motor.
6 . The motor rotational speed control system according to claim 5 , wherein, when the rotational speed of the motor that is driven according to the on-time signal having the duty cycle difference being equal to the duty cycle modulation difference by the motor driver is larger than or equal to the rotational speed limit value, the motor driver reduces the duty cycles of the subsequent ones of the plurality of waveforms of the on-time signal.
7 . The motor rotational speed control system according to claim 6 , wherein, when the rotational speed of the motor that is driven according to the on-time signal having the duty cycle difference being equal to the duty cycle modulation difference by the motor driver is not larger than the rotational speed limit value, the motor driver determines whether the duty cycle of one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is equal to a target duty cycle.
8 . The motor rotational speed control system according to claim 7 , wherein, when the duty cycle of the one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is equal to the target duty cycle, the motor driver does not further modulate the on-time signal.
9 . The motor rotational speed control system according to claim 8 , wherein, when the duty cycle of the one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is not equal to the target duty cycle, the motor driver determines whether the duty cycle of the one of the plurality of waveforms of the on-time signal is larger than the target duty cycle.
10 . The motor rotational speed control system according to claim 9 , wherein, when the duty cycle of the one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is larger than the target duty cycle, the motor driver reduces the duty cycles of the subsequent ones of the plurality of waveforms of the on-time signal for driving the motor.
11 . The motor rotational speed control system according to claim 10 , wherein, when the duty cycle of the one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is not larger than the target duty cycle, the motor driver increases the duty cycles of the subsequent ones of the plurality of waveforms of the on-time signal for driving the motor.
12 . The motor rotational speed control system according to claim 1 , wherein the motor driver includes: a control circuit connected to the rotational speed detector, wherein the motor driver, according to the rotational speed of the motor that is detected by the rotational speed detector, sets the duty cycle of each of the plurality of waveforms of the on-time signal, and sets the duty cycle difference between the duty cycle of each of the plurality of waveforms and the duty cycle of the previous one or every other one of the plurality of waveforms of the on-time signal, and outputs a control signal according to the on-time signal; a driver circuit connected to control circuit, and configured to output the on-time signal according to the control signal from the control circuit; and an output stage circuit connected to the motor, and configured to drive the motor according to the on-time signal from the driver circuit.
13 . The motor rotational speed control system according to claim 12 , further comprising: a rotor position detector circuit disposed on the motor and connected to the control circuit, wherein the rotor position detector circuit detects a position of a rotor of the motor to output a rotor position detected signal, and the control circuit controls the driver circuit to drive the motor according to the rotor position detected signal from the rotor position detector circuit.
14 . The motor rotational speed control system according to claim 13 , wherein the rotational speed detector is connected to the rotor position detector circuit, and configured to determine the rotational speed of the motor according to the rotor position detected signal from the rotor position detector circuit.
15 . The motor rotational speed control system according to claim 1 , wherein the motor is a single-phase motor.
16 . The motor rotational speed control system according to claim 1 , wherein the motor is a three-phase motor.
17 . A motor rotational speed control method having a duty cycle variable modulation mechanism, comprising processes of: (a) using a motor driver to drive a motor according to an on-time signal; (b) receiving a target duty cycle command by the motor driver; (c) setting, by the motor driver, a duty cycle of a latest one of a plurality of waveforms of the on-time signal to be equal to a target duty cycle instructed by the target duty cycle command; (d) detecting a rotational speed of the motor by a rotational speed detector; (e) determining, by the motor driver, whether or not the rotational speed of the motor is larger than or equal to a rotational speed limit value, in response to determining that the rotational speed of the motor is not larger than or equal to the rotational speed limit value, sequentially performing the processes (f) to (g) and then performing the process (l), and in response to determining that the rotational speed of the motor is larger than and not equal to the rotational speed limit value, sequentially performing the processes (h) to (j); (f) modulating, by the motor driver, the duty cycle difference between the duty cycle of each of the plurality of waveforms that are generated in the on-time signal within each of a plurality of time intervals and the duty cycle of each of the plurality of waveforms that are generated in the on-time signal within a next one of the plurality of time intervals to be equal to an initial duty cycle difference; (g) driving the motor according to the on-time signal having the duty cycle difference being equal to the initial duty cycle difference, by the motor driver; (h) setting, by the motor driver, the duty cycle difference between the duty cycles of each subsequent two of the plurality of waveforms of the on-time signal to be equal to a duty cycle modulation difference, wherein the duty cycle modulation difference is smaller than the initial duty cycle difference; (i) driving the motor according to the on-time signal having the duty cycle difference being equal to the duty cycle modulation difference, by the motor driver; (j) determining, by the motor driver, whether or not the rotational speed of the motor is larger than or equal to the rotational speed limit value, in response to determining that the rotational speed of the motor is larger than or equal to the rotational speed limit value, performing the process (k), and in response to determining that the rotational speed of the motor is not larger than and not equal to the rotational speed limit value, performing the process (l); (k) reducing the duty cycles of subsequent ones of the plurality of waveforms of the on-time signal for driving the motor, by the motor driver; (l) determining, by the motor driver, whether or not the duty cycle of one of the plurality of waveforms of the on-time signal that is currently used for driving the motor is equal to a target duty cycle, in response to determining that the duty cycle of the one of the plurality of waveforms of the on-time signal is equal to the target duty cycle, not performing the process (m) in which the on-time signal is further modulated, and in response to determining that the duty cycle of the one of the plurality of waveforms of the on-time signal is not equal to the target duty cycle, performing the process (m); and (m) determining, by the motor driver, whether or not the duty cycle of the one of the plurality of waveforms of the on-time signal is larger than the target duty cycle, in response to determining that the duty cycle of the one of the plurality of waveforms of the on-time signal is larger than the target duty cycle, reducing the duty cycles of the subsequent ones of the plurality of waveforms of the on-time signal for driving the motor, and in response to determining that the duty cycle of the one of the plurality of waveforms of the on-time signal is not larger than the target duty cycle, increasing the duty cycles of the subsequent ones of the plurality of waveforms of the on-time signal for driving the motor.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION This application claims the benefit of priority to Taiwan Patent Application No. 112149377, filed on Dec. 19, 2023. The entire content of the above identified application is incorporated herein by reference. Some references, which may include patents, patent applications and various publications, may be cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. FIELD OF THE DISCLOSURE The present disclosure relates to a motor rotational speed control system and method, and more particularly to a motor rotational speed control system and method having a duty cycle variable modulation mechanism. BACKGROUND OF THE DISCLOSURE In electronic devices, fans are used to cool heat generating components such as processors. When the heat generating components are cooled down by the fan, a rotational speed of a motor of the fan must be limited to an appropriate value such that the fans can properly cool down the heat generating components with high efficiency. However, when the motor is driven such that the rotational speed of the motor is limited by a conventional motor controller, the motor is prone to unstable or abnormal operations. SUMMARY OF THE DISCLOSURE In response to the above-referenced technical inadequacies, the present disclosure provides a motor rotational speed control system having a duty cycle variable modulation mechanism. The motor rotational speed control system includes a rotational speed detector and a motor driver. The rotational speed detector is connected to a motor. The rotational speed detector is configured to detect a rotational speed of the motor. The motor driver is connected to the rotational speed detector and the motor. When the rotational speed of the motor that is detected by the rotational speed detector is larger than or equal to a set rotational speed, the motor driver, according to the rotational speed of the motor, modulates duty cycles of a plurality of waveforms that are sequentially generated in an on-time signal, and modulates a duty cycle difference between the duty cycle of each of the plurality of waveforms and the duty cycle of a previous one or every other one of the plurality of waveforms in the on-time signal. The motor driver, according to the on-time signal that is modulated, drives the motor such that the rotational speed of the motor is limited to be smaller than the set rotational speed. In order to solve the above-mentioned problems, one of the technical aspects adopted by the present disclosure is to provide a motor rotational speed control method having a duty cycle variable modulation mechanism. The motor rotational speed control method includes processes of: (a) using a motor driver to drive a motor according to an on-time signal; (b) receiving a target duty cycle command by the motor driver; (c) setting, by the motor driver, a duty cycle of a latest one of a plurality of waveforms of the on-time signal to be equal to a target duty cycle instructed by the target duty cycle command; (d) detecting a rotational speed of the motor by a rotational speed detector; (e) determining, by the motor driver, whether or not the rotational speed of the motor is larger than or equal to a rotational speed limit value, in response to determining that the rotational speed of the motor is not larger than or equal to the rotational speed limit value, sequentially performing the processes (f) to (g) and then performing the process (l), and in response to determining that the rotational speed of the motor is larger than and not equal to the rotational speed limit value, sequentially performing the processes (h) to (j); (f) modulating, by the motor driver, the duty cycle difference between the duty cycle of each of the plurality of waveforms that are generated in the on-time signal within each of a plurality of time intervals and the duty cycle of each of the plurality of waveforms that are generated in the on-time signal within a next one of the plurality of time intervals to be equal to an initial duty cycle difference; (g) driving the motor according to the on-time signal having the duty cycle difference being equal to the initial duty cycle difference, by the motor driver; (h) setting, by the motor driver, the duty cycle difference between the duty cycles of each subsequent two of the plurality of waveforms of the on-time signal to be equal to a duty cycle modulation difference, wherein the duty cycle modulation difference is smaller than the initial duty cycle difference; (i) driving the motor according to the on-tim