DC-to-AC Converter Reactive Current Injection for Grid Overvoltage
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Solution Overview
Problem
Wind turbines with DC-link voltage source converters face challenges in managing temporary overvoltages, leading to potentially disruptive DC-link voltage increases when grid voltage exceeds a certain limit, necessitating a method to maintain connection to the grid while controlling output voltages.
Innovation Solution
A method involving a DC-to-AC voltage converter that determines line voltage and injects reactive current into the power line to keep the output voltage within a predetermined range, using phase lock loop algorithms and specific current reference calculations to optimize active and reactive current injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wind turbine remains connected to the grid during overvoltages, then grid stability and power supply continuity are improved, but the DC-link voltage rapidly increases which can damage the converter
Solution Approach 1:
The control system proactively detects overvoltage conditions and preemptively adjusts the converter operation by limiting output voltage and injecting reactive current, preventing the DC-link voltage from rising before the harmful effect occurs
Solution Approach 2:
The harmful overvoltage condition is converted into a beneficial situation by using the excess grid voltage to generate reactive current injection, which limits the converter output voltage and thereby prevents DC-link voltage increase, transforming the harmful overvoltage into a protective mechanism
2Object-affected harmful factors
If the wind turbine interrupts connection to the grid during overvoltages, then DC-link voltage is protected, but power supply continuity and grid stability are compromised
Solution Approach 1:
Reactive current injection acts as an intermediary mechanism between the converter and the grid, allowing the wind turbine to remain connected while the reactive current limits the converter output voltage, thereby protecting the DC-link voltage without interrupting the connection
Solution Approach 2:
The control system changes the operating parameters of the converter by limiting the output voltage magnitude and adjusting the current injection characteristics, enabling the converter to operate safely during overvoltage conditions while maintaining grid connection
3Object-affected harmful factors
If reactive current is injected to limit output voltage, then DC-link voltage stability is improved, but converter output current capacity is reduced
Solution Approach 1:
The control system dynamically adjusts the balance between active and reactive current components based on the severity of the overvoltage condition, optimizing the trade-off between voltage limitation and active power injection capacity in real-time
Solution Approach 2:
The control system applies partial reactive current injection only to the extent necessary to limit the output voltage, avoiding excessive reactive current that would unnecessarily reduce active power capacity, thereby achieving minimal impact on power injection
Data Source
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AI summary
According to an embodiment, a method of operating a wind turbine comprising a DC-to-AC voltage converter is provided, the wind turbine being connectable to a grid via the DC-to-AC voltage converter, the method comprising: determining a line voltage of a power line connecting the DC-to-AC voltage converter to the grid; if the determined line voltage exceeds a predefined voltage threshold value, injecting reactive current into the power line, wherein the amount of reactive current injected is chosen such that an output voltage of the DC-to-AC voltage converter is kept within a predetermined voltage range.