Kruno Miličević

Investigation of possible ferroresonance for a voltage range: realisation of a system event with a laboratory set-up

The paper presents an analytical and numerical investigation carried out on part of an electrical power network exhibiting ferroresonant behaviour as well as experimental investigation on its physical model. The investigations were carried out in order to estimate the extent of predicting the range of voltage source amplitude values at which the initiation of ferroresonance depends on values of initial conditions and phase shift. For this range of voltage source amplitude values (termed as possible ferroresonant range in the paper) the impact of initial conditions and phase shift of voltage source on the initiation of ferroresonance is determined using a numerical investigation and an experimental setup. Reasons and consequences of disagreement of parameter values of the original and physical model are determined.

Initiation of Characteristic Ferroresonance States Based on Flux Reflection Model

This brief focuses on the impact of basic circuit parameters to the initiation of characteristic ferroresonance states. Basic circuit parameters analyzed in this brief are the coil nominal voltage (which results to a range of inductance values and knee points for the coil characteristics), circuit capacitance, and the rms source voltage. It is shown that experimental results could be recreated by way of flux-reflection model, which is of particular interest due to its advantages, such as the possibility of primarily utilizing an analytical solution and the possibility it creates in using elementary data about the coil and circuit in general. Based on measurements and simulation results, it is shown that ferroresonant steady-state responses occur at higher values of rms source voltage as the coil nominal voltage is increased. Furthermore, increasing circuit capacitance increases the impact of initial conditions on the initiation of ferroresonance.

Experimental Investigation of Symmetry-Breaking in Ferroresonant Circuit

This study focuses on the impact of circuit parameters on the breaking of steady-state symmetry in a ferroresonant circuit. Symmetry-breaking occurs owing to pitchfork bifurcation and results in the ambiguousness of steady-state solution through two possible waveform types. The two types are distinguished in this study by positive and negative peak values of capacitor voltage. Circuit parameters analyzed in detail are source voltage RMS value U1 and initial values of capacitor voltage and coil remanent flux. There is symmetry of occurrence in the two types of waveform, which is expected because of the odd symmetry of characteristics of all passive circuit elements. It is shown that the property of symmetry could be experimentally demonstrated and through simulation using a mathematical model of the experimental ferroresonant circuit. In addition, measurements have been carried out with two further coils to investigate the impact of the nominal voltage and type of core material on the initiation of the two types of waveforms.

Flux Reflection Model of the Ferroresonant Circuit

The paper presents a linear model of ferroresonant circuit with flux reflection. The proposed model—flux reflection model—derives from observations of typical flux waveforms of nonlinear coil during ferroresonant steady states. Simulation results of the flux reflection model are compared with simulation results of the usual nonlinear model as well as with measurements carried out on the physical model of the ferroresonant circuit. The flux reflection model enables a novel comprehension of the ferroresonant circuit behavior and simplifies the modeling of the nonlinear coil in the ferroresonant circuit.

Frequency-translated differential chaos shift keying for chaos-based communications

Abstract In this paper, an efficient, differential chaos shift keying (DCSK) method, known as frequency-translated DCSK (FT-DCSK), is proposed. Ordinary DCSK is difficult to incorporate using CMOS integrated circuits because of the long wideband delay line that is required to separate reference and data chaotic sequences into two time-shifted slots of each frame. Another disadvantage of DCSK is the repetition of chaotic sequence in reference and data slots, which decreases data security and bandwidth efficiency. In the proposed method, the usage of a delay line is avoided by frequency translation of the reference chaotic sequence over the frame time. Frequency translation is achieved by amplitude modulation of two orthogonal sine carriers with reference chaotic sequences. As a result, the FT-DCSK scheme avoids the usage of wideband delay lines and increases the bandwidth efficiency. The analytical expression for bit error rate (BER) performance is derived and compared with simulation results. Finally, the obtained performance results are compared with similar modulation schemes. The proposed FT-DCSK scheme exhibits promising performance based on BER results.

Correlation-Multi-Delay-Shift-Keying for Chaos Based Communications

In this paper, the new correlation-multi-delay-shift-keying (CMDSK) modulation scheme for chaos based communications is proposed. In this scheme the information-bearing time delayed chaotic sequence is subtracted with original one. As a result, the higher data rate is obtained by defining a different time delays in order to maps a multiple bits within a frame. The number of transmitted bits per symbol is proportional to the number of possible delayed sequences. The analytical expression for error rate, based on Gaussian approximation, is derived and the results are confirmed with Monte-Carlo simulation. The performance of the CMDSK are analyzed and compared with differential-chaos-shift-keying (DCSK) and correlation-delay-shift-keying (CDSK). The result shows that CMDSK scheme outperforms DCSK and CDSK scheme with the increase of spreading sequence M. Due to the larger number of delay lines and correlators at transmitter and the receiver, CMDSK requires higher hardware complexity.

Non-Linear Least Squares and Maximum Likelihood Estimation of Probability Density Function of Cross-Border Transmission Losses

In the modern power system, transmission losses play an increasingly important role in determining the costs of transmission system operators, in particular in cross-border energy exchange. A variety of transmission losses calculation methods are present in scientific literature in recent years, but regularly neglecting the measurement uncertainty, which is an important contribution in calculating the final cost of exchanged energy. Due to the significant cost of transmission losses in total costs, all transmission system operators are interested in discovering the probabilistic nature of transmission losses as a fundamental requirement for finding the fair method for transmission losses allocation. In this paper, transmission losses are simulated on 110-kV cross-border transmission line using an adaptive Monte Carlo method. The probability density estimation procedure is performed by the non-linear least-squares method, using the Levenberg–Marquardt algorithm. The Gaussian, log-normal, Rayleigh, four-parameter beta, generalized trapezoidal, and the sum of uniform and normal distribution are fitted and the quality of the distribution estimates is compared according to the corresponding values of the Kolmogorov–Smirnov statistic. Furthermore, an additional example presents a distribution fitting procedure on the zero-impedance data of the same transmission line.