Patent Publication Number: US-2023163672-A1

Title: Method for controlling outputs of electric motors

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electric motors, and particularly to a method for controlling the outputs of electric motors. 
     2. Description of the Related Art 
     At present, devices that require electric motors to provide different output powers, such as compressors of air conditioners, are usually achieved by means of a variable-frequency drive. However, the time from starting to the rated load of an electric motor equipped with a variable-frequency drive is usually longer than that of a non-installed one, so it consumes more electric energy. In addition, a variable-frequency drive usually includes rectification (AC to DC), filtering, inverter (DC to AC), braking unit, drive unit, detection unit micro-processing unit, etc., so it is very costly in manufacturing. Taiwan Patent No. 1619886 disclosed an improved compressor to solve the aforementioned disadvantages. The compressor does not use a variable-frequency drive but provides two sets of operating windings with different output power and a switch which connects respectively an external electrical power source to each set of the operating windings to provide different output power. However, this improved compressor just provides two different output powers, so it is impracticability. 
     One of the objectives of the present invention is to provide a method for controlling the outputs of electric motors. This method does not use a variable-frequency drive, and can provide a variety of output modes to supply different loading states. 
     SUMMARY OF THE INVENTION 
     Thus, one method for controlling the outputs of electric motors according to the present invention comprises a step of providing at least an electric motor comprising a stator, a rotor being rotatable relative to the stator, the stator including a plurality of stator slots, a plurality of stator teeth, and a stator winding unit being wound on the stator teeth and installed in the stator slots. The stator winding unit is selected from a first winding group, a second winding group, a third winding group and a fourth winding group. The first winding group comprises a first primary winding with a first number of poles and a first rated power and a first secondary winding with the first number of poles and a second rated power being smaller than the first rated power. The second winding group comprises a second primary winding with a second number of poles and a third rated power, and a second secondary winding with a third number of poles and a fourth rated power being smaller than the third rated power. The third winding group comprises a third primary winding with a fourth number of poles and a fifth rated power, a fourth primary winding with a fifth number of poles and a sixth rated power being smaller than the fifth rated power, a third secondary winding with the fourth number of poles and a seventh rated power being smaller than the fifth rated power, and a fourth secondary winding with the fifth number of poles and an eighth rated power being smaller than the sixth rated power. The fourth winding group comprises a fifth primary winding with a sixth number of poles and a ninth rated power, a fifth secondary winding with the sixth number of poles and a tenth rated power being smaller than the ninth rated power, and a sixth second secondary winding with the sixth number of poles and an eleventh rated power being smaller than the tenth rated power. The method for controlling the outputs of electric motors further comprises another step of providing a first control device respectively coupled with the electric motor and an external electrical power source for sensing a needed loading state of the electric motor and suppling a required connection relationship between the stator winding unit and the external electrical power source based on the needed loading state sensed by the first control device. The required connection relationship between the stator winding unit and the external electrical power source selected from one of the following connection relationships: when the stator winding unit comprises the first winding group, and the first control device senses a first needed loading state, the first primary winding and the first secondary winding are simultaneously connected to the external electrical power source; when the stator winding unit comprises the first winding group, and the first control device senses a second needed loading state being smaller than the first needed loading state, only the first primary winding is connected to the external electrical power source; when the stator winding unit comprises the second winding group, and the first control device senses a third needed loading state, the second primary winding is connected to the external electrical power source; when the stator winding unit comprises the second winding group, and the first control device senses a fourth needed loading state being smaller than the third needed loading state, the second secondary winding is connected to the external electrical power source; when the stator winding unit comprises the third winding group, and the first control device senses a fifth needed loading state, the third primary winding and the third secondary winding are connected to the external electrical power source; when the stator winding unit comprises the third winding group, and the first control device senses a sixth needed loading state being smaller than the fifth needed loading state, only the third primary winding is connected to the external electrical power source; when the stator winding unit comprises the third winding group, and the first control device senses a seventh needed loading state, the fourth primary winding and the fourth secondary winding are connected to the external electrical power source; when the stator winding unit comprises the third winding group, and the first control device senses an eighth needed loading state being smaller than the seventh needed loading state, only the fourth primary winding is connected to the external electrical power source; when the stator winding unit comprises the fourth winding group, and the first control device senses a ninth needed loading state, the fifth primary winding, the fifth secondary winding and the sixth secondary winding are connected to the external electrical power source; when the stator winding unit comprises the fourth winding group, and the first control device senses a tenth needed loading state being smaller than the ninth needed loading state, the fifth primary winding and the fifth secondary winding are connected to the external electrical power source; when the stator winding unit comprises the fourth winding group, and the first control device senses a eleventh needed loading state being smaller than the tenth needed loading state, the fifth primary winding and the sixth secondary winding are connected to the external electrical power source; and when the stator winding unit comprises the fourth winding group, and the first control device senses a twelfth needed loading state being smaller than the eleventh needed loading state, only the fifth primary winding is connected to the external electrical power source. 
     It must be mentioned here that the number of poles refers to the number of magnetic poles contained in each phase of an electric motor. 
     Another method for controlling the outputs of electric motors according to the present invention is that the first control device comprises a sensing unit coupled with the electric motor for sensing a needed loading state thereof, and a controlling unit respectively coupled with the electric motor and an external electrical power source for suppling a required connection relationship between the stator winding unit and the external electrical power source based on the sensed loading state of the sensing unit. 
     Another method for controlling the outputs of electric motors according to the present invention comprises the steps of: providing a first electric motor comprising a first stator, a first rotor being rotatable relative to the first stator, the first stator including a plurality of first stator slots, a plurality of first stator teeth, and a first stator winding unit being wound on the first stator teeth and installed in the first stator slots, the first stator winding unit comprising a first winding group comprising a first primary winding with a first number of poles and a first rated power and a first secondary winding with the first number of poles and a second rated power being smaller than the first rated power; providing a second electric motor comprising a second stator, a second rotor being rotatable relative to the second stator, the second stator including a plurality of second stator slots, a plurality of second stator teeth, and a second stator winding unit being wound on the second stator teeth and installed in the second stator slots, the second stator winding unit comprising a second winding group comprising a second primary winding with the first number of poles and a third rated power and a second secondary winding with the first number of poles and a fourth second rated power being smaller than the third rated power; and providing a second control device respectively coupled with the first electric motor, the second electric motor and an external electrical power source for sensing a needed loading state of the first and second electric motors and suppling a required connection relationship between the first stator winding unit, the second stator winding unit and the external electrical power source based on the needed loading state sensed by the second control device, the required connection relationship between the first stator winding unit, the second stator winding unit and the external electrical power source selected from one of the following connection relationships: when the second control device senses a first needed loading state, the first primary winding, the first secondary winding, the second primary winding and the second secondary winding are simultaneously connected to the external electrical power source; when the second control device senses a second needed loading state, the first primary winding and the second primary winding are simultaneously connected to the external electrical power source; when the second control device senses a third needed loading state, the first primary winding and the first secondary winding are simultaneously connected to the external electrical power source; when the second control device senses a fourth needed loading state, only the first primary winding or the second primary winding is connected to the external electrical power source; and when the second control device senses a fifth needed loading state, only the first secondary winding or the second secondary winding is connected to the external electrical power source. 
     Another method for controlling the outputs of electric motors according to the present invention comprises the steps of providing a third electric motor comprising a third stator, a third rotor being rotatable relative to the third stator, the third stator including a plurality of third stator slots, a plurality of third stator teeth, and a third stator winding unit being wound on the third stator teeth and installed in the third stator slots, the third stator winding unit comprising a third winding group comprising a third primary winding with a third number of poles and a third rated power and a third secondary winding with the third number of poles and a fourth rated power being smaller than the third rated power; providing a fourth electric motor comprising a fourth stator, a fourth rotor being rotatable relative to the fourth stator, the fourth stator including a plurality of fourth stator slots, a plurality of fourth stator teeth, and a fourth stator winding unit being wound on the fourth stator teeth and installed in the fourth stator slots, the fourth stator winding unit comprising a fourth winding group comprising a fourth primary winding with a fourth number of poles and a fifth rated power and a fourth secondary winding with a fifth number of poles and a sixth rated power being smaller than the fifth rated power; and providing a third control device respectively coupled with the third electric motor, the fourth electric motor and an external electrical power source for sensing a needed loading state of the third and fourth electric motors and suppling a required connection relationship between the third stator winding unit, the fourth stator winding unit and the external electrical power source based on the needed loading state sensed by third control device, the required connection relationship between the third stator winding unit, the fourth stator winding unit and the external electrical power source selected from one of the following connection relationships; when the third control device senses a first needed loading state, the third primary winding and the third secondary winding are simultaneously connected to the external electrical power source; when the third control device senses a second needed loading state, only the third primary winding is connected to the external electrical power source; when the third control device senses a third needed loading state, only the third secondary winding is connected to the external electrical power source; when the third control device senses a fourth needed loading state, only the fourth primary winding is connected to the external electrical power source; and when the third control device senses a fifth needed loading state, only the fourth secondary winding is connected to the external electrical power source. 
     Another method for controlling the outputs of electric motors according to the present invention comprises the steps of: providing a fifth electric motor comprising a fifth stator, a fifth rotor being rotatable relative to the fifth stator, the fifth stator including a plurality of fifth stator slots, a plurality of fifth stator teeth, and a fifth stator winding unit being wound on the fifth stator teeth and installed in the fifth stator slots, the fifth stator winding unit comprising a fifth winding group comprising a fifth primary winding with a sixth number of poles and a seventh rated power and a fifth secondary winding with the sixth number of poles and a eighth rated power being smaller than the seventh rated power; providing a sixth electric motor comprising a sixth stator, a sixth rotor being rotatable relative to the sixth stator, the sixth stator including a plurality of sixth stator slots, a plurality of sixth stator teeth, and a sixth stator winding unit being wound on the sixth stator teeth and installed in the sixth stator slots, the sixth stator winding unit comprising a sixth winding group comprising a sixth primary winding with the sixth number of poles and a ninth rated power, a sixth secondary winding with the sixth number of poles and a tenth rated power being smaller than the ninth rated power, a seventh primary winding with a seventh number of poles and a eleventh rated power, a seventh secondary winding with the seventh number of poles and a twelfth rated power being smaller than the eleventh rated power; providing a fifth control device respectively coupled with the fifth electric motor, the sixth electric motor and an external electrical power source for sensing a needed loading state of the fifth and sixth electric motors, and suppling a required connection relationship between the fifth stator winding unit, the sixth stator winding unit and the external electrical power source based on the needed loading state sensed by the fourth control device; the required connection relationship between the fifth stator winding unit, the sixth stator winding unit and the external electrical power source selected from one of the following connection relationships; when the fourth control device senses a first needed loading state, the fifth primary winding, the fifth secondary winding, the sixth primary winding and the sixth secondary winding are simultaneously connected to the external electrical power source; when the fourth control device senses a second needed loading state, the fifth primary winding and the fifth secondary winding are simultaneously connected to the external electrical power source; when the fourth control device senses a third needed loading state, the sixth primary winding and the sixth secondary winding are simultaneously connected to the external electrical power source; when the fourth control device senses a fourth needed loading state, the fifth primary winding and the sixth primary winding are simultaneously connected to the external electrical power source; when the fourth control device senses a fifth needed loading state, the seventh primary winding and the seventh secondary winding are simultaneously connected to the external electrical power source; when the fourth control device senses a sixth needed loading state, only the fifth primary winding is connected to the external electrical power source; when the fourth control device senses a seventh needed loading state, only the sixth primary winding is connected to the external electrical power source; when the fourth control device senses an eighth needed loading state, only the seventh primary winding is connected to the external electrical power source; when the fourth control device senses a ninth needed loading state, only the fifth secondary winding is connected to the external electrical power source; when the fourth control device senses a tenth needed loading state, only the sixth secondary winding is connected to the external electrical power source; and when the fourth control device senses a eleventh needed loading state, only the seventh secondary winding is connected to the external electrical power source. 
     Another method for controlling the outputs of electric motors according to the present invention comprises the steps of; providing a seventh electric motor comprising a seventh stator, a seventh rotor being rotatable relative to the seventh stator, the seventh stator including a plurality of seventh stator slots, a plurality of seventh stator teeth, and a seventh stator winding unit being wound on the seventh stator teeth and installed in the seventh stator slots, the seventh stator winding unit comprising a seventh winding group comprising a seventh primary winding with an eighth number of poles and a twelfth rated power and a seventh secondary winding with the eighth number of poles and a thirteenth rated power being smaller than the twelfth rated power, providing an eighth electric motor comprising an eighth stator, an eighth rotor being rotatable relative to the eighth stator, the eighth stator including a plurality of eighth stator slots, a plurality of eighth stator teeth, and an eighth stator winding unit being wound on the eighth stator teeth and installed in the eighth stator slots, the eighth stator winding unit comprising an eighth winding group comprising an eighth primary winding with the eighth number of poles and a fourteenth rated power, an eighth secondary winding with the eighth number of poles and a fifteenth rated power being smaller than the fourteenth rated power, a ninth secondary winding with the eighth number of poles and a sixteenth rated power being smaller than the fifteenth rated power; and providing a sixth control device respectively coupled with the seventh electric motor, the eighth electric motor and an external electrical power source for sensing a needed loading state of the seventh and eighth electric motors, and suppling a required connection relationship between the seventh stator winding unit, the eighth stator winding unit and the external electrical power source based on the needed loading state sensed by the sixth control device; the required connection relationship between the seventh stator winding unit, the eighth stator winding unit and the external electrical power source selected from one of the following connection relationships; when the sixth control device senses a first needed loading state, the seventh primary winding, the seventh secondary winding, the eighth primary winding primary winding, the eighth secondary winding and the ninth secondary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses a second needed loading state, the seventh primary winding and the eighth primary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses a third needed loading state, the seventh primary winding and the seventh secondary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses a fourth needed loading state, the eighth primary winding, the eighth secondary winding and the ninth secondary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses a fifth needed loading state, only the seventh primary winding is connected to the external electrical power source; when the sixth control device control device senses a sixth needed loading state, only the seventh secondary winding is connected to the external electrical power source; when the sixth control device control device senses a seventh needed loading state, the eighth primary winding and the eighth secondary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses an eighth needed loading state, the eighth primary winding and the ninth secondary winding are simultaneously connected to the external electrical power source; when the sixth control device control device senses a ninth needed loading state, only the eighth primary winding is connected to the external electrical power source; when the sixth control device control device senses a tenth needed loading state, only the eighth secondary winding is connected to the external electrical power source; and when the sixth control device control device senses an eleventh needed loading state, only the ninth secondary winding is connected to the external electrical power source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG.  1    is a cross-sectional view of a first electric motor according to a first preferred embodiment of the present invention; 
         FIG.  2    is a schematic view of the winding pattern of a stator winding unit of the first electric motor; 
         FIG.  3    is a schematic view of the electric circuit of a stator winding unit of the first electric motor; 
         FIG.  4    is a block diagram illustrating the electric power connection of the first preferred embodiment; 
         FIG.  5    is a comparing chart of energy consumption between the first preferred embodiment and the three-phase induction motor thereof when controlled by a variable-frequency drive: 
         FIG.  6    is a block diagram illustrating the electric power connection of a third preferred embodiment of the present invention: 
         FIG.  7    is a schematic view of the winding pattern of a stator winding unit of the third preferred embodiment; 
         FIG.  8    is a cross-sectional view of an electric motor according to a fourth preferred embodiment of the present invention; 
         FIG.  9    is a block diagram illustrating the electric power connection of a fifth preferred embodiment of the present invention; and 
         FIG.  10    is a block diagram illustrating the electric power connection of a sixth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to  FIG.  1    to  FIG.  4   , a first electric motor  10  according to a first preferred embodiment of the present invention is shown comprising a rotor unit  12  and a stator unit  14 . The rotor unit  12  rotates relative to the stator unit  14 . The stator unit  14  includes a stator core  16 , a stator winding unit  18  and a through hole  19  inserted through by the rotor unit  12 . The stator core  16  includes thirty-six first stator slots  160  and first stator teeth  162  defined by two adjacent first stator slots  160 . In this embodiment, the stator winding unit  18  is a first winding group (the following is also indicated by  18 ). The first winding group  18  is wound on each of the first stator teeth  162  and installed in each of the first stator slots  160 . The first winding group  18  comprises a primary winding  180  and a secondary winding  182 . The primary winding  180  has four poles and 20 HP rated power. The secondary winding  182  also has four poles but only has 2.5 HP rated power. The pole pitch of the primary winding  180  and the secondary winding  182  are both nine (as shown in  FIG.  2   ). The difference between the rated power of the primary windings  180  and the secondary windings  182  can be achieved by the wire diameter or the number of turns of windings. In more detail, as shown in  FIG.  3   , in this embodiment, the primary windings  180  includes an R-phase primary winding  1800 , an S-phase primary winding  1802 , and a T-phase primary winding  1804 , which are connected in a Y-shape. The secondary winding  182  includes an R-phase secondary winding  1820 , an S-phase secondary winding  1822 , and a T-phase secondary winding  1824 , which are also connected in a Y-shape. 
     In addition, in this embodiment, a first control device  100  is provided, which can be a programmable logic controller (PLC). The first control device  100  comprises a first sensing unit  102  and a first controlling unit  104 . The first sensing unit  102  is respectively coupled with the electric motor  10  and the first controlling unit  104 . The first controlling unit  104  is respectively coupled with the electric motor  10  and an external electrical power source  200 . The sensing unit  102  will sense a needed loading state of the electric motor  10  and send it to the controlling unit  104 . The controlling unit  104  will supply a required connection relationship between the stator winding unit  18  and the external electrical power source  200  based on the needed loading states sensed by the sensing unit  102 . In this embodiment, the first control unit  104  may include a plurality of first switches S 1  disposed between the secondary winding  182  and the external electrical power source. In more detail, as shown in  FIG.  3   , the external electrical power source  200  has an R-phase output end, an S-phase output end and a T-phase output end, which are connected respectively to the control unit  104 . The R-phase primary winding  1800  is directly connected to the R-phase output end via a line A, the S-phase primary winding  1802  is directly connected to the S-phase output end via a line B. and the T-phase primary windings  1804  is directly connected to the T-phase output end via a line C. The R-phase secondary winding  1820  is connected to the R-phase output via a line D with the first switch S 1 , the S-phase secondary winding  1822  is connected to the S-phase output via a line E with the first switch S 1 , and the T-phase secondary winding  1824  is connected to the T-phase output via a line F with the first switch S 1 . When the sensing unit  102  senses that the electric motor  10  needs to operate in a first needed loading state, such as 22.5 HP, the control unit  104  connects each first switch S 1  to the external electrical power source  200  at the same time. At this time, the primary winding  180  and the secondary winding  182  are simultaneously connected to the external electrical power source  200  for suppling the first needed loading state. When the sensing unit  102  senses that the electric motor  10  only needs to operate under a second needed loading state that is smaller than the first loading state, such as 20 HP, each of the switches S 1  of the control unit  104  is shut off. At this time, only the primary winding  180  is connected to the external electrical power source  200  for suppling the second loading state. 
     To show the advantages of the present invention, please referring to  FIG.  5   , it shows that in a practical operation, the energy consumption of the first preferred embodiment of the present invention and the three-phase induction motor of the first preferred embodiment when controlled by a variable-frequency drive (hereinafter referred to as the prior art). In this operation, the external electrical power source  200  has a voltage of 220 volts and a frequency of 60 Hz. The vertical axis of  FIG.  5    shows the current I, and the unit is ampere. The horizontal axis of  FIG.  5    shows the time T, and the unit is second. And, the energy consumption formula used here is W=IVT (where I is current, V is voltage, and T is time). 
     The curve represented by the dotted line in  FIG.  5    shows the energy consumption of the prior art from an unstarted state to a started state, from the starting state to a fully loading state, and from the fully loading state to an unloading state. It can be seen from the dotted line curve that the prior art takes about 8 seconds from the unstarted state to the started state (that is, from point A to point E), and the average current used is 25 amperes; takes about 12 seconds from the started state to the fully loading state (that is, from point E to point F), and the average use current is (25+48)/2=36.5 amperes; and takes about 5 seconds from the fully loading state to the unloading state (that is, from point F to point G), and the average use current is (48+9)/2=28.5 seconds. According to this data, the electric energy consumed during this period is 
         W   P =25×220×8+36.5×220−12+28.5×220×5=171,710 joules.
 
     The curve represented by the solid line in  FIG.  5    shows the energy consumption of the electric motor  10  controlled by the first preferred embodiment of the present invention from an unstarted state to a started state, from the starting state to a fully loading state, and from the fully loading state to an unloading state. It can be seen from the solid line curve that the electric motor  10  takes about 4 seconds from the unstarted state to the started state (that is, from point A to point B), and the average current used is 48 amperes; takes about 8 seconds from the started state to the fully loading state (that is, from point B to point C), takes about 2 seconds from the fully loading state to the unloading state (that is, from point C to point D), and the average use current is (48+7)/2=27.5 amperes; and the electric motor  10  lasts for about 15 seconds (that is, from point D to point G), and the average current used is 7 amperes. According to this data, the electric energy consumed during this period is 
         Wi= 48×220×4+48×220×4+27.5×220×2+7×220×15=119,680 joules
 
     Thus, from the data shown in  FIG.  5   , it can be proved that under the same operating conditions, the electric motor  10  controlled by of the present invention can indeed reduce the consumed electric energy compared with the prior art. The reduced electric energy is about 52,030 joules, which is about 30% of the electric energy consumed by the prior art. 
     The following is a second preferred embodiment of the present invention. The electric motor provided in the second preferred embodiment is a three-phase induction motor as provided in the first preferred embodiment. As shown in  FIG.  1   , the difference between the first and second preferred embodiment is that the stator winding unit of the electric motor in the second preferred embodiment comprises a second winding group  18 ′. The second winding group  18 ′ includes a primary winding  180 ′ and a secondary winding  182 ′. The primary winding  180 ′ has four magnetic poles and 20 HP rated power. When the frequency of the external electrical power source  200  is 60 Hz, the rotating speed of the electric motor is 1800 rpm. The secondary winding  182 ′ has twelve magnetic poles and 2.5 HP. When the frequency of the external electrical power source  200  is 60 Hz, the rotating speed of the electric motor is 600 rpm. Whereby, when the first control device  100  senses that the electric motor needs to operate in a first needed loading state, only the primary winding  180 ′ is connected with the external electrical power source  200 , and when the first control device  100  senses that the electric motor needs to operate in a second needed loading state, only the secondary winding  182 ′ is connected with the external electrical power source  200 . 
     Next, as shown in  FIGS.  6  and  7   , a third preferred embodiment of the present invention is disclosed. An electric motor  20  provided in the third preferred embodiment is also a three-phase induction motor as provided in the first preferred embodiment. The difference between the first and third preferred embodiments is that a stator winding unit  22  of the electric motor  20  in the third preferred embodiment comprises a third winding group (the following is also indicated by  22 ). The third winding group  22  comprises a first primary winding  220 , a second primary winding  222 , a first secondary winding  224  and a second secondary winding  226 . The first primary winding  220  and the first secondary winding  224  both have a fourth number of poles, such as four, but the rated power of the first secondary winding  224  is smaller than that of the first primary winding  220 . The second primary winding  222  and the second secondary winding  226  both has a fifth number of poles, such as twelve, but the rated power of the second secondary winding  226  is smaller than that of the second primary winding  220 . In this embodiment, the rated power of the second primary winding  222  is smaller than that of the first primary winding  220 . 
     In more detail, the first primary winding  220  includes an R-phase first primary winding  2200 , an S-phase first primary winding  2202 , and a T-phase first primary winding  2204 , which are connected in a Y-shape. The first secondary winding  224  includes an R-phase first secondary winding  2240 , an S-phase first secondary winding  2242 , and a T-phase first secondary winding  2244 , which are also connected in a Y-shape. The second primary winding  222  includes an R-phase second primary winding  2220 , an S-phase second primary winding  2222 , and a T-phase second primary winding  2224 , which are connected in a Y-shape. The second secondary winding  226  includes an R-phase second secondary winding  2260 , an S-phase second secondary winding  2262 , and a T-phase second secondary winding  2264 , which are also connected in a Y-shape. The first primary winding  220  and the first second primary winding  222  are connected in parallel. The first secondary winding  224  and the second secondary winding  226  are also connected in parallel. 
     The third embodiment of the present invention provides a second control device  300  comprising a second sensing unit  302  and a second controlling unit  304 . The second sensing unit  302  is respectively coupled with the electric motor  20  and the second controlling unit  304 . The second controlling unit  304  is respectively coupled with the electric motor  20  and a three phase external electrical power source  200 . Similarly, the second sensing unit  302  will sense a needed loading state of the electric motor  20  and send it to the second controlling unit  304 . The controlling unit  304  will supply a required connection relationship between the third winding group  22  and the external electrical power source  200  based on the needed loading states sensed by the second sensing unit  302 . 
     In this embodiment, the second controlling unit  304  comprises a first switch S 1 , a second switch S 2 , a third switch S 3 , a fourth switch S 4 , a fifth switch S 5  and a sixth switch S 6 . The R-phase first primary winding  2200  is connected to the R-phase output via an A 1  line with the first switch S 1  and the third switch S 3 . The S-phase first primary winding  2202  is connected to the S-phase output via a B 1  line with the first switch S 1  and the third switch S 3 , and the T-phase first primary winding  2204  is connected to the T-phase output via a C 1  line with the first switch S 1  and the third switch S 3 . The R-phase first secondary winding  2240  is connected to the R-phase output via a D 1  line with the second switch S 2  and the third switch S 3 . The S-phase first secondary winding  2242  is connected to the S-phase output via a E 1  line with the second switch S 2  and the third switch S 3 , and the T-phase first secondary winding  2244  is connected to the T-phase output via an F 1  line with the second switch S 2  and the third switch S 3 . The R-phase second primary winding  2220  is connected to the R-phase output via a A 2  line with the fourth switch S 4  and the fifth switch S 5 . The S-phase second primary winding  2222  is connected to the S-phase output via a B 2  line with the fourth switch S 4  and the fifth switch S 5 , and the T-phase second primary winding  2224  is connected to the T-phase output via a C 2  line with the fourth switch S 4  and the fifth switch S 5 . The R-phase second secondary winding  2260  is connected to the R-phase output via a D 2  line with the fourth switch S 4  and the sixth switch S 6 . The S-phase second secondary winding  2262  is connected to the S-phase output via a E 2  line with the fourth switch S 4  and the sixth switch S 6 , and the T-phase second secondary winding  2264  is connected to the T-phase output via an F 2  line with the fourth switch S 4  and the sixth switch S 6 . 
     When the sensing unit  302  senses that the electric motor  20  needs to operate in a first loading state, the control unit  304  will make the first switch S 1 , the second switch S 2 , and the third switch S 3  on and fourth switch S 4  off. At this time, the first primary winding  220  and the first second primary winding  222  will be connected to the external electrical power source  200  at the same time to supply the power needed by the first loading state. When the sensing unit  302  senses that the electric motor  20  needs to operate in a second loading state, the control unit  304  will make the first switch S 1  and the third switch S 3  on, the second switch S 2  and fourth switch S 4  off. At this time, only the first primary winding  220  will be connected to the external electrical power source  200  to supply the power needed by the second loading state. When the sensing unit  302  senses that the electric motor  20  needs to operate in a third loading state, the control unit  304  will make fourth switch S 4 , the fifth switch S 5  and the sixth switch S 6  on, and the third switch S 3  off. At this time, the second primary winding  222  and the second secondary winding  226  will be connected to the external electrical power source  200  at the same time to supply the power needed by the third loading state. And when the sensing unit  302  senses that the electric motor  20  needs to operate in a fourth loading state, the control unit  304  will make fourth switch S 4  and the fifth switch S 5  on, and the third switch S 3  and the sixth switch S 6  off. At this time, only the second primary winding  222  will be connected to the external electrical power source  200  to supply the power needed by the fourth loading state. 
     Then, as shown in  FIG.  8   , a fourth preferred embodiment of the present invention is disclosed. An electric motor  40  provided in the fourth preferred embodiment is also a three-phase induction motor as provided in the first preferred embodiment. The difference between the first and fourth preferred embodiment is that a stator winding unit  42  of the electric motor  40  in the fourth preferred embodiment comprises a fourth winding group (the following is also indicated by  42 ). The fourth winding group  42  comprises a first primary winding  420 , a first secondary winding  422  and a second secondary winding  424 . The first primary winding  420 , the first secondary winding  422  and the second secondary winding  424  all have a fourth number of poles, such as four, but the rated power of the first secondary winding  422  is smaller than that of the first primary winding  420  and the rated power of the second secondary winding  424  is smaller than that of the first secondary winding  422 . When the frequency of the external electrical power source  200  is 60 Hz, the rotating speed of the electric motor  40  is 1800 rpm. The fourth preferred embodiment similarly provides a control device respectively coupled with the electric motor  40  and an external electrical power source for sensing a needed different loading state of the electric motor  40  and suppling a required connection relationship between the stator winding unit  42  and the external electrical power source based on the needed loading state sensed by the control device. For example, when the control device senses that the electric motor  40  needs to operate in a first loading state, it will make the first primary winding  420 , the first secondary winding  422  and the second secondary winding  424  all connect to the external electrical power source at the same time to supply the power required by the first loading state. When the control device senses that the electric motor  40  needs to operate in a second loading state, it will make the first primary winding  420  and the first secondary winding  422  connect to the external electrical power source at the same time to supply the power required by the second loading state. When the control device senses that the electric motor  40  needs to operate in a third loading state, it will make the first primary winding  420  and the second secondary winding  424  connect to the external electrical power source at the same time to supply the power required by the third loading state. And w % ben the control device senses that the electric motor  40  needs to operate in a fourth loading state, it will make only the first primary winding  420  connect to the external electrical power source at the same time to supply the power required by the fourth loading state. 
     Next, as shown in  FIG.  9   , a fifth preferred embodiment of the present invention is disclosed. The fifth preferred embodiment provides a fifth electric motor and a sixth electric motor  60 . The fifth electric motor  50  and the sixth electric motor  60  are also a three-phase induction motor as provided in the first preferred embodiment. The fifth electric motor  50  here comprises a fifth stator winding unit including the first winding group with four magnetic poles, a first primary rated power and a first secondary rated power being smaller than the first primary rated power. The sixth electric motor  60  here comprises a sixth stator winding unit including the first winding group with four magnetic poles, a second primary rated power and a second secondary rated power being smaller than the second primary rated power. 
     The external electrical power source  200  is connected to each of the electric motors  50 ,  60  via a fourth control device  400  comprising a fourth sensing unit  402  and a fourth controlling unit  404 . In more detail, the fourth sensing unit  402  is respectively coupled with each of the electric motors  50 , 60  and the second controlling unit  404 . The fourth control unit  404  is connected to a primary winding of the fifth electric motor  50  via lines A 3 , B 3 , and C 3 , and connected to a secondary winding of the fifth electric motor  50  via D 3 , E 3 , and F 3 . And the fourth control unit  404  is connected to a primary winding of the sixth electric motor  60  via lines A 4 , B 4 , and C 4 , and connected to a secondary winding of the sixth electric motor  60  via lines D 4 , E 4 , and F 4 . 
     Thereby, the fifth preferred embodiment will have at least five different power outputs. Please refer to the following table: 
     
       
         
           
               
               
               
            
               
                   
                   
               
               
                   
                 the fifth electric 
                 the sixth electric 
               
               
                   
                 motor 50 
                 motor 60 
               
            
           
           
               
               
               
               
               
            
               
                   
                 primary 
                 secondary 
                 primary 
                 secondary 
               
               
                   
                 winding 
                 winding 
                 winding 
                 winding 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 start up 
                 ON 
                 ON 
                 ON 
                 ON 
               
               
                 First loading state 
                 ON 
               
               
                 Second loading state 
                   
                 ON 
               
               
                 Third loading state 
                 ON 
                 ON 
               
               
                 Fourth loading state 
                   
                   
                 ON 
               
               
                 Fifth loading state 
                   
                   
                   
                 ON 
               
               
                   
               
            
           
         
       
     
     It can be seen from the above table that when the control device  400  senses that a needed loading is in the starting up state, the first winding group of the electric motors  50 ,  60  are simultaneously connected to the external electrical power source  200 . When the control device  400  senses a first needed loading state, only the primary winding of the electric motor  50  is connected to the external electrical power source  200 . When the control device  400  senses a second needed loading state, only the secondary winding of the electric motors  50  is connected to the external electrical power source  200 . When the control device  400  senses a third needed loading state needed, the first winding and the secondary winding of the electric motor  50  are simultaneously connected to the external electrical power source  200 . When the control device  400  senses a fourth needed loading state, only the primary winding of the electric motor  60  is connected to the external electrical power source  200 . And when the control device  400  senses a fifth needed loading state, only the secondary winding of the electric motors  60  is connected to the external electrical power source  200 . It must be mentioned here that the fifth preferred embodiment of the present invention can be used in an air-conditioning compressor or similar devices, for example, the two ends of an output shaft of an air-conditioning compressor can be respectively coupled with a fifth electric motor  50  and a sixth electric motor  60 . 
     Lastly, as shown in  FIG.  10   , a sixth preferred embodiment of the present invention is disclosed. The sixth preferred embodiment provides four three-phase induction motors as provided in the first preferred embodiment, that is, a seventh electric motor  70 , an eighth electric motor  72 , a ninth electric motor  74  and a tenth electric motor  76 . Each of the electric motors  70 ,  72 ,  74  and  76  includes a stator winding unit including the first winding group with four magnetic poles. The first winding group of the seventh electric motor  70  has a first primary rated power and a first secondary rated power being smaller than the first primary rated power. The first winding group of the eighth electric motor  72  has a second primary rated power and a second secondary rated power being smaller than the second primary rated power. The second primary rated power may be the same as or different from the first primary rated power, and the second secondary rated power may be the same or different from the first secondary rated power. The first winding group of the ninth electric motor  74  has a third primary rated power and a third secondary rated power being smaller than the third primary rated power. The third primary rated power can be the same as or different from the first primary rated power and the second primary rated power, and the third secondary rated power may be the same as or different from the first secondary rated power and the second secondary rated power. The first winding group of the tenth electric motor  76  has a fourth primary rated power and a fourth secondary rated power being smaller than the fourth primary rated power. The fourth primary rated power can be the same as or different from the first primary rated power, the second primary rated power and the third primary rated power, and the fourth secondary rated power may be the same as or different from the first secondary rated power, the second secondary rated power and the third secondary rated power. 
     In this embodiment, the external electrical power source  200  is connected to each of the electric motors  70 , 72 , 74  and  76  via a fifth control device  500  comprising a fifth sensing unit  502  and a fifth controlling unit  504 . In more detail, the fifth sensing unit  502  is respectively coupled with each of the electric motors  70 , 72 , 74  and  76  and the fifth controlling unit  504 . The fourth control unit  504  is connected to a primary winding of the seventh electric motor  70  via lines A 5 , B 5 , and C 5 , and connected to a secondary winding of the seventh electric motor  70  via D 5 , E 5 , and F 5 . The fifth control unit  504  is connected to a primary winding of the eighth electric motor  72  via lines A 6 . B 6 , and C 6 , and connected to a secondary winding of the eighth electric motor  72  via lines D 6 , E 6 , and F 6 . The fifth control unit  504  is connected to a primary winding of the ninth electric motor  74  via lines A 7 , B 7 , and C 7 , and connected to a secondary winding of the ninth electric motor  74  via lines D 7 , E 7  and F 7 . And the fifth control unit  504  is connected to a primary winding of the tenth electric motor  76  via lines A 8 , B 8 , and C 8 , and connected to a secondary winding of the tenth electric motor  76  via lines D 8 , E 8 , and F 8 . Thereby, the sixth preferred embodiment will have at least seven different power outputs. Please refer to the following table: 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 The seventh electric 
                 The eighth electric 
                 The ninth electric 
                 The tenth electric 
               
               
                   
                 motor 70 
                 motor 72 
                 motor 74 
                 motor 76 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 primary 
                 secondary 
                 primary 
                 secondary 
                 primary 
                 secondary 
                 primary 
                 secondary 
               
               
                   
                 winding 
                 winding 
                 winding 
                 winding 
                 winding 
                 winding 
                 winding 
                 winding 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 start up 
                 ON 
                   
                 ON 
                   
                 ON 
                   
                 ON 
                   
               
               
                 First loading 
                 ON 
                   
                 ON 
               
               
                 state 
               
               
                 Second loading 
                   
                 ON 
                   
                 ON 
               
               
                 state 
               
               
                 Third loading 
                   
                   
                   
                   
                 ON 
               
               
                 state 
               
               
                 Fourth loading 
                   
                   
                   
                   
                   
                   
                 ON 
               
               
                 state 
               
               
                 Fifth loading 
                   
                   
                   
                   
                   
                 ON 
               
               
                 state 
               
               
                 Sixth loading 
                   
                   
                   
                   
                   
                   
                   
                 ON 
               
               
                 state 
               
               
                   
               
            
           
         
       
     
     It can be seen from the above table that w % ben the control device  500  senses that a needed loading is in the starting up state, the primary winding of each of the electric motors  70 , 72 , 74  and  76  are simultaneously connected to the external electrical power source  200 . When the control device  500  senses a first needed loading state, only the primary winding of the electric motors  70  and  72  are connected to the external electrical power source  200 . When the control device  500  senses a second needed loading state, the secondary winding of each of the electric motors  70 , 72 , 74  and  76  are simultaneously connected to the external electrical power source  200 . When the control device  500  senses a third needed loading state needed, only the primary winding of the ninth electric motor  74  is connected to the external electrical power source  200 . When the control device  500  senses a fourth needed loading state needed, only the primary winding of the tenth electric motor  76  is connected to the external electrical power source  200 . When the control device  500  senses a fifth needed loading state needed, only the secondary winding of the ninth electric motor  74  is connected to the external electrical power source  200 . And when the control device  500  senses a sixth needed loading state needed, only the secondary winding of the tenth electric motor  76  is connected to the external electrical power source  200 . It must be mentioned here that the sixth preferred embodiment of the present invention can be used in electric vehicles or similar devices.