Grid-Forming Converter Virtual Impedance Current Limiting

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Solution Overview

Problem

Existing grid-forming converters face challenges in current limiting while maintaining voltage source characteristics, leading to instability during disturbances and complex transient transitions.

Innovation Solution

A current limiting control method for grid-forming converters that utilizes virtual impedance adjustment in a two-phase coordinate system to limit output current without altering voltage source characteristics, employing a processor to adjust reference voltages based on preset maximum current limits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional amplitude limiting control is used to limit output current, then current limiting is achieved, but the converter loses voltage source characteristics and becomes unstable in weak grids

Engineering Contradiction:

Improveconverter stabilityVSAvoidcurrent overlimit

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces virtual impedance as an intermediary element in the control system. By adding virtual impedance to the output, the system can limit current without directly controlling the output current, thus maintaining voltage source characteristics while achieving current limiting functionality.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent dynamically adjusts the virtual impedance parameters based on the operating state of the converter. By changing the impedance parameters, the system can adaptively limit current under different conditions while preserving the voltage source characteristics necessary for grid stability.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If current limiting control is activated during large disturbances, then converter protection is improved, but complex transient transition process and poor power angle stability occur

Engineering Contradiction:

Improveconverter protectionVSAvoidtransient transition duration

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent pre-calculates and stores the relationship between output voltage and current limiting thresholds. When disturbances occur, the system can quickly determine the appropriate current limit without complex real-time calculations, reducing transient transition time and improving response speed.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism that monitors the converter's operating state and adjusts the current limiting threshold accordingly. This feedback control ensures that the converter receives adequate protection during disturbances while maintaining stability and minimizing transient transitions.

Inventive Principle:

Principle #23Feedback

3Object-generated harmful factors

If virtual impedance current limiting is used, then voltage source characteristics are maintained, but additional control complexity is introduced

Engineering Contradiction:

Improvevoltage source characteristic preservationVSAvoidcontrol system complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent integrates virtual impedance current limiting into the existing voltage and current control loops, making the control system multi-functional. The same control structure serves both voltage regulation and current limiting purposes, reducing the need for separate control mechanisms and managing complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Reliability

If converter output current is limited during disturbances, then grid stability is improved, but power output reduction occurs

Engineering Contradiction:

Improvegrid stabilityVSAvoidconverter power output

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent dynamically adjusts the current limiting threshold based on the severity and type of disturbance. During minor disturbances, the current limit is relaxed to maintain power output, while during severe disturbances, the limit is tightened to ensure grid stability. This dynamic adjustment optimizes the trade-off between stability and power output.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS20250309753A1Current limiting control method for grid-forming converter, converter, and storage medium

Publication Date: 2025.10.02 XIAMEN KEHUA DIGITAL ENERGY TECH CO LTD

AI summary

A current limiting control method and apparatus for a grid-forming converter, a converter, and a storage medium are provided. The method includes the following operations. A three-phase output reference voltage of a converter is acquired. A transformation is performed to obtain an output reference voltage on a first axis and an output reference voltage on a second axis in a preset two-phase coordinate system corresponding to the three-phase output reference voltage. Virtual impedance current limiting adjustment is performed on the output reference voltage on the first axis and/or the output reference voltage on the second axis by using a preset maximum output current limit value of the converter, to obtain an target output reference voltage on the first axis and an target output reference voltage on the second axis in the preset two-phase coordinate system, so as to acquire a three-phase target output voltage of the converter.