N次谐波凸轮的设计方法

本文详细讨论了N 次谐波凸轮的设计方法,并提出一种适合于我国目前广泛采用的平面挺柱高速车用发动机的配气机构,即等曲率半径N 次谐波凸轮的设计方法。     

基于对称规则采样法的多模块APF并联系统谐波特性分析

在建立多模块APF并联系统数学模型的基础上,对基于对称规则采样法的APF单模块SPWM电压、电流谐波特性以及多模块并联系统载波相移(CPS)SPWM电压、电流谐波特性进行了分析研究,旨在为并联系统的参数选择、模块协调控制、并联环流机理分析以及保护等提供理论研究基础。通过理论分析和实验验证,得出以下结论 :N模块并APF联系统相比较于单个模块,在输出电流的低频调制分量上,相位同步,幅值提高了N倍;并联系统输出电流的高频开关谐波分量分布在m N倍的载波频率即m Nωc附近,呈奇数次分布,且在(2m-1)×(2N-1)ωc、m×2Nωc和m×(2N-1)ωc三个频率分布点具有不同的谐波特征,与单模块相比,谐波频率提高了N倍,而谐波幅值降低了N倍。     

MMC-HVDC谐波特性分析

为分析以模块化多电平换流器为主要工作元件的高压直流输电系统(MMC-HVDC)的传变特性,基于模块化多电平换流器(MMC)工作原理,利用开关函数法并引入谐波调制比概念,从理论上分析了MMCHVDC的传变特性,并通过仿真分析验证了理论的正确性。结果表明,整流侧交流系统注入h次正序谐波时,在直流侧会生成h-1次零序谐波,在逆变侧交流系统会生成h次正序谐波和h-2次负序谐波;整流侧交流系统注入h次负序谐波时,在直流侧会生成h+1次零序谐波,在逆变侧会生成h+2次正序谐波和h次负序谐波。     

RO-SBM的希尔伯特—黄变换谐波检测方法

针对希尔波特-黄谐波检测方法的端点效应问题,提出斜率再优化(RO-SBM)与希尔伯特-黄变换(HHT)相结合的方法(RO-SBM-HHT),该方法先采用RO-SBM法对原信号延拓,按照包络原则对延拓之后的信号进行经验模态分解(EMD),得到本征模态函数IMF分量,然后对各个IMF分量进行希尔伯特变换(HT),并采用最小二乘拟合可获得各次谐波的幅值和频率。仿真与试验数据表明,RO-SBM-HHT可有效地解决谐波检测端点效应,提高检测精度、减少冗余分量。     

基于dSPACE的电网谐波环境下双馈风机的适应性分析

文章以双馈电机(DFIG)机组及以含有5,7,11,13次谐波电压的电网为研究对象,针对风电机组应对电网谐波带来的扰动并维持正常运行等问题进行了研究。给出了一种基于多重谐振控制器的谐波抑制方法,并在dSPACE仿真平台上建立了一台2 MW风机模型,借助dSPACE系统提供的ControlDesk环境对其进行实时仿真分析。实时仿真结果表明,该方案能有效减少5,7,11,13次电网谐波电压带来的影响,使DFIG定子电流波形更加正弦化,改善直流母线电压波动问题,提高了电网谐波环境下风机系统的适应性。     

非对称式N次谐波凸轮型线设计方法的研究

提出了一种非对称N次谐波凸轮型线的优化设计方法。新设计方法能有效控制N次谐波凸轮型线的设计结果,实现凸轮型线在360°内二阶导数连续;气门开启速度高于关闭速度;上升缓冲段终点加速度大于下降缓冲段终点加速度;下降段正加速度极值低于上升段;解决了N次谐波凸轮型线设计中存在的缓冲段加速度波动突变的设计难点。     

基于LSSVM-RSM的边坡可靠度研究

由于岩土体材料复杂多变,边坡稳定的功能函数往往具有高度非线性,常规的二次多项式响应面法(RSM)往往很难对其拟合。对此,利用最小二乘支持向量(LSSVM)的小样本优良的拟合能力,提出了基于LSSVM-RSM的可靠度分析方法对边坡稳定的功能函数进行拟合,并通过网格搜索法优化LSSVM参数,最后通过两个算例进行对比验证。计算结果表明,与传统二次多项式响应面法相比,该方法能更好地拟合抗剪强度参数与边坡稳定性之间的非线性关系,有效地扩展了响应面法在边坡稳定的可靠度分析中的应用。     

基于PIR的并网逆变器低频次谐波抑制策略研究

针对电网电压畸变造成并网电流低频次谐波含量较高的问题,提出一种基于比例积分-准谐振（PIR）与电流谐波检测环相结合和控制策略抑制电流谐波。首先分析并网逆变器原理,建立电流内环数学模型。基于内模原理,引入电网电压全前馈消除电网电压对网侧电流和影响,其次分析电流谐波检测与抑制原理,采用电流特定次谐波检测环对逆变器侧电流提取谐波分量,并采用闭环控制抑制电流谐波,利用伯德图对准谐振控制器参数进行设定。最后建立Matlab/Simulink仿真模型并搭建dSPACE-DS1104半实物仿真平台,分析仿真与实验结果来验证所提控制策略和有效性与可行性。     

基于VC-综合赋权法的海上风电APF配置优化方法研究

大容量海上风电机组的接入改变了传统电力系统结构,给电网带来了谐波等问题,影响了电能质量。为抑制海上风电机组产生的低次谐波,文章首先建立了海上风电机组并网电流的低次谐波理论模型;然后,在仿真软件ETAP上搭建海上风电机组仿真模型,验证不同出力情况下风电场的输出谐波特性;最后,基于风电场输出谐波特性,提出变异系数（Variation Coefficient,VC）综合赋权法对风电场有源滤波器（APF）进行优化配置,提升了风电场谐波的治理效果。基于实际算例验证了所提方法的有效性。     

超高次谐波对配用电系统的影响

随着新型电力系统高电力电子化与电力线路通信的快速发展,超高次谐波问题日益突出,因此本文开展了超高次谐波对不同类型设备以及配电网的运行影响研究,主要是对计量装置、继电保护装置、通信系统的研究,在此基础上进行了超高次谐波对配电网影响的趋势预测,能够为超高次谐波的限值设定与防治技术提供一定的参考,具有实际意义。     

Harmonic compensation using a synchronous machine with resonantfield circuits

This paper deals with a harmonic compensation method using a synchronous machine with resonant field circuits. Harmonics have become one of the major problems in power systems and a lot of methods of harmonic suppression have been studied. The authors have proposed a new method of harmonic suppression using a synchronous machine excited with the 6th harmonic current. This paper shows that armature inductances for the 5th or 7th harmonics decrease when the field circuits are connected to capacitors resonating at the 6th harmonic. The variations of armature impedances are explained theoretically by Park's equations. The optimal capacitances are selected so as to resonate with field inductances for the short-circuited armature. The experiments to suppress the 5th and 7th harmonics using the synchronous machine are successful     

基于ETAP软件的矿热炉负荷谐波影响评估与治理

针对矿热炉负荷产生的谐波问题,给出了采用ETAP软件的负荷谐波影响评估方法。将矿热炉负荷谐波特性添加到用户自定义谐波源,搭建了谐波分析模型,进行谐波潮流计算,评估公共连接点母线的谐波水平。依据谐波评估结果,设计滤波器。利用ETAP的谐波频率扫描,找出滤波器投入后系统的并联谐振点,对滤波器投入后的效果进行谐波潮流分析。结果表明,所设计的滤波器达到了预期的滤波效果,仿真计算结果和实际测试基本吻合。利用ETAP软件进行谐波仿真分析和谐振分析,可以辅助进行滤波器设计,能避开系统谐振点,有效减少电网的谐波污染。     

齿谐波励磁的混合励磁发电机带整流负载的定子铁耗计算

针对混合励磁发电机带整流负载时谐波含量增加对定子铁心损耗的影响,建立了齿谐波励磁的混合励磁发电机带整流负载的有限元场路耦合模型,分析了发电机带整流负载在齿谐波励磁系统断开和接通两种工况下的线电压谐波分量,借助传统定子铁心损耗计算模型计算出线电压谐波分量对定子铁心损耗的影响。同时利用有限元电磁仿真软件计算出电机空载及两种工况下的定子铁心损耗,仿真与计算结果比较表明,该计算方法在一定的误差内准确性较高。     

Analysis of conduction heat transfer problems in steady, 2D regions with circular holes using a special boundary integral method

A special boundary integral method developed for two-dimensional regions containing circular holes is used to calculate temperature and heat transfer on the boundaries of several selected regions. The geometrical configuration of the region is arbitrary and convective boundary conditions are assumed. An important feature of the method is analytic representation of temperature and its normal derivative on the interior circular holes in the form of a harmonic series. This makes the application of the boundary integral method convenient and free from conditioning problems associated with small interior boundaries. Heat transfer from circular isothermal interior holes are calculated for several illustrative examples using three terms of the harmonic series representation for heat transfer at each of the circular boundaries. The results are presented and discussed.     

A new method for determining reference compensating currents of thethree-phase shunt active power filter

Among various solutions to electric power quality problems, the use of a shunt active power filter (SAPF) has been proven as an effective method to compensate reactive power and to mitigate harmonic currents of nonlinear loads. When designing a SAPF, it is crucial to generate reference currents for determining actual compensating current injections to the point of common coupling. In contrast to the conventional instantaneous reactive power theory that needs coordinate transformations, the new method proposed in this paper is to determine reference compensating currents based on the balance of the instantaneous reactive and active power generated in the SAPF. It is shown that the proposed method is suitable for reactive and harmonic power compensation by using a SAPF. In addition to maintaining the sinusoidal source currents, this method also eliminates the need for installing an energy storage device for reactive power compensation as well as the DC source for the harmonic compensation in the active power filter. Therefore, a simpler design of the SAPF with the minimal line losses can be expected     

基于二阶广义积分器的谐波电流检测算法

为解决谐波电流检测算法问题,依据三相负载电流在αβ坐标系下的表现形式,提出了一种基于二阶广义积分器的谐波电流检测方法,适用于三相三线制对称和不对称系统。该方法通过Clark变换将三相电流信号转化为静止坐标系下的两相电流,再分别利用二阶广义积分器的特性提取基波电流分量,最后通过反Clark变换将基波电流分量变换成三相电流,与电网电流相减后得到谐波电流,便于工程中有源滤波器只对谐波电流进行补偿。仿真结果表明,该方法简单可靠、易于数字实现、检测效果好。     

Dynamic harmonic field analysis of a cage type induction motor whenmagnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors     

A NEW METHOD FOR NUMERICAL TREATMENT OF DIFFUSION COEFFICIENTS AT CONTROL-VOLUME SURFACES

ABSTRACT

Diffusion coefficients at control-volume surfaces are required for numerical simulation of convection-diffusion equations. Various interpolation methods for these diffusion coefficients are briefly discussed and compared with the analytical solutions of both pure diffusion and convection-diffusion problems. It is found that the harmonic mean method is not as accurate and reliable as is supposed. A new method is thus developed. Extensive numerical comparisons are given for both the harmonic mean and the present method, and the results show that the method proposed is accurate, reliable, and easy to use.     

太阳能逆变器的消谐控制方法研究

为了降低逆变器的谐波，减小开关频率，以便减小开关损耗，提高逆变器效率，该文提出了在太阳能逆变器中采用消谐PWM控制策略，并分析了消谐控制逆变器的设计原理、控制系统结构、输出电压的闭环控制方法等，讨论了数字控制技术的分辨率对输出谐波大小的影响。分析和试验表明：对于类似于太阳能逆变器这种电压和频率变化不大的场合，采用消谐控制具有开关频率低、开关损耗小、输出谐波小、滤波器参数和体积小、易于实现闭环控制等优点，是一种极具潜力的控制策略。     

基于HHT变换的微网电压闪变与谐波检测新技术

微网中大规模的分布式电源由于其自身特点及大量电力电子设备的使用,容易引起电网电压波动、电压闪变及谐波等电能质量问题,影响电力用户的供电要求。利用HHT(Hilbert-Huang transform)变换方法对微网中的电压闪变、谐波等电能质量扰动信号进行了EMD分解,得到各IMF分量,通过对IMF分量进行Hilbert谱分析和边际谱分析。仿真结果表明,该方法能快速有效地检测出微网中电压闪变信号的频率和幅值及谐波信号产生及终止的时刻。