Fast short-circuit protection under current imbalance condition for multi-paralleled SiC-MOSFETs

This paper proposes methodology and gate drive circuit that can immediately detect short-circuit (SC) of multiparalleled SiC-MOSFETs even under current imbalance condition. Proposed method detects SC current using an integration circuit that can sense di/dt. The detection level of SC current can be adjusted to a desired value regardless of the number of SiC-MOSFETs connected in parallel. The effectiveness of the proposed approach was experimentally validated for four-paralleled SiC-MOSFETs under extreme current imbalance in SC condition. SC was detected within 0.5 μs and all SiC-MOSFETs were protected without destruction at most 2.2 μs after the onset of SC, for all types of SC 1, 2, and 3.     

定子撬棒和直流侧卸荷电路协调的故障穿越技术

目前,撬棒（crowbar）保护技术是双馈风电机组实现故障穿越的有效手段之一．但其最大的问题是．保护投入期间,舣馈风电机组（doubly fed induction generator,DFIG）处于失控状态,不利于系统稳定。因此,利Ⅲ定子撬棒方案代替传统撬棒保护已得到广泛关注。然而．仪仅采用定子撬棒的方法．并不能保证直流件线电压在限值之内,为此,提出定子撬棒和直流侧卸荷电路协调的故障穿越方案来解决该问题。首先分析定子书电阻对转子电流敞障影响的理沦基础,之后,确定和优化所串电阻的大小,分析说明该故障穿越方案的基本工作原理．并利用PSCAD／EMTDC专业仿真软件,验证所提方案的有效性和可行性。     

Implementation method of loss observer to power controller for overhead line and supercapacitor hybrid electric railway vehicle

In order to absorb the regenerative power and to reduce the peak input power of a train—in other words, to smooth the input power of the train—in this paper we repot a frequency‐domain‐based power controlling strategy for energy storage of hybrid electric railway vehicles. Applying a loss‐compensating method by using a disturbance observer improves the energy while keeping ability of this controller. However, that loss compensating method requires precise voltage–energy characteristics of the supercapacitor (SC) to estimate the correct loss. Hence, nonlinearity of the capacitance of the SC becomes a problem because it causes an error in the estimated loss. Therefore, this paper presents a method to measure the voltage–energy characteristics precisely of the SC that has a voltage dependence on the capacitance. A method to implement those characteristics into controllers is also proposed. The loss compensating method is applied to a controller by using the proposed method, and its effectiveness is verified by a small‐scale experimental system. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A simplified design-oriented analysis of switched-capacitor active filters

The method presented in this paper provides a simplified approach to obtain the z-domain equivalent circuit of an SC active filter by one-for-one substitution of each basic SC element with its z-domain equivalent admittance, if a specific terminal condition is met. Then, traditional circuit analysis techniques can be used to derive the z-domain transfer function of the filter. This method makes the analysis and the design of the SC active filter simple and similar to the S-domain method. Two application examples are given.     

利于集成且对杂散电容抑制性极佳的开关电容型滤波器

采用单位缓冲器设计对杂散电容不灵敏的开关电容(SC)频率相关负电阻(FDNR)元件,利用该元件对椭园函数式LC低通滤波器进行SC模拟。为了获得电容最佳值,提出了一种简单的最优化方法。并采用寄生电阻预畸变与SC负电阻相结合的办法,设计的SC滤波器对杂散电容不灵敏,且电路简单。本文采用分立元件制作了一个五阶椭园低通SC-FDNR滤波器,实验结果表明该方法实用可行,效果明显。     

SC网络的积木块等效及自动生成

本文讨论了将SC网络分解为积木块,进而进行模拟等效的过程,给出了SC积木块自动识别和建立的方法和实例。     

小功率电源SC-FDNR滤波器的设计

设计了一种小功率电源有源滤波器：利用一个单位缓冲器设计了对寄生电容不灵敏的开关电容 (SC) 频率相关负电阻(FDNR) 元件，利用该元件对椭园函数式LC低通滤波器进行SC模拟。为了获得电容最佳值，提出了一种简单的最优化方法；并采用寄生电阻预畸变与SC负电阻相结合的办法，设计的SC滤波器对寄生电容不灵敏，而且电路简单。本文用分立元件制作了一个五阶椭园低通SC-FDNR滤波器，实验结果表明该方法实用可行，效果明显。     

Recovery time to superconducting state after quench in superconducting fault‐current limiter

Since fault current tends to increase with electrical power demand, current‐limiting technology for overcurrents has been investigated. As a promising candidate, the superconducting fault‐current limiter (SC‐FCL) is expected to be introduced into power systems. One of the most important features of the SC‐FCL is recovery to a normal operating mode, that is, superconducting state rapidly after current interruption. In this paper, the recovery time of an SC‐FCL introduced into a distribution power system is discussed. To obtain the fundamental data, the recovery time of short Nb‐Ti superconducting cables was measured. We developed a method of calculation of the recovery time and it was confirmed that the calculated results agree with the measured ones. We studied the recovery characteristics of an SC‐FCL in a 6.6‐kV distribution system for the short‐circuit fault near the substation. We considered 3 and 17 cycles as the period from fault occurrence until current interruption. As a result, the superconducting cable length required to recover within the high‐speed reclosing time of 0.3 s are more that 270 and 480 m for 3 and 17 cycles, respectively. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 34–44, 2000     

推挽开关电容DC—DC升压变换器

采用推挽与开关电容网络相结合的拓扑结构,实现升压ＤＣ－ＤＣ变换器。研究了这种新型变换器的效率与拓扑结构间的关系,还采用等效电量关系法（ＥＥＱＲ）对变换器进行了稳态分析,并讨论了变换器的控制问题,实验与理论分析结果一致。     

Enhanced techniques on sequential unit commitment with interchangetransactions

This paper presents two enhanced techniques for improving the solution optimality and computation performance of the sequential unit commitment (SC) method with interchange transactions. The conventional SC method, although often presenting superior performance over other methods, can lead to nonnear-optimal solutions in some circumstances due to the use of a local decision scheme to identify the best unit to be committed at each stage. The proposed technique, instead, uses a global-like decision scheme. It defines a small set of locally advantageous units which are individually examined globally by generating tentative commitment schedules to identify the globally best unit to commit at each stage. Studies have shown that the global-like decision scheme can effectively improve the solution optimality. Meanwhile, while an interchange transaction is incorporated with the unit commitment study, the constant transaction price often causes solution oscillation during iterations. A varying-λ technique is proposed in this paper. This technique properly models the impact of the interchange transactions on the power system hourly energy prices and, hence, successfully overcomes the oscillation problem such that the loading level of a transaction can be optimally determined similarly as for a generating unit     

A day ahead price sensitive reactive power dispatch with minimum control

In this paper, a novel day ahead Price based Optimal Reactive Power Dispatch (PORPD) problem is proposed. The proposed approach aims to find the optimum real and reactive power output of thermal generators and searches for optimal operating schedule for Shunt Capacitors (SC) to minimize total reactive power supply cost. The proposed method is formulated to pay opportunity cost along with VAr supply cost of thermal generators. Moreover, the method recovers the investment cost and pays the operational cost of SC. The investment cost of SC is recovered from the depreciation cost and the operational cost is paid based on real time reactive energy cost. The SC output is made sensitive to reactive energy Marginal Price (MP) and the life span of the device is extended by obeying its operational limitations. The PORPD model is formulated as dynamic optimization problem and solved using Cuckoo Search (CS) algorithm. The program is developed on MATLAB and tested on IEEE 14 and IEEE 30 bus systems under different network complexities; like varying MP and non-linear loads. Moreover, to check the performance of CS algorithm, the results of basic PORPD problem is compared with other methods. Results confirm that the proposed method encourages the ancillary services to maintain a proactive role during higher market pricing hours and provides a guideline for the System Operator (SO) to ensure maximum operational gain for the market participants while maintaining system security.     

Analytical studies supplementing the Smith chart

The study of transmission lines is basic in undergraduate electrical engineering education. In relevant courses, a key subject is the Smith chart (SC), which is a graphical device providing insight. This paper develops certain formulas that can further enhance students' understanding, including an unconventional set of conductance/susceptance transformation equations, as well as simplified versions useful for highly mismatched lines, where it is sometimes difficult to use the SC. All formulas are developed from well-known facts of transmission-line theory. SC interpretations of many of the analytical results are provided. The analytical investigations thus supplement the SC. For highly mismatched lines, the formulas bring out certain resemblances to the resonant series RLC circuit, thus providing an interesting connection to the familiar subject of ordinary circuit theory. Lastly, students can also benefit from the mathematical tools used herein; these include simple ideas of asymptotic analysis.     

Soliton induced supercontinuum generation in photonic crystal fiber

Soliton induced supercontinuum (SC) generation using an index-guiding triangular photonic crystal fiber (PCF) is experimentally studied by pumping with 140-fs pulses at several wavelengths in the positive slope anomalous dispersion region. The focused beam incident upon the PCF core is first confirmed by in situ observation based on the reflection method to make sure accurate input coupling conditions. The influence of pumping wavelength on the spectral profile of SC is examined as a function of input peak power P/sub 0/. Processes initiating SC generation are governed by the fission of higher-order solitons, which lead to the soliton self-frequency shift (SSFS) by intrapulse Raman scattering associated with blue-shifted Cherenkov type phase matched radiation. The fission of higher-order solitons is clearly observed in the input P/sub 0/ dependent spectrum and a plot of the square root of frequency shift versus input P/sub 0/. Further increase of input P/sub 0/ leads to a new SSFS accompanied by an additional blue-shifted peak located at shorter wavelength than that of the previous one. These processes continue to develop successive blue-shifted and SSFS peaks as increasing the input P/sub 0/, which determine the spectral width of SC. Spectral profile of SC is also dominated by these initial and growth processes. SC spectra obtained in the vicinity of zero dispersion wavelength shows smooth but relatively narrow, while SC generation at deep anomalous dispersion site exhibits broad bandwidth at relatively low P/sub 0/. The input P/sub 0/ required for approaching a saturated SC which is almost the same feature within the tuning pump wavelengths is decreased as increasing the degree of anomalous dispersion.     

顺序控制在变电站倒闸操作中的应用

根据中山供电局辖内变电站的自动化情况,参考工业控制实现顺序控制的方法,提出在综合自动化变电站倒闸操作中应用顺序控制的思路,介绍了利用PLC实现顺序控制的原理,给出了在综合自动化变电站内增加PLC控制器以实现倒闸操作顺序控制的方案。     

Enhancement of continuous operation performance of HVDC withself-commutated converter

This paper describes a converter control scheme to enhance continuous operation performance of HVDC system with voltage source type self commutated (SC) converter. The continuous operation of SC converter can be achieved by suppressing converter overcurrents and AC overvoltages in the case of AC line faults including phase failure. Development of a new control scheme has been accomplished by experiment using an AC/DC power system simulator in CRIEPI and the EMTP (Electro Magnetic Transients Program) analysis. At first, we show that converter overcurrents and AC overvoltages are caused by lack of control information to static limiter and insufficient control performance to negative-sequence current of SC converter. Next, an adequate converter control scheme is proposed which is composed of an ACR's (automatic current legulator) adjustable dynamic limiter to suppress the converter overcurrents, and the limit logic of SC converter to suppress AC overvoltages during phase failure     

设备故障对同一变电站多套串补过电压保护装置参数的影响

在进行串补过电压保护设备参数设计时,一般只考虑不同的系统运行工况、不同的故障类型及故障时刻等系统因素,而很少考虑串补设备故障的影响,但在实际运行中串补设备故障的工况是存在的,而且对串补设备参数有直接影响。本文以南方电网百色串补站3套串补装置为例,利用最新电网数据及3套串补的设备参数和过电压保护配置,建立串补设备检修、保护误动及拒动等特殊工况模型,研究了在串补间隙误触发、拒触发、串补检修退出3种设备故障工况下,同一变电站多套串补之间参数的相互影响,并进行仿真分析。研究表明在进行串补主设备参数设计时,应适当考虑一套串补设备故障对其他串补过电压保护装置参数的影响。     

高压直流输电换相失败对带静偏心故障调相机的影响

为了研究高压直流输电逆变器换相失败对带静偏心故障调相机的影响,首先以一台TTS-300-2型双水内冷调相机为研究对象,基于Simulink+Maxwell/Simplorer构建了含同步调相机的高压直流输电的场-路-网耦合模型,联合仿真得到不同静偏心率下调相机的气隙磁场.其次,分析了换相失败对不同静偏心率下调相机气隙磁通密度的影响,并采用麦克斯韦应力张量法计算发生换相失败前后转子受到的不平衡磁拉力.最后,采用非线性Newmark隐式积分法计算换相失败对不同静偏心率下调相机转子振动的影响.结果表明,换相失败使带静偏心故障调相机气隙磁场增大,转子所受磁拉力与振动幅值明显增大,并且其影响程度随调相机静偏心率的增大而增大.换相失败对带静偏心故障调相机的影响分析对解释机组异常振动、诊断静偏心故障有一定的参考价值.     

Design criterion for high‐speed low‐power SC circuits

The settling behavior of switched‐capacitor (SC) circuits is investigated in this paper. The analysis is performed for typical SC circuits employing two‐stage Miller‐compensated operational amplifiers (op‐amps). It aims to evaluate the real effectiveness of the conventional design approach for the optimization of op‐amp settling performances. It is demonstrated that the classical strategy is quite inaccurate in typical situations in which the load capacitance to be driven by the SC circuit is small. The presented study allows a new settling optimization strategy based on an advanced circuit model to be defined. As shown by design examples in a commercial 0.35‐ µm CMOS technology, the proposed approach guarantees a significant settling time reduction with respect to the existing settling optimization strategy, especially in the presence of small capacitive loads to be driven by the SC circuit. Copyright © 2010 John Wiley & Sons, Ltd.     

The Potential for High Temperature Superconducting AC and DC Motors

ABSTRACT

The prospect of using superconductivity (SC) to power electrical machines has been a tantalizing but elusive goal ever since its discovery by Onnes in 1911. However, recent developments which have raised the critical temperature above liquid nitrogen (77K) has removed the major obstacle to practical application of SC to rotating machinery, namely the liquid helium refrigerant system. This paper addresses the potential for utilizing high temperature superconductivity (HTSC) in rotating (as opposed to linear) electrical motors and discusses several approaches to their implementation. Although SC at liquid nitrogen temperature is assumed, the implications of SC at room temperature is not considered in this paper.     

Analysis of wave switched-capacitor filters

For a special class of switched-capacitor filters, the wave SC filters, a very efficient analysis method will be given. It is based on a block partitioning technique, i.e. the whole wave SC network is divided into small subnetworks. Only small matrices have to be processed which saves computation time, so that even large wave SC filters can be analysed very fast and with high accuracy. It will also be shown that the methods can be extended for the analysis of other SC networks. Some numerical examples of different wave SC structures will be given.