Transformer Leakage Impedance Estimation for Grid-Forming Converters
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Solution Overview
Problem
The challenge is to accurately determine the leakage impedance of a transformer connected to an AC network, which is crucial for estimating the short-circuit current supply capability of an electric power converter, especially in grid-forming scenarios where transformer characteristics may be unknown or variable.
Innovation Solution
The method involves an electric power converter determining the leakage impedance of the transformer by measuring voltage and current values at specific points in the system when the transformer's secondary side is disconnected from the AC network, and using these measurements along with predetermined impedance parameters of the output filter to calculate the leakage impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the leakage impedance of the transformer is not determined accurately, then the short-circuit current supply capability cannot be determined accurately, but determining the leakage impedance requires additional measurements and calculations when the transformer characteristics are unknown or variable
Solution Approach 1:
The patent applies preliminary action by performing impedance measurements during the commissioning phase before the converter enters normal operation. The control unit executes a commissioning routine that measures voltage and current values at the converter output and transformer secondary side when the converter is operating in grid-forming mode, calculates the leakage impedance in advance, and stores it for future use. This preliminary determination eliminates the need for complex real-time measurements during normal operation, resolving the contradiction between measurement accuracy and operational complexity.
2Reliability
If the transformer characteristics are unknown or may change due to component replacement, then the short-circuit current supply capability becomes uncertain, but re-measuring and re-calculating the leakage impedance ensures accurate determination
Solution Approach 1:
The patent implements feedback by creating a commissioning routine that automatically measures voltage and current values, calculates the leakage impedance, and stores the results in the control unit's memory. This automated feedback loop eliminates manual measurement and calculation processes, making the system easier to configure while ensuring reliable impedance determination. The routine can be executed whenever transformer components are replaced, providing updated impedance values without requiring complex manual procedures.
3Reliability
If the converter operates in grid-forming mode to provide sufficient short-circuit current, then short-circuit protection operates reliably, but the converter must know its supply capability in advance to operate correctly
Solution Approach 1:
The patent applies preliminary action by determining the leakage impedance during the commissioning phase before the converter enters normal operation. The control unit executes a commissioning routine that measures voltage and current values at the converter output and transformer secondary side, calculates the leakage impedance in advance, and stores it for future use. This preliminary determination eliminates the need for complex real-time measurements during normal operation, resolving the contradiction between measurement accuracy and operational complexity.
Data Source
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AI summary
A method for determining a leakage impedance of a transformer (30) and an electric power converter (10) configured to obtain values of a first voltage and a first current in an AC output of the electric power converter (10), a value of a second current between an output filter (20) connected to the AC output and a primary side of a transformer (30) connected to the output filter and a value of a second voltage on a secondary side of the transformer (30), wherein said values are obtained when the secondary side of the transformer (30) is disconnected from an AC network (50), and to determine a leakage impedance of the transformer (30) on the basis of the values of the first voltage, the first current, the second current and the second voltage, and at least one predetermined impedance parameter value of the output filter (20).