Showing papers on "Forward converter published in 1993"

General-purpose sliding-mode controller for DC/DC converter applications

Abstract: A general-purpose sliding-mode controller is described, which can be applied to most DC-DC power converter topologies. It has the same circuit complexity as standard current-mode controllers, but provides extreme robustness and speed of response against supply, load, and parameter variations. Moreover, contrary to other sliding-mode techniques, the proposed solution features constant switching frequency in the steady state, synchronization to external triggers, and absence of steady-state errors in the output voltage. >

Power conversion and distribution system

Abstract: A power conversion system is described which includes a power input for accepting a waveform at a given power level and frequency, and a power output for providing an output waveform at a second given power level. A DC to AC converter accepts a waveform based on an input wave form from the power input and converts the waveform to an AC waveform having a frequency at least approximately an order of magnatude higher than the frequency of the input waveform for application to a DC to AC converter output. An AC converter accepts the output waveform from the DC to AC converter output and provides a converted waveform from an output of the AC converter to the power output. A coupling device operates at the frequency of the converter output for coupling the output of the DC to AC converter to the AC converter.

A current-sourced DC-DC converter derived via the duality principle from the half-bridge converter

Abstract: A current-sourced switch-mode power supply topology is developed by applying a duality principle to a voltage-sourced half-bridge converter. The converter has boost converter characteristics and is suited to low-voltage high-current input applications. It is shown to compare favorably with the center-tapped transformer converter. Two optional enhancements-nondissipative snubber networks and inductor clamping windings-are also examined. Some results obtained with a low-power prototype are presented. >

The three-level ZVS-PWM DC-to-DC converter

Abstract: A novel high-frequency DC-to-DC power converter for high voltage and high power is introduced which features zero voltage switching (ZVS), operation at constant frequency, regulation by pulse width modulation (PWM), and low RMS current stress upon power switches. Its greatest attribute, in comparison with the full-bridge (FB-ZVS-PWM) converter, is that the voltage across the switches is half of the input voltage, This property is achieved due to the use of a three-level leg in place of the conventional two-switch leg. Operation, analysis, design procedure and example, and simulation are presented. A prototype operating at 100 kHz, rated at 600 V input voltage, and 1.5 kW output power and 25 A output current has been fabricated and successfully tested in the laboratory. The measured efficiency at full load was 93%. >

New control scheme for AC-DC-AC converter without DC link electrolytic capacitor

Abstract: A novel concept for a static three-phase to three-phase power converter for an AC motor drive with unity power factor and reduced harmonics on the utility line is presented. The power circuit consists of two back-to-back connected six-pulse bridges having only a 5-/spl mu/F ceramic capacitor in the DC link. By controlling the active power balance between two bridges, the DC link voltage can be maintained within a 20-V deviation from the nominal value with the small ceramic capacitor regardless of the load variation. >

An improved full-bridge zero-voltage-switched PWM converter using a saturable inductor

Abstract: The saturable inductor is employed in the full-bridge (FB) zero voltage switched (ZVS) pulse width modulated (PWM) power converter to improve its performance. The current and voltage stresses of the switches as well as parasitic oscillations are significantly reduced compared to those of the conventional FB-ZVS-PWM power converter. The qualitative analysis is presented and is verified on a 500 kHz, 5 V/40 A converter. >

Asymmetrical pulse width modulated resonant DC/DC converter topologies

Abstract: Asymmetrical pulse width modulated (APWM) DC-DC resonant converter topologies which exhibit near zero switching losses while operating at constant and very high frequencies are presented. The converters include a bridged chopper to convert the DC input voltage to a high frequency unidirectional AC voltage which in turn is fed to a high frequency transformer through a resonant circuit. The bridged chopper has two switches which alternately conduct. The duty cycles of the conduction of the switches are complementary with one another and are varied to control the output voltage. Three resonant circuit configurations which are suitable for this type of control are presented. Frequency domain analysis of the converter is given and performance characteristics are presented. Experimental results for a 48 V to 5 V, 30 W converter show an efficiency of 88% at a constant operating frequency of 1 MHz. >

Selectable output power converter

Abstract: A power converter for providing a selectable desired voltage has a converter circuit having an input port for receiving an input of a first voltage and an output port for providing an output of a second voltage. The converter circuit also has a keyway for receiving a key. The key, which is configured to be received by the keyway, contains an electrical component and has a body within which the electrical component is disposed. The output voltage of the converter is determined by the value of the component disposed within the body of the key such that the output voltage can be varied by replacing the key with another key having an electrical component of a different value.

Analysis and design of a series-parallel resonant converter

Abstract: A high-frequency link series-parallel resonant power converter is analyzed using the state-space approach. Analysis is presented for both the continuous capacitor voltage mode and the discontinuous capacitor voltage mode. Steady-state solutions are derived. Design curves for the converter gain and other component stresses are obtained. A method of optimizing the converter under certain constraints is presented and a simple design procedure is illustrated by a design example. Experimental results are presented to verify the theory. >

Microprocessor control of multiple peak power tracking DC/DC converters for use with solar cell arrays

Abstract: A method and an apparatus for efficiently controlling the power output of a solar cell array string or a plurality of solar cell array strings to achieve a maximum amount of output power from the strings under varying conditions of use. Maximum power output from a solar array string is achieved through control of a pulse width modulated DC/DC buck converter which transfers power from a solar array to a load or battery bus. The input voltage from the solar array to the converter is controlled by a pulse width modulation duty cycle, which in turn is controlled by a differential signal comparing the array voltage with a control voltage from a controller. By periodically adjusting the control voltage up or down by a small amount and comparing the power on the load or bus with that generated at different voltage values a maximum power output voltage may be obtained. The system is totally modular and additional solar array strings may be added to the system simply be adding converter boards to the system and changing some constants in the controller's control routines.

Magnetically integrated full wave DC to DC converter

Abstract: A full wave DC to DC converter that is magnetically integrated so that the function of the output filter inductor is magnetically included in the transformer assembly. Two essentially symmetrical transformers have their primary windings connected in series and are driven by a full wave switched primary circuit such as a full bridge. The transformer secondaries are polarized so that their rectifying diodes conduct on opposite phases, so only one transformer secondary conducts for each half cycle. The conducting secondary winding conducts for each half cycle. The conducting secondary winding conducts both forward current reflected from the primary and flyback current from collapsing core flux. The transformer having the non-conducting secondary stores energy as magnetic flux. On the other half-cycle, the transformers reverse roles. Because stored transformer flux energy is released to the load through the secondary windings, continuous current is maintained and no separate output smoothing inductor is required.

Power converter having optimal dynamic operation

Abstract: A DC to DC, fixed frequency, Buck family power converter having a first feedback control loop for regulating output current or output voltage depending on the operational mode selected, a second feedback control loop for current mode control and a third feedback control loop for providing improved dynamic response for all conditions of line and load. The third feedback control loop senses the output voltage and generates a variable ramp signal having a slope (M) which is proportional to the converter output voltage. By maintaining as a constant (K) a ratio of the variable ramp slope (M) to the falling slope (M 2 ) of a voltage representation of the inductor current in an LC network of the Buck regulator or K=M/M 2 , improved dynamic operation of the power converter results for a plurality of output voltages particularly improving output ripple rejection and minimizing effects of injected noise in the current mode control loop.

Low cost DC to AC converter for photovoltaic power conversion in residential applications

Abstract: The development and experimental results of a low-cost 500-W DC-AC power converter for photovoltaic power conversion in residential applications are described. The converter uses low-cost technology usually applied in consumer products. The DC-AC converter is specially designed for operation at a wide DC input voltage range (30-170 V) in order to allow optimal power conversion with an arbitrary number of series connected solar arrays. A step-up chopper is used for MPP tracking and provides a constant 200-V DC link for the following push-pull power converter. This galvanic isolating power converter operates at 100 kHz and controls the current in the mains sinusoidally. A thyristor bridge alternates the current after each half line period. The required auxiliary power is kept below 7 W and is taken from the choke of the step-up chopper. >

Single phase unity power factor control for dual active bridge converter

Abstract: An AC line fed switching power supply with a single power converter stage is described which operates with high input power factor while maintaining good regulation of the desired output DC voltage. The single-power converter is a dual active bridge DC-to-DC power converter (DABC), comprising high-frequency transformer-coupled input and output bridge converters. The DABC receives a rectified AC line voltage via a diode-bridge rectifier connected to a small, high-frequency filter capacitor. The two active bridges, generating edge-resonant square waves at their transformer terminals, appropriately phase-shifted from each other to simultaneously perform the high-efficiency DC output regulation while maintaining unity power factor at the AC input. The soft-switching nature of the converter allows increased performance (in terms of efficiency and stresses) and reduction in size/weight at operating frequencies in the range of 50-250 kHz. Simulations, and experimental results are presented to corroborate the analysis. >

Phase-controlled series-parallel resonant converter

Abstract: A constant-frequency, phase-controlled, series-parallel resonant DC-DC converter is introduced, analyzed in the frequency domain, and experimentally verified. To obtain the DC-DC converter, two identical series-parallel resonant inverters are paralleled and the resulting phase-controlled resonant inverter is loaded by a voltage-driven rectifier. The converter can regulate the output voltage at a constant switching frequency in the range of load resistance from full-load resistance to infinity while maintaining good part-load efficiency. The efficiency of the converter is almost independent of the input voltage. For switching frequencies slightly above the resonant frequency, power switches are always inductively loaded, which is very advantageous if MOSFETs are used as switches. Experimentally results are given for a converter with a center-tapped rectifier at an output power of 52 W and a switching frequency of 127 kHz. The measured current imbalance between the two inverters was as low as 1.2:1. >

High frequency push-pull converter with input power factor correction

Abstract: A single stage high frequency push-pull converter with input power factor correction. The boost converter for input power factor correction and the high-frequency push-pull DC/AC inverter are combined into a single stage converter thereby reducing the number of circuit components while at the same time reducing the voltage stress on the high frequency switching transistors of the converter.

Characteristics of the multiple-input DC-DC converter

Abstract: A multiple-input DC-DC converter is proposed for realizing a clean electric power generation system. The two-input buck-boost type converter is analyzed, and the static and dynamic characteristics are clarified theoretically and are confirmed by experiment. >

Power converter for converting DC voltage into AC phase voltage having three levels of positive, zero and negative voltage

Abstract: An apparatus for a three-level DC/AC converter, in which the width of output pulse having the same polarity as the fundamental wave of the converter output phase voltage is adjusted depending upon the DC component of a differential voltage between two DC voltages in a dipolar modulation system of the converter. Whereby, the imbalance of DC components between the two DC voltages is easily and effectively suppressed.

Active clamp PWM forward converter with self driven synchronous rectification

Abstract: The necessity of developing high efficiency and high power density on board DC/DC power converters with low output voltage for telecommunication applications leads to substitution of the rectifier diodes of the output stage by synchronous rectifiers. Control complexity and driving losses are the main constraints of this technique. A very simple implementation of self driven synchronous rectification in the active clamp PWM forward power converter is proposed. The absence of control circuitry and the minimization of losses are the main benefits of this circuit, whose analysis and optimization are addressed. Very high overall efficiency (89%) has been obtained in an actual prototype (3.3 V, 20 A). >

Soft-switched DC/DC converter with PWM control

Abstract: In this paper, a soft-switched power converter with two variations is discussed. An asymmetrical 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 design of the converters are also presented. Two 50 W 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, the converters have high full load and partial load efficiencies. They are potential candidates for high efficiency, high density power supply applications. >

Isolated multiple output Cuk converter with primary input voltage regulation feedback loop decoupled from secondary load regulation loops

Abstract: A novel isolated, capacitive idling, Cuk switching-mode converter features two separate nonisolated feedback loops, one on the primary side to regulate against input voltage changes and the other on the secondary side to regulate against load current changes only While preserving cost, size and simplicity of conventional multiple output switching-mode converters, the new converter and feedback control approach offers the advantages of simple feedback control implementation due to elimination of isolation requirements in the feedback control circuits, simultaneous regulation of all output voltages from no load to full load, and greatly improved bandwidth and step-load transient response For operation from a rectified ac line, feedback control on the input to the transformer is modified to force the average input current to follow the full-wave rectified ac line voltage for unity power factor (UPF) performance on the input and wide bandwidth voltage regulation on the output Both are demonstrated simultaneously in a single, isolated, multiple ac-to-dc switching-mode power converter The novel decoupled feedback control is shown to be equally applicable to a number of Cuk-type converter topologies featuring capacitive energy transfer from a voltage source to a load

Analysis and design of a modified series resonant converter

Abstract: A modified series resonant converter (SRC) (also referred to as the LCL-type SRC) which overcomes the problems of the standard series resonant converter is presented. A state-space approach is used for the analysis. Analysis shows that the converter enters into three different modes. Converter gain and other component stresses are plotted with variation in the load current. Detailed experimental results obtained from a 500 W MOSFET converter are presented to verify the theory. With a proper selection of inductor ratio, only a narrow variation in switching frequency is required to regulate the output voltage for wide variation in the load current. It is shown that, by placing the parallel inductor on the secondary side, the parasitics of the high-frequency transformer can be used profitably. >

Forward converter with two active switches and unity power factor capability

Abstract: A power converter integrates an input boost converter and an output forward converter into a single power stage utilizing only two active switches. AC input power is provided through a rectifier to an input inductor which supplies current to a main node. The diode is connected from a main node to a DC bus supply line and current is returned to the rectifier by DC bus return line. An energy storage capacitor and a series connected switching device and diode are connected across the DC bus lines. A second control switching device is connected from the main node to the DC bus return line. The primary of a high frequency transformer is connected between the main node and the junction between the first switching device and diode, and the secondary of the transformer is connected to an output circuit which includes a rectifier and an inductor and capacitor filter to provide a DC output voltage to a load. When both switching devices are turned off, current from the input inductor is supplied to charge up the energy storage capacitor and to drive the transformer magnetizing current to zero. Turn on of both switching devices causes the capacitor to be discharged via the switching devices through the primary of the transformer to supply power to the load. Intermediate modes in which one or the other of the switching devices is on while the other is off are available. By proper selection of the time of turn on of the devices and the modes of switching of the devices, the AC input current can be controlled to be substantially sinusoidal, or the output voltage can be controlled to a selected level, and in either event the power factor as seen at the AC input lines is substantially unity.

Full shunt boost switching voltage limiter for solar panel array

Abstract: According to the present invention a bus voltage limiter is connected between a photovoltaic solar panel array and a load to limit the output voltage to a fixed dc reference voltage. The limiter includes a pulse width modulator which controls the duty cycle of a power switch from 0% to 100% to maintain a substantially constant output voltage V ref . A coupled inductor type boost DC to DC converter includes a pair of main windings which cooperate with the duty cycle modulated power switch to provide the output voltage. An auxiliary winding provides input ripple current cancellation in conjunction with a second inductor and a dc blocking capacitor.

An integrated high power factor three-phase AC-DC-AC converter for AC-machines implemented in one microcontroller

Abstract: A high power factor three-phase AC-DC-AC power converter for AC machines has been designed and tested. The AC-DC-AC converter is controlled by one single 16-b microcontroller. The converter has two PWM-VSI bridges with common snubber- and drive-circuit topologies. The high power factor rectifier is space vector controlled and the inverter controls an AC-induction machine by an energy optimized strategy. Common software tasks are utilized in order to minimize memory demands in the microcontroller. Measurements show a high power factor of the converter, and, in addition, the converter can very rapidly change from motor to generator operation during reversing of the AC machine. It is concluded that the AC-DC-AC converter works well, can be designed to be very compact, and represents some of the state-of-the-art integration and performance in three-phase AC-DC-AC converters. >

Power converter/inverter system with instantaneous real power feedback control

Abstract: A power converter/inverter system for a load comprises a converter circuit for converting an alternating current power input into a direct current power intermediate signal in response to a first PWM voltage. An inverter inverts the DC power intermediate signal into an AC power output in response to a second PWM voltage. A smoothing filter is arranged in series between a converter and the inverter for filtering the DC power intermediate signal. An instantaneous real power calculating circuit calculates an instantaneous real power (IRP) relative to the inverter and is determined by a torque current command value and a load angular speed signal. A converter controller controls the first PWM voltage of the converter in accordance of a combination a predetermined converter amplitude setpoint, a DC voltage present at the DC power intermediate signal, and the instantaneous real power product. An inverter controller controls the second PWM voltage of the inverter in accordance with the inverter amplitude setpoint and amplitude of the AC power output.

Analysis and design of weighted voltage-mode control for a multiple-output forward converter

Abstract: A power stage model of a multiple-output forward power converter with weighted voltage-mode control is derived incorporating all the major parasitics. The model is employed to identify the feasible region of the weighting factors to meet given DC regulation specifications. A design procedure that determines the optimal selection of the weighting factors is proposed. The DC model and the design procedure are verified on an experimental two-output forward converter. >

High voltage regulator for an integrated horizontal sweep system

Abstract: A voltage regulator for a flyback-type high voltage supply having: a pulse transformer with its secondary interconnected in series with the primary of a flyback transformer; a control circuit for sensing the generation of a flyback pulse, a reference voltage, and a feedback voltage signal appearing at the output of the flyback transformer; and a switch for selectively applying energy to the primary of the pulse transformer while uniformly maintaining the flow of current through the primary of the flyback transformer.

Switching converter with open-loop primary side regulation

Abstract: The isolated, multiple output, switching converter is created with a number of unique performance characteristics. The converter operates in continuous inductor current mode (CICM) of operation for all load currents from no load to full load on all outputs despite the presence of simple rectifier diodes only on the converter secondary sides. The regulation of output voltages on all outputs against the changes of the input voltage is provided by use of a simple open-loop control circuit connected to the primary side and thus eliminating the need for isolation in the control circuit. The regulation against the load current changes in the single output case is also provided on the primary side by a load current sensing circuit. An additional benefit of the switching converter is in the elimination of the losses and voltage overshoots associated with the leakage inductance of the isolation transformer when operated as pulse width modulated (PWM) converter.

Small-signal analysis and design of weighted voltage-mode control for a multiple-output forward converter

Abstract: The small-signal model for a multiple-output forward power converter with weighted voltage control is derived. The effects of the weighting factors on the small-signal behavior are investigated. In addition, the small-signal characteristics of weighted voltage control are compared with the characteristics of a multiple-output power converter with coupled output-filter inductors. Finally, the effects of weighted voltage control on the small-signal characteristics of the converter with coupled inductors are examined. Based on the analysis, the design procedure for loop compensation is presented. The small-signal model and the design procedure are verified on an experimental two-output forward power converter. >