Double-fed Asynchronous Generator Short-Circuit Current Control
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Solution Overview
Problem
Existing wind turbine generator systems face challenges in supplying sufficient short-circuit current to the network while protecting their components from inherent short-circuit currents, leading to potential device damage and safety risks due to inadequate triggering of protective devices.
Innovation Solution
A double-fed asynchronous generator is designed to maintain generator excitation during short circuits, allowing for the buildup of transient stator short-circuit currents, while protecting sensitive components by freezing the current value and adjusting it with correction values to meet network requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If converter systems are used to decouple generator frequency from mains frequency, then the generator can operate with variable speed and adapt to network requirements, but the converter components are destroyed by inherent short-circuit currents
Solution Approach 1:
The patent segments the current path by introducing a switching device that can separate the converter from the stator circuit during short-circuit events. This allows the converter to remain protected while the stator continues to supply short-circuit current to the network through an alternative path.
Solution Approach 2:
The switching device acts as an intermediary element between the converter and the stator. During normal operation, it connects both components; during short-circuit conditions, it redirects the current flow to protect the converter while maintaining network support capability.
2Reliability
If the converter is protected from short-circuit currents by switching devices, then converter components are saved, but no sufficient short-circuit current is supplied to trigger network protective devices
Solution Approach 1:
The switching device serves as a mediator that redirects rather than blocks the short-circuit current. It maintains the current flow path from the stator to the network while preventing the current from passing through the vulnerable converter components.
Solution Approach 2:
The patent extracts the harmful short-circuit current path from the converter circuit while preserving it in the stator circuit. The switching device effectively removes the converter from the current path during short-circuit conditions, allowing the stator to independently supply protective current to the network.
3Object-generated harmful factors
If synchronous generators are directly coupled to the grid, then short-circuit currents can be reliably supplied to trigger protective devices, but the system is susceptible to vibrations and high loads on the drive train
Solution Approach 1:
The switching device and control system act as intermediaries that enable the asynchronous generator to mimic the short-circuit current supply behavior of directly-coupled synchronous generators, while maintaining the operational advantages of variable speed operation and reduced mechanical stress.
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
This solution enables the generation of a predetermined short-circuit current in the stator winding, effectively triggering network protective devices and protecting converter systems from damage, ensuring safe operation and compliance with safety standards.
Implementation Method 1
the generator excitation is maintained and transient stator short-circuit currents can therefore build up
Data Source
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AI summary
The invention relates to a double-fed asynchronous generator, which is provided with a slipring rotor (1b), and to a method for its operation. In the normal manner, the asynchronous generator has a machine-side converter (5) and a network-side converter (6). According to the invention, the asynchronous generator is designed to supply short-circuit power in that at least one machine-side rotor current (iRM) is maintained in the event of a short circuit, in order to allow the formation of a stator-side short-circuit current. In order that inherent short-circuit currents in sensitive components of the converters (5, 6) are nevertheless avoided, at least the machine-side rotor current (iRM) is maintained in such a way that the actual rotor current (iRMact) in the event of a short circuit is used as the new nominal value in a control apparatus for the asynchronous generator.