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Aircraft Electrical Power Systems and Nonlinear Dynamic Loads
Abstract:
Aircraft utilize electrical power for many functions ranging from simple devices such as resistive heaters to highly advanced and complex systems responsible for communications, situational awareness, electronic warfare and fly-by-wire flight controls. The operational states of these electronic systems affect safety, mission success and the overall economic expense of operation and maintenance. These electronic systems rely on electrical power within established limits of power quality.
In recent years, electrical power quality is becoming excessively degraded due to increased usage of nonlinear and dynamic loads coupled to aircraft power systems that were neither designed nor tested for these loads.
Legacy power generation systems were designed for electrical loads with resistive and inductive properties, which previously represented the majority of actual aircraft electrical loads. As more complex and advanced electronic systems were invented, mostly due to developments in semiconductors, the characteristics of electrical load signatures evolved and transitioned from mostly linear to a dominant nonlinear and randomly dynamic composition. This transition to predominantly nonlinear loads is primarily due to the fundamental processing techniques of electrical power from its original state (i.e. AC/DC source) to the various required intermediate and final states of power in order to accomplish the tasks required of the electronic systems.
Switch Mode Power Supplies (SMPSs) and other rectifying circuits using SCRs and diodes, are commonly used on the inputs to avionics equipment, creating the nonlinear loads that adversely affect the power system's power quality. The adverse effects can reduce reliability and degrade the electronic systems resulting in various degrees of faults.
Understanding cause and effect relationships of the dominant nonlinear and dynamic loads on aircraft electrical power systems is the purposes of this paper. Actual test data of military aircraft power systems exhibiting these conditions is presented here to make the reader aware of the problem and provide a relative basis for comparison. An analytical model is used to replicate the issues and show how simulations can aid engineers with determining the effects on their systems without performing costly and possibly destructive tests on actual equipment. These efforts support future activities such as revision of standards for aircraft electrical power systems and ultimately how they are designed, tested and utilized in a more severe and complex environment.