Abstract:
A drive system powers a six-phase AC induction motor having a plurality of poles and a stator with a plurality of teeth where the number of teeth divided by six times the number of poles equals an integer number. The stator core has first and second groups of three-phase stator windings. The second group of three-phase windings is separated spatially by 30 electrical degrees from the first group. A first power supply is connectable to the first group of three-phase windings. A second power supply is connectable to the second group of three-phase windings. The second power supply provides power to the second group of three-phase windings that is shifted by 30 electrical degrees in time with respect to the first power supply. The first and second power supplies receive signals from identical pulse width modulator generators. The respective first and second pulse width modulator generators receive commands from one controller.

Description:
BACKGROUND AND SUMMARY 
     The following disclosure relates to a six-phase AC induction motor drive system. Specifically, the disclosure relates to a drive for a six-phase motor which has a single controller configuration that sends command signals to respective pulse width modulator generators associated with two three-phase power base drive sections. 
       FIG. 1  shows a drawing of a drive system for a six-phase AC induction motor utilizing a master and follower architecture for controlling the pulse width modulator generators associated with the drive system. The two drives are each controlled by their respective controller. Command signals are sent to each power base drive section by a respective controller. The follower controller receives command signals from the master controller, and subsequently provides command signals to its pulse width modulator generator in a shift of 30 electrical degrees in time. Although the master and follower controllers and the power base drive sections may be same model type provided by the same manufacturer, and the follower controller theoretically provides signals to its pulse width modulator generator in a precise and accurate shift of 30 electrical degrees in time relative to the master controller, slight variations in controllers and the system in general, for instance, the clocks associated with the CPUs of the controllers, nonetheless create variation which tends to destabilize and desynchronize the drive system. 
     The disclosure that follows provides a methodology to allow synchronizing of two three-phase power base drive sections to produce a reliable six (6) phase power system for induction loads. The disclosure herein allows for: (i) an increase in energy efficiency of an AC induction motor-drive system, (ii) a higher output power than an equivalent three-phase system operating at the same temperature and efficiency, and (iii) an extension of the life of motor winding installation for the motor of the corresponding system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a drive system for a six-phase AC induction motor-drive system utilizing a master and follower architecture for controlling respective pulse width modulator generators associated with two three-phase power base drive sections. 
         FIGS. 2-3  are schematic drawings of an exemplary open-loop drive system for a six-phase AC induction motor. 
         FIGS. 4-5  are schematic drawings of an exemplary closed-loop drive system for a six-phase AC induction motor. 
         FIG. 6  is a winding diagram associated with one embodiment of a stator of a six phase AC induction motor wherein the stator comprises a 48 slot stator with two three-phase windings groups wound using an 11 stator tooth pitch winding pattern. 
         FIG. 7  is a chart associated with the winding diagram of  FIG. 6 . 
         FIG. 8  is a winding diagram associated with another embodiment of a stator of a six phase AC induction motor wherein the stator comprises a 72 slot stator with two three-phase windings groups wound using a 16 stator tooth pitch winding pattern. 
         FIG. 9  is a chart associated with the winding diagram of  FIG. 8 . 
         FIG. 10  is a winding diagram associated with another embodiment of a stator of a six phase AC induction motor wherein the stator comprises a 72 slot stator with two three-phase windings groups wound using a 17 stator tooth pitch winding pattern. 
         FIG. 11  is a chart associated with the winding diagram of  FIG. 10 . 
         FIG. 12  is a schematic drawing showing location points for obtaining measurements to confirm the performance of a six-phase motor drive system. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary motor-drive system may comprise a six-phase AC induction motor powered by a six phase drive system having two three phase drive sections controlled by a single controller. The single controller may be configured to provide power to two, three-phase winding groups X,Y associated with a stator of the motor. The power provided to the two, three-phase winding groups X,Y of the stator may be shifted by 30 electrical degrees in time. The two sets of three-phase winding groups X,Y may be wound on the stator so that the two sets are spatially shifted by 30 electrical degrees. One such system which has proven useful comprises a single controller controlling two three-phase power converters. The two three-phase power converters may be configured to operate in an open or closed loop mode. Each three-phase power converter is controlled from a single, common controller that sends consistent commands to the pulse width modulator generators associated with the respective three-phase power base drive section. Other drives capable of being integrated with a single controller that generates command signals to the pulse width modulator generators of each three-phase power base drive section may also be utilized. The single controller allows the system to maintain synchronization between the power base drive sections and each of three-phase winding groups by generating commands to the respective pulse width modulator generators at the precise shift of 30 electrical degrees in time. 
       FIGS. 2 and 3  show a schematic drawing of a six-phase AC induction motor drive system using an open loop controller. The angle command for both of the three-phase winding groups X,Y is calculated based upon a speed reference. Because there is a 30 electrical degree in time phase shift between winding group X and winding group Y, winding group Y is spatially shifted by 30 degrees from winding group X on the stator. The corresponding, angle command for winding group Y is 30 degrees greater than that for winding group X. After the angle commands are calculated, both angle commands are sent to identical pulse width modulator generators of the control to generate pulse width modulated gate signals for each of the respective three-phase power base drive sections. 
       FIGS. 4 and 5  show a schematic drawing of a six-phase AC induction motor drive system using an alternate control scheme comprising a closed loop vector control. The angle command for both of the three-phase winding groups X,Y is calculated based upon a torque reference. Because there is a 30 electrical degree phase shift between winding group X and winding group Y, winding group Y is spatially shifted by 30 degrees from winding group X on the stator. The corresponding angle command for winding group Y is 30 degrees greater than that for winding group X. After the angle commands are calculated, both angle commands are sent to identical pulse width modulator generators of the control to generate pulse width modulated gate signals for each of the respective three-phase drive power sections. 
     The stator may be configured such that the number of slots (T) per pole (P) per phase (PH) associated with the stator (i.e., T/P/PH) equals an integral number. For instance, in the example of a 4 pole, 6 phase motor, with a 48 slot stator, the integer number is 2. In the example of a 4 pole, 6 phase motor, with a 72 slot stator, the integer number is 3. In the example of a 6 phase motor, the number of slots (T) divided by six times the number of poles (P) may be an integer number (i.e., T/(6×P)). The two, three-phase winding groups X,Y may be wound on the stator using a short pitch winding pattern. For instance, a 48 slot stator may be wound with an 11 stator tooth pitch winding pattern. A 72 slot stator may be wound with a 16 stator tooth pitch winding pattern or a 17 stator tooth pitch winding pattern. 
       FIG. 6  shows a winding diagram for the two three-phase winding groups X,Y of a 48 slot stator using an 11 stator tooth pitch winding pattern. Half of the stator represented by slots  1 - 24  is shown in  FIG. 6 , and the pattern would be followed in repeating sequence for slots  25 - 48  (not shown). The three phase windings of winding group X are indicated by phase windings A, B, and C, and are driven by power base drive section  1 . The three phase windings of winding group Y are indicated by phase windings (A+π/6) (hereinafter A′), (B+π/6) (hereinafter B′), and (C+π/6) (hereinafter C′), and are driven by power base drive section  2 . As shown in  FIG. 6  (radially outward to radially inward in the slot), slot  1  contains phase windings A and A; slot  2  contains phase windings A and A′; slot  3  contains phase windings A′ and A′; slot  4  contains phase windings A′ and B; slot  5  contains phase windings B and B; slot  6  contains phase windings B and B′; slot  7  contains phase windings B′ and B′; slot  8  contains phase windings B′ and C; slot  9  contains phase windings C and C; slot  10  contains phase windings C and C′; slot  11  contains C′ and C′; and slot  12  contains phase windings C′ and A. Slot  13  has the same configuration as slot  1 , and the pattern repeats for remaining slots of the motor. Thus, slot  25  and slot  37  have the same configuration as slots  1  and  13 . The start and termination point for each of the windings is shown on  FIGS. 6 and 7 . For instance, phase winding A starts as the top phase winding of slot  1  and terminates as the bottom phase winding of slot  12 ; phase winding A starts as the top phase winding of slot  2  and terminates as the bottom phase winding of slot  13 ; and phase winding B starts as the top phase winding of slot  3  and terminates as the bottom phase winding of slot  14 . The start and termination points are in accordance with the 11 stator tooth pitch winding pattern and repeat for the other slots of the stator. 
       FIG. 8  shows a winding diagram for the two three-phase winding groups X,Y of a 72 slot stator using an 16 stator tooth pitch winding pattern. Half of the stator represented by slots  1 - 36  is shown in  FIG. 8 , and the pattern would be followed in repeating sequence for slots  37 - 72  (not shown). The three phase windings of winding group X are indicated by phase windings A, B, and C, and are driven by power base drive section  1 . The three phase windings of winding group Y are indicated by phase windings (A+π/6) (hereinafter A′), (B+π/6)(hereinafter B′), and (C+π/6) (hereinafter C′), and are driven by power base drive section  2 . As shown in  FIG. 8  (radially outward to radially inward in the slot), slot  1  contains phase windings A and A; slot  2  contains phase windings A and A′; slot  3  contains phase windings A and A′; slot  4  contains phase windings A′ and A′; slot  5  contains phase windings A′ and B; slot  6  contains phase windings A′ and B; slot  7  contains phase windings B and B; slot  8  contains phase windings B and B′; slot  9  contains phase windings B and B′; slot  10  contains phase windings B′ and B′; slot  11  contains phase windings B′ and C; slot  12  contains phase windings B′ and C; slot  13  contains phase windings C and C; slot  14  contains phase windings C and C′; slot  15  contains phase windings C and C′; slot  16  contains phase windings C′ and C′; slot  17  contains phase windings C′ and A; and slot  18  contains phase windings C′ and A. Slot  19  has the same configuration as slot  1 , and the pattern repeats for remaining slots of the motor. Thus, slot  37  and slot  55  have the same configuration as slots  1  and  19 . The start and termination point for each of the windings is shown on  FIGS. 8 and 9 . For instance, phase winding A starts as the top phase winding of slot  1  and terminates as the bottom phase winding of slot  17 ; phase winding A starts as the top phase winding of slot  2  and terminates as the bottom phase winding of slot  18 ; and phase winding A starts as the top phase winding of slot  3  and terminates as the bottom phase winding of slot  19 . The start and termination points are in accordance with the 16 stator tooth pitch winding pattern and repeat for the other slots of the stator. 
       FIG. 10  shows a winding diagram for the two three-phase winding groups X,Y of a 72 slot stator using a 17 stator tooth pitch winding pattern. Half of the stator represented by slots  1 - 36  is shown in  FIG. 10 , and the pattern would be followed in repeating sequence for slots  37 - 72  (not shown). The three phase windings of winding group X are indicated by phase windings A, B, and C, and are driven by power base drive section  1 . The three phase windings of winding group Y are indicated by phase windings (A+π/6) (hereinafter A′), (B+π/6) (hereinafter B′), and (C+π/6) (hereinafter C′), and are driven by power base drive section  2 . As shown in  FIG. 10  (radially outward to radially inward in the slot), slot  1  contains phase windings A and A; slot  2  contains phase windings A and A; slot  3  contains phase windings A and A′; slot  4  contains phase windings A′ and A′; slot  5  contains phase windings A′ and A′; slot  6  contains phase windings A′ and B; slot  7  contains phase windings B and B; slot  8  contains phase windings B and B; slot  9  contains phase windings B and B′; slot  10  contains phase windings B′ and B′; slot  11  contains phase windings B′ and B′; slot  12  contains phase windings B′ and C; slot  13  contains phase windings C and C; slot  14  contains phase windings C and C; slot  15  contains phase windings C and C′; slot  16  contains phase windings C′ and C′; slot  17  contains phase windings C′ and C′; and slot  18  contains phase windings C′ and A. Slots  19  and  20  have the same configuration as slots  1  and  2 , and the pattern repeats for remaining slots of the motor. Thus, slot  37  and slot  55  have the same configuration as slots  1  and  19 . The start and termination point for each of the windings is shown on  FIGS. 10 and 11 . For instance, phase winding A starts as the top phase winding of slot  1  and terminates as the bottom phase winding of slot  18 ; phase winding A starts as the top phase winding of slot  2  and terminates as the bottom phase winding of slot  19 ; and phase winding A starts as the top phase winding of slot  3  and terminates as the bottom phase winding of slot  20 . The start and termination points are in accordance with the 17 stator tooth pitch winding pattern and repeat for the other slots of the stator. 
     Example 
     An AC induction motor comprising a NEMA 320-frame, 41 horsepower, 50 Hz, 6 phase, 4 pole, 48 slot stator, with two, three-phase winding groups wound with an 11 stator tooth pitch winding pattern, was powered with a drive system comprising two ACS 880 power base drive sections (provided by ABB) with a single controller configured to provide an open loop control, for instance, as shown in  FIGS. 2 and 3 . In accordance with the schematic drawing of  FIG. 12 , measurements of load speed and torque, power from each three-phase base power drive sections, and control signals from each pulse width modulator generator were obtained instantaneously at 0.05 second intervals over a ten minute period. When comparing the performance of the subject six phase system against a comparable three phase system using a premium efficiency three phase motor, the efficiency of the six-phase system was found to be up to 2 percent (2%) higher. The subject six-phase system was also found to have a 25 percent (25%) higher power output than the same frame size three-phase system using a premium efficiency three phase motor operating at rated power at the same temperature and efficiency. Life expectancy of winding insulation of the subject six-phase system is projected to be twice that of the comparable three-phase system due to a lower operating temperature of the six-phase motor for the same output power. 
     The embodiments were chosen and described in order to best explain the principles and their application to thereby enable others skilled in the art to best utilize the various embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.