Dynamic Cut-in Speed Control for DFIG Wind Turbines
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Solution Overview
Problem
Current wind generation systems are inefficient in low wind zones, as they have predetermined cut-in and cut-out wind speed thresholds, limiting their operational range and energy capture in conditions with average wind speeds below 6.0 m/s.
Innovation Solution
A method and system for controlling wind generation systems, specifically using a rotation speed calculation module to dynamically adjust the cut-in rotation speed of a doubly-fed induction generator (DFIG) by calculating a dynamic cut-in rotation speed based on target active power, reactive power, and grid voltage, and adjusting the DC link voltage and transformer turn ratio to extend the operational range in low wind conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If predetermined cut-in and cut-out wind speed thresholds are used, then the wind generation system operates reliably within safe limits, but the operational range is limited and energy capture is reduced in low wind zones
Solution Approach 1:
The patent implements dynamic adjustment of the cut-in wind speed threshold based on real-time converter status. When the converter is in voltage control mode with sufficient voltage headroom, the system dynamically lowers the cut-in threshold from the predetermined value (e.g., 3 m/s) to enable operation at lower wind speeds (e.g., 2 m/s or below), thereby extending the operational range and capturing more energy in low wind zones while maintaining reliability through continuous monitoring of converter capabilities
Solution Approach 2:
The system changes the operational parameter (cut-in wind speed threshold) based on the converter's voltage headroom availability. By monitoring the difference between the actual DC link voltage and the maximum allowable DC link voltage, the system adapts the cut-in threshold parameter in real-time, allowing operation at lower wind speeds when voltage margin exists and maintaining the higher predetermined threshold when voltage margin is insufficient, thus resolving the contradiction between reliability and energy capture
2Productivity
If the cut-in wind speed threshold is lowered to capture more energy, then energy capture increases in low wind zones, but system stability may be compromised
Solution Approach 1:
The system employs feedback control by continuously monitoring the DC link voltage and comparing it against the maximum allowable voltage. This feedback mechanism determines whether the converter has sufficient voltage headroom to operate at lowered cut-in thresholds. The control system adjusts the cut-in threshold based on this feedback, ensuring that lowering the threshold to capture more energy does not compromise system stability, as operation at reduced thresholds is only permitted when voltage margins confirm stable operation is possible
3Adaptability or versatility
If DC link voltage and transformer turn ratio are adjusted dynamically, then operational range extends to lower wind speeds, but control system complexity increases
Solution Approach 1:
The system performs preliminary assessment of converter status and voltage headroom before enabling operation at lowered cut-in thresholds. The control method pre-evaluates whether the converter can safely operate with reduced voltage margins by checking if the actual DC link voltage is sufficiently below the maximum allowable voltage. This preliminary action simplifies the control logic by establishing clear pre-conditions for dynamic threshold adjustment, avoiding the need for complex real-time control algorithms while still achieving extended operational range
Data Source
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AI summary
A wind generation system (100) includes a wind turbine (1) for generating mechanical power, a doubly-fed induction generator (2) for converting the mechanical power to electrical power, a converter (3) for converting the electrical power to a desired electrical power for supplying to a power grid, and a transformer (7) through which a stator of the generator (2) is coupled to the power grid. When a measured rotation speed feedback from the rotor (21) of the generator is lower than an original cut-in rotation speed of the rotor, a cut-in rotation speed of the rotor is lowered by determining a DC link (33) voltage margin of the converter, determining a DC link (33) voltage setpoint of the converter based on the determined DC link (33) voltage margin; and controlling the converter (3) based on the determined DC link (33) voltage setpoint; and/or by increasing a turn ratio of the transformer (7) to reduce a grid voltage from the power grid (6).