UPS整流滤波与电能质量

主要就目前大功率UPS所采用的几种整流、滤波方式对输入电流的影响,以及各种相应抑制谐波的方法而进行研究和比较,文中分析了五种不同的整流、滤波方式,还从理论上分析了各种整流、滤波方式对谐波的抑制效果,利用电能质量分析仪对以上五种类型大功率UPS测试其输入电能质量,得到真实、原始的数据。通过对这些数据分析、比较,总结出各种不同整流、滤波方式对输入电网电能质量的影响。     

三相三线制UPQC对电能质量问题的综合治理

统一电能质量调节器是一种综合治理调节电能质量的控制装置,可以对串联、并联补偿单元各自独立运行和协调控制两种工况下出现的电网电压跌落和电网电流谐波、无功电流等电能质量问题进行综合治理。首先分析了三相三线制UPQC的结构和各模块功能,然后采用同步坐标变换的畸变量检测算法和串联、并联协调控制策略,最后搭建UPQC实验平台,经过实验验证,UPQC在两种工况下对电能质量具有良好的治理能力。     

基于变分模态分解的低电压电能扰动抑制系统设计

低电压造成的扰动问题会直接影响供电系统正常运行,为了保证居民的用电质量,基于变分模态分解设计了一种新的低电压电能扰动抑制系统。硬件部分由网侧电流互感器、状态反馈控制器、状态观测器、光伏并网逆变器四部分组成,通过网侧电流互感器监测电流数据,利用状态观测器得到电流数据,并传输给状态反馈控制器,由状态反馈控制器反馈给控制系统,光伏并网逆变器则起到保护电流稳定电压的作用。软件部分由低电压电能扰动因子提取程序与低电压电能扰动抑制程序组成,在得到电流数据后,由低电压电能扰动因子提取程序结合变分模态分解来对扰动因子进行提取,判定扰动因子,应用低电压电能扰动抑制程序对电能扰动进行抑制,解决低电压电能扰动问题。实验结果表明,电能扰动故障发生时刻设计系统抑制时间仅为0.05 s,故障清除时刻抑制时间仅为0.02 s,具有很好的抑制能力。     

基于数字信号处理器的短时电能质量扰动检测算法研究

电网系统的高质量电能对于工农业生产及人民日常生活有极为关键的地位和作用,面对各种敏感电力电子设备的普及性运用趋势,暂态、短时的电能质量问题和扰动已经极大地引发了社会的关注,针对暂态、短时、突变非平稳状态的电能质量扰动现象,较难实现准确而全面的检测和有效辨识,为了更好地保障电网系统电能质量的高效性和稳定性,要全面了解和分析暂态、短时电能质量扰动检测方法,并基于数字信号处理器(DSP)芯片进行暂态、短时电能质量扰动检测算法的研究,从而较好地实现对暂态、短时电能质量的监测和有效治理。     

基于小波变换和快速傅立叶变换的电网谐波分析

谐波分析是谐波治理和研究谐波问题的基础。文中介绍了一种将小波变换和快速傅立叶变换结合起来的谐波分析方法,给出了电能质量信号突变点的确定公式,并对三相全控桥式整流电路产生的谐波电流进行仿真分析,得出了采用这种方法能够分别检测出扰动信号的起止时刻,也能够分析各次谐波的幅值和相角的结论。     

基于VSI的电力扰动发生装置的开发

电能质量问题包含频率偏差、电压偏差、谐波、电压波动与闪变以及电压暂降与暂升等几个方面。如果在教学实践环节中,让学生自己通过实验来产生和观察这些现象,显然有助于加深学生对电能质量知识的理解和掌握。这就需要有能产生这些现象的电能质量扰动发生装置。由于目前市场中的电能质量扰动发生装置不仅售价高且不能完全满足教学要求,因此开发了一套发生装置。该装置基于电压型逆变器VSI的拓扑结构与工作原理,不仅可以实现上述电能质量现象,还可以驱动一定功率的设备,从而对于电能质量问题引起的危害也可以有实际的认识。     

10kV电压扰动装置主电路设计及稳态运行特性

为了检测电能质量补偿装置在电能质量扰动情况下的性能,文章提出了适用于10kV电压等级的多功能电压扰动发生器的主电路结构设计方案,采用H桥级联的拓扑结构,将该装置直接串联在线路,形成了电压扰动发生源。结合该装置主电路拓扑,研究了装置的稳态运行特性,利用PSCAD/EMTDC软件对装置稳态运行特性进行了仿真,仿真结果验证了该装置主电路设计方案的可行性。     

用户侧电能质量问题及其治理解决对策

因为电能质量问题会对电网及其设备造成严重影响,所以这已经成为了国内外研究的热点问题之一。本文综述了关于电能质量的概念、问题产生的原因以及对电网产生的危害,特别是当电压跌落时对配电系统的危害。而在治理技术上,采用定制电力技术治理配电网电能质量问题最为有效。本文主要介绍了不间断电源、静止无功发生器、动态电压恢复器,将各种控制装置的优劣性,以及它们的经济性和应用进展进行了分析对比,针对动态电能的质量问题和谐波治理相关技术进行了讨论。     

电能质量监测技术在茂名电网的应用

近年来,随着对电能质量的要求越来越高,广东电网通过在特定地点设置电能质量分析和监测装置,对电能质量进行监测。茂名供电局2013年初在4个变电站13个间隔安装了电能质量监测装置,并建立电能质量监测系统,采集电能信息,分析电能质量的各项指标,为评价电力供应和改善电能质量提供依据。本文介绍了茂名电网建立的第一个电能质量监测系统,阐述了其在茂名电网的应用,并对其应用的情况进行分析。     

基于遗传规划的符号回归方法在电能质量分析中的新应用

谐波分析是电能质量分析的一个重要问题。Fourier变换与小波变换各有其局限性。文中提出一种采用基于遗传规划的符号回归方法进行电量分析的新方法。文章通过对传统研究方法的分析提出新方法。结合一个具体实例证明这种方法的可行性。设计了全桥逆变仿真实验用于产生分析数据,运用Eurqa软件采用符号回归的方法进行遗传选择计算得到了正弦分量与畸变分量的表达式,从而验证了符号回归应用于电能质量分析的实用性。与传统方法相比,该方法时间信息损失少,函数关系明确,在电能质量分析领域具有广泛的适用性和较好的应用潜力。     

The new generation of superconductor equipment for the electric power grid

High-temperature superconductor (HTS) power equipment, such as power cables, synchronous condensers, fault current limiters (FCLs), and transformers, are poised to address key technical issues in the U.S. Power grid. This equipment is enabled by the successful development of robust long-length HTS wire, available commercially from a variety of manufacturers worldwide. Compared to conventional cables, HTS power cables offer higher capacity with minimal disturbance to neighboring underground infrastructure, and their low series impedance opens the opportunity for cost-effective power flow control with phase angle regulators. HTS cables are being actively prototyped worldwide. Based on technology developed for industrial and ship propulsion motors, an HTS synchronous condenser has been developed and successfully tested in the Tennessee Valley Authority (TVA) grid; this is the first HTS power equipment to be offered commercially. It addresses the growing need for dynamic reactive power compensation for grid stability and power quality. HTS FCLs and transformers are also in active development.     

Current waveform quality from grid‐connected photovoltaic inverters and its dependence on operating conditions

The increasing installation of grid‐connected photovoltaics (PV) in the urban environment will lead to a significant penetration into the low voltage electricity supply network of small power electronic generators. Inevitably some disturbance to the electricity supply quality will result from these embedded generators. It is shown that the inverters used to grid connect PV arrays are susceptible to minor distortion of the network waveform and that this can result in higher levels of current waveform distortion, or harmonic disturbance, being sourced into the supply than would be expected from analyses which assume an ideal voltage waveform. The level of current distortion is shown to be very dependent on the type of inverter control used. Inverter operation is also a function of operating point; clearly a device at part load cannot be expected to deliver the same quality of current waveform as when operating under its rated design conditions. The impedance of the grid connection also has an impact on the inverter's operation. Copyright © 2000 John Wiley & Sons, Ltd.     

基于VSG的并网逆变器功率控制研究

虚拟同步发电机控制技术能够让并网逆变器自主稳定地参与电网运行。为验证虚拟同步发电机控制的作用并解决电磁功率收敛扰动较大的问题,文中分析了虚拟同步发电机的数学模型和控制策略,并基于同步旋转坐标的方法,提出一种优化的虚拟同步发电机控制。搭建 15 kVA的虚拟同步发电机仿真系统,并通过处理器在环实验验证。结果表明,所设计的控制策略不仅具有较好的功率跟踪和调频调压性能,还能为系统提供惯性和阻尼。同时,新的控制策略减少了电磁功率收敛扰动,提高了系统的稳定性和灵活性。     

Suppression of line voltage related distortion in current controlled grid connected inverters

The influence of selected control strategies on the level of low-order current harmonic distortion generated by an inverter connected to a distorted grid is investigated through a combination of theoretical and experimental studies. A detailed theoretical analysis, based on the concept of harmonic impedance, establishes the suitability of inductor current feedback versus output current feedback with respect to inverter power quality. Experimental results, obtained from a purpose-built 500-W, three-level, half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an output current total harmonic distortion (THD) some 29% lower than that achieved using output current feedback. A feed-forward grid voltage disturbance rejection scheme is proposed as a means to further reduce the level of low-order current harmonic distortion. Results obtained from an inverter with inductor current feedback and optimized feed-forward disturbance rejection show a THD of just 3% at full-load, representing an improvement of some 53% on the same inverter with output current feedback and no feed-forward compensation. Significant improvements in THD were also achieved across the entire load range. It is concluded that the use of inductor current feedback and feed-forward voltage disturbance rejection represent cost-effect mechanisms for achieving improved output current quality.     

Electrical fast-transient test: conducted and radiated disturbancedetermination by a complete source modeling

Tests against electrical fast transient/burst (EFT) represent a serious threat for modern high-speed electronics: besides the conducted injection of high amplitude pulse, a strong radiated field is produced during this test. The prediction of the effects of this test during the equipment early design stage requires the equivalent circuit of the generator: the output waveform into a resistive 50-Ω load is not sufficient to recover the complete circuit, including inductive component and parasitic elements. These are essential to predict the disturbance produced in arbitrary loads, as the equipment under test can be viewed. This paper describes how to characterize the EFT generator by means of the measurement of the output voltage and current produced in presence of known loads; moreover, a procedure to calculate the current on the equipment power cord is shown, based on the use of a circuit simulator (PSPICE). Finally, the disturbance produced on different loads and the radiated field during the test are calculated and experimentally validated     

Current Source Inverter Based Grid Connected Hybrid PV-Wind Power Generation Unit

ABSTRACT

This paper presents a current source inverter (CSI)-based hybrid power generation system, which uses wind turbine and photovoltaic cells (PVs). A permanent magnet synchronous generator (PMSG) is connected to the CSI using a diode rectifier and a buck converter that is used to control the speed of the rotor. Another buck converter is used to control the maximum power point tracking of PVs. The operation of proposed system is studied under normal and grid voltage dip conditions. According to new grid codes, most power generating units are supposed to remain connected to the grid during voltage sag conditions and inject reactive current to grid as defined by grid codes. The CSI has fault current limiting capability that makes it appropriate to use in grid-connected applications and during voltage sag conditions in particular. The proposed system tracks the maximum power point of wind turbine and PVs under normal mode and injects required reactive current to the grid during voltage drop. However, incorporation of CSI with the inherent behaviour of wind turbine and PVs causes fault current to be within the tolerable range for power electronic devices. Simulations are carried out by using PSCAD/EMTDC software to verify the proposed system.     

The Design of Triode Harmonic Generators

EXISTING analytical methods for predetermining the anode and grid currents of a triode harmonic generator are examined. These methods are found to give large unpredictable errors which may be of the order of 25 per cent. A new analytical method is devised, based on a power series representation of the tube characteristics, whereby the anode current components can be forecast with a maximum error of less than 6 per cent for harmonic generation up to fifth order. This method is also applied to the prediction of grid currents and is found to be more accurate than previous analytical methods.     

无线LED照明驱动系统方案设计

本文主要提出以电磁耦合与电磁共振的方式,为LED提供无线驱动电能。采用高精度的正激变换恒流源驱动LED,并利用光电池进行光照强度采集反馈调整恒流源电流以控制LED发光强度,保证光照恒定。此外该系统还在电网输入端增加有源电力滤波器（Active Power Filter,APF）,以减少该装置作为非线性负载而引入电网的高次谐波。本文所述方案能有效地提高LED照明分布的灵活性,解决电力线布线的繁琐,同时在高效管理光照能耗的情况下不影响电网电能质量,因此其具有深厚的实用价值和应用潜力。     

柴油发电机组-脉冲负载系统运行行为仿真

柴油发电机组-整流器供电系统是重要的移动装备电源形式,可作为重要工程的备用电源,也可作为直流微电网的重要支撑电源。脉冲负载集成了大量电力电子器件,是一类功率波动明显且切换频繁的负载形式,以含大功率收发组件的数字式雷达为代表。在脉冲负载工作过程中,线路中电流与电压呈强烈非线性,系统动态过程复杂,难以运用解析方法表示柴油发电机组内部的机电过渡过程与电磁暂态。文中建立了基于Matlab/ Simulink 的系统模型,分析了脉冲负载在不同工作模式时,柴油发电机组输出电压与频率的瞬态和稳态指标,结果表明:该模型能够较真实地反映柴油发电机组-整流器-脉冲负载系统的运行行为。