Abstract:
A motor speed control system includes a motor, a control module and a displaying module. The motor includes a rotor and a stator. The rotor includes at least one induction rotor portion. The stator includes at least one induction stator portion. The induction rotor portion is corresponding to the induction stator portion. The control module is electrically connected to the rotor and the stator. The control module controls an induction rotor current of the induction rotor portion and an induction stator current of the induction stator port on to produce a rotor speed. The control module decreases or turns off the induction rotor current to keep the rotor speed at a predetermined value according to a rotational inertia of the rotor and the induction stator current when the rotor speed reaches the predetermined value. The displaying module displays the rotor speed and variable currents.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to Taiwan Application Serial Number 103203039 filed Feb. 21, 2014 and Taiwan Application Serial Number 104100775, filed Jan. 9, 2015, which are herein incorporated by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a motor speed control system and a motor speed control method. More particularly, the motor speed control system and the motor speed control method of the present disclosure are capable of reducing magnetic force of a rotor and increasing motor operation efficiency. 
         [0004]    2. Description of Related Art 
         [0005]    In many industrials, operations of machines require a rotational movement. A motor is commonly used to produce this kind of rotational movement. The motor has become an indispensable device owing to its capability on converting magnetic energy or electrical energy into mechanical energy. There are various types of motors that can be applicable to different environments and operation conditions, such as induction motors and permanent magnet motors. 
         [0006]    The conventional permanent magnet motor includes a stator, a rotor and a shell. The stator is composed of an armature coil and an armature core. The armature core is formed by stacking a plurality of silicon steel sheet, and the armature is located on the stator. The rotor is made of permanent magnetic material. The shell not only can fix the stator, but also can be used as a part of the magnetic circuit. Furthermore, inner-rotor permanent magnet motors can be classified into different types according to the types that the stator winds, such as two-phase, three-phase or five-phase permanent magnet motor, and the three-phase permanent magnet motor is the most popular. In general, the permanent magnet motor has high operation efficiency. In the permanent magnet motor, a torque is generated from interaction between the permanent magnet of the rotor and the stator coils to keep the synchronous speed. Recently, due to the constantly improved material of the permanent magnet and magnetic energy product, the permanent magnet motor can achieve very high operation efficiency. 
         [0007]    However, the permanent magnet motor has the characteristics of slow starting time, and has insufficient torque at low speed, therefore its rotational speed takes a long time to reach a predetermined value. Furthermore, a complicated control system is required in the permanent magnet motor, thus the manufacturing cost of the motor is increased. Moreover, when the permanent magnet motor reaches the highest rotor speed, the power consumption of the motor is too large. Therefore, a motor speed control system and method having low cost, simple control, high-energy efficiency and high torque with maximum rotor speed is commercially desirable. 
       SUMMARY 
       [0008]    According to one aspect of the present disclosure a motor speed control system includes a motor, a control module and a displaying module. The motor includes a rotor and a stator. The stator is coaxially and pivotally connected to the rotor. The rotor includes at least one induction rotor portion and at least one permanent magnet rotor portion. The stator includes at least one induction stator portion and at least one permanent magnet stator portion. The induction rotor portion is corresponding to the induction stator portion. The induction rotor portion and the induction stator portion are separated by an induction distance. The permanent magnet rotor portion is corresponding to the permanent magnet stator portion. The permanent magnet rotor portion and the permanent magnet stator portion are separated by a permanent magnet distance. The control module is electrically connected to the rotor and the stator. The control module controls an induction rotor current of the induction rotor portion, an induction stator current of the induction stator portion and a permanent magnet stator current of the permanent magnet stator portion to produce a rotor speed. The control module decreases or turns off the induction rotor current to keep the rotor speed at a predetermined value according to a rotational inertia of the rotor and the induction stator current when the rotor speed reaches the predetermined value. The displaying module is electrically connected to the control module. The displaying module displays the rotor speed, the induction rotor current and the permanent magnet stator current. 
         [0009]    According to another aspect of the present disclosure, a motor speed control method for using the motor speed control system includes a first control step, a second control step, a third control step and a displaying, step. The first control step is for controlling the induction rotor current and the induction stator current to change the rotor speed by the control module when the rotor speed is less than the predetermined value. The second control step is for decreasing or turning off the induction rotor current by the control module when the rotor speed reaches the predetermined value, and the rotor speed is kept at the predetermined value according to the rotational inertia of the rotor and the induction stator current. The third control step is for controlling the permanent magnet stator current to increase the rotor speed by the control module when the rotor speed reaches the predetermined value. The displaying step is for displaying the rotor speed, the induction rotor current and the permanent magnet stator current by the displaying module. 
         [0010]    According to further another aspect of the present disclosure, a motor speed control system includes a motor, a control module and a displaying module. The motor includes a rotor and a stator. The rotor includes at least one induction rotor portion. The stator includes at least one induction stator portion. The stator is coaxially and pivotally connected to the rotor. The induction rotor portion is corresponding to the induction stator portion. The induction rotor portion and the induction stator portion are separated by an induction distance. The control module is electrically connected to the rotor and the stator. The control module controls an induction rotor current of the induction rotor portion and an induction stator current of the induction stator portion to produce a rotor speed. The control module decreases or turns off the induction rotor current to keep the rotor speed at a predetermined value according to a rotational inertia of the rotor and the induction stator current when the rotor speed reaches the predetermined value. The displaying module is electrically connected to the control module. The displaying module displays the rotor speed and the induction rotor current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
           [0012]      FIG. 1  is a schematic view of a motor speed control system according to one embodiment of the present disclosure; 
           [0013]      FIG. 2  is a cross-sectional vie of the motor of  FIG. 1 ; 
           [0014]      FIG. 3A  is a lateral view of the rotor of  FIG. 2 ; 
           [0015]      FIG. 3B  is a cross-sectional view of the motor of  FIG. 2 ; 
           [0016]      FIG. 4A  is a cross-sectional view of a motor according to another embodiment of the present disclosure; 
           [0017]      FIG. 4B  is a schematic view of the slip rings according to another embodiment of the present disclosure; and 
           [0018]      FIG. 5  is a flow chart of a motor speed control method according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a schematic view of a motor speed control system according to one embodiment of the present disclosure;  FIG. 2  is a cross-sectional view of the motor of  FIG. 1 ;  FIG. 3A  is a lateral view of the rotor of  FIG. 2 ; and  FIG. 3B  is a cross-sectional view of the motor of  FIG. 2 . In  FIG. 1 , the motor speed control system  100  includes a motor  200 , a control module  300 , a displaying module  400  and a power supply  500 . 
         [0020]    In detail; the motor  200  includes a rotor  210  a stator  220 , two slip rings  250  and a brush assembly  260 . The rotor  210  includes a rotational axis  230 , an induction rotor portion  212  and a permanent magnet rotor portion  214 . The stator  220  includes a shell  240 , an induction stator portion  222  and a permanent magnet stator portion  224 . The stator  220  is located outside of the rotor  210 . The induction rotor portion  212  is corresponding to the induction stator portion  222 . The induction rotor portion  212  and the induction stator portion  222  are separated by an induction distance d 1 . The permanent magnet rotor portion  214  is corresponding to the permanent magnet stator portion  224 . The permanent magnet rotor portion  214  and the permanent magnet stator portion  224  are separated by a permanent magnet distance d 2 . Moreover, the motor  200  has a motor current  270  that represents the amount of current consumed by the motor  200 . The induction rotor portion  212  has an induction rotor current  272  that represents the amount of current consumed by the induction rotor portion  212 . The induction stator portion  222  has an induction stator current  274  that represents the amount of current consumed by the induction stator ports  222 . The permanent magnet stator portion  224  has a permanent magnet stator current  276  that represents the amount of current consumed by the permanent magnet stator portion  224 . The motor current  270  is the sum of the induction rotor current  272 , the induction stator current  274  and the permanent magnet stator current  276 . The induction rotor portion  212 , the induction stator portion  222  and the permanent magnet rotor portion  214  all have coils, and the induction rotor portion  212  and the induction stator portion  222  are used to provide a torque interaction by the coils to start the rotor  210  and generate a rotor speed. The permanent magnet rotor portion  214  is made of permanent magnetic material. Furthermore, the rotor  210  has a plurality of magnetic north poles  216  and a plurality of magnetic south poles  218 , and each of the magnetic north poles  216  and each of the magnetic south poles  218  are interlaced with each other. The induction rotor portion  212  and the permanent magnet rotor portion  214  both have a plurality of magnetic north poles  216  and a plurality of magnetic south poles  218 . The magnetic north poles  216  of the induction rotor portion  212  are corresponding to the magnetic north poles  216  of the permanent magnet rotor portion  214 , respectively, so that they are mutually exclusive for reducing magnetic interference because of the same polarity. 
         [0021]    In  FIG. 2 , the induction stator portion  222  of the stator  220  and the permanent magnet stator portion  224  of the stator  220  are fixedly connected to the inner wall of the shell  240 , and the induction stator portion  222  and the permanent magnet stator portion  224  are located outside of the rotor  210 . The shell  240  is pivotally connected to the rotational axis  230 . The magnetic north poles  216  of the rotor  210  and the magnetic south poles  218  of the rotor  210  are alternately fixedly connected to the rotational axis  230 . When the motor  200  is rotated, the rotor  210  is pivotally rotated relative to the stator  220 , so that the rotational axis  230  is pivotally rotated relative to the shell  240 . In other words, the rotor  210  is coaxially pivotally connected to the stator  220  by the rotational axis  230  and the shell  240 . Moreover, the two slip rings  250  are both rotationally connected to the outside of the rotational axis  230  and electrically connected to the induction rotor portion  212  of the rotor  210 . The brush assembly  260  is electrically connected to the control module  300  by a plurality of wires (not be shown). The brush assembly  260  includes two brushes  262  which are connected to the two slip rings  250  for conducting current, respectively. Furthermore, the shell  240  is a hollow cylinder, and the rotational axis  230  is cylindrical. The stator  220  is cylindrical because the stator  220  is fixedly connected to the inner wall of the shell  240 . The rotor is also cylindrical because the rotor  210  is fixedly connected to the outer surface of the rotational axis  230 . The rotational direction of the rotor  210  can be clockwise or counterclockwise. The induction rotor portion  212  and the permanent magnet rotor portion  214  are separated by an induction magnet distance d 3 , which not only can prevent magnetic interference between the induction rotor portion  212  and the permanent magnet rotor portion  214 , but also can prevent magnetic interference between the induction stator portion  222  and the permanent magnet stator portion  224 . 
         [0022]    The control module  300  includes a first control member  310  and a second control member  320 . The control module  300  is electrically connected to the rotor  210 , the stator  220  and the brush assembly  260 . The control module  300  controls the induction rotor current  272  of the induction rotor portion  212  and the induction stator current  274  of the induction stator portion  222  by the first control member  310 , so that the rotor speed can be changed by the first control member  310  of the control module  300  when the rotor speed is lower than a predetermined value. 
         [0023]    In one example, if the predetermined value represents a maximum rotor speed, while the rotor speed reaches a maximum value, the first control member  310  can decrease or turn off the induction rotor current  272  to weaken the magnetism of the rotor  210  and reduce the hysteresis effect of the motor  200 , so that the rotor speed can be kept at the maximum value through a rotational inertia of the rotor  210  and the induced stator current  274 , thereby saving the energy. When the rotor speed of the rotor  210  is kept at the predetermined value, the coils of the rotor  210  will form a dosed loop owing to a short-circuit effect occurred. The coils of the rotor  210  still have an induced current produced from the induction stator current  274 . 
         [0024]    In another example, at the time that the rotor speed reaches the maximum value, the second control member  320  can be configured to control the permanent magnet stator current  276  (i.e. further increasing or decreasing the permanent magnet stator current  276 ). When the second control member  320  increases the permanent magnet stator current  276 , the aforementioned maximum value of the rotor speed can be further increased. The first control member  310  or the second control member  320  can be a knob or a button. 
         [0025]    The displaying module  400  includes a first display unit  410  and a second display unit  420 . The displaying module  400  is electrically connected to the control module  300 . The first display unit  410  displays the rotor speed. The second display unit  420  can display the motor current  270 , the induction rotor current  272 , the induction stator current  274  or the permanent magnet stator current  276 . The rotor speed, the motor current  270 , the induced rotor current  272 , the induced stator current  274  or the permanent magnet stator current  276  will be variable during operation. 
         [0026]    When a user adjust the first control member  310  or the second control member  320 , the user can obtain the operation conditions and power consumption of the motor  200  from the displaying module  400 . 
         [0027]    The power supply  500  is electrically connected to the control module  300  and the displaying module  400 . The power supply  500  provides a rotational power, a control power and a display power to the motor  200 , the control module  300  and the displaying module  400  for operation, respectively. The rotational power is provided to the motor  200  for generating the motor current  270 . Moreover, the rotational power will be converted into an induction power and a permanent magnet power by the control module  300 , and the induction power is provided to the induction rotor portion  212  and the induction stator portion  222  for generating the induction rotor current  272  and the induction stator current  274 , respectively. The permanent magnet power is provided to the permanent magnet stator portion  224  the permanent magnet stator current  276 . In detail, the power supply  500  provides the rotational power to the motor  200  by the control module  300 , so that the induction power of the rotational power is provided to the induction rotor portion  212  for generating the induction rotor current  272  according to the brush assembly  260  and the slip rings  250 . The first control member  310  can decrease or turn off the induction rotor current  272  to weaken the magnetism of the rotor  210  during operation. 
         [0028]      FIG. 4A  is a cross-sectional view of the motor  600  according to another embodiment of the present disclosure. In  FIG. 4A , the motor  600  includes a rotor  602  and a stator  604 . The rotor  602  includes an induction rotor portion  610  and a shell  616 , and the induction rotor portion  610  has a plurality of magnetic north poles  612  and a plurality of magnetic south poles  614 . The stator  604  includes an induction stator portion  620  and a rotational axis  622 . The rotor  602  is located outside of the stator  604 . The magnetic north poles  612  of the induction rotor portion  610  and the magnetic south poles  614  of induction rotor portion  610  are alternately fixedly connected to the shell  616 . The shell  616  is pivotally connected to the rotational axis  622 . When the motor  600  is rotated, the rotor  602  is pivotally rotated relative to the stator  604  so that the shell  616  is pivotally rotated relative to the rotational axis  622 . In other words, the rotor  602  is coaxially and pivotally connected to the stator  604  by the rotational axis  622  and the shell  616 . In  FIGS. 2 and 3B , it is showed that the rotor  210  is located inside of the stator  220 , and the rotation of the rotor  210  is an internal rotation. In  FIG. 4A , the rotor  602  is located outside of the stator  604 , and the rotation of the rotor  602  is an external rotation. Therefore, the manufacturer can select a suitable motor according to different applications, such as the motor  200  or the motor  600 . 
         [0029]      FIG. 4B  is a schematic view of the slip rings  252  according to another embodiment of the present disclosure. In  FIGS. 4A and 4B , the slip rings  252  are rotationally connected to the outside of the shell  616 , and the number of the slip rings  252  is two. The slip rings  252  are electrically connected to the induction rotor portion  610  of the rotor  602 . The brush assembly  264  is electrically connected to the control module  300  by a plurality of wires and connected to the two slip rings  252  by two brushes  266 . The slip rings  252  and the brush assembly  264  are both connected to the outside of the shell  616 . When the rotation of the rotor  602  is the external rotation, the shell  616  is corresponding to the location of the induction rotor portion  610  for easily connecting with the slip rings  252  and the induction rotor portion  610 , Therefore, this structure of the two slip rings  252 , the two brushes  266  and the brush assembly  264  can significantly reduce manufacturing costs. In other words, the manufacturer can select a suitable structure according to different applications, such as the slip rings  250  or the slip rings  252 . 
         [0030]      FIG. 5  is a flow chart of a motor speed control method  700  according to one embodiment of the present disclosure. In  FIG. 5 , the motor speed control method  700  includes a first control step s 1 , a second control step s 2 , a third control step s 3 , a displaying step s 4  and a power supplying step s 5 . 
         [0031]    The first control step s 1  is for controlling the induction rotor current  272  and the induction stator current  274  to change the rotor speed by the first control member  310  of the control module  300  when the rotor speed is less than the predetermined value. 
         [0032]    The second control step s 2  is for judging the rotor speed. When the rotor speed reaches the predetermined value, the second control step s 2  is for decreasing or turning off the induction rotor current  272  by the first control member  310  of the control module  300 , so that the rotor speed is kept at the predetermined value according to the rotational inertia of the rotor  210  and the induction stator current  274  of the induction stator portion  222 . While the rotor speed reaches the predetermined value, the first control member  310  can decrease or turn off the induction rotor current  272  to weaken the magnetism of the rotor  210  and reduce the hysteresis effect of the motor  200 , so that the rotor speed can be kept at the predetermined value for saving the energy. The coils of the rotor  210  will form a closed loop, that is, short-circuited condition, and the coils of the rotor  210  still have the induced current produced from the induction stator current  274 . 
         [0033]    The third control step s 3  is for controlling the permanent magnet stator current  276  to increase the rotor speed by the second control member  320  of the control module  300  when the rotor speed reaches the predetermined value, so that the second control member  320  can increase the permanent magnet stator current  276  to further increase rotor speed over the predetermined value. 
         [0034]    The displaying step s 4  is for displaying the rotor speed, the motor current  270 , the induction rotor current  272 , the induction stator current  274  and the permanent magnet stator current  276  by the displaying, module  400 . In detail, the first display unit  410  of the displaying module  400  displays the rotor speed. The second display unit  420  of the displaying module  400  can display the motor current  270 , the induction rotor current  272 , the induction stator current  274  or the permanent magnet stator current  276 . The user can obtain the operation conditions and power consumption of the motor  200  from the displaying module  400 . 
         [0035]    The power supplying step s 5  is utilizing a power supply  500  for providing a rotational power, a control power and a display power to the motor  200 , the control module  300  and the displaying module  400 , respectively. The rotational power is converted into an induction power and a permanent magnet power by the control module  300 . The induction power is provided to the induction rotor portion  212  and the induction stator portion  222  for generating the induction rotor current  272  and the induction stator current  274 , respectively. Furthermore, the permanent magnet power is provided to the permanent magnet stator portion  224  for generating the permanent magnet stator current  276 . The power supplying step s 5  effectively provides stable power in the process of the first control step s 1 , the second control step s 2 , the third control step s 3  and the displaying step s 4 . 
         [0036]    According to the aforementioned embodiments and examples, the advantages of the present disclosure are described as follows. 
         [0037]    1. The system and method of the present disclosure can reduce the thermal demagnetization under high load by substituting the permanent magnet by the induction. 
         [0038]    2. The system and method of the present disclosure can retain the maximum torque of the motor by increasing the induction rotor current when the rotor speed is less than the predetermined value. 
         [0039]    3. The system and method of the present disclosure can weaken the magnetism of the rotor and reduce the hysteresis effect of the motor for saving the energy. Moreover, the system and method of the present disclosure can further increase rotor speed over the predetermined value by the control module. 
         [0040]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.