Method and apparatus for controlling rotation of a magnetic rotor

Abstract

A method of capturing a sensorless magnetic rotor for acceleration and rotation with a rotating magnetic field generated by a stator is used in a turbogenerator including a compliant foil fluid film radial bearing. The method includes energizing the stator to generate a magnetic field and slowly rotating the magnetic field approximately 360° to capture the magnetic rotor. The rotational speed of the magnetic field is quickly accelerated to quickly accelerate the magnetic rotor, thereby quickly reaching a liftoff speed associated with the compliant foil fluid film radial bearing to prevent damage thereof.

What is claimed is:  
     
         1 . A method of capturing a sensorless magnetic rotor for acceleration and rotation with a rotating magnetic field generated by a stator for use in a turbogenerator including a compliant foil fluid film bearing, the method comprising: 
 energizing the stator to generate the magnetic field;    slowly rotating the magnetic field approximately 360° to capture the magnetic rotor; and    quickly accelerating the rotational speed of the magnetic field to quickly accelerate the magnetic rotor, thereby quickly reaching a liftoff speed associated with the compliant foil fluid film bearing to prevent damage thereof.    
     
     
         2 . The method of  claim 1 , wherein said step of slowly rotating the magnetic field comprises rotating the magnetic field approximately to 270° to 360° in approximately 1 second.  
     
     
         3 . The method of  claim 2 , wherein said step of quickly accelerating the rotational speed of the magnetic field comprises accelerating the rotational speed of the magnetic field to at least approximately 10,000 rpm within approximately 1 second after said slow rotation of approximately 270° to 360°.  
     
     
         4 . The method of  claim 3 , wherein said step of quickly accelerating the rotational speed comprises quickly accelerating to approximately 14,000 rpm within approximately  1  second.  
     
     
         5 . The method of  claim 1 , wherein said steps of energizing the rotor and slowly rotating the magnetic field comprises generating a peak current in one of three inductors in a three-phase permanent magnet rotor, and rotating the peak current through the three inductors.  
     
     
         6 . A turbogenerator comprising: 
 a rotatable rotor including at least one magnet, said rotor lacking means for determining its rotational position;    a compliant foil fluid film bearing positioned for supporting the rotor;    a stator configured for generating a rotatable magnetic field to capture said magnet for rotating the rotor;    a computer system operatively connected with the stator, and including a computer-readable storage medium having data thereon operative to instruct the stator to perform the steps of: 
 energizing to generate the magnetic field;  
 slowly rotating the magnetic field approximately 360° to capture the magnetic rotor; and  
 quickly accelerating the rotational speed of the magnetic field to quickly accelerate the magnetic rotor, thereby quickly reaching a liftoff speed associated with the compliant foil fluid film bearing to prevent damage thereof.  
   
     
     
         7 . The turbogenerator assembly of  claim 6 , wherein said step of slowly rotating the magnetic field comprises rotating the magnetic field approximately to 270° to 360° in approximately 1 second.  
     
     
         8 . The turbogenerator assembly of  claim 7 , wherein said step of quickly accelerating the rotational speed of the magnetic field comprises accelerating the rotational speed of the magnetic field to at least approximately 10,000 rpm within approximately 1 second after said slow rotation of approximately 270° to 360°.  
     
     
         9 . The turbogenerator assembly of  claim 8 , wherein said step of quickly accelerating the rotational speed comprises quickly accelerating to approximately 14,000 rpm within approximately 1 second.  
     
     
         10 . The turbogenerator assembly of  claim 6 , wherein said stator comprises a three-phase permanent magnet rotor including three inductors, and wherein said steps of energizing the rotor to generate the magnetic field and slowly rotating the magnetic field comprises generating a peak current in one of the inductors and rotating the peak current through the other two inductors.  
     
     
         11 . The turbogenerator assembly of  claim 9 , wherein the stator is further operative as a generator for generating power from the rotating rotor.  
     
     
         12 . A method of capturing a sensorless magnetic rotor for acceleration and rotation with a rotating magnetic field generated by a stator, the method comprising: 
 energizing the stator to generate the magnetic field;    slowly rotating the magnetic field approximately 360° to capture the magnetic rotor; and    quickly accelerating the rotational speed of the magnetic field to quickly accelerate the magnetic rotor.    
     
     
         13 . The method of  claim 12 , wherein said step of slowly rotating the magnetic field comprises rotating the magnetic field approximately 270° to 360° in approximately 1 second.  
     
     
         14 . The method of  claim 13 , wherein said step of quickly accelerating the rotational speed of the magnetic field comprises accelerating the rotational speed of the magnetic field to at least approximately 10,000 rpm within approximately 1 second after said slow rotation of approximately 270° to 360°.  
     
     
         15 . The method of  claim 14 , wherein said step of quickly accelerating the rotational speed comprises quickly accelerating to approximately 14,000 rpm within approximately 1 second.  
     
     
         16 . The method of  claim 12 , wherein said steps of energizing the rotor and slowly rotating the magnetic field comprise generating a peak current in one of three inductors in a three-phase permanent magnet rotor, and rotating the peak current through the three inductors.  
     
     
         17 . The method of  claim 12 , further comprising quickly decelerating the rotational speed of the magnetic field to quickly decelerate the magnetic rotor.  
     
     
         18 . The method of  claim 17 , wherein said step of quickly decelerating the rotational speed of the magnetic field comprises decelerating from approximately 14,000 rpm to 0 rpm in approximately  1  second.  
     
     
         19 . A method of capturing a sensorless magnetic rotor for acceleration, rotation and deceleration with a rotating magnetic field generated by a stator for use in a turbogenerator including a compliant foil fluid film radial bearing, the method comprising: 
 energizing the stator to generate the magnetic field;    slowly rotating the magnetic field approximately  360 ° to capture the magnetic rotor;    quickly accelerating the rotational speed of the magnetic field to quickly accelerate the magnetic rotor to its operating speed, thereby quickly reaching a liftoff speed associated with the compliant foil fluid film radial bearing to prevent damage thereof; and    quickly decelerating the rotational speed of the magnetic field from said operating speed to zero to quickly decelerate and stop rotation of the magnetic rotor, thereby preventing prolonged contact of the rotor with the compliant foil fluid film radial bearing to further prevent damage thereof.    
     
     
         20 . The method of  claim 19 , wherein said step of quickly decelerating comprises quickly decelerating the magnetic field from its operating speed to zero within approximately  1  second by decelerating a peak current of approximately 80 amps as it rotates through three inductors of a three-phase permanent magnet rotor.  
     
     
         21 . The method of  claim 19 , wherein said decelerating step further comprises dissipating inertial energy of the rotor by converting the inertial energy to a DC bus voltage and dissipating the DC bus voltage with an off-load device including an off-load resistor connected in series with an off-load switching device.  
     
     
         22 . A rotor assembly comprising: 
 a rotatable rotor including at least one magnet, said rotor lacking means for determining its rotational position;    a stator configured for generating a rotatable magnetic field to capture said magnet for rotating the rotor;    a computer system operatively connected with the stator, and including a computer-readable storage medium having data thereon operative to instruct the stator to perform the steps of: 
 energizing to generate the magnetic field;  
 slowing rotating the magnetic field approximately 360° to capture the magnetic rotor; and  
 quickly accelerating the rotational speed of the magnetic field to quickly accelerate the magnetic rotor, thereby quickly reaching a liftoff speed associated with the compliant foil fluid film radial bearing to prevent damage thereof.  
   
     
     
         23 . The rotor assembly of  claim 22 , wherein said stator comprises a three-phase permanent magnet rotor including three inductors, and wherein said steps of energizing the rotor to generate the magnetic field and slowly rotating the magnetic field comprise generating a peak current in one of the inductors and rotating the peak current through the other two inductors.  
     
     
         24 . The rotor assembly of  claim 22 , wherein said data on the computer-readable storage medium is further operative to instruct the stator to decelerate from an operating speed reached after the accelerating step to zero within approximately 1 second.  
     
     
         25 . A method of decelerating a magnetic rotor by controlling a rotating magnetic field generated by a stator for use in a turbogenerator including a compliant foil fluid film radial bearing, the method comprising: 
 increasing current in the stator using an open loop rotor position command to generate a peak rotating magnetic field to assure retention of the magnetic rotor; and    quickly decelerating the rotational speed of the magnetic field from an operating speed to zero to quickly decelerate and stop rotation of the rotor, thereby preventing prolonged contact of the rotor with the compliant foil fluid film radial bearing to prevent damage thereof; and    dissipating inertial energy of the rotor during said decelerating step by converting the inertial energy to a DC bus voltage and dissipating the DC bus voltage with an offload device including an offload resistor connected in series with an offload switching device.