Induction motor/generator system

Abstract

A generator/starter system for starting an engine and for tapping power from the engine in order to generate electricity includes a squirrel cage rotor, a main stator winding, an auxiliary stator winding, and an excitation source. The main stator winding is magnetically coupled to the squirrel cage rotor so as to provide an AC output in response to rotation of the squirrel cage rotor and so as to rotate the squirrel cage rotor in response to an AC input. The auxiliary stator winding is magnetically coupled to the squirrel cage rotor so as to provide excitation current when the main stator winding is providing the AC output. The source of excitation current is coupled to the auxiliary stator winding.

What is claimed is:  
     
         1 . An induction machine comprising: 
 a squirrel cage rotor;    a main stator winding magnetically coupled to the squirrel cage rotor;    an auxiliary stator winding magnetically coupled to the squirrel cage rotor; and,    a source of excitation current coupled to the auxiliary stator winding.    
     
     
         2 . The induction machine of  claim 1  wherein the source of excitation current comprises an inverter having a DC input and an AC output coupled to the auxiliary stator winding.  
     
     
         3 . The induction machine of  claim 2  wherein the inverter is a PWM inverter.  
     
     
         4 . The induction machine of  claim 2  wherein the inverter further includes a battery coupled to the DC input.  
     
     
         5 . The induction machine of  claim 2  wherein the inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         6 . The induction machine of  claim 2  wherein the inverter further includes an AC bus, and a rectifier coupled between the AC bus and the DC input.  
     
     
         7 . The induction machine of  claim 2  wherein the inverter includes a capacitor coupled to the DC input.  
     
     
         8 . The induction machine of  claim 7  wherein the inverter further includes a battery coupled to the DC input.  
     
     
         9 . The induction machine of  claim 7  wherein the inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         10 . The induction machine of  claim 7  wherein the inverter includes an AC bus, and a rectifier coupled between the AC bus and the DC input.  
     
     
         11 . The induction machine of  claim 2  further comprising a transformer having a primary winding and a secondary winding, wherein the primary winding is coupled to an output of the main stator winding, and wherein the secondary winding is coupled to an input of the inverter.  
     
     
         12 . The induction machine of  claim 11  wherein the secondary winding is a first secondary winding and wherein the transformer further includes: 
 a rectifier arranged to rectify an AC output of the secondary winding to DC for supply to the inverter; and,  
 a second secondary winding of the transformer coupled to a battery, wherein the battery is coupled to the inverter.  
 
     
     
         13 . The induction machine of  claim 11  wherein the secondary winding is a first secondary winding, wherein the primary winding has first, second, and third primary windings, wherein the first, second, and third primary windings are coupled between the main stator winding and a switch, wherein the transformer has a second secondary winding, wherein the second secondary winding provides a voltage to a battery, and wherein the switch is controlled in response to the voltage.  
     
     
         14 . The induction machine of  claim 1  further comprising a constant speed drive coupled to the squirrel cage rotor, wherein the main stator winding has output lines, and wherein the main stator winding is arranged to provide constant frequency output power on the output lines of the main stator winding in response to rotation of the squirrel cage rotor by the constant speed drive.  
     
     
         15 . The induction machine of  claim 14  wherein the source of excitation current comprises an inverter having a DC input and an AC output coupled to the auxiliary stator winding.  
     
     
         16 . The induction machine of  claim 15  wherein the inverter further includes a capacitor coupled to the DC input.  
     
     
         17 . The induction machine of  claim 16  wherein the inverter further includes a battery coupled to the DC input.  
     
     
         18 . The induction machine of  claim 16  wherein the inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         19 . The induction machine of  claim 16  wherein the inverter further includes an AC bus, and a rectifier coupled between the AC bus and the DC input.  
     
     
         20 . The induction machine of  claim 1  further comprising: 
 a rectifier coupled to the main stator winding, wherein the rectifier is arranged to rectify a variable frequency AC output from the main stator winding to DC; and,  
 an inverter coupled to the rectifier, wherein the inverter is arranged to invert the DC from the rectifier to AC.  
 
     
     
         21 . The induction machine of  claim 20  wherein the inverter is a first inverter, and wherein the source of excitation current comprises a second inverter having a DC input and an AC output coupled to the auxiliary stator winding.  
     
     
         22 . The induction machine of  claim 21  wherein the second inverter further includes a capacitor coupled to the DC input.  
     
     
         23 . The induction machine of  claim 22  wherein the second inverter further includes a battery coupled to the DC input.  
     
     
         24 . The induction machine of  claim 22  wherein the second inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         25 . The induction machine of  claim 22  wherein the second inverter further includes an AC bus, and a rectifier coupled between the AC bus and the DC input.  
     
     
         26 . The induction machine of  claim 20  wherein the main stator winding has an AC output, wherein the inverter has an AC output, wherein the induction machine further comprises: 
 an AC bus coupled to the AC output of the inverter; and,  
 a switch coupling the AC output of the inverter to the AC output of the main stator winding so that the induction machine can be used as a starter.  
 
     
     
         27 . The induction machine of  claim 26  wherein the inverter is a first inverter, and wherein the source of excitation current comprises a second inverter having a DC input and an AC output coupled to the auxiliary stator winding.  
     
     
         28 . The induction machine of  claim 27  wherein the second inverter further includes a capacitor coupled to the DC input.  
     
     
         29 . The induction machine of  claim 28  wherein the second inverter further includes a battery coupled to the DC input.  
     
     
         30 . The induction machine of  claim 28  wherein the second inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         31 . The induction machine of  claim 28  wherein the second inverter further includes an AC bus, and a rectifier coupled between the AC bus and the DC input.  
     
     
         32 . An induction machine comprising: 
 a squirrel cage rotor;    first, second, and third stator windings magnetically coupled to the squirrel cage rotor;    first, second, and third capacitors coupled to the first, second, and third stator windings, respectively; and,    a solid state switch coupled to the first, second, and third capacitors, wherein the solid state switch is arranged to switch the first, second, and third capacitors so as to control excitation current supplied to the first, second, and third stator windings.    
     
     
         33 . The induction machine of  claim 32  wherein the solid state switch comprises: 
 first and second lines;  
 a first pair of diodes connected across the first and second lines and having a common junction coupled to the first capacitor;  
 a second pair of diodes connected across the first and second lines and having a common junction coupled to the second capacitor;  
 a third pair of diodes connected across the first and second lines and having a common junction coupled to the third capacitor; and,  
 a solid state switching device having controlled terminals coupled across the first and second lines.  
 
     
     
         34 . The induction machine of  claim 32  further comprising fourth, fifth, and sixth stator windings magnetically coupled to the squirrel cage rotor, wherein the solid state switch is arranged to switch the first, second, and third capacitors so as to control the phase between voltages produced by the first, second, and third stator windings and by the fourth, fifth, and sixth stator windings.  
     
     
         35 . The induction machine of  claim 34  wherein the first, second, third, fourth, fifth, and sixth stator windings are wound so as to mechanically control the phase between voltages produced by the first, second, and third stator windings and by the fourth, fifth, and sixth stator windings.  
     
     
         36 . A generator/starter system for starting an engine and for tapping power from the engine in order to generate electricity comprising: 
 a squirrel cage rotor;    a main stator winding magnetically coupled to the squirrel cage rotor so as to provide an AC output in response to rotation of the squirrel cage rotor and so as to rotate the squirrel cage rotor in response to an AC input;    an auxiliary stator winding magnetically coupled to the squirrel cage rotor so as to excite the main stator winding; and,    a source of excitation current coupled to the auxiliary stator winding.    
     
     
         37 . The generator/starter system of  claim 36  further comprising a constant speed drive coupled to the squirrel cage rotor, wherein the main stator winding has output lines, and wherein the main stator winding is arranged to provide constant frequency output power on the output lines of the main stator winding in response to rotation of the squirrel cage rotor by the constant speed drive.  
     
     
         38 . The generator/starter system of  claim 36  further comprising: 
 a rectifier coupled to the main stator winding, wherein the rectifier is arranged to rectify a variable frequency AC output from the main stator winding to DC; and,  
 an inverter coupled to the rectifier, wherein the inverter is arranged to invert the DC from the rectifier to AC.  
 
     
     
         39 . The generator/starter system of  claim 38  wherein the inverter is a first inverter, and wherein the source of excitation current comprises a second inverter having a DC input and an AC output coupled to the auxiliary stator winding.  
     
     
         40 . The generator/starter system of  claim 39  wherein the second inverter further includes a capacitor coupled to the DC input.  
     
     
         41 . The generator/starter system of  claim 39  wherein the second inverter further includes a PMG generator having a permanent magnet coupled to the squirrel cage rotor, a PMG winding magnetically coupled to the permanent magnet, and a rectifier coupled between the PMG winding and the DC input.  
     
     
         42 . The generator/starter system of  claim 38  further comprising: 
 an AC bus coupled to the AC output of the inverter; and,  
 a switch coupling an AC output of the inverter to the AC output of the main stator winding.