Wind Turbine Pitch System Research Articles

New method for lubricating wind turbine pitch gears using embedded micro-nozzles

The increase of power generated by wind turbines has increased the stresses applied in all of its components, thereby causing premature failures. Particularly, pitch and yaw gears suffer from excessive wear mainly caused by inappropriate lubrication. This paper presents a novel method to automatically lubricate the wind turbine pitch gear during operation. A micro-nozzle to inject fresh grease continuously between the teeth in contact was designed, manufactured, and installed in a test bench of a 2 MW wind turbine pitch system. The test bench was used to characterize the fatigue behavior of the gear surface using conventional wind turbine greases under real cyclic loads. Measurements of wear evolution in a pitch gear with and without micro-nozzle show a decrease of 70 % of the wear coefficient after 2×104 cycles.

Fault-tolerant wind turbine pitch control using adaptive sliding mode estimation

Abstract Wind turbine pitch systems are essential for actuating desired blade angles and hence to keep the generator at rated speed in operation region 3. In the presence of parametric pitch actuator faults, pitch systems may have slow dynamics, affecting the pitching performance with the possibility of oscillation on the generator speed and making the turbine system unstable and unsafe. This work proposes a strategy for compensating the pitch actuator faults to recover the nominal pitch dynamics. The proposed fault-tolerant control (FTC) scheme incorporates a traditional Proportional-Integral (PI) controller as baseline system to achieve nominal pitch performance, along with a fault compensator to eliminate the actuator fault effects. The approach is based on estimation of the pitch system states and fault indicator function using an adaptive step-by-step sliding mode observer, effectively handling the nonlinear fault distribution function with a simple design. The effectiveness of the design strategy is verified using a 4.8 MW benchmark wind turbine system.

Fault Diagnostics for Electrically Operated Pitch Systems in Offshore Wind Turbines

This paper investigates the electrically operated pitch systems of offshore wind turbines for online condition monitoring and health assessment. The current signature based fault diagnostics is developed for electrically operated pitch systems using model-based approach. The electrical motor faults are firstly modelled based on modified winding function theory and then, current signature analysis is performed to detect the faults. Further, in order to verify the fault diagnostics capabilities in realistic conditions, the operating profiles are obtained from FAST simulation of offshore wind turbines in various wind conditions. In this way, the applicability of current signature analysis for fault diagnostics in offshore wind turbine pitch systems is demonstrated.

Predictive pitch control of an electro-hydraulic digital pitch system for wind turbines based on the extreme learning machine

An electro-hydraulic digital pitch system is proposed in this paper to regulate output power and drive-train torque for wind turbines. This pitch system is driven by an electro-hydraulic digital servo system and can be digitally controlled to regulate the blade pitch angle with relatively high control accuracy and fast response. A closed control loop of this pitch system is presented and an extreme learning machine is online trained to represent the nonlinear wind turbine characteristics in this control loop. Furthermore, a predictive pitch controller is designed to improve the final pitch control performances by using the established extreme learning machine. Comparative experimental results are presented to illustrate the achievable significant performance improvements on output power and drive-train torque regulations by using the proposed pitch system and predictive pitch controller.

Adaptive sliding mode back-stepping pitch angle control of a variable-displacement pump controlled pitch system for wind turbines

A variable-displacement pump controlled pitch system is proposed to mitigate generator power and flap-wise load fluctuations for wind turbines. The pitch system mainly consists of a variable-displacement hydraulic pump, a fixed-displacement hydraulic motor and a gear set. The hydraulic motor can be accurately regulated by controlling the pump displacement and fluid flows to change the pitch angle through the gear set. The detailed mathematical representation and dynamic characteristics of the proposed pitch system are thoroughly analyzed. An adaptive sliding mode pump displacement controller and a back-stepping stroke piston controller are designed for the proposed pitch system such that the resulting pitch angle tracks its desired value regardless of external disturbances and uncertainties. The effectiveness and control efficiency of the proposed pitch system and controllers have been verified by using realistic dataset of a 750 kW research wind turbine.

Automated on‐line fault prognosis for wind turbine pitch systems using supervisory control and data acquisition

Current wind turbine (WT) studies focus on improving their reliability and reducing the cost of energy, particularly when WTs are operated offshore. A supervisory control and data acquisition (SCADA) system is a standard installation on larger WTs, monitoring all major WT sub-assemblies and providing important information. Ideally, a WT's health condition or state of the components can be deduced through rigorous analysis of SCADA data. Several programmes have been made for that purposes; however, the resulting cost savings are limited because of the data complexity and relatively low number of failures that can be easily detected in early stages. This study proposes a new method for analysing WT SCADA data by using an a priori knowledge-based adaptive neuro-fuzzy inference system with the aim to achieve automated detection of significant pitch faults. The proposed approach has been applied to the pitch data of two different designs of 26 variable pitch, variable speed and 22 variable pitch, fixed speed WTs, with two different types of SCADA system, demonstrating the adaptability of the approach for application to a variety of techniques. Results are evaluated using confusion matrix analysis and a comparison study of the two tests is addressed to draw conclusions.

Input-to-State Stability Condition for Passive Fault-Tolerant Control of Wave and Wind Energy Converters

In this paper, the input-to-state stability (ISS) property of Takagi-Sugeno models is proposed to derive an LMI condition for the passive fault-tolerant; control (FTC) of renewable energy systems. In particular, the FTC problem of wave energy converters (WTC) and wind turbines (WT) is considered. From the control point of view, the renewable energy source is assumed to be an unknown input acting on the controlled system. In the faulty case, without active fault compensation, it must be ensured that the system can be further operated. For this purpose, an easily applicable sufficient condition is specified, whereby structural uncertainties are taken into account. The usability (of the ISS concept for FTC is demonstrated by means of a mechanical pitch system for small-scale wind turbines.

Control Engineering Analysis of Mechanical Pitch Systems

With the help of a local stability analysis the coefficient range of a discrete damper, used for centrifugal forced, mechanical pitch system of small wind turbines (SWT), is gained for equilibrium points. – By a global stability analysis the gained coefficient range can be validated. An appropriate approach by Takagi-Sugeno is presented in the paper.

Fault diagnosis of variable pitch for wind turbines based on the multi-innovation forgetting gradient identification algorithm

This paper presents the fault diagnosis algorithm of the variable pitch system for wind turbines. The considered variable pitch system model is characterized by a second- order differential equation and is transformed into the discretization equation and the difference equation. Then, the fault diagnosis problem is transformed into a parameter estimation issue, and the multi-innovation forgetting gradient (MIFG) identification algorithm is adopted. As the MIFG algorithm uses not only current data but also the past data at each iteration, the parameter estimation accuracy can be improved. The validity of fault diagnosis using MIFG algorithm for pitch system is verified by simulation examples.

Modelling and characteristics analysis of the pitch system of large scale wind turbines

The individual pitch drive system of large-scale wind turbines was analysed in this article. In this pitch system, the induction motor, three-stage planetary gearbox, and motor vector control were adopted. In order to investigate the system dynamic behaviour, its non-linear dynamical model was established, mainly including three parts: induction motor model in d— q frame, dynamic model of three-stage planetary gears, and transmission shaft model. The dynamic responses of gearbox—blade subsystem and motor—gearbox—blade system were analysed in detail, respectively. Then, the pitch system control model was established in which rotor flux field-oriented vector control and double close-loop servo control with speed and position feedback were employed. In simulation, the algorithm TR-BDF2 was adopted to solve the dynamic equations. The research results show that the deviation between the pitch angle and its command value is very small in steady state, pitch speed and acceleration fluctuations appear when impact effect is produced due to gear backlash, and the different blade may have different variable pitch speed and acceleration in some pitch region. The research results give a reasonable explanation for running mechanism of the individual pitch system and are helpful for optimization design and control for the individual blade pitch control system used in large-scale wind turbines.

Calculation and characteristics analysis of blade pitch loads for large scale wind turbines

Based on the electric pitch system of large scale horizontal-axis wind turbines, the blade pitch loads coming mainly from centrifugal force, aerodynamic force and gravity are analyzed, and the calculation models for them are established in this paper. For illustration, a 1.2 MW wind turbine is introduced as a practical sample, and its blade pitch loads from centrifugal force, aerodynamic force and gravity are calculated and analyzed separately and synthetically. The research results showed that in the process of rotor rotating 360°, the fluctuation of blade pitch loads is similar to cosine curve when the rotor rotational speed, inflow wind speed and pitch angle are constant. Furthermore, the amplitude of blade pitch load presents quite a difference at a different pitch angle. The ways of calculation for blade pitch loads are of the universality, and are helpful for further research of the individual pitch control system.