Patent Publication Number: US-10773922-B2

Title: Drive and control for six-phase electrical machines with negligible common-mode voltage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage of International Application No. PCT/US2016/016308, filed on Feb. 3, 2016, which claims priority to U.S. Provisional Application No. 62/112,272, filed on Feb. 5, 2015, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF INVENTION 
     The subject matter disclosed herein relates generally to the field of elevators, and more particularly to a multicar, ropeless elevator system. 
     BACKGROUND 
     Ropeless elevator systems, also referred to as self-propelled 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 ropeless 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. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment of the invention, a motor and drive system comprises at least one direct current source; a six phase inverter switching between positive and negative power of the at least one direct current source; and a six phase machine including six phase windings divided into at least two windings groups configured to result in a zero common-mode pulse width modulation across the at least two windings groups. 
     In the above embodiment, or in the alternative, common-mode noises can be conducted through the six phase windings of the six-phase machine through at least one parasitic capacitor to a ground during the zero common-mode pulse width modulation. 
     In the above embodiments, or in the alternative, the six phase windings can be distributed at a 60 degrees difference in space. 
     In the above embodiments, or in the alternative, the each windings group can form a three-phase, 120° phase-shift machine. 
     In the above embodiments, or in the alternative, the six phase windings can include at least two separate neutral connections, where a maximum modulation index is approximate to 1.15. 
     In the above embodiments, or in the alternative, a parasitic capacitance between windings and ground can be modeled as one common-mode capacitor for a common-neutral connection or two equal or substantially equal common-mode capacitors for two separate neutral connections. 
     In the above embodiments, or in the alternative, the six phase windings can include a common neutral connection, where a maximum modulation index is 1. 
     In the above embodiments, or in the alternative, the at least one parasitic capacitor can be a single parasitic common-mode capacitors that concentrates a common-mode capacitance from a common neutral connection. 
     In the above embodiments, or in the alternative, the motor and drive system can further comprise a six-phase power converter configured to drive the motor and drive system, wherein the six-phase power converter includes one phase-leg of two switches connected to one phase of the six phase windings 
     In the above embodiments, or in the alternative, the six-phase power converter can include twelve switches. 
     In the above embodiments, or in the alternative, a switching pattern of the six-phase power converter can be arranged for the at least two windings groups. 
     In the above embodiments, or in the alternative, switching actions of the switching pattern can be complementary for the at least two windings groups to maintain a common-mode voltage at zero. 
     In the above embodiments, or in the alternative, the switching pattern can be generated by reversing duty cycles and carriers for a first group of the at least two windings groups when generating switching actions for a second group of the at least two windings groups. 
     In the above embodiments, or in the alternative, motor and drive system of any preceding claim can be included in a ropeless elevator system. 
     In the above embodiments, or in the alternative, a method comprising switching, by a six phase inverter of a motor and drive system, between positive and negative power of at least one direct current source; and effecting a zero common-mode pulse width modulation across at least two windings groups, by a six phase machine, in accordance with the switching by the six phase inverter, the six phase machine including six phase windings divided into the at least two windings groups. 
     Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  depicts a multicar elevator system in an exemplary embodiment; 
         FIG. 2  shows of six-phase machine winding configurations in accordance with embodiments of the present invention; 
         FIG. 3  illustrates a six-phase voltage source inverter with six-phase machine according to an embodiment of the invention; 
         FIG. 4  illustrates another six-phase voltage source inverter with six-phase machine according to another embodiment of the invention; 
         FIG. 5  illustrates configurations of windings in six-phase machine space in accordance with embodiments of the present invention; 
         FIG. 6  illustrates voltage vectors for groups of inverter phases in accordance with embodiments of the present invention; 
         FIG. 7  illustrates a pulse width modulation generation for a six-phase motor drive according to an embodiment of the invention; and 
         FIG. 8  depicts a drive and a section of the primary portion and the secondary portion of a linear propulsion system in an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a multicar, ropeless 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 ropeless elevator systems that 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 . 
     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 . 
     Cars  14  are propelled using a motor and drive system (e.g., 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 both sides of the lanes  13 ,  15  and  17 . Secondary portion  18  includes permanent magnets mounted to one or both sides of cars  14 . Primary portion  16  is supplied with drive signals to control movement of cars  14  in their respective lanes. 
     The linear motor system of the ropeless elevator system can employ a power electronics inverter (e.g., as variable speed alternating drive (AC) motor drive) to improve the performance of the linear motor system. However, switching of power electronics devices in the motor drive includes inherent electromagnetic interference (EMI) problems. In general, EMI noise can be divided into two major groups: differential mode (DM) noise and common-mode (CM) noise. DM noises are conducted between phases. CM noises are conducted together with all phases through the parasitic capacitors to the ground. CM noises are with serious concern for motor drives because CM noises increase the EMI in the motor drive and damage the motor bearing and winding insulation. Unfortunately, solutions such as adding CM filters to attenuate CM noises are not viable in the linear motor system of the ropeless elevator system  10  due to the significant weight penalty of each CM filter significantly increase. 
     In view of the above, embodiments of the present invention set forth a drive and motor system and/or method for a six phase machine with negligible CM voltage. The six-phase machine includes six phase windings.  FIG. 2  illustrates six-phase machine winding configuration  200   a ,  200   b  with the six phase windings distributed at a 60 degrees difference in space. In both configurations, the six phase windings are divided into at least two groups: a first group being a 1 -b 1 -c 1  and a second is a 2 -b 2 -c 2 . Each winding group forms a three-phase, 120° phase-shift machine. 
     Further, embodiments of the drive and motor system can utilize the six-phase machine with a separate neutral connection or a common neutral connection, where a maximum modulation index can be approximate to 1.15 (e.g., wherein an exact value is 2/sqrt(3)) with separate neutral connection and a maximum modulation index can be approximate to 1 with common neutral connection. For example, in the first configuration  200   a , two neutral points N 1 , N 2  for the two groups of windings can be separated. In the second configuration  200   b , the neutral points for the two groups of windings are connected at neutral point N 3 . 
     The six-phase machine is also in electrical communication with a six phase inverter. In general, to produce a zero CM pulse width modulation (PWM), a space vector combination can be calculated with a first group of phases and be substantially or directly matched to complementary voltage vectors for a second group of phases. Note that, while the producing the zero CM PWM for the two groups of windings, the six phase windings may be divided into any number of groups. Further, the zero CM PWM is an active control signal produced by the drive and motor system (e.g., result in a zero common-mode pulse width modulation across the at least two windings groups). 
       FIGS. 3, 4  show six-phase voltage source inverters (VSIs)  305 ,  405  connected to six-phase machines  310 ,  410 , together with the parasitic CM capacitors Cg 1 , Cg 2 , Cg. In operation, the inverter terminal voltages of each six-phase VSI  305 ,  405  are switching between positive and negative direct current link (Vdc/ 2 +, Vdc/ 2 −) and generating an EMI noise source. Further, CM noises are conducted through the motor windings of the six-phase machines  310 ,  410  and the CM parasitic capacitors Cg 1 , Cg 2 , Cg to the respective grounds (e.g., during the zero common-mode pulse width modulation). 
     The six-phase machine  310  illustrates the first configuration  200   a  with two separate neutral points N 1 , N 2  for each group of windings. The six-phase machine  410  illustrates the second configuration  200   b  with a connected neutral point N 3  for the windings. With the separate neutral points N 1 , N 2 , the CM capacitance of the parasitic CM capacitors Cg 1 , Cg 2  are equal or substantially equal. With the connected neutral point N 3 , the CM capacitance is concentrated in the parasitic CM capacitor Cg. In this way, a parasitic capacitance between windings and ground can be modeled as one CM capacitor for common-neutral connection or two equal or substantially equal CM capacitors for separate neutral connection. In both cases, a CM voltage for the six-phase voltage VSIs can be expressed in equation (1). 
     
       
         
           
             
               
                 
                   
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     The drive and motor system can be driven by a six-phase power converter. The six-phase power converter includes at least one phase-leg of two switches connected to one phase of the six phase windings. In some embodiments, the six-phase power converter can include twelve switches with a pair of switches connected to a respective one winding of the six phase windings. The switching pattern of the six-phase power converter can be arranged for at least two groups of windings, which are located in opposite position with each other, where the switching actions are complementary so that the CM voltage for a full motor drive is kept/maintained to be zero. In this way, a switching pattern is achieved when duty cycles and carriers for the first group of windings are reversed together with generating switching actions for the second group of windings. 
     As shown in  FIG. 5 , based on the two winding space distribution  500   a ,  500   b  of the first and second groups, switch vectors are also calculated in equation (2), with equation (2a) for winding space distribution  500   a  and equation (2b) for winding space distribution  500   b . 
     
       
         
           
             
               
                 
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     In equation (2), x1, x2 and x3 are a switching status of a phase-leg, which are either 1 or 0. With these two equations, the voltage vectors for the two groups of inverter phases are shown in  FIG. 6 . 
       FIG. 6  illustrates voltage vectors for groups of inverter phases.  FIG. 6  includes a first formation  600   a  of 6 voltage vectors for the first group of phases and a second formation  600   b  of 6 voltage vectors for the second group of phases. The 6 voltage vectors of the second formation  600   b  are exactly opposite from the first formation  600   a . In turn, the complementary voltage vector in the second group of phases will achieve the same effect with the original voltage vector in the first group of phases. Note that a zero voltage vector 111 and 000 in two groups of phases are complementary, too. 
     To produce the negligible CM, a calculation of the duty cycle (e.g., with a −1˜1 range) for the first group of phases is performed, while a duty cycle is directly reversed for the second group of phases. A triangle carrier for the second group of phases is also reversed with respect to a triangle carrier for the first group of phases. Then, a first switching function for the first group of phases is generated in a first comparator, and a second switching function for the second group of phases is generated in comparator. In turn, when the first and second switching functions are combined, a zero CM voltage is achieved. 
     For example,  FIG. 7  illustrates a pulse width modulation generation for a six-phase motor drive to achieve zero CM voltage. After calculation of the duty cycle calculation  705  (−1˜1 range) of da 1 , db 1  and dc 1  for the first group of phases, the duty cycle is directly reversed for da 2 , db 2  and dc 2 . The triangle carrier for da 2 , db 2  and dc 2  are also reversed from that of da 1 , db 1  and dc 1 . Then, the switching function for first group of phases are generated in Comparator  1 , and the switching function for the second group of phases are generated in Comparator  2 . 
     With separate neutral points N 1 , N 2  in  FIG. 3 , a general space vector PWM can be used in the duty cycle calculation in  FIG. 7 . In this way, the duty cycles (−1˜1) of the first group windings are calculated and sent to Comparator  1 , while the reversed duty cycles are sent to Comparator  2 . Then the CM voltage in N 1  and N 2  will be complementary to each other. In this way, the CM voltage will be zero for the full motor drive in the whole period. With zero CM voltage, a phase current can include even less ripple and similar harmonics of other drive and motor systems. 
       FIG. 8  is schematic diagram of a linear propulsion system  800  according to one embodiment of the motor and drive system described above. The linear propulsion system  800  includes a drive  842  (e.g., embodiment of the six-phase VSI  305 ,  405 ), a section of the primary portion  816 , and a secondary portion  818  of the linear propulsion system. The drive  842  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  842  may be three level, or N-level, and embodiments are not limited to 2-level drives. In the depicted embodiment, the primary portion  816  of the linear propulsion system  800  includes twelve coils  854  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  854  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  816  of the linear propulsion system can be core-less. Alternatively, the coils  854  of the primary portion  816  may be formed about ferromagnetic cores with concentric coils wound around primary teeth. The coils  854  may be also placed on a ferromagnetic flat support  850 , forming toothless primary portion  816 . 
     The coils  854  of the primary portion  816  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  842  to a neutral point  858 . It is understood that other coil configurations may be utilized other than star configuration. 
     The secondary portion  818  of the linear propulsion system  800  includes twenty two magnetic poles  856 . The magnetic poles  856  may be arranged as shown in  FIG. 8  using twenty two permanent magnets, arranged in alternating polarity facing the primary portion  716 . In other embodiments, the twenty two magnetic poles  856  may be arranged as part of a Halbach array. The spacing of the permanent magnets or poles  856  (e.g., center-to-center) is referred to as the pole pitch. The spacing of the coils  854  (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 the secondary portion  818  may be mounted on a ferromagnetic flat support  852 . The secondary portion  818  may be positioned on one side of primary portion  816 , or on both sides of the primary portion  816 . 
     Although  FIG. 8  depicts twelve coils and twenty two magnetic poles, the linear propulsion system may be generalized as having 12N coils and 22N magnetic poles, where N is a positive integer. 
     In view of the above, the technical effects and benefits of embodiments of the drive and motor system include eliminating common-mode voltage for the inverter output, significant reductions of CM EMI noise and CM current, eliminating a need for extra coupling inductors, reduction of damage of CM current to the motor insulation and bearing. Further, the technical effects and benefits of embodiments can include a six-phase voltage source inverter that eliminates a need for extra hardware modification due to the drive being based on a normal six-phase VSI, such as elimination of CM filter which in turn significantly increases power density, along with no need for a coupling inductor. Furthermore, technical effects and benefits of embodiments can include a six-phase machine with separate neutral connection or with a six-phase machine with common neutral connection. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.