Hopf bifurcation in indirect field-oriented control of induction motors

The appearance of self-sustained oscillations in high performance AC drives, and in particular, in induction motors whose speed is regulated with the industry standard field-oriented control, is a well-documented but little understood phenomenon. It is well known that the oscillations may be quenched by returning the outer-loop PI speed control, but no precise rules to carry out this task, which may be time consuming, are known. In this paper, we show that these oscillations may arise due to the existence of Hopf bifurcations. Some simple rules for selecting the gains of the PI controller are obtained as a result of our analysis.     

Multivariable harmonic balance for central pattern generators

The central pattern generator (CPG) is a nonlinear oscillator formed by a group of neurons, providing a fundamental control mechanism underlying rhythmic movements in animal locomotion. We consider a class of CPGs modeled by a set of interconnected identical neurons. Based on the idea of multivariable harmonic balance, we show how the oscillation profile is related to the connectivity matrix that specifies the architecture and strengths of the interconnections. Specifically, the frequency, amplitudes, and phases are essentially encoded in terms of a pair of eigenvalue and eigenvector. This basic principle is used to estimate the oscillation profile of a given CPG model. Moreover, a systematic method is proposed for designing a CPG-based nonlinear oscillator that achieves a prescribed oscillation profile.     

Volumetric colon wall unfolding using harmonic differentials

Volumetric colon wall unfolding is a novel method for virtual colon analysis and visualization with valuable applications in virtual colonoscopy (VC) and computer-aided detection (CAD) systems. A volumetrically unfolded colon enables doctors to visualize the entire colon structure without occlusions due to haustral folds, and is critical for performing efficient and accurate texture analysis on the volumetric colon wall. Though conventional colon surface flattening has been employed for these uses, volumetric colon unfolding offers the advantages of providing the needed quantities of information with needed accuracy. This work presents an efficient and effective volumetric colon unfolding method based on harmonic differentials. The colon volumes are reconstructed from CT images and are represented as tetrahedral meshes. Three harmonic 1-forms, which are linearly independent everywhere, are computed on the tetrahedral mesh. Through integration of the harmonic 1-forms, the colon volume is mapped periodically to a canonical cuboid. The method presented is automatic, simple, and practical. Experimental results are reported to show the performance of the algorithm on real medical datasets. Though applied here specifically to the colon, the method is general and can be generalized for other volumes.     

便携式谐波监测系统设计

为实现对外场设备中电源谐波的快速准确监测,提出了一种基于Labwindows/CVI的通用谐波监测系统设计方案。系统采用便携式工控机作为硬件平台,软件采用Labwindows/CVI软件作为开发平台,用来实现数据的采集、分析与处理等功能,并将小波补偿的加窗插值F F T算法用于进行谐波分析,提高了谐波分析精度。     

Speed tracking control for the gimbal system with harmonic drive

This paper presents a composite controller based on a disturbance observer for the gimbal system of double-gimbal magnetically suspended control moment gyro (DGMSCMG) with harmonic drives. The controller removes the influence by coupling moments and nonlinear transmission torques. The disturbances are estimated by the designed disturbance observer. By introducing a state feedback controller, the disturbances can be eliminated from the output channel of the system. The gain selection principle of the disturbance observer is also analyzed. Both the simulation and experimental results indicate that the proposed control method can reject mismatched disturbances and improve system performance.     

Neural network control of a gas turbine

In this paper we explore the practical use of neural networks for controlling complex non-linear systems. The system used to demonstrate this approach is a simulation of a gas turbine engine typical of those used to power commercial aircraft. The novelty of the work lies in the requirement for multiple controllers which are used to maintain system variables in safe operating regions as well as governing the engine thrust.     

Approximately harmonic projection: Theoretical analysis and an algorithm

Manifold learning have attracted considerable attention over the last decade. The most frequently used functional is the l²-norm of the gradient of the function. In this paper, we consider the linear manifold learning problem by minimizing this functional with appropriate constraint. We provide theoretical analysis on both the functional and the constraint, which shows the affine hulls of the manifold and the connected components are essential to linear manifold learning problem. Based on the theoretical analysis, we introduce a novel linear manifold learning algorithm called approximately harmonic projection (AHP). Unlike canonical linear methods such as principal component analysis, our method is sensitive to the connected components. This makes our method especially applicable to data clustering. We conduct several experimental results on three real data sets to demonstrate the effectiveness of our proposed method.     

一种用于高精度电能表的谐波算法研究

高电压、大容量的冲击性设备的广泛应用,导致电力系统中呈现大量谐波,对电能计量提出了新的要求,采用快速傅立叶变换(FFT)进行谐波分析存在较大的泄漏误差,本文对FFT的泄漏误差进行了分析并对FFT的结果进行修正,提高了计算精度,修正后的算法适用于电力系统谐波分析与电能计量。     

On linear system reduction by stable precompensation and stable state feedback

A unified framework for the problem of reduction of a finite dimensional linear system by stable state feedback and bistable precompensation is presented. The results extend the work of [1] to include in an algebraic setting stability considerations.     

Stability analysis of the simplest Takagi-Sugeno fuzzy control system using circle criterion

In this paper, we present two sufficient conditions in the frequency domain for the global stability analysis of the simplest Takagi-Sugeno (T-S) fuzzy control system, based on the circle criterion and its graphical interpretation. These conditions are significant in graphically designing the simplest T-S fuzzy controller in the frequency domain. Four numerical examples are provided to demonstrate the efficiency of our two frequency domain-based conditions. Furthermore, this T-S fuzzy controller and the linear proportional controllers are also compared. It is concluded that the simplest T-S fuzzy controller can outperform the linear proportional controllers in a noisy environment with external disturbances.     

Stabilization and synchronization for a heterogeneous multi-agent system via harmonic control

In this paper, a class of heterogeneous multi-agent systems with directed cycle graphs is investigated. The stabilization and synchronization problems via harmonic control are solved under some conditions and the feedback control gains are constructively designed. Several numerical examples are presented to demonstrate the effectiveness of the proposed method.     

基于神经网络的PMSM自适应滑模控制

结合滑模控制和神经网络各自的优点,对永磁同步电机(PMSM)提出了一种基于神经网络的PMSM自适应滑模控制方案.首先设计了带积分操作的滑模变结构位置控制器,通过递归神经网络的在线学习来实时估计系统参数变化和外部负载扰动等不确定性的界限,减小滑模控制器的控制量.进而,在滑模控制器中又引入饱和函数取代符号函数,进一步减弱"抖振"现象.理论分析和实验仿真对比研究的结果表明所提出方法具有优越的动态性能和鲁棒性.     

基于谐波线性化的滞环电流优化控制

滞环控制的PWM变换器是强非线性环节,难以通过优化控制和常规线性化处理来提高电流控制质量.为此,分析了滞环电流控制原理、谐波线性化方法及系统稳定性,得到了滞环电流控制传递函数模型,时滞和环宽与其他参数的一般关系以及系统自振荡频率的计算方法.根据滞环电流控制的特点,提出了将谐波线性化方法与ITAE优化控制律相结合的方法,以实现对PWM变换器的优化控制.Matlab仿真结果表明了所提出方法的有效性.     

A new model of the harmonic control based on Hadamard product

In terms of Hadamard product, a new model is proposed for the control of connection coefficients of the state variables of the systems. The control law to stabilize the systems via the regulations of connection coefficients is obtained via a Hadamard product involved bilinear matrix inequalities. This new control model may be of significant applications in many fields, especially may be of some special sense in the emergency control such as isolation and obstruction control.     

A stable block model predictive control with variable implementation horizon

In this paper, we present a stable model predictive control method for discrete-time nonlinear systems. The standard MPC scheme is modified to incorporate (1) a block implementation scheme where a sub-string of the optimized input sequence is applied instead of a single value; (2) an additional constraint which guarantees that a Lyapunov function will decrease over time; (3) a variable implementation window that facilitates the stability constraint enforcement. Stability of the closed-loop system with the proposed algorithm is established. Examples are given to illustrate the effectiveness of the control scheme. The impacts of several key design parameters on the overall performance are also analyzed and discussed.     

Neural-network-based identification and control of a thin plate using piezoelectric actuators and sensors

This paper proposes a novel neural network approach for the identification and control of a thin simply supported plate. For the control purpose, the piezoelectric sensors and actuators are attached on a flexible structure. The motion behaviour of a two-dimensional model of piezoelectric materials bounded to the surface of the plate is analytically investigated. A novel linear differential inclusion is developed for a class of multilayer feedforward networks. With this technique, it is shown that the plant identified by the neural network can be represented as a linear time-invariant system. On the basis of the identified model, advanced linear control theory can be directly applied to design the stabilizing flexible structure controller. Extensive simulations are conducted to show the effectiveness of the proposed method.     

High-gam adaptive regulator for a string equation with uncertain harmonic disturbance under boundary output feedback control

This paper considers the boundary stabilization and parameter estimation of a one-dimensional wave equation in the case when one end is fixed and control and hamaomc disturbance with uncertain amplitude are input at another end. A high-gain adaptive regulator is designed in terms of measured collocated end velocity. The existence and uniqueness of the classical solution ofthe closed-loop system is proven. It is shown that the state of the system approaches the standstill as time goes to infinity and mean-while, the estimated parameter converges to the unknown parameter.     

Facial hexahedral mesh transferring by volumetric mapping based on harmonic fields

Hexahedral mesh has obvious mechanical advantages over tetrahedral mesh, but it is no trivial task to generate hexahedral mesh for complex object shapes such as individual faces. This paper presents a novel method to generate patient-specific hexahedral meshes of facial soft tissue models, based on a volumetric cross-parameterization mapping from a standard hexahedral mesh to the individual model. The volumetric parameterization is constructed based on triple of the volumetric harmonic fields, which are adapted to be as close to mutually orthogonal as possible, to achieve some quasi-conformal effect. In addition, some piecewise constraints on the harmonic fields are added to ensure anatomical feature correspondence. Experimental results show that our approach works efficiently for facial soft tissue modeling, avoids element flipping and preserves mesh element angles to a significant extent.     

基于滑窗迭代DFT的谐波参考电流控制信号快速检测方法

为解决电网中非线性负荷形成的无功电流和谐波电流对电网的影响,针对需为有源滤波器的控制提供谐波参考电流控制信号的特点,确定了谐波参考电流控制信号快速检测方法,并详细对谐波参考电流控制信号采用滑窗迭代DFT检测方法进行了理论分析,给出了谐波检测滑窗迭代算法软件流程图。MATLAB仿真结果证明,该方法简单可靠、实时性好、检测精度高。     

基于四次谐波选择法的磁通门传感器分析

采用分段折线近似磁滞回线,分析了矫顽力对磁通门输出的影响,通过理论推导得到各偶次谐波灵敏度解析表达式.比较了二次谐波选择法和四次谐波选择法灵敏度,量程和非线性度.详细讨论了四次谐波的适用条件.研究结果表明选取四次谐波还是选取二次谐波,不仅取决于激励磁场与饱和磁场强度比值,还取决于矫顽力与饱和磁场强度比值.研究结果对实际...