Islanding Detection via Negative-Sequence Current Injection
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Solution Overview
Problem
Existing islanding detection methods in power systems are inadequate, particularly for distributed energy sources like solar power regulators, as they often fail to detect islanding operations quickly due to factors like load state variations and resonance points, leading to unstable voltage and frequency, and prolonged detection times.
Innovation Solution
The method involves detecting negative-sequence voltage values, adding a small negative-sequence current variation, and using a weighting factor to adjust the current command, allowing for early detection of islanding operations even when voltage limits are not exceeded, thereby triggering protection mechanisms promptly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive detection methods (voltage, frequency, phase jump detection) are used, then the detection system is simple, but the detection capability is insufficient and non-detection zones exist
Solution Approach 1:
The patent introduces a negative-sequence current as an intermediary signal to detect islanding conditions. By injecting this specific current component and monitoring its interaction with the system impedance, the method creates a reliable detection mechanism that works across all load conditions, eliminating the non-detection zones inherent in passive voltage/frequency-based methods.
Solution Approach 2:
The patent replaces traditional passive electrical measurement methods (voltage, frequency detection) with an active current injection method. This substitution transforms the detection approach from observing natural system behavior to actively probing the system with a controlled current signal, enabling reliable detection regardless of load conditions.
2Reliability
If active anti-islanding detection methods (frequency or magnitude adjustment) are used, then the detection reliability is improved, but the detection time is prolonged due to slow voltage drift
Solution Approach 1:
The patent employs periodic injection of negative-sequence current at specific frequencies. By using periodic action rather than continuous gradual adjustment, the method achieves rapid detection of system changes while maintaining operational stability during normal conditions.
Solution Approach 2:
The patent changes the detection parameter from gradual voltage/frequency drift to immediate negative-sequence current response. By monitoring the system's reaction to injected current at different frequencies, the method achieves rapid parameter change detection that significantly reduces detection time compared to traditional active methods.
3Use of energy by moving object
If distributed energy generating equipment operates near maximum power point, then the energy efficiency is maximized, but the ability to perturb the power system for detection is insufficient
Solution Approach 1:
The patent applies partial action by injecting a small negative-sequence current component rather than significantly altering the operating point. This partial perturbation is sufficient to detect system changes while maintaining operation near the maximum power point, thus preserving energy efficiency while enabling detection.
Solution Approach 2:
The patent uses composite current injection by combining the normal operating current with a negative-sequence current component. This composite approach allows the system to maintain its primary function (power generation at maximum efficiency) while simultaneously performing detection through the superimposed current signal.
Data Source
AI summary
An islanding detection and protection method of a parallel-type power converter is proposed, which performs perturbation to a power system to detect the frequency of the system voltage and the variation of the magnitude of the negative-sequence voltage as the basis for deciding the occurrence of an islanding operation. When the system operates normally, the frequency or phase and magnitude of the system voltage and the magnitude of the negative-sequence voltage won't be affected by the perturbation. On the other hand, if an islanding operation occurs, this perturbation will cause an apparent drift of the frequency or phase and magnitude of the system voltage and the magnitude of the negative-sequence voltage. Through detection of this apparent drift, the perturbation can be amplified by means of positive feedback to quickly detect the islanding operation phenomenon and trigger the protection mechanism.