Integrated M/G
StarRotor is developing an integrated compressor/motor and expander/generator. Although many electrical devices can be integrated (e.g., induction, permanent magnet), the most promising technology is a switched reluctance (SR) motor/generator. Instead of using permanent magnets or windings on the rotating equipment, SR devices use iron laminate poles that address two issues that occur with integration: fluid compatibility and elevated temperatures.
Fluid compatibility - SR devices can have external windings that are isolated from potentially aggressive fluids, and the iron laminates can be appropriately coated.
Elevated temperatures - At high temperatures, permanent magnets lose magnetism and winding insulation degrades. In contrast, the iron laminates work at elevated temperatures.
SR motors work as follows: iron laminate rotor poles are attracted to sequentially energized electromagnetic stator poles. Increasing the firing rate of the stator poles increases the rotational speed. Energizing multiple stator poles at the same time increases the torque density.
SR generators work as follows: a small seed current is invested to energize the magnetic circuit comprised of the stator and aligned rotor pole. Once the seed current is cut off, electrical energy is created in the stator pole as the rotor pulls away.
Benefits:
- Hermetic - eliminates shaft seal
- Compact
- Light weight
- Torque/power dense
- Variable speed