Doubly Fed Asynchronous Generator Reactive Current Distribution
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Solution Overview
Problem
Existing methods for controlling wind energy plants with double-fed asynchronous generators during asymmetrical network faults do not efficiently manage reactive current distribution between rotor-side and grid-side converters, leading to potential overloading and inadequate support during severe asymmetrical conditions.
Innovation Solution
A method that measures actual mains voltage values, transforms them into negative sequence system values, and sets target reactive current values using a characteristic curve, distributing these between rotor-side and grid-side converters to ensure coordinated reactive current injection, thereby preventing excessive load on the rotor-side converter and effectively supporting the network during asymmetrical faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reactive current is injected during asymmetrical network faults to support the electrical supply network, then network support capability is improved, but the rotor-side converter may become overloaded
Solution Approach 1:
The patent divides the reactive current injection task between two separate converters: the rotor-side converter and the grid-side converter. The control device calculates a total reactive current requirement and distributes it as a first reactive current to the rotor-side converter and a second reactive current to the grid-side converter. This segmentation prevents overloading of the rotor-side converter while maintaining network support capability.
Solution Approach 2:
The control device acts as an intermediary that coordinates between the reactive power requirement and the two converters. It determines the total reactive current needed for network support, then intelligently distributes this current between the rotor-side and grid-side converters based on their respective capabilities and operating conditions, preventing overload while achieving the required support level.
2Stability of the object's composition
If reactive current injection is used to support voltage during network faults, then voltage stability is improved, but converter complexity increases
Solution Approach 1:
The control device continuously monitors the actual reactive current being injected and compares it with the target value calculated from the characteristic curve. Based on this feedback, it adjusts the distribution of reactive current between the two converters to maintain voltage stability while preventing overload conditions. The system uses feedback from voltage measurements and converter status to dynamically adjust control parameters.
Solution Approach 2:
The patent implements dynamic control where the distribution of reactive current between converters is continuously adjusted based on real-time operating conditions. The control device modifies the reactive current setpoints for both converters dynamically during fault conditions, allowing the system to adapt to changing network conditions and converter capabilities rather than using fixed distribution ratios.
Data Source
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AI summary
The present invention relates to a method for controlling a wind turbine connected to a three-phase electrical supply network during an asymmetrical grid fault. The present invention also relates to a wind turbine designed for carrying out the method. In particular, the method is designed for wind turbines with a doubly fed asynchronous generator. In the method according to the invention, the reactive current to be fed into the grid is generated in the counter system by the grid-side and rotor-side converters in a coordinated manner, depending on the grid voltage. Furthermore, in the method according to the invention, the reactive current to be fed into the electrical supply network is distributed between the rotor-side and grid-side converters.This allows the reactive power to be supplied even in the case of highly asymmetrical grid faults, and prevents excessive strain on the rotor-side converter using simple means.