Doubly Fed Induction Generator Line Side Converter Grid Stability
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Solution Overview
Problem
Wind turbines face challenges in providing grid stability reactive power currents while maintaining frequency support, as existing systems require strengthening of equipment, leading to high costs and limitations in operating capacity.
Innovation Solution
A control method and apparatus that couples the stator and rotor of a doubly fed induction generator to the grid using a line side converter with high current carrying capacity switches and a dynamic brake, allowing for increased grid stabilizing currents and reduced stator current demand, thereby enhancing power production during disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If known shorting devices (crowbar circuit) are used to absorb or deflect power during excessive power level conditions, then DC link voltage can be protected from damage, but high torque peaks are caused to the generator shaft that excite vibrations in the coupled drive train and additional cost is added to the system
Solution Approach 1:
The patent extracts the grid stabilizing current function from the stator and transfers it to the rotor through the power converter. This allows the stator to focus on power production while the rotor handles grid stability currents, eliminating the need for crowbar circuits and their associated harmful torque peaks and vibrations.
Solution Approach 2:
The power converter acts as an intermediary between the rotor and the grid, enabling the rotor to supply grid stabilizing reactive power currents. This intermediary mechanism protects the DC link voltage without requiring direct shorting devices that cause harmful torque peaks.
2Reliability
If the generator is required to provide current for grid stability, then grid stability is improved, but the generator's capability to provide frequency support is reduced
Solution Approach 1:
The patent segments the current supply functions by having the rotor provide grid stabilizing reactive power currents while the stator provides frequency supporting currents. This segmentation allows both functions to operate simultaneously without compromising either grid stability or frequency support capability.
Solution Approach 2:
The patent utilizes the rotor-stator dimension separation to independently control different current functions. The rotor handles reactive power for grid stability while the stator manages active power for frequency support, effectively using dimensional separation to resolve the contradiction.
3Reliability
If equipment is strengthened to account for excessive forces from sudden power changes, then system reliability is improved, but cost increases significantly
Solution Approach 1:
The patent implements beforehand cushioning by using the power converter to smoothly manage power transfer and prevent sudden power changes that cause excessive forces. This proactive control prevents the need for strengthened equipment while maintaining system reliability under transient conditions.
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 reliable frequency support and increased grid stabilizing currents, allowing the stator to produce more power while reducing the need for equipment strengthening, thus improving the wind turbine's response to grid transients and stability.
Implementation Method 1
The spin of the blades caused by the wind spins a shaft of the rotor, which connects to a generator that generates electricity
Implementation Method 2
Power converters are used to transfer the power for the wound rotor of the generator to a grid connection
Data Source
AI summary
A system and method for supplying increased frequency supporting current from a doubly fed induction generator (DFIG) to assist in maintaining grid stability is provided. The output capability of a line side converter associated with the DFIG is enhanced by significantly increasing the current handling capacity of electric switches forming the converter. A dynamic brake is also provided across a DC link bus coupling the line side converter to another converter coupled to the rotor of the DFIG. The dynamic brake is controlled based on the voltage across the DC link bus.