Intelligent control for large-scale variable speed variable pitch wind turbines

Large-scale wind turbine generator systems have strong nonlinear multivariable characteristics with many uncertain factors and disturbances. Automatic control is crucial for the efficiency and reliability of wind turbines. On the basis of simplified and proper model of variable speed variable pitch wind turbines, the effective wind speed is estimated using extended Kaiman filter. Intelligent control schemes proposed in the paper include two loops which operate in synchronism with each other. At below-rated wind speed, the inner loop adopts adaptive fuzzy control based on variable universe for generator torque regulation to realize maximum wind energy capture. At above-rated wind speed, a controller based on least square support vector machine is proposed to adjust pitch angle and keep rated output power. The simulation shows the effectiveness of the intelligent control.

CFD Simulation of Fixed and Variable Pitch Vertical Axis Tidal Turbine

In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.

Numerical and Experimental Analysis of A Vertical-Axis Eccentric-disc Variable-Pitch Turbine(VEVT)

A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.

小型涡轮平面叶栅试验段设计

Performance improvement of the high-load transonic turbine is the key method of improving the thrustto-weight ratio or the power density of gas turbine engines. In order to investigate the flow behaviors inside the high load turbine cascades, a linear turbine cascade test section is designed, which enables the Schlieren photography and static pressure measurement along the cascade profile can be conducted. Variable pitch is realized in the test section to achieve different Zweifel coefficients. Due to the capability limitation of the air supplier, the test section is designed to have only5 blade channels with shortened blade height to achieve high Mach number flow conditions. Numerical investigations were carried out to investigate the wall effect and its in fluences on the flow fields inside the test section. The result indicates that the shape of the connecting part of the test section has a significant influence on the flow similarity among different blade passages. With the proper design, a good repetition flow is achieved between neighbored blade passages.

PROPER CONDITIONS OF MESHING FOR Hy-Vo SILENT CHAIN AND SPROCKET

Proper meshing of Hy-Vo silent chain and sprocket is important for realizing the transmission of the silent chain with more efficiency and less noise. Based on the study of the meshing theory of the Hy-Vo silent chain with the sprocket and the roll cutting machining principle of the sprocket with the hob, the proper conditions of the meshing for the Hy-Vo silent chain and the sprocket are put forward with the variable pitch characteristic of the Hy-Vo silent chain taken into consideration, and the proper meshing design method on the condition that the value of the link tooth pressure angle is unequal to the value of the sprocket tooth pressure angle is studied. Experiments show that this new design method is feasible. In addition, the design of the pitch, the sprocket tooth pressure angle and the fillet radius of the sprocket addendum circle are studied. It is crucial for guiding the design of the hob which cuts the Hy-Vo silent chain sprocket.

Design of variable screw pitch rib snapping roller and residue cutter for corn harvesters

The blocking between two snapping rollers will seriously constrict the harvesting efficiency for corn harvester.A variable screw pitch rib snapping roller was developed to solve this problem.The comparative experiment between fixed screw pitch rib snapping rollers and variable screw pitch rib snapping rollers illustrated that variable screw pitch ribs can avoid corn-stalk blocking effectively,and it can improve working efficiency by 56.7%.Conservation tillage with standing corn residue was testified that it had a strong control of soil wind erosion.In order to implement this mode of conservation tillage at a production scale,a cutter was developed in this study.Subsequently,two experiments were conducted,one was to test the cutting ratio(defined as the totally cut off stalk population divided by total stalk population),and the other one was to test standing-residue height.The experiment results showed that the mean cutting ratio increased significantly(p<0.05)along with increasing height of cutter-head above the ground(cutting height);the cutting ratio’s mean value increased significantly(p<0.05)along with the decreasing angle between the cutter-head and the ground(cutting angle).The average standing-residue height increased along with the increase of cutting height from 300 mm to 500 mm.The average standing-residue height increased significantly(p<0.05)along with the decrease of cutting angle from 15°to 0°.Therefore,the newly designed snapping roller can improve the harvesting efficiency and prolong the working life of the cutting table;and the cutter can promote the popularization of the conservation tillage with standing corn residue in Northeast China.

Layered Multi-mode Optimal Control Strategy for Multi-MW Wind Turbine

The control strategy is one of the most important renewable technology,and an increasing number of multi-MW wind turbines are being developed with a variable speed-variable pitch(VS-VP)technology.The main objective of adopting a VS-VP technology is to improve the fast response speed and capture maximum energy.But the power generated by wind turbine changes rapidly because of the continuous fluctuation of wind speed and direction.At the same time,wind energy conversion systems are of high order,time delays and strong nonlinear characteristics because of many uncertain factors.Based on analyzing the all dynamic processes of wind turbine,a kind of layered multi-mode optimal control strategy is presented which is that three control strategies:bang-bang,fuzzy and adaptive proportional integral derivative(PID)are adopted according to different stages and expected performance of wind turbine to capture optimum wind power,compensate the nonlinearity and improve the wind turbine performance at low,rated and high wind speed.

Variable-step integration method for milling chatter stability prediction with multiple delays

This paper analyzes the stability of milling with variable pitch cutter and tool runout cases characterized by multiple delays,and proposes a new variable-step numerical integration method for efficient and accurate stability prediction. The variable-step technique is emphasized here to expand the numerical integration method,especially for the low radial immersion cases with multiple delays. First,the calculation accuracy of the numerical integration method is discussed and the variable-step algorithm is developed for milling stability prediction for single-delay and multiple-delay cases,respectively. The milling stability with variable pitch cutter is analyzed and the result is compared with those predicted with the frequency domain method and the improved full-discretization method. The influence of the runout effect on the stability boundary is investigated by the presented method. The numerical simulation shows that the cutter runout effect increases the stability boundary,and the increasing stability limit is verified by the milling chatter experimental results in the previous research. The numerical and experiment results verify the validity of the proposed method.