Dynamics and stabilization of peak current-mode controlled buck converter with constant current load

The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.

Dynamic Response Analysis of Risers Subjected to Combined Wave and Current Loading

A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.

Robust Nonlinear Current Sensorless Control of the Boost Converter with Constant Power Load

The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the design of stabilizing controllers. A PWM-based current-sensorless robust sliding mode controller is developed that requires only the measurement of the output voltage. An extended state observer is developed to estimate a lumped uncertainty signal that comprises the uncertain load power and the input voltage, the converter parasitics, the component uncertainties and the estimation of the derivative of the output voltage needed in the implementation of the controller. A linear sliding surface is used to derive the controller, which is simple in its design and yet exhibits excellent features in terms of robustness to external disturbances, parameter uncertainties, and parasitics despite the absence of the inductor’s current feedback. The robustness of the controller is validated by computer simulations.

Research on the Dynamic Response of Submerged Floating Tunnels to Wave Currents and Traffic Load

Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element method able to account for fluid-structure interaction.The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections.Under ultimate traffic load condition,one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.

Analysis of load status and management strategies of main caregivers of patients with malignant tumors of digestive tract

Caregiver load refers to the subjective and objective negative impact of caregivers in the care of patients,and excessive load will have a serious impact on patients and caregivers themselves and can reduce their quality of life.For the main caregivers,it not only needs to care for the patients in life and daily life,but also needs to pay the cost of treatment for the patients,coupled with the need to carry out their own original work,life,etc.excessive life pressure,economic pressure,work pressure,emotional pressure,etc.lead to heavy load of the main caregivers,which can easily cause caregivers to have different degrees of psychological problems,which will cause serious adverse effects on the caregivers themselves and cancer patients,not conducive to the construction of a harmonious family and society.This article analyzes the current situation of primary caregiver burden in patients with gastrointestinal malignant tumors,analyzes its influencing factors,and specifies specific treatment strategies.It is hoped to provide scientific guidance for later related research and application.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

Effects of drive current rise-time and initial load density distribution on Z-pinch characteristics

A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z- pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power

A DISCUSSION ON CURRENTS AND SUSPENDED LOAD TRANSPORT IN SURF ZONE

In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the breaking wave current and the sediment concentration of suspended load in the offshore surf zone near Nouakchott, the Islamic Republic of Mauritania, the author has analized the law governing the distribution of longshore current and sediment concentration of suspended load by means of statistical method, and presented a calculation method for the longshore sediment transport in offshore surf zone.

Simulations of the Allowable Load Current of the Overhead Lines in the Latvian Power Network

This paper considers the influence of changes of the transmission lines of permissible load current depending on conductor and ambient temperatures, climate conditions. The theoretical background of the allowable conductor temperature as well as load current determination principles are proposed. On one hand, the principles are based on mechanical limitations; on the other hand, they are based on thermal limitations. The simulation tasks were based on specific data information of three existing overhead lines of Latvian power system as well as the planned 330 kV overhead line. Moreover, the special thermovision device was used for precious determination of conductor temperature of the existing transmission lines. The simulation results of the obtained data are reviewed in the paper.

双路电源的主动均流电路系统研究

广泛使用的低成本电源管理芯片或直流电源模块通常并未集成输出均流控制功能,因此不能直接并联输出使用。而使用特殊的电源管理芯片或是额外的均流控制电路会提高电源电路的复杂程度,造成电路成本的提高。针对此应用场景,提出了一种具有主动均流功能的双路电源开关,作为负载开关或电源多路复用器应用于电路之中,利用开关电流的方法均分输出电流,在几乎不增加电路成本的同时对两路电源进行均流。阐述了所提双路电源开关的工作原理与参数设计方法,并通过仿真与实验证明了所提方法的正确性与可行性。

地铁车站弱电设备间设备发热量确定方法

介绍了一种地铁车站弱电设备间设备发热量确定新方法,该方法利用弱电设备发热量实测数据与模型预测数据相互验证,可以有效提高弱电设备发热量确定结果的准确性。研究了室内气温、地铁是否运营、设备额定功率和车站类型等因素对设备发热量的影响。研究结果表明:基于间接测量和预测模型的地铁车站弱电设备间设备发热量确定方法可以提高和保障设备发热量计算结果的准确性;室内气温会显著影响设备外表面和围护结构内表面温度及围护结构内表面热流密度,但对设备外表面热流密度的影响较小;地铁是否运营对弱电设备间设备发热量有较大影响,地铁运营期间设备发热量大于非运营期间;设备额定功率对弱电设备间设备发热量峰值有较大影响,车站类型和建筑面积对设备发热量峰值的影响很小。

含逆变型分布式电源和分支负荷的配电网自适应电流差动保护

电流差动保护具有良好的选择性和灵敏性。但是,逆变型分布式电源(inverter-interfaced distributed generator,IIDG)和分支负荷接入改变了配电网的故障特性,现有配电网的电流差动保护面临拒动或误动的风险。为解决以上问题,该文在计及P/Q控制的IIDG和分支负荷的故障等值建模基础上,从故障点、IIDG和分支负荷的相对位置出发,挖掘配电网线路两端正序电流差的幅值特征以及正序电流故障分量的相位特征。在此基础上,提出一种正序电流幅值与故障分量相角阈值配合的双比例制动系数自适应差动保护方案,并且利用幅相平面分析所提保护判据的可靠性和灵敏性。最后通过PSCAD/EMTDC验证了所提保护方案的有效性,仿真结果表明该方案适应不同故障类型、位置和过渡电阻,且不受IIDG以及分支负荷接入的影响。

深中通道沉管隧道水下基槽开挖边坡稳定性分析

在沉管隧道整体施工过程中,特别是外海沉管隧道,其深基槽通常面临海流作用复杂、基槽泥沙回淤等问题,给基槽边坡的安全稳定性带来不利影响。以深中通道沉管隧道工程为背景,采用数值模拟方法,通过对边坡形态、边坡回淤物分布以及海流荷载等因素的研究,分析了在相应条件下水下基槽边坡的安全系数和破坏特性。结果表明,边坡的土体特性与几何形态、边坡回淤物的分布与厚度以及海流荷载的大小与方向的变化均会对基槽边坡的稳定性造成不同程度的影响。

Feasibility study on buoyancy-weight ratios of a submerged floating tunnel prototype subjected to hydrodynamic loads

The research progress of a novel traffic solution,a submerged floating tunnel（SFT）,is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio（BWR） is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype（SFTP） project in Qiandao Lake（Zhejiang Province,China）,the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design.

考虑精确磁通的电磁加载装置等效磁路建模

为提高电磁加载装置在控制应用时的模型预测快速性与精确性,考虑电磁加载装置硅钢片表面涡流磁场生成因素与不同轴偏心下有效气隙长度,采用非线性方程拟合硅钢片磁化曲线,建立包含磁极边缘效应、磁极铁心、转子硅钢片动态磁阻与涡流磁场的电磁加载装置非线性等效磁路模型。研究了硅钢片表面涡流磁场生成因素与气隙磁场分布,并与有限元仿真结果比较分析。应用该模型在水润滑轴承试验台上进行电磁加载力测试试验。研究结果表明:等效磁路法对磁场分布的表征与有限元法一致,且对气隙的计算更为精确;电磁加载力稳态误差小于4%,响应时间低于0.55 s。

基于栅极限流的SiC MOSFET栅电荷测试方案

SiC MOSFET是一种高性能的电力电子器件,其开通/关断过程中积累/释放的栅电荷Q_(g)对MOSFET的开关速度、功率损耗等参数有重要影响。通常采用在栅极设置恒流源驱动,对时间进行积分的方法来测量Q_(g)。为了降低驱动复杂度,提高测试结果精度和可视性,基于双脉冲测试平台的感性负载回路,改用耗尽型MOSFET限制栅极电流实现恒流充电,对SiC MOSFET进行测试。同时利用反馈电阻将较小的栅极电流信号转换为较大的电压信号。实验结果表明:在误差允许范围(±5%)内该测试方案能较为准确地测得SiC MOSFET的Q_(g),测试结果符合器件规格书曲线。

水轮机调节系统与轴系耦合模型对系统参数的敏感性分析

抽水蓄能电站频繁地暂态过程对轴系振动有重要影响,建立一个能够反映水电机组暂态响应的调节系统与轴系的耦合模型对于研究抽水蓄能电站的安全运行至关重要。以拉日朗日公式推导的扭矩方程为纽带,构建了水轮发电机组调节系统与考虑多振动诱发因素的轴系系统的瞬态耦合模型。计算了甩不同负荷下轴系的动态响应过程,分析了发电机偏心质量以及发电机励磁电流对轴系暂态过程的影响。研究发现,甩去的负荷越多,轴系在动态响应的过程中振动越剧烈,甩30%负荷,甩60%负荷,以及甩100%负荷后,发电机转子在x方向上的振幅较甩负荷前分别增加了68.7%,109.3%,以及126.3%。发电机的偏心质量越大,水轮发电机组轴系在动态响应过程中的幅值越高,系统越不稳定,而励磁电流越大,轴系在响应过程中的幅值越小,越有利于系统稳定运行。本文的目的是为水轮发电机组调速系统-轴系系统瞬态耦合模型的建立提供一种方法,探讨和评价甩负荷下瞬态耦合模型的参数敏感性,保障机组暂态下的安全稳定运行。

瞬时电流预测的逆变器启动冲击负载的方法

针对通用逆变器启动冲击负载能力很弱的问题,此处提出一种利用瞬时负载电流预测来控制输出调制比的方法来增强逆变器启动冲击负载的能力。冲击性负载,通常是感性负载投入时会产生5~10倍的冲击电流,而通用逆变器抗冲击电流能力较弱,通常只能启动20%的额定负载。这里根据检测到的负载瞬时电流来瞬时减小逆变器的输出调制比,将负载电流控制在额定电流范围内,感性负载投入后会逐渐稳定,输出调制比也逐渐恢复到正常值,完成感性负载的启动。此方法已在油田储能电源上得到广泛应用,可将逆变器启动感性负载的能力从20%额定提高到70%额定。

基于中性线电流离散分析治理三相负荷不平衡

当三相负荷不平衡时,必然会引起中性线电流的产生。针对三种不同三相负荷不平衡条件下中性线电流的变化情况,建立与之对应的三相负荷不平衡度算法模型。采用中性线电流的离散分析建立三相负荷不平衡度算法,作为三相负荷不平衡治理的有效判据,结合试验分析,得到了三相负荷不平衡度与中性线电流的变化规律,并应用于低压供配电系统三相负荷不平衡的治理分析。结果表明:所提三相负荷不平衡度算法对低压供配电系统三相负荷不平衡的治理具有较强的实用性。提出的以三相负荷不平衡度为自适应变量,以中性线电流为过程监测量,采用有功调配与无功补偿相结合策略,能够有效反映三相负荷不平衡的治理情况。

深海采矿立管在波流载荷下的弯矩响应分析

采矿立管是深海采矿系统的重要组成部分,立管的弯矩分析是确保立管正常使用的重要指标。立管所处海洋环境复杂,且立管底部的自由边界条件使得立管弯矩特性难以分析。本文基于波浪理论,使用Abaqus有限元软件建立海洋采矿立管的模型,运用Abaqus中的AQUA海洋工程模块,考虑立管在轴向力、自重、浮力、波浪载荷、海流载荷及模拟海上平台水平和升沉运动共同作用下,对采矿立管进行弯矩分析,计算了提升泵不同安装位置、不同中继仓重量变化对弯矩的影响,结果表明:提升泵会增大安装位置的弯矩幅度,且安装在不同位置对立管弯矩会产生叠加影响;中继仓重量的增加提高了立管整体稳定性,但会使提升泵处弯矩波动产生向中部延伸的不利影响。