Abstract:
A hybrid permanent magnet machine has a stator including armature windings. A rotor includes permanent magnets, a main field winding, and a rechargeable energy source. An output voltage control circuit, including an H bridge circuit configured to provide control current magnitude and direction in the main field winding to control the current passing across the main field windings.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a control for an electric machine having both wound coils and permanent magnets on its rotor and wherein an output voltage is controlled with a rotating energy source. 
         [0002]    Electric machines are known. Two typical applications of an electric machine may be operation as a motor, in which a current is passed through a stator to cause a rotor to rotate. The rotor rotates a shaft to, in turn, rotate a component. 
         [0003]    Another typical application is a generator. In a generator application, a source of rotation drives the shaft to drive the rotor and this generates current in the stator. 
         [0004]    Two general types of rotors are known. A wound field rotor has coils to pass current. When only the wound coils are utilized, the resultant machine requires a relatively large synchronous exciter. 
         [0005]    Another type of machine utilizes a permanent magnet motor. However, a permanent magnet rotor cannot supply constant voltage over operating speed and load variation. 
         [0006]    Hybrid rotors are known which utilize both coils and permanent magnets. However, the control of such machines is not well developed. 
         [0007]    Another challenge with hybrid rotors is that at fault conditions continued rotation of the permanent magnets will result in some continuing generation of power, which is undesirable, particularly, in aircraft operation. 
       SUMMARY OF THE INVENTION 
       [0008]    A hybrid permanent magnet machine has a stator including armature windings. A rotor includes permanent magnets, a main field winding, and a rechargeable energy source. An output voltage control circuit, including an H bridge circuit configured to provide control current magnitude and direction in the main field winding to control the current passing across the main field windings. 
         [0009]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a hybrid machine. 
           [0011]      FIG. 2  shows a first control circuit. 
           [0012]      FIG. 3  shows an alternative control circuit. 
           [0013]      FIG. 4  shows yet another alternative control circuit. 
           [0014]      FIG. 5  shows yet another alternative control circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a machine  20  including a rotor  21  rotating within a stator  22 . A system  24  is associated with a machine  20  and connected to the rotor  21  by a shaft  26 . If the associated system  24  is an item to be driven, then the machine  20  may be a motor. On the other hand, the associated system  24  could be a source of rotation, such as a gas turbine engine on an aircraft. In such applications, machine  20  may provide a starter motor function for the gas turbine engine  24 . During operation of the gas turbine engine  24 , the engine would drive the shaft  26  to cause the rotor  21  to rotate and generate electric current in the stator  22 . 
         [0016]    The rotor  21  is shown having electric coils  28 , as well as permanent magnets  30 . 
         [0017]      FIG. 2  is an electric circuit schematic for the machine  20 . As shown, the stator  22  has stator armature windings  32  along with an exciter field winding  34 . The stator armature windings communicate with main field windings  28 . The exciter field winding  34  communicates with exciter armature windings  36 . A rotating rectifier  38  converts the power received from the exciter armature windings and passes it across an H bridge  40  to control the current in the windings  28 . 
         [0018]    As known, an H bridge comprises four transistors and four diodes. By selectively opening and closing the transistors, current can flow in the same direction, or in an opposed direction, to the main field current in the windings  28 . As also shown, a communication transformer  42  communicates with an encoder/decoder  44 , which controls the H bridge  40 . A main control  46  receives a signal  48  indicative of the voltage output of the machine  20 . The control  46  operates the H bridge  40  to either increase or decrease the current passing across the windings  28  to achieve a desired voltage from the machine  20 . 
         [0019]      FIG. 3  shows an embodiment  60 , which is similar to the embodiment of  FIG. 2 . However, the stator  62  has its stator armature windings  32  and also has a high frequency transformer primary winding  68 . The rotor  67  is provided with high frequency transformer secondary windings  69 . The rotor  67  is otherwise similar to the  FIG. 2  rotor. 
         [0020]      FIG. 4  shows an embodiment  70  having a rotor  72  and a stator  74 . The stator armature windings  32  are illustrated. The control power at the rotor  72  is generated by a battery  78 . Inductor  80  and a battery field monitor  82  are also illustrated. The battery field monitor  82  monitors the voltage and power from the battery along with its temperature. These are sent to the encoder/decoder  44  and may be utilized by the control  46 . 
         [0021]      FIG. 5  shows another embodiment  90  having a rotor  92  and a stator  94 . Stator  94  is provided with a stator armature windings  32 . Rotor  92  is provided with a super capacitor  98 . During certain periods of operation, the capacitor  98  has its power dissipated to provide the control current. 
         [0022]    The  FIGS. 4 and 5  embodiments  70  and  90  utilize the stored power at the battery  78 , or super capacitor  98  to provide the control voltage. During normal operation, power will flow from the battery  78  or super capacitor  98 . However, when normal operation is stopped, a recharge mode may be entered at which power is supplied, such as from the stator armature windings  32 , through the main field windings  28 , and then back to battery  78  or super capacitor  98  to charge the items. 
         [0023]    In each of the  FIGS. 3-5 , the H bridge  40  is controlled as the  FIG. 2  embodiment to achieve a desired voltage. In addition, at fault condition, the control  46  can drive the output voltage to zero rapidly canceling the continuing effect of the rotating permanent magnets  30 . 
         [0024]    In essence, the main control  46  takes in the voltage signal  48 , and compares it to a desired signal. If the voltage signal  48  is below that which is desired, then the H bridge will be controlled such that the power will flow in the same direction as that in the coils  28  to increase the output voltage. Alternatively, should the voltage sensed from the signal  48  be too high, the H bridge will be controlled such that current will flow in an opposed direction to that flowing through the coil  28 , and the output voltage will then move downwardly. During fault conditions, it will likely be this flow in opposition to the current otherwise generated such as by the continued rotation of the permanent magnets  30  that will be utilized. 
         [0025]    The overall system provides benefits reducing the weight and volume by utilizing a hybrid machine including both wound coils and permanent magnets, but also providing accurate control. The disclosed embodiments enable voltage regulation over large speed and load variation. As mentioned, the disclosed systems will allow rapid reduction of excitation to zero during a fault condition. Further, the system efficiency is improved due to reduced losses in the generator. The disclosed systems will also facilitate advance diagnostics and prognostics and add some level of intelligence to the system. 
         [0026]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.