Phase-Locked Loop Pole Placement for Islanding Detection
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Solution Overview
Problem
Current islanding detection methods in power generation systems often fail to meet stringent standards, particularly in terms of zero non-detection zone and rapid detection of disconnection from the grid, especially in systems with renewable energy sources, due to inadequate positive feedback mechanisms and instability issues in phase-locked loops.
Innovation Solution
A phase-locked loop (PLL) system with large signal non-linear positive feedback and small signal modifications is used to detect frequency drift, moving the pole from the left half-plane to the right half-plane, ensuring unconditional instability in the absence of phase information from the grid, thereby achieving a zero non-detection zone and rapid islanding detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional islanding detection methods are used, then the system can operate continuously, but the detection reliability and speed fail to meet IEEE 1547 standards with zero non-detection zone
Solution Approach 1:
The patent implements a modified PLL system with positive feedback mechanism that introduces a pole in the right half-plane, creating unconditional instability when grid synchronization is lost. This feedback mechanism ensures that any islanding condition triggers immediate frequency drift detection, achieving zero non-detection zone while maintaining systematic operation
Solution Approach 2:
The patent changes the stability parameter of the PLL system by introducing a pole in the right half-plane through modification of the synchronization loop. This parameter change transforms the system from stable to unconditionally unstable under islanding conditions, enabling rapid detection without requiring complex additional detection apparatus
2Speed
If the PLL system is made unstable to detect islanding, then detection speed improves, but the system becomes overly sensitive to normal grid variations
Solution Approach 1:
The patent applies local quality by making the instability condition specific to the loss of grid synchronization rather than a general system property. The modified PLL maintains stability during normal operation but becomes unconditionally unstable only when grid connection is lost, as indicated by the pole placement that responds specifically to synchronization loss
3Measurement precision
If positive feedback is increased to ensure unconditional instability, then zero non-detection zone is achieved, but system stability during normal operation deteriorates
Solution Approach 1:
The patent applies dynamics by designing the PLL system to have different stability characteristics under different operating conditions. The system maintains stability during normal grid-connected operation but transitions to unconditional instability when grid synchronization is lost, achieving condition-dependent behavior that satisfies both detection precision and operational stability requirements
Data Source
AI summary
A small signal feedback loop or feed-forward loop having gain provides substantially unconditional instability in a phase locked loop when a reference phase signal is lost. The small signal feedback or feed-forward also modifies phase locked loop bandwidth when the reference phase signal is lost to increase rapidity of response to loss of reference phase signal while maintaining insensitivity to reference voltage amplitude change while the reference phase signal is present. The performance thus achieved is particularly suitable for rapid condition detection response and control of a grid connected power converter under islanding conditions.