Patent Application
20170179860
The present invention is related to a method for controlling a motor, more particularly to a method and a system for controlling a motor to reduce the noises of the motor.
In general, it is necessary to detect the rotor position and change the phase of the current by using a phase change switch to drive a brushless-dc motor. The current is not stable during the period of phase switching, this causes the motor to resonante and produce annoying noises.
The U.S. Pat. No. 7,009,351 disclosed a control method which stops the current output during the period of phase switching, and inertia carries the rotor to rotate and pass through the point of phase switching. In this case, the single phase motor loses driving power near the point of phase switching and causes the speed of the motor to be unstable. Moreover, a circuit for detecting the predetermined period starting immediately before and ending immediately after the point of phase switching is needed.
Another U.S. Pat. No. 7,915,843 disclosed a control method to smooth the output current during the period of phase switching. In this case, it is emphasized on the modulation of current surge at the point of phase switching to prevent noises caused by the current surge. A circuit for detecting the predetermined period starting immediately before and ending immediately after the point of phase switching is also needed.
The aforementioned methods only take care of the current surge at the point of phase switching, and do not provide smooth current output to drive the motor. Consequently, it is a problem to provide smooth current output to drive a motor for preventing noises.
It is an objective of the present invention to provide a control method, more particularly a method and a system for controlling a motor to reduce noises.
The present invention provides a system and a method for controlling a motor, wherein a full cycle pulse-width modulation driving method is used. By using the inductance effect to output smoother and more sinusoidal-like driving current, noises of the motor are reduced.
In one embodiment of the present invention, the system for controlling a motor comprises a sensing module, a control module and a pulse-width modulation (PWM) module. The sensing module is configured to detect a period information of a rotor of the motor and generate a sensing signal. The control module is connected to the sensing module and is configured to receive the sensing signal and the period information and comprise a predetermined rule. The control module controls the PWM module to output PWM signals with proper duty cycles to drive the motor.
In one embodiment of the present invention, the method for controlling a motor comprises: detecting the period information of a rotor of the motor to obtain an operation cycle of the rotor; dividing the operation cycle into a plurality of timing segments; calculating one or more variations of the rotating speed of the rotor during the operation cycle; determining a duty cycle of a PWM signal corresponding to each timing segment according to a predetermined rule; and driving the motor with the PWM signal.
According to the aforementioned content, the system and method for controlling a motor of the present invention determine the duty cycle of the PWM signal corresponding to each timing segment according to the predetermined rule and the variations of the rotating speed. Consequently, the output current of the motor is rather smooth and close to a sinusoidal waveform because of the inductance effect, and noises of the motor are greatly reduced.
Referring to
In the present embodiment, the predetermined rule is a predetermined power. The motor 16 is but not limited to a single phase full wave motor. This type of motor can be used in an electric fan. The waveform of the driving current Icoil of the motor 16 is controlled by the driving signal Vdrive.
In one embodiment of the present invention, the period information can be detected by sensing the variations of the magnetic field with a Hall sensor, sensing the variations of the current and sensing the counter electromotive force, to obtain the phase information of the rotor during an operation cycle.
In one embodiment of the present invention, the Hall sensor is selectively one of a Hall sensor with magnetic field transformation effect or a Hall sensor without magnetic field transformation effect.
In one embodiment of the present invention, the sensing module 10 detects the variation of the current to detect the point of phase changing.
In one embodiment of the present invention, the sensing module 10 can also detect the counter electromotive force to detect the point of phase changing.
Referring to
In one embodiment of the present invention, the control module 12 obtains the operation cycle according to the sensing signal Vs and calculates the variations of the rotating speed of the rotor during the operation cycle according to the period information of the rotor. The control module 12 divides the operation cycle into a plurality of timing segments according to the requirement of the designer.
The control module 12 adjusts the duty cycle of the driving signal Vdrive according to the predetermined power (predetermined rule) and the variations of the rotating speed. It is well-known for the person skilled in the art that the output power of the motor is the product of the torque and the rotating speed, and the torque and the rotating speed can be obtained from the variations of the rotating speed. Consequently, when the control module 12 receives the sensing signal Vs according to the period information of the rotor, the duty cycle of the driving signal Vdrive is determined according to the variations of the rotating speed. The predetermined power determines the amplitude of the waveform of the current Icoil.
In the present embodiment, an operation cycle is divided into 8 timing segments (each timing segment is equal to 45 degree). The half cycle of 0-180 degree is divided into a first segment I, a second segment II, a third segment III and a fourth segment IV. The other half cycle of 181-360 degree is symmetric to the half cycle of 0-180 degree. If the predetermined power is the 60% of the max output power, the PWM module 14 outputs PWM signals with duty cycles of 35%, 75%, 75% and 35% respectively.
As shown in
The aforementioned embodiments are only used for descriptions. It is not limited to divide the operation cycle into 8 timing segments. For example, the half operation cycle can also be divided into 5 timing segments, and the PWM module 14 outputs PWM signals with duty cycles of 80%, 40%, 40%, 20% and 20%. In one embodiment of the present invention, the timing segments are not necessary to be equal to each other.
Referring to
In one embodiment of the present invention, the period information of the rotor in step S10 is detected by a Hall sensor which makes use of the inductance effect of the motor 16 as the aforementioned descriptions.
In the present invention, the system and method for controlling a motor is embodied by using the sensing module to detect the period information of the rotor of the motor, calculating the variations of the rotating speed, determining the duty cycle of each timing segment according to the predetermined power, and driving the motor with the PWM signals of corresponding duty cycles. Consequently, the output current is rather smooth and close to a sinusoidal waveform, and noises of the motor are reduced effectively.
Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the scope of the invention specified by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 104142645 | Dec 2015 | TW | national |
