Wind Turbine Rotor Frequency Control via Pitch Offset

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Solution Overview

Problem

Conventional methods for controlling rotor frequency in wind turbines are not accurate enough, especially in low wind conditions, and may not prevent resonance frequencies from coinciding with rotor frequencies, leading to mechanical stress and inefficiencies.

Innovation Solution

A method and system that use a pitch angle offset signal to adjust the blade pitch angle of wind turbine rotor blades, calculated based on rotational frequency, to avoid critical resonance frequencies by generating a pitch angle offset signal that changes with rotational speed, thereby reducing the time spent in critical motion regions and minimizing mechanical stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If generator torque or power is controlled to avoid critical frequencies, then rotor frequency can be controlled, but this method is not accurate enough in low wind conditions and may not prevent resonance coincidence

Engineering Contradiction:

Improve rotor frequency control accuracyVSAvoid effectiveness in low wind conditions

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The invention changes the control parameter from generator torque/power to blade pitch angle. By adjusting the pitch angle of the rotor blades, the rotor frequency can be controlled directly and accurately without relying on generator torque control, which is ineffective in low wind conditions. This parameter change enables precise frequency control across all wind conditions including low wind scenarios.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the electrical control mechanism (generator torque control) with a mechanical control mechanism (blade pitch angle control). The pitch angle offset signal mechanically adjusts the blade orientation to control rotor frequency, providing a more direct and reliable control method that works independently of generator operating conditions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Strength

If rotor frequency is controlled to avoid resonance, then mechanical stress is reduced, but the control method may not work during curtailment or low wind conditions

Engineering Contradiction:

Improve mechanical stress reductionVSAvoid operability during curtailment

Core Design Contradiction:

StrengthVSAdaptability or versatility

Solution Approach 1:

The invention uses blade pitch angle as the control parameter instead of generator torque. The pitch angle offset signal is calculated based on the difference between current rotor frequency and target frequency, enabling continuous adjustment of rotor frequency to avoid resonance frequencies regardless of generator operating status or wind conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The control system continuously monitors rotor frequency and automatically adjusts pitch angle to maintain frequency away from resonance values. The system serves itself by using real-time frequency measurements to generate the appropriate pitch angle offset signal, ensuring continuous protection against resonance without external intervention.

Inventive Principle:

Principle #25Self-service

3Power

If conventional torque control is used, then power flow can be controlled, but rotor frequency control accuracy is insufficient and resonance avoidance fails

Engineering Contradiction:

Improve power flow controlVSAvoid rotor frequency control precision

Core Design Contradiction:

PowerVSMeasurement precision

Solution Approach 1:

The invention separates the control functions by introducing a dedicated pitch angle offset control layer that specifically targets rotor frequency control, while the default pitch angle signal handles power flow control. This segmentation allows independent optimization of frequency control accuracy without compromising power management.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The pitch angle offset signal acts as an intermediary between the frequency measurement and the blade pitch actuation. It translates the frequency difference into the appropriate pitch angle adjustment, providing precise control of rotor frequency while working in conjunction with the default pitch control for power management.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8979492B2Methods and systems for determining a pitch angle offset signal and for controlling a rotor frequency of a rotor of a wind turbine for speed avoidance control

Publication Date: 2015.03.17 SIEMENS GAMESA RENEWABLE ENERGY AS

AI summary

A method for determining and applying a pitch angle offset signal for controlling a rotor frequency of a rotor of a wind turbine is disclosed. The method includes obtaining a motion quantity indicative of a motion of the rotor and determining the pitch angle offset signal based on the motion quantity such that the pitch angle offset signal is adapted to be used for adjusting a blade pitch angle of a rotor blade mounted at the rotor for controlling the rotor frequency in order to reduce a time span during which the rotor is in a critical motion region. A corresponding system and a method for controlling a rotor frequency are also disclosed.