Abstract:
A multiphase motor comprises a plurality of ferromagnetic stator core segments, the core segments being substantially uniformly spaced around an axis of rotation and isolated from direct contact with each other. Each core segment forms at least one pair of poles having coils wound thereon to form a phase winding. Each stator phase winding is configured with a topology different from the topology of each of the other phase windings. Each phase winding has a different total number of coils from one or more of the other phase windings. Each phase winding comprises coils of a gauge different from the coil gauge of one or more of the other phase windings. Preferably, all of the phase windings have substantially the same total coil mass.

Description:
RELATED APPLICATIONS 
   This application contains subject matter related to copending U.S. application Ser. No. 09/826,423 of Maslov et al., filed Apr. 5, 2001, copending U.S. application Ser. No. 09/826,422 of Maslov et al., filed Apr. 5, 2001, copending U.S. application Ser. No. 10/173,610 of Maslov et al., filed Jun. 19, 2002, and U.S. application Ser. No. 10/290,505, of Maslov et al. filed Nov. 8, 2002, all commonly assigned with the present application. The disclosures of these applications are incorporated by reference herein. 

   FIELD OF THE INVENTION 
   The present invention relates to dynamoelectric machine structure, more particularly to a stator structure comprising a plurality of segments with respective windings of different total numbers of winding coils and wire gauges. 
   BACKGROUND 
   The progressive improvement of electronic systems, such as microcontroller and microprocessor based applications for the control of motors, as well as the availability of improved portable power sources, has made the development of efficient electric motor drives for vehicles, as a viable alternative to combustion engines, a compelling challenge. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, functional versatility that is virtually indistinguishable from alternating current synchronous motor operation can be achieved. 
   The above-identified copending related U.S. patent application of Maslov et al., Ser. No. 09/826,423, identifies and addresses the need for an improved motor amenable to simplified manufacture and capable of efficient and flexible operating characteristics. In a vehicle drive environment, it is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability at minimum power consumption. The copending related U.S. application incorporates electromagnet poles as isolated magnetically permeable structures configured as segments in an annular ring, relatively thin in the radial direction, to provide advantageous effects. With this arrangement, flux can be concentrated, with virtually no loss or deleterious transformer interference effects in the electromagnet cores, as compared with prior art embodiments. 
   The Maslov et al. applications recognize that isolation of the electromagnet segments permits individual concentration of flux in each magnetic core segment, with virtually no flux loss or deleterious transformer interference effects from flux interaction with other core segments. Operational advantages can be gained by configuring a single pole pair as an autonomous electromagnet. Magnetic path isolation of the individual pole pair from other pole pairs eliminates a flux transformer effect on an adjacent group when the energization of the pole pair windings is switched. 
   The above-identified copending U.S. patent application Ser. No. 10/173,610 is directed to a control system for a multiphase motor having these structural features. A control strategy is described that compensates for individual phase circuit characteristics and offers a higher degree of precision controllability since each phase control loop is closely matched with its corresponding winding and structure. Control parameters are specifically matched with characteristics of each respective stator phase. Successive switched energization of each phase winding is governed by a controller that generates signals in accordance with the parameters associated with the stator phase component for the phase winding energized. 
   While the motors described in the above-identified applications provide operational advantages, these motors and prior art motors do not exhibit uniformly high efficiency at all speeds of a wide operating speed range, even with non-variable loads. For a fixed motor topology, the available magnetomotive force (MMF) is dependent upon the number of winding turns and energization current. The term “motor topology” is used herein to refer to physical motor characteristics, such as dimensions and magnetic properties of stator cores, the number of coils of stator windings and wire diameter (gauge), etc. The available magnetomotive force dictates a variable, generally inverse, relationship between torque and speed over an operating range. An applied energization current may drive the motor to a nominal operating speed. As the motor accelerates toward that speed, the torque decreases, the current drawn to drive the motor decreases accordingly, and thus efficiency increases to a maximum level. As speed increases beyond the level of peak efficiency, additional driving current is required, thereby sacrificing efficiency thereafter. Thus, efficiency is variable throughout the speed range and approaches a peak at a speed well below maximum speed. 
   Motors with different topologies obtain peak efficiencies at different speeds, as illustrated in FIG.  1 . This figure is a plot of motor efficiency versus operating speed over a wide speed range for motors having different topologies. The topologies represented in this figure differ solely in the number of stator winding turns. Each efficiency curve approaches a peak value as the speed increases from zero to a particular speed and then decreases toward zero efficiency. Curve A, which represents the motor with the greatest number of winding turns, exhibits the steepest slope to reach peak efficiency at the earliest speed V 2 . Beyond this speed, however, the curve exhibits a similarly steep negative slope. Thus, the operating range for this motor is limited. The speed range window at which this motor operates at or above an acceptable level of efficiency, indicated as X% in  FIG. 1 , is relatively narrow. 
   Curves B through E represent motors with successively fewer winding turns. As the number of winding turns decreases, the motor operating speed for maximum efficiency increases. Curve B attains peak efficiency at speed V 3 , Curve C at V 4 , Curve D at V 5  and Curve E at V 6 . Each motor has peak efficiency at a different motor operating speed, and none has acceptable efficiency over the entire range of motor operating speeds. 
   In motor applications in which the motor is to be driven over a wide speed range, such as in a vehicle drive environment,  FIG. 1  indicates that there is no ideal single motor topology that will provide uniformly high operating efficiency over the entire speed range. For example, at speeds above V 6  curves A and B indicate zero efficiency. At the lower end of the speed range, for example up to V 2 , curves C through E indicate significantly lower efficiency than curves A and B. 
   In motor vehicle drives, operation efficiency is particularly important as it is desirable to extend battery life and thus the time period beyond which it becomes necessary to recharge or replace an on-board battery. The need thus exists for motors that can operate with more uniformly high efficiency over a wider speed range than those presently in use. This need is addressed in the above identified Maslov et al. Application (&#39;030). The approach taken therein is to change, on a dynamic basis, the number of active coils of each stator winding for each of a plurality of speed ranges between startup and a maximum speed at which a motor can be expected to operate. The speed ranges are identified in a manner similar to that illustrated in  FIG. 1 and a  different number of the motor stator winding coils that are to be energized are designated for each speed range to obtain maximum efficiency for each of a plurality of operating speed ranges. The number of energized coils is changed when the speed crosses a threshold between adjacent speed ranges. Each winding comprises a plurality of individual, serially connected, coil sets separated by tap connections. Each respective tap is connected by a switch to a source of energization during a single corresponding speed range. The windings thus have a different number of energized coils for each speed range. 
   While this arrangement expands the speed range in which high efficiency may be obtained, the inductive characteristics of the motor windings require precisely timed connection and disconnection of the taps to and from the power source. A significant amount of electronic power circuitry and control circuitry therefor must be provided to obtain accurate functionality. Structural constraints in particular motor configurations may limit the number of taps, and thus coil sets, that are available from individual stator windings. 
   The need thus remains for alternative ways in which high efficiency motor operation can be obtained over extended speed ranges. 
   DISCLOSURE OF THE INVENTION 
   The present invention fulfills the above-described needs of the prior art and provides additional advantages for configurations such as the isolated individual stator core arrangements disclosed in the above identified Maslov et al. applications. The concepts of the present invention are advantageous also to a motor or generator of any stator configuration, including a single unitary core structure. 
   Advantages are obtained for example, at least in part, in a multiphase motor in which the stator comprises a plurality of ferromagnetic core segments, the core segments substantially uniformly spaced around an axis of rotation and isolated from direct contact with each other. Each core segment forms at least one pair of poles having coils wound thereon to form a phase winding. Each stator phase winding is configured with a topology different from the topology of each of the other phase windings. Winding topology is characterized by the total number of coil turns and the wire gauge of the coils in each phase winding. Each phase winding may have a different total number of coils from one or more of the other phase windings. Each phase winding may comprise coils of a gauge different from the coil gauge of one or more of the other phase windings. While the winding topology of a phase winding is different from that of other phase windings, it is particularly advantageous that all of the phase windings have substantially the same total coil mass. That is, windings with fewer coil turns have larger wire diameters (gauges). Preferably, all phase windings have a different total number turns and different wire gauges, the gauge sizes and numbers of coil turns being in inverse relationship with respect to each other. 
   The motor structure of the present invention is advantageous in that winding energization can be tailored to obtain maximum efficiency in each of several operating speed ranges from startup to the maximum speed at which a motor can be expected to operate. The individual speed ranges can be identified and the degree of energization of each phase winding, as manifested in the voltage applied thereto, can be derived to maximize operational efficiency in each speed range. Derivation of optimal applied voltages for each phase winding at each operating speed range can be made on a theoretical basis or empirically through experimentation. As an example, for a machine structure that accommodates a large number of phases, the derived voltages for each speed range may dictate that some phase windings are to have no voltage applied while each of the remaining phase windings is to have applied thereto a different voltage. The number of, and identity of, the phase windings that are to be energized, as well as the magnitude of the individually applied voltages, may differ for each speed range. The optimal voltages to be applied to each phase winding for each speed range are predetermined so that, in operation, the particular phase windings energized, and the magnitude of voltage applied to each phase winding, can be changed dynamically as the operating speed of the motor increases or decreases to an adjacent speed range. 
   Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawing and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  is a plot of motor efficiency versus motor operating speed over a wide speed range for different conventional motors having different numbers of winding turns. 
       FIG. 2  is an exemplary configuration of rotor and stator elements that may be employed in the present invention. 
       FIG. 3  is a chart exhibiting wire gauges and total number of winding turns for each phase of a multiphase motor exemplifying the present invention. 
       FIG. 4  is a partial block diagram of a voltage supply circuit for the motor of FIG.  2 . 
       FIG. 5  is an exemplary plot of voltage applied to each phase winding of the motor of  FIG. 2  over the operating speed range. 
       FIG. 6  is a plot of motor efficiency versus motor operating speed for voltages applied in accordance with FIG.  5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  is an exemplary configuration of rotor and stator elements that may be employed in the present invention. Reference is made to the above identified copending Maslov et al. application Ser. No. 09/826,422 for a more detail description of the motor exemplified herein. Rotor member  20  is an annular ring structure having permanent magnets  21  spaced from each other and substantially evenly distributed along cylindrical back plate  25 . The permanent magnets are rotor poles that alternate in magnetic polarity along the inner periphery of the annular ring. The rotor surrounds a stator member  30 , the rotor and stator members being separated by an annular radial air gap. Stator  30  comprises a plurality of electromagnet core segments of uniform construction that are evenly distributed along the air gap. 
   The stator comprises seven core segments, each core segment formed in a generally unshaped magnetic structure  36  with two poles having surfaces  32  facing the air gap. The legs of the pole pairs are wound with windings  38 , although the core segment may be constructed to accommodate a single winding formed on a portion linking the pole pair. Each stator electromagnet core structure is separate, and magnetically isolated, from adjacent stator core elements. Each of the core segments can be considered to represent a phase, the phase windings identified successively along the air gap by labels  38   a - 38   g . The stator elements  36  are secured to a non-magnetically permeable support structure, thereby forming an annular ring configuration. This configuration eliminates emanation of stray transformer flux effects from adjacent stator pole groups. Appropriate stator support structure, which has not been illustrated herein so that the active motor elements are more clearly visible, can be seen in the aforementioned patent application. 
   Windings  38   a - 38   g  differ from each other in winding topology with respect to wire gauges and total number of winding coil turns. While it is preferable in this embodiment that each phase winding has a unique number of total winding turns and a unique wire gauge, two or more phase windings may have similar wire gauges or number of turns. Other embodiments may comprise a greater number of isolated core segment pole pairs. It may be preferable in such embodiments that some phase windings have the same winding topology. 
     FIG. 3  is a chart exemplifying phase winding topologies for a seven phase motor illustrated in FIG.  2 . Each phase winding has a unique number of coil turns and is constructed of a unique wire gauge. The total copper mass of each of the phase windings is the same. 
     FIG. 4  is a partial block diagram of a voltage supply circuit for the motor of FIG.  2 . Phase windings  38   a - 38   g  are connected to d-c power supply  40  via a series connection, respectively, with voltage converters  42   a - 42   g . A control terminal of each voltage converter is coupled to controller  44 , which is also connected across power supply  40 . The controller and voltage converters are conventional devices as described more fully in the copending Maslov et al. application Ser. No. 10/173,610. The controller  44 , which may comprise a microprocessor and associated storage means, may have one or more user inputs and a plurality of inputs for motor conditions sensed during operation. For clarity of explanation of the present invention, a motor speed input is the only motor condition feedback input shown. The speed input signal may be generated by any conventional motor speed sensor. Stored in the controller is a table that identifies a voltage level to be applied to each phase winding for each of a plurality of speed ranges over the operating range. Voltage values that have been found to provide maximum operating efficiency for each of the phase windings  38   a - 38   g  in various speed ranges are identified in the table below. The efficiency of operation for each range is also set forth in the table. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 
             
             
                 
             
             
                 
               Voltage 
               Voltage 
               Voltage 
               Voltage 
               Voltage 
               Voltage 
               Voltage 
                 
             
             
                 
               for phase 
               for phase 
               for phase 
               for phase 
               for phase 
               for phase 
               for phase 
             
             
                 
               winding 
               winding 
               winding 
               winding 
               winding 
               winding 
               winding 
             
             
               RPM 
               38a 
               38c 
               38e 
               38g 
               38b 
               38d 
               38f 
               Efficiency 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               0 
               24.0 
               16.3 
               10.8 
               6.8 
               0.0 
               0.0 
               0.0 
               0.0 
             
             
               10 
               24.0 
               16.4 
               10.9 
               6.9 
               0.0 
               0.0 
               0.0 
               13.3 
             
             
               20 
               24.0 
               16.7 
               11.2 
               7.2 
               0.0 
               0.0 
               0.0 
               26.1 
             
             
               30 
               24.0 
               17.1 
               11.7 
               7.6 
               0.0 
               0.0 
               0.0 
               38.1 
             
             
               40 
               24.0 
               17.8 
               12.4 
               8.1 
               0.0 
               0.0 
               0.0 
               49.1 
             
             
               50 
               24.0 
               18.6 
               13.3 
               8.9 
               0.0 
               0.0 
               0.0 
               59.0 
             
             
               60 
               24.0 
               19.6 
               14.4 
               9.8 
               0.0 
               0.0 
               0.0 
               67.6 
             
             
               70 
               24.0 
               20.8 
               15.7 
               10.8 
               0.0 
               0.0 
               0.0 
               74.6 
             
             
               80 
               24.0 
               22.2 
               17.2 
               12.1 
               0.0 
               0.0 
               0.0 
               79.3 
             
             
               90 
               24.0 
               23.8 
               18.9 
               13.5 
               0.0 
               0.0 
               0.0 
               80.9 
             
             
               100 
               0.0 
               24.0 
               20.8 
               15.0 
               0.0 
               0.0 
               0.0 
               83.5 
             
             
               110 
               0.0 
               24.0 
               22.9 
               16.7 
               0.0 
               0.0 
               0.0 
               83.2 
             
             
               120 
               0.0 
               0.0 
               24.0 
               18.6 
               12.7 
               0.0 
               0.0 
               84.1 
             
             
               130 
               0.0 
               0.0 
               24.0 
               20.7 
               14.1 
               0.0 
               0.0 
               86.2 
             
             
               140 
               0.0 
               0.0 
               24.0 
               22.9 
               15.8 
               0.0 
               0.0 
               84.3 
             
             
               150 
               0.0 
               0.0 
               0.0 
               24.0 
               17.5 
               0.0 
               0.0 
               84.5 
             
             
               160 
               0.0 
               0.0 
               0.0 
               24.0 
               19.3 
               0.0 
               0.0 
               86.8 
             
             
               170 
               0.0 
               0.0 
               0.0 
               24.0 
               21.3 
               14.0 
               0.0 
               85.6 
             
             
               180 
               0.0 
               0.0 
               0.0 
               24.0 
               23.4 
               15.5 
               0.0 
               82.8 
             
             
               190 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               17.0 
               0.0 
               85.0 
             
             
               200 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               18.6 
               0.0 
               87.7 
             
             
               210 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               20.3 
               0.0 
               87.4 
             
             
               220 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               22.1 
               0.0 
               84.4 
             
             
               230 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               23.9 
               15.3 
               80.5 
             
             
               240 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               16.6 
               84.9 
             
             
               250 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               18.0 
               87.9 
             
             
               260 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               19.4 
               88.6 
             
             
               270 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               20.8 
               87.2 
             
             
               280 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               22.3 
               84.0 
             
             
               290 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               23.9 
               79.7 
             
             
               300 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               81.9 
             
             
               310 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               84.6 
             
             
               320 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               87.4 
             
             
               330 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               90.1 
             
             
               340 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
               92.8 
             
             
               350 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
             
             
               360 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               0.0 
               24.0 
             
             
                 
             
           
        
       
     
   
   In operation, the controller  44  accesses data from the table to determine which phase windings are to be energized at startup and the level of voltage to be applied to each phase winding. The controller outputs the appropriate control voltages for these values to the respective voltage converters connected to the phase windings. As the motor accelerates, motor speed is repetitively sampled and fed as a signal input to the controller. In response to the received speed input signal, the controller accesses the stored table to receive voltage data for each phase winding at the speed range in which the sensed speed is located. New control signals, corresponding to the accessed data, are output to the voltage converters to change, if appropriate, the voltages applied to the phase windings. As motor load varies, the motor speed may vary accordingly. The controller, in turn, will adjust its output control voltages for these changes as provided by the table thereby to maintain optimum operation efficiency over the entire operating speed range. 
   The table represents a speed operating range of 360 rpm that is very finely divided for application of precisely adjusted voltage levels. This information is provided in graphic form in  FIG. 5 , each curve representing voltages applied to a respective phase winding throughout the range. Curve  1  represents voltages applied to phase winding  38   a ; curve  2  represents voltages applied to phase winding  38   c ; curve  3  represents voltages applied to phase winding  38   e ; curve  4  represents voltages applied to phase winding  38   g ; curve  5  represents voltages applied to phase winding  38   b ; curve  6  represents voltages applied to phase winding  38   d ; and curve  7  represents voltages applied to phase winding  38   f.    
   During different portions of the operational speed range, different combinations of phase windings will be energized. At no time are all seven phase windings energized. As evident from the table and  FIG. 5 , at starting, four phase windings are energized with changing voltage levels as shown up to speed of 100 rpm. For speeds between 100 and 140 rpm, three phase windings are energized with voltage levels as shown; between 140 and 160 rpm. two phase windings are energized; between 160 and 180 rpm. three phase windings are energized; between 180 and 220 rpm. two phase windings are energized; between 220 to 230 three windings are energized; between 230 and 290 two phase windings are energized; and at speeds greater than 290 only a single winding is energized. For each of these ranges, different combinations of energized phase windings are identified and are to be supplied with different energization voltages. 
   Motor efficiency for operation in accordance with the table over the entire speed range is illustrated graphically in FIG.  6 . Comparison of this curve with the efficiency curves of conventionally operated motors, shown in  FIG. 1 , illustrates the improved operating efficiency of the present invention. The stator winding configuration of the present invention, when energized in accordance with the voltages indicated in the table over the motor operating range, provides a motor operating efficiency in excess of eighty percent over approximately three quarters of the speed range. 
   In this disclosure there are shown and described only preferred embodiments of the invention and but a few examples of its versatility. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. For example, as can be appreciated, motor topologies can vary significantly for different numbers of poles, pole dimensions and configurations,pole compositions, etc. Different numbers of coil turns and speed range subsets can be chosen to suit particular topologies. Instead of winding each stator core segment with wires of different gauges, the number of turns on each stator core segment can be varied with all wire being of the same gauge. The configuration of the coil sections may be varied to meet optimum efficiency curves for different topologies. Threshold levels may be adjusted to increase and/or decrease one or more speed ranges, thus setting a more even or uneven speed range subset distribution.