Estimating power-frequency characteristics in power systems by means of spectral analysis techniques

This paper shows that normal power system operating data may be used to determine the power-frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power-frequency characteristics as transfer functions. The generator characteristics K_g are determined as a transfer function of the system in which input signals are frequency fluctuation ΔF and generator power setting signal ΔP_g, and output signal is generator power output ΔP_e, To estimate the load characteristics K_l, a difficulty arises. There is a relation ΔP_/ = ΔL_o + K_lΔF between actual load ΔP_l, ideal load under the state of nominal frequency ΔL_o, and fluctuation of system frequency ΔF. Because it is impossible to measure ΔL_o directly, ΔL_o and K_lΔF cannot be separated. With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of ΔL_o in a partial system to ΔF of the total system may be ignored, that is, ΔF and ΔL_o are considered as independent phenomena. Thus the cross spectrum of ΔF and ΔL_o decreases to zero according to the increase of data in number, and K_l of the partial system can be estimated.     

A design guideline of parasitic inductance for preventing oscillatory false triggering of fast switching GaN‐FET

Gallium nitride field‐effect transistors (GaN‐FETs) are attractive devices because of its low on‐state resistance and fast switching capability. However, they can suffer from false triggering caused by fast switching. Particularly, a disastrous oscillation of repetitive false triggering can occur after a turn‐off, which may deteriorate the reliability of power converters. To address this issue, we give a design guideline to prevent this phenomenon. We analyze a simple circuit model to derive the condition of occurrence of this phenomenon, which is then verified experimentally. Results show that the parasitic inductance of the gating circuit, L_g, and that of the decoupling circuit, L_d, should be designed so that the LC resonance frequency of L_g and the gate–source capacitance of the GaN‐FET does not coincide with that of L_d and the drain–source capacitance, respectively. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Complex permeability of polycrystalline Mn-Zn and Ni-Zn ferrites

The complex permeability of ferrites is frequency dependent. The real part of the complex permeability deteriorates in a high frequency range and the imaginary part has a peak after starting the deterioration. This paper examines the possibility that the frequency characteristics for some ferrites can be approximately derived from a first-order linear differential equation for the magnetic field intensity and magnetic flux density. The first-order differential equation is expressed by the reciprocal of the complex permeability and provides first-order magnetic and electric circuits for ferrite cores. In contrast with the commonly used series R_s-L_s, circuit for the cores, obtained from B = (μ′ − jμ′)H, the first-order electric circuit derived consists of an inductance (L) and resistance connected in parallel. In this paper, it is demonstrated that the inductance L remains constant, whereas Ls decrease with the increase in frequency. In other words, the real part of the reciprocal of the complex permeability remains constant for an increase in frequency. In addition, it is found that the imaginary part of the reciprocal of the complex permeability is approximately proportional to the frequency. © 1998 Scripta Technica, Electr Eng Jpn, 123(2): 1–7, 1998     

Inner Intrinsically Safe Criterion and Design Considerations of Buck Converter Based on Equivalent Inductance

To obtain the intrinsic safety criterion of the Inner-intrinsic-Safety-Buck-Converter (ISBC) based on equivalent-inductance to guide its optimal design, the Inductor Disconnected Discharge (IDD) behavior of ISBC is researched, and the Equivalent-Simple-Inductive-Circuit (ESIC) based on the equivalent inductance is defined. According to ESIC based on the equivalent-current and the energy equivalence, the expression of the equivalent inductance L_ei is derived. The effect of the inductance L, the capacitance C, the input voltage V_i and the load resistance R_L on L_ei is deeply studied, and it’s pointed out that L_ei increases with the increase of V_i, L, C, and R_L, respectively. According to the minimal ignition current curve of the Simple-Inductive-Circuit (SIC), the nonexplosive intrinsically safe criterion based on L_ei is proposed. Combining the proposed criterion, the output ripple voltage and the expression of L_ei, the design region of the capacitance and inductance of the Buck converter meeting the demands of both inner intrinsic safety and electric performance is obtained. The feasibility of the design method and the proposed criterion is proved by the simulation and experimental results.     

Study on grounding in the vicinity of the work site on 1000-kV power transmission line. Part 2. Electromagnetic induction and its protection

In order to clarify the grounding conditions for protecting workers on a de-energized circuit from induction from a live circuit and to determine the required current capacity of the grounding conductor for a 1,000 kV double-circuit power transmission line, the phenomena caused by electromagnetic induction resulting from a live circuit are discussed. The electromagnetic induction current I_g flowing through the body of a worker and the electromagnetic induction current I_gO flowing through the grounding conductor can be analyzed by dividing the various power line conditions into three main factors, and using electromagnetic induction current calculations for a power line of infinite length. The zone where I_g does not exceed 1 mA is within 1 km of the grounding point on the de-energized circuit owing to the grounding resistance (0.1 Ω) of the substations at the ends of the line and the difference in the phase configurations on the line when the current I₁ of the live circuit is a constant 1 kA through the line. Similarly the value of I_gO is determined by the grounding resistance of the substations at the ends of the line and the difference in the phase configurations on the line. I_gO is approximately 10 A per 1 kA of I₁. The currents I_g and I_gO produced by electromagnetic induction are additive, allowing I_g and I_gO in the actual power line to be evaluated by summation.     

Deliverable‐power dependence on distribution‐line resistance and number of loads in low‐voltage DC distribution system

In this paper, we show that in a low‐voltage DC distribution system the deliverable power to a load has an upper limit P_lim due to the voltage instability at the receiving ends. On the basis of the previously derived concept of P_lim, we obtain the dependence of P_lim on the distribution line resistance R. In addition, we investigate the influence of the number of loads on P_lim. The result shows that a distribution line of lower R causes P_lim to be lower. This reduction in P_lim becomes more distinct for a larger number of loads. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Impedance spectroscopy of acceptor-doped CaZrO3 with cation nonstoichiometry

The electrical conductivities of acceptor-doped Ca_1−x Zr_0.99M_0.01O_3−δ (M = Mg²⁺, In³⁺) systems have been investigated as a function of cation nonstoichiometry (0 ≤ x ≤ 0.05). The electrical characterization was carried out using impedance spectroscopy at different temperatures in dry air. The contributions of grain (R _g) and grain boundary resistance (R _gb ) to the total resistance (R _t) were examined with the impedance and/or modulus plane representation. For the stoichiometric composition, the R _t of the specimen decreased with acceptor doping. When Ca deficiency was small, both the R _g and the R _gb slightly increased with nonstoichiometry (x). However, when Ca deficiency was large and excess zirconia was found as a second phase, the R _gb and the contribution of the R _gb to the R _t significantly increased with x.     

Lumped network model of a resistive type high Tc fault current limiter for transient investigations

In general, simulations of superconducting fault current limiters (SFCL) include the thermal- and electrical-behaviour of the limiter. Thermal properties deal with resistive heating caused by AC losses, increasing resistivity, etc. Electrical behaviour includes the U–I or E–J characteristics which are specific for every type of superconductor. This type of simulations is mainly made to predict the performance of the limiter in the electric power system if a short circuit occurs. The rise time of this signals is in the region of milliseconds.Signals with a smaller rise time can cause high voltage stresses if the frequency of the signal corresponds to the natural frequencies of the winding system. In this case, resonance excitations are caused in the windings of the limiter, which can lead to insulation faults and therefore have to be considered during the design. High voltage stresses in electric power systems can be caused by lightning strikes, disconnecting operations or system disturbances. The rise times of the initiated travelling waves are in the range of ms to ns and correspond to frequencies in the range of kHz to several MHz.In this paper, the transient behaviour of a high T_c resistive SFCL made of BSCCO 2212 tubes is modelled and evaluated. A lumped network model of a 15 MVA limiter is established and simulations in both, time- and frequency-domain are performed. The model includes the frequency dependence of the resistance R, being caused by the skin effect and the frequency dependence of the inductance L.     

基于UPFC抑制HVDC换相失败的控制方法研究

针对高压直流输电(high-voltage direct current,HVDC)系统发生换相失败的问题,运用统一潮流控制器(unified power flow controller,UPFC)减小HVDC系统发生换相失败的概率,并对UPFC的原有控制策略进行改善。当系统交流侧发生故障,UPFC并联侧控制策略采用交流侧母线电压参考值调节方法抑制换相失败的发生。引入故障水平FL来表征HVDC系统的故障严重程度,通过理论分析和PSCAD/EMTDC仿真验证:当故障水平FL为18.7%时,UPFC原有控制策略与改善后的控制策略均可抑制换相失败的发生;故障水平FL为23.1%时,只有改善后的控制策略可有效抑制换相失败的发生;故障更为严重,当故障水平达到FL为93.56%时,改善后的控制策略可有效降低连续换相失败的发生概率。运用UPFC动态无功补偿能力可增强HVDC系统受端交流系统强度,提高换相失败的抵御能力,从而有效改善了HVDC系统的运行特性。     

Single-phase inverter with Z.V.S. capacitors connected on the D.C. side and the load in parallel with the resonance inductance

Contents The paper presents one new version of single-phase inverters having the capacitors for the Z.V.S. connected in the D.C. side and the load in parallel with the resonance inductance. The output frequency of this inverter can be changed in certain ranges, from a maximum frequencyf _max to a minimum frequencyf _min, without imposing a constant load impedanceL–R. The power losses due to the commutation process of the switching devices comprising the inverter are drastically reduced and the resonant pulses have small dv/dt-values, allowing a high electromagnetic compatibility of the proposed inverter.

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Einphasenwechselrichter mit Kondensatoren im Gleichstromzwischenkreis zum Kommutieren auf die Nullspannung und Parallelbelastung mit Resonanzinduktanz

Übersicht Die Arbeit stellt eine neue Variante von Einphasenwechselrichtern vor, die Kondensatoren im Gleichstromzwischenkreis zum Kommutieren auf die Nullspannung und Parallelbelastung mit Resonanzinduktanz haben. Die Ausgangsfrequenz dieser Wechselrichter kann in gewissen Grenzen variiert werden, zwischen der maximalen Frequenzf _max und der minimalen Frequenzf _min, ohne daß es notwending ist, die LastimpedanzL–R konstant zu halten. Die Leistungsverluste in den Kommutierungsprozessen der in den Kondensatoren befindlichen Halbleiterelemente werden drastisch reduziert, und die Schwingungspulse haben Anstiegeschwindigkeiten dv/dt von ebenfalls reduzierten Werten, was zu einer erhöhten elektromagnetischen Kompatibilität der vorgeschlagenen Wechselrichter führt.

     

一种Buck输出纹波比的简化计算及设计方法

Buck变换器是一种高效的DC-DC降压开关电路,其输出的直流电压受到纹波干扰。纹波比是一个重要的性能指标,它受开关频率、滤波电感电容、占空比和负载电流（或负载电阻）等参数共同影响,不易精确计算。先构建一种与Buck变换器（电感电流连续）完全等效的理想电路拓扑;分析此电路的频率响应特性后得到电路的稳态输出;进一步的纹波理论计算及仿真分析表明,电路输出纹波比的计算完全可以由基波纹波比代替。基于上述简化纹波比计算的结论,又提出了一种设计滤波元件L、C参数的方法,并将这种方法运用于实例设计中,最后的仿真及实验数据都说明采用此方法能有效地计算出满足纹波比指标要求的L、C参数范围。     

Impedance spectroscopy of Ba4Ti13O30 film prepared by laser chemical vapor deposition

The impedance and electrical conductivity of Ba₄Ti₁₃O₃₀ film prepared by laser chemical vapor deposition were investigated as functions of temperature (300–1073?K) and frequency (10²–10⁷?Hz). The impedance response was resolved into two contributions, which were associated with the grains (R _g C _g) and grain boundaries (R _gb C _gb). With increasing temperature, both R and C decreased. R _gb was much higher than R _g and C _g were close to C _gb. Below 876?K, a step-like behavior was observed in the ac conductivity plots as functions of frequency due to two dispersion regions. The low-frequency dispersion was associated with grain boundaries and the high-frequency one corresponded to grains. The activation energies of grain conduction (E _g) and grain boundary conduction (E _gb) were 0.20 and 1.49?eV, respectively, which indicated that the relaxation process in grains arose from hopping electron and that in grain boundaries from the diffusion of oxygen vacancies.     

Capacitor and battery charging from hot/cold air using pyroelectric ceramics

This study is an experimental investigation on thermal energy harvesting using pyroelectric ceramics. Hot and cold air sources were used for generating temperature gradient in PbZr_xTi_1?xO₃ (PZT-5H) ceramics. Four different frequencies of (heating and cooling process) 0.025, 0.05, 0.1 and 0.2 Hz were investigated for optimizing power/voltage output. Maximum output voltage of 2.51 V (across 4.7 μF and 5 MΩ) was achieved at 0.05 Hz frequency with temperature variation between 100°C and 65°C. Furthermore, maximum power density of 2.35 μW/cm³ was obtained at 0.05 Hz across 4.7 μF load capacitor and 5 MΩ load resistance. In addition to this a battery of 7 mAh capacity was charged up to 1.21 V in 55 minutes using continuous heating and cooling processes with frequency of 0.4 Hz.     

Adaptive impedance matching system for downlink of passive semi‐ultra wideband ultra‐high frequency radio frequency identification tag

The input impedance of ultra‐high frequency radio frequency identification tag varies with the received power on the chip. It will induce impedance mismatch between the receiver antenna and microchip, thus drastically affect the performance of communication. In this paper, a low cost and fully integrated automatic impedance matching system was presented to solve this problem. It consists of two control loops for independent control of the real and imaginary parts of impedance. The first control loop realizes resistance correction using a parallel LC tuning network, whereas the second control loop achieves reactance compensation using a series LC tuning network. In both loops, the mismatch information is detected for direct control of the variable elements, varactors, which are tuned in a sequential manner. For unambiguous control of the resistance correction, the sign of the intermediate reactance is used as a secondary control criterion to enforce operation into a stable region. The functionality of the proposed automatic matching system was verified for different input impedances of a specifically semi‐ultra wideband ultra‐high frequency radio frequency identification tag as the available input power varies. The results indicate that all matched impedances are clustered around the target impedance 50 + j0 Ω after acquisition of both loops. Copyright © 2012 John Wiley & Sons, Ltd.     

Zur Theorie des induktiven Blindwiderstandes

Zusammenfassung Es wird eine Spule mit der InduktivitätL betrachtet, an der eine sich beliebig ändernde SpannungU (t) liegt. Auf dieses Aggregat wird formal das ohmsche Gesetz angewendet, also der Quotient Spannung: Strom gebildet. Dies führt zu einem allgemeinen Ausdruck für den induktiven BlindwiderstandR _L der Spule, wobei dieser in der FormR _L =R _L (U, L), also als Funktion der Spannung und der Induktivität ausgedrückt wird, daher also für beliebigenL-bzw.U-Verlauf die jeweilige Induktivität zu berechnen gestattet. Die Herleitung der bekanntesten Blindwiderstandsgrößen,R _L =0 undR _L =jL aus dem allgemeinen Ausdruck sowie weitere Anwendungen desselben werden gezeigt. Zum Schluß wird kurz auf die Lösung der umgekehrten Problemstellung hingewiesen.     

基于R_d阻尼型LCLLC滤波器的永磁同步发电机绕组谐波抑制

在永磁风力发电系统中,为了减轻机侧变流器产生的脉宽调制(PWM)高频脉冲波对定子绕组的绝缘损害,降低谐波电流造成的发电机损耗,在分析传统PI控制策略的基础上,提出了一种新的策略。将谐振控制器与二自由度(2DOF)PID控制器相结合,设计谐振二自由度PID(R-2DOF PID)控制器,并通过粒子群(PSO)算法优化控制器参数,获得较强的电流跟踪能力、稳定的控制和良好的谐波电流抑制效果。同时,在机侧变流器端设计Rd阻尼型(滤波器电容支路串联电阻)LCLLC滤波器衰减PWM高频脉冲中的高次谐波,与传统PI控制结合Rd阻尼型LCL滤波器的谐波抑制策略相比,提出的控制器不仅能抑制电流谐波,实现电流环的无差拍控制,而且能减小外界扰动带来的影响,增强控制器的动态稳定性。使用MATLAB/Simulink对永磁同步发电机进行仿真试验,仿真结果表明,LCLLC滤波器对于滤除PWM高频脉冲的谐波成分效果较好,R-2DOF PID控制器可对周期信号进行无误差跟踪,达到抑制谐波的目的。     

A simple and efficient honey bee mating optimization approach to performance characterization of a microwave transistor for the maximum power delivery and required noise

In this work, a simple, efficient and multi objective Honey Bee Mating Optimization (HBMO) is presented for the performance characterization of a microwave transistor to deliver maximum power to the load with the required noise F_req. Thus all the possible compatible {F_req ≥ F_min, V_out = 1, G_Tmax} triplets and the corresponding source Z_S and load Z_L = Z^*_out (Z_S) terminations can be obtained in the device operation domain of (V_DS, I_DS and f) without working analytically for the nonlinear performance and stability equations. HBMO is a recently emerging meta‐heuristic algorithm that combines the powers of the simulated annealing and genetic algorithms. Here, a microwave transistor is chosen as a case study, effectiveness and efficiency of the HBMO are shown by comparing its performance to those of the standard meta‐heuristics Genetic and Particle Swarm algorithms and the mean cost results for 10 runs are found to be 0.22, 1.65 and 1.85, respectively, for the comparable execution times. Furthermore, all the numerical results are found to agree with their analytical counterparts obtained using the microwave, linear circuit and noise theories. The Feasible Design Target Space FDTS can be built by the cross relations among all the possible compatible {F_req ≥ F_min, V_out = 1, G_Tmax} triplets together their terminations {Z_S, Z_L = Z^*_out (Z_S)} covering all the possible amplifier designs where both noise figure and output power are at a premium. Copyright © 2015 John Wiley & Sons, Ltd.     

An integrated controller for high‐frequency LCLC resonant inverter with phase‐shifted control and frequency regulation

High‐frequency alternating current has an extensive application as a result of outstanding advantages. The aim of the study is to develop a high‐frequency power source to feed the auxiliary loads of vehicle application such as electric fans, blower motors, and lighting. A feasible implementation of high‐frequency power source is examined by a full‐bridge LCLC resonant inverter. The corresponding control scheme is proposed for the fourth‐order resonant inverter to confront the control challenges of low output harmonics and dynamic nonlinear load. Firstly, an analysis parameter S _r is defined to address the possible impacts of the varying operational frequency to output THD and ZVS features. Secondly, an integrated control scheme is presented to implement pulse‐width control at heavy load and frequency regulation at light load. Lastly, an experimental prototype is accomplished with the peak voltage of 35 V and the output power of 120 W. The accordance of experimental results and theoretical analysis testifies that the proposed control scheme can achieve the low harmonics and high conversion efficiency over a wide scope of operational conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

矩阵变换器系统小信号模型稳定性分析

提供了一种基于小信号模型的矩阵变换器稳定性分析方法。以电源、二阶输入L-C滤波器、矩阵变换器和R-L负载为对象,建立矩阵变换器系统小信号模型。获得传递函数,通过对其零极点的分布进行分析,探明了各参数对系统稳定性影响的规律,并着重研究了矩阵变换器管压降、换流和死区这些非线性因素对系统稳定性的影响。通过傅里叶分析给出了谐波表达式,分析了这些非线性因素与稳定性的关系。仿真结果验证了建模和分析结论的正确性。     

An efficient neural network approach for nanoscale FinFET modelling and circuit simulation

The present paper demonstrates the suitability of artificial neural network (ANN) for modelling of a FinFET in nano‐circuit simulation. The FinFET used in this work is designed using careful engineering of source–drain extension, which simultaneously improves maximum frequency of oscillation ƒ_max because of lower gate to drain capacitance, and intrinsic gain A_V0 = g_m/g_ds, due to lower output conductance g_ds. The framework for the ANN‐based FinFET model is a common source equivalent circuit, where the dependence of intrinsic capacitances, resistances and dc drain current I_d on drain–source V_ds and gate–source V_gs is derived by a simple two‐layered neural network architecture. All extrinsic components of the FinFET model are treated as bias independent. The model was implemented in a circuit simulator and verified by its ability to generate accurate response to excitations not used during training. The model was used to design a low‐noise amplifier. At low power (J_ds∼10 µA/µm) improvement was observed in both third‐order‐intercept IIP₃ (∼10 dBm) and intrinsic gain A_V0 (∼20 dB), compared to a comparable bulk MOSFET with similar effective channel length. This is attributed to higher ratio of first‐order to third‐order derivative of I_d with respect to gate voltage and lower g_ds in FinFET compared to bulk MOSFET. Copyright © 2009 John Wiley & Sons, Ltd.