Volume 66 (2015): Issue 3 (May 2015)

This paper presents a Variable Structure Sliding Mode Control (VS-SMC) scheme and Direct Torque Control (DTC) for Wind Farm (WF) based on the Permanent Magnet Synchronous Generator (PMSG). The WF consists of a 3 PMSGs which are connected to a common dc bus system with rectifier. The dc-bus is connected to the electrical network using only one inverter system, a grid-side filter as well as the transformer. The efficiency of the WF can be greatly improved using an appropriate control approach. So, the control strategy uses the technique of DTC to regulate the speeds of PMSGs for Maximum Power Point Tracking (MPPT) mode. Besides, by employing VS-SMC the grid-side inverter is controlled to inject the generated power into the electrical network, to regulate DC-link voltage and to achieve Unity Power Factor. The used control strategies provide an optimal control solution for WF systems based on the PMSG.

This manuscript proposes an extension to the water flow algorithm for text line segmentation. Basic algorithm assumes hypothetical water flows under few specified angles of the document image frame from left to right and vice versa. As a result, unwetted image regions that incorporate text are extracted. These regions are of the major importance for text line segmentation. The extension of the basic algorithm means modification of water flow function that creates the unwetted region. Hence, the linear water flow function used in the basic algorithm is changed with its power function counterpart. Extended method was tested, examined and evaluated under different text samples. Results are encouraging due to improving text line segmentation which is a key process stage.

Visual information is very important in human communication. It is used in any type of sign language communication, and in non-verbal communication of the entire population, as well. Therefore, visual information is crucial for communication of hearing impaired people. Video is the most common way to capture this type of information and it is very important to correctly process it. In this paper we propose a method for finding video frames representing single sign in the finger alphabet. The single sign is identified using standard video quality metrics. The calculations of the metrics are performed only within a region, which is determined by combination of object tracking and salient regions detection method based on human visual attention. For key frame selection, combination of sliding system for finding local extreme and adaptive threshold based on local averaging and variation is used. Proposed method is effective and achieves significantly better results in comparison with other commonly used methods.

This paper proposed an auto-configurable algorithm for wireless sensor network (WSN) to efficiently re-organize the network topology. The auto-configurable algorithm is based on self- configurable cellular architecture and it has been observed from simulation result that the proposed algorithm achieves lower power consumption than the existing one.

Non contiguous orthogonal frequency division multiplexing (NC-OFDM) is an efficient and adaptable multicarrier modulation scheme to be used in cognitive radio communications. However like OFDM, NC-OFDM also suffers from the main drawback of high peak to average power ratio (PAPR). In this paper PAPR has been reduced by employing three different trigonometric transforms. Discrete cosine transform (DCT), discrete sine transform (DST) and fractional fourier transform (FRFT) has been combined with conventional selected level mapping (SLM) technique to reduce the PAPR of both OFDM and NC-OFDM based systems. The method combines all the transforms with SLM in different ways. Transforms DCT, DST and FRFT have been applied before the SLM block or inside the SLM block before IFFT. Simulation results show the comparative analysis of all the transforms using SLM in case of both OFDM and NC-OFDM based systems.

In this work, we improved Correlation Power Analysis (CPA) attack against Digital Signature Algorithm (DSA) and its various derivations, such as Elliptic Curve Digital Signature Algorithm (ECDSA). The attack is aimed against integer multiplication with constant secret operand. We demonstrate this improvement on 16-bit integer multiplier in FPGA. The improvement makes it possible to guess more blocks of key, and the improvement also eliminates errors of simulated attacks what is very important when approximating attack success rate and complexity based on simulated attacks. We also discus a possible efficient countermeasure.

The ionospheric observatory Pruhonice serves to monitor the state of ionosphere using ground-based vertical sounding instrument - the Digisonde DPS-4D. Measured ionograms are automatically evaluated (scaled) and basic characteristics are derived. The ionograms and the scaled parameters are sent to the international databases. Especially during disturbed conditions the automatic scaling could give unreliable results. This paper presents simple method how to detect accidental errors in automatic scaling based on the parameters derived from ionograms and on an application of the finite impulse response filters.

Speaker recognition is the process of automatically recognizing who is speaking on the basis of speaker specific characteristics included in the speech signal. These speaker specific characteristics are called features. Over the past decades, extensive research has been carried out on various possible speech signal features obtained from signal in time or frequency domain. The objective of this paper is to introduce two-dimensional information entropy as a new text-independent speaker recognition feature. Computations are performed in time domain with real numbers exclusively. Experimental results show that the two-dimensional information entropy is a speaker specific characteristic, useful for speaker recognition.

This article deals with non-destructive testing of conductive materials by eddy current method based on swept frequency. A 2D numerical model of eddy current air-core probe was created in the LTspice software at first. The probe consists of two coils: exciting coil and receiving. The probe is positioned in air in this case. Experimental and calculated frequency responses of the probe are obtained within a wide frequency range using swept frequency in order to validate the model. Frther a 3D model used for non-destructive testing of austenitic steel plate with three electro-discharge machined notches is then developed accordingly. Results of measurement are compared with 3D numerical model using COMSOL Multiphysics software.

This article offers useful algorithms for estimating the parameters of the Gaussian curve fitted to observed data, gained in testing of sensors. Fitting was realized using two algorithms Caruanas and Guos, which have been compared.

Error control codes (ECC) as well as translation codes (TC) are used today in many different systems such as computer storages, communications systems and consumer electronic devices. ECC introduce redundancy into the encoded digital sequence in order to decrease the number of errors at output of its decoder [1]. TC introduce redundancy, in order to translate any digital sequence at the input of TC encoder to such output sequence, which fulfills constrains deduced from practical requirements. It is possible to construct codes, which have both of these properties, so called Transcontrol codes or their subclass error control run length limited (ECRLL) codes. In this manuscript a new approach to construction of EC-RLL codes is presented. The new construction is based on some parity check matrix properties of a linear binary block code from which the new EC-RLL code is obtained.