Grid Impedance Estimation for Islanding Detection Without Signal Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for detecting islanding conditions in grid-tied power converters using LCL filters introduce harmonic components that can affect other systems, leading to efficiency issues and potential disconnection, as they require signal injection to estimate grid impedance.
Innovation Solution
A method that estimates grid impedance without injecting additional signals by using a digital controller to separate the transfer function of the power converter, LCL filter, and grid, employing a recursive least squares algorithm to calculate coefficients, and adjusting current controller parameters to maintain system efficiency and detect islanding conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal injection methods are used to estimate grid impedance, then measurement precision is improved, but object-generated harmful factors worsen due to harmonic components affecting other systems
Solution Approach 1:
The patent extracts only the necessary information (grid impedance parameters) from the system's normal operation signals without requiring additional signal injection. The recursive least squares algorithm processes existing current and voltage measurements to obtain impedance estimates, eliminating the need to inject periodic or non-periodic signals that would generate harmful harmonics.
Solution Approach 2:
The system uses its own operational signals (current and voltage measurements during normal operation) to estimate grid impedance. The method enables the system to self-diagnose grid conditions using data already available from its operation, without requiring external signal injection that would disturb the grid and affect other connected systems.
2Reliability
If signal injection is performed to detect islanding conditions, then detection capability is improved, but productivity worsens due to system disconnections and efficiency loss
Solution Approach 1:
The patent enables continuous monitoring of grid impedance parameters during normal system operation without interrupting power flow or causing system disconnections. The recursive least squares algorithm continuously updates impedance estimates using ongoing current and voltage measurements, allowing islanding detection while maintaining uninterrupted system operation and productivity.
Solution Approach 2:
The patent replaces traditional signal injection methods (which require active perturbation of the system) with a computational approach using recursive least squares algorithm. This substitution allows detection of islanding conditions through mathematical processing of normal operational signals, eliminating the need to disrupt system operation for detection purposes.
3Object-affected harmful factors
If LCL filters are used in power converters, then switching noise attenuation is improved, but device complexity worsens due to high-order dynamics and resonant modes
Solution Approach 1:
The patent implements a feedback mechanism where the estimated grid impedance parameters are continuously used to adjust the current controller settings. The recursive least squares algorithm provides real-time impedance information that feeds back to the controller, enabling adaptive tuning that compensates for the complex dynamics of LCL filters and maintains stability despite the high-order system characteristics.
Solution Approach 2:
The patent dynamically changes controller parameters based on estimated grid impedance conditions. By continuously updating impedance estimates and adjusting controller gains accordingly, the system adapts to varying operating conditions and compensates for the resonant modes inherent in LCL filter configurations, maintaining performance without requiring oversimplified filter designs.
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
This invention describes a method (100) for estimating the electrical parameters of a grid (1) which are relevant for detecting islanding conditions and for the operation of a power converter (5) connected to said grid (1).