Voltage Source Converter Impedance Prediction Under Variable Operating Points
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Solution Overview
Problem
Current methods for analyzing small signal stability in power-electronics-based power systems, particularly for voltage source converters, are hindered by the need for known system parameters and structures, making impedance prediction under variable operating points time-consuming and impractical when these parameters are unknown.
Innovation Solution
A method is developed to construct a fully decoupled impedance model that separates impedance information into a coefficient parameter vector and an operating point vector, allowing for impedance prediction by measuring impedance under multiple operating points and identifying system parameters, enabling analysis of small signal stability even when parameters and structures are unknown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurement is performed under multiple operating points to obtain accurate impedance data, then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The patent performs impedance measurements at multiple operating points in advance to identify system parameters (resistive and reactive components). These identified parameters are stored and used for rapid impedance prediction at any operating point without requiring additional measurements, thus resolving the time-precision contradiction
Solution Approach 2:
The patent creates a mathematical model (equation 3) that copies the impedance characteristics from measured operating points. This model allows prediction of impedance at unmeasured operating points by substituting operating point parameters, eliminating the need for time-consuming repeated measurements while maintaining accuracy
2Reliability
If traditional impedance measurement methods are used under variable operating points, then reliability of impedance data is improved, but device complexity increases due to multiple measurements
Solution Approach 1:
The patent changes the approach from direct impedance measurement at each operating point to parameter identification (resistive and reactive components) at multiple points, followed by mathematical prediction. This parameter-based approach simplifies the measurement system while maintaining data reliability across variable operating points
3Measurement precision
If complete system parameters and structures are known for state-space modeling, then analysis accuracy is improved, but ease of operation deteriorates due to inability to obtain trade secret information
Solution Approach 1:
The patent extracts only the necessary impedance characteristics (resistive and reactive parameters) from the power electronic device through external measurements, without requiring access to internal structures or trade secret information. This extracted parameter approach enables accurate stability analysis while preserving commercial confidentiality
Solution Approach 2:
The patent uses an intermediary mathematical model that relates externally measurable impedance characteristics to stability analysis requirements. This model acts as a mediator between external measurements and internal stability assessment, eliminating the need for direct access to proprietary system parameters
Data Source
AI summary
A method for predicting impedance of a voltage source converter under variable operating points is disclosed, pertaining to the field of analysis of small signal stability in an electrical power system. When the parameters and topology of the control system are fully unknown, the theoretical expression of impedance cannot be applied to a voltage source converter, and impedance is highly dependent on operating points. A fully decoupled impedance model disclosed is constructed in this disclosure. The fully decoupled impedance model decomposes the impedance into a system parameter vector and an operating point vector, and then identifies parameters through impedance measurement, thereby realizing impedance prediction in a voltage source converter grid-connected system under variable operating points when the parameters and topology of the control system are fully unknown, expanding the scope of application of the impedance method and laying a foundation for using the impedance method to analyze small signal stability in engineering practices.