Abstract:
A rotary transformer for an electrical machine includes a rotary printed circuit board and a stator printed circuit board. The rotary printed circuit board is operatively connected to the stator printed circuit board for relative rotation with respect to the stator printed circuit board. A conductor is fixed to the one of the printed circuit boards and includes a spiral coil for transferring electrical energy between the rotary printed circuit board and stator printed circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. Provisional Patent Application No. 61/895,097 filed on Oct. 24, 2013 and is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to electrical machines, and more particularly to rotating transformers for wound field synchronous machines. 
     2. Description of Related Art 
     Electrical machines such as wound field synchronous generators and wound field synchronous motors include rotating and stationary parts. Typically, the rotating part includes field windings configured for rotation relative to armature windings arranged on the stationary part. In the case of wound field synchronous generators, a current flow through the field windings generates a magnetic field. As the rotating part rotates about the armature windings the magnetic field induces current flow in the armature windings, thereby converting mechanical rotation into electrical energy. In the case of wound field synchronous motors operation is reversed. Current flow to the armature windings generates a magnetic field. The magnetic field pushes a magnetic field excited into the field windings, thereby generating an electromagnetic torque that mechanically rotates the rotating part of the motor. 
     In both types of electrical machines, the rotating parts of the machine need communicate with the stationary part of the machine. The communication is typically in the form of electrical energy transferred from the stationary part to the rotating part of the machine, such as exciter current for main field windings. Typically, mechanical devices effect communication between the rotating and stationary parts of the electrical machine, such as through contacts, cables or slip rings. Alternatively, winding and armature sets can effect communication between the rotating and stationary parts of electrical machines. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for apparatus and methods for providing communication between rotating and stationary parts of electrical machines. There is also a continuing need to transfer electrical energy between rotating and stationary parts of electrical machines that is efficient, suited for high frequency and/or power, and which is light weight and contactless. The present disclosure provides a solution for these problems. 
     SUMMARY OF THE INVENTION 
     A rotary transformer for an electrical machine includes a rotary printed circuit board (PCB) and a stator PCB. The rotary PCB is operatively connected to the rotary PCB for relative rotation with respect to the stator PCB circuit board. A conductor is fixed to the one of the PCBs and includes a spiral coil for transferring electrical energy between the rotary PCB and the stator PCB. 
     In certain embodiments, the coil can be planar. The coil can be a foil structure adhered to the PCB. The coil can be disposed on a PCB including an electrically insulating substrate. A ferromagnetic core can be connected to the substrate opposite the PCB. The isolating substrate and ferromagnetic core can also be disk-shaped. 
     In accordance with certain embodiments, the coil can be a first coil and the PCB can further include a second coil. The first and second coils can be radially offset from a rotation axis of the rotary transformer. The first and second coils can also be connected in series. 
     It is contemplated that the printed circuit board include any number of coils arranged about a circumference of the printed circuit board and configured to generate electromagnetic poles alternating polarities. The coil can be a single coil disposed on the printed circuit board extending about a rotation axis of the rotary transformer. 
     A wound field synchronous machine is also provided. The wound field synchronous machine has a rotary transformer as described above, a main field rotating power converter, and a control power module. The main field rotating power converter is connected to the rotary PCB of the rotary transformer. The control power module is connected to the stator PCB of the rotary transformer such that the control power module is electromagnetically connected by the rotary PCB and the stator PCB of the rotary transformer to the main field rotating power converter. 
     In certain embodiments, the rotary PCB of the rotary transformer can be connected to an internal power supply disposed a rotating part of the machine that is configured to provide current to main field windings of the machine. A demodulating module can be disposed on the rotating part of the wound field synchronous machine and connected to the rotary PCB for modulating current flow through the main field windings of the machine. 
     In accordance with certain embodiments, the rotary transformer can be a first rotary transformer and the machine can include a second rotary transformer connected to the control power module. A pulse width module can be connected to the stator PCB of the first rotary transformer for supplying power to the main field windings and a modulator/driver can be connected the stator PCB of the second rotary transformer for modulating current flowing through the main field windings. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a schematic of an exemplary embodiment of a wound field synchronous generator constructed in accordance with the present disclosure, showing rotary transformers electromagnetically coupling stationary parts and rotating parts of the generator for transferring electrical energy therebetween; 
         FIG. 2A  is a cross-sectional side elevation view of an embodiment of a rotary transformer of  FIG. 1 , showing a rotary printed circuit board (PCB) and stator PCB of the rotary transformer; 
         FIG. 2B  is a plan view of the rotary transformer of  FIG. 2A , showing the layout of the single spiral coil of the rotary PCB and stator PCB; 
         FIG. 3A  is a cross-sectional side elevation view of another embodiment of a rotary transformer, showing a rotary PCB and a stator PCB or the rotary transformer; 
         FIG. 3B  is a plan view of the rotary transformer of  FIG. 3A , showing the layout of the multiple coils of the rotary PCB and stator PCB; 
         FIG. 4A  is a magnetic flux distribution associated with the rotary transformer of  FIGS. 3A and 3B , showing magnetic flux excited by multiple spiral coils one of the PCBs; and 
         FIG. 4B  is a magnetic flux distribution associated with the rotary transformer of  FIGS. 3A and 3B , showing magnetic flux excited by multiple spiral coils of the rotary PCB and stator PCB. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of the rotary transformer in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of rotary transformers in accordance with the disclosure, or aspects thereof, are provided in  FIGS. 2-4 , as will be described. The systems and methods described herein can be used for electrical machines, such as wound field synchronous generators, motors, and generator/motors for example. 
     With reference to  FIG. 1 , an electrical machine  10  is shown. Electrical machine  10  is a wound field synchronous generator (WFSG), and includes a stationary part  20  and a rotating part  50 . Rotating part  50  is operably coupled to stationary part  20  and configured such that rotating part  50  rotates with respect to stationary part  20 . 
     Stationary part  20  includes main armature windings  22  and an exciter field coil  24 . Stationary part  20  also includes a primary coil  102  of a first PCB rotary transformer  100  and a primary coil  202  of a second rotary transformer  200 . An electrical load  30  and voltage and current sensor module  32  are electrically connected to main armature windings  22 . Main armature windings  22  are configured such that a magnetic field generated by rotating part  50  induces current flow in main armature windings  22 . This provides a current flow to electrical load  30  for powering electrical load  30 . A voltage and current sensor module  32  is configured and adapted to monitor current and voltage generated within main armature windings  22  and provided to electrical load  30 . Voltage and current sensor module  32  is electrically connected to a voltage regulator module  40 , and provides information relating the sensed voltage and current thereto. 
     A control power source  42  is electrically connected to voltage regulator module  40 . An exciter converter and control module  44  is electrically connected between control power source  42  and exciter field coil  24 . Exciter converter control module  44  is configured and adapted to provide a current flow through exciter field coil  24 . 
     Control power source  42  is also electrically connected to a pulse width modulation (PWM) module  46 . PWM module  46  is electrically connected to a stator PCB  102  of a first rotary transformer  100 . PWM module  46  is configured and adapted to provide a flow of current to rotary transformer  100  for transferring electrical energy from control power source  42  to rotating part  50  of WFSG  10  through stator PCB  102 . 
     Control power source  42  and voltage regulator  40  are electrically connected to a modulator/driver module  48 . Modulator/driver module  48  is electrically connected to a stator PCB  202  of second rotary transformer  200 . Modulator/driver module  48  is configured and adapted to provide a flow of current to rotary transformer  200  for transferring electrical energy including voltage regulation information from control power source  42  and voltage regulator  40  to rotating part  50  of WFSG  10  through stator PCB  202 . 
     With continued reference to  FIG. 1 , rotating part  50  of WFSG  10  includes exciter armature windings  52 , a rotating direct current (DC) power supply  54 , a main field rotating power converter  56 , and main field windings  58 . Exciter armature windings  52  are electromagnetically coupled with exciter field winding  24  such that current flow through exciter field winding  24  induces current flow within exciter armature windings  52 . This induces an alternating current flow through exciter armature windings  52 . 
     Exciter armature windings  52  are electrically connected to rotating DC power supply  54 . Rotating DC power supply  54  includes a diode bridge. The diode bridge operates as a rotating rectifier, and converts the alternative current flow received from exciter armature windings  52  into a DC flow. DC power supply  54  supplies the DC flow to main field rotating power converter  58 . 
     Main field rotating power converter  58  is electrically connected rotating DC power supply  54  and main field windings  58 . Main field rotating power converter  58  is also electrically connected to PWM driver  46  through first rotating transformer  100  and modulator driver  48  through second rotating transformer  200 . Main field rotating power converter  56  receives a DC flow from rotating DC power supply  54 , power from PWM driver  46  (through an internal power supply and associated electrical components shown in  FIG. 1 ), and a modulation signal from modulator/driver  48  (through a demodulator and associated electrical components shown in  FIG. 1 ). Main field rotating power converter  56  is configured to convert these inputs into a controlled current flow through main field windings  58 . The controlled current flow alters the magnetic field between main field windings  58  and main armature windings  22 , thereby controlling power supplied to electrical load  30 . 
     Generally, in electrical machines like WFSG  10 , there is a need to transfer electrical energy from voltage regulator module  40  to the rotating main field current regulator module, labeled as the Field Current Regulator (FCR) in  FIG. 1 , through a contactless energy supply and without use of contacts, cables, or similar devices requiring physical contact between stationary and fixed components. First and second PCB rotary transformers  100  and  200  perform this function. For example, in the illustrated embodiment of WFSG  10  FCR module receives a current feedback signal from the current sensor connected to main field winding. It also receives a main field current reference signal from a demodulator module, labeled Demodulator in  FIG. 1 . The main field current reference signal (in analog form) is generated as an output from voltage regulator  40  in response to output of voltage and current sensors  32 , and converted into a PWM signal in modulator driver module  48  for driving primary winding (coil) of rotary transformer  200 . This modulated current reference signal is passed across the gap between primary and second coils  202  and  204  of rotary transformer  200 . Secondary winding  204  is electrically connected to the demodulator module for reconstructing the main field current reference signal into an analog signal. This analog signal is then passed from the demodulator module to the FCR module. The FCR module in turn is electrically connected to the gate drives of the main field rotating power converter, and opens and closes the gates in accordance with the received signal. 
     With reference to  FIG. 2A , rotary transformer  100  is shown. Rotary transformer  100  includes stator PCB  102  and a rotary PCB  102 A. Rotary PCB  102 A is operatively connected to stator PCB  102  for relative rotation with respect to stator PCB  102  about a rotation axis R, such as by stator PCB  102  being coupled to stationary part  20  of electrical machine  10  and rotary PCB  102 A being connected to rotating part  50  of electrical machine  10 . Stator PCB  102  and rotary PCB  102 A are configured and adapted to electromagnetically couple one or both of PWM driver  46  to internal power supply  46 A and modulator  48  to demodulator  48 A, thereby transferring electrical energy between stationary part  20  and rotating part  50  of electrical machine  10 . In the illustrated embodiment, transfer of electrical energy (AC current) is effected through a single spiral coil connected to each of stator PCB  102  and rotary PCB  102 A. 
     Stator PCB  102  includes an isolating substrate  106 , a coil  108 , and a ferromagnetic core  110 . Isolating substrate  106  has a core surface  112  and a coil surface  114 , and is a PCB constructed from a dielectric material such as a polyimide substrate. Core  110  is connected to isolating substrate  106  at core surface  112 , and is constructed from a material such as ferrite or any other ferromagnetic material. Coil  108  is attached, e.g. adhered, to coil surface  114  and is formed from a conductive material, such as by etching or being stamped from copper sheet for example. Coil  108  occupies a common plane, and in embodiments is a thin foil-like material. 
     Rotary PCB  102 A is similar in construction to stator PCB  102 , and includes an isolating substrate  106 A, a coil  108 A, and a ferromagnetic core  110 A. Isolating substrate  106 A has a core surface  112 A and coil surface  114 A, and is a PCB constructed from a dielectric material such as a polyimide substrate. Core  110 A is connected to isolating substrate  106 A on core surface  112 A. Coil  108 A is constructed from a conductive material formed from an etching process or can be stamped from a copper sheet for example, and is attached to coil surface  112 A. Coil surface  114 A and coil  108 A of rotary PCB  102 A are disposed opposite from coil surface  114  and coil  108  of stator PCB  102 , and a gap G separating the coil surfaces  114  and  114 A. Each of isolating substrate  106 A and core  110 A are disk-shaped, thereby providing balance to the rotary PCB  102 A for vibration-free rotation. 
     With reference to  FIG. 2B , coil surface  114  is shown. Coil surface  114  has single coil  108  disposed thereon. Coil  108  has a radially outward current source  109  on an end, and is a radially inward current return  111 . Coil  108  traces a single path extending between current source  109  and current return  111  such that current flows about the coil in a clockwise direction relative to rotation axis R. This causes the associated magnetic field to have a polarity. In the illustrated embodiment, coil  108  circumferentially traverses coil surface  114  in four loops  113 . Coil  108  is supplied with alternating current. As will be appreciated by those skilled in the art, embodiments can include fewer or greater numbers of coil traverses as may be suitable for a given application of rotary transformer  100 . As will also be appreciated, coil  108  can be arranged so that current flows in an opposite direction such that the associated field has an opposite pole. 
     While the foregoing discussion is limited to the construction of stator PCB  102 , it will be appreciated that coil surface  114 A of rotary PCB  102 A is similarly constructed such that current flow within coil  106  of stator PCB  102  generates a magnetic field spanning gap G. The generated magnetic field induces a corresponding current flow in coil  106 A of rotary PCB  102 A, thereby transferring electrical energy across gap G using an electromagnetic coupling across gap G formed by stator PCB  102  and rotary PCB  102 A. 
     With reference to  FIG. 3A , a rotary transformer  200  is shown. Rotary transformer  200  is similar to rotary transformer  100 , and includes stator PCB  202  and a rotary PCB  202 A. Rotary PCB  202 A is operatively connected to stator PCB  202  for relative rotation with respect to stator PCB  202  about a rotation axis R, such as by stator PCB  202  being coupled to stationary part  20  of electrical machine  10  and rotary PCB  202 A being connected to rotating part  50  of electrical machine  10 . Stator PCB  102  and rotary PCB  102 A are configured and adapted to electromagnetically couple one or both of PWM driver  46  to internal power supply  46 A and modulator  48  to demodulator  48 A. This enables transfer of electrical energy between stationary part  20  and rotating part  50  of electrical machine  10  across one or both of PWM driver  46  and internal power supply  46 A and modulator  48  and demodulator  48 A. In the illustrated embodiment, transfer of electrical energy is effected through a plurality of spiral coils connected to each of stator PCB  202  and rotary PCB  202 A. 
     Stator PCB  202  includes a core  210  connected to a core surface  212  of an isolating substrate  206 , i.e. a PCB. With reference to  FIG. 3B , stator PCB  202  includes a first coil  220 , a second coil  230  (shown in  FIG. 3B ), a third coil  240 , and a fourth coil  250  (shown in  FIG. 3B ) each disposed on a coil surface  214  of stator PCB  202 . First, second, third, and fourth coils  220 ,  230 ,  230 , and  250  are planar structures arranged substantially orthogonally with rotation axis R. The minimum number of coils in this illustrative example is two. As will be appreciated by those skilled in the art, the maximum number of coils depends on the construction of the transformer, application of the transformer, and the available space for coils on PCB  202 . 
     Each of first coil  220 , second coil  230 , third coil  240 , and fourth coil  250  are radially offset from rotation axis R by a common radial distance. Respective current sources and current returns of first, second, third, and fourth coils  220 ,  230 ,  240  and  250  are offset radially from rotation axis, the source and return of each coil being radially offset by different distances. 
     First coil  220  is electrically connected to a voltage source (shown in  FIG. 1 ). Second coil  230  is electrically connected in series to first coil  220 . Third coil  240  is electrically connected in series to second coil  230 . Fourth coil  250  is electrically connected in series to third coil  240 . With respect to the 12 o&#39;clock position at the top of drawing sheet  5 , current enters first coil  220  at a radially inward current source  222 . The current traverses first coil  220  through four loops  224  in a clockwise direction, and thereafter exits through a current return  226  positioned radially outboard of current source  222 . 
     Current return  226  is coupled by a bridge segment  228  (illustrated with a dotted line segment) to a current source  232  positioned radially inboard. Bridge segment  228  extends within isolating substrate  206  to electrically connect current return  226  and current source  232 . Current entering source  232  traverses second coil  230  through four loops  234  (only one labeled for clarity purposes) in a counterclockwise direction. The current thereafter exits through a current return  236  positioned radially outboard of current source  232 . Current return  236  is coupled by a bridge segment  238  (illustrated with a dotted line segment) to current source  242  positioned radially inboard with respect to current return  236 . Bridge segment  238  extends within isolating substrate  206  and electrically connects current return  236  with current source  242 . 
     Current entering current source  242  traverses third coil  240  through four loops  244  in a clockwise direction, thereafter exiting through a current return  246  positioned radially outboard of current source  242 . Current return  246  is coupled by a bridge segment  248  (illustrated with a dotted line segment) to a current source  256  positioned radially inboard. Bridge segment  248  extends within isolating substrate  206  to electrically connect current return  246  and current source  252 . Current entering source  256  traverses fourth coil  250  through four loops  254  (only one labeled for clarity purposes) in a counterclockwise direction. The current thereafter exits through a current return  252  positioned radially outboard of current source  232 . 
     Current flowing through first coil  230 , second coil  240 , third coil  250 , and fourth coil  260  generates a magnetic field. The magnetic field induces corresponding current flow in rotary PCB  202  rotatably arranged on an opposite side of gap G. Since current directional flow, e.g. clockwise or counterclockwise, determines polarity of the generated magnetic field, and current flows alternate successively through each of the coils about the circumference of coil surface  114 , respective poles alternate. This is indicated in  FIG. 3B  with first coil  220  being identified with an N (North), second coil  230  begin identified with an S (South), etc. As will be appreciated, reversing current flow (such as by providing alternating current) causes the poles to switch polarities. This enables rotary transformer  200  to transfer electrical energy across gap G as a contactless electromagnetic coupling using either AC or DC power (due to rotation of the poles associated with the current flows). As will be appreciated, rotary transformer  200  can be constructed with two or more coils as suitable for a given application of rotary transformer  200 . As will also be appreciated, each coil can have one or more loops as suitable for a given application. 
     While the following is above discussion is limited to the construction of stator PCB  202 , it will be appreciated rotary PCB  202  is similarly constructed such that current flow through the illustrated coils of stator PCB  202  generates a magnetic field in gap G. The generated magnetic field induces a corresponding current flow in the coils of rotary PCB  202 , thereby transferring electrical energy across gap G using an electromagnetic coupling across gap G formed by stator PCB  202  and rotary PCB  202 A. 
     With reference to  FIG. 4A , an axial magnetic flux distribution  300  is shown. Magnetic flux distribution  300  is resultant from flowing current through stator PCB  202  of rotary transformer  200 . The illustrated flux distribution  300  results from current flow through the primary (stator) coils only shown on the left hand side of the figure. With reference to  FIG. 4B , a magnetic flux distribution  400  resultant from both stator PCB  202  and rotary PCB  202 A of rotary transformer  200  is shown. The illustrated flux distribution  400  results from current flow through both primary (stator) coils and secondary (rotor) coils on the left and right sides of the figure. This magnetic flux distribution visualizes the operation of PCB transformer  200  under load. 
     Embodiments of rotary transformers described herein provide improved electrical energy transfer by using ferrite or other ferromagnetic cores and high transmission frequencies. In the context of WFSG machines, rotary transformers provide independent control power to the rotating main field current regulator module, e.g. the FCR module. Embodiments of rotatory transformers described herein also enable transfer of control signals between stationary voltage regulators and rotating main field current regulators without mechanical contact through a rotary transformer. Embodiments of rotatory transformers described herein further reduce electrical machine volume and weight by replacing conventional rotary transformers with PCB rotary transformers. 
     Embodiments of rotary transformers described herein can supply control power from stationary components to control electronics located within rotating parts of wound field synchronous machines such as rotating part  50  of electrical machine  10  at high frequency. For example, embodiments powered by a PWM driver operating in the range of about 100 to about 400 Hertz can deliver more than a kilowatt of control power at more than 90% efficiency over an air gap to the rotating part of an electrical machine. It does so contactless, without the use of slip rings, cabling or other devices requiring physical contact between rotating and fixed components of the electrical machine. 
     Embodiments of rotary transformers described herein can also provide a communications link between stationary components, i.e. voltage regulator  40 , and the rotating part of a wound field synchronous machine such as rotating part  50  of electrical machine  10 . For example, embodiments of the rotary transformers described herein can provide a current reference signal in the transferred electrical energy to the main field current regulator. The communications link can also be bi-directional, thereby allowing sensors located on the rotating part of the electrical machine to communicate information such as main field current and voltage of the main field or device temperatures to a stationary voltage regulator. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for wound field synchronous machines with superior properties including contactless transfer of energy between the rotating and stationary parts of the machine for providing current and current modulation to the main field windings of the machine. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.