An APU power section compressor anti-surge control method based on generator priority

In cases the total demand for aircraft exceeds APU capability, it may cause EGT over-temperature or power section compressor surge, which may damage APU. Currently, most APUs of commercial aircraft are set with control logic to prevent EGT over-temperature, but there is no similar control method to prevent power section compressor surge. In this paper, an APU power section compressor anti-surge control method based on generator priority was established. ECU monitors fuel flow and compare it with fuel flow limit in real time to determine whether the operating point of power section compressor is beyond the surge control line. If so, generator load is prioritized, ECU command IGV to cut back to reduce the pneumatic load, so that the APU operates within the surge control line. APU steady-state performance calculation model with generator priority anti-surge control logic was established. Using this model, the variation of IGV angle and corresponding bleed performance under the limitation of surge can be predicted. On-board flight tests were conducted, through which the effective accomplishment of this method on aircraft was verified and validated. Through comparing of flight test data and model simulation results verified error of the model is within acceptable engineering range.