DFIG Wind Turbine Mode Switching for Low-Speed Reactive Power
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Solution Overview
Problem
Wind turbines with doubly-fed induction generators face challenges in providing reactive power, especially at low wind speeds, making them non-compliant with stringent grid code requirements and necessitating costly full converter topologies or additional compensation equipment.
Innovation Solution
A method and control system that switches operational modes based on monitored parameters, increasing generator speed at the expense of active power to maintain reactive power capability, reducing rotor currents and voltages, and avoiding the need for additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wind turbine operates in maximum power point tracking mode to maximize active power generation, then the active power output is maximized, but the reactive power capability is significantly reduced at low wind speeds
Solution Approach 1:
The control system dynamically switches between two operational modes based on wind speed conditions. In the first mode (higher wind speeds), the turbine operates at maximum power point tracking. In the second mode (lower wind speeds), the turbine operates with reduced active power to maintain reactive power capability. This dynamic adaptation resolves the contradiction by allowing the system to optimize for active power when available and switch to maintaining reactive power capability when needed.
Solution Approach 2:
The invention changes the operational parameters (active power output and rotor speed) based on wind speed conditions. By reducing the active power output and adjusting the rotor speed in low wind conditions, the system maintains the generator speed within a range that preserves reactive power capability, thus resolving the trade-off between active power generation and reactive power provision.
2Reliability
If a full converter topology is used to maintain reactive power capability across all generator speeds, then the reactive power capability is maintained, but the system complexity and costs increase significantly
Solution Approach 1:
The invention extracts only the necessary reactive power provision capability from the power converter system by using a doubly-fed induction generator with a partial converter (converter connected only to the rotor). This approach maintains reactive power capability at low speeds without requiring a full converter topology, thus reducing system complexity and costs while preserving the essential function.
Solution Approach 2:
The doubly-fed induction generator is designed to perform multiple functions: active power generation, reactive power provision, and speed control. By utilizing the inherent capabilities of the DFIG and implementing a dual-mode control strategy, the system achieves reactive power capability across a wide speed range without requiring additional dedicated equipment, thus reducing overall system complexity.
3Reliability
If additional compensation equipment is added to enhance reactive power provision, then the reactive power capability is improved, but the system complexity and costs increase
Solution Approach 1:
The wind turbine system provides its own reactive power compensation through the doubly-fed induction generator's inherent capability. By controlling the rotor current through the partial converter, the system can generate or consume reactive power as needed without requiring external compensation equipment such as STATCOMs or capacitor banks, thus reducing system complexity and costs.
4Reliability
If the generator speed is increased to maintain reactive power capability at low wind speeds, then the reactive power provision is enhanced, but the active power generation is reduced
Solution Approach 1:
In low wind conditions, the system operates with partial active power generation to maintain the generator speed within a range that preserves reactive power capability. Rather than attempting to maximize both active and reactive power simultaneously (which is not feasible), the system accepts reduced active power output as a partial action to ensure sufficient reactive power provision, thus resolving the contradiction.
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
Enhances reactive power provision across a wide range of operating conditions without significant active power reduction, meeting grid code requirements and maintaining efficiency while avoiding costly full converter topologies.
Implementation Method 1
a power generating system including a doubly-fed induction generator (DFIG) that converts rotational mechanical power to electrical power
Data Source
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AI summary
A method of operating a wind turbine is provided, wherein the wind turbine comprises a power generating system (20) including a doubly-fed induction generator (21) that converts rotational mechanical power to electrical power. The method includes operating the wind turbine (100) in a first operational mode in which a speed of a rotor (101) of the wind turbine is controlled so as to maximize the power generation by the wind turbine. Upon a monitored parameter reaching or dropping below a respective threshold, the wind turbine is operated in a second operational mode. The monitored parameter may include at least one of the rotational speed of the rotor, the rotational speed (ωgen) of the doubly-fed induction generator (21), a wind speed, an active electrical power (Pactive) produced by the doubly-fed induction generator (21), or generator torque. Operating the wind turbine in the second opera- tional mode may include increasing the rotational speed (ωgen) of the doubly-fed induction generator (21) at the expense of the generation of active electrical power by the power generating system