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 environmental control system includes an air cycle machine, an electrical machine coupled to the air cycle machine, and a controller for the electrical machine. The controller can cause electrical energy to be extracted from the electrical machine whenever cooling capacity and/or airflow rate of the air cycle machine are greater than necessary. The electrical machine can also be operated as a motor to increase the airflow rate and cooling capacity of the air cycle machine.

Abstract: A hybrid electrical power system includes a solid oxide fuel cell and a turbomachine. Fuel flow to the turbomachine is increased in response to demands for boost power, whereby the turbomachine's electrical generator provides the boost power. The turbomachine supplies heated, high pressure air to the solid oxide fuel cell, bringing the solid oxide fuel cell to its required operating temperature. Waste from the solid oxide fuel cell, including exhaust air and unreacted fuel, is utilized by the turbomachine.

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.