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This paper describes a new procedure for design of complementary IIR digital filters based on group delay approximation. The filters are realized as parallel sum of two all-pass filters, a structure for which low complexity implementations exist. The problem with phase warping which is inevitable if filter design is made through phase approximation will be solved using a proposed method. Adequate initial solution is also proposed. Realized amplitude characteristics of complementary filters will be approximately equiripple. The design examples illustrate that the proposed algorithm is very efficient in terms of computation time and number of iterations.

New IIR multiple-notch filters design methods, whose utilization lead to complete satisfaction of specifications regarding positions of notch frequencies and notch-bandwidths defined for an arbitrary attenuation value at cutoff frequencies, are investigated in this thesis. Most of the proposed design methods offer the possibility of further pass-bands magnitude response improvement by increasing the order of the filter. On the other hand, since proposed design methods are based on the assumption that IIR multiple-notch filter with desired magnitude response can be obtained by parallel connection of the delay line and the stable allpass filter, pass-bands magnitude response improvement is followed by the improvement of linearity of the pass-bands phase response. Comparison with the existing IIR multiple-notch filter design methods showed that proposed design methods could result in shorter duration of transient response to sum of sinusoidal interferences, as well as in improvement of pass-bands phase response. Sensitivity of the IIR multiple-notch filter’s magnitude response to coefficient quantization is considered from the point of view of the right choice of existing (standard) and development of the new realization structures. Algorithm for determination of the multipliers coefficients’ quantized values such that needed number of bits for theirs representation is minimized, as well as the algorithm for determination of the optimal representations of the all-pass filter transfer function (characterizing the IIR multiplenotch filter), realized by cascade connection of the first- and second-order nonstandard all-pass sections, are proposed. Efficiency of the proposed algorithms is verified through several examples. General conclusion is that significant reduction in total number of bits needed for representation of multipliers coefficients can be achieved if nonstandard realization structures are used.

The dissertation presents the design, development and realization of two novel structures of high-power composite ultrasonic transducers. The proposed composite transducers as a novelty contain a central metal mass, so instead of the classical structure of the Langevin’s transducer (back mass - active piezoceramic block - front mass) the following structure is obtained: back mass - active piezoceramic block - central mass - active piezoceramic block - front mass. Active blocks contain one or more pairs of piezoceramic rings, which are mechanically connected in series and have opposite polarized orientations. The difference between the proposed structures is that in the first structure, the central mass is connected to the metal endings with two central bolts, while in the second structure the prestressing is achieved with a single central bolt, which connects only metal endings and is not in contact with the central mass. With the proposed composite transducer without the direct contact between the central mass and the bolt, problems related to impedance adjustment with a mechanical load can be avoided. The proposed structures also increase the total output ultrasonic power of the transducers. If the mechanical load is connected via an acoustic transmission line, composite transducers can produce thickness, radial, flexion, edge, torsion and other vibration modes in the working environment. In order to model the proposed composite transducers, one-dimensional models and approximate three-dimensional matrix models are developed. Firstly, general one-dimensional models, which include all the constituent parts of the transducers, have been developed. Also, a one-dimensional model, which does not include impact of the central bolt, has been developed. A one-dimensional model, which neglects the central bolt impact, is, according to its structure, suitable for simultaneous operation analysis of both proposed composite ultrasonic transducers. Due to the complexity of the proposed structures, the three-dimensional matrix electromechanical models of complete composite transducers were developed using modular solutions of the three-dimensional model of piezoceramic rings and the three-dimensional model of passive metal endings. The advantage of the newly developed three-dimensional models of the transducers is reflected in the possibility of predicting the thickness and radial oscillation modes, as well as their mutual couplings. With a minor modification of the three-dimensional models it is possible to determine any transfer function of the observed composite transducer. In the dissertation, in addition to the analysis of the basic thickness resonant mode, special emphasis is devoted to the shape and position of higher resonant modes, as well as to the impact of various parameters on their characteristics. By comparing the experimental measurements of the input electrical impedance, of the realized novel composite transducers, and the corresponding Matlab/Simulink simulation results, the accuracy of the proposed three-dimensional models compared to the one-dimensional models was confirmed.

n this dissertation, the analysis, development and experimental verification of new current mode control methods of power electronics converters is performed, in order to obtain improved performances compared to other relevant current mode control methods. New proposed current mode control methods have been developed by modification and improvement of the conventional dual current mode control (DCMC) method, which besides its excellent features, such as constant switching frequency, simple implementation and stability for the entire range of duty cycle, has a main drawback, and that is a current error – a difference between the average and reference inductor current. Two ways for eliminating the current error of DCMC method are proposed in this dissertation: using an adaptive current bandwidth, which is equal to the measured instantaneous peak-to-peak ripple of the inductor current, resulting in a new adaptive dual current mode control (ADCMC) method; inserting an inner current-loop compensator (application of I2 concept) in the DCMC structure, which leads to a new I2 DCMC method. By using the I2 concept on ADCMC, a new I2 ADCMC method is also derived. After mathematical analysis and modelling, the operation of the proposed current mode control methods, applied on three basic DCDC converters: buck, boost and non-inverting buck-boost converter, was tested with simulations in Matlab/Simulink. Afterwards, development and realization of the experimental platform (multipurpose converter’s prototype, control and measurement electronic module), which is used for experimental verification of the proposed control methods on different types of converters, were performed. The obtained simulation and experimental results confirmed the excellent performances of the proposed current mode control methods: equality between the average and reference inductor current, stability for whole range of duty cycle, excellent dynamics of the current loop, robustness to the input voltage and load disturbances of converters, etc. Thanks to these qualities, the proposed control methods can be applied to practically all types of converters. Some new ideas for further improvements of the proposed control methods and for their implementation in specific applications of existing and some future converters topologies are also presented in this dissertation.

This PhD discusses the research related to the approximation and implementation of the twochannel hybrid filter banks. Special attention is paid to the analogue part, i.e. analysis part of the hybrid filter banks. Two approximations of the filter bank pair for analysis have been proposed. The first approximation of the transfer function of the low-pass filter is based on the simple adaptation of the orthogonal Jacobi polynomials in order to obtain the Pseudo-Jacobian polynomials. In relation to other known approximations, the Pseudo-Jacobian polynomial one has two prime parameters, which can adjust the characteristics of the filter in wide ranges. This approximation can be successfully applied for the realization of a complementary bank of filters. It is known that recursive double-complementary digital filter banks can be implemented with all-pass filters, and research has shown that double-complementary filter banks can also be realized in the analogue domain. The realization of the proposed filter bank has been done in two steps. In the first step, with the complementary decomposition, the prototype transfer function is obtained by two all-pass filters, while in the second step, by their addition or subtraction, transfer functions of lowpass and highpass filters are obtained. The advantage of such a system is that the same hardware can be used for realization of both low frequency and high frequency transfer functions. Monte Carlo simulation of the realization of a double complementary analog filter pair based on a parallel connection of two analogue all-pass filters showed that all-pass realization is characterized by a small sensitivity of the attenuation characteristics to the component tolerances in the filter pass-band, while the sensitivity in the stop-band is substantially higher compared to the case of a standard cascade realization of the low-pass filter and the high-pass filter. By a suitable selection of the analysis filter bank and the synthesis filter bank, a condition for suppressing the effects arising from the overlapping of the spectrum in banks for analysis and synthesis can be fulfilled. The all-pass complementarity of an analogue filter bank points to the fact that amplitude distortion, which is introduced by the analog bank of the analysis filters, can be completely suppressed, so that the non-linearity of the group delay characteristics is the predominant distortion. In order to achieve a near perfect reconstruction of the signal, a new realization of the group delay corrector was proposed, which makes it possible for the group delay to be constant in a flat sense, i.e. with a number of flatness at the origin. An analysis of the sensitivity has shown that the sensitivity of the correction of the group waveform in the filter pass-band that is proportional to the square of the Q -factor of the pole. In other words, the group delay corrector is very sensitive to the component tolerances.

This thesis investigates possibilities for fusion, i.e. combining of different types of image descriptors, in order to improve accuracy and efficiency of image classification. Broad range of techniques for fusion of color and texture descriptors were analyzed, belonging to two approaches – early fusion and late fusion. Early fusion approach combines descriptors during the extraction phase, while late fusion is based on combining of classification results of independent classifiers. An efficient algorithm for extraction of a compact image descriptor based on early fusion of texture and color information, is proposed in the thesis. Experimental evaluation of the algorithm demonstrated a good compromise between efficiency and accuracy of classification results. Research on the late fusion approach was focused on artificial neural networks and a recently introduced algorithm for extremly fast training of neural networks denoted as Extreme Learning Machines - ELM. Main disadvantages of ELM are insufficient stability and limited accuracy of results. To overcome these problems, a technique for combining results of multiple ELM-s into a single classifier is proposed, based on probability sum rules. The created ensemble of ELM-s has demonstrated significiant improvement of accuracy and stability of results, compared with an individual ELM. In order to additionaly improve classification accuracy, a novel hierarchical method for late fusion of multiple complementary descriptors by using ELM classifiers, is proposed in the thesis. In the first phase of the proposed method, a separate ensemble of ELM classifiers is trained for every single descriptor. In the second phase, an additional ELM-based classifier is introduced to learn the optimal combination of descriptors for every category. This approach enables a system to choose those descriptors which are the most representative for every category. Comparative evaluation over several benchmark datasets, has demonstrated highly accurate classification results, comparable to the state-of-the-art methods.

Temperature increase of photovoltaic cells above 25 C, causes a decrease in its output power. That is why it is absolutely necessary to measure this temperature accurately. Unfortunately, there are no many materials dealing with this problem in the existing literature. The main goal of this doctoral dissertation is increase of temperature measurement accuracy of photovoltaic modules.

In this PhD thesis two-channel QMF IIR filter banks have been discussed. As a part of this research, direct synthesis of a new IIR filter class, as a lowpass protoype function which satisfies condition for complementary decomposition, has been proposed. Since attenuation characteristic of the new filter class lies in the area between the Butterworth’s and the Elliptic’s attenuation characteristics of the same order, new class has been referred to as Transitional Butter-Elliptic filters. Transfer function of the the lowpass prototype function was separated into two allpass filters by complementary decomposition. Then, lowpass and highpass filters, as power symmetric filter pair, are obtained using those allpass filters. The main advantage of complementary IIR filters based on parallel connection of two allpass filters, is its smaller sensitivity to digital word length change compared to standard filters and low-cost implementation since the same hardware is used for the lowpass and the highpass transfer function. Within the analysis of the new filter class, transfer functions of the odd order with one, two, three and four extremal values of attenuation characteristics in the passband and in the stopband, has been discussed. All types of Transitional filters have been compared with the Butterworth’s and the Elliptic’s filters of the same order. It is shown that in comparison with Butterworth filter, the Transitional filter has better selectivity but lower selectivity than Elliptic filter. However, the proposed new filter class has pure imaginary poles and accuracy in complementary decomposition is at very high level, which the Elliptic filter cannot achieve. Also, the practical realization of the new filter class is easier than for the Elliptic filter since the new class has conjugate-complex zeros on the unit circle and one multiple zero at z = −1. Further, poles and zeros of the Elliptic filter are accumulated near the passband edge and the distance between them decreases as the filter order increases. This requires a very long digital word length for high-order filter realization. The new class filter has approximately equidistant arrangement of poles so it can be realized with shorter digital word length than it is required for the Elliptic filter realization. For Transitional filters class with one extremum of multiplicity L in the passband and in the stopband, closed-form expression for the transfer function coefficients has been obtained. Application of these kind of filters is significant since for sample rate conversion the lowestcomplexity filter is required. With appropriate selection of filters in analysis and synthesis section, the conditions for ii removing the aliasing effects are fulfilled. Magnitude distortions in IIR filter bank can also be completely eliminated and therefore output signal of the QMF bank has only phase distortion. In order to obtain nearly perfect reconstruction of the output signal, the allpass equalizer has been proposed for group delay compensation. Also, effect of the equalizer order on the accuracy of signal reconstruction has been analyzed.

Lack of universal approach for transforming analog filter prototypes into digital domain opens a possibility for further research in the field thus enabling both, improving existing and deriving novel methods. In the dissertation, a novel method in a form of transformation function for mapping complex angular frequency s into z domain will be covered. Digital counterparts of analog filters based on a special class of filters exhibiting critical monotonic pass-band amplitude characteristic will be presented for the first time. Complete procedure for designing IIR filters based on this class of filters will be implemented as a software solution. Phase-Invariance Method will be exploited for designing linear phase IIR filters. Hardware realization of the filters will be considered. The practical part of the thesis is devoted to IIR filter design in a form of (very large-scale integration) integrated circuit exploiting standard cells. Representative examples of IIR filter designs are realized up to the fabrication masks level (layout). Power consumption estimations based on layout parasitic elements are given as well.