Volumen 14 (2018): Edición 2 (December 2018)

The first-year students at the technical universities often face the problem of using the previously acquired knowledge at a higher level required by engineering education. To solve this problem, the authors developed a series of lectures dedicated to establishing theoretical background, based on simulations in DigSILENT Power Factory software. In the lectures, the physical values and quantities as well as the purpose and characteristics of the power equipment are explained on the example of the simple models.

This article includes the detailed description of a lesson “Introduction into Power Systems” and presents some models and ways of explaining the material. The sections below concentrate on the lecture format focusing on methods for explanation of physical quantities and introducing power system components. Sequential parts create the mosaics of grid, with the following description of basic laws and principles in power systems.

Currently, microgrids are regarded one of the main substations in distribution networks that generate electrical energy locally. The advantages of microgrids include easy management, optimization, and highly reliable supply. In this paper, the recommended model is based on economic and emission optimal scheduling in connection to the main grid mode; implementation model implies the short-term mode with optimal operation units and the use of real-time pricing (RTP) plan. In this study, a multi-objective function for operating costs and emission with the augmented ɛ-constraint method has been considered; fuzzy decision-making process has been employed to obtain the best solution. In addition, it has been considered that a microgrid has interruptible and shiftable loads that can participate in demand response programs. The presented results have been evaluated based on different demand response programs.

Digitalization of the industrial sector and Industry 4.0 have opened new horizons in many technical fields, including electrical machine diagnostics and operation, as well as machine condition monitoring. This paper addresses a selection of electrical machine diagnostics methods that are applicable for the use in the perspective of Industry 4.0, to be used in hand with cloud environments and the possibilities granted by the Internet of Things. The need for further research and development in the field is pointed out. Some potentially applicable future approaches are presented.

Electrical machines, induction motors in particular, play a key role in domestic and industrial applications. They act as a work horse in almost every industry and are responsible for a big proportion of total generated electricity consumption worldwide. The faults in induction motors are degenerative in nature and can lead to a catastrophic situation if not diagnosed earlier. The failures can cause considerable financial loss in the form of unexpected downtime. Broken rotor bar is a very common and frequently occurring fault in most of industrial induction motors. To select a better, more accurate and reliable fault diagnostic technique, this paper presents a comprehensive literature survey on the existing motor current signature analysis (MCSA) based fault diagnostic techniques. Different well-known MCSA based fault diagnostic techniques are summarized in the form of basic theories, considering complexity of their implementation, merits and demerits.

The observer design for estimation of back EMF to control the Brushless DC (BLDC) motor is proposed in this paper. Rotor position of the BLDC motor is estimated using the sequence of estimated back EMF. During speed reversal of motor, the actual and estimated values of speed fail to track the reference speed and if corrective action is not taken by the observer, the motor goes into the unstable region. To overcome this problem, the speed estimation algorithm is proposed for BLDC motor control during its speed reversal operation. Infinite Impulse Response (IIR) Butterworth first order low-pass filters are used in the observer for smoothing the estimated back EMFs of the BLDC motor. A new controller scheme based on Modified Hybrid Fuzzy PI (MHFPI) controller is proposed to control the speed of the BLDC motor. The effectiveness of the proposed method has been validated through simulations for different disturbances such as step changes in the reference speed and load torque of the motor and results are compared with the existing methods.

Models of open cylindrical multilayer gyroelectric-anisotropic-gyroelectric waveguides are presented in this paper. The influence of density of free carriers, temperature and the presence of the external dielectric layer on the wave phase characteristics of the models of n-GaAs waveguides has been evaluated. Differential Maxwell’s equations, coupled mode and partial area methods have been used to obtain complex dispersion equation of the models of gyroelectric-anisotropic-gyroelectric waveguides with or without the temperature sensitive external anisotropic dielectric layer. The analysis has shown that the phase characteristics are practically unchanged when the density of electrons is equal to N = (10¹⁷–5·10¹⁸) m⁻³, d/r^s = 0, the changes of wave phase coefficients are obtained in the models of waveguides with the external anisotropic dielectric layer. The largest differences of wave phase coefficient are obtained when the density of electrons is N = 10²¹ m⁻³. The external dielectric layer improves the control of gyroelectric n-GaAs waveguides with temperature.

Well-deployed cellular networks offer a cheap wireless solution for the control channel deployment of Remote-Control Vehicles (RCV) and Unmanned Aerial Vehicles (UAV). However, a cellular data transfer service performance is affected by a different kind of User Equipment (UE) mobility. Operating conditions of UAV imply working at different altitudes, variable velocities with accelerations/decelerations and rapidly changed antennas angular position, which lead the wireless signal to be prone to negative effects. Available field measurement studies are not sufficient to provide excessive information on degradation problem causes for UEs moving along a complex trajectory. This paper presents an evaluation of the service quality of live operational 3G and LTE networks for both ground moving and flying UE. It has been found that antennas angular position variations in 3D (for example, during UAV manoeuvers) increase data transfer latency and jitter. Moreover, this effect in conjunction with higher interference at high altitudes may partially or fully block the data transfer service. This paper has been prepared to draw attention to the problem that makes the cellular data transfer service unusable for highly-manoeuvrable UAVs.

In order to increase the efficiency of dedicated frequency channels, i.e. to increase the specific data transfer rate, multipositional quadrature phase shift keying (QPSK, aka 4-PSK) should be used. The problems with QPSK signal demodulation is a rotation of the signal constellation plane by an angle multiple of 90° and a slow response of the carrier oscillation recovery scheme. The study considers the existing methods for eliminating the phase ambiguity of the recovered carrier frequency in typical QPSK modems, and identifies the shortcoming of a low-speed response oscillation recovery circuit. The authors propose a QPSK demodulator circuit with a fast adjustment of the reference oscillator, which is due to the fact that no loop filter is used in the feedback and that a digital calculator of the required phase shift is used. An algorithm for the frame synchronization restoration with the simultaneous elimination of the phase ambiguity multiple of 90° was also developed using synthesized binary sequences with an ideal non-periodic autocorrelation function (NACF) at even shifts that do not have the rotary symmetry property. The phase ambiguity elimination algorithm proposed in the article can be used as an alternative to standard modems with differential coding.

The topical question studied in this paper is how many receptive fields (filters) a convolutional layer of a convolutional neural network should have. The goal is to find a rule for choosing the most appropriate numbers of filters. The benchmark datasets are principally diverse CIFAR-10 and EEACL26 to use a common network architecture with three convolutional layers whose numbers of filters are changeable. Heterogeneity and sensitiveness of CIFAR-10 with infiniteness and scalability of EEACL26 are believed to be relevant enough for generalization and spreading of the appropriateness of filter numbers. The appropriateness rule is drawn from top accuracies obtained on 10 × 20 × 21 parallelepipeds for three image sizes. They show, knowing that the number of filters of the first convolutional layer should be set greater for the more complex dataset, the rest of appropriate numbers of filters are set at integers, which are multiples of that number. The multipliers make a sequence similar to a progression, e.g., it may be 1, 3, 9, 15 or 1, 2, 8, 16, etc. With only those multipliers, such a rule-of-progression does not give the number of filters for the first convolutional layer.

Twin rotor system is a laboratory setup resembling a simplified helicopter model that moves along both horizontal and vertical axes. The literature on control of twin rotor systems reflects a good amount of research on designing PID controllers and their extensions considering several aspects, as well as onsome nonlinear controllers. However, there is almost no previous work on design of lag-lead type compensators for twin rotor systems. In this study, by considering this open research problem, lag and lead type compensators are designed and then experimentally verified on the twin rotor system. Specifically, first, lag and lag-lag compensators are designed to obtain a reduced steady state error as compared with proportional controllers. Secondly, lead compensation is discussed to obtain a reduced overshoot. Finally, lag-lead compensators are designed to make use of their favorable properties. All compensators are applied to the twin rotor system in our laboratory. From experimental studies, it was observed that steady state error was reduced when a lag compensator was used in conjunction with a lead compensator.

This paper presents a systematic procedure to design a simple control for a three-phase VSC-based static synchronous compensator (STATCOM) in order to overcome the problems caused by the presence of the non-linear load at the point of common coupling (PCC). The proposed control method regulates the STATCOM in such a way that the source quadrature current component is forced to be zero so that only the active current component is drawn from the source and the harmonic and reactive current demands of the non-linear load are met by the STATCOM. The tuning of the inner and outer loop PI controllers is carried out with the help of the modulus optimum and symmetric optimum criteria, respectively. At last, a few case studies are presented using MATLAB simulation to exemplify the success of the proposed control method.