Octavian Dranga

Stability analysis of a feedback-controlled resonant DC-DC converter

This paper reports on the stability analysis of one member of a dual-channel resonant DC-DC converter family. The study is confined to the buck configuration in symmetrical operation. The output voltage of the converter is controlled by a closed loop applying constant-frequency pulsewidth modulation. The dynamic analysis reveals that a bifurcation cascade develops as a result of increasing the loop gain. The trajectory of the variable-structure piecewise-linear nonlinear system pierces through the Poincare plane at the fixed point in state space when the loop gain is small. For stability criterion the positions of the characteristic multipliers of the Jacobian matrix belonging to the Poincare map function defined around the fixed point located in the Poincare plane is applied. In addition to the stability analysis, a bifurcation diagram is developed showing the four possible states of the feedback loop: the periodic, the quasi-periodic, the subharmonic, and the chaotic states. Simulation and test results verify the theory.

Bifurcation Behavior of a Power-Factor-Correction Boost Converter

The aim of the paper is to investigate the bifurcation behavior of the power-factor-correction (PFC) boost converter under a conventional peak current-mode control. The converter is operated in continuous-conduction mode. The bifurcation analysis performed by computer simulations reveals interesting effects of variation of some chosen parameters on the stability of the converter. The results are illustrated by time-domain waveforms, discrete-time maps and parameter plots. An analytical investigation confirms the results obtained by computer simulations. Such an analysis allows convenient prediction of stability boundaries and facilitates the selection of parameter values to guarantee stable operation.

Malicious Node Detection in Wireless Sensor Networks Using an Autoregression Technique

In this paper we propose a strategy based on past/present values provided by each sensor of a network for detecting their malicious activity. Basically, we will compare at each moment the sensors output with its estimated value computed by an autoregressive predictor. In case the difference between the two values is higher then a chosen threshold, the sensor node becomes suspicious and a decision block is activated.

Stability analysis of nonlinear power electronic systems utilizing periodicity and introducing auxiliary state vector

Variable-structure piecewise-linear nonlinear dynamic feedback systems emerge frequently in power electronics. This paper is concerned with the stability analysis of these systems. Although it applies the usual well-known and widely used approach, namely, the eigenvalues of the Jacobian matrix of the Poincare/spl acute/ map function belonging to a fixed point of the system to ascertain the stability, this paper offers two contributions for simplification as well that utilize the periodicity of the structure or configuration sequence and apply an alternative simpler and faster method for the determination of the Jacobian matrix. The new method works with differences of state variables rather than derivatives of the Poincare/spl acute/ map function (PMF) and offers geometric interpretations for each step. The determination of the derivates of PMF is not needed. A key element is the introduction of the so-called auxiliary state vector for preserving the switching instant belonging to the periodic steady-state unchanged even after the small deviations of the system orbit around the fixed point. In addition, the application of the method is illustrated on a resonant dc-dc buck converter.

Bifurcation analysis of a power-factor-correction boost converter: uncovering fast-scale instability

Bifurcation analysis is performed to a power-factor-correction (PFC) boost converter to examine the fast-scale instability problem. Computer simulations and analysis reveal the possibility of period-doubling for some intervals within the line cycle. The results allow convenient prediction of stability boundaries. Analytical equations and design curves are given to facilitate the selection of parameter values to guarantee stable operation.

Multimedia based e-learning tools for dynamic modeling of DC-DC converters

Exploiting the recent achievements of the information and communication technologies, a new e-learning initiation entitled Yoto project was launched in 2004. On longer run its most important objective is to build up and maintain an electrical engineering knowledge base, on shorter run it helps giving more and more publicity to some relevant fields, especially power electronics, drives and motion control. The multimedia rich content can be utilized in the high level academic education, in the industrial vocational trainings and also in supporting the circuit and system design specialists by fast interactive tools. This paper presents a new e-module attached to the Yoto project about the dynamic operation and modeling of dc-dc converters.

Stability Analysis of Two-Stage PFC Power Supplies

Power-factor-correction (PFC) power supplies are required to provide high input power factor and tight output voltage regulation. The usual configuration takes a two-stage cascade structure, consisting of a PFC preregulator and a dc/dc converter. Previous studies of the dynamical behaviour mainly focused on the boost PFC preregulator, assuming that it is being terminated by a resistive load. However, in practice, as the PFC preregulator is terminated by a dc/dc converter whose characteristics differ from resistive loads, the assumption of resistive load termination gives rather inaccurate information about the stability of the system. In this paper we study the complete two-stage PFC power supply and show that the interaction between the PFC stage and the dc/dc converter stage plays an important role in determining the stability of the system.

Bifurcation in parallel-connected buck converters under current-mode control

This paper studies a system of parallel-connected dc/dc buck converters under current-mode control. The effects of variations of the reference current are studied. It has been observed that the system exhibits low-frequency bifurcation behaviour while period-doubling at switching frequency is suppressed. Extensive simulations are used to capture the behaviour. Time-domain waveforms, stroboscopic maps and trajectories are shown. The paper reveals the drastic alteration of bifurcation behaviour of dc/dc converters due to subtle coupling.

Virtual Power Electronics: Novel Software Tools for Design, Modeling and Education

The current paper is dedicated to present browser-based multimedia-rich software tools and e-learning curriculum to support the design and modeling process of power electronics circuits and to explain sometimes rather sophisticated phenomena. Two projects will be discussed. The so-called Inetele project is financed by the Leonardo da Vinci program of the European Union(EU). It is a collaborative project between numerous EU universities and institutes to develop state-of-the art curriculum in electrical engineering. Another cooperative project with participation of Japanese, European and Australian institutes focuses especially on developing e-learning curriculum, interactive design and modeling tools, furthermore on development of a virtual laboratory. Snapshots from these two projects will be presented.

MALICION NODE DETECTION IN SENSOR NETWORK USING AUTOREGRESSION BASED ON NEURAL NETWORK

Abstract In this paper we propose a strategy based on antecedent values provided by each sensor for detecting their malicious activity. We compare at each time moment the sensors output with its estimated value computed by a robust autoregressive neural predictor. In case that the difference between the two values is higher then a chosen threshold, the sensor node becomes suspicious and a decision block is activated.