液压型风力发电机组功率追踪及功率平滑多目标控制研究

以液压型风力发电机组为研究对象,针对低风速条件下液压型机组的最佳功率追踪和功率平滑多目标寻优控制问题进行研究。建立液压型风力发电机组逆系统模型,分析模型非线性形式,确定逆系统的解耦方法,利用逆系统的方法设计液压系统转矩控制器,实现最佳功率追踪控制。通过线性二次型最优控制方法,设计功率追踪与功率平滑的多目标优化控制器。依托30 k VA液压型风力发电机组实验台进行仿真和实验研究,验证了该方法的可行性。仿真和实验结果表明该方法具有较好的控制效果,在保证最佳功率追踪的同时实现了功率平滑控制。研究结果对液压型风力发电机组具有重要的理论意义和工程价值。     

RESEARCH ON BLADE PITCH NONLINEAR PID CONTROL FOR A LARGE-SCALE WIND TURBINE UNDER CONSTANT POWER

建立了基于功率/桨距敏感性的变桨系统模型,综合出桨距非线性PID控制方法.通过Bladed软件计算不同桨距角下功率变化的敏感性,在Bladed外部控制器条件下,获得该方法和固有方法下系统输出的对照结果并进行分析和总结.     

基于LQG-I的风力发电机组优化控制策略研究

文章针对风电系统的随机性、不确定性和未建模动态等特征,提出了LQG-I优化控制策略。首先,运用机理分析的方法建立了风力发电系统数学模型。在此基础上,设计了LQG-I控制策略,既保留了LQG在克服随机扰动方面的优势,又利用了积分控制在解决系统的不确定性和未建模动态方面的优势。为了进一步改善对系统的控制性能,采用粒子群优化算法对加权矩阵Q,Qe,R的参数进行整定。最后,以高风速区功率和发电机转矩优化控制问题为例,在matlab/simulink平台下仿真验证了所提优化控制策略的可行性和有效性。仿真结果表明:所提出的LQG-I优化控制策略能够实时跟踪风速的变化,保证发电机角速度、转矩和输出功率的稳定;在同等条件下,该控制策略比传统LQG控制器性能更优越。     

电站锅炉-汽轮机系统的模糊H2/H∞负荷跟踪控制

针对火电机组机炉协调系统的非线性以及现场运行存在多种不确定性干扰等特性,提出一种在混合H_2/H_∞性能指标约束下的T-S模糊负荷跟踪控制器设计方法。该方法以混合H_2/H_∞跟踪性能为目标,利用并行分配补偿方法对系统T-S模糊模型设计模糊状态反馈增益和误差积分增益控制器,并利用Lyapunov函数对闭环系统进行稳定性分析,得到满足H_2/H_∞跟踪性能的线性矩阵不等式。在不同负荷下对Bell-■str■m机炉协调系统T-S模糊模型(以下简称T-S模型)进行仿真实验,并基于该方法对被控系统的T-S模型、失配T-S模型和线性模型进行控制比较。结果表明:所设计的控制方法具有良好的控制性能,对失配T-S模型的控制具有较好的鲁棒性。     

核反应堆功率的协调型标准传递函数控制

针对国内核反应堆功率控制技术存在的不足,提出将协调型多容惯性(MCP)标准传递函数控制器应用于核电站功率的控制,设计了串联校正与状态反馈协调型多容惯性标准传递函数控制器,并在Simulink中建立仿真系统对该方法进行验证,同时将该方法与经典PD控制系统进行比较.结果表明:该方法对有零点的高阶无自平衡过程有较理想的跟踪控制性能;与PD控制相比,斜坡升负荷试验中该系统具有超调小和调整时间短的优点.     

双级式光伏并网发电前级变换器系统建模与控制器参数设计

针对双级式光伏并网发电前级变换器系统功率电压双闭环MPPT结构的控制器参数设计问题,基于前级变换器系统的等效电路,采用状态空间平均法建立了系统的非线性模型,进而采用平衡点附近线性化方法得到其线性模型。根据对象特性引入控制器结构,在频率特性和根轨迹分析的基础上,给出了前级控制器参数的系统化设计方法。12 k W双级式光伏并网发电系统仿真结果表明,在标准光强和模拟自然条件光强变化时,该控制器能快速实现前级MPPT跟踪控制及单位功率因数并网控制,获得了良好的动静态性能。     

基于滑模控制的光伏系统MPPT控制策略

针对现有的太阳电池最大功率点跟踪方法中存在的跟踪速度慢、在最大功率点附近存在振荡、外界环境发生变化时可能产生误判等不足,提出一种基于滑模控制的太阳电池最大功率点跟踪方法。在建立DC-DC变换器模型的基础上设计滑模控制器,得出控制函数,并通过李雅普诺夫方法进行稳定性和存在性分析。利用Matlab/Simulink对太阳电池模型进行仿真,验证该滑模控制策略的可行性;建立基于扰动观察法的太阳电池最大功率点跟踪模型,与滑模控制方法进行比较。结果表明在外界环境变化的情况下,该方法可实现较快的跟踪速度和较好的稳定精度,在自适应和抗干扰上具有较大优势。     

神经网络非线性逆控制方法实现PEMFC分布式发电系统的负荷响应

质子交换膜燃料电池(PEMFC)分布式发电系统的负载典型特点是时时有瞬间的大的峰值功率。因此,系统必须找到实时的最佳工作点才能响应负载的功率需求。以往采用的优化搜索方法需要在负载连续变化和峰值现象之间权衡搜索步长,影响控制的速度和精度。分析PEMFC分布式发电系统的工作特点以及各工作参数与净输出功率之间的关系,提出利用BP神经网络实现PEMFC输出功率的复杂非线性逆模型。在此基础上,根据非线性逆控制的思想设计了系统实时功率响应的逆控制器。经分析和仿真验证,利用神经网络非线性逆控制方法,PEMFC系统在稳定运行过程中能够满足系统内部功率损耗的同时良好的响应系统负载的实时功率需求。与优化搜索方法比较,该实时控制设计在实现精度和速度上都有所改进。图5表1参6     

具有双约束条件的云模型控制策略在风储联合发电系统中的应用

在一阶低通滤波器平抑风电功率方法的基础上,从风电平抑波动需求和储能自身吞吐波动能力两方面考虑,提出基于云模型理论的储能系统平抑风电功率波动的方法。该方法以风电功率的波动率和储能系统的荷电状态作为二维云模型控制器的规则前件,以低通滤波器的时间常数作为云模型控制器的规则后件,设计适于风储联合发电系统的二维云模型控制器。该方法通过调整低通滤波器的时间常数,自适应地使储能系统协调风电功率输出,在不同工况下合理地平抑风电功率波动。最后通过仿真实例验证该方法的有效性和正确性,达到合理利用储能且较好地抑制风电功率波动的控制目的。     

基于根轨迹法的高压直流输电附加控制器设计

针对高压直流输电系统受扰动故障出现振荡的问题,提出一种基于根轨迹校正方法的附加阻尼控制器设计方法。首先通过采用最小二乘—旋转不变算法辨识出系统的低阶线性化模型,再根据根轨迹校正方案设计直流附加控制器。为进一步提高控制效果,基于该方法设计发电机励磁附加控制器,进行机网协调控制。在PSCAD/EMTDC中搭建四机两区域仿真模型,并分别对比传统控制器和根轨迹控制器在系统发生扰动故障时的振荡控制效果,结果表明轨迹控制器可有效控制系统振荡,具有较强的鲁棒性,提高了系统稳定性。研究成果可应用于工程实际。     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Coupling a two-temperature model and a one-temperature model at a fluid-porous interface

We study a convective heat transfer problem in a fluid-porous domain in the case of the local thermal non-equilibrium assumption (LTNE). The issue of this study is to determine appropriate boundary conditions to model heat transfer, while using models with a different number of equations: a two-temperature model in the homogeneous porous region versus a one-temperature model in the free region. To proceed, a two-step up-scaling approach is used, which has the particularity to provide closed jump relations depending on intrinsic characteristic of the interface. Thus, the use of jump or continuity conditions depend only on the interface location inside the fluid-porous transition region. The pertinence of the approach is illustrated on a 2D convective heat transfer problem considering a solid heat source in the porous medium.     

Studies on a two-staged micro-combustor for a micro-reformer integrated with a micro-evaporator

A new micro-combustor configuration for a micro fuel-cell reformer integrated with a micro-evaporator is studied experimentally and computationally. The micro-combustor as a heat source is designed for a 10–15 W micro-reformer using the steam reforming method. In order to satisfy the primary requirements for designing a micro-combustor integrated with a micro-evaporator, i.e., stable burning in a small confinement and maximum heat transfer through a wall, the present micro-combustor is a simply cylinder, which is easy to fabricate, but is two-staged (expanding downstream) to control ignition and stable burning. The aspect ratio and wall thickness of the micro-combustor substantially affect ignition and thermal characteristics. For optimized design conditions, a pre-mixed micro-flame is easily ignited in the expanded second-stage combustor, moves into the smaller first-stage combustor, and finally is stabilized therein. The measured and predicted temperature distributions across the micro-combustor walls indicate that heat generated in the micro-combustor is well transferred. Thus, the present micro-combustor configuration can be applied to practical micro-reformers integrated with a micro-evaporator for use with fuel cells.     

Using a fin with a parabolic concentrator

The consequences of using a fin collector in focusing solar collectors is examined and is found to have merits.     

Bioconvection in a squeezing flow of a micropolar fluid in a horizontal channel

The bioconvection flow of an incompressible micropolar fluid containing microorganisms between two infinite stretchable parallel plates is considered. A mathematical model, with a fully coupled nonlinear system of equations describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms is presented. The governing equations are reduced to a set of nonlinear ordinary differential equations with the help of suitable transformations. The resulting nonlinear ordinary differential equations are linearized using successive linearization method, and the resulting system of linear equations is solved using the Chebyshev collocation method. The detailed analysis illustrating the influences of various physical parameters, such as the micropolar coupling number, squeezing parameter, the bioconvection Schmidt number, Prandtl numbers, Lewis number, and bioconvection Peclet number on the velocity, microrotation, temperature, concentration and motile microorganism distributions, skin friction coefficient, Nusselt number, Sherwood number, and density number of motile microorganism, is examined. The influence of the squeezing parameter is to increase the dimensionless velocities and temperature and to decrease the local Nusselt number and local Sherwood number. The density number of motile microorganism is decreasing with squeezing parameter, bioconvection Lewis number, bioconvection Peclet number, and bioconvection Schmidt number.     

Exploration of heat transfer effect in a magnetohydrodynamics flow of a micropolar fluid between a porous and a nonporous disk

An analysis is carried out for the flow characteristics of a conducting micropolar fluid. The fluid was passed in between two parallel disks of infinite radii. The novelty of the study is to consider one of the disks as porous and the other one as nonporous, and the external magnetic field is applied along the transverse direction of the flow. The flow phenomena for the polar fluid characterized by the magnetic effect in conjunction with the temperature equation reduce to a set of coupled nonlinear ordinary differential equations using the requisite transformations and nondimensionalization. An analytical approach such as the variation parameter method is employed to tackle the system efficiently. To emphasize the effect of various physical parameters contributing to the flow phenomena, that is, non-zero tangential slip, Reynolds number, Prandtl number, magnetic parameter, and material parameter on the flow profiles of axial and radial velocities, the microrotation and temperature profiles are presented graphically. To validate the simulated results, a comparison with established results is made, and it is concluded that both are in good correlation.     

Development of a system model for a hydrogen production process on a solar tower

An attractive path to the production of hydrogen from water is a two-step thermo chemical cycle powered by concentrated sunlight from a solar tower system. In the first process step the redox system, a ferrite coated on a monolithic honeycomb absorber, is present in its reduced form while the concentrated solar energy hits the ceramic absorber. When water vapour is fed to the honeycomb at 800 °C, oxygen is abstracted from the water molecules, bond in the redox system and hydrogen is produced. When the metal oxide system is completely oxidised it is heated up for regeneration at 1100–1200 °C in an oxygen-lean atmosphere. Under those conditions and in the second process step, oxygen is set free from the redox system, so the metal oxide is being reduced and after completion of the reaction again capable for water splitting.Since the overall process consists of two core reaction steps, which need to be carried out sequentially in a reactor unit at two different temperature steps, a special process and plant concept had to be developed enabling the continuous supply of product regardless of the alternating nature of the solar reactor operation. The challenge of the process control is to keep the two core reaction temperatures constant and to ensure regular temperature switches after completion of the individual process steps, independent of the weather conditions, like DNI fluctuation, clouds and wind speed. Also start-up, the fast switching after completion of half-cycles and the shutdown must be controlled. State of the art is the manual switching of heliostats to fulfil those control tasks.This paper describes the development and use of a system model of this process. The model consists of three main parts: the simulation of the solar flux distribution at the receiver aperture, the simulation of the temperatures in the reactor modules and the simulation of the hydrogen generation. It can be used for the analysis of the operational behaviour. The model is intended to be used in the future for the control of the whole process.     

Evaporating characteristics of a microlayer under a bubble

Using the Hallinan‐Ervin model, the flow and evaporation in a bubble microlayer were theoretically analyzed, and the dryout characteristics and Staub's criterion were discussed in detail. It was revealed that the critical dryout radius is associated with the wettability of the heated surface, and that the dominant role for microlayer evaporation is disjoining pressure, not surface tension gradient. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 456–462, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10052     

Solidification of a liquid about a cylindrical pipe

The temperature distribution and the rate of removal of heat by a coolant are predicted for the process of solidification of a liquid about a cold, isothermal pipe. The heat balance integral method incorporating spacial sub-division is used. It is found that acceptable results can be obtained by using only a small number of sub-divisions together with a piece-wise, linear profile. Furthermore, the results illustrate that the sensitivity which is normally associated with the heat balance integral method is overcome.