Grid-Connected Inverter Islanding Detection via Adaptive Phase Locking
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Solution Overview
Problem
Existing islanding detection methods in grid-connected power supply systems are excessively slow, leading to safety risks due to the inability to promptly detect the islanding effect, which occurs when a portion of the grid remains live during an outage, posing hazards to maintenance personnel and equipment.
Innovation Solution
A method and apparatus that utilize closed-loop and open-loop phase-locking mechanisms to detect frequency deviations at the point of common coupling, injecting a frequency perturbation to rapidly identify islanding by switching phase-locking modes based on frequency thresholds, ensuring precise and swift detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional perturbation injection methods are used for islanding detection, then the detection method is simple to implement, but the detection speed is excessively slow
Solution Approach 1:
The patent dynamically switches between closed-loop phase-locking (for normal operation) and open-loop phase-locking (for islanding detection) based on frequency deviation thresholds. This dynamic switching enables the system to rapidly detect islanding conditions by injecting frequency perturbations only when needed, significantly improving detection speed while minimizing detection delay
Solution Approach 2:
The patent changes the phase-locking mode parameter from closed-loop to open-loop based on frequency deviation conditions. When frequency deviation exceeds a threshold, the system transitions to open-loop mode to inject frequency perturbations, enabling rapid islanding detection. This parameter change allows the system to achieve fast detection without continuous perturbation injection
2Speed
If closed-loop phase-locking is used continuously, then the system maintains stable operation, but the islanding detection speed becomes excessively slow
Solution Approach 1:
The system dynamically adjusts the phase-locking mode based on operating conditions. During normal operation, closed-loop phase-locking maintains system stability. When frequency deviation exceeds the threshold, the system switches to open-loop mode for rapid islanding detection. This dynamic adjustment resolves the contradiction by maintaining stability when needed and enabling fast detection when conditions warrant
Solution Approach 2:
The patent implements periodic monitoring of frequency deviation and periodically switches between closed-loop and open-loop modes based on detected conditions. This periodic action allows the system to maintain stability through closed-loop operation during normal conditions while periodically attempting islanding detection through open-loop operation, achieving both stability and detection speed
Data Source
AI summary
An islanding detection method includes: continuously detecting a voltage frequency at a point of common coupling; calculating, according to the voltage frequency, a frequency deviation of the voltage frequency between two adjacent detections; obtaining, when the frequency deviation is less than a preset frequency threshold, a voltage phase in a preset closed-loop phase-locking manner; obtaining, when the frequency deviation is greater than or equal to the preset frequency threshold, the voltage phase in a preset open-loop phase-locking manner; determining, according to the frequency deviation, the voltage frequency, and the voltage phase, a reference current for injecting a frequency perturbation; controlling, according to the reference current, the grid-connected inverter to output a current to the point of common coupling; and determining, when the voltage frequency exceeds a preset range, that an islanding effect occurs.