Turbocharged auxiliary power unit with controlled high speed spool

Abstract

An APU system includes a gas turbine engine having a low pressure spool, a high pressure spool and an electrical generator. The electrical generator is driven by the high pressure spool which is governed to a constant speed. Conversely, the low pressure spool is not governed at all, but is allowed to seek a speed that balances the power developed by the low pressure turbine (LPT) and power absorbed by the low pressure compressor (LPC). A step increase/decrease in electrical power demand is met with a step increase/decrease in fuel flow, which results in an overshoot/undershoot of the new equilibrium turbine inlet temperature TIT. The TIT returns to the new equilibrium when the LP spool has achieved it's new shaft speed and new equilibrium power balance. The HP Spool and generator maintain essentially constant speed and frequency, while the LP Spool responds to restore equilibrium. The APU's response to sudden power change is thereby effectively immediate as the power change is decoupled from the large mechanical inertia of the HP and LP spools.

Dependencies are inferred from the claim text.