MMC Converter Charging for Wind Farm Blackstart HVDC Links
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Solution Overview
Problem
Existing methods for charging capacitors in modular multilevel converters (MMC) and high voltage DC links require an external power source, preventing renewable power plants like wind farms from offering blackstart services during a blackout.
Innovation Solution
A method that uses the power generated by the wind farm itself to charge the capacitors of MMC converters and DC links through controlled and uncontrolled charging steps, synchronizing with the AC network and controlling charging currents without external power sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external power source is used to charge capacitors, then capacitors can be charged to nominal voltage, but renewable power plants cannot provide blackstart service
Solution Approach 1:
The wind farm uses its own generated power to charge the capacitors of MMC converters and DC links through controlled and uncontrolled charging steps, eliminating the need for external power sources and enabling blackstart service capability
Solution Approach 2:
The method performs preliminary charging of capacitors in two stages: first uncontrolled charging to build up voltage, then controlled charging to reach nominal voltage. This preliminary action enables the system to start up independently without external power support
2Device complexity
If uncontrolled charging is used, then charging process is simpler, but charging currents are not controlled
Solution Approach 1:
The charging process is divided into two distinct stages: uncontrolled charging phase for initial voltage buildup, and controlled charging phase for precise voltage regulation. This segmentation allows each stage to optimize for its specific function, simplifying overall control while ensuring reliability
Solution Approach 2:
The charging process alternates between uncontrolled and controlled modes in a periodic sequence. The system first performs uncontrolled charging, then transitions to controlled charging when certain voltage thresholds are reached, creating a rhythmic charging pattern that balances simplicity and precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the capacitors to be charged to nominal voltage without external power, allowing the wind farm to restore the electrical network and offer blackstart services, reducing downtime and equipment needs.
Implementation Method 1
voltage and frequency control of said AC network by means of the wind turbines
Implementation Method 2
charging of the capacitors of the cells and synchronisation with the AC network
Data Source
Figure 1A~1B
Figure 2~3B
Figure 4
AI summary
Disclosed is a method for supplying an external supply network (8) through a DC link (4), the external supply network (8) being connected to the DC link (4) by a DC/AC converter (3) and the power plant (1) being connected to the DC link (4) by means of an AC/DC converter (2), allowing start-up without an external power transmission network, comprising: increasing the voltage in the AC network (7); charging the AC/DC converter (2) and DC link (4); reducing the voltage in the AC network (7); synchronising the AC/DC converter (2) and the AC network (7); increasing the voltage of the DC/AC converter (3); charging the DC/AC converter to a nominal voltage; and starting-up the DC/AC converter (3).