Islanding Detection Using Reactive Power and Frequency Shift
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Solution Overview
Problem
Existing islanding detection methods, both passive and active, suffer from non-detection zones and false detections due to system disturbances and distortions, particularly harmonics, especially when multiple distributed powers are involved.
Innovation Solution
A method involving calculating reactive power injection based on specific equations and a determination process that includes measuring AC voltage frequency and angular frequency, with reactive power injection in controlled cycles and directions, to accurately determine islanding even in distorted systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reactive power is injected to determine islanding, then detection accuracy is improved, but false detection occurs in systems with disturbances and distortions
Solution Approach 1:
The patent introduces frequency and angular frequency as intermediary parameters to mediate between reactive power injection and islanding detection. By measuring frequency deviation and angular frequency changes caused by reactive power injection, the system can determine islanding conditions without directly relying on reactive power measurements alone, thereby reducing false detections in distorted systems
Solution Approach 2:
The patent implements a feedback mechanism where frequency and angular frequency measurements are continuously monitored and fed back to adjust the islanding determination logic. The controller uses the measured frequency deviation and angular frequency to dynamically adjust detection thresholds and confirmation requirements, improving reliability while maintaining detection accuracy
2Ease of manufacture
If passive method is used to detect islanding, then implementation simplicity is improved, but detection performance deteriorates in non-detection zones
Solution Approach 1:
The patent applies preliminary action by injecting reactive power before islanding detection is performed. This proactive injection creates measurable frequency and angular frequency deviations that make islanding detection more reliable, especially in non-detection zones where passive methods fail. The reactive power injection is performed as a preparatory step to ensure detectable signals are present
Solution Approach 2:
The patent uses periodic reactive power injection at specific cycles of the AC voltage waveform. By injecting reactive power during predetermined cycles and measuring frequency responses during these periodic intervals, the system achieves both simplicity (through structured periodic measurement) and improved detection performance (through enhanced signal characteristics)
3Speed
If active method is used to detect islanding, then detection speed is improved, but false detection occurs due to lack of detailed determination logic
Solution Approach 1:
The patent changes the parameters used for islanding detection from conventional voltage/current magnitude changes to frequency and angular frequency parameters. By monitoring frequency deviation and angular frequency changes caused by reactive power injection, the system achieves fast detection (inheriting active method speed) while improving reliability through parameters that are less susceptible to false detections in distorted systems
4Power
If multiple distributed powers are applied, then power supply capacity is improved, but detection performance deteriorates
Solution Approach 1:
The patent uses frequency and angular frequency as intermediary parameters that are system-wide and unaffected by the number of distributed power sources. These intermediary measurements provide a unified detection basis that works consistently whether one or multiple distributed powers are present, maintaining detection performance while allowing increased power supply capacity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate islanding detection without false positives, even in the presence of harmonics, by calculating reactive power injection through precise frequency and angular frequency measurements.
Implementation Method 1
measuring a frequency and angular frequency of the AC voltage
Implementation Method 2
measuring a frequency and angular frequency of the AC voltage
Implementation Method 3
injecting reactive power during a preset cycle among predetermined cycles of an AC voltage
Data Source
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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.