Inverter Islanding Detection via Harmonic Change Rates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing voltage THD-based islanding detection method for inverters has low reliability due to a large detection dead zone, as it fails to accurately detect islanding conditions when changes in harmonics do not significantly affect the total harmonic distortion.
Innovation Solution
The proposed method involves sampling and performing harmonic analysis on the alternating voltage signal from the inverter's AC port, calculating voltage harmonics and their change rates, and determining the voltage total harmonic distortion based on these factors, triggering anti-islanding protection when the distortion exceeds a specified threshold, without degrading output power quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If voltage THD-based islanding detection method is used, then the detection method is simple to implement, but the islanding detection reliability is low due to large detection dead zone
Solution Approach 1:
The patent changes the detection parameter from total harmonic distortion (THD) to individual harmonic components and their change rates. By monitoring the change rate of specific harmonics (particularly 3rd, 5th, 7th harmonics) rather than the aggregate THD value, the method can detect islanding conditions that do not significantly affect total harmonic content, thereby eliminating the detection dead zone while maintaining implementation feasibility through standard signal processing techniques.
2Device complexity
If voltage THD-based detection is used, then the calculation is straightforward, but various harmonic changes cannot be reflected accurately
Solution Approach 1:
The patent segments the total harmonic distortion into individual harmonic components (3rd, 5th, 7th, etc.) and monitors each component's change rate separately. This segmentation allows the detection method to capture specific harmonic variations that aggregate THD calculations miss, improving measurement precision while keeping computational complexity manageable through focused analysis of key harmonic orders.
Solution Approach 2:
The patent adds a temporal dimension by introducing the change rate of harmonic components over time. Instead of only measuring the magnitude of harmonics, the method evaluates how rapidly harmonic components are changing, which provides an additional detection dimension that enhances accuracy in identifying islanding transitions while maintaining computational efficiency.
Data Source
Figure 1~2
Figure 3a~3b
Figure 4
AI summary
The present invention discloses an islanding detection method and apparatus for an inverter, and a power supply system, to resolve a problem that an existing voltage THD-based islanding detection method has low islanding detection reliability due to existence of a relatively large detection dead zone. The method includes: sampling an alternating voltage signal output from an alternating current port of an inverter (50); performing harmonic analysis on the alternating voltage signal to obtain various voltage harmonics and change rates of the voltage harmonics (51); determining a voltage total harmonic distortion based on the voltage harmonics and the change rates of the voltage harmonics (52); and if the voltage total harmonic distortion is greater than a specified threshold of the voltage total harmonic distortion, determining that an islanding effect of the inverter is detected (53). According to this detection method, the voltage total harmonic distortion changes more significantly before and after the islanding effect of the inverter occurs, so as to reduce an islanding detection dead zone and improve islanding detection reliability.