Aircraft DC Power Quality Characteristics of a PCTRU 2008-01-2890
An overview of aircraft DC power quality specifications reveals that only minor changes have occurred in recent years within industry standards. Current and future advanced electronic aircraft are requiring significant power quality improvements due to increased use of digital and COTS (commercial off the shelf) systems.
Certain electronic systems do not function properly due to various types of electrical disturbances. Some systems shutdown, fault or exhibit operational delays due to power interruptions or “blackout” conditions. Undervoltage or “brownout” conditions also cause this effect. Some electronic systems exhibit critical faults that can affect safety or mission success due to overvoltage conditions. Additional effects of high voltage spikes or overvoltage transients are known to reduce the life of utilization equipment , which is directly related to the health of the aircraft's electronic system and creates an economic burden.
These disturbances are described as high voltage transients, low voltage transients or brownouts, power interruptions and voltage modulation. Another type of perceived perturbation on the DC bus is caused by ripple voltage. All of these are fundamental DC power quality characteristics that can induce problems in electronic systems.
These disturbances are caused by various portions of the entire electrical power system consisting of AC generators, transmission lines, power converters, contactors, electrical power distribution controls and AC/DC loads from utilization equipment.
Presented here is a power supply system described as a Passively Controlled Transformer Rectifier Unit (PCTRU) that preserves the desired reliability of a traditional transformer rectifier unit (TRU) while providing stability to the aircraft 28 VDC bus and mitigating risks caused by these various electrical disturbances.