C.A. Gallo

A Passive Lossless Snubber Applied to the AC–DC Interleaved Boost Converter

High switching frequency operation of static power converters is often required to reduce size, weight, and electromagnetic interference levels, at the cost of increased switching losses and reduced efficiency. Switching losses include the current and voltage overlap loss during the switching interval and the capacitance loss during turn-on. Recently, the use of passive soft switching methods has been emphasized as a better alternative to active methods, mainly because they do not require extra switches or additional control circuitry. This paper proposes a passive lossless snubber applied to the interleaved boost converter. The use of a soft commutation cell causes the main switches to be turned on and off under null current and null voltage conditions, respectively, as high efficiency results over the entire load range. The theoretical analysis including the description of the operating stages and the design procedure are included. Experimental results on a 2 kW prototype are presented and discussed to validate the proposal.

A low-cost electromechanical impedance-based SHM architecture for multiplexed piezoceramic actuators

The electromechanical impedance (EMI) method has been regarded as a promising tool for structural health monitoring (SHM) in real time. Usually, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent, EMI functions, from which features related to the presence, position, and extent of damage can be extracted. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively so as to increase the probability of successful detection of damage in an early phase. In this context, a miniaturized, low-cost, highly expandable SHM architecture for monitoring an array of multiplexed piezoelectric transducers is proposed. Each logical block of the proposed architecture is presented in detail. The proposed architecture does not use costly fast Fourier transform analyzers/algorithms nor requires a digital computer for processing. A personal computer is only necessary for user interfacing. It has been verified that the system can work for frequencies ranging from 0 to 400 kHz with high accuracy and stability. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer; however, a WiFi® connection is also available.

Two-Stage Isolated Switch-Mode Power Supply With High Efficiency and High Input Power Factor

This paper presents the conception and analysis of a switch-mode power supply (SMPS) with desirable characteristics of high-frequency isolation, high input power factor, low harmonic distortion, and high efficiency. Nearly unity input power factor can be obtained by using an interleaved boost converter associated with a nondissipative snubber, as high efficiency of the ac-dc front-end stage results. Additionally, a soft-switching full-bridge topology performs the dc-dc conversion, providing isolation to the SMPS by using a high-frequency transformer. By cascading both stages, the aforementioned characteristics are achieved. Theoretical background on each one of the converters is presented, and experimental results obtained from a laboratory prototype are presented and discussed in order to validate the proposal. In addition, the evaluation tests demonstrate the operation with nearly unity power factor, high efficiency, and good dynamic response over a wide load range.

An unity high power factor power supply rectifier using a PWM AC/DC full bridge soft-switching

This paper proposes an improvement of an isolated unity-power-factor rectifier AC/DC PWM based on a PWM full bridge converter using a commutation cell. This converter operates using soft switching technique. It presents high power factor, full control of the output dc voltage and high-frequency line filter inductor and insulation transformer. It is based in an auxiliary voltage source that feeds the resonant circuit, charging a capacitor that provides the condition for zero voltage switching (ZVS) of the main switches. This paper presents a detailed analysis of the topology, which is then verified by means of complete theoretical analysis, operating principles and simulation results are presented to show the feasibility of proposed power factor correction converter. This work presents simulations and experimental results of a prototype converter operating at 100 kHz.

Non-isolated DC-DC converters with wide conversion range used to drive high-brightness LEDs

Light emitting diodes (LEDs) have many features that make them attractive for use in an increasing number of applications. Particularly in lighting, the small size of LEDs compared to fluorescent and incandescent bulbs is a prominent advantage. This paper presents two topologies based on the buck converter, which have higher step-down characteristic than that of the original converter. The quadratic buck converter is studied and used to drive series-connected LEDs. Improved characteristics if compared with the traditional converter include the continuous current maintained through the LEDS and the possibility of driving several types of LED arrays. The study is then extended to the cubic buck converter, as a novel arrangement to obtain the mentioned step-down characteristic is introduced in this work. The use of such converter allows obtaining lower output voltages than those resulting from the quadratic buck converter. Experimental prototypes of the converters are implemented and fully tested. It must be also mentioned that a PIC microcontroller is used to control the current through the LED array, what provides robustness and flexibility in the adjust of the control algorithm without the need of hardware modification.

A novel microprocessor-based battery charger circuit with power factor correction

An effective microcontrolled battery charger circuit that monitors the charging process avoiding the battery damage by overcharge is described, where a PWM forward topology with power factor correction is employed in order to provide DC/DC conversion. Depending on the battery charge state, which is determined by microcontroller PIC 16F873, the charging process is modified. In this way, fast charging does not have negative effects on the effective capacity of the battery and on battery cycle-life.

Proposal of a SMPS with AC output voltage employing a quadratic boost converter, a new topology of soft-switched two-switch forward converter and a new topology of PWM three-level half-bridge inverter

An AC SMPS can be obtained from the association of a new topology of forward converter and a new topology of half-bridge inverter. The DC-DC stage is composed of a quadratic boost converter providing large voltage step-up and a double-ended forward converter, whose output voltages are +200 V/sub dc/ and -200 V/sub dc/. The DC-AC stage consists of a symmetrical three-level inverter topology. The operation of the converters is analyzed, as some results concerning the proposed system are presented.

An electronic ballast employing a boost half-bridge topology

This paper proposes a new electronic ballast employing a boost half-bridge topology. A boost converter is used to control the input power factor, and a half-bridge topology is used to drive the fluorescent lamp. Both stages are associated in order to simplify the design procedure, as the proposed scheme represents a simple and robust converter. A comparison between this arrangement and another one previously proposed is still presented.

Soft-switched PWM high-frequency with PFC converter using boost-flyback converter interleaved

This paper proposes as a power factor correction pre regulator converter an AC-DC interleaved boost-flyback using a nondissipative snubber and operating at 100 kHz per cell. That is composed by switches working in ZCS and ZVS way, controlled by PWM. By using interleaved converters, an overall reduction of the boost inductor can be obtained, reducing switching losses without increasing current and voltage stresses. This topology has the advantages of interleaved flyback that eliminates an auxiliary source and an inductor in this configuration. The complete operating principles, theoretical analysis, relevant equations and simulation results are given to show the feasibility of the proposed power factor correction converter. Experimental results are presented in this work, with a power tested with the prototype rated at 2000 Watts.

A low cost single-phase grid-connected photovoltaic system with reduced complexity

This paper presents a grid-connected photovoltaic (PV) system using the classical DC-DC buck converter, which is responsible for stepping down the resulting voltage from several series-connected panels. Besides, the buck converter provides sinusoidal current injected into the utility grid, which is possible by using hysteresis modulation. A CSI inverter employing thyristors is cascaded with the DC-DC stage so that AC voltage results. The inverter output voltage level is adjusted by using a low frequency transformer, which also provides galvanic isolation. Low cost, simplicity, and reduced harmonic content of the injected current are direct advantages of the proposed system, which is designed and analyzed by simulation. An experimental prototype is also implemented, as relevant results are presented and discussed.