Showing papers on "Forward 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.

Study of bi-directional buck-boost converter topologies for application in electrical vehicle motor drives

Abstract: The use of a bi-directional DC-DC converter in motor drives devoted to EVs allows a suitable control of both motoring and regenerative braking operations. In particular, during motoring operations of a battery-fed DC motor drive, a DC-DC converter is to be used to adjust the motor current in order to follow the torque reference signal. On the other hand, a bi-directional arrangement of the converter is needed for the reversal of the power flow, in order to recover the vehicle kinetic energy in the battery by means of motor drive regenerative braking operations. This paper deals with the study and comparison of two bi-directional buck-boost converter topologies. Each of them allows stepping the battery voltage level either up or down, according to motor drive modes of operation. For each converter topology computer simulations of modes of operation are presented together with experimental test results.

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 feedback linearizing control scheme for a PWM converter-inverter having a very small DC-link capacitor

Abstract: This paper addresses a control method of reducing the size of the DC link capacitors of a power converter-inverter system. The main idea is to utilise the inverter operation status in the current control of the power converter. Specifically, information on the load power is incorporated in synthesizing the converter current control input so that a proper DC voltage level is maintained. The authors describe the dynamics of load current and apply feedback linearization theory to obtain an input output linearized system. Theoretically, this control strategy is effective in regulating the DC voltage level even though the DC link capacitor is arbitrarily small and load varies abruptly. The superior performance is demonstrated through simulation and experiment. Experiment was performed with a 9 kW PWM power converter-vector inverter system having a 75 /spl mu/F DC-link capacitor.

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.

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.

Dynamics of a buck converter with a constant power load

Abstract: The dynamic properties of the buck converter with a constant power load are studied in this paper. The line-to-output and control-to-output transfer functions are derived, for voltage mode control and current mode control, in continuous conduction mode and discontinuous conduction mode. A comparison with the case of a resistive load is made in each case.

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.

Disk drive including DC to DC voltage converter for increasing voltage to its spindle motor and VCM

Abstract: A disk drive is connectable to a power supply having a fixed DC voltage. The disk drive includes a voice coil motor and a spindle motor. A DC to DC voltage converter converts the fixed DC voltage to an increased DC voltage greater than the fixed DC voltage. A voice coil motor driver has switching elements which are controllable to supply the increased DC voltage to the voice coil motor. A spindle motor driver has switching elements which are controllable to supply the increased DC voltage to the spindle motor. The increased VCM voltage allows faster access times and more efficient VCM operation. The increased spindle motor voltage allows for more efficient spindle motor operation.

High frequency synchronous buck converter for low voltage applications

Abstract: The effect of dead time delays on the efficiency of a constant frequency, 1 MHz low voltage, synchronous buck power converter is investigated. The overall efficiency is calculated as a function of the load current and the switching frequency with the dead time as a parameter. It was calculated, and subsequently experimentally verified, that the efficiency can be improved by over 3.5% by eliminating unnecessary body diode conduction.

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.

Single-stage single-switch isolated PFC regulator with unity power factor, fast transient response and low voltage stress

Abstract: In this paper, a simple control method is presented for a single-stage single-switch isolated power-factor-correction (PFC) regulator that can simultaneously achieve unity power factor and fast output voltage regulation while keeping the voltage stress of the storage capacitor low. The converter topology comprises essentially a cascade combination of a discontinuous-mode boost converter and a continuous-mode forward converter. The proposed control utilizes variation of both duty cycle and frequency. The role of varying the duty cycle is mainly to regulate the output voltage. Changing the frequency, moreover, can achieve unity power factor as well as low-voltage stress. Basically, the switching frequency is controlled such that it has a time periodic component superposed on top of a static value. While the time periodic component removes the harmonic contents of the input current, the static value is adjusted according to the load condition so as to maintain a sufficiently low-voltage stress across the storage capacitor. The theory is first presented which shows the possibility of meeting all three requirements using a combined duty cycle and frequency control. An experimental prototype circuit is presented to verify the controller's functions.

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.

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.

Electric arc welder and plasma cutter

Abstract: A single phase power supply module for electric arc welders and plasma arc cutters comprising: a single phase input stage; positive and negative output terminals; a full wave rectifier connected to the input stage for rectifying the single phase voltage at the input stage; a buck converter type power factor correcting circuit for controlling current flow from the input stage to the rectifier, which buck converter has an output capacitor regulated to an intermediate voltage in the range of 100-150 volts; and, a high speed DC to DC converter having an internal transformer coupling applying voltage across the output terminals and means for regulating the applied voltage to an output voltage in the range of 0-113 volts. The module is universal and several can be connected in parallel, in series or to switch networks to construct several welders or cutters.

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.

Power supply having means for extending the operating time of an implantable medical device

Abstract: A power supply comprising: a power source including a capacitive, nuclear or an electrochemical device for storing electrical energy; sensing circuitry for sensing when the voltage on power source is above or below a certain level; a DC-DC converter coupled to the power source switching circuitry coupled to the sensing circuitry and operable to connect the DC-DC converter to an output load and disconnect the power source from the output load when the voltage on the power source falls below a certain level and for connecting the power source to the output load and disconnecting the DC-DC converter from the output load when the voltage on the power source rises above a certain level; circuitry for activating the DC to DC Converter when the voltage on the power source falls below a certain level; and circuitry means for shutting down the DC to DC Converter when the voltage on the power source rises above a certain level. The method for extending the operating time of a capacitive, nuclear or electrochemical power source includes the steps of: sensing when the voltage level on the power source is below or above a certain level; producing a first logic signal when the voltage on the power source falls below a certain level and producing a second logic signal when the voltage on the power source is above a certain level; providing a DC-DC converter coupled to the output of the power source; switching the connections to an output load from the power source to the DC-DC converter when the first logic signal is produced; connecting the power source to an output load and disconnecting the DC-DC converter from the output load when the second logic signal is produced; activating the DC to DC Converter when the first logic signal is produced; and shutting down the DC to DC Converter when the second logic signal is produced.

New single-stage PFC regulator using the Sheppard-Taylor topology

Abstract: This paper describes a new usage of the DC/DC converter developed by D.I. Sheppard and B.E. Taylor in 1983 for achieving high power factor and output regulation. This converter may be viewed as a cascade of a modified boost stage and a buck stage, with the two stages sharing the same active switch. Two possible operation regimes are described. In the first regime, the converter's input part, which is a modified boost converter, operates in discontinuous mode, and the output part, which is a buck converter, operates in continuous mode. In this regime, high power factor is naturally achieved, and the output voltage is regulated by duty-cycle modulation via a simple output feedback. In the second regime, the input part operates in continuous mode, and the output part operates in discontinuous mode, with duty-cycle modulation maintaining a high power factor and frequency modulation regulating the output. Some comparisons between the Sheppard-Taylor converter and conventional boost and buck cascade are given in the paper.

Large-signal transient analysis of forward converter with active-clamp reset

Abstract: The forward converter with the active-clamp reset offers many advantages over the forward converters with other transformer-reset methods. However, during the line and load transients, the maximum magnetizing current of the transformer and the peak voltage of the primary switch are strongly affected by the active-clamp circuit dynamics. As a result, the design of a forward converter with the active-clamp reset cannot be optimized based only on its DC characteristics. Due to the nonlinearity of the circuit, it is very difficult to derive the closed-form equations for the transient response of the active-clamp circuit. In this paper, an average-state-trajectory approach is proposed to analyze the transient behavior so that the trends of the maximum magnetizing current of the transformer and the peak voltage of the primary switch can be easily predicted under worst-case conditions and parameter variations.

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.