Analysis of discontinuous current in a 12-pulse thyristor DC motordrive

The discontinuous current magnitude in a 12-pulse DC drive is determined in terms of the significant parameters including motor internal inductance, the interphase inductance, and the firing delay angle to the drive power converters. It is shown that there are two significant ranges of firing angle advance in discontinuous current. In range 1, from 0 to 15° advance, the current is discontinuous in both converters and the DC motor. In range 2, from 15 to 30° of firing angle advance, the current is discontinuous in both converters but continuous to the DC motor. Further firing angle advance causes continuous current in both converters and the motor. Both firing angle ranges of discontinuous current are analyzed to determine the magnitude of average output current as a function of the significant parameters     

Centrifugal pump operation monitoring with motor phase current measurement

Centrifugal pumps often operate inefficiently because of their incorrect dimensioning and inefficient control. The economic potential of improving the pumping efficiency has generated a wide market for energy auditing products and services, which determine the prevailing energy efficiency of pump operation. Energy audits are commonly based on additional measurements that might be carried out for a short period of time, covering only a fraction of the pump operation cycle. Often the most feasible solution would be to use the existing measurements in the pumping system to determine its typical operation. Then, the correctness of pump dimensioning and the efficiency of the applied flow control method could be determined simultaneously for a large group of pumps, as there would be no requirements for additional measurement sensors on each device.In this paper, a current measurement-based approach to monitor centrifugal pump operation and its energy efficiency is studied. This approach allows a simple realization of energy audits for fixed-speed pumping systems, where only current consumption of the electric motor is measured. Approach is based on adjustable models for motor and pump operation, which in this case are configured for a laboratory pumping system. Factors affecting the estimation accuracy of the motor operation are also analyzed in the paper. According to the conducted tests with the laboratory setup, the motor shaft power can be estimated with the accuracy of 3.2%, and the pump flow rate with the accuracy of 16%. This accuracy class can be considered sufficient for energy auditing and monitoring purposes, since it allows detection of inefficiently operating pumps. After this, more accurate measurements with separate measurement instrumentation and more detailed pumping system energy efficiency analysis can be carried out.     

Design and performance of a high-frequency link induction motordrive operating at unity power factor

The design and performance of a complete three-phase converter system and field-oriented induction motor drive based upon a 20 kHz AC link is described. By using the same converter for the AC input side and the output load side, it is shown that power can be transferred in either direction. It is also shown that, with the use of a current regulator, both power flow on the link and the link voltage amplitude can be regulated. In addition, by suitable feedback control, the power factor at the input to the converter can be adjusted to unity. Both computer and experimental results show unity power factor operation, low harmonic current in both the input and output of the system, and bidirectional power flow capability     

Compensator of a multiphase inductive crucible furnace

A method is proposed for calculating the compensator of a multisection inductive crucible furnace, to which power is supplied by means of a single-phase thyristor frequency converter. The results of computer simulation and physical modeling of a multiphase inductor with compensators are compared.     

A system with a multiphase asynchronous generator and several active converters

A stand-alone system with a 6-phase asynchronous generator and several active semiconductor converters is considered. The algorithms of the device operations are developed and a model for calculating the steady-state and transient operating modes is described. The results of the analysis of the system are presented.     

Electromagnetic model of a multiphase inductive crucible furnace

An electromagnetic model of a multiphase inductive furnace is considered in the early stages of smelting. The furnace is charged with a set of metallic pieces that are not electrically connected to one another. They may or may not have magnetic properties, depending on the temperature. Electromagnetic processes in furnaces with such a charge are investigated in the case of single-phase and multiphase power supply to the inductor.     

Analysis of multiphase induction machines with winding faults

The paper shows how the techniques of generalized harmonic analysis may be used to simulate the steady-state behavior of a multiphase cage induction motor with any form of open-circuit or short-circuit fault in the stator winding. The analytical model is verified using a four-pole machine with a 48-slot stator. Each coil of the stator winding of this machine is brought out to a patchboard that enables the stator to be configured for single-phase, two-phase, three-phase, four-phase, six-phase, or 12-phase excitation. Experimental results are compared with computer predictions for a six-phase machine with both open-circuit and short-circuit faults.     

能量变换器进相运行时的建模与仿真

为了研究能量变换器进相运行性能,依据其数学模型,采用SIMULINK/SPS软件建立了能量变换器的仿真模型.给出了单机无穷大系统中能量变换器由迟相转为进相运行时定子电压、电流、功角等主要物理量的变化规律,然后对能量变换器的进相深度进行了分析.最后利用实验对能量变换器样机进相运行时的参数进行了测定.实验证明了仿真分析结论的正确性,为能量变换器的设计和运行提供了参考.     

Increasing the efficiency of joint operation of a solar-power plant with an industrial alternating-current network

The use of photoelectric-converter modules (PCM) with integrated direct-current regulators in low- and medium-power-supply systems working jointly with an industrial network permits production to be increased of the power generated by photoelectric-converter modules due to operation of all modules in the maximum power-generation mode. With the decrease in the intensity of solar radiation of some of the chain of the series-connected photoelectric-converter modules, the simultaneous work of all modules of the chain in the maximum power selection mode can lead to the appearance of overvoltages on elements of direct-current regulators integrated into the modules. A means is proposed in this article to control the chain of seriesconnected photoelectric-converter modules with integrated direct-current regulators. The control algorithm of the direct-current regulators permitting one to equalize the voltage at the output of the series-connected regulators under very nonuniform illumination of the photoelectric-converter modules. Computer models are studied, and results of simulation in Matlab/Simulink software system are presented.     

黑龙江电网机组进相运行研究及实践

论述了发电机进相运行的诸多限制,提出了相应的技术措施。详细分析了黑龙江电网的发电机进相运行试验的情况,并进行了暂态稳定校验。实践证明,对改善黑龙江电网的电压质量起到了明显效果。     

发电机非全相运行分析及处理

在发电厂运行过程中,发电机组非全相运行将会严重危及到发电机与电网的安全,本文利用对称分量法分析了单元发电机组主变出口开关非全相运行情况下,主变高压侧与低压侧的相位关系,得出了单元发电机组主变出口开关非全相运行时,发电机定子各相电流的相互关系。并结合电厂实际情况,分析其现象、危害,最后提出相应的处理方法。     

多相集中整距绕组感应电机的建模与仿真

提出一种基于多回路理论的多相整距绕组异步感应电机建模方法,并且从绕组的空间排布出发推导出各互感参数的计算方法.与传统的基于d-q-n轴变换的数学模型相比,这一模型能够考虑转子的槽数,同时具有简洁的参数计算方法,不仅避免了传统建模方法中的折算处理,而且能够充分反映各次谐波的影响;因此具有良好的通用性与准确性,适合对多相电机在非正弦供电方式下的仿真分析研究.通过与样机试验数据的对比,验证了建模方法的正确性.     

一次110 kV线路单相断线故障的继电保护动作分析

针对我局110 kV某线路单相断线故障,通过理论公式的推导,证明了网络结构确定的110 kV线路发生单相断线故障时,其零序电流保护动作情况只取决于当时的负荷电流大小,与断线位置无关.另外,通过实际理论计算,验证了此次故障中保护及自动装置的动作行为都是正确的.     

Sensorless rotor position estimation at standstill of cylindrical brushless dc motors using opened phase voltage change caused by eddy currents

A rotor position estimation of a cylindrical brushless dc motor at standstill has been difficult to obtain. Therefore, torque control of a motor has been difficult at starting of the motor, and realization of the position estimation at standstill has been sought. This paper proposes a simple processing of a rotor for which nonmagnetic materials are pasted on the rotor surface. This processing generates an eddy current on nonmagnetic materials and causes an opened phase voltage change according to rotor position. The experimental results using a microcomputer show that it is possible to estimate rotor position of the cylindrical motor despite a standstill by using the opened phase voltage change. ©�1998 Scripta Technica, Electr Eng Jpn, 126(1): 52–60, 1999     

多相复合富锂锰基材料的合成及性能

采用共沉淀-高温固相法合成具有六方层状-单斜层状-立方尖晶石复合结构的Li1.2 Mn0.54 Ni0.13 Co0.13 O2富锂锰基三元正极材料,通过XRD、SEM、X射线能量色散谱(EDS)和恒流充放电等方法,对富锂锰基三元正极材料进行晶体结构、微观形貌、组分和电化学性能分析.在920℃下烧结(氧气条件)获得的富...     

Cooperative operation of a wind energy conversion system with a hydrogen electrolyzer by using an adjustable speed flywheel generator

Hydrogen is considered as the energy source of the next generation. This paper proposes a system which consists of Flywheel Generator (FWG), Wind Energy Conversion System (WECS), and Hydrogen Electrolyzer (HE), for the purpose of hydrogen generation and grid output power smoothing. The cooperative control among flywheel generator, hydrogen electrolyzer, and wind generator is performed by controlling the flywheel generator. Simulations have been done by PSCAD/EMTDC. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(3): 19–27, 2009; Published online in Wiley InterScience ( www.interscience.wiley. com ). DOI 10.1002/eej.20863     

Optimizing the operation of a stand-alone photovoltaic power system with distinctive insolation profiles using an on-line computer

To optimize the operation of an array of solar cells, Z. Zinger and A. Braunstein (IEEE Trans. PAS-100 (1981) 1189 – 1192) approximated the insolation profile by three discrete levels only throughout the day. In our previous two papers, the problem was solved using a clear, but real, insolation profile. This paper presents an accurate and computer-aided algorithm to achieve this optimization continuously for any insolation profile. The computer is programmed so that it can deal with any dynamic changes in the insolation and load demand. Its commands to switch on or off the parallel strings of the array are decided so that the technical constraints imposed will be satisfied. In addition, the daily delivered, stored and total output energies are deduced for two different arrangements of the system. They differ mainly with regard to the battery location with respect to the other subsystems. The numerous results obtained are analysed fully and discussed.     

Rationalization of operation of an industrial network

The paper deals with the rationalization of the electric power supply of an industrial network. The relevant indices characterizing daily load diagrams are defined, and measurement data are statistically processed to select the representative days for the optimization of reactive power compensation. Mathematical models for the optimization of compensation and load shifting are provided and efficiently processed by applying the Hooke and Jeeves’ discrete search approach. Optimal allocation of capacitor banks at available network load points and their sizes have been determined to maximize the annual cost saving related to real and reactive energy consumption charges. The optimal solution recommended is analyzed for harmonics resonance conditions. The optimal phase shifts of daily load diagrams of feeders supplying various groups of loads are determined potentially minimizing the peak of the aggregated load and associated charges.     

基于图像识别的变电站核相验电操作机械臂研究

针对目前变电站人工核对相序中存在的人员安全性不足、检测质量可靠性不佳的缺陷,提出了一种基于图像识别的变电站核相验电操作机械臂.该系统由运动平台、机械臂系统和软件算法部分组成.运动平台是履带式地面自主循迹运动平台,依靠图像识别进行室内定位和运动控制.该系统包括一套能够操作核相仪进行核相验电操作的机构装置,以及一套软件系统...     

300MW发电机组进相运行的讨论分析

云南电网属于送端电网,由于负荷中心离大容量电源点距离较远,造成系统无功功率的过剩。中枢点母线电压长期偏高。进相试验通过静稳定试验,确定了发电机按稳定极限条件进相的运行范围;结合发电机端部及构件的温度测量,确定了按端部发热条件所限制的运行范围,进而确定了部分大机组进相运行的能力。