考虑低压释放特性的双机综合负荷模型参数识别策略研究

首先介绍了考虑低压释放特性的综合负荷模型,然后从电动机聚类和实际负荷类型两方面分析了双机和单机模型各自的适用情况。通过对双机模型轨迹灵敏度分析,得出大电动机和小电动机参数不能一起辨识。从电动机稳定性和低压释放特性分析,提出了固定大电动机参数辨识小电动机参数的辨识策略。仿真算例表明提出的双机参数辨识策略精度较高,能提高参数辨识精度。

基于Crowbar的双馈机组风电场等值模型与并网仿真分析

针对双馈机组(DFIG)风电场并网中亟须解决的低电压穿越问题,提出了一种基于Crowbar的双馈机组风电场等值方法。通过对DFIG在电网故障情况下的机理分析,给出了电网故障时DFIG转子电流的表达式。根据DFIG转子电流值判别是否投入Crowbar,将DFIG风电场分为投入与不投入Crowbar两组;运用容量加权法计算各组参数,建立DFIG风电场的双机等值模型。算例仿真分析表明,DFIG风电场的双机等值模型能够较准确地反映电网故障期间风电场变化,采用快速无功补偿提高了风电场的低压穿越能力。

考虑低电压穿越的风电场双机聚合模型

场内风速分布不均、集电线路分布不匀等因素造成各发电机间继电保护状态和外特性的差异,使得常规单机聚合模型难以准确反映真实风电场的故障穿越行为。为此,基于逆向建模方法与宏观特征参数,提出了对双馈异步机组(doubly-fed induction generator,DFIG)风电场具有更强适应的双机聚合模型。首先,分析了过流短接保护对风电场外特性指标的影响。其次,考虑到DFIG的功率源特性,低电压穿越中对其转子侧Crowbar的描述决定了是否能精确模拟风电场的功率调制响应,而短路电流水平又决定了Crowbar是否动作,是引起发电机间调性不同的最主要因素。基于该不同调性对故障过程中的DFIG进行分类,在双机等值模型的基础上实现了对风电场内分布行为的描述,并可根据具体风电场参数和风资源特性主动调节宏观参数组,从而平滑设定影响外特性的场内分布因素水平。最后,为提高该模型的实用性,还提出了一套参数辨识策略,依据故障深度提取出能体现风电场于该次扰动中最大的可能性响应的宏观参数组。多机系统仿真验证了单机等值存在的问题以及双机等值模型的性能。所提方法可考虑风电场自身的风资源特性,同时有效提高对风电场功率响应、相邻同步机功角稳定和负荷电压稳定行为的模拟精度。

Predictive current control system of PMSM based on LADRC

For a permanent magnet synchronous motor(PMSM)model predictive current control(MPCC)system,when the speed loop adopts proportional-integral(PI)control,speed regulation is easily affected by motor parameters,resulting in the inability to balance the system robustness and dynamic performance.A PMSM optimal control strategy combining linear active disturbance rejection control(LADRC)and two-vector MPCC(TV-MPCC)is proposed.Firstly,a mathematical model of a PMSM is presented,and the PMSM TV-MPCC model is developed in the synchronous rotation coordinate system.Secondly,a first-order LADRC controller composed of a linear extended state observer and linear state error feedback is designed to reduce the complexity of parameter tuning while linearly simplifying the traditional active disturbance rejection control(ADRC)structure.Finally,the conventional PI speed regulator in the motor speed control system is replaced by the designed LADRC controller.The simulation results show that the speed control system using LADRC can effectively deal with the changes in motor parameters and has better robustness and dynamic performance than PI control and similar methods.The system has a fast motor speed response,small overshoot,strong anti-interference,and no steady-state error,and the total harmonic distortion is reduced.

Identity-based ring signature scheme based on quadratic residues

Identity-based （ID-based） ring signature has drawn great concerns in recent years and many ID-based ring signature schemes have been proposed until now. Unfortunately, all of these ID-based ring signatures are constructed from bilinear pairings, a powerful but computationally expensive primitive. Hence, ID-based ring signature without pairing is of great interest in the field of cryptography. In this paper, the authors firstly propose an ID-based ring signature scheme based on quadratic residues. The proposed scheme is proved to be existentially unforgeable against adaptive chosen message-and-identity attack under the random oracle model, assuming the hardness of factoring. The proposed scheme is more efficient than those which are constructed from bilinear pairings.

Evidence of Dual Scale Porous Mechanisms During Fluid Migration in Hardwood Species (Ⅱ) A Dual Scale Computational Model to Describe the Experimental Results

The second part of this paper is devoted to the computational modelling of transient water migration in hardwood. During re-saturation, the moisture content, measured during the process by using X-ray attenuation (see part 1 of this paper), increases quickly very close to the cavity, but requires a very long time for the remaining part of the sample to absorb the moisture in wetting. For this configuration and this material, the macroscopic approach fails. Consequently, a dual-porosity approach is proposed. The computational domain uses a 2-D axisymmetric configuration for which the axial coordinate represents the macroscopic longitudinal direction of the sample whereas the radial coordinate allows the slow migration from each active vessel towards the fibre zone to be considered. The latter is a microscopic space variable. The moisture content field evolution depicts clearly the dual scale mechanisms:a very fast longitudinal migration in the vessel followed by a slow migration from the vessel towards the fibre zone.The macroscopic moisture content field resulting from this dual scale mechanism is in quite good agreement with the experimental data.

COUPLING MODEL OF TWO PHASE FLOW IN A FRACTURE-ROCK MATRIX SYSTEM AND ITS STOCHASTIC FEATURE ANALYSIS

This study is concerned with developing a two-dimensional two-phase model that simulate the movement of non-aqueous phase liquid (NAPL) in a fracture-rock matrix system. The intrinsic permeability and the fracture aperture are represented in the model via its KarhunenLoeve expansion. Other parameters and the nodal unknowns, water saturations and water pressures, are represented by their stochastic spectral expansions. The errors resulting from truncation of Karhunen - Loeve and polynomial chaos expansions to a finite number of terms are analyzed. The eigenvalues of stochastic process is found out for any point in the special domain of the problem at any instant in time.

Identity-based Verifiably Committed Signature Scheme without Random Oracles

An identity-based verifiably committed signature scheme (IB-VCS) was proposed, which is proved secure in the standard model (i.e., without random oracles). It enjoys the setup-free property and stand-alone property, both of which make an exchange protocol more practical. The scheme is unconditionally secure against the cheating signer, its security against the cheating verifier is reduced to the computational Diffie-Hellman (CDH) problem in the underlying group, it is secure against the cheating trusted third party if the underlying Paterson Schuldt's identity based signature (IBS) scheme is secure, which is proven true based on the CDH assumption in the standard model.

Knock prediction for dual fuel engines by using a simplified combustion model

The present work used a methane-air mixture chemical kinetics scheme consisting of 119 elementary reaction steps and 41 chemical species to develop a simplified combustion model for prediction of the knock in dual fuel engines. Calculated values by the model for natural gas operation showed good agreement with corresponding experimental values over a broad range of operating conditions.

Modeling bidirectional reflection distribution function of microscale random rough surfaces

The radiative properties of three different materials surfaces with one-dimensional microscale random roughness were obtained with the finite difference time domain method(FDTD) and near-to-far-field transformation.The surface height conforms to the Gaussian probability density function distribution.Various computational modeling issues that affect the accuracy of the predicted properties were discussed.The results show that,for perfect electric conductor(PEC) surfaces,as the surface roughness increases,the magnitude of the spike reduces and eventually the spike disappears,and also as the ratio of root mean square roughness to the surface correlation distance increases,the retroreflection becomes evident.The predicted values of FDTD solutions are in good agreement with the ray tracing and integral equation solutions.The overall trend of bidirectional reflection distribution function(BRDF) of PEC surfaces and silicon surfaces is the same,but the silicon's is much less than the former's.The BRDF difference from two polarization modes for the gold surfaces is little for smaller wavelength,but it is much larger for the longer wavelength and the FDTD simulation results agree well with the measured data.In terms of PEC surfaces,as the incident angle increases,the reflectivity becomes more specular.

Provably Secure Self-Certified Signature Schemes with Message Recovery

To solve the key escrow problem of the identity-based cryptosystem, Girault introduced the notion of a self-certified public key, which not only eliminates the need to authenticate a public key but also solves the key escrow problerrL This paper proposes a Self-Certified Signature （SCS） scheme with message recovery and two variants without using bilinear pairings： one is the authenticated encryption scheme in which only the designated re- ceiver can verify the signature, and the other is the authenticated encryption scheme with message linkage that deals with large messages. These three SCS schemes are provably secure in the random oracle model and are more efficient than previous schemes .

T-S Fuzzy Stochastic Bilinear Model and Fuzzy Controller Design Based on Switching Piecewise Lyapunov Functions

Based on a piecewise quadratic lyapunov function （PQLF）, this paper presents stochastic stability analysis and synthesis methods for ItO and discrete T-S fuzzy bilinear stochastic systems. Two improved stochastic stability conditions have been established in terms of linear matrix inequalities （LMIs）. It is shown that the stability in the mean square for T-S fuzzy bilinear stochastic systems can be established if a PQLF can be constructed. Considering the established stability criterion, the controller can be designed by solving a set of （LMIs）, and the closed loop system is asymptotically stable in the mean square. Two illustrative examples are provided to demonstrate the effectiveness of the results proposed in this paper.

Flow Visualization around a Double Wedge Airfoil Model with Focusing Schlieren System

In the present study, aerodynamic characteristics of the double wedge airfoil model were investigated in a transonic flow by using the shock tube as an intermittent wind tunnel. The driver and driven gases of the shock tube are dry air. The airfoil model of double wedge has the span of 58 mm, chord length c = 75 mm and its maximum thickness is 7.5 mm. The apex of the double wedge airfoil model is located on the 35% chord length from the leading edge. The range of hot gas Mach numbers are from 0.80 to 0.88, and the Reynolds numbers based on chord length are 3.11× 10^5- 3.49× 10^5, respectively. The flow visualizations were performed by the sharp focusing schlieren method which can visualize the three dimensional flow fields. The results show that the present system can visualize the transonic flowfield clearer than the previous system, and the shock wave profiles of the center of span in the test section are visualized

A PAIRING-BASED PUBLICLY VERIFIABLE SECRET SHARING SCHEME

A publicly verifiable secret sharing （PVSS） scheme is a verifiable secret sharing scheme with the special property that anyone is able to verify the shares whether they are correctly distributed by a dealer. PVSS plays an important role in many applications such as electronic voting, payment systems with revocable anonymity, and key escrow. Up to now, all PVSS schemes are based on the traditional public-key systems. Recently, the pairing-based cryptography has received much attention from cryp- tographic researchers. Many pairing-based schemes and protocols have been proposed. However, no PVSS scheme using bilinear pairings is proposed. This paper presents the first pairing-based PVSS scheme. In the random oracle model and under the bilinear Diffie-HeUman assumption, the authors prove that the proposed scheme is a secure PVSS scheme.

A new cellular automaton model for traffic flow considering realistic turn signal effect

In real traffic,any vehicle must give lane-changing signal(i.e.the turn signal) before changing lanes;at this time,the vehicles behind the lane-changing vehicle will be hindered and may form "plugs" due to the turn signal effect.However,few studies focus on exploring the effect.In this paper,the turn signal effect was taken into account by proposing a new symmetric two-lane cellular automaton(T-STCA) model,and the new model was set to compare with the STCA,H-STCA and A-STCA models.Numerical results show that using the T-STCA model to describe lane-changing or overtaking,the process appeared in several consecutive time steps;while using the other three models,the process appeared only in one time step.In addition,the T-STCA model could describe the mixed traffic flow more realistically and the turn signal effect could help the plugs to dissolve more quickly.

On a Dual Risk Model Perturbed by Diffusion with Dividend Threshold

In the dual risk model, the surplus process of a company is a L′evy process with sample paths that are skip-free downwards. In this paper, the authors assume that the surplus process is the sum of a compound Poisson process and an independent Wiener process. The dual of the jump-diffusion risk model under a threshold dividend strategy is discussed. The authors derive a set of two integro-differential equations satisfied by the expected total discounted dividend until ruin. The cases where profits follow an exponential or mixtures of exponential distributions are solved. Applying the key method of the Laplace transform, the authors show how the integro-differential equations are solved. The authors also discuss the conditions for optimality and show how an optimal dividend threshold can be calculated as well.

Location and Design Decisions of Facilities in a Distribution System with Elastic Customer Demand

This paper describes a bi-level programming model that seeks to simultaneously optimize location and design decisions of facilities in a distribution system in order to realize company's maximal total profit subject to the constraints on the facility capacity and the investment budget.In the upper-level problem,twoechelon integrated competitive/uncompetitive capacitated facility location model,which involves facility location and design,is presented.In the lower-level problem,customer is assumed to patronize store based on facility utility which is expressed by service time cost in the store and its travel cost to customer.Customer's facility choice behavior is presented by a stochastic user equilibrium assignment model with elastic demand.Since such a distribution system design problem belongs to a class of NP-hard problem,a genetic algorithm(GA)-based heuristic procedure is presented.Finally,a numerical example is used to illustrate the application of the proposed model and some parameter sensitivity analyses are presented.