Search

While in numerous power electronics applications, transformers and inductors with nonlayered windings are used, the absence up until now of any theoretical or even empirical model for their HF effective resistance calculation leads magnetic component designers to make high-error approximations. The typical approach until now has been to consider them as layered and apply some of the existent relevant models. The present paper establishes a new semiempirical model for the accurate determination of HF copper losses in windings with the random conductor distribution, a case that cannot be treated by any analytical method. This model is based on the statistical treatment of numerical results coming from a large number of simulations carried out with finite-element analysis software, and incorporates only three easily determinable parameters. The selected range for each of these parameters ensures that the model is suitable for the majority of practical applications. The theoretical analysis is verified by experimental measurements on different forms of winding geometries. A detailed investigation of the new formula reveals its inherent advantages on copper loss calculation when designing nonlayered coils. Index Terms--Coils, HF transformers, loss measurement, skin effect, transformer windings.

Active clamp topologies of low power dissipation have become a very attractive solution in order to limit overvoltages in flyback converters. Although many suitable topologies have been introduced for the case of discontinuous conduction mode (DCM), where the duty cycle value depends on the load level, in continuous conduction mode (CCM) it is more difficult to appropriately design such topologies so as to 'sense' load changes--due to the small duty cycle divergence under wide load variation. Taking for granted that in order to achieve high power-factor correction in these converters, CCM is a more attractive mode of operation, a drastic solution for this case that will manage to eliminate voltage stresses under wide load changes has become very essential. For this purpose, this paper presents an active clamp topology with small power dissipation, suitable for flyback converters operating in CCM mode. Its main idea is the use of a load-dependent current source, consisting of an auxiliary converter operating in DCM mode. Experimental results highlight the effectiveness of the proposed topology under wide load changes, establishing it as an appropriate solution in order to develop flyback converters, even at the power range of 500 W. Index Terms--Active voltage clamp, flyback converter, snubbers.

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. Index Terms--Field-oriented control, induction machine, stator-flux orientation, stator resistance identification.

This work focuses on a new non‐isolated interleaved DC‐DC converter with very high step‐down voltage conversion ratio. By employing the switched/series capacitor concept, along with the proper component interconnection, the converter features a high step‐down voltage conversion ratio where, in the private case of equal duty ratios, it is six times higher than the conventional buck converter. This high step‐down voltage conversion ratio is achieved with the lowest number of components compared to other similar topologies of the same conversion ratio. Also, due to the blocking/series capacitors, the voltage stress on the switches is reduced, improving the converter efficiency. One of the key features of the proposed converter is the inherent automatic current sharing between the interleaved phases, which in the case of equal duty ratios, is uniformly distributed. To add on, due to the use of only two interleaved phases, the converter has a wide output voltage range, since the duty cycle can be extended to 0.5. To validate the proposed converter operation, a 250 W wide‐input/wide‐output experimental prototype was built, achieving a peak efficiency of 94%. [ABSTRACT FROM AUTHOR]

In this article, the impact of the coupling coefficient K on the static continuous conduction mode (CCM) dc voltage gain of the basic passive clamp coupled inductor boost converter is investigated. First, an analytical method for the extraction of the accurate static CCM dc voltage gain and all the necessary formulas for the comprehensively description of the operating behavior of the converter is presented. Next, a comparison between the previous methods from which the proposed approximate static CCM dc voltage gain formulas are derived and the proposed one takes place. Subsequently, from the analysis and the plots, it appears that the coupling coefficient creates a dependence on the operation by the output current of the converter, which is more intense as the coupling coefficient decreases. Furthermore, it is concluded that the decrease in the dc voltage gain depends not only on the coupling coefficient K, but also on the turns ratio of the coupled magnetic component. Finally, experimental results based on a 250-W laboratory prototype with four different magnetic components are presented for the evaluation of the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a systematic and analytical study of non-isolated topologies belonging to the family of reduced redundant power processing (R2P2) converters is presented. Based on this study, all the non-isolated R2P2 topologies that can be implemented in reality are derived. Detailed examples clarify all possible cases of this analysis. In addition to this, the voltage ratio and the efficiency for each one of the R2P2 configurations are calculated, being further illustrated with examples. A comparison among configurations is also discussed with criteria the high step-up voltage gain and efficiency, aiming for high-power applications. One of these R2P2 converters is selected for further examination, as the most suitable for such applications. The theoretical analysis, as well as the calculations of the step-up voltage ratio and efficiency of the selected converter, is compared to experimental results conducted on a 2-kW laboratory prototype designed to operate in various step-up voltage ratios and in a high-power range, proving the effectiveness of the proposed investigation. [ABSTRACT FROM AUTHOR]

In this paper, a nonisolated high step-up dc/dc converter, belonging to the family of reduced redundant power processing converters (R2P2), is investigated for high-power applications. The selection of this topology as the most suitable for such applications among those belonging to the R2P2 family is justified. Emphasis is given on the theoretical analysis of the real step-up voltage ratio of the converter, and voltage and current stresses under continuous and discontinuous conduction modes of operation, taking into account the nonideality of the topology components, namely the parasitic resistances of semiconductor devices and inductors and the voltage drop of diodes. The theoretical analysis and the behavior of the selected converter are experimentally validated through a 2 kW prototype. Moreover, the overall efficiency of the chosen converter is experimentally investigated for various step-up voltage ratios and for a high-power range, considering a waste heat recovery system for a maritime application. [ABSTRACT FROM AUTHOR]

The output characteristics of Buck zero-voltage switching quasi-resonant converters (ZVS-QRCs), presented in previously published works, are calculated considering equal input and output energies. Nevertheless, measurements that were taken with breadboarded Buck ZVS-QRCs demonstrate an important deviation between the results of the theoretical analysis and the experimental ones. This deviation becomes greater when the load current increases. This paper deals with a novel simulation method to approximate the real behavioral characteristics of Buck ZVS-QRCs. Analytical expressions are derived to calculate the power losses in each converter component as well as the dc-Voltage conversion ratio. Computer simulation results are confronted, to experimental ones proving the effectiveness of the proposed method. Index Terms--DC-DC converters, power losses, soft switching, zero-voltage switching quasi-resonant converters.

The current-source flyback inverter has been proven an excellent solution for ac–PV modules. The two principal modes of operation of this converter are the discontinuous conduction mode (DCM) and the boundary conduction mode (BCM). Although BCM offers higher power density, it suffers at lower power levels, because of the significantly increased switching frequency that consequently leads to higher switching losses and lower overall converter efficiency. In this paper, a hybrid operating mode is presented, that combines both DCM and BCM during a utility grid period, so as to improve the converter performance as well as the efficiency and the power density on a wider power range. The mathematical analysis that describes the control specifics especially for a smooth transition between the two modes of operation is presented and demonstrated through computer simulations and experimental results on a laboratory prototype. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The prescribed perspective of high accession of distributed generation photovoltaic (DG‐PV) units on low‐voltage distribution networks has brought up many issues regarding their performance in case of network transient phenomena. In this study, the design principles that DG‐PV units must incorporate in order to meet the requirements of low‐voltage ride through capability (LVRTC) are investigated through detailed theoretical analysis and calculations. The analysis shows that a realistic over‐sizing of interfaced inverters of DG‐PV as well as an appropriate selection of the equivalent interconnecting reactance XDG, in conjunction with high penetration levels, can lead to satisfaction of LVRTC demands without violating the protection limits of the network. Moreover, the scenario of uniform dispersion along the distribution lines is proved rather favourable concerning the demand of LVRTC for voltage selectivity. Finally, considering the derived outcomes, a methodology of optimum design about LVRTC is proposed within the framework of reasonable constraints, which can be applied to any low‐voltage distribution network. [ABSTRACT FROM AUTHOR]

This paper deals with the theoretical analysis and construction of an inverter that is suitable as an excitation source for high-frequency measurements (up to 1.3 MHz) on magnetic components. Quantities as output current, operation frequency range, and harmonic content of the output voltage are discussed. The interaction between the power part and the control circuit is investigated by experimental verification of the theoretically extracted equations that describe the inverter's operation. As an application example, the proposed inverter is used for the implementation of ferrite core specific loss measurements in a frequency range not included in the data sheet and for the investigation of high-frequency insulation performance of enameled wires. [ABSTRACT FROM AUTHOR]