Wind Turbine Converter Control for Mechanical Oscillation Damping
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Solution Overview
Problem
Conventional wind turbine converter systems struggle to effectively damp mechanical oscillations and reduce speed ripples, leading to inefficiencies and increased load on generator and drive train components.
Innovation Solution
A control method for wind turbine converters that uses separate control signals for the generator and utility grid converter portions, with the generator side portion maintaining constant torque for high-frequency rotational speed variations, and the utility grid side portion adjusting power accordingly to damp mechanical oscillations and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If generator power is held constant at varying generator rotational speed, then power control simplicity is improved, but mechanical resonance damping capability deteriorates
Solution Approach 1:
The control system dynamically adjusts the torque reference signal based on the frequency characteristics of generator rotational speed variations. A frequency-dependent control strategy is implemented where the torque reference is modified according to whether the speed variation frequency is above or below a threshold frequency, enabling the system to adapt its control behavior to different operating conditions and effectively damp mechanical resonances while maintaining power control simplicity
2Device complexity
If conventional converter control is used with single control signal, then device complexity is reduced, but mechanical oscillation damping and speed ripple reduction are insufficient
Solution Approach 1:
The converter control is segmented into two independent control loops: a generator converter portion controlled by a first control signal and a utility grid converter portion controlled by a second control signal. This segmentation allows each portion to be optimized for specific functions - the generator side for torque control and resonance damping, and the grid side for power delivery - thereby improving mechanical oscillation damping performance without significantly increasing overall system complexity
Solution Approach 2:
Different control strategies are applied to different portions of the converter system. The generator converter portion uses a control strategy focused on torque regulation and resonance damping, while the utility grid converter portion uses a control strategy optimized for power delivery and grid synchronization. This local optimization of control quality enables effective damping of mechanical oscillations while maintaining acceptable system complexity
3Adaptability or versatility
If generator torque varies with rotational speed, then power adjustment capability is improved, but load on generator and drive train components increases
Solution Approach 1:
The control system implements dynamic torque management by adjusting the torque reference signal based on the frequency characteristics of rotational speed variations. For high-frequency speed variations above a threshold frequency, the torque reference is modified to maintain constant torque, thereby reducing mechanical loads on the generator and drive train components while still allowing power adjustment for low-frequency variations where it is beneficial
Data Source
AI summary
Provided is a method of controlling a converter, in particular of a wind turbine, the converter including a first converter portion connected to a generator, a DC-link, and a second converter portion connected to a utility grid. The method including: controlling the first converter portion and the second converter portion by a first control signal and a second control signal, respectively, both being derived based on a requested power signal, in particular requested active power signal, and a generator rotational speed, wherein the first control signal indicates substantially constant generator torque for rotational speed variations of the generator rotational speed above a frequency threshold.