A Direct Solver for 2D Non-Stationary Boltzmann-Poisson Systems for Semiconductor Devices: A MESFET Simulation by WENO-Boltzmann Schemes

We present preliminary results of a high order WENO scheme applied to deterministic computations for two dimensional formulation of the transients for the Boltzmann-Poisson system describing electron transport in semiconductor devices. The collisional term models optical-phonon interactions which become dominant under strong energetic conditions corresponding to nanoscale active regions under applied bias. We treat the Boltzmann Transport equation in a spherical coordinate system for the wave-vector space. The problem is three dimensional in the wave-vector space and two dimensional in the physical space, plus the time variable driving to steady states. The new formulation avoids the singularity due to the spherical coordinate system.     

Neutron production rate and plasma characteristics of spherically convergent beam fusion

Experimental and simulation results of a spherical glow discharge for a portable neutron source are presented. The experimental device is a 45‐cm‐diameter, 31‐cm‐high stainless‐steel cylindrical chamber, in which a spherical mesh‐type anode 30 cm in diameter is installed. The spherical grid cathode consists of 2.0‐mm‐diameter stainless‐steel wire, which is made into an open spherical grid of 5‐cm diameter. The system is maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The basic characteristics of breakdown voltages versus pressure and electrostatic potential profiles were measured for hydrogen discharge. Using deuterium, a steady‐state neutron production of 10⁴ s^–1 was observed at a discharge of 40 kV, 2 mA. Motions of ions and electrons in the device were simulated by using a particle code, which is one‐dimensional in coordinate system and two‐dimensional in velocity space. It was confirmed by both the measurement and simulation that a virtual anode is formed in the central part inside the grid cathode. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 1–8, 2001     

非正交三维坐标系下多电平空间矢量调制策略

脉冲宽度调制是三相四线制多电平变流器控制的难点,脉冲宽度调制策略将直接影响零序分量输出控制的优劣,传统三维空间矢量调制策略在电压零序分量控制和算法复杂度两个方面很难取得良好的平衡。提出一种非正交三维坐标系下的空间矢量调制策略。该方法通过建立一种三维非正交坐标系,将传统正交三维空间坐标系下的三角函数运算简化为简单的代数运算,在降低三维空间矢量调制算法复杂性的同时保留对于零序分量的独立控制。另外,针对多电平变流器固有中点电位不平衡问题提出一种简单的控制策略。仿真分析和实验结果验证了所提出的非正交三维坐标系下的调制策略的正确性及有效性。     

A new MEMS gyroscope drift suppression method for the low‐cost untwisting spin platform

The microelectromechanical system (MEMS ) gyroscope provides a new method to design a low‐cost untwisting spin platform to be used in a single‐axis, stable strap‐down inertial navigation system. However, the MEMS gyroscope's drift reduces the effectiveness of the closed‐loop feedback control. Thus, a new method of drift suppression is proposed in this paper based on phase space reconstruction in order to improve the platform's performance. The feasibility of the MEMS gyroscope's drift suppression is analyzed using linear decomposition based on phase space. The system drift is estimated by phase space reconstruction. The optimal embedding dimension is found through a grid search. The number of dimensions for dimension reduction analysis is selected according to the minimum eigenvalue. The mapping from the high‐dimensional phase space onto the low‐dimensional phase space is obtained by minimizing the variance. A Kalman filter is used to compensate the residual sequence further. The proposed method is applied to an untwisting spin platform based on the MEMS gyroscope L3G4200D . The experimental results show that it can reduce the platform drift rate effectively.     

基于坐标变换的风电变流器电压信号CS压缩方法

为了解决直接利用压缩感知(CS)理论对风电变流器输出端三相电压监测数据存储空间的资源浪费以及重构性能差等问题,提出了一种基于坐标变换的风电变流器电压信号CS压缩方法。该方法的关键是利用dq0变换、空间矢量变换将三相电压信号转换为一维信号;然后将传统的多频带融合思想用于CS稀疏表示中,构造稀疏字典矩阵,并分析了稀疏字典与测量矩阵的不相关性;最后利用高斯随机矩阵进行压缩测量,使用追踪算法实现一维信号的恢复,将其转化为两相信号并作坐标反变换,即得到重构的三相电压信号。仿真结果表明,与直接对监测的三相电压数据进行CS处理相比,该方法可有效的压缩原始三相电压数据,使得运行时间降低,重构误差减小,并且节约了测量数据的存储空间,因而更加具有实际应用价值。     

基于毕奥-萨伐尔定律的永磁球形电动机定子线圈磁场分布研究

永磁球形电动机定子绕组采用集中式绕制方式,分层均匀镶嵌在定子球壳内壁。为得到永磁球形电动机单个定子线圈在三维空间中的磁场分布,建立球形电动机全局坐标系与定子线圈局部坐标系之间的映射关系,然后运用毕奥-萨伐尔定律对定子线圈产生的磁场进行求解分析。在对磁场解析表达式求解过程中借鉴“割圆法”思想,得到了磁场的数值解表达式,给出了单个定子线圈在三维空间中的磁场分布,并通过有限元方法验证了所提方法的有效性。     

一种任意次谐波电流检测算法的仿真研究

提出了一种适用于三相三线制不平衡系统的任意次谐波电流检测方法。该方法基于d-q旋转坐标变换,采用不同的旋转角速度旋转,以检测出不同次谐波电流的正负序分量。把所得的正负序分量相加便可得到所要检测的谐波分量。经过理论分析和仿真验证说明了该方法的正确性。     

三维正弦稳态场矢量最大值的直接计算方法

基于矢量相量推导了三维正弦稳态场矢量最大值、最小值及方向余弦的直接计算公式,并将二维情况作为特例纳入公式体系;研究了三维正弦稳态场矢量端点轨迹,利用坐标变换,证明了端点轨迹是三维空间的椭圆,且椭圆长、短半轴分别对应场矢量模的最大值和最小值。将公式应用于特高压交流变电站空间电场的计算,通过对比计算结果和测量结果,验证了公式的正确性。     

四桥臂APF电流跟踪控制方法研究

为解决三相四线制不对称电网系统的谐波污染问题,通过对三相四桥臂电路拓扑结构进行分析。针对传统的三维空间矢量调制方法,首先阐明了其不能用于四桥臂APF电流跟踪的原因。在此基础上,结合三桥臂APF的电流跟踪控制方法,在二维空间矢量控制策略上增加三维坐标垂直坐标轴上的电流跟踪策略,将三维空间矢量划分为12个三棱柱,而非传统的24个四面体,并根据垂直坐标轴分量的正负情况给出了电压,电流矢量的判定方法,得到了三维矢量电流跟踪控制下的输出矢量的选取判定表,实现了四桥臂APF对谐波电流的有效补偿。仿真和实验结果证明了该方法的正确性与有效性。     

一种考虑死区的PMSM无速度传感器滑模辨识及控制

本文设计了一种基于旋转坐标系自适应滑模观测器并考虑死区补偿的转速和转子位置估算方法。为了解决传统估算方法导致的抖振问题,引进了近似滑模Sigmoid函数,提高了系统的可靠性。采用Lyapunov函数对角速度进行辨识,保证了系统稳定,取消了数字锁相环,使得算法变得更加简单。针对逆变器死区对估计模型的影响,引入了一种坐标变换补偿法的死区补偿算法到自适应滑模观测器控制中,消除了实际电机和模型电机之间的相位误差。仿真和实验结果表明,所提出的算法具有较强的鲁棒性,加快了系统的响应速度。