Abstract:
An integrated rotary transformer and resolver and a motor including an integrated rotary transformer and resolver is provided. The integrated rotary transformer and resolver may include, but is not limited to, a stator having an outer surface and a plurality of slots disposed along the outer surface, a plurality of sensing coils, the plurality of sensing coils disposed in at least some of the plurality of slots, a rotor having a surface varying from a first predetermined thickness to a second predetermined thickness, and a controller electrically coupled to the plurality of sensing coils and configured to determine a position of the rotor based upon a voltage induced in each of the coils due to a relative thickness of the rotor opposed to the respective sensing coil.

Description:
TECHNICAL FIELD 
     Embodiments of the subject matter described herein relate generally to traction motors and more particularly to an integrated high frequency rotary transformer and resolver for a traction motor. 
     BACKGROUND 
     Plug-in Hybrid and fully electric vehicles have become increasingly popular in recent years. These vehicles typically utilize traction motors. Some traction motors have a wound rotor and use a rotary transformer to pass electrical power from a stationary side (i.e., a stator) to a rotating side (i.e., a rotor). Current traction motor configurations also utilize a separate resolver to determine an angular position of the motors rotor. 
     Accordingly, it is desirable to reduce the size and cost of the traction motor. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     BRIEF SUMMARY 
     In accordance with one embodiment, an integrated rotary transformer and resolver is provided. The integrated rotary transformer and resolver may include, but is not limited to, a stator having an outer surface and a plurality of slots disposed along the outer surface, a plurality of sensing coils, the plurality of sensing coils disposed in at least some of the plurality of slots, a rotor having a surface varying from a first predetermined thickness to a second predetermined thickness, and a controller electrically coupled to the plurality of sensing coils and configured to determine a position of the rotor based upon a voltage induced in each of the coils due to a relative thickness of the rotor opposed to the respective sensing coil. 
     In accordance with another embodiment, a motor is provided. The motor may include, but is not limited to, an interface configured to receive an alternating current, a stator coupled to the interface the stator having a primary winding and having an outer surface and a plurality of slots disposed along the outer surface, a plurality of sensing coils, the plurality of sensing coils disposed in at least some of the plurality of slots, a rotor having a secondary winding positioned opposite the first winding of the stator and having a surface varying from a first predetermined thickness to a second predetermined thickness, and a controller electrically coupled to the plurality of sensing coils and configured to determine a position of the rotor based upon a voltage induced in each of the coils due to a relative thickness of the rotor opposed to the respective sensing coil. 
     In yet another embodiment, an apparatus is provided. The apparatus includes, but is not limited to, a rotor having an sinusoidal upper surface and having a notch in an inner surface, a first winding wound in the notch in the rotor, a stator having a notch on an outer surface, the outer surface of the stator positioned opposite the inner surface of the rotor, the outer surface further including a plurality of slots, a secondary winding wound in the notch in the stator, a plurality of sensing coils wound in at least some of the plurality of slots, and a controller electrically coupled to the plurality of sensing coils and configured to determine a position of the rotor based upon an output of the plurality of sensing coils. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures. 
         FIG. 1  is a block diagram of an exemplary traction motor having an integrated rotary transformer and resolver, in accordance with an embodiment; 
         FIG. 2  is an exemplary stator which could be used in the traction motor illustrated in  FIG. 1  in accordance with an exemplary embodiment; 
         FIG. 3  is an exemplary rotor which could be used in the traction motor illustrated in  FIG. 1  in accordance with an exemplary embodiment; 
         FIG. 4  illustrates an exemplary integrated rotary transformer and resolver in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
       FIG. 1  is a block diagram of an exemplary traction motor  100  having an integrated rotary transformer and resolver  110 . The motor  100  has a stationary side  102  and a rotating side  104 . The motor  100  includes a motor stator  170  having a motor stator winding  172 . The motor stator  180  is electrically connected to a multi-phase inverter  195 . The motor  100  also includes motor rotor  180  having a field winding  182 . The traction motor  100  may otherwise be known as a wound rotor synchronous machine. The integrated rotary transformer and resolver  110  provides brushless power to the field winding  182  and provides rotor position information necessary for the control of the motor  100 . The rotor  130  of the integrated rotary transformer and resolver  110  rotates with the motor rotor  180 . Accordingly, the rotor  130  and the rotor  180  have the same angular position. 
     Because the traction motor  100  includes an integrated rotary transformer and resolver  110 , the size and cost of the traction motor  100  can be reduced relative to traction motors that have separate rotary transformers and resolvers. The integrated rotary transformer and resolver  110  includes a stator  120  having a primary winding  122  and a rotor  130  having a secondary winding  132 . 
     The stator  120  of the integrated rotary transformer and resolver  110  is electrically coupled to a high frequency alternating current (AC) energy source  160 . The integrated rotary transformer and resolver  110  delivers electrical energy to the rotor  170  of the motor  100  using the magnetic coupling of the primary winding  122  to the secondary winding  132 . The voltage induced in the secondary winding  132  is converted to DC (rectification) by a rectification circuit  190  and is used to supply the field winding of the motor  100 . 
     In order to provide mechanical position information of the rotor  170  of the traction motor  100 , the integrated rotary transformer and resolver  110  includes a series of additional sensing coils  140 . In one embodiment, for example, the sensing coils  140  are coupled to an outer surface of the stator  120  and are adjacent to the rotor  130 , as discussed in further detail below. Each of the sensing coils  140  are electrically coupled to a controller  150  and output a voltage. The controller  150  is configured to receive the voltage from the sensing coils  140  and determine a position of the rotor  130  based upon the received voltages, as discussed in further detail below. 
     In one embodiment, for example, the controller  150  is a processor. The controller  150  may be any type of processor. For example, the controller  150  may be a central processing unit, a graphical processing unit, a digital signal processor, an application specific integrated circuit (for example, a resolver-to-digital converter), a field programmable gate array, a microcontroller, or any other type of processor or combination of processors. 
       FIG. 2  is an exemplary stator  120  which could be used in the traction motor  100  illustrated in  FIG. 1  in accordance with an exemplary embodiment. In one embodiment, for example, the stator  120  is substantially cylindrical. The stator  120  also includes a notch  210  along a perimeter of the stator  120  where the primary windings (not illustrated) may be wound. 
     The stator  120  also includes multiple slots  220 . The slots  220  are disposed substantially periodically around an upper perimeter of the stator  120 , ninety degrees apart on a pole pair basis, four slots per resolver pole pair. In the embodiment illustrated in  FIG. 2 , there are eight slots  220 . The number of slots  220  in the stator  120  will vary depending upon the number of poles intended for the resolver function of the integrated rotary transformer and resolver  110 . For example, a six-pole resolver could include twelve slots. Each slot  220  is formed by two indentations in the upper surface of the stator  120 . Sensing coils  140  may be wrapped around some or all of the slots  220 , as discussed in further detail below. 
     In one embodiment, for example, each sensing coil  140  may be an insulated copper wire. Each sensing coil  140  is connected to the controller  150 . The sensing coils  140 , in conjunction with the controller  150 , determine a position of a rotor, as discussed in further detail below. The number of sensing coils  140  will correspond to the number of poles of the resolver  130 . For example, the stator  120  illustrated in  FIG. 2  may be used in a four-pole resolver functionality or application and could have either four or eight sensing coils  140 . Likewise, a six-pole resolver could use six or twelve sensing coils  140 . The sensing coils  140  are wound around adjacent slots  220 . As discussed in further detail below, by placing the sensing coils  140  in four adjacent slots, the position of a rotor  130  can accurately be determined every resolver pole pair of rotation. When the sensing coils  140  are wound in each slot  220 , four types of coils will emerge following this approach: (sin), (cos), (−sin), (−cos), depending on their position on the stator. All the coils of the same type will be connected for example in series, so that four voltages will sent to the controller  150 , no matter how many poles the resolver has. 
       FIG. 3  is an exemplary rotor  130  which could be used in the traction motor  100  illustrated in  FIG. 1  in accordance with an exemplary embodiment. The rotor  130  includes a notch  310  along an inner surface. The secondary winding of the rotor can be wound in the notch  310 . 
     As illustrated in  FIG. 3 , the rotor  130  has a sinusoidal upper surface having a varied thickness or height. In one embodiment, for example, an upper surface of the rotor  130  may vary according to two cycles of a sine wave for a four-pole resolver. In other embodiments, the upper surface of the rotor may have a different undulating patterns may be used. The height of each peak  320  and valley  330  may be selected such that a sensing coil  140  on a stator  120  outputs a predetermined voltage, as discussed in further detail below. The total number of peaks  320  and valleys  330  of the rotor  130  correspond to the number of poles intended for the resolver function. For example, the rotor  130  illustrated in  FIG. 3  is for a four-pole resolver and includes two peaks and two valleys. Accordingly, a peak  320  and valley  330  of the rotor  130  will pass by each sensing coil  140  twice per a single rotation of the rotor, as illustrated in further detail below. 
     While the above description refers to a stator  120  having a number of slots  220  and a rotor  130  having an undulating upper surface, the physical characteristics of the stator and rotor for the integrated rotary transformer and resolver  110  may be reversed. In other words, the stator  120  can be configured to have an undulating upper and the rotor  130  can be configured to have the slots  220 . In another embodiment, for example, the role of the two cores could be reversed. In other words, the core in  FIG. 2  could be the rotor and the core in  FIG. 3  could be the stator. 
       FIG. 4  illustrates an exemplary integrated rotary transformer and resolver  110  in accordance with an embodiment. As seen in  FIG. 4 , the stator  120  has a diameter which is smaller than the diameter of the rotor  130 . Accordingly, when the stator receives a the high frequency AC signal from the AC energy source  160  a magnetic flux is created across the stator  120  and rotor  130 . Because the upper surface of the rotor is sinusoidal, the magnetic flux is not distributed evenly. The magnetic flux, which varies based upon the thickness of the rotor, causes each sensing coils  140  to output a voltage proportional to the magnetic flux. In other words, the voltage sensed by each respective sensing set of coils  140 [ 1 ]- 140 [ 4 ] is proportional to the surface area of the rotor  130  in front (i.e., opposing) the respective sensing coil  140 . The position of the rotor  130  can be determined by the controller  150  based upon the voltage induced in each of the coils, as discussed in further below. 
     When the integrated rotary transformer and resolver  110  is used in a four-pole traction resolver, the voltages of the four sensing coils  140 [ 1 ]- 140 [ 4 ] would follow the following equations:
 
 V 1 =K 1 *V ac*(sin( P*Θr )+ K 2)
 
 V 2 =K 1 *V ac*(−sin( P*Θr )+ K 2)
 
 V 3 =K 1 *V ac*(cos( P*Θr )+ K 2)
 
 V 4 =K 1 *V ac*(−cos( P*Θr )+ K 2)
         where:
           K 1  and K 2  are constant values defined by the magnetic coupling structure;   Vac is the voltage of the high frequency AC source applied to the primary winding;   Θr is the mechanical angle of the rotor; and   P is number of pole pairs of the resolver.   
               

     By processing these four voltages, the controller  150  can determine an electrical angle Θe of the rotor, where the electrical angle Θe is equal to P times the value of the mechanical angle Θr. In this embodiment, the controller determines the electrical angle Θe according to the following equation:
 
Θ e =a tan 2([ V 1 −V 2 ],[V 3 −V 4])
 
     A tan 2 is a two-argument function and is a variation of the arctangent function. For any real arguments x and y not both equal to zero, a tan 2(y, x) is the angle in radians between the positive x-axis of a plane and the point given by the coordinates (x, y) on it. The angle is positive for counter-clockwise angles (upper half-plane, y&gt;0), and negative for clockwise angles (lower half-plane, y&lt;0). 
     As discussed above, the voltage output by each sensing coil  140  is proportional to the surface area of the rotor  130  in front (i.e., opposing) the respective sensing coil  140 . By adjusting the thickness of the rotor, the values of K 1  and K 2  can be changed. Accordingly, the rotor can be constructed such that any desired voltage can be sensed by the sensing coils. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.