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 s...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.展开更多
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 turb...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.展开更多
自然界风速的多变性与风机变桨系统的迟缓性会导致风机输出功率的不稳定。为了改善风机输出功率的稳定,首先基于RBF神经网络RBFNN(radial basis function neural network),以功率差作为信号来源,设计了RBF-PID自适应变桨控制器,建立了...自然界风速的多变性与风机变桨系统的迟缓性会导致风机输出功率的不稳定。为了改善风机输出功率的稳定,首先基于RBF神经网络RBFNN(radial basis function neural network),以功率差作为信号来源,设计了RBF-PID自适应变桨控制器,建立了风力机及变桨距机构仿真模型。其次,建立了2种风况模型,较好地模拟了自然界基本风况。仿真表明:在不同风况下对比常规模糊控制与PID控制,RBF-PID参数自适应方法在风速波动较大的情况下能够更好地稳定输出功率,且减小了变桨的幅值与频率,增加了风机的寿命。展开更多
基金supported by the National Key Basic Research Program (Grant No. 2011CB706804)the National Natural Science Foundation of China (Grant No. 50835004)the Ministry of Science and Technology of China (Grant No. 2010ZX04016-012)
文摘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.
文摘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.
文摘自然界风速的多变性与风机变桨系统的迟缓性会导致风机输出功率的不稳定。为了改善风机输出功率的稳定,首先基于RBF神经网络RBFNN(radial basis function neural network),以功率差作为信号来源,设计了RBF-PID自适应变桨控制器,建立了风力机及变桨距机构仿真模型。其次,建立了2种风况模型,较好地模拟了自然界基本风况。仿真表明:在不同风况下对比常规模糊控制与PID控制,RBF-PID参数自适应方法在风速波动较大的情况下能够更好地稳定输出功率,且减小了变桨的幅值与频率,增加了风机的寿命。
