Roger Gules

Voltage Multiplier Cells Applied to Non-Isolated DC–DC Converters

This paper introduces the use of the voltage multiplier technique applied to the classical non-isolated dc-dc converters in order to obtain high step-up static gain, reduction of the maximum switch voltage, zero current switching turn-on. The diodes reverse recovery current problem is minimized and the voltage multiplier also operates as a regenerative clamping circuit, reducing the problems with layout and the EMI generation. These characteristics allows the operation with high static again and high efficiency, making possible to design a compact circuit for applications where the isolation is not required. The operation principle, the design procedure and practical results obtained from the implemented prototypes are presented for the single-phase and multiphase dc-dc converters. A boost converter was tested with the single-phase technique, for an application requiring an output power of 100 W, operating with 12 V input voltage and 100 V output voltage, obtaining efficiency equal to 93%. The multiphase technique was tested with a boost interleaved converter operating with an output power equal to 400 W, 24 V input voltage and 400 V output voltage, obtaining efficiency equal to 95%.

Isolated DC-DC converters with high-output voltage for TWTA telecommunication satellite applications

Two alternatives for the implementation of an isolated DC-DC converter operating with a high output voltage and supplied by an unregulated low input voltage are presented in this paper. The proposed topologies are especially qualified for the implementation of travelling wave tube amplifiers (TWTA) utilized in telecommunication satellite applications due to their low mass and volume and their high-efficiency. The converters studied follow different principles and the main operational aspects of each topology are analyzed. A two-stage structure composed by a regulator connected in series with a ZVS/ZCS isolated DC-DC converter is the first topology proposed. The second topology studied is an isolated single-stage converter that continues being highly efficient even with a large input voltage variation. The experimental results obtained from two prototypes, implemented following the design procedures developed, are presented, verifying experimentally the characteristics and the analysis of the proposed structures. The prototypes are developed for an application requiring an output power of 150 W, a total output voltage of 3.2 kV and an input voltage varying from 26 V to 44 V. The minimum efficiency obtained for both converters operating at the nominal output power, is equal to 93.4% for the two-stage structure and equal to 94.1% for the single-stage converter.

A Modified SEPIC Converter for High-Power-Factor Rectifier and Universal Input Voltage Applications

A high-power-factor rectifier suitable for universal line base on a modified version of the single-ended primary inductance converter (SEPIC) is presented in this paper. The voltage multiplier technique is applied to the classical SEPIC circuit, obtaining new operation characteristics as low-switch-voltage operation and high static gain at low line voltage. The new configuration also allows the reduction of the losses associated to the diode reverse recovery current, and soft commutation is obtained with a simple regenerative snubber circuit. The operation analysis, design procedure, and experimental results obtained from a 650-W universal line power-factor-correction prototype of the proposed converter are presented. The theoretical analysis and experimental results obtained with the proposed structure are compared with the classical boost topology.

Reduced-Order Model and Control Approach for the Boost Converter With a Voltage Multiplier Cell

The boost converter with a voltage multiplier cell allows the static gain extension by means of the switching capacitor technique, reducing the duty cycle needed to achieve the same voltage gain when compared to the conventional boost converter. However, the modeling of this converter is complex and requires the use of advanced techniques due to the resonant inductor. Thus, this paper aims to present a reduced-order model of this converter without the resonant energy exchange between the capacitors, so that the state-space averaging technique can be applied assuming small ripple in the state variables. In addition, this paper presents the design of a control system for the boost converter with a voltage multiplier cell. The adopted strategy employs an inner loop to control the input current and an outer loop for the output voltage regulation. Extensive analysis based on simulations and an experimental prototype demonstrate that the proposed modeling, although simplified, is sufficient for an adequate control system design, ensuring good voltage regulation, and fast transient responses.

A Modified SEPIC Converter With High Static Gain for Renewable Applications

A high step-up DC-DC converter based on the modified SEPIC converter is presented in this paper. The proposed topology presents low switch voltage and high efficiency for low input voltage and high output voltage applications. Two alternatives with and without magnetic coupling are analyzed. The magnetic coupling allows to increase the static gain with a reduced switch voltage. The theoretical analysis and experimental results are presented. Two experimental prototypes were developed with an input voltage equal to 12 V and an output power equal to 100 W. The efficiency obtained with the prototype without magnetic coupling was equal to 91.2% with an output voltage equal to 120 V and nominal output power. Efficiency equal to 95% was obtained with the prototype with magnetic coupling operating with an output voltage equal to 240 V and nominal output power.

DC-DC converter: four switches V/sub pk/=V/sub in//2, capacitive turn-off snubbing, ZV turn-on

A new four-switch full-bridge dc-dc converter topology is especially well-suited for power converters operating from high input voltage: it imposes only half of the input voltage across each of the four switches. The two legs of a full-bridge converter are connected in series with each other, across the dc input source, instead of the usual topology in which each leg is connected across the dc source. The topology reduces turn-off switching losses by providing capacitive snubbing of the turn-off voltage transient, and eliminates capacitor-discharge turn-on losses by providing zero-voltage turn-on. (Switching losses are especially important in converters operating at high input voltage because turn-on losses are proportional to the square of the input voltage, and turn-off losses are proportional to the input voltage). The topology is suitable for resonant and nonresonant converters. It adds one bypass capacitor and one commutating inductor to the minimum-topology full-bridge converter (that inductor is already present in many present-day converters, to provide zero-voltage turn-on, or is associated with one or two capacitors to provide resonant operation), and contains a dc-blocking capacitor in series with the output transformer, primary winding, and some nonresonant converters (that capacitor is already present in resonant power converters). The paper gives a theoretical analysis, and experimental data on a 1.5-kW example that was built and tested: 600-Vdc input, 60-Vdc output at up to 25A, and 50-kHz switching frequency. The measured performance agreed well with the theoretical predictions. The measured efficiency was 93.6% at full load, and was a maximum of 95.15% at 44.8% load.

High-Power-Factor Rectifier Using the Modified SEPIC Converter Operating in Discontinuous Conduction Mode

The theoretical and experimental analysis of a modified version of the SEPIC dc-dc converter used as preregulator operating in discontinuous conduction mode (DCM) is presented in this paper. The proposed converter presents a low input current ripple operating in DCM, and the switch voltage is lower than the output voltage. The switch voltage reduction increases the converter reliability and a low drain-to-source on-resistance (RDSon) MOSFET can be used depending on the converter specification. Moreover, a digital control technique is applied to the proposed converter in order to reduce the third-harmonic input current distortion resultant of the operation in DCM. Finally, a 100-W prototype was developed operating with efficiency equal to 95.6%.

An Auxiliary Self-Oscillating Preheating System for Self-Oscillating Fluorescent Lamp Electronic Ballasts

The fluorescent lamp lifetime is very dependent of the start-up lamp conditions. The lamp filament current and temperature during warm-up and at steady-state operation are important to extend the life of a hot-cathode fluorescent lamp, and the preheating circuit is responsible for attending to the start-up lamp requirements. The usual solution for the preheating circuit used in self-oscillating electronic ballasts is simple and presents a low cost. However, the performance to extend the lamp lifetime is not the most effective. This paper presents an effective preheating circuit for self-oscillating electronic ballasts as an alternative to the usual solution.

Reduced order model of the boost converter with voltage multiplier cell

The boost converter with voltage multiplier cell allows the extension of static gain by means of the switching capacitor technique, reducing the duty cycle needed to achieve the same voltage gain when compared to the conventional boost converter. However, the modeling of this converter is complex and requires the use of advanced techniques due to the resonant inductor. For this reason, the dynamic model of this converter is still unpublished in the literature. This paper aims to present a reduced order model of this converter, without the resonant energy exchange between the capacitors, so that one can apply the state-space averaging technique assuming small ripple in the state variables. Extensive analysis demonstrates that the proposed modeling, although simplified, is sufficient for an adequate control system design for the converter.

Development of a new single phase high power factor rectifier with ZVS commutation and high frequency isolation

A new high-power-factor rectifier with high-frequency isolation is presented in this paper. The proposed topology presents intrinsic ZVS commutation allowing the operation with high-switching frequency. It also presents the multiphase operation reducing the input inductance and input current ripple. The structure is a bridgeless rectifier, reducing the number of semiconductors in conduction, presenting less conduction losses. The proposed structure is composed by a multiphase boost converter operating in CCM integrated with a ZVS DC-DC full-bridge converter without the output inductor and operating in DCM. The experimental results are obtained from a 2 kW prototype and switching frequency equal to 44 kHz, presenting efficiency equal to 91% at nominal power.