Dynamic characteristics of autonomous wind–diesel systems

In this paper the dynamics of a small autonomous system, comprising a diesel generator and a wind turbine, are investigated. The analysis is performed both in the frequency and time domain, using simplified models of the system components and taking into account the diesel engine speed governor and the wind turbine pitch controller (for pitch regulated machines). The investigation is extended to include different types of wind turbines, equipped with induction or synchronous generator and using pitch or stall regulation, as well as operation of the wind turbine in an autonomous or infinite system. The objective is to determine the main factors affecting the behaviour of the system and to illustrate the effect of the speed governor and pitch controller settings on the expected performance. Particular emphasis is placed on identifying the main modes of the system and determining their dependence on the controllers' parameters. A comparative assessment of the dynamic characteristics of different types of wind turbines is also included and the operation of the wind turbine in a small system and against an infinite bus is addressed and discussed.     

2001 International Symposium on Lightning Protection

In this letter an investigation of the harmonics of the slip energy recovery drive is presented. The analysis takes into consideration not only the rotor-side rectifier, as is customary, but also accounts for the harmonics introduced by the recovery inverter. Simple relations are provided that predict all harmonic frequencies of the drive currents and torque as a function of its supply frequency and operating slip.     

An Investigation of the Harmonic Emissions of Wind Turbines

Harmonic emissions of variable speed wind turbines (WTs) are a well-known issue, but little information that is based on field measurements on actual machines has been published on the subject. In this paper, the harmonic behavior of modern WTs using extensive measurements performed on commercially available machines is discussed. Specific issues addressed include the shape and the frequency range of the harmonic current spectrum, the variation of the harmonics with the WT operating point, the statistical characteristics of their magnitude and phase angle, the effect of grouping and time-averaging, as well as their symmetrical component characteristics. The objective of the paper is to outline important general characteristics of the harmonic behavior of WTs, rather than to analyze specific machines or compare alternative WT designs     

Smart antennas for combined DOA and joint channel estimation intime-slotted CDMA mobile radio systems with joint detection

In cellular mobile radio systems, the directional inhomogeneity of the mobile radio channel can be exploited by smart antennas to increase the spectral efficiency. In this paper, a novel smart antenna concept applying receiver antenna diversity at the uplink receiver is investigated for a time-slotted code-division multiple-access (CDMA) mobile radio air interface termed time-division CDMA (TD-CDMA), which has been selected by the European Telecommunications Standards Institute (ETSI) in January 1998 to form part of the Universal Mobile Telecommunications System (UMTS) air interface standard. First, a combined direction-of-arrival (DOA) and joint channel estimation scheme is presented, which is based on DOA estimation using the Unitary ESPRIT algorithm and maximum likelihood estimation of the channel impulse responses associated with the estimated DOA's, which can also be used as an input for advanced mobile positioning schemes in UMTS. The performance of the combined DOA and joint channel estimation is compared with the conventional channel estimation through simulations in rural and urban propagation environments. Moreover, a novel joint data detection scheme is considered, which explicitly takes into account the signal DOA's and the associated channel impulse responses. The link level performance of a TD-CDMA mobile radio system using these novel schemes is evaluated by Monte Carlo simulations of data transmission, and average bit error rates (BER's) are determined for rural and urban propagation environments. The simulation results indicate that, depending on the propagation environment, the exploitation of the knowledge of the directional inhomogeneity of the mobile radio channel can lead to considerable system performance enhancements     

Long aging time thermal degradation of the ac conductivity and complex permittivity of conducting polypyrrole

The modification of the ac conductivity and the complex permittivity of conducting polypyrrole was monitored throughout a two years thermal aging at 343 K. Reduction of the cross-over frequency is correlated with the degradation of dc-conductivity, while the ac conductivity region corresponding to the so-called ‘universal’ dielectric relaxation remains practically insensitive during the first year of ageing, which implies a collective co-operativity among multiple degradation processes that yield a practically time-independent effective disordered environment. A broad dielectric loss peak recorded in fresh specimens splits into two distinct relaxations for intermediate stages of the annealing process. The aging-time evolution of the dc component and the relaxations are qualitatively analysed and time constants are determined.     

Commutation angle analysis of the slip energy recovery drive

A well known characteristic of the slip energy recovery drive (SERD) is the large commutation overlap of the rotor side rectifier, which compromises the accuracy of simplified dq models often used for its simulation. In this paper the variation of the rectifier commutation angle and the factors that determine its magnitude are investigated using a detailed hybrid abc-dq model of the SERD, the accuracy of which is validated by experimental results. The dependence of the commutation angle on the DC current and the operating slip is shown for a case study drive and practical relations are deduced which permit the evaluation and a-posteriori correction of the steady state error of simplified dq models, where the commutations and converter harmonics are ignored     

Wind turbine effect on the voltage profile of distribution networks

The operation of wind turbines in the distribution networks may affect the power quality offered to the consumers. One of the most important considerations is the effect on the voltage profile, i.e. the induced slow voltage variations, which are the subject of this paper. Two alternative approaches are presented for their evaluation. The first, adopted by many utility guides and recommendations, is deterministic, seeking to ensure that the voltage deviations always remain within certain limits. The other recognises the statistical nature of the voltage variations and conforms to latest European Norm, EN 50160. Rather than assessing the maximum deviations that can possibly appear, the probability distribution of the voltage is calculated and then the conformity to the standards is assessed. In applying the statistical method, either time series, or directly probability distributions can be used. As a study case, the methods are applied to an existing MV distribution feeder, where significant wind power is installed. Measurement data are provided for the same feeder.     

Pine Forest Height Inversion Using Single-Pass X-Band PolInSAR Data

A sparse pine forest is investigated at X-band on a single-pass polarimetric synthetic aperture radar interferometry (PolInSAR) data set using HH and HV channels. These first preliminary results show that the associated phase centers present a significant vertical separation (about 6 m) allowed by penetration through gaps in the canopy. Forest parameter inversion using the random volume over ground (RVoG) model is evaluated and adapted at this frequency. The forest height can be retrieved accurately by supposing a high mean extinction coefficient (around 1.6 (dB/m). The penetration depth is estimated to be around 4 m, based on the forest height ground measurements. Finally, a time-frequency analysis using a sublook decomposition is performed to increase the vertical separation of the polarimetric phase centers. As a consequence, RVoG-inversion performance is improved, and a penetration depth that is in better accordance with a previous work (of the order of 2 m) is found. This paper has shown that the height inversion of a pine forest was possible using PolInSAR X-band data and that the performance was more dependent on the forest density than at lower frequencies.     

Optimization of composite patch repair processes with?the?use of genetic algorithms

The aim of this contribution is the optimization of some parameters of the composite patch repair technique (CPR). This technique is mainly used by the aircraft industry, as it offers high reliability, short repair times and reduced cost in compare to other methods, such as the riveted joints. CPR consists of adhesively bonding thin composite patches over cracked or corroded areas with heat supply. As the polymer-matrix composite patch is heated, it cures and toughens. Proper curing insures structural reliability of the repair. Short duration curing cycles are of great importance for the aircraft availability. With the use of Genetic Algorithms, we design minimum time curing cycles. The optimization is subjected to the following constraints: (1) Maximum allowed temperature in order to avoid residual stresses, (2) Minimum temperature in order to initiate the cure reaction, (3) Sufficient degree of cure at the end of the process and (4) Maximum heat generation rate that can be achieved by the device. Our design vector contains the duration of the plateau stage of the cure cycle and the characteristic thermal profile. The degree of cure is estimated with the use of the Kamal cure rate model for thermosetting polymers. For the numerical time integration of the cure rate equation, a second order, implicit Runge-Kutta scheme is employed.     

Single-baseline polarimetric SAR interferometry

Examines the application of single-baseline polarimetric SAR interferometry to the remote sensing and measurement of structure over forested terrain. For this, a polarimetric coherent scattering model for vegetation cover suitable for the estimation of forest parameters from interferometric observables is introduced, discussed and validated. Based on this model, an inversion algorithm which allows the estimation of forest parameters such as tree height, average extinction, and underlying topography from single-baseline fully polarimetric interferometric data is addressed. The performance of the inversion algorithm is demonstrated using fully polarimetric single baseline experimental data acquired by DLR's E-SAR system at L-band