High‐order sensitivity invariants

The aim of the research reported in this paper is to extend the notion of invariant sensitivity sum, widely known for electrical networks, from first‐order sensitivities to high‐order sensitivities. The results are high‐order invariant sums of sensitivities of the first and the second kind, formulated for nonlinear lumped circuit, which consists of one‐port and two‐ports only. One‐ports are generalized resistances, capacitances, inductances, voltages, and current sources, whereas two‐ports are nonlinear generalizations of four types of controlled sources. It is observed that the invariant sums actually found for nonlinear lumped networks are generalizations of sums given earlier by authors for linear lumped networks. The article is illustrated by numerical sensitivity analysis of simple linear and nonlinear circuits. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of oil aging on the space charge dynamics of oil‐immersed paper insulation under a DC electric field

The formation of space charge in oil/paper insulation system can lead to material degradation in the region of high electric field. Therefore, it is important to understand the factors that affect space charge formation in oil/paper insulation system. In this paper, the effect of oil aging on space charge dynamics in oil/paper insulation system is investigated using the pulsed electroacoustic (PEA) technique under a DC electric field at room temperature. The ultraviolet/visible (UV/vis) spectrum of the oil shifts to longer wavelengths, and the oil acidity increases as the aging time increases. It has been found that the oil property has a significant effect on the space charge distribution in the oil/paper insulation sample. The more the deterioration of the oil, the larger amount of negative and positive charges accumulated in the bulk of the oil/paper insulation sample. The total amount of slow moving charges, the surface trap energy density, and the electric field distortion of the oil/paper insulation sample increased with the degree of deterioration due to oil aging. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

改进电声脉冲法的交流空间电荷测量新方法

提出一种交流电压下的电声脉冲法空间电荷测试新方法。采用电脉冲作为触发源,利用数字示波器的长存储功能同时获取空间电荷信号和高压交流电压信号,从而避免了传统交流空间电荷测试方法的硬件同步。通过调整脉冲发生器的频率可获取不同相位下的高压交流下的空间电荷响应,并通过平均若干个交流周期的空间电荷信号获得足够信噪比的相位相关的空间电荷信号。通过对低密度聚乙烯工频50 Hz下的空间电荷测量结果表明,在交流电场下,下电极附近区域会形成异号电荷;与传统的交流空间电荷测量系统相比,由于测量时间得到很大程度缩短空间电荷信息能够最大限度保存,并且新系统较老系统有更高的相位分辨率,空间电荷衰减图形更能逼真的反映电荷动态变化。     

Space change behavior in full scale ±250 kV dc XLPE cables

Space charge in full size ±250 kV dc cables was measured using a pulse-electroacoustic method. Two newly developed types of dc XLPE cables with 20 mm thick insulation were subjected to measurements at a dc voltage of 500 kV, keeping the conductor temperature either at room temperature or at 85°C. Qualitative analyses of the space charge distribution and the quantitative analysis of the electric fields in the vicinity of semicon interfaces were made. It was shown that the field in the vicinity of the inner semiconductor tends to increase by 10 to 40% when the polarity of the applied voltage was switched, in the case when the conductor was kept at 85°C. However, the distortion of the electric field was significantly smaller than that expected with conventional XLPE cables. As a result, dc cables are considered to have stable dc characteristics from the viewpoint of space charge behavior. © 1998 Scripta Technica, Electr Eng Jpn, 124(2): 16–28, 1998     

Electrical Breakdown and Space Charge Formation at High‐Temperature Region in Long‐Time Heating Treatment PVC

Polyvinyl chloride (PVC) is widely used as an insulating material in various electrical products. It is reported that an exothermic reaction reaching temperatures above 150 °C can be caused by overload currents or inferior electrical wire connections before the ignition of electrical products. The exothermic phenomenon may cause deterioration of insulating properties in PVC due to its chemical decomposition. It is necessary to clarify the degradation of insulating properties in PVC under thermal stress exceeding 150 °C for the safe use of electric products. In this investigation the space charge distribution and conduction current in the heat‐treated PVC sheet were measured in the range from room temperature to 200 °C in the presence of a dc electric field, using a high‐temperature PEA system. Positive charge injection and increasing conduction currents were observed before breakdown above 100 °C in 100 °C 300‐h heat‐treated samples and in non–heat‐treated samples. The results indicate the thermal breakdown process from the analysis of conduction currents and electric fields. In samples exposed to higher temperatures (150 °C 100 h), the breakdown strength deteriorated strongly in the range from room temperature to 90 °C. Increases in conduction current were observed in the entire temperature range before breakdown of the 150 °C 100‐h heat‐treated PVC. This indicates that heat treatment above 150 °C degrades the breakdown properties in the range from room temperature to 90 °C due to thermal decomposition accompanied by dehydrochlorination in PVC. The electric field is intensified near the cathode due to positive charge accumulation, and the breakdown strength begins to deteriorate only above 90 °C. This shows that thermal stress exceeding 150 °C causes deterioration of insulating properties and that the breakdown process is affected by space charge formation in PVC.     

Thermally stimulated current and thermally stimulated charge distribution in electron‐beam‐irradiated PMMA

The relationship between the external current J_ter(t), the conduction current J_c(x, t), and the displacement current ϵ∂E(x, T)/∂t of an electron‐beam‐irradiated PMMA is discussed in terms of measurements of the thermally stimulated current (TSC) and the thermally stimulated space charge distribution (TS‐SCD). ϵ∂E(x, T)/∂t is calculated from TS‐SCD measurements obtained with an improved pulsed electroacoustic (PEA) system. By virtue of the conservation of charge, J_c(x, t) is easily calculated from the measured J_ter(t) and the calculated ϵ∂E(x, T)/∂t. In this report, an approach to the conduction current analysis using the theory of conservation of charge is described and an analysis of the conduction current in an electron‐beam‐irradiated PMMA is introduced as a typical example. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 1–6, 1999     

High‐field electrical properties under AC voltage application in acetophenone‐coated LDPE film

This paper deals with the effects of acetophenone coating on dielectric properties such as tan δ and capacitance and on space charge formation up to electrical breakdown under AC voltage application in low‐density polyethylene (LDPE) film. The existence of acetophenone at the electrical interface enhances tan δ. tan δ in acetophenone‐coated specimens increased with electric field and decreased with the frequency in the high‐field and high‐temperature region. AC breakdown test revealed that the electric strength in noncoated specimens was higher than in acetophenone‐coated specimens, and that the electric strength also decreased with temperature. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 1–7, 2003; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.10086     

High‐efficiency and low‐acoustic‐noise drive system using an open‐winding AC motor and two space vector modulated inverters

The combining of the outputs of two inverters using interphase reactors is a widely used method for supplying large AC drives rated at more than several thousand kilowatts. Certain drawbacks are associated with this method, such as high acoustic noise and high losses due to the interphase reactors. To overcome this problem, in this paper a new low‐acoustic‐noise and high‐efficiency drive system using an open‐winding AC motor and two space vector modulated inverters is proposed. This configuration consists of a three‐level inverter with switching once per cycle and a two‐level inverter of about 1 kHz switching frequency, connected to the opposite terminals of the open‐winding motor. With the proposed configuration, good current waveforms and high efficiency can be obtained. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 46–57, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10157     

High‐sensitivity surface micromachinable accelerometer using a ferroelectric substrate and its characterization

The present study reports the fabrication and characterization of a high‐sensitivity surface micromachinable accelerometer using a ferroelectric material having a large dielectric constant, such as bulk PZT (ε_r = 2600). The measurement principle is the detection of capacitance change with respect to the dielectric mass movement in the fringe electrical field. Considering the practical fabrication, a ferroelectric material is used for the substrate instead of the suspended proof mass. Since capacitance is increased not mechanically but electrically, high sensitivity can be expected while maintaining mechanical stiffness, which has the advantage of preventing touch down of the proof mass and widening the allowable measuring range of acceleration. A fabricated sensor is characterized. A high sensitivity of several sub‐pF/g is confirmed, which is hundreds of times higher compared to that of a sensor fabricated using the Parylene polymer (ε_r = 3.15). This sensitivity is an order higher compared to those of other reported capacitive microaccelerometers, which have comparable proof mass sizes and comparable detectable acceleration ranges to the newly fabricated sensor. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An architecture of small‐scaled neuro‐hardware using probabilistically coded pulse neurons

In this paper, we present an architecture for neuro‐hardware that can be realized in circuits of far smaller scale than in the conventional approach. In order to reduce the scale of the circuits, the architecture employs a new method of computing the membrane potential and the sigmoidal function by encapsulating the probabilistic properties into the relative delay between two pulses. The proposed architecture makes it possible to integrate more than 100 neurons in the latest FPGA chip, which is a 13‐fold miniaturization compared to the conventional architecture. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 48–55, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1168     

Coaxial magnetic pulse compression system to generate fast‐rising pulsed power

A fast‐rising pulsed power generator (PPG) using a coaxial magnetic pulse compression (MPC) system has been developed. Two kinds of magnetic cores, a Co‐based amorphous metal and a nanocrystalline Fe‐based soft magnetic metal, have been used in the coaxial MPC system to evaluate losses of magnetic cores and leakage current of a saturable inductor. The PPG produced a pulsed‐high‐current of 3.7 kA with a risetime of 7 ns (20–80%) at a repetition frequency of 1000 pulses per second. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

High‐precision positioning of table drive system using strain feedback and disturbance observer

This paper presents a control design methodology for high‐precision positioning. In particular, the compensation for the effects of vibration modes and nonlinear friction on the positioning performance is taken into account in this methodology. In the controller design, the servo bandwidth of the feedback control loop should be expanded to compensate for nonlinear friction, while robust stability with respect to frequency variations in the vibration modes should be ensured. In this study, therefore, strain feedback for vibration modes is adopted to provide robustness with respect to frequency variations and to improve the disturbance suppression performance by expanding the bandwidth of a disturbance observer. This strain feedback is based on the use of a piezoelectric element. The efficiency of the proposed positioning control approach has been verified by conducting experiments using a prototype for industrial table drive systems. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 46–55, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21306     

High‐precision positioning with strain feedback using piezoelectric element

This paper presents a novel control methodology for robust high‐precision positioning systems. This methodology is based on strain feedback using a piezoelectric element. The mechanical vibration modes at around the control bandwidth cause deterioration of system stability. This prevents the positioning performance from being robust, particularly against variations in the vibration frequency. In this research, therefore, a robust positioning system was designed by applying an additional compensation loop by strain feedback; here, a piezoelectric element that acts as a strain sensor detects the vibration signal. This makes the performance of the system robust. The proposed compensation approach has been verified by numerical analyses and by experiments using a positioning device for industrial galvano scanners. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 41–50, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21267     

A high‐resolution hybrid digital pulse width modulator with dual‐edge‐triggered flip‐flops and hardware compensation

In this paper, a hybrid architecture of digital pulse width modulator (DPWM) which applies a counter, a phase‐shifted circuit, and a carry chain is proposed. Dual‐edge‐triggered flip‐flops are used in the phase‐shifted circuit to generate signals with 45° phase shift, which not only improves the resolution of the DPWM but also reduces the resource consumption in the carry chain. Furthermore, a hardware compensation method is used to solve the duty cycle increment phenomenon that affects the regulation accuracy of converter. An 11‐bit DPWM with the proposed architecture is implemented and tested by Xilinx Artix‐7 FPGA. The experimental results show a high resolution of 32 ps and a good linearity where R² is 0.99 and verify the effect of duty cycle compensation.     

Calculation of steady‐state solution of parallel‐connected buck converters with active current sharing and its parameter sensitivity

In this paper, the effect of active current‐sharing control on the steady‐state operation of parallel‐connected buck converters is investigated. The system under study consists of N voltage‐mode‐controlled buck converters connected in parallel. Three kinds of active current‐sharing schemes are considered, namely, master–slave scheme with automatic master, master–slave scheme with dedicated master, and democratic scheme. Using the principle of charge balance, the mechanism of the operating point drift arising from active current sharing is examined. A general formulation of the steady‐state solution under active current sharing is derived. Moreover, detailed parameter sensitivity analysis is performed to evaluate the effect of parameters' variation on the operating point. The results from sensitivity analysis can be used to categorize parameters for facilitating practical design. Computer simulations are presented to verify the analytical results. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐order harmonic resonance phenomena of a voltage‐sourced converter in cable system

This paper presents high‐order harmonic resonance phenomena of voltage‐sourced converters (VSC). When a voltage‐sourced converter is connected to a power system with cables, there is a possibility that minute high‐order harmonic voltages of a voltage‐sourced converter are magnified by a series resonance and a parallel resonance, and high‐order harmonic resonance phenomena are determined by this study. The cause of high‐order harmonic resonance phenomena is investigated and elucidated by the analysis using EMTP. In addition, it is verified that high‐order harmonic resonance phenomena occur as a practical matter. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 26–35, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20054     

High‐bandwidth design of hard disk control system using H∞ control with feedback‐type uncertainty

In hard disk drives, it is important to enlarge the control bandwidth in order to shorten the track pitch for larger data capacity. However, it is difficult for the H_∞ control method to increase the control bandwidth if the mechanical resonance modes have uncertainty. This is because the robustness of the H_∞ control method is assured by the small‐gain theorem for additive or multiplicative perturbation and the control bandwidth is limited by the uncertainty. In this study, we propose an H_∞ control method for high‐bandwidth design by introducing a new uncertainty model with a feedforward and a feedback path in order to reduce the conservatism of robust design. The effectiveness is shown by numerical simulations. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 54–62, 2010; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21025     

基于灵敏度分析的新能源电力系统同步机组调差系数优化方法

随着新能源的持续并网以及特高压交直流互联电网的形成,电力系统暂态频率稳定事件风险增加。在高渗透率新能源场景下,充分挖掘同步发电机组的调频能力成为提升电力系统频率响应能力的重要手段。针对同步机组的调速器参数,文章利用轨迹灵敏度分析影响最大频率偏差的主导参数,进而通过优化主导参数来提高电力系统的暂态稳定性。通过建立主导参数优化问题的数学模型,解析分析了主导参数对最大频率偏差的影响程度,采用灵敏度分析方法,将非线性优化问题转化为线性规划问题,以减少计算量。在此基础上,文章提出了适用于多机系统的调差系数优化方法,最后通过仿真算例验证了方法的有效性。     

Stabilization of a large‐capacity,long‐distance transmission system by an adjustable‐speed flywheel generator

An adjustable‐speed flywheel generator (FWG) can control both active power and reactive power rapidly. We have studied the effect of FWG installation on a large‐ capacity, long‐distance transmission system, especially when the system includes loops. In this paper, we describe the selection of FWG location, the selection of stabilizing control input signal, and the required quantities of FWG. FWG location is selected by a PQ‐sensitivity method, calculation of which is simple and permits easy understanding of the effect of both FWG's active and reactive power. As a stabilizing control input signal, we use bus voltage frequency instead of power flow because the flow changes stepwise by opening three‐phase single‐circuit. Additionally, we clarify the FWG quantities that must be designed, such as FWG's active power and reactive power. We considered FWG's slip to determine the quantity because the capacity of the exciter depends on slip. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 32–41, 1999     

Non‐linear analog circuit fault diagnosis with large change sensitivity

Large change sensitivity has been proved efficient at, but restricted to, generating a linear circuit fault dictionary. This paper discusses the extension of large change sensitivity to non‐linear analog circuit fault diagnosis. The fault dictionary is divided into d.c. and a.c. sections. In the d.c. domain, non‐linear components are approximated with piecewise linear models. By relating the operating region of each piecewise linear model to the magnitude of a single fault in a procedure termed preconditioning, it is shown that large change sensitivity can efficiently compute the response of a faulty non‐linear circuit. Results presented of an analysis of computational complexity show a significant reduction in the cost of simulating single linear resistor faults in a non‐linear circuit using this method. In addition, after establishing that the resistive portion of the circuit is fault free, a fault dictionary is constructed for dynamic components using large change sensitivity in the small signal a.c. domain. Included with a discussion on the issues of large change sensitivity based simulation‐before‐test, a small non‐linear circuit is used to demonstrate the effectiveness of the proposed fault diagnosis algorithm. Copyright © 2000 John Wiley & Sons, Ltd.