Showing papers on "Forward converter published in 1996"

An improved soft switching PWM FB DC/DC converter for reducing conduction losses

Abstract: An improved soft-switching topology of a full-bridge (FB) pulsewidth-modulated (PWM) DC/DC converter is described. The new topology employs an energy-recovery snubber to minimize a circulating current flowing through the transformer and switching devices. By using an energy-recovery snubber instead of adding a tapped inductor and a saturable reactor to reduce RMS current stress, the converter achieves zero-current switching (ZCS) for the right leg due to the minimized circulating current and achieves zero-voltage switching (ZVS) for the left leg due to the reflected output current during the interval of left leg transition. Both analysis and experiments are performed to verify the proposed topology by implementing a 7 kW (120 VDC, 58 A) 30 kHz insulated gate bipolar transistor (IGBT) based experimental circuit.

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.

Switched-capacitor power supplies: DC voltage ratio, efficiency, ripple, regulation

Abstract: A comprehensive and accurate steady-state analysis of a step-up DC-DC switched-capacitor power converter is performed. No approximations, such as average techniques, are invoked. Parasitic elements such as diode forward voltages, on-resistances of transistors and equivalent-series resistances of capacitors are included into the model. The converter performance functions, i.e. DC voltage ratio, efficiency, output voltage ripple, are expressed in terms of the number of switched-capacitor stages, number of capacitors per stage, values of the capacitors and parasitic elements, switching frequency and load. Design criteria aiming at high efficiency, low ripple and achievable output voltage are formulated. Trade-offs between the efficiency requirement and good regulation capability are discussed.

A comparison between two current-fed push-pull DC-DC converters-analysis, design and experimentation

Abstract: This paper compares two current-fed push-pull DC-DC power converters: the current-fed push-pull power converter or isolated boost and an alternative topology named here as the dual inductor push-pull power converter (DIC). Since this latter converter has just one primary winding, the voltage across the main switches is reduced to the half of that in the isolated boost topology; the average current in the input inductors is also halved and the RMS current in the output capacitor is smaller. The overall efficiency is increased and the power converter's volume is reduced in the DIC converter. These and other improved design characteristics make this alternative topology more attractive than the isolated boost for equivalent applications. Analytical equations, output characteristic curves and computer simulations of both power converters are compared. An experimental breadboard of 480 W power has been assembled in order to verify the performance of the DIC power converter. The main results are provided.

Three-pin buck and four-pin boost converter having open loop output voltage control

Abstract: A controlled output voltage is provided for a switching mode power converter operating in the continuous conduction mode without requiring a feedback path coupled to monitor the output voltage. Instead, a voltage related to the input voltage is monitored. The monitored voltage is compared to a periodic waveform for forming a switch control signal. In the case of a buck converter operating as a voltage regulator, over each period of the periodic waveform, the periodic waveform is representative of the inverse function. In the case of a boost converter operating as a voltage regulator or buck converter operating as a bus terminator or power amplifier, over each period of the periodic waveform, the periodic waveform has a linear slope. The switch control signal controls a duty cycle of the power switches. Therefore, switching is controlled in an open loop, rather than in a closed loop. By monitoring a voltage related to the input voltage, rather than the output voltage, an integrated circuit for controlling the buck converter or boost converter requires few pins and can sink or source current.

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.

DC-to-DC power conversion with high current output

Abstract: A DC-to-DC converter for high current outputs is provided having an input side circuit, including two converter bridges, and an output side circuit, including two diode rectifier configurations. The input and output circuits are preferably connected by a co-axial winding transformer (CWT). Switches in the input side bridges alternately connect and disconnect a DC input voltage to and from the primary side of the transformer. The waveform appearing on the secondary of the transformer is rectified by the output side rectifier configurations. A switched-in bias voltage in each input side converter bridge provides for reversal of the current in the bridge after the bridge is switched off, and before the other bridge is switched on. This current reversal allows a current in one of the rectifier configurations of the output side circuit to be brought softly to zero before being reversed biased by the switching on of the other converter bridge. Thus, a reverse recovery spike in the output circuit is avoided. For high current outputs, the CWT is preferably constructed of a copper tube secondary winding enclosing the primary windings. The rectifier configurations include multiple diodes arranged in symmetrical configurations for optimal sharing of the high output currents. Air and water cooling of the diode configurations and output bus bars is provided. The output side circuit assembly can be provided as an integrated unit which is attached between the CWT and the load attached to the converter output.

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.

Converter comprising a piezoelectric transformer and a switching stage of a resonant frequency different from that of the transformer

Abstract: In a DC--DC converter comprising a piezoelectric transformer (25) having an input capacitance between a pair of transformer input teminals and a transformer resonant frequeney, an input switching stage (27) responsive to a DC input signal for supplying a sinusoidal transformer input signal, and an output rectifier stage (29) for producing a converter output voltage across a load resistor (23), the switching stage includes an input series inductor (39) connected in series to one of the transformer input terminals and having an input series inductance that defines a switching resonant frequency in cooperation with the input capacitance to be different from the transformer resonant frequency. It is preferred when the switching stage is operable in zero volt switching that the input series inductance be either between 1.0 and 2.2 μH or between 3.0 and 3.4 μH, or more preferably either between 1.4 and 1.8 μH or about 3.0 μH, if the input series inductance should be 2.8 μH for rendering the switching resonant frequency equal to the transformer resonant frequency. The converter output voltage is controlled by a control stage (51) for feeding the converter output voltage back to the switching stage to reduce an on-off switching frequency of the DC input signal with an increase in load.

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.

Dual output three-level boost power factor correction converter with unbalanced loads

Abstract: In this paper, a control strategy for three-level boost power factor correction converter with fully regulated two outputs is proposed. Beyond two outputs which are completely regulated, a switching logic law is established to minimize the input current ripple. Besides the features of the three-level boost power converter already known, the proposed approach has the advantage of regulating two output voltages for unbalanced loads, guaranteeing voltage sharing across the semiconductor device independent of the load, based on a Lyapunov-like technique. The robustness of the feedback control system is investigated, and experimental results are reported.

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.

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

Analysis of the chaotic regime for DC-DC converters under current-mode control

Abstract: The possibility of chaotic behavior in DC-DC power converters under current-mode control has been well established by prior work. Although the spectral modifications that are associated with chaotic operation may provide an important motivation for actual operation in this regime, the literature on chaos in power electronics has tended to treat it more as an exotic effect than as a feasible mode of operation. This may explain why no prior work has attempted-for the chaotic regime-to characterize even the most basic property of DC-DC power converters, namely the input-output gain (which is the ratio of the average output voltage to the DC input voltage). The present paper shows how to compute this gain, and other averages of interest, for the chaotic regime of buck, boost, and buck-boost power converters under constant-frequency current-mode control and in continuous conduction. The authors' approach invokes the fact that the chaotic sampled inductor current is ergodic, hence governed by a "probability" density, which permits time averages to be replaced by ensemble averages. Although the density can be computed in detail, it turns out that approximating it (quite crudely) as a uniform density still yields very good results. In contrast, traditional computations based on the nominal (and unstable) periodic solution can be considerably in error.

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%.

Double forward converter with soft-PWM switching

Abstract: A double forward DC-to-DC converter with soft-PWM switching provides two voltage pulses to the output low-pass filter within one switching cycle (hence, the name double forward) The double forward DC to DC converter includes a transformer having a single primary winding and a two secondary windings A main switch, under the control of a PWM control circuit, is connected is series with the primary winding An auxiliary switch is coupled across with the main switch by way of a resonant capacitor The resonant capacitor and auxiliary switch are used to automatically reset the transformer core while the main switch is on back to the voltage source connected to the transformer primary A diode and snubber capacitor is connected across the drain-source terminals for both the main and auxiliary switches for minimizing switching losses The current mirror used in prior art is abandoned in order to avoid the locked-up mode of operation The secondary windings of the transformer are connected to a pair of saturable reactors which, in turn, are connected to rectifier diodes in order to eliminate the reverse recovery losses of the rectifier diodes A freewheeling diode is connected across the secondary winding and cooperates with the saturable reactors to maintain the load current to the secondary windings during the transitions of the main and auxiliary switches

Circuit for supplying electric load such as fan or storage battery of vehicle from solar generator

Abstract: A power supply circuit for an electric load (2) like a fan or battery in a car driven off a solar generator (1) has impedance matching between the solar generator and a DC converter (6) in front of the load. There is a control member (18) which can short out the converter depending on the value of at least one operational parameter during a regime when the converter losses are expected to be higher than the losses caused by the mismatch if the load is coupled directly to the solar generator. The converter is a pulse-width modulated (PWM) step-down converter. It has a switching transistor between input and output and another across the output terminals.

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.

Voltage source type power converting apparatus

Abstract: A voltage source type power converting apparatus having voltage source type power converter units and phase-shifting transformers. The transformers have either a common multiple-phase primary winding or a group of parallel connected multiple-phase primary windings, either of which being connected in parallel or series to a multiple-phase AC system. The transformer further include a group of multiple-phase secondary windings with phase differences with respect to each other and which are connected to voltage source type power converter units. The voltage source type power converter units are operated with the phase differences. Accordingly, the construction of the multiplexing phase-shifting transformer is simple, and fundamental electric variables can be controlled by a simple phase controlling operation. In addition, a higher harmonic defect of the AC system can be reduced, and the DC voltage can be easily raised.

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.

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.