Fault-Tolerant Synchronisation Source for Three-Phase Generator Excitation
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Solution Overview
Problem
In three-phase synchronous generators, especially those used in aeronautical integral drive generators, the synchronization of excitation voltage control using a Point Of Regulation (POR) voltage source is compromised by unbalanced load conditions, short circuits, and open phase voltage sense conditions, leading to significant modulation of the POR voltage when the PWM frequency is not synchronized.
Innovation Solution
A synchronisation source that utilizes all three phase voltages and currents, allowing the system to continue functioning even if five out of six signals are lost, by summing and subtracting POR signals from two phases and one phase to produce a summer output signal with a frequency corresponding to the selected POR signals, and using a zero cross detector to convert this signal into a constant amplitude exciter synchronisation signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single POR phase voltage is used as a synchronisation source, then the excitation control can be simplified, but the system becomes vulnerable to faults and unbalanced conditions
Solution Approach 1:
The patent combines three POR phase voltages into a single synchronisation signal by summing them together. This merging approach creates a more reliable synchronisation source that remains functional even when individual phases fail or become unbalanced, as the combined signal maintains the necessary frequency characteristics for excitation control.
Solution Approach 2:
The synchronisation signal generation circuit is designed to serve multiple functions: it works under normal balanced conditions, continues to function under unbalanced load conditions, and remains operational during fault conditions such as open phase voltage sense conditions. This multi-functionality ensures reliable excitation control across all operating scenarios.
2Loss of energy
If PWM frequency is kept low to minimise switch losses, then energy efficiency improves, but synchronisation with POR frequency becomes difficult
Solution Approach 1:
The patent introduces an intermediary synchronisation signal generation circuit that processes the three POR phase voltages to create a reliable reference signal. This intermediary circuit acts as a mediator between the low-frequency PWM operation and the POR frequency requirements, enabling proper synchronisation without requiring high PWM frequencies and thus avoiding excessive switch losses.
3Device complexity
If only one phase voltage is monitored for synchronisation, then the measurement system is simpler, but fault detection capability is reduced
Solution Approach 1:
The measurement system combines information from all three phase voltages to generate the synchronisation signal. This combining approach enhances fault detection capability because the system can detect abnormalities in any individual phase while still maintaining operational synchronisation through the combined signal, providing both simplicity and improved measurement precision.
Data Source
AI summary
A fault-tolerant synchronisation source for excitation control of a three-phase generator system that combines point of regulation (POR) signals representing parameters comprising voltage and current for each phase at the POR to generate a fault-tolerant synchronisation signal.