Analysis of atmospheric electric field variation signals using digital natural observation method

As the atmospheric electric field always fluctuates, its observed waveforms are very complicated. It is important to detect the characteristic variation from the observed signals and determine its cause. The natural observation method is adequate for analyzing such nonperiodic signals as the atmospheric electric field signals. In this method the aspectum is proposed as the quantity to estimate the instantaneous power. In this study signal processing by the aspectum was applied to signals of atmospheric electric field variation. It was clarified that a strong correlation exists between the instantaneous fluctuations of atmospheric electric field and the wind speed in the convenient meteorological environment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(1): 27–34, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20302     

An egg‐shaped diagram and its discrepancies in switched reluctance machines

Recently, switched reluctance motors have attracted attention from industries. It is a common practice to develop several test machines for performance evaluation. One way to make a comparison among several test machines is to draw an efficiency map in a speed and torque plane, but this is rather complicated. For an easy comparison, a machine parameter measurement with an egg‐shaped diagram has been proposed by the authors. In this method, it is possible to measure an inductance ratio, which indicates the saliency of switched reluctance machines. In this paper, a calculation of tolerance between theoretical egg‐shaped curves and measured powers is proposed. It is found that the tolerances are within 4% as a result of several test machines. Although discrepancies in instantaneous current waveforms and voltage phase angles are seen, the obtained machine parameters indicate an exact relation between input power and required apparent power. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 61–71, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10286     

A new approach to an individual‐phase reactive power compensator for nonsinusoidal and unbalanced three‐phase systems

Many researchers have attempted to clarify the definitions of active power, reactive power, active current, reactive current, etc. for unbalanced and nonsinusoidal three‐phase situations. The so‐called pq theory has given a new definition of instantaneous reactive power, and it has been discussed and developed by many authors. In this paper, the merits and demerits of the instantaneous reactive power compensator are discussed. It is shown theoretically that applying instantaneous reactive power compensation to unbalanced three‐phase systems has a serious disadvantage in that it causes third‐order harmonic currents on the source side, which problem cannot be avoided. To overcome this problem the authors propose a new approach, and name it the “quasi‐instantaneous” reactive power compensator. It compensates individual‐phase reactive currents. The basic principles of the quasi‐instantaneous reactive current compensator are discussed in detail, and its validity is confirmed using digital simulation. In particular the authors show that the power factor of each phase becomes unity on the source side, but the source currents remain unbalanced when the proposed method is applied. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 73–81, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1162     

Time–frequency higher‐order spectra with adjustment to the instantaneous frequency variation

Novel time–frequency techniques are proposed: the short time instantaneous higher‐order spectra (HOS) with adjustment to measured or known a priori time variation of the instantaneous frequency of transient signals. It is shown that the proposed transforms are more effective than the non‐instantaneous HOS (i.e. without adjustment to time variation of the instantaneous frequency) in recognizing a non‐stationary nonlinearity. Copyright © 2008 John Wiley & Sons, Ltd.     

An investigation of methods to improve input/output waveforms in matrix converters

The matrix converter is a three‐phase AC‐to‐AC direct converter without any energy storage requirement such as DC link capacitors. However, the matrix converter has some practical problems such as the necessity for bidirectional power devices, necessity for special commutation sequence, and complexity of the control method. Thus, there are no practical systems in which matrix converters are used. In this paper, the control strategy for matrix converters with basic configuration is investigated so as to realize practical matrix converters. First, the necessity of the phase detector for the input voltage and the output current sensor is pointed out from the viewpoint of realization of the basic operation. With these sensors required in the basic configuration, the instantaneous control of the output current is realized. It is also pointed out that three‐phase switching is effective in improving the input current waveforms. Some methods for implementation of three‐phase switching are proposed. The effectiveness of the proposed control methods is confirmed by some experimental results employing a test system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 55–64, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20031     

Performance and maximum load capacity of uninterruptible power system using double‐layer capacitor

Power service interruptions cause problems in various facilities. Even an instantaneous voltage drop may give rise to serious problems in computer systems or electronic equipment. The uninterruptible power system (UPS) has been used to compensate for the power service interruptions. Also, the instantaneous voltage drop compensator using the electrolytic capacitor has been developed for the instantaneous voltage drop. Recently, the double‐layer capacitor has been considered as a new energy storage element. This capacitor has many advantages such as no maintenance, long lifetime, and quick charge/discharge characteristics with large current and it has higher energy density than the electrolytic capacitor. Therefore, we developed the UPS using the double‐layer capacitor. In this paper, the performance of the UPS using the double‐layer capacitor is shown by simulated and experimental results. Furthermore, the discharge characteristics of the double‐layer capacitors are investigated on the basis of the equivalent circuit including the capacitors and a voltage booster. Finally, the maximum load capacity to compensate is clarified for the system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 73–81, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20190     

CVCF inverter based on nonlinear control of instantaneous active and reactive power and its operation characteristics

This paper describes a direct‐power‐controlled CVCF inverter and presents its experimentally examined operation characteristics. The most important feature of this strategy is the direct selection of the switching states of the CVCF inverter to restrict errors between the feedback and command values of active and reactive power. In addition, this paper presents a theoretical analysis of the relationship between the instantaneous power and the switching state, which is essential for deriving a switching‐state table for the controller. The feasibility of the proposed method was verified through several computer simulations and experimental tests using a 2.0‐kVA prototype setup. The output voltages were confirmed to be stable sinusoidal waveforms with a total harmonic distortion of 1.13% under nonlinear load conditions. Excellent voltage balance was achieved by the proposed strategy even under unbalanced load conditions. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 62–69, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21023     

用小波变换和瞬时功率定位电能质量扰动源

为经济合理地精确定位电能质量扰动,根据监测点的电压电流波形,基于小波多分辨率,提出了一种扰动源定位新方法。该法首先对电压电流波形进行小波变换确定扰动的起止时刻,然后基于瞬时功率计算扰动功率和扰动能量,最后通过分析确定扰动源在监测设备的位置。针对电压暂降和电容器投切造成的扰动,运用此法分别依据ATP仿真数据和实际监测数据进行了分析,准确判断了扰动源在监测点的位置。结果表明,只要电网中的监测设备足够多,依据对扰动源定位的方法可实现扰动源的精确定位。     

A study of the loss characteristics of the amorphous magnetic material under nonsinusoidal wave magnetic flux

This paper presents a study on iron loss characteristics of an amorphous magnetic material under nonsinusoidal wave magnetic flux. The iron loss characteristics of the amorphous magnetic material have been compared to those of grain‐oriented magnetic steel sheets. Measurements of the iron loss have been carried out by means of an SST. It was found that the ratio of the iron loss increase of the amorphous magnetic material under the excitation by distorted waveforms and symmetric PWM waveforms is lower than that of grain‐oriented magnetic steel sheets. On the other hand, the ratio of the iron loss increase of the amorphous magnetic material under the excitation by asymmetric PWM waveforms is higher than that of grain‐oriented magnetic steel sheets. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 11–18, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20004     

A pulsed power supply with sag compensation using controlled gradational voltage

A pulsed power supply with sag compensation using controlled gradational voltage to increase the flatness of output waveforms has been developed. The sag compensation circuit consists of compensation units connected in series. Each compensation unit consists of capacitances, diodes, and semiconductor switches. The capacitances of each unit are charged with different voltages by 2ⁿ(V₀,2V₀,4V₀,…). The compensation voltage, which has 2ⁿ?1 steps, is generated by switching the semiconductor switches of each unit in a binary sequence. Using this method, compensation voltage waveforms up to 6.2 kV with 31 steps can be obtained with five compensation units. The sag compensation circuit has been adapted to a direct switch‐type pulsed power supply, which generates 7 kV pulsed voltage with a pulse width of 700µs, thus realizing sag compensation. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 54–63, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20017     

基于独立分量分析的电力系统瞬时电压畸变信号判别方法

提出一种基于独立分量分析(independent component analysis,ICA)的瞬时电能质量扰动信号检测与判别方法。利用ICA可将相互独立的源信号从其线性混合信号中分离出来的特点,以负熵作为衡量信号独立性的目标函数,通过优化此函数,得到一种固定点算法：FastICA算法,用此算法对包含瞬时电能质量扰动信号的电网电压信号进行计算,可分离出与扰动相对应的信号。对于不同类型的扰动,分离出的信号具有不同的波形特征,根据这一特点,可对扰动进行判别并确定其位置和持续时间。仿真试验结果表明,该方法对瞬时电压跌落、瞬时电压上升、瞬时脉冲、瞬时电压中断、谐波等多种瞬时电压畸变信号有较好的检测与判别效果。     

逆变器并联系统中谐波环流的抑制

逆变器中，死区等因素可造成输出电压波形的畸变，而瞬时值反馈调节对这种畸变有很好的校正作用。但在实验中发现，对于大功率逆变器，由于其滤波电感及并机电抗都很小，使得死区等因素可引起很大的谐波环流。瞬时值反馈控制虽然可获得良好的输出波形，但对于这种谐波环流的抑制能力却是非常有限的。本文为研究谐波环流的产生机理及瞬时值反馈控制对谐波环流的抑制作用，建立了基于谐波扰动的逆变器模型。研究表明，波形控制效果较好的瞬时值反馈控制技术，对谐波环流也有较好的抑制作用，而并机电抗将大大影响瞬时值反馈的谐波环流抑制能力。仿真与实验验证了上述结论。     

用电子电源干预工频电源来提高电力用户用电电压和电流的质量

本文以电流、电压的瞬时值为研究对象,利用电子器件实现对电流、电压的运算处理,通过调整其瞬时值大小来控制有效值的大小和波形形状,已达到改造电力用户用电电压和用电电流质量的目的。文章先介绍了负反馈补偿法,并以此法为基础,通过对交流电压和交流电流的调整控制,详细介绍了检定补偿法的原理、特点及应用。     

基于阶梯波与瞬时值反馈混合控制的光伏并网级联逆变器

针对传统光伏并网系统结构存在的问题,提出了一种新的阶梯波与电流瞬时值反馈混合控制的光伏并网级联逆变器方案。该方案一部分级联单元采取梯形波控制,一部分级联单元采取带电流瞬时值反馈的倍频正弦脉冲宽度调制,2个部分串联叠加形成输出电压。逆变器输出电压的谐波分析表明:调节正弦脉冲宽度调制波的移相角可以调节输出电压幅值和功率因数;逆变器输出电压低频谐波主要由阶梯波引起,为输出滤波器的设计提供了理论依据。对阶梯波调制逆变器的触发角提出了一种简易算法,该算法适用于电压级差不等模式且可实现触发角在线计算。实验结果表明,该方案结构简单,可靠性高,能有效降低开关损耗。     

一种改进小波阈值的电力线通信信号消噪方法

电力线通信信号包含大量噪声干扰,这些噪声严重干扰电力线通信,为此,提出一种改进阈值法和平移不变小波相结合的消噪方法.该方法对含噪的电力线通信信号进行小波分解,对分解后不同尺度下的小波信号进行平移不变并同时按改进阈值法进行处理,最后重构信号.以实测信号为例,提取去噪前后信号波形和误码率2个特征量,与传统消噪方法相比较,结...     

Direct power control of PWM converter without power-source voltagesensors

This paper proposes a novel control strategy of a pulsewidth modulation (PWM) converter with no power-source voltage sensors. The strategy has two main features to improve a total power factor and efficiency, taking harmonic components into account without detecting the voltage waveforms. One feature is a direct instantaneous power control technique for the converter, which has been developed to control the instantaneous active and reactive power directly by selecting the optimum switching state of the converter. The other feature is an estimation technique of the power-source voltages, which can be performed by calculating the active and reactive power for each switching state of the converter from the line currents. A digital-signal-processor-based experimental system was developed, and experimental tests were conducted to examine the controllability. As a result, it was confirmed that the total power factor and efficiency were more than 97% and 93% over the load power range from 200 to 1400 W, respectively. These results have proven the excellent performance of the proposed system     

改善电压型PWM整流器DPC系统性能的策略

通过电压型PWM整流器的数学模型,分析了PWM整流器直接功率控制(DPC)的原理,讨论了功率滞环比较器环宽对PWM整流器的影响.为降低开关频率和减少开关损失,需增加功率滞环比较器环宽,否则引起瞬时有功功率和直流电压波动,影响系统的性能;对此,提出了一种设置扇形边界死区的控制策略,即消除在扇形边界误选开关量,使瞬时有功功率和直流电压波形趋于平稳,从而改善了系统的性能.通过Simulink环境下的仿真模型仿真,证明了该策略的可行性.     

Analysis of even harmonics generation in an isolated electric power system

Harmonics bred from loads are mainly odd order because the current waveforms have half‐wave symmetry. Since the even harmonics are negligibly small, they generally are not measured in electric power systems. However, even harmonics were measured at a 500/275/154 kV substation in Hokuriku Electric Power Company after a transmission line fault was corrected. The even harmonics caused malfunctions of protective digital relays because the relays used 4th harmonics at the input filter as the automatic supervisory signal. This paper describes mechanisms of generation of the even harmonics by comparing the measured waveforms with the ATP‐EMTP simulation results. Analysis of these results has clearly shown that there are three different mechanisms of generation of even harmonics. The first mechanism is the appearance of a magnetizing current in transformers due to flux deviation by the DC component of the fault current. The second mechanism is harmonic conversion of a synchronous machine which generates even harmonics when the DC component or the even harmonic current flow into the machine. The third mechanism is an increase of harmonic impedance due to an isolated power system, thus producing the harmonic voltages. The design of the input filter of protective digital relays should take into account even harmonics generation in an isolated power system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 56–63, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20592     

Power differential method for discrimination between fault andmagnetizing inrush current in transformers

To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for the blocking differential relay in power transformers. However, the second harmonic component in fault current is increased by the introduction of underground 500 kV lines. This paper describes a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal. The average power is almost zero for energizing, but an internal fault consumes large power. To check the performance of this method, actual inrush current and voltage waveforms of a 500/154 kV transformer are accurately measured by digital equipment. The usefulness is confirmed by applying the method to the measured inrush and simulated fault data     

Breakdown characteristics of gas‐insulated switchgear for nonstandard lightning impulse waveforms under nonuniform electric field

To improve the insulation specification of gas‐insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF₆ gas during actual surges (called nonstandard lightning impulse waveforms) occurring at field substations. The authors observed the insulation characteristics of SF₆ gas gap under various types of nonstandard lightning impulse waveforms and compared them quantitatively with those obtained with standard lightning impulse waveforms. The experimental results were used to derive an evaluation method for real surges, which was applied to typical surges for various UHV and 500‐kV systems. In the preceding study, therefore, only the case of a quasi‐uniform electric field (with a typical range of field utilization factors in the bus of a GIS) was investigated. In the present investigation, the insulation characteristics of an SF₆ gas gap for a nonuniform electric field were observed experimentally and an evaluation method for converting nonstandard lightning impulse waveforms equivalently to the standard lightning impulse waveform was investigated. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 11–18, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21144