Wei Li

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.

Integrated pitch control for wind turbine based on a novel pitch control system

A novel pitch control system is proposed for wind turbine to smooth output power and load fluctuations. This system is driven by a servo-valve controlled hydraulic motor and is precisely controlled to track the desired pitch angle trajectory. Nonlinear modeling and characteristics of this system are presented and analyzed. An adaptive nonlinear sliding mode pitch angle controller is designed to deal with the uncertainties and external disturbances in this system. An integrated pitch control strategy is proposed to generate the reference pitch commands for this system by considering the load reductions. The proposed system, pitch controller, and the control strategy have been validated for efficient and accurate pitch control performances by comparative experimental results under realistic wind speeds.

Adaptive back-stepping pitch angle control for wind turbine based on a new electro-hydraulic pitch system

A new electro-hydraulic pitch system is proposed to smooth the output power and drive-train torque fluctuations for wind turbine. This new pitch system employs a servo-valve-controlled hydraulic motor to enhance pitch control performances. This pitch system is represented by a state-space model with parametric uncertainties and nonlinearities. An adaptive back-stepping pitch angle controller is synthesised based on this state-space model to accurately achieve the desired pitch angle control regardless of such uncertainties and nonlinearities. This pitch angle controller includes a back-stepping procedure and an adaption law to deal with such uncertainties and nonlinearities and hence to improve the final pitch control performances. The proposed pitch system and the designed pitch angle controller have been validated for achievable and efficient power and torque regulation performances by comparative experimental results under various operating conditions.

Hybrid Power Transmission Technology in a Wind Turbine Generation System

The direct-drive hydraulic pump suffers the disadvantages of large displacement and difficulty of manufacture. This paper thus proposes a hybrid power transmission technology that utilizes a single-stage gear transmission and low-speed hydraulic pump. The transmission technology reduces the displacement of the hydraulic pump and retains the torque-stable feature of a hydrostatic transmission. This paper designs the basic structure of a hybrid power transmission system and constructs the system model using the AMESim and MATLAB software. Under the grid-connected circumstance, the variable-speed constant-frequency control algorithm when the wind speed is below the rated value and the pitch control algorithm when the wind speed is above the rated value are simulated and analyzed. A 20-kW prototype has been developed. The simulation and the experimental data demonstrate that a hybrid power transmission meets the demands in various working conditions and stabilizes the torque of a wind turbine generation system.

Fuzzy-Logic Sliding-Mode Control Strategy for Extracting Maximum Wind Power

A fuzzy-logic sliding-mode control strategy is proposed to capture the maximum wind energy and reduce the generator-side current harmonics for a direct-driven wind power system. The control strategy mainly consists of a fuzzy logic controller for generating the optimum dc-side current and a double integral sliding-mode current controller capable of accurately tracking the optimum dc-side current. A resonant filter is also incorporated into the fuzzy logic controller to eliminate the generator-side current harmonics. Detailed design procedure, existence, and stability conditions of the proposed control strategy have been thoroughly investigated and presented. The capability and effectiveness of the proposed control strategy have been validated by comparative experimental results.

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.

Wave energy converter of inverse pendulum with double action power take off

This article describes a double action hydraulic power take off for a wave energy converter of inverse pendulum. The power take off converts slow irregular reciprocating wave motions to relatively smooth, fast rotation of an electrical generator. The design of the double action power take off and its control are critical to the magnitude and the continuity of the generated power. The interaction between the power take off behavior and the wave energy converter’s hydrodynamic characteristics is complex, therefore a time domain simulation study is presented in which both parts are included. The power take off is modeled using AMESim®, and the hydrodynamic equations are implemented in MATLAB®; simulation is used to predict the behavior of the complete system. The simulation results show that the design of the double action hydraulic power take off for wave energy converter of inverse pendulum is entirely feasibility and its superiority has been verified by the preliminary experiments, especially compared with the existing single action power take off system.

Experimental results from wave tank trials of a multi-axis wave energy converter

A 1/64th scale prototype of multi-axis wave energy converter (WEC) has been tested in the wave tank and the overall concept has been verified. It is shown that when multiple directions of motion are involved, the multi-axis WEC proves to be able to supply more power generation than a single axis one. Results demonstrated that the optimal resonant frequency for maximum power output under different damping values does not vary with wave climate. It is also shown that large overload capability of the system is critical, and indicated that, electric power system is essential to reduce power fluctuations.

Operating Modes and Control Strategy for Megawatt-Scale Hydro-Viscous Transmission-Based Continuously Variable Speed Wind Turbines

A megawatt (MW)-scale hydro-viscous transmission-based continuously variable speed wind turbine is proposed to guarantee a smooth transition among different operating regions and hence to improve power efficiency and quality. This turbine is achieved by highly integrating a hydro-viscous element into the turbine drive-train to mitigate the upstream wind-loading fluctuations. This element allows the turbine speed to be directly regulated by continuously changing the oil film thickness in this element. Three important operating modes of this turbine system are proposed. The control-oriented drive-train model is also established and validated based on experimental data. A cooperative control strategy over the full operating range is then proposed based on such modes. A series of comparative cosimulations are carried out to evaluate the stability and effectiveness of the proposed turbine system in speed and power regulations. This proposed system holds several advantages such as large power capacity, high efficiency, downsized power converters, and low cost. Such advantages make this turbine system particularly attractive and promising for medium-to-large-scale wind power applications.

A New Method Based on Immune Algorithm to Solve the Unit Commitment Problem

A new method based on immune algorithm to solve the thermal unit commitment problem(UCP) is proposed. Through analysis of mathematical model of UCP, application method of immune algorithm was discussed in detail. In the algorithm, the objective function was deemed antigen and the solutions were deemed antibodies. If an antibody fits the antigen best, this antibody was deemed the optimum solution. Encoding the continuous operating time shortened the code length and the searching speed of algorithm was improved greatly. The proposed method was applied in a ten-unit system for a 24 hours period. The calculation results showed immune algorithm had well global searching performance and it was efficient to use this algorithm to solve UCP.