Showing papers on "Flyback converter published in 1998"

Comparison of basic converter topologies for power factor correction

Abstract: Basic types of DC-DC converters, when operating in discontinuous conduction mode, have self power factor correction (PFC) property, that is, if these converters are connected to the rectified AC line, they have the capability to give higher power factor by the nature of their topologies. Input current feedback is unnecessary when these converters are employed to improve power factor. In this paper, basic types of DC-DC converter topologies are studied to investigate their self-PFC capabilities. Their input characteristics are compared and their input line current waveforms are predicted.

Bi-directional DC to DC converters for fuel cell systems

Abstract: This paper first describes the need of a bi-directional DC to DC converter for a fuel cell system. Various combinations of current-fed and voltage-fed converters are explored for the application of different voltage levels. With a preliminary study, putting current-fed on low-voltage side and voltage fed on high voltage side indicated higher efficiency than the other way around. Two low-side circuit topologies were then selected for hardware implementation. One is the L-type half-bridge current-fed converter, and the other is full-bridge current-fed converter. The high-side circuit topology is fixed with a full-bridge voltage-fed converter. Two systems were built and tested to full power. The results indicate that the combination with the full-bridge converter on the low-voltage side is more efficient than the combination with the L-type half-bridge converter on the low-voltage side for both charging and discharging modes.

Modelling and control of DC-DC converters

Abstract: This tutorial article shows how the widely used analysis techniques of averaging and linearisation are applied to the buck or step-down DC-DC converter to obtain simple equations which may then be used for control design. Three common control methods are described. Their principal characteristics are illustrated using Matlab and the Simulink block diagram system along with experimental results. The analysis procedures described may be applied directly to other DC-DC converters and the principles may be extended to more complex power electronic systems.

A three-phase multilevel converter for high-power induction motors

Abstract: A new converter topology for drives is presented in this paper: a three-phase multilevel converter with separately regulated DC power supplies. The DC voltages are provided by medium-frequency DC-DC converters. The applications for the converter are especially high-power traction systems, where the voltage applied to the induction motor is bigger than 1 kV. The motor current is of a very high quality, compared to a classical three-phase converter. This allows keeping the switching frequency low by using phase-shifted pulsewidth modulation (PWM) carriers. Different modulation methods have been developed and simulated. Experimental tests have been made on a 12 kW prototype.

Reduction of power converter EMI emission using soft-switching technique

Abstract: Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested.

Design considerations and performance evaluations of synchronous rectification in flyback converters

Abstract: Design tradeoffs and performance comparisons of various implementations of the flyback converter with a synchronous rectifier (SR) are presented. Specifically, the merits and limitations of the constant-frequency (CF) continuous-conduction mode (CCM), CF discontinuous-conduction mode (DCM), variable-frequency (VF) DCM, and zero-voltage-switched (ZVS) DCM flyback converters with SRs are discussed. The theoretical efficiency improvements of the discussed synchronous rectification approaches relative to Schottky diode implementations are derived. Finally, theoretical results are verified on an experimental universal-input off-line 15 V/36 W flyback prototype.

DC voltage control and stability analysis of PWM-voltage-type reversible rectifiers

Abstract: A PWM voltage rectifier has useful characteristics on its DC and AC sides. On its DC side, a DC-link unidirectional voltage is obtained and bidirectional power transfer capability is possible by reversing the flow direction of the DC-link current. On its AC side, near sinusoidal current waveforms and AC four-quadrant operation can be obtained, leading to high-quality power being exchanged between the power converter and the mains. The use of AC filters becomes unnecessary. The rectifier DC voltage must be regulated to a constant value. In this paper, three solutions for the DC voltage control are presented. In the first solution, the DC voltage is controlled by acting upon the quadrature component of the power converter fundamental Park's voltages with relation to the mains voltages. Slow responses are necessary because of stability reasons. Also, load power variations produce both active and reactive power variations in the power converter AC side. To improve the DC voltage response, a second control solution is presented. The power converter currents in Park's coordinates must be controlled. The DC voltage is controlled by controlling the direct Park's current component and, thus, acting only on the active power of the converter AC side. Faster responses are achieved. In this case, load power variations do not produce reactive power variations in the converter AC side. The third control solution is a simplified version of this last one. Experimental results from a 2 kVA IGBT-based prototype showing good system dynamic performance are presented.

A multiple-winding magnetics model having directly measurable parameters

Abstract: A general model of the multiple-winding transformer and coupled inductor is presented, in which all parameters can be directly measured. The approach is suitable for all winding geometries, and simplifying approximations can be easily made. This model can be applied in the determination of cross-regulation, current ripple and small-signal dynamics of multiple-output DC-DC power converters. An experimental four-winding flyback transformer example is investigated. Observed leakage inductance parameter measurements are interpreted physically, and are related to observed flyback converter waveforms. It is also shown that the model correctly predicts small-signal dynamics.

Asymmetrical duty cycle flyback converter

Abstract: An asymmetrical duty cycle flyback converter comprising a main transformer for transforming an input voltage at a desired ratio, the main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage, a switching circuit for switching the input voltage to the main transformer, the switching circuit including first and second switches, a rectifying/smoothing circuit for rectifying and smoothing an output voltage from the main transformer, a controller for generating a control signal in response to an output voltage from the rectifying/smoothing circuit to control the switching operation of the switching circuit, and a switch driver for generating first and second drive signals in response to the control signal from the controller to drive the first and second switches in the switching circuit in such a manner that they can complementarily be switched on the basis of on-time duties asymmetrical with respect to each other and at an interval of a dead time therebetween to perform a zero voltage switching operation. With this construction, the present invention has the effect of realizing a miniaturation and improvement in power efficiency.

AC/DC flyback converter with improved power factor and reduced switching loss

Abstract: A new single stage, single switch input current shaping circuit features substantially reduced turn-on switching losses of the switch in the flyback-converter. In this technique, the turn-on switching losses due to the discharge of the output capacitance of the switch are reduced by turning on the switch when its voltage is minimal or close to the minimal. To achieve the turn-on loss reduction for a wide range of line and load conditions, the flyback-converter stage is continuously operated at the boundary of the CCM and DCM by employing a variable-frequency control. In this technique the boost inductor can work either in the DCM or the CCM. The wide-bandwidth, variable-frequency control is implemented by detecting the onset of the DCM/CCM boundary and, subsequently, turning the switch on at the minimum switch voltage. The switch is turned off when the increasing primary current reaches a reference level set by the output-voltage feedback control circuit.

Double ended isolated d.c.-d.c. converter

Abstract: A D.C.-D.C. down converter utilizes a controlled converter primary switching circuit and a full-wave rectified secondary circuit employing synchronous rectification. An isolation transformer having split first and second secondary windings supplies current to the full-wave secondary circuit. The gating signals for synchronous rectification are produced by a switch conduction control including a secondary switch control receiving control signals from the primary switch control through a control current isolating transformer. The secondary switch control is powered by the secondary converter circuit. Through the use of a split secondary winding of the isolation transformer and a full-wave rectifying circuit, the secondary converter circuit of the D.C.-D.C. converter may readily generate drive voltages for supply to the secondary switch control, allowing the secondary converter circuit and load to be fully isolated from the primary converter circuit and input source.

Capacitor commutated converter circuit configurations for DC transmission

Abstract: Two nonconventional HVDC converter arrangements are compared. These include the capacitor commutated converter (CCC) in which series capacitors are included between the converter transformer and the valves, and the controlled series capacitor converter (CSCC), based on more conventional topology, in which series capacitors are inserted between the AC filter bus and the AC network. Results show that both options have comparable steady state and transient performance. Danger of ferroresonance with the CSCC option is eliminated by controlling the amount of series compensation.

Soft-switched DC/DC converter with PWM control

Abstract: In this paper, a new power converter with two variations is proposed. A novel asymmetrical pulse-width-modulation (PWM) control scheme is used to control the power converter under constant switching frequency operation. The modes of operation for both variations are discussed. The DC characteristics, which can be used in the design of the power converters, are also presented. Two 50 W power converters were built to verify the characteristics of the converters. Due to the zero-voltage-switching (ZVS) operation of the switches and low device voltage and current stresses, these power converters have high full- and partial-load efficiencies. They are, therefore, potential candidates for high-efficiency high-density power supply applications.

Analysis and experimental results of a single-stage high-power-factor electronic ballast based on flyback converter

Abstract: A new single-stage high-power-factor electronic ballast based on a flyback power converter is presented in this paper. The ballast is able to supply a fluorescent lamp, assuring a high input power factor for the utility line. Other features are lamp power regulation against line voltage variations and low lamp current crest factor, both assuring long lamp life. The ballast is analyzed at steady-state operation and design equations and characteristics are obtained. Also, a procedure for the ballast design is presented. Finally, simulation and experimental results from a laboratory prototype are shown.

A ZVS clamping mode-current-fed push-pull DC-DC converter

Abstract: This paper introduces a new technique to recover the energy trapped in the leakage inductor of the current-fed push-pull converter, by means of an active clamping mode circuit. Theoretical analysis and experimental results, taken from a 800 W/40 kHz are presented in the paper. The studied converter also features ZVS (zero voltage switching) in all switches, preserving all the main properties of the original circuit. As a result, the efficiency is improved and the electromagnetic disturbances are minimized.

Re-lift converter: design, test, simulation and stability analysis

Abstract: The 're-lift' power converter is derived from the self-lift power converter and performs a positive-to-positive DC-DC step-up voltage conversion with high efficiency, high power density and cheap topology in a simple structure. The output voltage and current of this power converter are smooth. Two capacitors are applied to lift the output voltage by twice of the input voltage. The output voltage of the re-lift power converter is double that of the self-lift converter.

Single-switch two-output flyback-forward converter operation

Abstract: A double power converter with fully independent regulated outputs is introduced. The proposed topology results from magnetic integration of flyback and forward power converters. The derived converter shares a single power switch having a single magnetic component. Also, only one standard pulsewidth modulation (PWM) integrated modulator is needed in order to keep independent closed-loop control of both output voltages. The double regulation may be sustained over a wide spread of current loads. Boundaries of full regulation and experimental results are presented.

A high-efficiency single-stage single-switch high-power-factor AC/DC converter with universal input

Abstract: A single-stage single-switch power-factor-correction (PFC) AC/DC converter with universal input is presented in this paper. The PFC can be achieved based upon the charge-pump concept, and the PFC stage operates in the continuous current mode (CCM). The switch has less current and voltage stresses over a wide range of load variation so that a low-voltage rating device can be used. The presented converter features high power factor, high efficiency, and low cost. An 80-W prototype was implemented to show that it has 85% efficiency with low-voltage stress from 0.5% to 100% load variation over universal line input.

Temperature protection circuit for power converter and method of operation thereof

Abstract: A temperature protection circuit, a method of protecting a power converter and a power converter employing the circuit or the method. In one embodiment, the circuit includes: (1) a temperature sensor, located in thermal communication with the power converter, that produces a signal based on a temperature associated with the power converter and (2) a current controller, coupled to the temperature sensor, that reduces an output current of the power converter to an intermediate level based on the signal.

Fault isolation in a redundant power converter

Abstract: Aspects for isolating faults in a redundant power converter are described. An exemplary system aspect includes a first switch at an input of the redundant power converter for protecting the redundant power converter from a high input voltage, and a second switch coupled within the redundant power converter prior to an output capacitor, wherein efficiency of fault isolation is improved.

A novel soft-switching high-frequency transformer isolated three-phase AC-to-DC converter with low harmonic distortion

Abstract: A high-frequency transformer isolated, fixed-frequency, 3-/spl phi/ single-stage ac-to-dc converter using a boost-integrated bridge converter that employs a new gating scheme is proposed. This converter enjoys natural power factor correction with low line current harmonic distortion and symmetric high frequency voltage and current waveforms while ensuring zero-voltage switching for all the switches for a wide variation in load and line voltage. Various operating modes of the converter are presented and analyzed. Based on the analysis, design curves are obtained and an optimum design is given. A design example is presented. Results obtained from SPICE simulation and a 500 W output experimental prototype are given to verify the performance of the proposed converter for varying load as well as line voltage.

Transformer isolated driver and isolated forward converter

Abstract: A DC-DC converter has a main forward converter stage with a snubber at a source side and a sample and hold circuit at a load side. Feedback is provided by a pulse width modulated controller connected at the load side, which feeds an isolation transformer via a differentiating capacitor. The isolation transformer has its output connected to a pulse regenerator which feeds a driver and a volt-time limiter that connects to a main switch at the source side of the forward converter.

Analysis and design of a three-phase LCC-type resonant converter

Abstract: A three-phase dc-to-dc LCC-type resonant converter with high-frequency transformer isolation is proposed. The operation and a simple analysis of the converter are presented. Design curves are obtained and a design example is given. SPICE simulation and experimental results are presented to verify the performance of the proposed converter for varying load conditions. The converter proposed has several advantages, e.g., operation in lagging PF mode for the entire load range, requires a narrow variation required in switching frequency, reduced component size and stresses, etc.

Efficiency improvement of piezoelectric-transformer DC-DC converter

Abstract: Piezoelectric-transformers (PT) have a lot of merits in comparison with magnetic transformers. We have previously presented some types of piezoelectric-transformer DC-DC converters (PT-converters) for AC-adapters, but their efficiency was restricted. The maximum efficiency was less than 80%. Furthermore, the frequency characteristics of efficiency are not good due to the power loss generated in the input filter circuit of the PT. In this paper the improvement of the converter efficiency by using a different rectifier circuit topology and a synchronous-rectifier technique is described. Furthermore, the frequency characteristics of efficiency are improved by using a different topology of the input filter circuit and its optimum design. As a result, the converter efficiency has been increased up to 88% and the frequency characteristics of the efficiency is also improved.

Comparative study of AC/DC converters for More Electric Aircraft

Abstract: The More Electric Aircraft concept has been seen as the direction of the next generation for aircraft. This paper describes the major concern of the AC/DC converters in the power conditioning system of the aerospace industry. There are many types of AC/DC converter circuits used in aircraft systems. Some of them use transformer rectifier units, passive or active rectifiers with or without a step-up or step-down converter. Their performances versus the power density is an important factor for selection and this paper analyses various circuits for the AC/DC converters used in More Electric Aircraft.

Half-bridge DC to DC converter with low output current ripple

Abstract: A method and apparatus for maintaining relatively low ripple current in a dc-dc converter while minimizing the size of an inductive line filter utilizes a transformer having at least a pair of secondary windings in which the secondary windings are selected to have different numbers of winding turns depending on the specific design of the ideal duty factor at which the converter will be operated. In addition, the converter is provided with an active pre-load which establishes a continuous conduction current when load current is below some selected minimum value in order to provide control stability during light load conditions without converter oscillations. In an illustrated embodiment, the active pre-load circuit comprises a resistor connected in series with a transistor across the voltage output of the converter with the gate terminal of the transistor connected through a zener diode to the control circuit so that when the control voltage feedback signal drops to a selected low value, the transistor is biased into conduction to connect the resistor as a load to maintain a minimum load current. Alternatively, the transistor can be connected across one of the diodes in the transformer secondary and arranged so as to conduct current in a direction opposite to the direction of current through the diode so that under low current conditions, a current loop is formed through the transformer to maintain continuous current flow and allow the converter to operate at very light loads.

AC/CD converter with a piezoelectric transformer

Abstract: An AC/DC converter of the present invention includes a transformer implemented by a piezoelectric transformer. Power fed from a commercially available power source (14) is converted to a DC voltage by rectification and smoothing. The DC voltage is transformed to a high frequency (about 100 kHz) pulse voltage by switching FETs (Field Effect Transistors) (5) and 6. The pulse voltage is applied to the input of a piezoelectric transformer (9). The transformer (9) has its vibration mode and dimension selected such that the resonance frequency of the transformer is substantially identical with the frequency of the above pulse wave. A high frequency AC voltage is produced from the output side of the transformer (9). The AC voltage is transformed to a DC voltage by rectification and smoothing and then fed to a load resistor (13). The piezoelectric transformer is easy to miniaturize, compared to an electromagnetic transformer. The entire AC/DC converter can therefore be reduced in size.

Single-stage single-switch input-current-shaping technique with fast-output-voltage regulation

Abstract: A new single-stage single-switch input-current-shaping (S/sup 4/ICS) technique, which combines the boost-like input-current shaper with a continuous-conduction-mode (CCM) DC/DC output stage, is described. In this technique, the boost inductor can operate in both the discontinuous conduction mode (DCM) and CCM. Due to the ability to keep a relatively low voltage (<450 V/sub DC/) on the energy-storage capacitor, this technique is suitable for the universal line-voltage applications. The voltage on the energy-storage capacitor is kept within the desirable range by the addition of two transformer windings. The principle of operation of the S/sup 4/ICS circuit with a forward DC/DC converter is presented. Experimental results obtained on a 100 W (5 V/20 A) prototype circuit are also given.

A modified asymmetrical pulse-width-Modulated resonant DC/DC converter topology

Abstract: A modified asymmetrical pulse-width-modulated resonant dc/dc converter employing an auxiliary circuit will be proposed in this paper. The auxiliary circuit consists of a network of two capacitors and an inductor. The aim of this network is to produce zero-voltage-switching (ZVS) over a wide input voltage range, while reducing the voltage stress on the resonant component. A detailed analysis and performance characteristics are presented. Experimental results for a 5 V, 35 W converter show an efficiency of 83% at a constant operating frequency of 500 kHz. Using metal oxide semiconductor field effect transistors (MOSFETs) as synchronous rectifiers can further reduce power losses and improve the efficiency to be greater than 90%.

DC/DC converter for high input voltage: four switches with peak voltage of V/sub in//2, capacitive turn-off snubbing and zero-voltage turn-on

Abstract: 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 converters, to provide zero-voltage turn-on, or is associated with one or two capacitors to provide resonant operation), and contains a capacitor in series with the output transformer (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 V output at up to 25 A, and 50 kHz switching frequency. The performance agreed well with the predictions. The measured efficiency was 93.6% at full load, and was a maximum of 95.15% at 44.8% load.