Power Dissipation Optimization for Solid State Power Control Modules in the Aircraft Secondary Power Distribution System

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. For that reason, Power Control Modules with multiple SSPC channels, at room ambient operating temperature, cannot utilize maximum power capacity, which means that a certain number of power control channels cannot be used for power distribution. As a result of that, to accommodate power dissipation potential growth over extended ambient operating temperature range, additional hardware has to be used. With the emergence of more electric aircraft, where a significant number of AC and DC type aircraft electrical loads have been connected to Power Control Modules, total power dissipation limitation with additional hardware has been creating significant impact on total equipment weight and cost. In an attempt to increase power density of the Power Control Modules and to mitigate the risk of permanent damage caused by excessive power dissipation at high ambient operating temperatures, this article presents a unique systems integration concept based on power management and electrical load shed as a function of critical ambient operating temperatures. The presented concept is scalable and can be implemented with no effect on aircraft performances and critical system functions.