Abstract:
An elevator system includes an elevator car to travel in a hoistway; a linear propulsion system to impart force to the elevator car, the linear propulsion system including: a secondary portion mounted to the elevator car, the secondary portion including a plurality of magnetic poles; and a primary portion mounted in the hoistway, the primary portion including a plurality of coils; and a drive coupled to the primary portion, the drive providing drive signals to at least a section of the primary portion; wherein the drive generates 6 phases of drive signals, each coil associated with one of the 6 phases.

Description:
FIELD OF INVENTION 
       [0001]    The subject matter disclosed herein relates generally to the field of elevators, and more particularly to using a six-phase motor to impart force on elevator cars. 
       BACKGROUND 
       [0002]    Self-propelled elevator systems, also referred to as ropeless elevator systems, are useful in certain applications (e.g., high rise buildings) where the mass of the ropes for a roped system is prohibitive and there is a desire for multiple elevator cars to travel in a single lane. There exist self-propelled elevator systems in which a first lane is designated for upward traveling elevator cars and a second lane is designated for downward traveling elevator cars. A transfer station at each end of the hoistway is used to move cars horizontally between the first lane and second lane. 
         [0003]    Existing linear motors that may be employed in an elevator system are three-phase motors. These existing three-phase motors may need to offset or skew drive signals to reduce torque or thrust ripple in the motor. Three-phase motors may also experience high magnitude harmonics in back emf waveforms. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one embodiment, an elevator system includes an elevator car to travel in a hoistway; a linear propulsion system to impart force to the elevator car, the linear propulsion system including: a secondary portion mounted to the elevator car, the secondary portion including a plurality of magnetic poles; and a primary portion mounted in the hoistway, the primary portion including a plurality of coils; and a drive coupled to the primary portion, the drive providing drive signals to at least a section of the primary portion; wherein the drive generates 6 phases of drive signals, each coil associated with one of the 6 phases. 
         [0005]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the primary portion includes 12N coils and the secondary portion includes 22N magnetic poles, where N is a positive integer. 
         [0006]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein a coil pair is associated with each phase of drive signals, wherein current flows in opposite directions in each coil of a respective coil pair. 
         [0007]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the coils are mounted on a ferromagnetic support. 
         [0008]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the coils have ferromagnetic cores. 
         [0009]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of magnetic poles includes a plurality of permanent magnets. 
         [0010]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are located on one side of the coils. 
         [0011]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are located on both sides of the coils. 
         [0012]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are arranged in a Halbach array. 
         [0013]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the ratio of a pitch of the magnetic poles to a pitch of the coils is 6/11. 
         [0014]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of magnetic poles includes a plurality of excitation coils wound around a plurality of ferromagnetic poles. 
         [0015]    According to another embodiment, a linear propulsion includes a primary portion including a plurality of coils; a secondary portion including a plurality of magnetic poles; and a drive coupled to the primary portion, the drive providing drive signals to at least a section of the primary portion; wherein the drive generates 6 phases of drive signals, each coil associated with one of the 6 phases. 
         [0016]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the primary portion includes 12N coils and the secondary portion includes 22N magnetic poles, where N is a positive integer. 
         [0017]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein a coil pair is associated with each phase of drive signals, wherein current flows in opposite directions in each coil of a respective coil pair. 
         [0018]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the coils are mounted on a ferromagnetic support. 
         [0019]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the coils have ferromagnetic cores. 
         [0020]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein plurality of magnetic poles includes a plurality of permanent magnets. 
         [0021]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are located on one side of the coils. 
         [0022]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are located on both sides of the coils. 
         [0023]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of permanent magnets are arranged in a Halbach array. 
         [0024]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the ratio of a pitch of the magnetic poles to a pitch of the coils is 6/11. 
         [0025]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the plurality of magnetic poles includes a plurality of excitation coils wound around a plurality of ferromagnetic poles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0027]      FIG. 1  depicts an multicar ropeless elevator system in an exemplary embodiment; 
           [0028]      FIG. 2  depicts components of a drive system in an exemplary embodiment; 
           [0029]      FIG. 3  depicts a drive and a section of the primary portion and the secondary portion of the linear propulsion system in an exemplary embodiment; 
           [0030]      FIG. 4  depicts a vector diagram for 6 phase drive signal in an exemplary embodiment; 
           [0031]      FIG. 5  depicts a section of the primary portion and the secondary portion of the linear propulsion system in an exemplary embodiment; and 
           [0032]      FIG. 6  depicts a secondary portion of the linear propulsion system in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]      FIG. 1  depicts a multicar, self-propelled elevator system  10  in an exemplary embodiment. Elevator system  10  includes a hoistway  11  having a plurality of lanes  13 ,  15  and  17 . While three lanes are shown in  FIG. 1 , it is understood that embodiments may be used with multicar, self-propelled elevator systems have any number of lanes. In each lane  13 ,  15 ,  17 , cars  14  travel in one direction, i.e., up or down. For example, in  FIG. 1  cars  14  in lanes  13  and  15  travel up and cars  14  in lane  17  travel down. One or more cars  14  may travel in a single lane  13 ,  15 , and  17 . In other embodiments, cars  14  may travel in both directions in a lane. 
         [0034]    Above the top floor is an upper transfer station  30  to impart horizontal motion to elevator cars  14  to move elevator cars  14  between lanes  13 ,  15  and  17 . It is understood that upper transfer station  30  may be located at the top floor, rather than above the top floor. Below the first floor is a lower transfer station  32  to impart horizontal motion to elevator cars  14  to move elevator cars  14  between lanes  13 ,  15  and  17 . It is understood that lower transfer station  32  may be located at the first floor, rather than below the first floor. Although not shown in  FIG. 1 , one or more intermediate transfer stations may be used between the first floor and the top floor. Intermediate transfer stations are similar to the upper transfer station  30  and lower transfer station  32 . 
         [0035]    Cars  14  are propelled using a linear motor system having a primary, fixed portion  16  and a secondary, moving portion  18 . The primary portion  16  includes windings or coils mounted at one or more locations of the lanes  13 ,  15  and  17 . Secondary portion  18  includes magnetic poles (e.g. permanent magnets, electromagnetics) mounted to one or more locations on cars  14 . In other embodiments, the secondary portion  18  mounted on car  14  includes coils and the primary portion  16  includes magnetic poles. Primary portion  16  is supplied with drive signals to control movement of cars  14  in their respective lanes. 
         [0036]      FIG. 2  depicts components of a drive system in an exemplary embodiment. It is understood that other components (e.g., safeties, brakes, etc.) are not shown in  FIG. 2  for ease of illustration. As shown in  FIG. 2 , one or more DC power sources  40  are coupled to one or more drives  42  via one or more DC buses  44 . DC power sources  40  may be implemented using storage devices (e.g., batteries, capacitors) or may be active devices that condition power from another source (e.g., rectifiers). Drives  42  receive DC power from the DC buses  44  and provide drive signals to the primary portion  16  of the linear propulsion system. Each drive  42  may be an inverter that conditions DC power from DC bus  44  to a multiphase drive signal provided to a respective section of the primary portions  16 . The primary portion  16  is divided into a plurality of motor sections, with each motor section associated with a respective drive  42 . 
         [0037]    A controller  46  provides control signals to the each of the drives  42  to control generation of the drive signals. Controller  46  may use pulse width modulation (PWM) control signals to control generation of the drive signals by drives  42 . Controller may generate dive signals using other techniques, and embodiments are not limited to PWM drive signals. Controller  46  may be implemented using a processor-based device programmed to generate the control signals. Controller  46  may also be part of an elevator control system or elevator management system. 
         [0038]      FIG. 3  is schematic diagram of a drive  42  and a section of the primary portion  16  and the secondary portion  18  of the linear propulsion system in an exemplary embodiment. The drive  42  is a two level, six phase drive, have six phase legs labeled A, B, C, D, E, and F. It is understood that the drive  42  may be three level, or N-level, and embodiments are not limited to 2-level drives. In an exemplary embodiment, the primary portion  16  of the linear propulsion system includes 12 coils  54  designated as A*, E, B, F*, C*, D, A, E*, B*, F, C and D*. The letter designates which phase the coil belongs to, and the presence or absence of the * indicates the current direction. A pair of coils  54  is associated with each phase (e.g., A and A*). Current flow in coil A is in the opposite direction as current flow of coil A*. The primary portion  16  of the linear propulsion system can be core-less. Alternatively, coils  54  of the primary portion  16  may be formed about ferromagnetic cores with concentric coils wound around primary teeth. The coils  54  may be also placed on a ferromagnetic flat support  50 , forming toothless primary portion  16 . 
         [0039]    The coils  54  of primary portion  16  are arranged in a star configuration, where coils for each phase (e.g., A and A*) are in electrical series from a respective phase leg of the drive  42  to a neutral point  58 . It is understood that other coil configurations may be utilized other than star configuration. 
         [0040]    The secondary portion  18  of the linear propulsion system includes 22 magnetic poles  56 . The magnetic poles  56  may be arranged as shown in  FIG. 3  using 22 permanent magnets, arranged in alternating polarity facing the primary portion  16 . In other embodiments, the 22 magnetic poles  56  may be arranged as part of a Halbach array. The spacing of the permanent magnets or poles  56  (e.g., center-to-center) is referred to as the pole pitch. The spacing of the coils  54  (e.g., center-to-center) is referred to as the coil pitch. The ratio of the magnetic pole pitch to the coil pitch equals 6/11. Permanent magnets of secondary portion  18  may be mounted on a ferromagnetic flat support  52 . Secondary portion  18  may be positioned on one side of primary portion  16 , or on both sides of primary portion  16 . 
         [0041]    Although  FIG. 3  depicts  12  coils and 22 magnetic poles, the linear propulsion system may be generalized as having 12N coils and 22N magnetic poles, where N is a positive integer. 
         [0042]      FIG. 4  depicts a vector diagram for 6 phase drive signals, labeled as A, B, C, D, E and F. Phases A, B and C are equally distributed (e.g., 120 degrees electrical apart). Phases D, E and F are also equally distributed (e.g., 120 degrees electrical apart). Phase D is offset from phase A by an offset angle (e.g., 30 degrees electrical), phase E is offset from phase B by an offset angle (e.g., 30 degrees electrical) and phase F is offset from phase C by an offset angle (e.g., 30 degrees electrical). The drive signals in  FIG. 4  generate flux in the primary portion  16  which coacts with magnetic poles in the secondary portion  18  to move the car  14  in one direction (e.g. up). To move the car  14  in the opposite direction, the angular offset is reversed with respect to that shown in  FIG. 4  (i.e., A=0 deg, B=−120 deg, C=−240 deg, D=−30 deg, E=−30 deg-120 deg, F=−30 deg-240 deg). 
         [0043]      FIG. 5  depicts a section of the linear propulsion system in an exemplary embodiment.  FIG. 5  depicts  12  coils of primary portion  16  arranged in the same manner as  FIG. 3 .  FIG. 5  also depicts the permanent magnets for secondary portion  18  arranged in a Halbach array forming the 22 magnetic poles. The coil pitch and pole pitch are also labeled in  FIG. 5 . Magnetic poles are provided on both sides of the primary portion  16  in  FIG. 5 . 
         [0044]      FIG. 6  depicts a secondary portion  18  in another exemplary embodiment. In the embodiment of  FIG. 6 , the magnetic poles of the secondary portion  18  are implemented using electromagnetics. Each magnetic pole of the secondary portion  18  includes an excitation coil  60  formed around a ferromagnetic pole  62 . The excitation coils  60  may be connected in series with a direct current (DC) power source  64 . The direction of the winding of excitation coils  60  established the polarity of the magnetic pole facing the primary portion  16 , such that the polarity of the magnetic poles alternates along the secondary portion. 
         [0045]    Embodiments utilizing a six phase linear propulsion system provide better thermal distribution in the drive compared to existing designs. The six phase linear propulsion system reduces torque and/or thrust ripple, as compared to three phase drives. The six phase linear propulsion system generates lower, high order harmonics. Also, using six phases allows the drive  42  to use lower power rated transistors (e.g., IGBTs) in higher volume, which reduces cost. 
         [0046]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.