Showing papers in "Bulletin of The Polish Academy of Sciences-technical Sciences in 2006"

Modern active filters and traditional passive filters

Abstract: Unlike traditional passive filters, modern active filters have the following multiple functions; harmonic filtering, damping, isolation and termination, reactive-power control for power factor correction and voltage regulation, load balancing, voltage-flicker reduction, and/or their combinations. Significant cost reductions in both power semiconductor devices and signal-processing devices have inspired manufactures to put active filters on the market. This paper deals with general pure active filters for power conditioning, and specific hybrid active filters for harmonic filtering of three-phase diode rectifiers, as well as traditional passive filters.

Technology and applications of Low Temperature Cofired Ceramic (LTCC) based sensors and microsystems

Abstract: The paper presents general information on LTCC materials, manufacturing processes and properties of fired modules. A Multichip Module package has been the main application of Low Temperature Cofired Ceramic (LTCC) technology. Recently, this technology is also used for production of sensors, actuators and microsystems. The research and development on the LTCC sensors and microsystems carried out in the Laboratory of Thick Film Microsystems at Wroclaw University of Technology are presented. LTCC microfluidic system is described in detail. Moreover, a short information is given on other LTCC applications .

Computation of realizations of discrete-time cone-systems

Abstract: A new notion of a realization of transfer matrix of (P,Q,V)-cone-system for discrete-time linear systems is proposed. Necessary and sufficient conditions for the existence of the realizations are established. A procedure is proposed for computation of a realization of a given proper transfer matrix T (z) of (P,Q,V)-cone-system. It is shown that there exists a realization of T (z) of (P,Q,V)-cone-system if and only if there exists a positive realization of T (z) = V T (z)Q−1, where V, Q and P are non-singular matrices generating the cones V,Q and P respectively.

Predictive direct power control of three-phase boost rectifier

Abstract: In this paper, a new control scheme of an active boost rectifier has been presented. Proposed power control method uses a discretetime model of the converter to predict future behaviour for all possible voltage vectors. The most effective vector is chosen for next sampling period by minimizing a cost function. Presented Predictive Direct Power Control (P-DPC) scheme has been compared with classical Switching Table based Direct Power Control (ST-DPC) method. Laboratory results shows that predictive control in relation to classical ST-DPC method works properly at low sampling frequency and owns better dynamic and steady state performance.

Assessment of direct torque control for induction motor drives

Abstract: Among all control methods for induction motor drives, Direct Torque Control (DTC) seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The DTC scheme is characterized by the absence of PI regulators, coordinate transformations, current regulators and PWM signals generators. In spite of its simplicity, DTC allows a good torque control in steady state and transient operating conditions to be obtained. However, the presence of hysteresis controllers for flux and torque could determine torque and current ripple and variable switching frequency operation for the voltage source inverter. This paper is aimed to analyze DTC principles, the strategies and the problems related to its implementation and the possible improvements.

Extended Kalman filters in the control structure of two-mass drive system

Abstract: The paper deals with the application of the extended Kalman filters in the control structure of a two-mass drive system. In the first step only linear extended Kalman filter was used for the estimation of mechanical state variables of the drive including load torque value. The estimation algorithm showed good robustness to mechanical parameters variations. For the system with some parameters changing in the wide range, simultaneous estimation of the state variables and chosen system parameters is required. For this reason the non-linear extended Kalman filter, which estimates simultaneously state variables and mechanical parameters of the two-mass drive system, was developed. Parameters of covariance matrices of used Kalman filters were set using the genetic algorithm. Both proposed estimators were investigated in simulation and experimental tests, in the open-loop operation and in the state-feedback control system of the two-mass system.

Linearization of non-linear state equation

Abstract: The paper presents an overview of linearization methods of the non-linear state equation. The linearization is developed from the point of view of the application in the theoretical electrotechnics. Some aspects of these considerations can be used in the control theory. In particular the main emphasis is laid on three methods of linearization, i.e.: Taylor’s series expansion, optimal linearization method and global linearization method. The theoretical investigations are illustrated using the non-linear circuit composed of a solar generator and a DC motor. Finally, the global linearization method is presented using several examples, i.e. the asynchronous slip-ring motor and non-linear diode. Furthermore the principal theorem concerning the BIBS stability (bounded-input bounded state) is introduced.

Crack system evaluation in concrete elements at mesoscale

Abstract: An automated method for crack identification and quantitative description of crack systems in concrete was developed in order to aid a service life assessment of concrete elements in structures. Flat polished specimens for crack analysis were impregnated with epoxy resin containing fluorescent dye. The examination of the crack system was performed in ultraviolet light using a stereomicroscope and an Image Pro Plus image analysis system on specimens cored out of several concrete structures. The laboratory tests were performed on cast specimens to establish correlations between water penetration and chloride diffusion and crack system parameters. The analysis of cracks in concrete cores taken from structures resulted in interesting conclusions based on the crack width distribution and crack localization with respect to steel reinforcement. The method was found very effective to support standard concrete diagnostics methods.

Wettability and interface considerations in advanced heat-resistant Ni-base composites

Abstract: Oxide fiber-reinforced Ni-base composites have long been considered as attractive heat-resistant materials. After several decades of active research, however, interest in these materials began to decline around mid-1990’s due chiefly to 1) a lack of manufacturing technology to grow inexpensive single-crystal oxide fibers to be used in structural composites, and 2) fiber strength loss during processing due to chemical interactions with reactive solutes in the matrix. The cost disadvantage has been mitigated to a large extent by the development of innovative fiber fabrication processes such as the Internal Crystallization Method (ICM) that produces monocrystalline oxide fibers in a cost-effective manner. Fiber strength loss has been an equally restrictive issue but recent work has shown that it may be possible to design creep-resistant composites even when fiber surface reconstruction from chemical interactions has degraded the strength of extracted fibers tested outside the matrix. The key issue is the optimization of the compositeand interface structure. Reaction-formed defects may be healed by the matrix (or a suitable coating material) so that the fiber residing in the matrix may exhibit diminished sensitivity to flaws as compared to fibers extracted from the matrix and tested in isolation of the matrix. Generally, the Ni-base/Al2O3 composites exhibit acceptable levels of wettability and interface strength (further improved with the aid of reactive solutes), which are required for elevated-temperature creep-resistance. In order to harness the full potential of these composites, the quality of the interface as manifested in the fiber/matrix wettability, interface composition, interphase morphology, and interface strength must be designed. We identify key issues related to the measurement of contact angle, interface strength, and chemical and structural properties at the fiber/matrix interface in the Ni/alumina composites, and present the current state-ofthe-art in understanding and designing the Ni/alumina interface. There should be no doubt that optimization of the interfaceand composite microstructure through judicious control of the fabrication process and surface modification shall yield technologically promising Ni-base/oxide fiber composites.

Evolutionary design and optimization of combinational digital circuits with respect to transistor count

Abstract: In the paper an application of evolutionary algorithm to design and optimization of combinational digital circuits with respect to transistor count is presented. Multiple layer chromosomes increasing the algorithm efficiency are introduced. Four combinational circuits with truth tables chosen from literature are designed using proposed method. Obtained results are in many cases better than those obtained using other methods.

Transresistance CMOS neuron for adaptive neural networks implemented in hardware

Abstract: A simple analog circuit is presented which can play a neuron role in static-model-based neural networks implemented in the form of an integrated circuit. Operating in a transresistance mode it is suited to cooperate with transconductance synapses. As a result, its input signal is a current which is a sum of currents coming from the synapses. Summation of the currents is realized in a node at the neuron input. The circuit has two outputs and provides a step function signal at one output and a linear function one at the other. Activation threshold of the step output can be conveniently controlled by means of a voltage. Having two outputs, the neuron is attractive to be used in networks taking advantage of fuzzy logic. It is built of only five MOS transistors, can operate with very low supply voltages, consumes a very low power when processing the input signals, and no power in the absence of input signals. Simulation as well as experimental results are shown to be in a good agreement with theoretical predictions. The presented results concern a 0.35 μm CMOS process and a prototype fabricated in the framework of Europractice.

Thermo-mechanical phenomena in the process of friction welding of corundum ceramics and aluminium

Abstract: In the paper the modelling of thermo-mechanical effects in the process of friction welding of corundum ceramics and aluminium is presented. The modelling is performed by means of finite element method. The corundum ceramics contains 97% of Al2O3. The mechanical and temperature fields are considered as coupled fields. Simulation of loading of the elements bonded with the heat flux from friction heat on the contact surface is also shown. The heat flux was modified in the consecutive time increments of numerical solutions by changeable pressure on contact surface. Time depending temperature distribution in the bonded elements is also determined. The temperature distribution on the periphery of the cylindrical surfaces of the ceramics and Al was compared to the temperature measurements done with a thermovision camera. The results of the simulation were compared to those obtained from the tests performed by means of a friction welding machine.

Nanocrystalline Cr/CrN and Ti/TiN multilayer coatings produced by pulsed laser deposition at room temperature

Abstract: Mechanical components and tools in modern industry are facing increasing performance requirements leading to the growing need for advanced materials and thus, for modern frictional systems. In the last decades, the Pulsed Laser Deposition (PLD) has emerged as an unique tool to grow high quality monoas well as multilayers surfaces in metallic/ceramic systems. Building up a knowledge base of tribological properties of industrially-scaled, room temperature deposited PLD hard coatings are the most important step for the application of these coatings in engineering design. Although single-layer coatings find a range of applications, there are an increasing number of applications where the properties of a single material are not sufficient. One way to surmount this problem is to use a multilayer coating. Application of metallic interlayers improves adhesion of nitride hard layer in multilayer systems, which has been used in PVD processes for many years, however, the PLD technique gives new possibilities to produce system comprising many bilayers at room temperature. Tribological coatings consisted of 2, 4 and 16 bilayers of Cr/CrN and Ti/TiN type were fabricated with the Pulsed Laser Deposition (PLD) technique in the presented work. It is found in transmission electron examinations on thin foils prepared from cross-section that both nitride-based multilayer structures studied are characterized by small columnar crystallite sizes and high defect density, what might rise their hardness but compromise coating adhesion. The intermediate metallic layers contained larger sized and less defective columnar structure compared to the nitride layers, which should improve the coatings toughness. Switching from single layer to multi-layer metal/nitride composition improved resistance to delamination.

Biocompatibile TiN-based novel nanocrystalline films

Abstract: Titanium nitride (TiN) is regarded as a potential biomaterial for blood-contact applications. TiN thin films were fabricated by pulsed laser deposition with the Nd:YAG laser on biologically applied polyurethane. Transmission electron microscopy (TEM) study of 250 nm thick films revealed columnar structure. Such films were observed to be brittle, which led to crack formation and secondary nucleation of microcolumn. TEM studies showed a kinetic mechanism of growth (columnar) in films of 250 nm thickness. It was stated that thinner films were much smoother and uniform than the thicker ones, which could be associated with the surface diffusion mechanism to appear. In order to improve the coatings elasticity, the thickness was reduced to 50 nm, which limited the deposition mechanism operation to the early stage. TEM cross-section observation revealed elastic properties of thin films. A biological test showed that TiN surface film produced on polyurethane is characterized by good biocompatibility and decreased surface affinity for cell adhesion. Films of 0.25 and 0.5 μm thick of TiN were selected for theoretical finite element modelling (FEM) using ADINA program. The micro cracks formation predicted in simulation was verified by phenomena observed in microstructure examinations.

Formal approach to modelling a multiversion data warehouse

Abstract: A data warehouse (DW) is a large centralized database that stores data integrated from multiple, usually heterogeneous external data sources (EDSs). DW content is processed by so called On-Line Analytical Processing applications, that analyze business trends, discover anomalies and hidden dependencies between data. These applications are part of decision support systems. EDSs constantly change their content and often change their structures. These changes have to be propagated into a DW, causing its evolution. The propagation of content changes is implemented by means of materialized views. Whereas the propagation of structural changes is mainly based on temporal extensions and schema evolution, that limits the application of these techniques. Our approach to handling the evolution of a DW is based on schema and data versioning. This mechanism is the core of, so called, a multiversion data warehouse. A multiversion DW is composed of the set of its versions. A single DW version is in turn composed of a schema version and the set of data described by this schema version. Every DW version stores a DW state which is valid within a certain time period. In this paper we present: (1) a formal model of a multiversion data warehouse, (2) the set of operators with their formal semantics that support a DW evolution, (3) the impact analysis of the operators on DW data and user analytical queries. The presented formal model was a basis for implementing a multiversion DW prototype system.

A new method for identification of RTS noise

Abstract: In the paper a new method, called the Noise Scattering Pattern (NSP) method, for RTS noise identyfication in a noise signal is presented. Examples of patterns of the NSP method are included.

Direct torque control of doubly fed induction machine

Abstract: This paper presents novel bi-converter structure to supply the Doubly Fed Induction Machine (DFIM). Two Voltage Source Inverters (VSI) feed the stator and rotor windings. The outputs of two VSI are combined electro-mechanically in the machine and, as a result, novel features can be obtained. For example, for high power drive applications, this configuration use two inverters dimensioned for a half of the DFIM power. A new Dual-Direct Torque Control scheme is developed with flux model of DFIM. Two Switching Tables (ST) linked to VSI are defined for stator and rotor flux vector control. Experimental and simulation results confirm good dynamic behaviour in the four quadrants of the speed-torque plane. Moreover, experimental results show the correct flux vector control behaviour and speed tracking performances.

Modern micropassives: fabrication and electrical properties

Abstract: This paper presents the concept and modern technological approach to the fabrication of discrete, integrated and integral micropassives. The role of these components in modern electronic circuits is discussed too. The material, technological and constructional solutions and their relation with electrical and stability properties are analyzed in details for linear and nonlinear microresistors made and characterized at the Faculty of Microsystem Technology, Wroclaw University of Technology.

FSMs state encoding targeting at logic level minimization

Abstract: The paper concerns the problem of state assignment for finite state machines (FSM), targeting at PAL-based CPLDs implementations. Presented in the paper approach is dedicated to state encoding of fast automata. The main idea is to determine the number of logic levels of the transition function before the state encoding process, and keep the constraints during the process. The number of implicants of every single transition function must be known while assigning states, so elements of two level minimization based on Primary and Secondary Merging Conditions are implemented in the algorithm. The method is based on code length extraction if necessary. In one of the most basic stages of the logic synthesis of sequential devices, the elements referring to constraints of PAL-based CPLDs are taken into account.

Distribution of potential barrier height local values at Al-SiO2 and Si-SiO2 inter-faces of the metal-oxide-semiconductor structures

Abstract: Using the photoelectric measurement methods distributions have been determined of the gatedielectric EBG(x, y) and semiconductor-dielectric EBS(x, y) barrier height values in square gate (1 x 1 mm) Al-SiO2-Si(n) structures. Measurements have been made on a series of 26 MOS capacitors with semitransparent gates (tAl = 35 nm), on one silicon wafer. Barrier heights were measured using the modified Powell-Berglund and the modified Fowler methods. Measurement methods were modified in such a way as to allow determination of EBG(x, y) and EBS(x, y) distributions, as described in the text. It has been found that the EBG(x, y) distribution has a characteristic dome-like shape which is identical with the independently determined shape of the effective contact potential difference φMS(x, y) distribution. The EBS(x, y) distribution is of a random character and differences between highest and lowest values of EBS for any of the measured capacitors are much smaller than the respective differences in EBG values. These results show that it is the gate-dielectric barrier height distribution EBG(x, y) which causes the dome-like shape of the φMS(x, y) distribution, observed for several years in our laboratory. This finding supports our hypothesis that the characteristic φMS(x, y) distribution over the gate area of Al-SiO2-Si structures results from the mechanical stress distribution under the gate electrode.

Predictive torque and flux control for the synchronous reluctance machine

Abstract: This paper presents a predictive torque and flux control algorithm for the synchronous reluctance machine. The algorithm performs a voltage space phasor pre-selection, followed by the computation of the switching instants for the optimum switching space phasors, with the advantages of inherently constant switching frequency and time equidistant implementation on a DSP based system. The criteria used to choose the appropriate voltage space phasor depend on the state of the machine and the deviations of torque and flux at the end of the cycle. The model of the machine has been developed on a d-q frame of coordinates attached to the rotor and takes into account the magnetic saturation in both d-q axes and the cross saturation phenomenon between both axes. Therefore, a very good approximation of this effect is achieved and the performance of the machine is improved. Several simulations and experimental results using a DSP and a commercially available machine show the validity of the proposed control scheme.

On temperature distributions in a semi-infinite periodically stratified layer

Abstract: The paper presents some problems of heat conduction in a semi-infinite periodically stratified layer. The layer is subjected to acting a constant temperature on the part of boundary, normal to the layering. The free heat exchange with surroundings is assumed on the remaining part of the boundary. The composite layer is supposed to be composed of n periodically repeated two-component lamina. The problem is solved in two ways: (1) directly as a heat conduction problem, ( 2) by using model with microlocal parameters [1,2]. The main aim of the paper is a comparison of the obtained results and to conclude possibilities of applications of the homogenized model with microlocal parameters.

Wow defect reduction based on interpolation techniques

Abstract: In this paper the capacity of non-uniform sampling rate conversion techniques, involving different interpolation methods, aimed at wow defect reduction, is examined. Involved are: linear interpolation, four polynomial-based interpolation methods and the windowed sincbased method. The examined polynomial methods are: Lagrange interpolation, polynomial fitting with additional noise reduction, Hermitan and Spline. The performance of an artificially distorted audio signal, restored using non-uniform resampling, is evaluated on the basis of standard audio defect measurement criteria and compared for all of the aforementioned interpolation methods. The chosen defect descriptors are: total harmonic distortion, total harmonic distortion plus noise and signal to noise ratio.

Energy flow control system based on neural compensator in the feedback path for autonomous energy source

Abstract: In this paper an artificial neural network, which realizes a nonlinear adaptive control algorithm, has been applied in a control system of variable speed generating system. The speed is adjusted automatically as a function of load power demand. The controller employs a single layer neural network to estimate the unknown plant nonlinearities online. Optimization of the controller is difficult because the plant is nonlinear and no stationary. Furthermore, it deals with the situation where the plant becomes uncontrollable without any restrictive assumptions. In contrast to previous work [1] on the same subject, the number of neural networks has been reduced to only one network. The number of the neurons in a network structure as well as choosing certain design parameters was specified a priori. The computer test results have been presented to show performance of proposed neural controller.

Efficient algorithm for designing multipurpose control systems for invertible and right-invertible MIMO LTI plants

Abstract: In the paper an approach to design of multipurpose control systems is considered. It is presented an universal and efficient algorithm for synthesis of multipurpose control system for proper, invertible and right-invertible multi-input multi-output dynamic (MIMO) plants which can be both unstable and/or non-minimumphase. The developed control systems feature both dynamic (either block or row-by-row) decoupling and arbitrary closed-loop pole placement and zero steady-state errors for regulation or tracking processes in presence of (non-diminishing) disturbances.

Stochastic dynamics and reliability of degrading systems

Abstract: In this paper the basic methodology of the coupled response-degradation modelling of stochastic dynamical systems is presented along with the effective analysis of selected problems. First, the general formulation of the problems of stochastic dynamics coupled with the evolution of deterioration process is given. Then some specific degrading oscillatory systems under random excitation are analyzed with a special attention on the systems with fatigue-induced stiffness degradation. Both, the general discussion and the analysis of selected exemplary problems indicate how the reliability of deteriorating stochastic dynamical systems can be assessed.

A study on liquefaction susceptibility of some soils from the coast of Marmara sea

Abstract: The paper presents an estimation of liquefaction susceptibility of some soils from the coast of the Marmara Sea, which was heavily striken by the Kocaeli earthquake in 1999. Firstly, the results of field investigations are summarized. Then, the results of laboratory investigations of physical and mechanical properties of the soils collated from the sites investigated are presented. The mechanical properties relate to the compaction/liquefaction model of saturated soils. This model is briefly outlined, then respective experimental procedures dealing with its calibration described, and values of material parameters listed. Liquefaction potential of investigated soils is analysed using standard procedures, based on the grain size distribution curves and SPTs. Finally, the simulation of pore-pressure generation and onset of liquefaction of Turkish soils is carried out, using the compaction/liquefaction model. Discussion of some standard empirical procedures of estimation of liquefaction potential of saturated soils, conducted from the analytical point of view, is also presented.

Modelling of nanoindentation to simulate thin layer behaviour

Abstract: The work presents a computer simulation realized with the ADINA program concerning nanoindendation test. A shape of nanoindenter was proposed to be similar to the real surgical tools. The theoretical model was used to predict phenomena which would appear in practice. The contribution of the TiN coating thickness to the implant rigid properties was simulated. Three types of extortion conditions could be considered, i.e., short contact with surgery tool (i); long continuous contact with natural tissue (ii); long cyclic contact with natural tissue (iii). In the first part of the work, the authors focused on the first type of extortion (i). The second part of the work is dedicated to the calculations of temperature impact to layer behaviour. Two layer thicknesses are considered i.e., 250 nm and 50 nm. The examined coatings find serious practical applications as a blood-contacting material in medicine. The coatings were subjected to transmission electron microscopy investigations. Columnar mechanism of film growth controlled by kinetic process is stated to operate for the considered range of layer thickness. Plasma temperature is observed to influence the substrate behaviour. Examinations of thinner layers, i.e. under 100nm, revealed higher degree of smoothness and uniformity, which could be related to the operation of the surface diffusion mechanism at the early stage of deposition. The physical explanation of TEM images was based on the finite element calculations of the temperature distribution using the ADINA program .

Analysis of dynamic loads on lightweight footbridge caused by lorry passing underneath

Abstract: W artykule przedstawiono analize drgan lekkiej kladki dla pieszych wywolanych przejazdem ciezarowki z duzą predkością pod spodem konstrukcji.