A robust adaptive pole‐placement controller without strictly positive real condition

This paper considers the adaptive pole‐placement control problem for system (1) with unmodelled dynamics η_n dominated by a small constant ε multiplied by a quantity independent of ε but tending to infinity as the past input, output, and noise grow. Using bounded external excitation and randomly varying truncation techniques, we give a design method of adaptive pole‐placement controller. It is shown that the closed‐loop system is globally stable, the estimation error for the parameter contained in the modelled part is of order ε, and the closed‐loop system under the adaptive pole‐placement control law is suboptimal in the sense of $$\mathop{\lim\sup}\limits_{{n\to\infty }}{1\over n}\mathop{\sum}\limits_{i=0}^n{\left({A^{*}(z)y_{n}‐L(z)C(z)w_{n}‐B(z)R(z)y_{n}^{*}}\right)^{2}{\leq}O({\varepsilon}^{2})+\gamma^{2}\mathop{\sum}\limits_{j=1}^q{b_{j}^{2}}}$$\nopagenumbers\end while the SPR condition used usually in other papers is replaced by a stability condition. Copyright © 2001 John Wiley & Sons, Ltd.     

State criterion of wind turbine generator operation using tower shadow effect (Part 2)

In order to obtain wind energy effectively, the pole‐change‐type induction generators are used as the wind turbine generators. Otherwise, the pole‐change‐type induction generator causes the voltage dips at pole changing time. To maintain the power quality, it is important to know the state change of the generator operation. Therefore, the authors have studied a state criterion of generator using the tower shadow effect, which is the active power oscillation caused by a rotation torque drop when the tower and the turbine blade overlap each other. In this paper, an improved identification method of oscillation frequency, which is the criterion of wind turbine generator operation, is proposed. The proposed method is applied to measured data and good results are obtained. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 25–31, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20395     

Development of trouble diagnosis technology of 50‐W‐grade micro wind turbine generator

The establishment of an early trouble diagnosis system is needed in order to prevent damage to wind turbine generators. Therefore, acoustic emission (AE) signals resulting from damage to a wind blade were detected with an AE sensor installed on the body of the wind turbine generator and on the mounting pole. In this study, the length of a blade of a micro wind turbine generator was varied to simulate trouble at constant wind velocity. The AE signals which occurred at this time were measured with an AE sensor. The signal was processed by FFT analysis, and the change of spectral strength was examined. A trouble diagnosis technology for 50‐W‐grade micro wind turbines generator was then developed. A method of counting the number of occurrences of above‐threshold AE signals was suggested by the wave pattern of the AE signals. It was found that the number of occurrences could be used as a standard to judge the normality or abnormality of 50‐W‐grade micro wind turbine generators. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 33–39, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21017     

Evaluation of material constants in NdCa4O(BO3)3 piezoelectric single crystal

A neodymium calcium oxoborate NdCa₄O(BO₃)₃ piezoelectric single crystal that belongs to the monoclinic system with point group m was grown by the Czochralski technique. A practical evaluation method was developed to determine the 27 independent material constants for acoustic wave device applications. A longitudinal effect face–shear vibration was analyzed and used in the resonance–antiresonance measurement. This method avoided measuring d ₁₁ and d ₃₃ directly by use of X-bar and Z-bar, in which leak of electric field would cause large errors because of the very small dielectric constants. At room temperature, dielectric constants were ${{\varepsilon _{11}^{\text{T}} } \mathord{\left/{\vphantom {{\varepsilon _{11}^{\text{T}} } {\varepsilon _0 }}} \right.\kern-0em} {\varepsilon _0 }} = 9.9$ , ${{\varepsilon _{22}^{\text{T}} } \mathord{\left/{\vphantom {{\varepsilon _{22}^{\text{T}} } {\varepsilon _0 }}} \right.\kern-0em} {\varepsilon _0 }} = 15$ , ${{\varepsilon _{33}^{\text{T}} } \mathord{\left/{\vphantom {{\varepsilon _{33}^{\text{T}} } {\varepsilon _0 }}} \right.\kern-0em} {\varepsilon _0 }} = 10$ and ${{\varepsilon _{13}^{\text{T}} } \mathord{\left/{\vphantom {{\varepsilon _{13}^{\text{T}} } {\varepsilon _0 }}} \right.\kern-0em} {\varepsilon _0 }} = - 0.8$ , respectively. All the independent dielectric and elastic constants were determined in this work. The simulation of surface acoustic wave velocity showed a good agreement with the measured value.     

Transient stability simulation of wind generator expressed by two‐mass model

Recently, wind power generation is increasing worldwide. In wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as a one‐mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two‐mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 27–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20394     

A salient‐pole synchronous generator with permanent magnets between the field poles

In this paper, a new salient‐pole synchronous generator (SG) termed the PMa‐SG is presented. In the PMa‐SG, permanent magnets (PMs) are placed between the pole shoes to reduce the magnetic saturation in the field poles. By using finite element analysis (FEA), the internal magnetic fields and basic characteristics of a 2.8‐MVA PMa‐SG are compared with those of a conventional SG of the same size, and the reduction effect of the magnetic saturation of the PMs is examined. The FEA simulations are also validated by experiments on a 2.0‐kVA prototype machine. The PMs placed between the pole shoes reduce the magnetic saturation in the pole bodies and pole tips and effectively increase the terminal voltage and output power. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(4): 58–67, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21132     

Matching between straight‐wing nonarticulated vertical axis wind turbine and a new wind turbine generator

In the current wind turbine generation system, there are substantial problems such as the fact that the maximum power of the wind turbine cannot be obtained in the presence of fluctuating wind speed, as well as high cost and low annual net electricity production (due to mismatch between generators and wind turbines). A new wind turbine generator optimized for the wind turbine output is presented in order to solve such problems. This wind turbine generator consists of a permanent magnet generator, a reactor, and a rectifier, and uses neither a control circuit which requires standby electricity nor a PWM converter having a switching element. By selecting the most appropriate combination of a permanent magnet generator with multiple windings and a reactor connected in series with each winding, the maximum output of the wind turbine can be obtained without using a control circuit. The new wind turbine generator was directly coupled with a straight‐wing nonarticulated vertical‐axis wind turbine (SW‐VAWT), and matching of the generator with the wind turbine was examined in field tests. The test results and review confirm that the new wind turbine generator is highly matched with the wind turbine in the presence of fluctuating wind speed. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 26–35, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21036     

Transport Properties of the Mixed-Conducting SrFe1.2Co0.3Ox

Single phase SrFe_1.2Co_0.3O_x sample with layered crystal structure was prepared using a solid state reaction method. Electrical conductivity and apparent oxygen diffusion coefficients of the SrFe_1.2Co_0.3O_x sample were measured as functions of temperature in atmospheres of various oxygen partial pressures . Total and ionic conductivities were determined by using the conventional four-probe and electron blocking four-probe methods, respectively. The apparent oxygen diffusion coefficient was derived from the time-dependent conductivity relaxation data of the reequilibrium process after abruptly changing the in the surrounding atmosphere. Several atmospheres of different were established by the use of premixed gas cylinders. The conductivity of SrFe_1.2Co_0.3O_x increases with increasing temperature and . At 900°C in air, the total conductivity and ionic conductivity are 10 and 8S · cm^-2, respectively. The ionic transference number ( 0.8 in air) does not have strong temperature dependence. The activation energy increases with decreasing . In air, the activation energy has a low value of 0.37 eV. The apparent oxygen diffusion coefficient was at 950°C over a wide range of .     

Study of asynchronizing phenomena using generator model with field mutual leakage reactance

This paper describes the effect of mutual leakage reactance in the rotor circuit on the analysis of generator transient characteristics. The authors derive a detailed equivalent circuit model for a 48P‐15,750‐kVA generator, analyze sudden short circuits and asynchronization phenomena of the generator by simulations with an electromagnetic transients program (ATP‐EMTP), and compare the results with experimental data. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 31–40, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20147     

基于补偿跃变量算法的发电机同步模型

从Ｐａｒｋ方程出发,计及定子绕组暂态、凸极效应以及转子动态特性,运用机电量类比和综合友模的方法,将同步发电机的电磁暂态、机械暂态和接口方程统一,建立了可与系统同步计算的统一友模,从而在避免预测校正、简化机网接口的同时,大大提高了仿真的精度。文中还利用频谱分析的方法,对同步机跃变量模型的误差进行了修正,使修正后的友模不仅避免了数值振荡,而且尽可能地提高了精度。所了的发电机同步友模适用于复杂系统的同步     

Electrical properties of rutile-type relaxor ferroelectric-like Fe0.9W0.05TiMO6 (M = Ta,Nb) ceramics

Electrical properties of rutile-type $\mathrm {Fe}_{0.9}{\kern 1pt} \mathrm {W}_{0.05}\\\mathrm {TiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics $\mathrm {FeTiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ . The aliovalent ${\rm W}^{6+}$ cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant $\epsilon (\omega )$ , and further electrical quantities can possibly shed additional light on the nature of the mechanism leading to extraordinary values in $\epsilon (\omega )$ . In part similar electrical data were established such as very high $\epsilon (\omega )$ but also different results were noted. Apart from $\epsilon (\omega )$ , the electrical response was analysed by measuring losses, dissipation factor $\tan \delta $ , DC conductivity $\sigma _{DC}$ and AC conductivity $\sigma _{AC}(\omega )$ using impedance spectroscopy, and thermopower; the results are discussed in conjunction with literature data. The role of grain boundaries and sample-electrode processes was investigated in particular with respect to the sample capacitance. Eventual microstructural local inhomogeneities were checked by means of ⁵⁷Fe Mössbauer spectroscopy. For both compounds, the temperature dependence of bulk $\sigma _{DC}$ showed Arrhenius behaviour with activation energy ${E_{A}}\sim $ 0.35 eV and $\sigma _{DC}$ (295 K) $\sim 5\times 10^{-5} \Omega ^{-1}\text{cm}^{-1}$ ; grain boundaries exhibited slightly higher ${E_{A}}$ but the value of $\sigma _{DC}$ was a factor of up to $\sim 10$ lower at all temperatures. From $\sigma _{AC}(\omega )$ data, a power law frequency dependence of grain boundary conductivity was derived. Relaxation processes were established from loss and $\tan \delta $ data. The thermopower is negative and varies weakly with temperature, pointing to long-range charge transfer by a hopping-type mechanism of electron polarons.     

Pitch control based on voltage dip detection for improving the LVRT of wind farm

For the stability of power systems including large‐scale generation of wind power, wind farms are expected to fulfill the requirement with the capability to remain connected to the systems during a momentary voltage dip occurring in power networks. This has prompted many utilities to adopt the low‐voltage ride‐through (LVRT) of wind turbine generators (WTGs) as one of the requirements in interconnection of large wind farms. This paper presents a new method of pitch angle control for fixed‐speed wind turbine (FSWT) to achieve LVRT capability improvement. The FSWT is equipped with directly grid‐coupled squirrel‐cage induction generator and the LVRT behavior of such wind turbine is closely related to the overspeeding of wind turbine rotor during voltage dip. If the turbine rotor speed can be reduced quickly during voltage dip so as not to rise over the maximum speed, then the sudden disconnection of WTG can be avoided. The proposed pitch control system can modify the pitch angle in the short response time by the coordination of protective relay. Then the pitch angle is adjusted by a feedback proportional integral controller based on the measurement of induction generator terminal voltage. Simulation study shows that the application of the proposed pitch control system can improve the LVRT performance of a wind farm equipped with FSWTs. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Oxygen permeability, stability and electrochemical behavior of \Pr _{2} {\text{NiO}}_{{4 + \delta }} -based materials

The high-temperature electronic and ionic transport properties, thermal expansion and stability of dense $ \Pr _{2} {\text{NiO}}_{{4 + \delta }} ,\Pr _{2} {\text{Ni}}_{{0.9}} {\text{Fe}}_{{0.1}} {\text{O}}_{{4 + \delta }} $ and $ \Pr _{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ ceramics have been appraised in comparison with K₂NiF₄-type lanthanum nickelate. Under oxidizing conditions, the extensive oxygen uptake at temperatures below 1073–1223 K leads to reversible decomposition of Pr₂NiO₄-based solid solutions into Ruddlesden–Popper type Pr₄Ni₃O₁₀ and praseodymium oxide phases. The substitution of nickel with copper decreases the oxygen content and phase transition temperature, whilst the incorporation of iron cations has opposite effects. Both types of doping tend to decrease stability in reducing atmospheres as estimated from the oxygen partial pressure dependencies of total conductivity and Seebeck coefficient. The steady-state oxygen permeability of $ \Pr _{2} {\text{NiO}}_{{4 + \delta }} $ ceramics at 1173–1223 K, limited by both surface-exchange kinetics and bulk ionic conduction, is similar to that of $ {\text{La}}_{2} {\text{NiO}}_{{4 + \delta }} $ . The phase transformation on cooling results in considerably higher electronic conductivity and oxygen permeation, but is associated also with significant volume changes revealed by dilatometry. At 973–1073 K, porous $ \Pr _{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ electrodes deposited onto lanthanum gallate-based solid electrolyte exhibit lower anodic overpotentials compared to $ {\text{La}}_{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ , whilst cathodic reduction decreases their performance.     

Defect structure of oxide ferroelectrics—valence state,site of incorporation,mechanisms of charge compensation and internal bias fields

The defect structure of aliovalent transition-metal and rare-earth functional centers in ferroelectric perovskite oxides is characterized by means of multifrequency electron paramagnetic resonance spectroscopy, assisted by density-functional theory calculations. The review is mainly focused on lead zirconate titanate (Pb[Zr _x Ti_1−x ]O₃, PZT) compounds. However, where available also results on ferroelectric ’lead-free’ compounds are discussed. The results include the formation of charged defect dipoles, causing internal bias fields, multivalence manganese centers, acceptor-type copper functional centers creating isolated oxygen vacancies that promote ionic conductivity, as well as donor-type centers. Moreover, the impact of the defect structure on macroscopic material properties is discussed.     

Effect of annealing temperature on the electrostrictive properties of 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 thin films

0.94(Na_0.5Bi_0.5)TiO₃-0.06BaTiO₃ (NBT-BT6) thin films were fabricated by metal-organic decomposition (MOD) at the different annealing temperatures. Based on the electrostrictive effect and converse piezoelectric effect, the phenomenological approach is provided to characterize the electrostrictive properties of the perovskite relaxor, and it is used to determine the effective electrostriction coefficients $ Q_{33}^{\mathrm{eff}} $ and electrostrictive strains $ {S_3} $ of NBT-BT6 thin films annealed at the range of 650?C800?°C. After the microstructure, ferroelectric, dielectric and piezoelectric properties of the thin films were determined, the maximum values of $ Q_{33}^{\mathrm{eff}} $ and $ {S_3} $ of NBT-BT6 thin film annealed at 750?°C are respectively determined as 0.0289?m⁴/C² and 0.26?% under the bipolar driving field of 391?kV/cm. They are strongly influenced by annealing temperature due to the bismuth evaporation and crystallization of perovskite phase, and the enhanced electrostrictive properties could make NBT-based thin film a promising candidate to the design and application of stacked actuators, microangle-adjusting devices, and oil pressure servo valves.     

A study of generator system selection for large wind turbine generator system

This paper focuses on selection of wind turbine generation systems that include generators, converters, and gears. We study three systems: a permanent magnet generator (PMG) system, a doubly‐fed generator (DFG) system, and a synchronous generator (SYG) system in terms of the system efficiencies and running costs. The system efficiencies and running costs are calculated by considering the relationship between wind power and wind conditions. According to these results, the one‐step gear PMG system is the best choice for a large wind turbine system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(1): 51–57, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20506     

双馈风力发电机组系统接入与稳定运行仿真

分析了包含大量异步风力发电机组的风电场并网运行后对电力系统静态和动态稳定性的影响。从系统接入和稳定运行的角度研究了双馈风力发电机组及普遍采用的定子磁链定向矢量控制策略在提高风电系统稳定性方面的优势与不足。以实际机组为例在PSCAD/EMTDC平台上建立了仿真模型,结果表明双馈风力发电机组在风速发生变化时不仅能够以变速恒频方式运行并追踪最大风能,且电网电压也比传统鼠笼式风力发电机组更为稳定。在系统发生最严重的三相接地故障时,风电场具有更好的暂态稳定性。     

Effects of the gas flow rate on the ionic conductivity of {\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } ceramics

With coarse CaCO₃, nano ZrO₂ and In₂O₃ as raw materials, fine ${\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } $ powders were synthesized at 1000°C by an optimized solid-state method. With the powders, ceramics with relative density as high as 98% were successfully fabricated at the temperature as low as 1400°C. The effects of gas flow rate on the conductivity of the ${\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } $ ceramics under wet air conditions were first studied. The results showed that with the increase of temperature, the effects became more and more significant. In order to gain insight into the ion transfer mechanism of the electrolyte, the absorption and diffusion processes were analyzed. It was suggested that at lower temperature, the diffusion step was the rate-determining step. However, with the increase of the temperature, the adsorption process became the rate-determining step at lower flow rates.     

Starting method of a superconducting generator in a combined‐cycle power plant

In the combined‐cycle power plant generators are started by using the igniting arrangement up to the ignition rotational speed of the gas turbine. On the other hand, in the case of using the superconducting generator, it is difficult to apply the igniting arrangement used to generate electricity on the combined cycle for the structure as is. We examined the induction motor starting method for the superconducting generator by using the 70‐MW‐class quick‐response excitation superconducting model generator and the VVVF power supply. From the examination, we confirmed the ability to raise the rotational speed from 6 to 360 rpm. Moreover, it was found to be able to start 200‐MW‐class superconducting generators by the induction motor starting method with the analysis. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 30– 38, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20283     

Characteristics of a MHD power generator using a low-melting-point Gallium alloy

An experimental investigation of a magneto hydrodynamics power generator using a low-melting-point Gallium alloy at high Reynolds numbers is presented in this paper. The power output is found to increase with increasing the flow Reynolds number. By considering the non-uniform distribution of the magnetic field in the test channel, theoretical evaluation gives a more accurate prediction to the experimental data. The present generator demonstrates the maximum power generation efficiency of $8.3\times 10^{-4}$  % and the maximum output electric power of 1.5 mW.