Showing papers on "Flyback converter published in 1996"

Characterization of an active clamp flyback topology for power factor correction applications

Abstract: Flyback derived power convertor topologies have long been attractive because of their relative simplicity when compared with other topologies used in low-power applications. Incorporation of active clamp circuitry provides the additional benefit of recycling transformer leakage energy while minimizing switch voltage stress. This paper presents the analysis, design, and experimental results of 500 W single stage and 600 W interleaved active clamp flybacks used for power factor correction. Several practical issues, including the application of charge control, the use of mixed power devices, and a solution to the hold-up time problem are discussed and experimentally verified.

Off-line flyback converter with input harmonic current correction

Abstract: An offline flyback power converter employing coupled primary transformer windings to achieve input harmonic current correction is introduced. By controlling the turn-ratio of the windings, the input current harmonic contents can be reduced to comply with EN611000-3-2 limits while boosting only slightly the bulk capacitor voltage. Such a topology allows the use of commercially available electrolytic capacitors for energy storage and introduces minimum cost penalty. The basic operation of the power converter is discussed and hardware results from a prototype circuit presented.

Soft switching DC-to-DC converter with coupled inductors

Abstract: A DC-to-DC converter topology is provided having switching devices that are switched under zero voltage switching conditions to minimize switching losses. The converter of the present invention includes two input side converter bridges, each based on a two switch forward converter topology. The input side converter bridges may be connected in series for high input voltage levels and in parallel for low voltage levels. The switching devices of each input side converter bridge are coupled together by coupling inductors. The turning-off of a switching device in one bridge causes part of the energy stored in the corresponding coupled inductor to discharge an output capacitance of an incoming switching device in the other bridge, causing an anti-parallel connected diode to conduct. The incoming switch can thus be turned on under zero voltage switching conditions. Zero voltage switching can be achieved over a wide load range by properly sizing the coupled inductors. The converter switching devices are preferably provided switching signals from a peak current control controller that controls the duty cycle of the converter to regulate the peak of the output currents to control the output power delivered to a load.

High frequency AC/AC converter with PF correction

Abstract: A high frequency AC/AC converter apparatus with power factor correction includes an AC/DC converter circuit part to provide power factor correction and a DC/AC inverter circuit part to produce a high frequency AC signal for operation of a load, for example, a discharge lamp. The AC/DC converter circuit part includes a diode and an inductor. The converter apparatus utilizes first and second semiconductor controlled switching devices, one of which is common to each part of the overall converter apparatus. A single control circuit controls both parts of the converter apparatus by controlling the switching of the first and second semiconductor switching devices. There are two possible control techniques, constant duty ratio control or duty ratio sweeping control. A voltage clamp circuit inhibits undesired oscillation of the diode voltage.

An integrated flyback converter for DC uninterruptible power supply

Abstract: An integrated flyback power converter performing the combined functions of uninterruptible power supply (UPS) and switch-mode power supply (SMPS) is presented. This power converter has a high voltage main power input and a low voltage backup battery input. DC output is obtained from the main input via a flyback power converter during normal operation and from the backup battery via another flyback power converter when input power fails. High conversion efficiency is achieved in normal, backup, and charging modes as there is only a single DC-DC conversion in each mode. The power converter circuit is very simple, with two switching transistors, a relay for mode switching, and a single magnetic structure only. This new design offers substantial improvement in efficiency, size, and cost over the conventional cascade of UPS and SMPS due to single voltage conversion, high frequency switching, and removal of design redundancy. The operation, design, analysis, and experimental results of the power converter are presented.

Switched-capacitor-based DC-to-DC converter with improved input current waveform

Abstract: A new type of DC-to-DC converter is proposed by using dual basic quasi-switched-capacitor (QSC) converter cells. The prominent feature of this converter is its improved input current waveform, which can reduce the electromagnetic interference due to the conducted emissions as compared to the classical PWM-type and SC-based converters. The concept of energy transfer is realized by two symmetrical converter cells, operating in two cyclical phases. The d.c. voltage conversion ratio is determined by the voltage applied to the quasi-switch in each cell for controlling the charging trajectory of the capacitors in order to maintain a constant output voltage for a wide range of load and supply voltage. As the converter does not contain any inductive element, it makes the converter of small size, light weight, high power density and possible in IC form. The small-signal frequency response shows that the designed converter has good operation stability. A prototype of 36 W, 12 V/9 V, step-down DC-to-DC converter has been built, giving an overall efficiency of 73% with power density of 20 W/in/sup 3/.

An approach to harmonic current-free AC/DC power conversion for large industrial loads: the integration of a series active filter with a double-series diode rectifier

Abstract: This paper proposes a new harmonic-free AC/DC power converter characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The DC terminals of the series active filter are directly connected in parallel with those of the double-series diode rectifier, thereby forming a common DC bus. The series active filter enables the diode rectifier to draw three-phase sinusoidal currents from the utility. In addition, it can provide the supplementary value-added function of regulating the common DC bus voltage to a limited extent of /spl plusmn/5%, with slightly increased RMS voltage rating but without increasing peak voltage rating. Experimental results obtained from a 5 kW laboratory system verify the practical viability and cost-effectiveness of the proposed AC/DC power converter.

Harmonic correction of 3-phase rectifiers and converters

Abstract: An AC-DC converter for connecting an AC supply and a DC has a rectifier, and a harmonic correction circuit formed of (a) thyristor inverter legs connected at a common output point to form a Y switch, or separately at positive and negative terminals and (b) a voltage selection circuit for selecting a voltage derived from one of the positive and negative DC rails, or the AC lines, to control current shape and turn-off the thyristors. The thyristors are turned on by, and may also be turned off by, a controller. The voltage selection network may be a resonant circuit that uses ramping of the voltage at the outputs from the thyristors to turn the thyristors off or switches controlled by the controller. A converter for converting DC to AC power has an inverter bridge, a DC input line inductor on each DC rail, a generator for generating a waveshape output that has a frequency equal to the number of AC lines times the frequency of the AC supply; and a multiplexer for multiplexing the output of the generator onto the AC lines to reduce total harmonic distortion of current in the AC lines. The DC to AC converter may use the thyristor networks used for the AC to DC converter for the multiplexing function, under control of the controller. The generator may be a voltage selection network or switch network that selects a voltage source from one of the positive DC rail, the negative DC rail and a center tap on the DC rail.

Multi-frequency averaging of DC/DC converters

Abstract: This paper presents some of the issues involved in applying frequency-selective averaging to modeling the dynamic behavior of PWM DC-DC converters. We use the boost converter as an example to show the details involved in deriving some novel averaged models and use simplifications to highlight the accuracy of the models even when traditional small-ripple conditions are not satisfied.

Capacator storage circuit for sustaining a DC converter

Abstract: Circuitry for extending the sustain time of a DC converter power supply in the event of interruption of AC power. Where in the circuit includes a capacitor storage element, an associated charge path for controllably charging the capacitor bank and discharge and disconnect paths for discharging the energy stored in the capacitor to sustain operation of the DC power converter and for disconnecting the capacitor from the DC converter when the voltage across the capacitor has discharged below a threshold level and prevents the capacitor from creating and introducing periodic ringing transient oscillations into the same charging means, with the charging means and discharging means therefore being connected to said DC voltage source to provide a charging path to said raw DC voltage source during normal operation of the AC power source, and a discharging means to provide a discharging path for said capacitor means to sustain operation of a power converter means during momentary interruption of the AC power source and to disconnect said capacitor means from the DC source means and dc converter means wherein said capacitor means has been discharged to a minimum level required to insure proper operation of said power converter means.

An AC-AC power converter for custom power applications

Abstract: A versatile AC-AC converter that can be utilized as a control device for custom power applications is presented. The converter has the ability to regulate bus voltage through voltage sags and overvoltages, and act as a solid state circuit breaker. Performance characteristics under typical conditions are presented along with experimental verification of converter operation. Technical feasibility, protected efficiency and other practical implementation issues are discussed. Operation of the power converter is illustrated using EMTP simulations.

Analysis and modeling of a two-input DC/DC converter with two controlled variables and four switched networks

Abstract: A two-input tri-state DC/DC converter was presented by the authors (1994) capable of performing solar array peak-power tracking, battery power conditioning, and output voltage regulation all within the same converter structure. At light loads and during periods of low insolation, converter operation will naturally evolve through four linear switched networks. In this paper, the small-signal stability of the tri-state converter is analyzed and a large-signal averaged model is derived capable of predicting the dynamic behavior during and following transitions to and from this fourth state.

Fault tolerant power converter

Abstract: A power converter having fault tolerant capability for use with a switched relucance machine isolates power converter legs in the event of a failed component coupled to the DC bus of the power converter.

Measured performance of a high-power-density microfabricated transformer in a DC-DC converter

Abstract: Experimental measurements are reported on microfabricated power conversion transformers. A device fabricated using a simplified 'sandwich' process confirms predicted performance in an 8 MHz DC-DC power converter, where it achieves a power-handling density of 22.4 W/cm/sup 2/ at 61% efficiency. Preliminary test results are reported for transformers based on a closed-core design, which is expected to achieve higher efficiency.

Optimizing the winding strategy of the transformer in a flyback converter

Abstract: This work presents a study of the influence of the winding strategy in the parameters of the flyback transformer. A frequency and geometry dependent model generated from FEM simulations has been employed in order to study the influence of the position of the windings on the leakage energy and AC resistance. A study of the interleaving technique in the flyback transformer has also been developed using the FEM solver. Conclusions of the advantages of the interleaving technique in the flyback transformer compared with its application in common transformers have been extracted. The influence of the leakage inductance in primary and secondary windings has been studied by means of SPICE simulations. The final goal of this paper is to obtain winding strategy design rules to minimize the leakage inductance and AC resistance in order to optimize power converter performance.

Constant-switching-frequency AC-DC converter using second-harmonic-injected PWM

Abstract: This paper describes the operation of an AC-DC converter employing second-harmonic-injected PWM. The boost converter operating on the rectified output uses a constant switching frequency PWM and a discontinuous current mode to reduce the total harmonic distortion in the input current. The implementation and the characteristics of the converter are presented.

Multimode power converter

Abstract: A particularly advantageous power converter, suitable for use in an engine powered generator system A signal simulating a desired AC waveform is produced by a converter circuit at first and second converter output terminals The converter circuit, responsive to respective switching signals applied thereto, selectively effects current paths between a juncture node and one of the first and second converter output terminals and between a common rail and the other of the first and second converter output terminals A controller selectively generates control signals to the converter circuit and to a mechanism for varying the magnitude of the juncture node voltage, to create a predetermined waveform at the converter output terminals simulating the desired AC waveform A number of alternative embodiments for producing a simulated sine wave are described, as well as accommodations for inductive loads, and mechanisms for minimizing power dissipation during the switching interval

Piezoelectric transformer converter with PWM control

Abstract: A piezoelectric transformer (PT) converter with PWM is presented. The active-clamp technique makes it possible to control the output voltage with PWM even if the PT converter operates in a resonant fashion. The PT converter with PWM control was implemented on a printed circuit board. The line and load regulation was successfully achieved under the input-voltage variation of 20 to 30 V, Vo=5 V, Io=0-4 A, and fs=2.08 MHz. Maximum efficiency achieved 82%.

Integrated AC/DC and DC/DC converter

Abstract: In an illustrative embodiment, a power converter for starting an AC machine comprises at least one transformer for stepping-up AC source voltages, at least one rectifier for rectifying output voltages from the at least one transformer, a three phase inverter for inverting rectified voltages from the at least one rectifier for providing three phase voltages for starting the AC machine, and a DC to AC converter for converting DC source voltage to AC inverted voltages. The three phase voltages for starting the AC machine are derived from one of the AC and DC source voltages through the at least one transformer and the at least one rectifier.

A direct coupled 4-quadrant multilevel converter for 16 2/3 Hz traction systems

Abstract: The main fields of applications are today especially broadcast amplifiers and fast power-supplies for plasma physics or neutral Beam Injection. The fisrst interests on the proposed technique is the series connected step inverter stages, which represents a mature solution as an alternative to the true series connection of a great number of modern turn-on and turn-off power semiconductor devices.

Power-supply and communication

Abstract: A power-supply and communication circuit is based on a flyback converter with a transformer (6) whose primary winding (10) is periodically connected to a supply voltage by means of a switching element (8) in the rhythm of control pulses from an oscillator (24) Data communication to the secondary electronic circuitry (4) is effected by interrupting the control pulses in response to a first data signal (SDTA1) to be transmitted The absence of the alternating voltage across the secondary winding (18) is detected by means of a peak detector (28) and converted into a received first data signal (RDTA1) Data communication to the primary electronic circuitry (2) is effected by actively modulating the rectified voltage at the secondary side by means of a modulator (30) in response to a second data signal (SDTA2) to be transmitted The resulting fluctuations in the flyback voltage across the primary winding are detected by means of a second peak detector (32) and converted into a received second data signal (RDTA2)

Self-compensating switching power converter

Abstract: A self-compensating high voltage switched power converter monitors the variations in real time of the resonant frequency of the converter, and controls a switching transistor of the converter to establish an operating frequency which corresponds to the resonant frequency. The collector voltage of the switching transistor is monitored, and the transistor is switched only when the collector voltage is decreasing toward a minimum value and is below a predetermined reference level. This enables the power converter to operate at a high frequency, which affords small size, light weight, and high efficiency.

Three-phase AC power converter with power factor correction

Abstract: A solid-state, PFC power converter for converting 3-phase AC to DC in a single, isolated conversion step, using 3 forward converters. Converter outputs share a common output choke, permitting operation at low instantaneous AC input voltage. Each forward converter is "duty" modulated proportional to its rectified AC input voltage, producing unity input power factor. The constant of proportionality for 3 converters is controlled to regulate the DC output voltage. A control circuit provides immunity to AC input distortion and noise. The control circuit operates with various forward converter topologies, and is compatible with integrated circuit processes. A version using phase or symmetry modulated full-bridge converters, requires only 2 output rectifiers.

Passive clamp and ripple control for buck boost converter

Abstract: A power conversion circuit, in which a flyback converter is modified with additional elements to provide both dissipationless snubbing and also input ripple cancellation. This is achieved by appropriate connection of an additional winding to the isolating transformer, without any need for a second transformer. The configuration of the secondary is conventional, and the switching transistor is connected in series with the primary winding across DC inputs (taken e.g. from a full-wave-rectified line voltage). The additional winding is connected on the primary side, and preferably has a near-unity turns ratio with the primary which is the inverse of the coupling coefficient. However, the additional winding is not connected between the two DC inputs, but instead has one end coupled through an intermediate capacitor to the corresponding end of the primary, and the other end coupled through a capacitor to the negative DC input. By use of appropriate reactances a balancing current is maintained in the additional winding, which keeps the total current through the primary absolutely flat. The intermediate capacitor which links the primary and additional windings also provides efficient snubbing: it catches the energy stored in the primary leakage inductance, and also limits the maximum voltage on the switch. This results in a converter with no ripple at the input, high efficiency, and very efficient snubbing. Moreover, by using a second active element for regeneration, energy loss during switching of the primary switch is minimized.

Optimum dynamic performance of a buck converter

Abstract: The application of optimal control theory concepts justifies the use of a bang-bang control to reach in minimum time a specified reference in steady-state in the case of the buck converter. The derived control function is unique and insensitive to the converter initial conditions. The converter trajectories in the phase-plane are used as control functions and sliding-mode control is introduced to regulate the output voltage.

A single stage power factor corrected AC/DC converter

Abstract: This paper presents a single-stage isolated power converter topology to achieve a regulated DC output voltage having no low frequency components and a high input power factor. The topology is derived from the basic two-switch forward power converter, but incorporates an additional transformer winding, an inductor and a few diodes. The proposed circuit inherently forces the input current to be discontinuous and AC modulated to achieve high input power factor. The power converter's output is operated in the discontinuous mode to minimize the bulk capacitor voltage variations when the output load is varied. Analysis of the power converter is presented and performance characteristics are given. Further, design guidelines to select critical components of the circuit are presented. Finally, experimental results on a 160 W, universal input, 54 VDC output power converter are given which confirm the high efficiency and high power factor features of the proposed topology.

A new control method preventing transformer DC magnetization for voltage source self-commutated converters

Abstract: A DC component contained in an output of a voltage source self-commutated converter causes a converter transformer to be DC-magnetized, in the worst case causing an overcurrent due to saturation. We experienced the DC-magnetization of the converter transformer of a 50 MVA self-commutated SVC installed in the Shinshinano Substation of Tokyo Electric Power Company when system disturbances occurred by energizing of an adjacent large capacity transformer. After analysing the problem, a novel DC magnetization prevention control was developed that makes a fast flux correction according to the voltage DC component detected in the converter output. This method was applied to the 50 MVA self-commutated SVC and produced satisfactory operation results.

High-voltage AC to low-voltage DC converter

Abstract: A high-voltage AC to low-voltage DC converter includes a rectifier circuit for providing a pulsating high-voltage DC signal from the high-voltage AC input and a switch having its main current path coupled between the rectifier circuit output and an output terminal of the converter. A filter capacitor is coupled to the output terminal to filter the low-voltage DC output, and first and second voltage sensors are coupled to the rectifier output and the low-voltage DC output terminal of the converter circuit, respectively. The first voltage sensor is set to sense a low (typically zero) voltage, and the second voltage sensor is set to sense the desired low-voltage DC output level. The outputs of the first and second voltage sensors are coupled to the set and reset inputs, respectively, of a latch circuit, with the output of the latch circuit being coupled to a control terminal of the switch in order to turn on the switch upon receiving a set input from the first voltage sensor and then turn off the switch on receiving a reset input from the second voltage sensor. This converter configuration provides a compact and highly-efficient circuit.

A buck quadratic PWM soft-switching converter using a single active switch

Abstract: High-switching frequency associated with soft commutation techniques is a trend in switching converters. Following this trend, a buck pulsewidth modulation (PWM) converter is presented. The DC voltage conversion ratio of this converter has a quadratic dependence on duty cycle, providing a large stepdown. This new buck quadratic PWM soft-single-switched converter, having only a single active switch, provides a high efficient operating condition for a wide load range at high-switching frequency. In order to illustrate the operating principle of this new converter, a detailed study including theoretical analysis, relevant equations and simulation, and experimental results is carried out.

Single stage high power factor converter using the Sheppard-Taylor topology

Abstract: This paper describes a new usage of the DC/DC converter developed by D.I. Sheppard and B.E. Taylor in 1983, for achieving high power factor and output regulation. This converter may be viewed as a cascade of a modified boost stage and a buck stage, with the two stages sharing the same active switch. Two possible operation regimes are described. In the first regime, the converter's input part, which is a modified boost converter, operates in discontinuous mode, and the output part, which is a buck converter, operates in continuous mode. In this regime, high power factor is naturally achieved and the output voltage is regulated by duty cycle modulation via a simple output feedback. In the second regime, the input part operates in continuous mode and the output part operates in discontinuous mode, with duty cycle modulation maintaining a high power factor and frequency modulation regulating the output. Compared to the usual boost-buck cascade operating in the first regime, the proposed converter has a wider operating range. When operating in the second regime, the modified boost stage has the ability of producing a harmonic free input current, unlike the standard boost PFC whose current always suffers a cusp distortion.