Abstract: An air conditioning system for an aircraft includes cascaded high and low pressure turbines, an electric generator that is driven at variable speeds by the low pressure turbine, and a fan that is also driven by the low pressure turbine. During operation of the air conditioning system, ac power is generated by the electric generator and provided to electrical equipment onboard the aircraft. Because the electric generator is driven at variable speeds, it generates ac power having variable frequency. The air conditioning system further includes a bypass valve for bypassing the high pressure turbine when speed of the electric generator approaches a lower limit. Bypassing the high pressure turbine allows generator speed to be increased. The fan has a speed-cubed load characteristic that maintains the generator speed below an upper limit. Thus, the bypass valve and the fan can be used to limit the speed of the electric generator and thereby maintain frequency of the ac power between upper and lower limits.

Abstract: An electrical power system for an aircraft includes an ac generator bus, an air conditioning system ("ACS") generator and a main engine generator. The ACS generator supplies primary ac power to the bus while the frequency of the ac power is within a frequency range. If the frequency of the ac power goes outside the frequency range, the main engine generator supplies backup ac power to the bus. The frequency of the ac power generated the ACS generator is maintained between upper and lower limits. Such ac power can be used directly by certain ac loads onboard the aircraft. Other ac loads onboard the aircraft are supplied with fixed frequency ac power by reduced-size inverters.