Diagnosing Power Quality-Related Computer Problems

Total reliance on sensitive electronic systems for such important functions as data processing, communications, and process control is now a way of life in our commercial, industrial, and governmental activities. This development has necessitated a new concern toward the quality of the electric power supply. Intermittent power disturbances, capable of disrupting electronic equipment are inherent to both commercial and industrial power systems. Any disruption causing downtime and financial loss, power-related or otherwise, is likely to precipitate a study to determine appropriate corrective actions. Unfortunately, analyzing the cause and effect of power disturbances can be difficult, particularly when sophisticated computer systems are involved. The ultimate purpose is to assist the electronic equipment users in reducing power-related downtime.     

Analysis and Evaluation of Residential Air Conditioners for Power System Studies

Air conditioners deserve special attention because they represent a significant part of the power system load, mainly in high temperature regions. This work takes into account conventional and variable-speed types, as the latter one presents two possible arrangements, i.e., with and without undervoltage protection. The modeling of equipments is analyzed for simulation purposes, as a novel representation of variable-speed units with undervoltage protection is introduced. The behavior of each air conditioner is verified in steady state operation considering typical power quality and voltage disturbances that occur in power systems such as voltage sags and interruptions. Furthermore, the influence of the aforementioned equipment on the power system is analyzed within the context of a distribution network     

Expansion of a Power System using Existing Switchgear

Today's power system engineer is often faced with expansion of his system with additions usually small, yet sometimes large. With the exception of brand new plants, he must utilize his existing power system equipment and add to it as necessary to increase its power handling capacity. Increased capacity nearly always means increased interrupting duty, and a problem comes with what to do with existing switchgear to prevent exceeding its fault-interrupting capability. A number of system tools or methods are outlined to aid the power system designer with sufficient choice to provide the optimum expansion while utilizing his existing switchgear equipment.     

空调器的低功耗待机和电加热控制方案研究

本文介绍了一种家用变频空调器室外机辅助电加热的控制方案,其中包括底盘电加热带和压缩机曲轴电加热带的控制研究,主要研究方向是在空调器具备低功耗待机的模式下,可以保证两种不同电加热带可以正常控制,在低温环境下空调器可以正常的化霜和压缩机预热处理,确保空调系统的可靠和稳定。     

计及电气特性的空调负荷建模及集群控制策略

为充分发挥温控负荷的调控潜力,以空调负荷为例,对空调负荷建模及集群控制策略进行了研究。首先从热力学模型与电气模型两方面建立了完善的空调负荷模型;其次考虑空调的启停次数以及使用寿命等实际因素,提出了一种基于改进温度优先序列的空调负荷集群群内控制策略;最后分析了负荷电压变化对集群响应功率的影响,基于频率下垂控制,提出了一种考虑功率响应偏差、电压约束以及集群等效荷电状态的空调负荷集群控制策略。基于MATLAB/Simulink的仿真结果表明,所提的空调负荷集群控制策略能够平抑微电网功率波动,同时能够有效降低空调的启停次数,减小对空调使用寿命的影响。     

考虑变频空调负荷聚合调节的电网规划问题研究

在对变频空调负荷特性的研究基础上,建立变频空调负荷模型;在满足用户舒适度要求并约定用户补偿方案的情况下,确定以较低频率持续运行并固定操作时长的变频空调控制方法,并以此为基础设计一种直接易行的聚合控制算法,同时根据空调调控顺序的不同,分别达到充分利用负荷削减潜力或经济性最优两种目标;建立计入需求响应激励费用的电网规划模型进行优化求解,利用算例证明聚合控制方法和规划方案的有效性。     

电能质量问题与统一电能质量管理

电网中存在谐波、无功、电压闪变及负序电流等问题，严重影响电能质量，危害电力设备。传统解决电能质量问题的措施往往只能消除某个方面的危害。随着电子技术和控制技术的迅速发展，统一电能质量调节器和统一潮流控制器等综合电能质量管理装置的研究与应用日趋成熟，有望全面提高电网电能质量。     

上海地区家用电器待机能耗的研究和对策

对上海地区主要的家用电器(空调,家庭视频、音频系统,电脑)的待机能耗现状进行了调研,介绍了调研情况和分析结果。调研表明了家用电器的待机能耗后果是惊人的,提出了降低我国家用电器待机能耗的措施。     

柔性功率调节器动态运行特性实验

柔性功率调节器(FPC)是一种集成了飞轮储能技术和双馈电机技术两者优点的新型FACTS装置,具有电能存储、有功功率和无功功率解耦调控等多种功能。本文介绍了所研制的380V/4kW FPC样机的构成,对该样机进行了全面的运行特性实验研究,对实验数据进行了分析,结果表明,FPC样机可以直接变频启动,在亚同步状态和超同步状态下均可以进行有功功率和无功功率的双向独立调控,具有良好的动态运行特性,从而验证了FPC技术的可行性。     

Power quality site surveys: facts, fiction, and fallacies

Site surveys are generally initiated to evaluate the quality of the power available at a specific location with the aim of avoiding equipment disturbances in a planned installation or of explaining (and correcting) disturbances in an existing installation. Monitoring disturbances of the power supply has been an objective of various site surveys, but results often appear to be instrument-dependent or site-dependent, making comparisons difficult. After a review of the origins and types of disturbances, the authors describe the types of monitoring instruments. A summary of nine published surveys reported in the last 20 years is presented, and a close examination of underlying assumptions is carried out allowing meaningful comparisons which can reconcile some of the differences. Finally, the authors appeal for improved definitions and applications in the use of monitoring instruments     

Dual-Mode Time-Sharing Sinewave-Modulation Soft Switching Boost Full-Bridge One-Stage Power Conditioner Without Electrolytic Capacitor DC Link

This paper is aimed at presenting a novel system topology and control scheme of a selective dual-mode pulse-modulated high-efficiency single-phase sinewave power-conversion circuit for the new energy generation and storage applications. This power-conversion system is composed of a time-sharing-operated sinewave-absolute-modulation boost chopper with a bypass diode in the first power conditioning and processing stage and time-sharing sinewave partially pulse-modulated full-bridge inverter in the second stage. The proposed power conditioner is operated by a selective time-sharing dual-mode pulse pattern signal processing control scheme without electrolytic capacitor dc link. The unique operating principle of the two-power conditioning and processing stages with sectional time-sharing dual-mode partial sinewave-modulation scheme is described and discussed with a design example. In addition, this paper proposes also a sinewave tracking voltage controlled soft switching pulsewidth-modulation boost chopper with a bypass-diode loop, which includes a passive auxiliary edge-resonant snubber. The new conceptual operating principle and the control implementation of this novel power conditioner are presented and evaluated through experimental and simulation results     

Process Control Protection Against Power Line Interruptions

Power dips, interruptions, and disturbances occur frequently throughout a plant power distribution system that adversely affect plant lighting, computers, process controls, and drive systems. Critical processes that must operate continuously require an uninterruptible power supply to protect against both long-and short-term interruptions. However, most industrial processes are not critical and need only be protected against power transients and short duration outages. Process equipment with properly supplied ride-through capability can prevent waste and downtime. It is the intent of this paper to discuss short duration power line disturbances; the type of , control and stored energy system available to protect against these disturbances; and the advantages and disadvantages of the various approaches available to ride through power line disturbances.     

Synchronous control of indirect matrix converter for three-phase power conditioner

This paper describes an average model of indirect matrix converter (IMC) with an output LC filter in stationary and rotating reference frames. The developed model is non-linear and should be linearized in order to design linear controllers. Transient performance of the IMC is compared with that of conventional inverter in classic AC/DC/AC system. In order to make the IMC applicable for power conditioner applications a synchronous controller is designed. A power conditioner acts in one or more ways to deliver a voltage of the proper level and characteristics to enable load equipment to function properly. In order to afford the power conditioner requirements the controller has two segments. One segment controls the IMC with balanced input supply voltage and the other controls the system with unbalanced input supply voltage. The system can provide balanced output voltages with slight distortion of line side currents. Theory analyses, the model validation and simulation results are presented to verify the effectiveness of this control method.     

Power system disturbance patterns

Power system disturbances (e.g. surges) may or may not affect the performance of sensitive electronic and electrical equipment. When the performance of a utility's customer's sensitive equipment is significantly affected by alleged power supply disturbances, then the utilities may become involved in a complex process of detecting the possible patterns of the occurrences of these disturbances which may identify the origins of the power supply anomalies affecting the customer's electronic equipment. The activities, involving the utility and its customers, directed at mitigating the impact of power system disturbances on sensitive electronic equipment are discussed. The importance is stressed of having an adequate knowledge of the utility and its customer's electrical power system configurations and their operational activities prior to initiating a monitoring scheme to detect power supply anomalies. The disturbance patterns in a power supply system monitored continuously at a single site over a two-year period are presented, and the problems that might evolve from short-term site monitoring are discussed     

广西电网GIS设备运行缺陷分析

针对近年来广西电网公司GIS变电站设备缺陷日益增多的现象,为了维护电网的稳定、安全运行,急需找出原因。通过对网内110 kV及以上的GIS设备所出现的缺陷进行统计及分析,找出造成缺陷的主要原因,提出具有针对性的防范措施,对今后GIS设备的采购、运行管理及日常维护具有较好的借鉴作用。     

Voltage sags in industrial systems

The cause of voltage sags in industrial plants, their impacts on equipment operation, and possible solutions are described. The definition proposed focuses on system faults as the major cause of voltage sags. The sensitivity of different types of industrial equipment, including adjustable speed drive controls, programmable logic controllers, and motor contactors is analyzed. Available methods of power conditioning for this sensitive equipment are also described     

Microcomputer Control of a Residential Photovoltaic Power Conditioning System

Microcomputer-based control of a residential photovoltaic power conditioning system is described. The microcomputer is responsible for array current feedback control, maximum power tracking control, array safe zone steering control, phase-locked reference wave synthesis, sequencing control, and some diagnostics. The control functions are implemented using Intel 8751 single-chip microcomputer-based hardware and software. The controller has been tested in the laboratory with the prototype power conditioner and shows excellent performance.     

Expert system for analysis of electric power system harmonics

The proliferation of power electronics devices that cause harmonic voltages and currents and the widespread use of harmonics-sensitive electronic equipment are creating a near-epidemic of “power quality” issues that are being addressed by both users and suppliers of electric energy. Numerous types, styles, and capabilities exist in the field of instrumentation and diagnostic equipment for the detection, recording, and analysis of the distorted waveform. This article reports on one effort to employ artificial intelligence (Al) in the form of a Harmonics Analysis Expert System (HAES). The resulting PC-based software program has captured the knowledge of expert power system engineers in a “rule base” which can be applied to information about the topology, power signature, operating practices, symptoms, equipment, type and ratings, and chronology of system development to diagnose the power system for harmonics-caused problems. The goal is to accomplish the analysis with a less experienced engineer, thereby multiplying the available nationwide pool of expertise. Additionally, repeated use of the system does result in impartation of knowledge from the system to the user. The process of applying this AI approach involves: (1) training the user, (2) measurements (optional), (3) diagnosis, and (4) solution of the power system for harmonics disturbances to acceptable power quality. The emphasis of this paper is on the diagnostic module (Al program) with a usage example presented     

适用于双馈风电系统的九开关型统一电能质量调节器

为减小电压谐波、电压跌落与骤升、电压不平衡等电能质量问题对双馈感应发电机(DFIG)风电系统的影响,在对多种统一电能质量调节器(UPQC)拓扑结构研究对比和九开关变换器建模分析的基础上,提出一种应用于双馈风电系统的九开关型UPQC方案。在对UPQC电压、电流补偿单元运算电路建模的基础上,设计相应的控制策略。按照电网工况,设定谐波电流补偿、轻度电压补偿、重度电压补偿3种工作模式,优化UPQC运行方案。仿真与实验结果表明,九开关型UPQC可以有效治理电压、电流谐波,消除电压偏差与相位跳变,提高DFIG机端电能质量,使机组可以在多种故障电压工况下实现柔性故障穿越。     

Power quality and factory automation

A case study involving monitoring power quality disturbances at a representative plant and identifying the disturbances that disrupt production is described. The sensitivities of representative electronic control equipment to the identified disturbances were measured and then projected to form a plant disturbance threshold. For the monitoring effort, six disturbance analyzers were installed at four voltage levels extending from the utility 40 kV station to 120 V control power in an individual machine tool. Voltage sags were the only disturbance to directly cause lost production and were the most common disturbance at 68% of the total number of events recorded. Two programmable logic controller (PLC) transfer lines and a computerized numerically controlled (CNC) lathe were tested with a sag generator to determine the sensitivities of the equipment. The most sensitive components required the voltage during a sag to drop to less than 80-86% of rated to malfunction, whereas the least sensitive required the voltage to drop below 30% of rated. From the test results, the calculated sag threshold at the utility feed to the plant to disrupt production was 87% of the nominal voltage for more than 8.3 ms