Converter Thevenin Modeling for Harmonic Grid Interaction Analysis
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Solution Overview
Problem
The increasing presence of converter systems in power grids, particularly in renewable energy sources like offshore wind farms and solar farms, poses challenges due to the production of harmonics, which existing methods struggle to accurately model and analyze, affecting grid stability and operation.
Innovation Solution
A method to determine a converter Thevenin equivalent model by measuring voltage and current at a coupling point between a grid emulator system and the converter system, transforming these measurements into the frequency domain, and using a coupled system model to calculate the Thevenin impedance and voltage source, while accounting for grid emulator parameters to optimize grid operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If converter systems are used in renewable energy sources, then energy generation capability is improved, but harmonic production increases causing grid stability issues
Solution Approach 1:
The patent introduces a grid emulator system as an intermediary device between the converter system and the actual grid. This emulator includes a converter, filter, and transformer that collectively model the grid's impedance characteristics, allowing harmonic analysis to be performed in a controlled laboratory environment rather than directly on the live grid, thus resolving the contradiction between energy generation and harmonic control
2Ease of operation
If Thevenin equivalent model is used for analyzing converter harmonics, then steady state impact analysis is simplified, but measurement accuracy at point of common coupling is reduced
Solution Approach 1:
The patent performs preliminary characterization of the grid emulator system before conducting converter system measurements. By first determining the Thevenin equivalent parameters of the grid emulator itself (open-circuit voltage and impedance), the system establishes a known reference model that compensates for measurement inaccuracies, thereby maintaining both analytical simplicity and measurement precision
3Reliability
If grid emulator system is used to model grid impedance, then converter system analysis is improved, but device complexity increases
Solution Approach 1:
The patent divides the grid emulator system into distinct functional segments: a converter unit, a filter unit, and a transformer unit. Each segment can be independently modeled and characterized, with the converter modeled as a voltage source, the filter as an impedance network, and the transformer providing galvanic isolation. This segmentation reduces overall system complexity while maintaining analysis reliability
4Measurement precision
If multiple measurement passes with different grid emulator settings are performed, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent implements a two-pass measurement approach where the first pass collects preliminary data for initial parameter estimation, and the second pass performs refined measurements with adjusted grid emulator settings. This partial repetition of measurements provides sufficient precision improvement without the excessive time cost of multiple full measurement sequences, balancing accuracy requirements with time efficiency
Data Source
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AI summary
A method for determining a converter Thevenin equivalent model (52) for a converter system (12), comprises: receiving measurement values of a coupling point voltage (vm) and of a coupling point current (im) measured at a point of common coupling (24) between a grid emulator system (14) and the converter system (12), wherein the grid emulator system (14) supplies the converter system with a supply voltage; and determining a converter Thevenin impedance (zd(ω)) and a converter Thevenin voltage source (vd(ω)) of the converter Thevenin equivalent model (52) by inputting the measurement values of the coupling point voltage (vm) and of the coupling point current (im) into a coupled system model (58), which comprises equations modelling the converter system (12) and the grid emulator system (14) and from which the converter Thevenin impedance (zd(ω)) and a converter Thevenin voltage source (vd(ω))) are calculated.