DFIG Rotor Current Control via Speed-Dependent Active Damping
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Solution Overview
Problem
Doubly-Fed Induction Generator (DFIG) systems in wind turbines face instability due to poorly damped oscillations in flux dynamics, leading to potential system instability and complicating rotor current control, especially under varying rotor speeds.
Innovation Solution
A compensation method that computes an instantaneous compensation control output based on the rotor's angular speed, decoupling rotor currents into orthogonal components and using lead filters to dampen oscillations, making the generator transfer function independent of rotor speed variations and reducing the need for additional hardware or signal differentiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard DFIG system is used with direct stator-to-grid connection, then the system structure is simplified and cost is reduced, but oscillations in flux dynamics are poorly damped leading to potential instability
Solution Approach 1:
The patent introduces an active damping controller as an intermediary component between the existing rotor current controller and the generator. This controller computes a damping torque reference that compensates for oscillations in flux dynamics, thereby stabilizing the system without requiring fundamental structural changes or additional hardware beyond the control system.
Solution Approach 2:
The patent changes the control parameters by dynamically adjusting the damping torque reference based on instantaneous rotor speed and flux dynamics. The active damping controller modifies the torque reference signal to counteract oscillations, effectively changing the system's dynamic characteristics to improve stability while maintaining the simplified DFIG structure.
2Reliability
If the bandwidth of the rotor current controller is reduced to avoid oscillations, then system stability is improved, but the controller reacts slower to changes in grid conditions
Solution Approach 1:
The patent implements feedback through the active damping controller that continuously monitors flux dynamics and rotor speed, then adjusts the damping torque reference in real-time. This feedback mechanism allows the system to maintain high controller bandwidth for fast response while actively compensating for oscillations that would otherwise require bandwidth reduction for stability.
3Manufacturing precision
If controller performance is optimized for specific rotor speeds through high qualification and test costs, then controller performance at those speeds is improved, but the system may become unstable or fail at other speeds
Solution Approach 1:
The patent makes the controller adaptive to varying rotor speeds by implementing speed-dependent active damping. The damping torque reference is computed based on instantaneous rotor speed, allowing the controller to automatically adjust its behavior for optimal performance and stability across the entire operating speed range without requiring extensive qualification and testing at each specific speed.
Data Source
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AI summary
A variable rotational speed wind turbine is disclosed, comprising a doubly-fed induction generator, a rotor current controller for controlling the rotor currents of the generator, compensation means having computation means, and means for providing input to the compensation means, the input being representative of at least the instantaneous angular speed of the rotor of the generator. The computation means is arranged to compute an instantaneous compensation control output in dependency of said instantaneous angular speed of the rotor of the generator and feed the compensation control output to the rotor of the generator, and to compute said compensation control output during operation of the wind turbine to compensate at least partly for dependencies on the rotor angular speed of the locations of poles of a generator transfer function, thus making a resulting generator transfer function substantially independent of variations in the rotor angular speed during operation of the wind turbine.