TRU Backfeed Interlock Using AC/DC Sensing and Contactor Isolation
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Solution Overview
Problem
Conventional aircraft electrical power systems face challenges in preventing backfeed from alternate sources, such as batteries, when AC input power is lost, due to limited space for AC relays and the inability of DC relays to provide equivalent functionality.
Innovation Solution
A system incorporating a transformer rectifier unit (TRU) with a backfeed sense module and contactor driver that detects backfeed by monitoring AC and DC input lines, triggering the contactor to open and disconnect the DC bus from the TRU when backfeed is detected, thereby preventing overload of alternate power sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AC relay is used to open primary system contactors when TRU input power is lost, then proper load shedding is ensured, but insufficient room is available in the AC system for the relay
Solution Approach 1:
The patent introduces a backfeed sense module as an intermediary device that monitors both AC input lines and DC output lines. This module detects backfeed conditions and generates signals to control contactor opening, serving as a mediator between power sources and contactors without requiring additional AC relay space
Solution Approach 2:
The backfeed sense module performs multiple functions: it monitors AC input power status, detects DC backfeed from alternate sources, and controls contactor operation. This multi-functional approach replaces the need for separate AC relay while ensuring proper load shedding
2Area of stationary object
If a DC relay is placed downstream of the TRU, then space constraints are addressed, but the relay cannot provide equivalent backfeed prevention functionality
Solution Approach 1:
The backfeed sense module implements a feedback mechanism by continuously monitoring DC output lines for backfeed conditions and AC input lines for power status. When backfeed is detected (DC power present while AC power is lost), the module generates a signal to open the contactor, providing active backfeed prevention without requiring additional space
3Stability of the object's composition
If primary system contactors remain closed during AC power loss, then DC bus continuity is maintained, but alternate power sources become overloaded
Solution Approach 1:
The backfeed sense module performs preliminary detection of backfeed conditions by monitoring both AC and DC lines. When it detects that AC power is lost while DC power is still present (indicating backfeed from alternate sources), it proactively opens the contactor before the alternate power source becomes overloaded, preventing power capacity issues while maintaining DC bus stability through controlled transition
Data Source
AI summary
A system includes a transformer rectifier unit (TRU) including a backfeed sense module. A contactor is operatively connected to the TRU for selectively supplying DC power to a DC bus from the TRU with the contactor closed and isolating the DC bus from the TRU with the contactor opened. A contactor driver is operatively connected to receive a signal from the backfeed sense module and to control opening and closing of the contactor based on the signal. The contactor driver is configured to open the contactor upon receipt of the signal indicative of backfeed detected in the TRU.