Quasi-3-D beam-propagation method for modeling nonlinear wavelengthconversion

The two-dimensional (2-D) iterative finite difference beam-propagation method (IFD-BPM) is modified to model the cylindrically symmetric three-dimensional (quasi-3-D) second-order nonlinear wavelength conversion in quasi-phase-matched condition. The study shows that the difference between the 2-D and 3-D schemes is small for the guided waves but large for the nonguided beams. The comparison with experimental results shows that the quasi-3-D IFD-BPM is closer to reality than the 2-D scheme. In addition, simulation using the quasi-3-D IFD-BPM reveals that plane-wave and Gaussian-beam assumptions are not sufficient for estimating the nonlinear conversion and beam propagation in second-order nonlinear devices     

一种接收机非线性行为建模方法

提出一种基于多项式的接收机行为建模方法。采用Hammerstein模型构建接收机行为模型,分别用非线性模块与记忆线性模块表征接收机非线性特性和记忆效应;利用傅里叶级数和最小二乘法分别辨识行为模型的非线性模块参数与线性模块参数;最后通过接收机ADS模型仿真数据,验证所提出的接收机非线性行为建模方法。对比分析了ADS仿真和行为模型的AM-AM特性及单音时域波形,实验结果表明,接收机行为模型的AM-AM特征曲线及时域波形与ADS仿真数据吻合程度较好。本文方法可预测接收机的非线性响应,对在复杂电磁环境下的接收机非线性效应评估具有理论价值。     

Switching flow-graph nonlinear modeling method formultistate-switching converters

Switching power converters operating in a multistate switching mode (more than two states) feature multidimensional control over their state variables. In this paper, a large-signal multistate modeling method is developed based on the switching flow-graph method to study the steady-state and dynamic properties of pulse-width-modulated (PWM) multistate-switching power converters for the continuous conduction mode. This modeling method translates a switching power converter directly to its graphic dynamic model and uses graphical representation to reveal the cause and effect relationship of the dynamics within a multidimensional power converter. A three-state buck-boost circuit is conceived with two duty ratios controlling two outputs as an example to test this modeling method. Experimental results confirm the theoretical prediction. This multistate-switching flow-graph modeling method is very general, easy to use and accurate, and it provides deep physical insight for engineering design     

Automatic control of excitation parameters for switched-reluctance motor drives

This paper presents a new approach to the automatic control of the turn-on angle used to excite the switched-reluctance motor (SRM). The control algorithm determines the turn-on angle that supports the most efficient operation of the motor drive system, and consists of two pieces. The first piece of the control technique monitors the position of the first peak of the phase current (/spl theta//sub p/) and seeks to align this position with the angle where the inductance begins to increase (/spl theta//sub m/). The second piece of the controller monitors the peak phase current and advances the turn-on angle if the commanded reference current cannot be produced by the controller. The first piece of the controller tends to be active below base speed of the SRM, where phase currents can be built easily by the inverter and /spl theta//sub p/ is relatively independent of /spl theta//sub m/. The second piece of the controller is active above base speed, where the peak of the phase currents tends to naturally occur at /spl theta//sub m/ regardless of the current amplitude. The two pieces of the controller naturally exchange responsibility as a result of a change in command or operating point. The motor, inverter and control system are modeled in Simulink to demonstrate the operation of the system. The control technique is then applied to an experimental SRM system. Experimental operation documents that the technique provides for efficient operation of the drive.     

Behavioral modeling of the IGBT using the Hammerstein configuration

The Hammerstein model configuration, which includes a nonlinear static block followed by a linear dynamic block, is applied to model the static and dynamic characteristics of the insulated gate bipolar transistor (IGBT). Using least-squares methods, the parameters in the behavioral model can be extracted from the electrical measurements of physical devices or from the circuit simulations of physics-based models. A single set of extracted parameters has been found to yield satisfactory efficiency and accuracy for the tested hard- and soft-switched converters under prescribed ranges of operating conditions     

优化Hammerstein模型的电磁脉冲效应建模仿真

针对采用Hammerstein模型描述电磁脉冲效应时模型参数确定困难的问题,提出一种基于优化Hammerstein模型的非线性电磁脉冲效应建模仿真方法。该方法利用高阶累积量求解模型线性延迟阶数,采用赤池信息准则（Akaike Information Criterion,AIC）优化模型非线性阶次,两者共同确定出一个参数最少、精度较高的最优模型,并以瞬态抑制器的电磁脉冲效应建模为例验证了该方法。     

Behavioral IGBT modeling for predicting high frequency effects inmotor drives

A first-order behavioral IGBT/gate drive model is proposed together with a procedure for deriving all model parameters. Despite the simplicity of the proposed model, comparison of model predictions with hardware measurements demonstrate the model to be accurate in predicting turn-on and turn-off transients     

Investigation of the Hammerstein hypothesis in the modeling ofelectrically stimulated muscle

To restore functional use of paralyzed muscles by automatically controlled stimulation, an accurate quantitative model of the stimulated muscles is desirable. The most commonly used model for isometric muscle has had a Hammerstein structure, in which a linear dynamic block is preceded by a static nonlinear function. To investigate the accuracy of the Hammerstein model, the responses to a pseudo-random binary sequence (PRES) excitation of normal human plantarflexors, stimulated with surface electrodes, were used to identify a Hammerstein model but also four local models which describe the responses to small signals at different mean levels of activation. Comparison of the local models with the linearized Hammerstein model showed that the Hammerstein model concealed a fivefold variation in the speed of response. Also, the small-signal gain of the Hammerstein model was in error by factors up to three. We conclude that, despite the past widespread use of the Hammerstein model, it is not an accurate representation of isometric muscle. On the other hand, local models, which are more accurate predictors, can be identified from the responses to short PRES sequences. The utility of local models for controller design is discussed     

基于机载激光雷达技术的三维景观自动建模方法

当前三维景观建模方法存在建模精度低,误差大,而且实时性差等不足,为了提高三维景观建模精度,克服当前三维景观建模方法存在的局限性,提出了基于机载激光雷达技术的三维景观自动建模方法.首先分析三维景观建模的工作原理,找到影响三维景观建模效果的因素,然后采用机载激光雷达技术采集景观的相关数据,并引入虚拟现实技术构建三维景观模型...     

Neural networks for modeling nonlinear memoryless communicationchannels

This paper presents a neural network approach for modeling nonlinear memoryless communication channels. In particular, the paper studies the approximation of the nonlinear characteristics of traveling-wave tube (TWT) amplifiers used in satellite communications. The modeling is based upon multilayer neural networks, trained by the odd and even backpropagation (BP) algorithms. Simulation results demonstrate that neural network models fit the experimental data better than classical analytical TWT models,     

Switching Flow-Graph nonlinear modeling technique

A unified graphical modeling technique, “Switching Flow-Graph” is developed to study the nonlinear dynamic behavior of pulse-width-modulated (PWM) switching converters. Switching converters are variable structure systems with linear subsystems. Each subsystem can be represented by a flow-graph. The Switching Flow-Graph is obtained by combining the flowgraphs of the subsystems through the use of switching branches. The Switching Flow-Graph model is easy to derive, and it provides a visual representation of a switching converter system. Experiments demonstrate that the Switching Flow-Graph model has very good accuracy     

Reverse matrix converter control method for PMSM drives using DPC

This paper proposes a control method for a reverse matrix converter (RMC) that drives a three-phase permanent magnet synchronous motor (PMSM). In this proposed method, direct power control (DPC) is used to control the voltage source rectifier of the RMC. The RMC is an indirect matrix converter operating in the boost mode, in which the power-flow directions of the input and output are switched. It has a minimum voltage transfer ratio of 1/0.866 in a linear-modulation region. In this paper, a control method that uses DPC as an additional control method is proposed in order to control the RMC driving a PMSM in the output stage. Simulations and experimental results verify the effectiveness of the proposed control method.     

A hybrid implicit-explicit FDTD scheme for nonlinear opticalwaveguide modeling

A hybrid implicit-explicit finite-difference time-domain (FDTD) method for solving the wave equation in nonlinear optical waveguiding structures is proposed. The new scheme combines the computational simplicity of the explicit scheme in linear medium regions with the superior stability property of the partially implicit scheme in regions of nonlinear materials, thus eliminating potential problems of instability associated with nonlinearity. Simulation results for Kerr-type nonlinear slab waveguides and corrugated waveguides are presented and compared with those obtained using the conventional noniterative FDTD scheme     

A hybrid backtracking search algorithm with wavelet mutation-based nonlinear system identification of Hammerstein models

In this paper a novel and accurate approach is presented to identify varieties of nonlinear Hammerstein models (closed loop and open loop) with the help of an optimization algorithm that combines a recently proposed backtracking search algorithm with wavelet theory-based mutation scheme (BSA-WM). The optimum output MSE associated with each plant along with its statistical information justifies the better precision and accuracy of BSA-WM-based identification approach as compared to the other methods reported in earlier literature.     

物理诊断设备精确自φ直方法

为了获确的激光打靶实验数据,需要使用诊断搭载平台搭载物理诊断设备对打靶目标进行高精直.针对传统方法存在耗时、误差(RMS)较大的问题,根据搭载平台与物理诊断设备的特点,提出了一种基于视觉伺服的精确自直方法.首先,构建三直向量估算立体视觉系统中靶的偏差,在弱透视条件下,估算值接近于真值;然后,建立三自由度姿态调节模型,提高姿态调节精度.最后,运直向量与调节模型设计视觉伺服控制器,仅需一次离线标定即可进行快直.通过以上改进,实现了物理诊断设备的精确自直.实验结果表明,诊断设备直精度(RMS)分别为:x 指向为11m,y 指向为12m.搭载分幅相机进行激光打靶考核验证,得到了物理实验过程的X光焦斑图像,表直方法满足工程使用要求.     

Time domain modeling of nonlinear loads

The behavior of an antenna or scatterer when loaded with a nonlinear element can be changed greatly from that observed under linear conditions. In some cases, the nonlinearity causes effects such as the intermodulation products arising from the nonlinear mixing of two frequencies. In other cases, the nonlinearity may be exploited, for example, to reduce late-time ringing on a pulse-excited antenna. A procedure for treating general nonlinear loads is described and illustrated. This procedure is applied using a computer to several specific types of nonlinearities. The treatment within the framework of the thin-wire approximation to the electric field integral equation is developed. As such, the treatment can be applied to the large class of objects modeled by wires. The nonlinear load types that are considered include those with piecewise-linear voltage-current curves (e.g., one or more diodes), a load with a time varying resistance (which permits modulating the scattered fields), and a general nonlinear load represented by specified voltage-current functions.     

GaAs MESFET modeling and nonlinear CAD

Equivalent circuit modeling techniques are described for both small-signal and large-signal models of GaAs MESFETs. The use of large-signal model in an interactive program for amplifier analysis is shown. The computed load-pull results and IMD (intermodulation distortion) predictions are shown to be in good agreement with measured data at 10 GHz     

Geometric modeling of nonlinear RLC circuits

In this paper, the dynamics of nonlinear RLC circuits including independent and controlled voltage or current sources is described using the Brayton-Moser equations. The underlying geometric structure is highlighted and it is shown that the Brayton-Moser equations can be written as a dynamical system with respect to a noncanonical Dirac structure. The state variables are inductor currents and capacitor voltages. The formalism can be extended to include circuits with elements in excess, as well as general noncomplete circuits. Relations with the Hamiltonian formulation of nonlinear electrical circuits are clearly pointed out.     

Small-signal nonlinear modeling of television IOTs

The inductive output tube (IOT) is a high power vacuum tube amplifier popularly used in UHF television broadcasting. A small-signal nonlinear model is presented for the IOT. Several simplifying assumptions are made to make the proposed model more tractable mathematically. Component values are then assigned to this simplified model based on measured IOT S/sub 11/ performance. This model is used to predict IOT intermodulation performance for a unique test case. The results predicted by the proposed model compare favorably to the real world measured results for the same test case.