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A number of technology breakthroughs in the past ten years rekindled the concept of a more-electric aircraft. High-power solid-state switching devices, electrohydro-static actuators (EHAs), electromechanical actuators (EMAs), and high-speed generators are just a few examples of component developments. These developments have made dramatic improvements in properties such as weight, size, power, and cost. However, these components cannot be applied piecemeal. A complete, and somewhat revolutionary, system design approach was needed to exploit the benefits that a more-electric aircraft can provide. Traditional-mounted auxiliary drives, and bleed air extraction will disappear, to be replaced with integral engine starter/generators and electrically driven actuators and pumps. A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991.

The Fault Tolerant Electrical Power System (FTEPS) Air Force program conducted by Boeing concluded that future electrical systems can be designed to meet the stringent requirements of fly-by-wire and power-by-wire equipment on aircraft. A power system architecture was designed and implemented in a ground demonstrator that provides electrical power to flight-critical loads after three major system faults, provides electrical power to mission-critical loads after two major system faults, and provides electrical power to non-flight/mission critical loads after one major system fault. In addition, the system provides electrical power to the load buses that is 100 times more reliable than the typical loads on those buses. The FTEPS design is based on the ability of the system to manage the system loads by optimizing the distribution of the available source capacity.

Brushless Variable Speed Constant Frequency (VSCF) electric power generation may be obtained using cascaded symmetrically wound machines. The feasibility of using these machines as the basis for a stand-alone aircraft generator system was investigated by the USAF Aero Propulsion Laboratory. The concept is attractive as the system operates without hydraulics and employs a solid state power converter which operates at a fraction of the system output power and frequency. These factors combine to offer a system of relatively low complexity with the potential for high-reliability operation. This paper will discuss the operation of the cascaded doubly fed VSCF generator system and microprocessor control unit.