Showing papers on "Forward converter published in 1999"

Performance characteristics of a cascaded two-level converter

Abstract: A cascaded two-level power converter is proposed which utilizes two six-transistor inverters and is capable of producing voltages which are identical to those of three-level and four-level converters. Since the machine voltages are the same, the converter performance is the same as is verified through laboratory tests. The advantages and disadvantages of the proposed cascaded converter are explored. The proposed converter is simpler to construct and offers more nonredundant switching states per number of active semiconductors than standard multi-level converters.

Full-bridge isolated current fed converter with active clamp

Abstract: The full-bridge isolated current fed converter with active clamp advantages are in its ZVS capability and its well-clamped operation devoid of voltage overshoot on the converter switches and the rectifier diodes. Another relative advantage is that the isolation transformer magnetising current does not have a DC component. An analysis defines the converter voltage transfer ratio taking into consideration the switches' parasitic capacitance and the transformer leakage and magnetizing inductance. The analysis defines the selection criteria for power stage component values. Two breadboard models were built and tested utilizing the current fed full bridge topology. One model was realized as a DC/DC and the other as a single stage PFC. The models' experimental data confirmed calculations.

Hysteretic regulator and control method having switching frequency independent from output filter

Abstract: A DC to DC power converter (58) and method of controlling the DC to DC power converter (58). The converter (58) has a first switch (S 1 ) coupled to a second switch (S 2 ). The converter (58) is adapted to receive an input voltage V in , generate an output voltage V out , and operate at a switching frequency. A hysteretic mode control circuit (52) includes a first circuit generating a ramp signal at input (56) for controlling the converter (58). The first circuit includes a first capacitor (C 1 ) with the ramp signal generated at an end of the first capacitor (C 1 ). The hysteretic mode control circuit (52) is coupled to the first (S 1 ) and second (S 2 ) switches, where the switching frequency of the first and second switches is dependent upon the ramp signal (56) determined by the value of the components of the first circuit rather than on the voltage from the output filter of the DC to DC power converter. The invention is particularly useful for applications such as DSPs and mixed signal or analog circuits.

Dual-mode non-isolated corded system for transportable cordless power tools

Abstract: A dual-mode system for inexpensively operating electrically powered double-insulated devices ( 12 ), such as hand-held power tools and appliances. The system includes a cordless battery pack ( 14 ) that supplies the power and current demands of the device ( 12 ) in a cordless mode or a non-isolated corded voltage converter ( 16 ) that supplies the necessary power and current demands in a physical envelope commensurate in size and interchangeable with that of the battery pack ( 14 ). The corded voltage converter ( 16 ) is provided with a non-isolated high efficiency power supply that allows the converter ( 16 ) to generate the power and current required by the driven device ( 12 ). The double insulation of the driven device ( 12 ) negates the need for a transformer-isolated voltage converter. Eliminating the power transformer from the converter significantly reduces the cost of the module ( 16 ). Additionally, the need for multiple battery packs and fast rechargers is minimized by the availability of a low-cost converter. The voltage converter ( 16 ) includes an inrush current limiter ( 103 ) and power conditioner for filtering AC or DC input power. The filtered voltage is chopped by a transformerless buck-derived converter. The chopped voltage is rectified and filtered to provide low-voltage DC power to the drive motor of the powered double-insulated device ( 12 ).

A 'zero' ripple technique applicable to any DC converter

Abstract: Coupled magnetics filter techniques are important tools in a converter designer's arsenal, but are not well understood. Evidence of this is one basic building block of coupled filters, reinvented numerous times during the past 65 years. A detailed analysis of coupled magnetics for DC-DC converters, based on a key building block, is given.

Interleaved zero current switching in a power factor correction boost converter

Abstract: A method and apparatus for interleaving switching of multiple transistor switches in a power factor correction (PFC) boost converter and for timing the switching to occur when a current through a freewheeling diode corresponding to each switch is at a minimum level. The converter draws input current from an alternating current power supply for forming a regulated output voltage. A controller senses an input current and an output voltage across an output capacitor for controlling switching to regulate the output voltage and to ensure that the input current is substantially in phase with an input voltage. Current through a first inductor associated with a first switch is allowed to fall substantially to zero upon discharging the first inductor prior to re-charging the first inductor. Charging of a second inductor associated with a second switch, however, is initiated prior to completion of discharging the first inductor. Similarly, current through the second inductor is allowed to fall substantially to zero prior to re-charging the second inductor. An advantage is that from the perspective of the power supply, the converter operates in continuous conduction mode, while from the perspective of each of the switches, the converter operates in discontinuous conduction mode. The invention reduces power dissipated in the switches, increasing reliability and allowing higher frequency operation. In accordance with another aspect of the invention, a synchronizing signal is generated by the PFC converter for synchronizing operation of a second converter, such as a pulse-width modulation converter, with the PFC converter.

A three-switch high-voltage converter

Abstract: A novel single active switch two-diodes high-voltage converter is presented. This converter can operate into a capacitor-diode voltage multiplier, which offers simpler structure and control, higher efficiency, reduced electromagnetic interference (EMI), and size and weight savings compared with traditional switched-mode regulated voltage multipliers. Two significant advantages are the continuous input current and easy isolation extension. The new converter is experimentally verified. Both the steady-state and dynamic theoretical models are correlated well with the experimental data.

Analytical calculation of the RMS current stress on the DC link capacitor of voltage DC link PWM converter systems

Abstract: In this paper a simple analytical expression for the current stress on the DC link capacitor of a voltage DC link converter system, as caused by the load-side inverter is derived. There, a sinusoidal inverter output current and a constant value of the DC link voltage are assumed. The DC link capacitor current RMS value is determined by the modulation depth and by the amplitude and the phase angle of the inverter output current. Despite the neglection of the output current ripple the results of the analytical calculation match very well with a digital simulation even if the output current ripple is relatively high as given, e.g., for low-frequency IGBT inverter systems. Thus, the approximation can advantageously be used for designing the DC link capacitor of PWM converter systems.

Design and analysis of a switched-capacitor-based step-up DC/DC converter with continuous input current

Abstract: This paper presents the use of the current control scheme in switched-capacitor (SC)-based step-up dc/dc converter. It not only includes all positive characteristics of previous SC converters, including small size, light weight, high power density, and the amenability to IC hybridization, but also has the prominent features of continuous input current waveform and better regulation capability than the traditional SC converters. The problem of conducted electromagnetic interference with the supply network, which generally exists in previous SC converters, is highly suppressed. The concept of energy transfer is achieved by using dual SC step-up converter cells operating in antiphase. Each cell is switching between two topologies for the same duration. The dc voltage conversion ratio is controlled by the current control scheme in order to adjust the charging profile of the capacitors. A generalized n-stage converter is presented and is analyzed by a simplified third-order state-space equation set. The static and dynamic behaviors and the design constraints of the converter are derived. A prototype of the 30 W 5 V/12 V two-stage converter has been built, giving an overall efficiency of 78% with power density of 15 W/in/sup 3/. Its stability of operation is also presented.

An approach to achieve ride-through of an adjustable speed drive with flyback converter modules powered by super capacitors

Abstract: Adjustable speed drives (ASDs) under short-term power interruptions (STPIs) can interrupt a critical process. In this paper an approach to provide ride-through with flyback converter modules (FBCMs) powered by super capacitors is explored. The proposed approach is modular and facilitates additional modules to be added to suit higher voltage/power ratings. Both unidirectional and bidirectional flyback DC/DC converter topologies are examined. Simulation and experimental results are presented.

Fuel cell system capable of reducing electric power loss

Abstract: A fuel cell system minimizes the power loss that may occur in a conduction passage during supply of electric power from a fuel cell (36) to a load. A bypass (48) connects between the input of a DC/DC converter (38) and the output thereof, and therefore supplies power generated by the fuel cell (36) to an inverter (44), bypassing the DC/DC converter (38). A changeover switch (37) selectively changes the connection of the output of the fuel cell (36) between the connection to the input of the DC/DC converter (38) and the connection to the bypass (48). When the fuel cell (36) is connected to the DC/DC converter (38), the power from the fuel cell (36) is supplied to the inverter (44) or a battery (40) via the DC/DC converter (38). When the fuel cell (36) is connected to the bypass (48), the power from the fuel cell (36) is supplied to the inverter (44), bypassing the DC/DC converter (38). A cutoff switch (41) disconnects the output of the battery (40) from a connecting line. That is, the cutoff switch (41) disconnects the battery (40) from the inverter (44), the bypass (48) and the like when turned off. When turned on, the cutoff switch (41) connects the battery (40) to those components.

Transformers for multipulse AC/DC converters

Abstract: In a 12-pulse converter system a 3-phase auto transformer with 4 windings per phase is used to power two 6-pulse converter bridges connected in parallel with a large dc filter capacitor. The transformer rating is typically about 40% of the dc kW load. The voltage ratio is typically 1:1 so that the average dc output of a multi-pulse converter is generally the same as that of a conventional 3-phase bridge rectifier without transformer, however, ac input harmonic currents are greatly reduced. A small single-phase transformer is used to block unwanted circulating currents between the two 6-pulse converters. Where necessary to further reduce high frequency harmonic currents, a 3-phase ac line reactor may be connected in series with the source of ac power. Where a smaller degree of harmonic reduction is acceptable, only 3 windings per phase are required on the transformer and the small single-phase transformer is eliminated by raising the zero-sequence impedance of the auto transformer by means of an additional magnetic path. This method provides a higher zero-sequence impedance compared to a conventional 3-limb magnetic structure used in most 3-phase transformers. The 1:1 voltage ratio feasible in this invention facilitates retrofit applications, also the concept can be applied to a greater number of parallel converters such as those giving 18-pulse operation.

Isolated and soft-switched power converter

Abstract: An isolated and soft-switched power converter is used for DC/DC and DC/DC/AC power conversion. The power converter includes two resonant tank circuits coupled back-to-back through an isolation transformer. Each resonant tank circuit includes a pair of resonant capacitors connected in series as a resonant leg, a pair of tank capacitors connected in series as a tank leg, and a pair of switching devices with anti-parallel clamping diodes coupled in series as resonant switches and clamping devices for the resonant leg. The power converter is well suited for DC/DC and DC/DC/AC power conversion applications in which high-voltage isolation, DC to DC voltage boost, bidirectional power flow, and a minimal number of conventional switching components are important design objectives. For example, the power converter is especially well suited to electric vehicle applications and load-side electric generation and storage systems, and other applications in which these objectives are important. The power converter may be used for many different applications, including electric vehicles, hybrid combustion/electric vehicles, fuel-cell powered vehicles with low-voltage starting, remote power sources utilizing low-voltage DC power sources, such as photovoltaics and others, electric power backup systems, and load-side electric storage and generation systems.

Integrated planar inductor scheme for multi-module interleaved quasi-square-wave (QSW) DC/DC converter

Abstract: Compact, high-efficiency, low-voltage and large-current DC/DC power converters with a fast transient slew rate are needed for future generation microprocessors. The interleaved quasi-square-wave (QSW) topology is a good candidate to improve their transient response significantly. Inductors are critical components in these converters. An integrated planar inductor scheme for multi-module interleaved QSW power converters is proposed. This integrated inductor utilizes the phase relationships of the currents in each module to integrate all the separate inductors for each module into one core, resulting in great reductions in the size and power losses of the inductor.

Universal pulse width modulating power converter

Abstract: A controller for a pulse width modulating (PWM) power converter. The controller monitors an output voltage and a current through a magnetic element for modulating a duty cycle of a main power switch. The controller is an eight-pin integrated circuit which controls either a forward converter or a post regulator without internal modifications. The monitored current of the forward converter forms a positive sensing signal. The monitored current of the post regulator forms a negative sensing signal. A current sense circuit of the controller forms an absolute value of either sensing signal. A soft-start circuit of the controller forms a start-up voltage ramp which is proportional to the level of a V CC supply without requiring an external capacitor. A duty cycle of the main switch is gradually increased by comparing the start-up voltage ramp to the absolute value of the sensing signal. A pulse skipping circuit of the controller disables switching of the main switch under light load conditions. An error signal representative of a difference between the output voltage and a desired output voltage is compared to a pulse skip reference voltage. When the error signal falls below the reference voltage, the main switch is disabled. Because the pulse skip reference voltage is inversely related to the V CC supply, pulsing of the main switch under light load conditions is spread out in time. A clock signal utilized to control switching of the main switch is generated internally or externally to the integrated circuit.

A single-stage power-factor-corrected AC/DC converter

Abstract: This paper presents a single-stage isolated converter topology designed 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 converter, but incorporates an additional transformer winding, 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 converter output is operated in discontinuous mode to minimize the bulk capacitor voltage variations when the output load is varied. Analysis of the converter is presented, and performance characteristics are given. Design guidelines to select critical components of the circuit are presented. Experimental results on a 150 W 50 kHz universal input (90-265 V) 54.75 V output AC/DC converter are given which confirm the predicted performance of the proposed topology.

Single stage high power-factor converter

Abstract: An output of a first converter for switching a rectified line current and an output of a second converter for switching a direct current are added together so that an efficiency, a power factor, a holding time, and a ripple characteristic can be improved. Further, the power supply apparatus can be made compact and the cost for manufacturing the apparatus can be reduced. A flyback converter type output circuit and a forward converter type output circuit are used in a parallel manner so that a transformer having a high efficiency can be used, and it becomes easier to control the apparatus.

A novel current-control method for three-phase PWM AC/DC voltage-source converters

Abstract: This paper presents a novel current-control-based control strategy, obtained in stationary frame, for a three-phase pulsewidth-modulated AC/DC voltage-source converter. In this control strategy, an error voltage is produced from the comparison of the output DC voltage with a DC reference voltage. This error voltage is then utilized by a proportional plus integral controller to generate a command signal for the input line current amplitude and is automatically controlled to the desired value. Therefore, there is no need to measure the input line currents. Stability analysis of the closed-loop system is made, and the stability region for proportional and integral gains which makes the operating point stable is also found. The resulting closed-loop system not only exhibits good transient response, but also provides sinusoidal line currents and unity power factor, both in the rectifying and regenerating modes. Experimental results are presented and compared with simulations.

Forward-flyback converter with current-doubler rectifier: analysis, design, and evaluation results

Abstract: Complete design-oriented steady-state analysis of the forward-flyback converter, with the current-doubler rectifier is provided. Advantages and disadvantages of this topology compared to the conventional forward converter are discussed. In particular, the transformer-secondary copper losses are evaluated. In addition, a step-by-step design procedure is given, Finally, experimental evaluation results obtained on a 3.3 V/50 A DC/DC converter prototype for the 40-60 V input-voltage range are presented.

Analysis and design of a single stage power factor corrected full-bridge converter

Abstract: A simple PWM full-bridge converter that integrates input power factor correction (PFC) with DC-DC conversion is examined in the paper. The converter's operation is analyzed, and the results of the analysis are used to determine its steady-state characteristics. A design procedure for the selection of components is derived and demonstrated with an example. The feasibility of the converter and its ability to satisfy the IEC 1000-3-2 Class D requirements for electrical equipment are shown with results obtained from an experimental prototype.

A zero-current-switching PWM flyback converter with a simple auxiliary switch

Abstract: A simple and effective approach of turning an isolated hard-switched converter design into a soft-switched one is presented. By adding an auxiliary winding, switch and small capacitor to the conventional pulsewidth modulation (PWM) isolated flyback converter, all switches and diodes are softly turned on and off. No extra active or passive voltage clamp circuit is needed to suppress voltage stress on the switching devices that were usually found in classical converters. A zero-current-switching (ZCS) PWM flyback converter topology with multiple outputs is analyzed and examined. The proposal inherently utilizes the leakage inductance of the "flyback" transformer to achieve ZCS of all switching devices. A complete steady-state DC analysis and the operating principle are described. The performance of an 80 W experimental converter prototype with dual-voltage outputs is included.

Calculation of the periodic spectral components in a chaotic DC-DC converter

Abstract: A simple mapping is derived, which describes the behavior of a peak current-mode controlled boost converter operating chaotically. The invariant density of this mapping is calculated iteratively and, from this, the power density spectrum of the input current at the clock frequency and its harmonics are deduced. The calculation is presented, along with experimental verification. The possibility of a novel application of chaos-amelioration of power supply interference-is discussed,.

Output ripple analysis of multiphase DC-DC converters

Abstract: This paper presents an output ripple analysis of multiphase DC-DC power converters having an output LC filter. Analytical expressions for the output voltage ripple of two- and three-phase DC-DC power converters are derived. Influence of the coupling coefficient of the output filter inductor on the output ripple is investigated. Because the unique parameters of the LC filter cannot be determined solely based on the specified maximum output ripple, an additional criterion based on minimum energy storage is introduced. A comparative evaluation of single-phase, two-phase, and three-phase DC-DC power converters is presented. The validity of the proposed analysis method is verified by experimental results.

Power supply device for electromotive railcar

Abstract: A power supply device for an electromotive railcar, including a series circuit composed of a plurality of first capacitors, connected to receive a first DC voltage from an electric power line; a plurality of DC/AC/DC converters. Each of the DC/AC/DC converters including an inverter bridge with an input thereof connected in parallel to one of the first capacitors and having a plurality of power transistors, an insulating transformer with a high carrier frequency and having a primary winding connected to an output of the inverter bridge, and a rectifier circuit connected to a secondary winding of the insulating transformer to output a DC voltage. The power supply device further including a smoothing circuit including a DC reactor and a second capacitor for smoothing the DC voltages output from the rectifier circuits of the DC/AC/DC converters, the smoothing circuit generating a second DC voltage; and a three-phase inverter including a bridge circuit having a plurality of power transistors, the three-phase inverter generating a three-phase AC voltage on the basis of the second DC voltage. The respective outputs of the rectifier circuits of the DC/AC/DC converters are connected to each other in parallel.

Modular transformer arrangement for use with multi-level power converter

Abstract: A modular transformer arrangement providing power to a multi-level power converter includes a plurality of three phase transformers having delta or extended delta connected primary windings and delta or extended delta or wye or zig zag wye connected secondary windings and the multi-level power converter has full bridge power modules inputs connected to isolated secondaries of the transformer modules and outputs connected in series and/or in parallel to provide increased voltage and/or current or multiple phases which can be phase shifted with respect to the input to the transformer.

Analysis and design of three-phase AC-to-DC converters with high power factor and near-optimum feedforward

Abstract: This paper presents a three-phase pulsewidth modulated AC-to-DC power converter with unity power factor and near-optimum dynamic regulation. A general mathematical model of the converter has been established to lead to a comprehensive analysis. The averaged small-signal technique is used to obtain the near-optimum feedforward compensator, thus resulting in the output impedance, and the audio susceptibility become zero, that is, the output voltage of the converter presented in this paper is independent of variations of the DC load current and the utility voltage. The proposed procedure of analysis is simple and effective, and it is also easy to implement. Finally, the theoretical formulations are verified both by simulated and experimental results in a 5 kW laboratory prototype system.

Ballast circuit for high intensity discharge lamps

Abstract: A ballast circuit for a high intensity discharge lamp (24) includes a boost converter (16), a boost controller (36), responsive to the boosted dc output voltage, for driving the boost converter (16) to maintain the boosted output voltage at a predetermined level; a buck converter (18); and a buck controller (38) for driving the buck converter to operate the lamp in a transition mode and maintaining the reduced dc output voltage at a preselected level for operating the lamp in a steady mode.

Analysis and design of an isolated single-stage converter achieving power-factor correction and fast regulation

Abstract: This paper presents the analysis and design of an isolated single-stage converter achieving high-power-factor correction and fast regulation. By using the technique suggested by Wu et al., a buck-boost converter and a flyback converter can be integrated to form the discussed converter. The buck-boost semistage working in the discontinuous conduction mode (DCM) functions as a power-factor corrector, and the flyback semistage operating in the DCM is a voltage regulator which is controlled, theoretically, to be independent of load variation. An approximated small-signal model of the converter operating in the DCM is developed. Design of a peak-current feedback loop with an optimal proportional integral controller is also presented. A prototype is implemented to verify that the analysis and design are effective and feasible.

DC/DC converter with synchronous switching regulation

Abstract: A DC/DC converter combines elements of a boost and a buck converter with synchronous switching and a single controller to provide a step-up or step-down regulator with continuous input and output currents. A boost converter composed of an inductor in series with the input, a switch to ground, and a diode to an intermediate voltage node provides an intermediate voltage that is greater than the input voltage. A buck converter composed of a switch in series with the intermediate voltage node, a diode to ground, and an inductor in series with the output provides an output voltage that is less than the intermediate voltage. The output is regulated by a single pulse width modulating controller which drives the boost switch and buck switch simultaneously. This technique provides a DC/DC converter that can operate with an input voltage greater than or less than the output voltage. Further, series inductance on both input and output nodes provides continuous input and output AC current reducing conducted noise effects. Further, the input and output inductors have equivalent volt-second characteristics allowing for the possibility to couple the input and output inductors on a single magnetic element. An isolated form of the invention is possible by replacing the buck stage with a transformer-isolated forward converter.

Modified asymmetrical ZVS half-bridge DC-DC converter

Abstract: A modification is proposed for the asymmetrical zero-voltage-switched (ZVS) half-bridge DC-DC converter topology that substantially changes the static transfer function and the voltage stress distribution within the converter power mesh. This modification allows the converter circuit to be optimised for higher efficiency and power density. It is also postulated that the modification with its corresponding benefits can be utilised in other complementary driven topologies. Although the asymmetrical H-B converter is inherently capable of ZVS switching, only the proper choice of parameters can insure ZVS in all modes of operation. The DC circuit analysis and design procedure for the power stage components are presented. Experimental results, in good agreement with the analysis, are presented for a 300 W converter operating at 500 kHz, with 5 VDC/60 Amp output, and 84% efficiency at 75 W/in/sup 3/.