Volume 68 (2017): Issue 5 (September 2017)

Evaluation of seismic signals is one of the most important research topics on Volcanology. Volcanoes have daily activity; therefore, high speed evaluation of recorded signals is a challenge for improving the study of the natural phenomena occurring inside these natural formations. The aim of this paper is the evaluation (denoising, localization and classification) and analysis of Llaima volcano activities, one of the most actives volcanoes in South America. Different already proposed methods, such as, Butterworth, Spectral Subtraction (SS) and Wiener Filter (WF) are compared to the proposed Modified Spectral Subtraction (MSS) and Modified Wiener Filter (MWF) to find the best method for denoising the volcano signals. Then, event localization based on received signals of volcano is performed. In this step, Time Delay Estimation (TDE)-based method is used on data acquired from 3 mechanical sensors located in the volcano area. The proposed method is used to estimate the area for event location. The proposed denoising methods make the starting point for the event more evident to increase the localization accuracy for events where the starting point is difficult to find. In the last step, a method based on the novel DNN technique is proposed to classify the three main events occurring in the Llaima volcano (TR (Tremor), LP (Long Period) and VT (Volcano Tectonic)).

Paper analyzes the influence of various design parameters on torque of permanently split capacitor motor. Motor analytical model is derived and it is used for calculating the performance characteristics of basic motor model. The acquired analytical model is applied in optimization software that uses genetic algorithms (GA) as an optimization method. Optimized motor model with increased torque is derived by varying three motor parameters in GA program: winding turns ratio, average air gap flux density and motor stack length. Increase of torque has been achieved for nominal operation but also at motor starting. Accuracy of the derived models is verified by Simulink. The acquired values of several motor parameters from transient characteristics of Simulink models are compared with the corresponding values obtained from analytical models of both motors, basic and optimized. Numerical analysis, based on finite element method (FEM), is also performed for both motor models. As a result of the FEM analysis, magnetic flux density in motor cross-section is calculated and adequate conclusions are derived in relation to core saturation and air gap flux density in both motor models.

A unique approach to the design of gain scheduled controller (GSC) is presented. The proposed design procedure is based on the Bellman-Lyapunov equation, guaranteed cost and robust stability conditions using the parameter dependent quadratic stability approach. The obtained feasible design procedures for robust GSC design are in the form of BMI with guaranteed convex stability conditions. The obtained design results and their properties are illustrated in the simultaneously design of controllers for simple model (6-order) turbogenerator. The results of the obtained design procedure are a PI automatic voltage regulator (AVR) for synchronous generator, a PI governor controller and a power system stabilizer for excitation system.

The process of power transmission lines, from source to load is a well-known, if the voltages and currents vary harmonically. With the lines is transmitted active power that is dissipated in load (this power exits from the system) and reactive power (this power oscillates between the source and the load). Note that it would be more appropriate designation the external power and the internal power. Such systems are known as cyclo-dissipative. The active power is dissipated in the load and the reactive power oscillates between the source and the load. Physically, reactive power is delivered to reactive elements of load. Transmitting reactive power increases Joule’s losses and voltage drops on lines. Reactive power can be compensated in a known manner. Compensation reduces the effective value of the current in the line. To the case of periodic but non-sinusoidal voltages and currents has been devoted many publications, conferences, etc. during the past 100 years. But despite much e ort, this problem has not yet been fully solved. In the present article, we show that in a system with a harmonic source of voltage even in the case of a linear pure resistive load a reactive power can be generated and can be compensated. A necessary, but not sufficient, condition is that the resistive load is time-varying. The presented study deals with a periodically sampled resistive load.

This article is focused on the analysis of the use of distributed fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load. The authors focused on the measurements of deformation utilizing Brillouin Time Domain Reflectometry (BOTDR). The principle is based on the measurement of stimulated Brillouin scattering. The article describes and analyses real measurements within a period of 5 months, which were carried out during the tunnelling and the whole process of building a new tunnel in Žilina, Slovakia. The performed experimental measurements were carried out using a standard optic telecommunication cable with water-absorbing aramid yarns and a jacket with a diameter of 4.2 mm. The contribution of this article lies in the introductory analysis of the implementation and use of the fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load.

We report an improvement of the artificial neural network (ANN) modelling of a piezoelectric actuator vibration based on the experimental data. The controlled vibrations of an actuator were obtained by utilizing the swept-sine signal excitation. The peak value in the displacement signal response was measured by a laser displacement sensor. The piezoelectric actuator was modelled in both linear and nonlinear operating range. A consistency from 90.3 up to 98.9% of ANN modelled output values and experimental ones was reached. The obtained results clearly demonstrate exact linear relationship between the ANN model and experimental values.

The normal life of a transformer is well above 25 years. The economical operation of the distribution system has its roots in the equipments being used. The economy being such, that it is financially advantageous to replace transformers with more than 15 years of service in the second perennial market. Testing of transformer is required, as its an indication of the extent to which a transformer can comply with the customers specified requirements and the respective standards (IEC 60076-3). In this paper, induced over voltage testing on transformers using enhanced Z source inverter is discussed. Power electronic circuits are now essential for a whole array of industrial electronic products. The bulky motor generator set, which is used to generate the required frequency to conduct the induced over voltage testing of transformers is nowadays replaced by static frequency converter. First conventional Z-source inverter, and second an enhanced Z source inverter is being used to generate the required voltage and frequency to test the transformer for induced over voltage test, and its characteristics is analysed.

The magnetic Barkhausen noise (MBN) measurement method is a widely used non-destructive evaluation technique used for inspection of ferromagnetic materials. Besides other influences, the excitation yoke lift-off is a significant issue of this method deteriorating the measurement accuracy. In this paper, the lift-off effect is analysed mainly on grain oriented Fe-3%Si steel subjected to various heat treatment conditions. Based on investigation of relationship between the amplitude distribution of MBN and lift-off, an approach to suppress the lift-off effect is proposed. Proposed approach utilizes the digital feedback optimising the measurement based on the amplitude distribution of MBN. The results demonstrated that the approach can highly suppress the lift-off effect up to 2 mm.

A fast and reliable current control is often the base of power electronic converters. The traditional constant frequency peak control is unstable above 50 % duty ratio. In contrast, the constant off-time peak current control (COTCC) is unconditionally stable and fast, so it is worth analyzing it. Another feature of the COTCC is that one can combine a current control together with a current protection. The time dynamics show a zero-transient response, even when the inductor changes in a wide range. It can also be modeled as a special transfer function for all frequencies. The article shows also that it can be implemented in a simple analog circuit using a wide temperature range IC, such as the LM2903, which is compatible with PV conversion and automotive temperature range. Experiments are done using a 3 kW step-up converter. A drawback is still that the principle does not easily fit in usual digital controllers up to now.

A new approach to estimation of unknown material parameters and boundary conditions of physical models was developed. The approach is based on processing measured data by advanced optimization techniques connected with penalization. The data are supposed to be in the form of random variables with normal probability distributions. Several examples were calculated proving the strength of the proposed algorithm.

Recently a new construction of run length limited block error control codes based on control matrices of linear block codes was proposed. In this paper a similar construction for obtaining trellis run length limited error control codes from convolutional codes is described. The main advantage of it, beyond its simplicity is that it does not require any additional redundancy except the one which is already contained in the original convolutional error control code. One example is presented how to get such a code from a convolutional low density parity check code.