Reactive Power Islanding Detection Under Harmonics and Distortion
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Solution Overview
Problem
Existing islanding detection methods in power systems face challenges such as non-detection zones, poor detection performance under sudden load changes, and false detection issues, especially in systems with harmonics and distortions.
Innovation Solution
A method involving the calculation and injection of reactive power based on specific equations and a determination process, using a processor to measure frequency and angular frequency, and adjusting the reactive power injection cycles according to a failure confirmation count, to accurately determine islanding without false detection in disturbance and distortion systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If passive method is used for islanding detection, then implementation simplicity and detection speed are improved, but detection accuracy deteriorates due to non-detection zones and susceptibility to load changes
Solution Approach 1:
The patent introduces reactive power injection as an intermediary element to detect islanding conditions. By injecting a known reactive power signal into the system and measuring the resulting voltage change, the method creates a measurable intermediary effect that reliably indicates islanding status, overcoming the passive method's inability to detect small changes.
Solution Approach 2:
The patent changes the system parameter by injecting reactive power rather than using passive measurement only. This active parameter change (reactive power injection) creates a detectable voltage frequency shift that occurs only during islanding conditions, transforming the detection from passive observation to active measurement with higher accuracy.
2Measurement precision
If active method with reactive power injection is used, then detection accuracy is improved, but false detection occurs in systems with disturbances and harmonics
Solution Approach 1:
The patent employs feedback by measuring the voltage frequency change resulting from reactive power injection and comparing it against expected values. The system continuously monitors the frequency shift and uses this feedback to confirm islanding detection, which helps distinguish true islanding events from false conditions caused by disturbances or harmonics.
Solution Approach 2:
The patent uses dynamic measurement of voltage frequency change rather than static threshold comparison. By measuring the actual frequency shift caused by reactive power injection and comparing it to the expected dynamic response, the system can adapt to varying system conditions and distinguish true islanding from false conditions caused by disturbances.
3Device complexity
If conventional active method is used without specific injection equations, then implementation is simpler, but detection reliability deteriorates due to lack of detailed determination logic
Solution Approach 1:
The patent segments the islanding detection process into distinct calculation steps: calculating base reactive power from active and reactive power commands, determining injection amount based on system parameters, measuring voltage frequency change, and comparing against thresholds. This segmentation provides detailed determination logic for each stage, improving reliability while maintaining implementation clarity.
Solution Approach 2:
The patent performs preliminary calculations of reactive power injection amount based on active power command, reactive power command, and system parameters before actual injection. This preliminary action establishes the expected frequency change baseline, which is then used to reliably determine islanding conditions during actual operation.
Data Source
AI summary
Apparatus and method for determining islanding of a system are provided. The method includes: calculating an amount of reactive power injection based on an active power command and reactive power command received from an upper controller of the distributed power; setting a failure confirmation count to 0; controlling injection of reactive power during a preset cycle among predetermined cycles of an AC voltage that is an output of the distributed power according to the failure confirmation count; measuring a frequency and angular frequency of the AC voltage, which is performed simultaneously with the injection of reactive power; and after the injection of reactive power is completed, increasing the failure confirmation count if a determination criteria based on the measurement of the frequency and the angular frequency of the AC voltage; and determining an islanding failure when the failure confirmation count reaches a preset value.