Twelve-pulse ATRU Missing Phase Detection via Common-Mode Voltage
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Solution Overview
Problem
Existing twelve-pulse autotransformer rectifier units (ATRUs) face challenges in detecting missing phases and input supply drops, particularly in configurations where access to the 3-phase supply is restricted, such as within a fuel tank, leading to potential damage or malfunction and requiring complex and costly sealed feed-through connections.
Innovation Solution
A method and apparatus for detecting missing phases and input supply drops by monitoring the frequency and amplitude of the common-mode voltage impressed on the rectified DC output of a twelve-pulse ATRU, eliminating the need for direct connection to the 3-phase supply, using either analogue or digital circuits to determine these conditions relative to the generator neutral voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a monitoring circuit is placed outside the fuel tank to avoid complex sealed feed-through connections, then the device complexity and cost are reduced, but the ability to detect missing phases is compromised due to restricted access to the 3-phase supply
Solution Approach 1:
The patent uses the common-mode voltage as an intermediary signal that carries information about the 3-phase supply status. By monitoring this voltage that is already present on the DC output lines, the system can detect missing phases without requiring direct access to the AC supply or complex sealed connections through the fuel tank wall.
Solution Approach 2:
The monitoring circuit utilizes the existing DC output lines and the common-mode voltage naturally present on them for detection purposes. The system serves itself by using its own output signals as the monitoring source, eliminating the need for separate sensing connections to the AC input supply.
2Reliability
If sealed feed-through connections are added to enable monitoring of the 3-phase supply, then the missing phase detection capability is improved, but the device complexity and cost increase
Solution Approach 1:
The common-mode voltage serves as a mediator that transfers information about the AC supply status to the DC output side. This allows the monitoring circuit to obtain detection information without physical access to the AC input, avoiding the need for sealed feed-through connections.
Solution Approach 2:
The DC output lines serve dual functions: delivering power to the load and carrying the common-mode voltage signal for monitoring purposes. This multi-functionality eliminates the need for separate monitoring connections.
3Productivity
If the bridge drive is switched off quickly to enable hot restart, then the productivity is improved, but the risk of damage from undetected missing phases increases
Solution Approach 1:
The monitoring circuit continuously monitors the common-mode voltage before the bridge drive is switched off, ensuring that missing phase conditions are detected in advance. This preliminary detection allows the system to safely execute the quick shutdown required for hot restart capability without risking damage from undetected abnormalities.
Data Source
AI summary
A method and apparatus for detecting a missing phase in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU) which, in use, receives a 3-phase input and delivers a nominal DC output on which a common-mode voltage is impressed. At least one of the frequency and amplitude of the common-mode voltage are monitored thereby to determine whether there is a missing phase in the input. The frequency and/or amplitude of the common-mode voltage may also be monitored thereby to determine whether there is a loss of input voltage.