1,721,206 research outputs found
A High-Quality Rectifier Based on the Forward Topology with Secondary-Side Resonant Reset
No full textThe use of buck-derived topologies for unity power factor ac-to-dc applications is limited by their inherent inability to draw current from the line in those intervals, during the line half period, in which the input voltage is lower than the output one.
This drawback is overcome in the proposed high-quality rectifier
based on the forward topology with secondary-side resonant
reset. The employed secondary side reset capacitor is able to provide proper transformer reset by recycling the transformer stored energy to the load and, at the same time, it allows to draw energy from the line even when the input voltage is lower than the output one. Consequently, besides to a better utilization of the transformer core (bipolar core excitation), a low distorted input current waveform can be obtained with a power factor close to unity.
Experimental results of a 200 W prototype confirm the theoretical
expectations
A High-Quality Rectifier Based on the Forward Topology with Secondary-Side Resonant Reset
No full textThe use of buck-derived topologies for unity power factor AC-to-DC applications is limited by their inherent inability to draw current from the line in those intervals, during the line half period, in which the input voltage is lower than the output one. This drawback is overcome in the proposed high-quality rectifier based on the forward topology with secondary-side resonant reset. The employed secondary side reset capacitor is able to provide proper transformer reset by recycling the transformer stored energy to the load and, at the same time, it allows energy to be drawn from the line even when the input voltage is lower than the output one. Consequently, besides a better utilization of the transformer core (bipolar core excitation), a low distorted input current waveform can be obtained with a power factor closer to unity. Experimental results of a 200 W prototype confirm the theoretical expectation
Accurate Magnetic Core Losses Measurement Under Arbitrary Excitation Waveforms
Full text linkPrecise core loss measurements are essential for magnetic design and the development of efficient and high-power density converters. This letter introduces a novel approach, leveraging the fast Fourier transform (FFT), to couple with the already demonstrated partial cancellation concept adopted for transformer core loss measurements. The proposed method perfectly eliminates the reactive voltage of the transformer under test contrary to the widely used two-winding method, yielding accurate core loss measurements regardless of the type of excitation waveform and design of the reference air core transformer. Experimental validation is performed by testing material N97 under both sinusoidal and rectangular excitations in the frequency range from 100 kHz to 500 kHz
A Low-Inductance Line-Frequency Commutated Rectifier Complying with EN 61000-3-2 Standards
No full textThis paper presents a high power factor rectifier, based on a modified conventional rectifier with passive – filter, which utilizes a line-frequency-commutated switch and a small auxiliary circuit in order to improve both harmonic content of the input current and power factor, thus allowing compliance with EN 61000-3-2 European standards. Being the switch turned on and off only wice per line period, the associated losses are very small.
Moreover the limited di/dt and dv/dt considerably reduce the high-frequency noise emission, thus avoiding heavy EMI filters.
The switch operation results in a boost action, which compensates
for the filter inductor voltage drop, thus providing output voltage
stabilization against load variations. Compared with other similar
approaches, the presented topology can achieve higher power
levels with a reasonable overall magnetic component size
Common Mode Filter Project by means of Internal Impedance Measurements
No full textThe EMI filter used in switching apparatus are usually designed on the basis of the designer personal experience and by a trial and error approach. This is especially true for the common mode part of the input filter for which a systematic procedure that, by means of proper calculations and measurements, gives an idea of the filter component values is missing. This work presents a rigorous method to estimate the filter component values needed to achieve the desired attenuation for the common mode noise generated by the switching apparatus. This method is based on the indirect measurement of the common mode impedance of the equivalent noise generator
Analysis of Instabilities in Piezoelectric Transformers Driving Cold Cathode Fluorescent Lamps
No full textThis paper analyzes the behavior of power supplies for cold cathode fluorescent lamps (CCFL) employing piezoelectric transformers (PTs). It has been demonstrated that the non-linear equivalent lamp resistance interacts with the PT that behaves like a high-Q resonant circuit, giving rise to instabilities in the audible frequency range [Spiazzi, G. et al. 2004]. Moreover, when the PTs are driven by a voltage-fed inverter and its DC supply voltage is used to control the lamp voltage, the relation between the control variable and the lamp current can become nonmonotonic, depending also on the coupling network used between the inverter and the PT. This paper extends the analysis reported in Spiazzi, G. et al. (2004) by considering different coupling networks as well as considering the inverter switching frequency as the control variable for controlling the lamp current. SPICE simulations and analytical models are employed to explain the unstable behaviors observed in different experimental prototypes
High-quality rectifier based on coupled-inductor Sepic topology
No full textA high-quality rectifier employing a coupled-inductor Sepic topology is described, featuring high-frequency insulation and low input current ripple. Moreover, sinusoidal and in-phase input current is obtained even with constant duty-cycle. The magnetic structure is simple and cheap, allowing considerable size and cost reduction. Converter analysis, design criteria of both power and control sections and experimental results are reported in the paper
A New Family of Zero-Current-Switching-Variable Frequency dc-dc Converters
No full textA new family of zero-current-switching variable-frequency DC-DC power converters is presented. It employs two unidirectional current switches, one diode, two small reactive components and a filter capacitor. Zero current turn-on and turn-off ensure low switching losses and smooth current waveforms result in low electromagnetic noise emission. The discontinuous operating mode and the variable switching frequency make the presented topology suitable for low-power applications or for high-power low-frequency applications where SCRs can be profitably used. Experimental results of a prototype confirm the theoretical expectations of the proposed solution
Phase-Modular Approach for Avionic Three-Phase Rectifier Applications
No full textThis paper presents the analysis and design of a single-phase, high-power-factor rectifier module to be integrated in a three-phase modular architecture for avionic applications. The target is an aircraft fuel pump drive, where the rectifier feeds the voltage source inverter (VSI) connected to the pump's electrical motor. The proposed topology, based on isolated SEPIC submodules with a regenerative snubber, can withstand a line frequency variation from 250 Hz to 800 Hz, as well as a 70 - 180V line RMS voltage range. Experimental results are taken on a 270V-1500W module prototype
Reduced redundant power processing concept: A reexamination
No full textThe Reduced Redundant Power Processing (R2P2) concept was introduced in literature with the aim of improving the overall conversion efficiency of two-stage high-quality rectifiers, capable of providing high power factor and tight output voltage regulation, but it has been applied to DC-DC conversion too. The idea is to have one converter processing only a fraction of the total output power, the remaining part coming directly from the other converter or, in DC-DC converter applications, directly from the input source. This idea, that is at first sight very appealing, has been implemented in different ways using basic converter topologies. In this paper, it is demonstrated that most of the R2P2 implementations that have been proposed in literature are actually not able to achieve a better efficiency compared with a full power processing, because they do not represent a correct implementation of the concept. Indeed, it is possible to demonstrate that they are equivalent to solutions that process the entire load power. It is demonstrated that it is possible to develop R2P2 structures that achieve better efficiencies compared to the full power processing counterparts, but only at the expense of more complicated topologies, and for specific applications in which the processed power is a tiny fraction of the overall output power
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