Hydraulic Pitch Velocity Feedforward Control
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Solution Overview
Problem
Hydraulic pitch systems in wind turbines face challenges in efficiently controlling blade pitch angles due to structural dynamics, which increase bandwidth in feedback loops and slow reaction times to environmental changes.
Innovation Solution
Implementing a feed-forward path that uses the reference velocity of a hydraulic cylinder, combined with a setting generated by a pitch controller, to reduce bandwidth requirements and improve control system responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a feedback loop is used to control the hydraulic pitch system, then the system can maintain stability and accuracy, but the structural dynamics increase the bandwidth requirements which slows down the reaction time to environmental changes
Solution Approach 1:
The feed-forward path calculates the required hydraulic cylinder velocity based on the derivative of the reference pitch angle in advance, before the feedback loop processes the error signal. This preliminary velocity command is combined with the feedback control output, allowing the system to proactively respond to reference changes without waiting for the feedback loop to detect and correct the error, thereby reducing reaction time while maintaining stability
Solution Approach 2:
A velocity filter is introduced as an intermediary element between the feed-forward velocity calculation and the final control output. This filter processes the velocity signal to reduce bandwidth requirements by attenuating high-frequency components that would otherwise increase system complexity and instability risks, while still allowing the feed-forward path to improve response speed
2Speed
If the bandwidth of the feedback loop is increased to improve response speed, then the reaction time decreases, but the system becomes more sensitive to structural dynamics and less stable
Solution Approach 1:
By calculating the velocity command in advance through the feed-forward path based on the reference pitch angle derivative, the system prepares the appropriate control action before disturbances or errors occur. This eliminates the need to increase feedback loop bandwidth for faster response, as the fast response is achieved through proactive control rather than high-bandwidth reactive control, thereby maintaining system stability
Solution Approach 2:
The system maintains a balanced combination of feed-forward and feedback control paths. The feedback loop continues to operate at moderate bandwidth to ensure stability and correct disturbances, while the feed-forward path provides the fast response to reference changes. This dual-path approach allows the system to achieve high response speed without compromising stability by over-increasing feedback bandwidth
3Speed
If a velocity filter is added to reduce bandwidth requirements, then the system complexity increases, but the reaction time to changes improves
Solution Approach 1:
The velocity filter serves as an intermediary that processes the feed-forward velocity signal to reduce its bandwidth requirements. By filtering the velocity command before it reaches the hydraulic actuator, the system reduces the bandwidth demands on the feedback loop and overall control system, thereby improving reaction time to reference changes while keeping the added complexity manageable through a single filtering stage
Data Source
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AI summary
Embodiments herein describe a hydraulic pitch system where a velocity (e.g., the velocity of a hydraulic cylinder or the piston rod in the cylinder) is fed forward and combined with a setting outputted by a pitch controller. The velocity of the hydraulic cylinder is derived from the reference pitch angle or a continuous pitch signal (e.g., a cyclic pitch or ramp rate) in the control system. In either case, the velocity can be determined by monitoring the change in the reference pitch angle or the continuous pitch signal. Using a gain control, the velocity is converted into a position setting of the hydraulic pitch system (e.g., a spool setting in a valve) which is combined with another position setting generated by the pitch controller.