无刷双馈风力发电机滑模功率解耦控制

首次采用现代控制理论中的滑模变结构方法研究了无刷双馈发电机(BDFM)运行时有功功率与无功功率的解耦控制,在状态方程的基础上,应用Lyapunov函数求得了有功功率与无功功率的滑模控制律,并在Matlab/Simu-link基础上建立了系统的仿真模型。仿真结果表明,滑模变结构控制能够有效的实现有功功率与无功功率的解耦控制,并实现了风能的最大功率捕获,证明了该控制策略的有效性。     

无刷双馈风力发电机组的自抗扰功率解耦控制

对无刷双馈风力发电机组稳态运行时的功率分配关系进行了详细分析,在此基础上确定了最大风能捕获的控制策略.将自抗扰控制应用到无刷双馈电机有功功率与无功功率的解耦控制,将功率控制系统分解为有功功率子系统和无功功率子系统,从而建立了风力发电机组完整的功率控制模型.基于Matlab/Simulink的仿真结果表明无刷双馈风力发电机组自抗扰控制成功实现了有功功率与无功功率的解耦控制,不仅能够实现最大风能捕获,而且可以根据电网的实际需求调节机组无功功率的输出,验证了控制算法的有效性.     

Two-axis model development of cage-rotor brushless doubly-fedmachines

A two-axis model of a cage-rotor brushless doubly-fed machine (BDFM) which is suitable for machine and BDFM drive system dynamics studies is presented. The technique enables the two-axis model to be derived from a detailed model recently developed for investigation of design aspects of the machine. Unlike the conventional approaches to self-cascaded machines analysis, this method permits analysis of the machine characteristics in both dynamic and steady state conditions, and also facilitates machine and drive system design by directly correlating machine performance with machine structure and parameters. The approach allows the machine parameters to be calculated from machine geometry and developed into the model parameters     

基于反馈线性化的无刷双馈电机模型预测控制策略

提出一种无刷双馈电机(BDFM)基于反馈线性化的模型预测控制策略。基于BDFM状态空间方程,在控制电机磁场定向同步坐标系下,采用输入输出反馈线性化将BDFM转化为线性系统并证明系统稳定性,以此为基础计算系统预测值,根据BDFM离散预测模型,设计模型预测控制器,实现电磁转矩和控制侧电机磁链的独立控制。仿真试验结果证明该控制器具有优良的控制性能,能够实现平滑控制和系统解耦。     

Dynamic simulation of brushless doubly-fed machines

Dynamic and steady-state models for the simulation of the performance of experimental brushless doubly-fed machines (BDFM) are presented. The dynamic simulation results are obtained using a two-axis representation which has been developed from a detailed machine design model. In turn, it is shown that several forms of steady-state equivalent circuit can be developed from the two-axis model for different specific modes of operation. Test data in dynamic conditions are compared with the predictions given by the two-axis model. It is concluded that these simplified models will provide adequate representation of full performance for control, stability, and scoping studies     

无刷双馈风力发电机的自抗扰解耦控制

针对无刷双馈电机(BDFM)结构的复杂性、随环境的可改变性及传统的PID控制在BDFM中应用不理想等,提出了一种新型基于扩张观测器的非线性PID控制——自抗扰控制方法来实现对风力发电系统有功功率和无功功率的解耦控制。仿真结果证明了该方法的正确性和有效性,具有更强的鲁棒性和可实现性。     

Calculation of interturn voltages in machine windings duringswitching transients measured on terminals

This paper describes a technique for calculating interturn voltages in machine windings during transient conditions. The technique is based on the measurement of switching transients at the machine terminals and computer simulation of the surge travelling through the winding. The machine winding is treated as a multiconductor transmission line and the discrete Fourier transform and convolution techniques are used for calculating the switching transient distribution along the winding. Switching transients results obtained on two electrical motors in the Manzanillo II power plant are used in the analysis     

Performance analysis of a three-phase induction generator connectedto a single-phase power system

This paper analyzes the performance of a three-phase induction generator which is connected to a single-phase power system. Significant improvement in machine performance can be obtained by using a single static phase-converter, provided that the machine is driven in the reverse direction. If two phase-converters, are employed, perfect phase balance can be obtained at any desired value of slip. The theoretical analysis is validated by experiments on a 2-kW test machine     

A compact,closed‐form solution for the optimum,ideal wind turbine

The classical momentum solution for the optimum induced‐flow distribution of a wind turbine in the presence of wake swirl can be found in many textbooks. This standard derivation consists of two momentum balances (one for axial momentum and one for angular momentum), which are combined into a formula for power coefficient in terms of induction factors. Numerical procedures then give the proper induction factors for the optimum inflow distribution at any radial station; and this, in turn, gives the best possible power coefficient for an ideal wind turbine. The present development offers a more straightforward derivation of the optimum turbine. The final formulas give the identical conditions for the ideal wind turbine as do the classical solutions—but with several important differences in the derivation and in the form of the results. First, only one momentum balance is required (the other being redundant). Second, the solution is provided in a compact, closed form for both the induction factors and the minimum power—rather than in terms of a numerical process. Third, the solution eliminates the singularities that are present in current published solutions. Fourth, this new approach also makes possible a closed‐form solution for the optimum chord distribution in the presence of wake rotation. Copyright © 2013 John Wiley & Sons, Ltd.     

Bioenergy from forest thinning: Carbon emissions,energy balances and cost analyses

The growing demand for bioenergy in Sweden has drawn attention to the potential of forest thinning as bioenergy feedstock. There are, however, concerns regarding the cost effectiveness and environmental challenges of harvesting and processing forest thinnings into bioenergy. It is against this background that cost, energy and carbon balances were analysed to evaluate some of the economic and environmental sustainability issues of forest thinning based bioenergy systems. Primary data was collected from two thinning operations in two forest plots comprising spruce and birch stands. One operation involved the use of the conventional two machines (one separate machine for cutting or felling and another for forwarding felled trees) for the thinning work. The second operation involved a harwarder, which combines tree felling/cutting and forwarding in one unit machine. The results showed that forest thinnings provide a potential resource for the sustainable production of bioenergy.     

Complex chemical systems with power production driven by heat and mass transfer

In this paper, we investigate power production in complex multireaction systems propelled by either uncoupled or coupled multicomponent mass transfer. The considered system contains two mass reservoirs, one supplying and one taking out the species, and a power-producing reactor undergoing the chemical transformations characterized by multiple (vector) efficiencies. To establish a suitable basis for these efficiencies, an approach is applied that implements balances of molar flows and reaction invariants to complex chemical systems with power production. Reaction invariants, i.e., quantities that take the same values during a reaction, follow by linear transformations of molar flows of the species. Flux balances for the reacting mixture may be written down by equating these reaction invariants before and after the reactor. Obtained efficiency formulas are applied for steady-state chemical machines working at the maximum production of power. Total output of produced power is maximized at constraints which take into account the (coupled or uncoupled) mass transport and efficiency of power generation. Special attention is given to non-isothermal power systems, stoichiometric mixtures and internal dissipation within the chemical reactor. Optimization models lead to optimal functions that describe thermokinetic limits on power production or consumption and extend reversible chemical work W_rev to situations in which reduction of chemical efficiencies, caused by finite rates, is essential. The classical thermostatic theory of reversible work is recovered from the present thermokinetic theory in the case of quasistatic rates and vanishing dissipation.     

An Approximate Relation of a Regenerative Heat Exchanger Effectiveness in Off-Design Conditions

A regenerative heat exchanger is an important component of a thermal system in power units. It is crucial to know the performance of the regenerative heat exchanger in off-design conditions during its design and operation. Advanced regenerative heat exchanger simulators have been developed for many years to describe the performance in off-design conditions. The simulators involve the use of equations for mass, momentum, and energy balances and criteria relations for heat transfer coefficients; the geometrical data of the heat exchanger are also required. Due to high complexity, the calculations are performed iteratively. For this paper, a different approach was taken: The heat exchanger was considered as a “black box.” Based on the data obtained from the simulator, the effect of input variables on the output ones was investigated, so as to propose a relation describing the regenerative heat exchanger performance. To assess this performance, heat transfer effectiveness was proposed, and its two variants were considered. Since two heat transfer effectiveness definitions were assumed, two approximate relations concerning the regenerative heat exchanger were determined. The relations were verified against data obtained from a simulator of a high-pressure regenerative heat exchanger in a medium-power steam condensing unit. A satisfactory accuracy of the proposed relations was obtained.     

Experimental study of the saturation and the cross-magnetizingphenomenon in saturated synchronous machines

The cross-magnetizing effect in both the d- and q-axis in a small salient-pole machine was measured. Two simple equations describing the cross-magnetizing effect in both axis directions are derived. An accurate saturation representation that includes the effect of both the machine-saturated reactances and the cross-magnetizing phenomena is also given. In addition to this, the modified phasor diagram and power/load angle relationship are obtained. The results of the machine output power obtained by this technique show a good agreement with those obtained from test. The saturation effect in changing the power/load angle curves is seen to be noticeably large and depends mainly upon the cross-magnetizing effect     

Impact of wind power generating system integration on frequency stabilization in multi-area power system with fuzzy logic controller in deregulated environment

Among the available options for renewable energy integration in existing power system, wind power is being considered as one of the suited options for future electrical power generation. The major constraint of wind power generating system (WPGS) is that it does not provide inertial support because of power electronic converters between the grid and the WPGS to facilitate frequency stabilization. The proposed control strategy suggests a substantial contribution to system inertia in terms of short-term active power support in a two area restructured power system. The control scheme uses fuzzy logic based design and takes frequency deviation as input to provide quick active power support, which balances the drop in frequency and tie-line power during transient conditions. This paper presents a comprehensive study of the wind power impact with increasing wind power penetration on frequency stabilization in restructured power system scenario. Variation of load conditions are also analyzed in simulation studies for the same power system model with the proposed control scheme. Simulation results advocates the justification of control scheme over other schemes.     

基于容阻建模技术的SOFC电堆数值模拟

借助MATLAB软件，通过建模对固体氧化物燃料电池堆的运行进行仿真。为了计算的方便，模型采用了容阻建模技术。采用由质量守恒、能量守恒、动量守恒和电化学过程组成的模型，对SOFC电堆通道中的气体组成、温度分布、电压分布和电流密度分布进行了计算分析。这些分析结果可对电堆的设计提供参考。     

基于改进粒子群算法的多目标无功优化

提出了一种基于粒子群算法的多目标优化方法,该算法采用Pareto支配关系来更新粒子的个体最优和全局最优值,用存储池保存搜索过程中发现的非支配解;采用聚类算法裁剪非支配解,以保持解的分散性;采用动态惯性权重来平衡粒子的局部和全局搜索能力,并将该算法应用于IEEE14节点系统的多目标无功优化。     

新型链传动式风力机的理论分析

对新型的链传动式风力机进行了理论分析,发现该机的叶片位于前面时和运转于后面时冲角不一样,理论分析表明该机运行于前面的叶片的冲角大于最佳值的工况下,前后叶片都可以截取风能,整机有较高的风能利用系数,随后给出了该风力机的风能利用系数曲线,对这种风力机的设计和运行有一定的指导意义和参考价值。     

Intelligent power management in a vehicular system with multiple power sources

This paper presents an optimal online power management strategy applied to a vehicular power system that contains multiple power sources and deals with largely fluctuated load requests. The optimal online power management strategy is developed using machine learning and fuzzy logic. A machine learning algorithm has been developed to learn the knowledge about minimizing power loss in a Multiple Power Sources and Loads (M_PS&LD) system. The algorithm exploits the fact that different power sources used to deliver a load request have different power losses under different vehicle states. The machine learning algorithm is developed to train an intelligent power controller, an online fuzzy power controller, FPC_MPS, that has the capability of finding combinations of power sources that minimize power losses while satisfying a given set of system and component constraints during a drive cycle. The FPC_MPS was implemented in two simulated systems, a power system of four power sources, and a vehicle system of three power sources. Experimental results show that the proposed machine learning approach combined with fuzzy control is a promising technology for intelligent vehicle power management in a M_PS&LD power system.     

On the Mass and Energy Balances of Two-Phase Systems

Mass and energy balances of a two-phase system undergoing a phase transition are given for different flow arrangements of the phases, taking the system boundary as diabatical. The expressions obtained are illuminated from different points of view stressing the consequences of the corresponding energy balances occasionally adopted in literature.     

Analysis of Thermal Stress in a Functionally Graded Coating on a Parabolic Substrate

The thermal stress field in a functionally graded coating on a parabolic substrate, where the material properties vary along the thickness direction, is considered. The closed-form solutions of thermal stresses related to compositional gradient, coating thickness and substrate curvature were obtained based on force and moment balances, and then numerical results are presented for several special examples. It is found that the magnitude and distribution of thermal stress in the functionally graded coating system with general geometrical shape can be designed properly by controlling the compositional gradient, coating thickness and substrate curvature.