Hybrid modeling of DFIGs for wind energy conversion systems

The synchronous reference frame is widely used in Doubly Fed Induction Generation (DFIG) modeling. In a DFIG, it is usually assumed that slip control is in place at the rotor-side converters to make sure that the injected rotor voltage at slip frequency gives a constant stator frequency (60 Hz or 50 Hz). In the analysis, the injected rotor voltages are directly expressed in the synchronous reference frame. In the cases where slip control is not available, the above modeling will not work. This paper implements a hybrid model (dqabc) of a DFIG. The key modeling idea is to use the frequencies of the injected rotor voltages as explicit inputs and further transform the injected rotor voltage into the synchronous reference frame. This allows one to model and simulate scenarios including: (i) acceleration via rotor injection, (ii) harmonic simulation for six-pulse rotor injection, and (iii) negative sequence compensation using rotor injection. Matlab/Simulink is used to perform the simulations of three cases listed above. Laboratory experiments on two of the cases confirm the validity of the model and simulation results.     

Simplified detection of broken rotor bars in induction motors controlled in field reference frame

In this paper, a simple method for additional on-line detection of broken rotor bars in a squirrel cage induction motor controlled in rotor field co-ordinates using existing hardware is presented. Based on a previously presented approach, an algorithm for on-line calculation of the variance of stator voltage reference, which depends on the number of broken bars, has been developed. Due to its simplicity, it could run in parallel with a standard control algorithm in field reference frame using contemporary fixed- and floating-point processors, thus requiring minimum processing time. The algorithm uses internal reference values of the stator voltage; therefore no additional dedicated measurements are needed. Results were obtained at different operating points on an induction motor with gradually damaged rotor. Comparison with commonly used diagnostic method confirms the validity of the approach.     

Direct Power Control of Dfig by Using Nonlinear Model Predictive Controller

This paper proposes a nonlinear model predictive direct power control (PDPC) strategy for a double fed induction generator (DFIG)‐based wind energy generation system. Active and reactive power variations of DFIG are calculated based on machine rules, and a nonlinear model of DFIG is given. A nonlinear model predictive controller (NMPC) is presented based on the useful cost function and constraint that it results in more proximity between simulations and reality. The power and current ripples are reduced and the optimal rotor voltage is generated based on an objective function and the constraints. The rotor voltage vector is calculated in the synchronous reference frame and transferred into the rotor reference frame. Simulation results of a 2 MW DFIG system show good performance of the proposed method during variation of active and reactive powers, machine parameters, and wind speed. Also, the transient responses of active and reactive powers are within a few milliseconds.     

Definition of the Elastic Forces in the Finite-Element Absolute Nodal Coordinate Formulation and the Floating Frame of Reference Formulation

The equivalence of the finite-element formulations used inflexible multibody dynamics is the focus of this investigation. Thisequivalence will be used to address several fundamental issues related tothe deformations, flexible body coordinate systems, and the geometriccentrifugal stiffening effect. Two conceptually different finite-elementformulations that lead to exact modeling of the rigid body dynamics will beused. The first one is the absolute nodal coordinateformulation in which beams and plates can be treated as isoparametricelements. This formulation leads to a constant and symmetric mass matrix andhighly nonlinear elastic forces. In this study, it is demonstrated thatdifferent element coordinate systems which are used for the convenience ofdescribing the element deformations lead to similar results as the elementsize is reduced. In particular, two element frames are used;the pinned and the tangent frames. The pinned frame has one ofits axes passing through two nodes of the element, while the tangent frame isrigidly attached to one of the ends of the element. Numerical resultsobtained using these two different frames are found tobe in good agreement as the element size decreases. The relationshipbetween the coordinates used in the absolute nodal coordinate formulationand the floating frame of reference formulation is presented. Thisrelationship can be used to obtain the highly nonlinear expression of thestrain energy used in the absolute nodal coordinate formulation from thesimple energy expression used in the floating frame of referenceformulation. It is also shown that the source of the nonlinearityis due to the finite rotation of the element. The result of the analysispresented clearly demonstrates that the instability observedin high-speed rotor analytical models due to the neglect of the geometriccentrifugal stiffening is not a problem inherent to a particular finite-element formulation. Such a problem can only be avoided by considering the known linear effect of the geometric centrifugal stiffening or by using a nonlinear elastic model as recently demonstrated. Fourier analysis of the solutions obtained in this investigation also sheds new light on the fundamental problem of the choice of the deformable body coordinate system in the floating frame of reference formulation. Another method forformulating the elastic forces in the absolute nodal coordinate formulationbased on a continuum mechanics approach is also presented.     

A Long-Range Generalized Predictive Control Algorithm for a DFIG Based Wind Energy System

This paper presents a new Long-range generalized predictive controller in the synchronous reference frame for a wind energy system doubly-fed induction generator based. This controller uses the state space equations that consider the rotor current and voltage as state and control variables, to execute the predictive control action. Therefore, the model of the plant must be transformed into two discrete transference functions, by means of an auto-regressive moving average model, in order to attain a discrete and decoupled controller, which makes it possible to treat it as two independent single-input single-output systems instead of a magnetic coupled multiple-input multiple-output system. For achieving that, a direct power control strategy is used, based on the past and future rotor currents and voltages estimation. The algorithm evaluates the rotor current predictors for a defined prediction horizon and computes the new rotor voltages that must be injected to controlling the stator active and reactive powers. To evaluate the controller performance, some simulations were made using Matlab/Simulink. Experimental tests were carried out with a small-scale prototype assuming normal operating conditions with constant and variable wind speed profiles. Finally, some conclusions respect to the dynamic performance of this new contro-ller are summarized.      

Interface reduction methods for mechanical systems with elastohydrodynamic lubricated revolute joints

In this contribution, three different reduction methods for elastic structures with lubricated interfaces are presented and compared with each other. While for the first two methods, classical reduction strategies from component mode synthesis are applied, for the third method, a dual reduction basis is used, consisting of vibration modes of the free floating structure, attachment modes and residual modes. Within this new dual approach, it is shown how the residual modes can be obtained by applying pressure distributions of analytical solutions of the hydrodynamic equations. The described methods are compared for two classical simulation example—for a one-sided elastohydrodynamic lubricated joint of a slider–crank mechanism in a floating frame of reference formulation as well as for an elastic rotor in a flexible journal bearing.     

一种无速度传感器矢量控制系统的研究

本文基于同步轴系下的感应电动机电压磁链方程式,提出了一种感应电动机转子磁场定向的矢量控制方法,利用在同步轴系中q轴电流的误差信号实现对电机速度的估算。在该无传感器矢量控制系统中,由于采用了经典的PI调节器,使得控制系统更为简单。最后利用MATLAB建立的该无传感器矢量控制系统的仿真模型,通过仿真验证了本文所提出的无传感器矢量控制系统具有良好的动态和静态性能。     

Implementation and efficiency of two geometric stiffening approaches

When the modeling of flexible bodies is required in multibody systems, the floating frame of reference formulations are probably the most efficient methods available. In the case of beams undergoing high speed rotations, the geometric stiffening effect can appear due to geometric nonlinearities, and it is often not captured by the aforementioned methods, since it is common to linearize the elastic forces assuming small deformations. The present work discusses the implementation of different existing methods developed to consider such geometric nonlinearities within a floating frame of reference formulation in natural coordinates, making emphasis on the relation between efficiency and accuracy of the resulting algorithms, seeking to provide practical criteria of use.     

不依赖于定转子参数的感应电动机转子磁链的自适应观测器设计

给出了一种新的感应电劝机转子磁链观测器的设计方案,以克服劝机参数发生变化时矢量控制系统性能的下降,这种设计方案下依赖于感应电动机的定转子参数,算法的稳定性和收敛性由正实误差传递函数条件下的参数调整算法保证,数字仿真结果说明限它的有效性。     

基于MATLAB的感应电机矢量控制系统的仿真

该文根据感应电机矢量控制的基本原理，基于MATLAB／SIMULINK构造了电压型SPWM逆变器供电的感应电机按转子磁场定向的矢量控制系统的仿真模型。通过仿真试验验证了模型的正确性，并分析验证了该文所建立的调速系统具有快速的启动性能及良好的抗扰动性能，基本上实现了完全解耦控制；另外，分析了感应参数变化对调速系统的影响，说明转子电阻及励磁电感等参数对获得良好的调速系统的性能的重要性。该模型可通用于笼型异步电机，在使用时只需输入不同的电机参数即可。     

基于新型Type-1 PLL的永磁同步电机转子位置估计方法

为了提高表贴式永磁同步电机的调速性能,提出一种基于新型锁相环(PLL)的转子位置估计方法.首先,针对表贴式永磁同步电机定子反电动势进行谐波分析,定义谐波成分在旋转坐标系下的表现形式;然后,为提高转子位置估计性能,针对特定谐波成分设计由自适应陷波器(ANF)和低通滤波器(LPF)串级组成的新型滤波器;最后,对新型PLL与同步旋转坐标系锁相环(SRF-PLL)进行对比仿真实验,实验结果表明,所提出的新型PLL不仅能保证较高的估计精度,而且具有较快的转子位置跟踪速度和较强的滤波性能.     

Numerical simulation of aerodynamic and acoustic characteristics of a ducted rotor

This work is devoted to the numerical simulation of the problem about a rotor rotation in a duct in a noninertial reference frame based on the Euler equations. The configuration is a model of a tail rotor of a helicopter. The calculations were carried out using highly accurate EBR schemes on unstructured tetrahedral meshes with the variables determined at the nodes. The numerical results on the aerodynamic forces, as well as the intensity and direction of the acoustic radiation in the far field, are presented and analyzed.     

磁通检测式异步电机矢量控制计算机仿真研究

该文从同步速M—T坐标系下异步电机方程和异步电机矢量控制的基本原理出发，详细分析转子参数（电感和电阻）对磁通检测式矢量控制性能的影响。考虑到实际实验系统中电机转子参数会随着电机的运行状态而改变，而MATLAB仿真软件电力系统工具箱中的异步电机模型在运行中不能实时改变自身的参数，运用MATLAB中的s函数自行编写能够模拟转子参数实时变化的电机模型。在此基础上建立整个异步电机矢量控制仿真系统，首次分别对忽略转子参数变化和考虑转子参数时变这两种情况下的系统进行仿真和分析。仿真结果表明实际中由于集肤效应产生的转子参数变化使异步电机矢量控制的动态性能变差。     

永磁同步电机的级联自适应扰动观测器控制策略

受电压源逆变器非线性特性的影响,转速控制通常不能精确抑制齿槽转矩。为精确补偿齿槽转矩,提高永磁同步电机转速控制精度,提出一种级联自适应扰动观测器控制策略。首先,采用参考电流指令建立了同步旋转坐标系下逆变器死区电压模型,并通过自适应扰动观测器对其进行补偿。然后,针对齿槽转矩为转子位置的周期函数的特点,设计了速度环自适应扰动观测器,实现了对齿槽转矩的有效补偿,所提控制策略只需已知电机参数的界。仿真结果表明,所提出的控制策略能够有效抑制电机齿槽转矩、提高转速控制精度。     

Terminal bang-bang impulsive control of linear time invariant dynamic systems

For a linear time-invariant dynamic system with bang-bang impulsive actuators whose position (off, on negative, or on positive) is determined by the switching points in time, an algorithm is developed that makes it possible to use methods of modal control for solving the terminal control problem. This algorithm is used to control the rendezvous of space vehicles with constant thrust engines arranged along the axes of a Cartesian reference frame.     

Experimental validation of rigid-flexible coupling dynamic formulation for hub–beam system

The aim of this paper is to compare the accuracy of the absolute nodal coordinate formulation and the floating frame of reference formulation for the rigid-flexible coupling dynamics of a three-dimensional Euler–Bernoulli beam by numerical and experimental validation. In the absolute nodal coordinate formulation, based on geometrically exact beam theory and considering the torsion effect, the material curvature of the beam is derived, and then variational equations of motion of a three-dimensional beam are obtained, which consist of three position coordinates, two slope coordinates, and one rotational coordinate. In the floating frame of reference formulation, the displacement of an arbitrary point on the beam is described by the rigid-body motion and a small superimposed deformation displacement. Based on linear elastic theory, the quadratic terms of the axial strain are neglected, and the curvatures are simplified to the first order. Considering both the linear damping and the quadratic air resistance damping, the equations of motion of the multibody system composed of air-bearing test bed and a cantilevered three-dimensional beam are derived based on the principle of virtual work. In order to verify the results of the computer simulation, two experiments are carried out: an experiment of hub–beam system with large deformation and a dynamic stiffening experiment. The comparison of the simulation and experiment results shows that in case of large deformation, the frequency result obtained by the floating frame of reference formulation is lower than that obtained by the experiment. On the contrary, the result obtained by the absolute nodal coordinate formulation agrees well with that obtained by the experiment. It is also shown that the floating frame of reference formulation based on linear elastic theory cannot reveal the dynamic stiffening effect. Finally, the applicability of the floating frame of reference formulation is clarified.     

A new nonlinear multivariable control strategy of induction motors

A new real-time control strategy for induction motors is introduced. This paper shows that rotor speed and rotor flux magnitude reference tracking of an induction machine can be originally obtained. The proposed control law is based on two points: an open-loop reference control which allows to obtain perfect tracking since outputs are planned and on a closed-loop strategy based on PI controllers for the stabilization around the desired trajectories. This innovative structure ensures rotor speed and rotor fluxes tracking despite uncertainties on rotor resistance and load torque variations. Simulation and experimental results, including an estimation of the rotor flux norm, are given to illustrate the originality and effectiveness of this control law.     

Predictive Power Control of PMSG based WECS: Development and Implementation for Smooth Grid Synchronisation,Balanced and Unbalanced Grid

In this paper, the distributed generation unit is controlled to operate in both stand-alone (SA) and grid-connected (GC) modes and offers a smooth transition between these modes using the model predictive control scheme. The permanent magnet synchronous generator (PMSG), along with a 2-level back-to-back converter, is named a DGU. A simple and intuitive approach using predictive control is presented in a stationary reference frame for a load-side converter (LSC). A voltage control loop is used during SA mode to fix the voltage and frequency at the load end. The smooth synchronization technique is developed without a phase-locked loop. During GC, a predictive power control regulates active and reactive power during the symmetry and unbalanced grid voltage conditions. The designed strategy makes the power factor improvement, reduction of grid current harmonics, and elimination of twice grid frequency ripple from power during grid unbalance possible. This work has proposed a solution to reduce the overall computational burden on the processor by eliminating the state prediction in each sampling period. The machine-end converter control is formulated in the rotor flux reference frame to keep the power flow across the dc-link capacitor constant. Comprehensive experiments are conducted with the designed scaled laboratory prototype to successfully validate the control’s theoretical claim.     

不平衡电网电压下双馈风力发电系统强励控制

针对电网电压不平衡造成的双馈风力发电机(DFIG)定子有功和无功功率振荡、电磁转矩脉动、定、转子电流不平衡等问题,提出了一种双馈风力发电系统转子侧变换器强励控制方案。推导了不平衡电网电压下DFIG定子有功、无功功率的二次谐波分量在同步旋转坐标系中的表达式,并以此为依据设计了电压强励补偿环。分析了有功、无功功率,电磁转矩及定、转子电流二次谐波分量之间的关系,采用单一强励补偿控制器对不同控制目标进行切换强励控制。对1.5MWDFIG系统的控制特性研究验证了所提控制策略的可行性和优越性。     

Backstepping Control of Speed Sensorless Permanent Magnet Synchronous Motor Based on Slide Model Observer

This paper presents a backstepping control method for speed sensorless permanent magnet synchronous motor based on slide model observer. First, a comprehensive dynamical model of the permanent magnet synchronous motor(PMSM) in d-q frame and its space-state equation are established. The slide model control method is used to estimate the electromotive force of PMSM under static frame, while the position of rotor and its actual speed are estimated by using phase loop lock(PLL) method. Next,using Lyapunov stability theorem, the asymptotical stability condition of the slide model observer is presented. Furthermore, based on the backstepping control theory, the PMSM rotor speed and current tracking backstepping controllers are designed, because such controllers display excellent speed tracking and anti-disturbance performance. Finally, Matlab simulation results show that the slide model observer can not only estimate the rotor position and speed of the PMSM accurately, but also ensure the asymptotical stability of the system and effective adjustment of rotor speed and current.