Emmanuel C. Tatakis

Optimum Design of the Current-Source Flyback Inverter for Decentralized Grid-Connected Photovoltaic Systems

Two alternative modes of operation for the current-source flyback inverter are investigated in this paper. The discontinuous conduction mode (DCM), where a constant switching frequency (CSF) control method is applied, and the boundary between continuous and DCM (BCM) that is introduced for photovoltaic (PV) applications in this paper (where a variable switching frequency control method is applied). These two control methods are analytically studied and compared in order to establish their advantages as well as their suitability for the development of an inverter for decentralized grid-connected PV applications. An optimum design methodology is developed, aiming for an inverter with the smallest possible volume for the maximum power transfer to the public grid and wide PV energy exploitation. The main advantages of the current-source flyback inverter are very high-power density and high efficiency due to its simple structure, as well as high-power factor regulation. The design and control methodology are validated by personal computer simulation program with integrated circuit emphasis (PSPICE) simulation and experimental results, accomplished on a laboratory prototype.

A Weighted-Efficiency-Oriented Design Methodology of Flyback Inverter for AC Photovoltaic Modules

An innovative design methodology that optimizes the weighted efficiency of a single-phase, single-stage flyback inverter for ac-photovoltaic (PV) module applications is proposed. This novel approach combines the essential advantages of the flyback topology with high-efficiency design in the direction of a reliable, cost-effective, and high-performance PV system. The proposed methodology focuses exclusively on choosing the inverter design parameters, taking into consideration the PV module characteristics and the topology operation constraints. In order to meet this goal, an analytical losses calculation should be performed. Since the problem is complicated, special effort is given to manipulate the equations and variables in such a way to minimize the number of parameters. The proposed methodology is also verified experimentally.

A new stator resistance tuning method for stator-flux-oriented vector-controlled induction motor drive

Field-oriented-controlled induction motor drives have been widely used over the last several years. Conventional direct stator-flux-oriented control schemes have the disadvantage of poor performance in the low-speed operating area when the stator flux is calculated using the voltage model, due to the stator resistance uncertainties and variations. In this paper, a new closed-loop stator-flux estimation method for a stator-flux-oriented vector-controlled induction motor drive is presented in which the stator resistance value is updated during operation. This method is based on a simple algorithm capable of running in a low-cost microcontroller, which is derived from the dynamic model of the induction machine. The effects of stator resistance detuning, especially in the low-speed operating region, are investigated and simulation results are shown. The motor drive system as well as the control logic and the resistance estimator are simulated and characteristic simulation results are derived. In addition, the proposed control scheme is experimentally implemented and some characteristic experimental results are shown. The simulation as well as the experimental results reveal that the proposed method is able to obtain precise flux and torque control, even for very low operating frequencies.

Development and Evaluation of a Computer-Based Laboratory Teaching Tool

Effective evaluation of educational software is a key issue for successful introduction of advanced tools in the curriculum. This paper focuses on our experience of developing and evaluating a tool for computer‐assisted teaching of engineering laboratory courses. Various categories of educational softwares that can be used for laboratory courses are described. An example of such experimental system is also provided. Finally issues and techniques relating with usability evaluation of instructional software are described with examples of application of these techniques during the design and experimental use of electrical‐machines laboratory educational software.

Enhanced Current Pulsation Smoothing Parallel Active Filter for single stage grid-connected AC-PV modules

On single stage PV converters the output power has a large amount of power pulsation at twice line frequency, causing PV module voltage and current fluctuation. However, a PV module should operate at a sufficiently small area around the maximum power point, in order to maximize PV generation. To overcome this defect a buffering storage unit between the PV module and the inverter, which performs the well known power decoupling, is inevitable. This paper presents an enhanced configuration of a current pulsation smoothing parallel active filter (CPS-PAF) which permits the elimination of the low frequency PV current ripple with significant smaller capacitor comparatively to the classical configuration. The enhanced CPS-PAF conception, control and effectiveness are validated by PSpice simulation results as well as by experimental results accomplished on a laboratory prototype.

Optimal Design of a Half-Wave Cockcroft–Walton Voltage Multiplier With Minimum Total Capacitance

Even though the half-wave Cockcroft-Walton voltage multiplier (H-W C-W VM) is one of the most common ac-dc step-up topologies, VM designers tend to use equal capacitances in every stage, a fact that leads to a nonoptimal design. The aim of this paper is to introduce a new design method of H-W C-W VM that lays on the calculation of the optimal number of stages, which is necessary to produce the desired output voltage with the minimum total capacitance value. For this purpose, an adequate choice of the capacitance values per stage is considered, leading to the investigation of four different cases. The theoretical analysis is validated by PSPICE simulations and experimental results, accomplished on laboratory prototypes.

High-Frequency Copper Losses in Magnetic Components With Layered Windings

Copper losses in magnetic coils depend on several geometrical parameters, as well as on frequency, in a way that makes their analytical modeling a quite difficult task. In this paper, we describe how we use a finite-element-analysis software to investigate a series of issues critical to the accurate determination of high-frequency copper losses in layered coils. Some of the issues we investigate are the impact of the edge effect and the winding pitch on the overall copper losses. We examine the effective resistance of windings with a hexagonal conductor arrangement and the validity range of the classic models for copper losses in windings with round solid wire. The results of this work help us to fully understand the real impact of two-dimensional effects in layered windings of real rather than ideal magnetics. They constitute a tool for the accurate calculation of losses, which is necessary for an optimized magnetic component design in power electronics applications.

Weighted Efficiency Optimization of Flyback Microinverter Under Improved Boundary Conduction Mode (i-BCM)

The flyback topology is proven to be a very strong candidate solution for use in ac-PV module applications. Operation in the boundary condition mode (BCM) provides high power density, while maintaining the characteristics of a current source inverter. In this paper, a design methodology is presented, that maximizes the weighted efficiency of the converter through an optimization algorithm. The inverter operation is investigated and the behavior under the improved BCM is documented by analytical equations followed by the power loss calculations for each component. This enables to accurately define the relation between the design parameters and the efficiency of the implemented converter and so, an optimization algorithm is established, that takes into consideration the design specifications and constraints. The proposed methodology is also verified with an experimental prototype.

Design and control of a current source flyback inverter for decentralized grid-connected photovoltaic systems

This paper presents a new design and control strategy of the flyback inverter for decentralized grid-connected PV systems, in order to achieve high power density, high efficiency, and high power factor regulation. The design and control methodology which are investigated are aiming either to the achievement of a converter with the smallest possible volume for a given power or to the maximization of the power transfer that can be achieved for given converter parameters. The validation of the proposed design and control methodology will be confirmed by experimental results accomplished on a laboratory prototype

A new model for the determination of copper losses in transformer windings with arbitrary conductor distribution under high frequency sinusoidal excitation

Magnetic components (inductors and transformers), when present in power electronics converters, consist undoubtedly, along with the semiconductor switches, the main power loss contribution. This fact emerges the necessity of having some easily applicable tools for their effective resistance accurate calculation. The up to now widely used relative theoretical or empirical formulas have been extracted under assumptions or experimental conditions that invalidate their results over several application cases. Some lately released computer aided analyses, though useful, do not make it to escape from the strictly bounded logic and assumptions on which the previous formulas were based. In this paper a new expression for the calculation of high frequency copper losses in transformer and inductor coils with round conductors, more general than the existent models and without any of the traditionally imposed assumptions and limitations, is proposed and established by finite element analysis (FEA) and measurement results. No complicated tables with coefficient numerical values are necessary and the final formula extracted is simple and ready to use. Additional to this work, a comparison between the results determined by the existent theoretical analyses and FEA clarifies their discrepancy over specific ranges of the several parameters involved.