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In the last two decades, an aerospace industry trend in the secondary power distribution concept has been dominated by power electronics technology which includes power converters and Power Control Modules based on Solid State Power Control (SSPC) switching elements. These Power Control Modules, grouped around microprocessor based controllers and combined in a single electronic chassis, have become a backbone of electrical power distribution systems on all major commercial and military transport aircraft. Due to the resistive properties of the semiconductor-based SSPC devices, whose behaviors can be described as nonlinear functions of ambient operating temperature, power distribution system integration with SSPCs is challenged and heavily affected by operating temperatures and power dissipation limits. Although aircraft compartments where Power Control Modules are located are considered temperature and pressure controlled, high ambient operating temperatures are possible and expected.

In a more electric aircraft, with strong demand for numerous independently controlled AC and DC power utilities, a new concept of secondary power distribution system has emerged. Based on common core software applications, local area network, and electronic modules with Solid State Power Controllers (SSPC), secondary power distribution system becomes a network of independent Power Distribution Units (PDU), installed in various locations throughout aircraft fuselage. This new decentralized concept has many benefits, including wiring weight reduction, electronic over-current and arc fault protection, and software controlled circuit breakers status and indication. An attempt to optimize allocation of SSPCs to aircraft electric utilities and the number of electronic Power Modules in Power Distribution Units has become a more complex problem. Each Power Distribution Unit contains several Power Electronics modules, where each module has its own power dissipation limit.