Showing papers on "Buck–boost converter published in 1996"

Direct power control of PWM converter without power source voltage sensors

Abstract: This paper proposes a novel control strategy of a pulsewidth modulation (PWM) converter with no power-source voltage sensors. The strategy has two main features to improve a total power factor and efficiency, taking harmonic components into account without detecting the voltage waveforms. One feature is a direct instantaneous power control technique for the converter, which has been developed to control the instantaneous active and reactive power directly by selecting the optimum switching state of the converter. The other feature is an estimation technique of the power-source voltages, which can be performed by calculating the active and reactive power for each switching state of the converter from the line currents. A digital-signal-processor-based experimental system was developed, and experimental tests were conducted to examine the controllability. As a result, it was confirmed that the total power factor and efficiency were more than 97% and 93% over the load power range from 200 to 1400 W, respectively. These results have proven the excellent performance of the proposed system.

Bidirectional buck boost converter

Abstract: A bidirectional buck boost converter and method of operating the same allows regulation of power flow between first and second voltage sources in which the voltage level at each source is subject to change and power flow is independent of relative voltage levels. In one embodiment, the converter is designed for hard switching while another embodiment implements soft switching of the switching devices. In both embodiments, first and second switching devices are serially coupled between a relatively positive terminal and a relatively negative terminal of a first voltage source with third and fourth switching devices serially coupled between a relatively positive terminal and a relatively negative terminal of a second voltage source. A free-wheeling diode is coupled, respectively, in parallel opposition with respective ones of the switching devices. An inductor is coupled between a junction of the first and second switching devices and a junction of the third and fourth switching devices. Gating pulses supplied by a gating circuit selectively enable operation of the switching devices for transferring power between the voltage sources. In the second embodiment, each switching device is shunted by a capacitor and the switching devices are operated when voltage across the device is substantially zero.

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.

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/.

A new control strategy to achieve sinusoidal line current in a cascade buck-boost converter

Abstract: This work presents a detailed theoretical analysis and experimental results of a novel means of obtaining sinusoidal input current and unity power factor (UPF) via a cascade buck-boost power converter. Using the new configuration, sinusoidal line current in phase with the bus voltage is achieved, thanks to a new and simple to implement control strategy. Comparison between the input and output voltages is used to select the instantaneous operating mode of the converter. Offline references are calculated and stored in two EPROM circuits and then compared to measured currents to generate the gating signals of the appropriate switches. Complete theoretical analysis, simulation results and experimental data on a 500 W power converter are presented, to demonstrate the superiority of the new control strategy. Low order harmonics in the input current are eliminated and the input power factor is found to be over 0.99.

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.

DC-to-DC converter functioning in a pulse-skipping mode with low power consumption and PWM inhibit

Abstract: Switching losses in a DC-to-DC converter idling in a pulse-skipping mode are reduced by inhibiting any intervening turn-off command by a PWM control loop of the converter for as long as the current through the inductor of the converter remains below a minimum threshold value set by a dedicated comparator The method is implemented by employing a comparator with a certain hysteresis and by logically masking the switching to a logic "0" of a high frequency clock (switching) signal of the converter for the entire period of time the current in the inductor remains below the minimum threshold

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.

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

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%.

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.

Variable-frequency variable-input-voltage converter with minimum frequency limit

Abstract: A variable-input-voltage variable-switching-frequency power converter with a minimum frequency limit. The switching frequency never goes below a certain minimum while the converter is on. Thus switching frequency is dependent on input voltage, for input voltages in one range, and is NOT dependent on input voltage, for input voltages in another range.

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.

Single-stage AC-to-DC full-bridge converter with magnetic amplifiers for input current shaping independent of output voltage regulation

Abstract: An ac-to-dc switching full-bridge converter employing voltage bidirectional switches as controllable series input switches, preferably implemented with magnetic amplifiers, that couple ac rectifiers to a single-stage full-bridge dc-to-dc converter in order to provide unity power factor operation by control of input current using a fast current loop to modulate the duty ratio d1 of the voltage bidirectional amplifier switches while independent output voltage regulation is maintained by voltage feedback to the full-bridge converter switches through modulation of the switch duty ratio d of the converter (where d1

Three-phase AC power converter with power factor correction

Abstract: A solid-state, PFC power converter for converting 3-phase AC to DC in a single, isolated conversion step, using 3 forward converters. Converter outputs share a common output choke, permitting operation at low instantaneous AC input voltage. Each forward converter is "duty" modulated proportional to its rectified AC input voltage, producing unity input power factor. The constant of proportionality for 3 converters is controlled to regulate the DC output voltage. A control circuit provides immunity to AC input distortion and noise. The control circuit operates with various forward converter topologies, and is compatible with integrated circuit processes. A version using phase or symmetry modulated full-bridge converters, requires only 2 output rectifiers.

Passive clamp and ripple control for buck boost converter

Abstract: A power conversion circuit, in which a flyback converter is modified with additional elements to provide both dissipationless snubbing and also input ripple cancellation. This is achieved by appropriate connection of an additional winding to the isolating transformer, without any need for a second transformer. The configuration of the secondary is conventional, and the switching transistor is connected in series with the primary winding across DC inputs (taken e.g. from a full-wave-rectified line voltage). The additional winding is connected on the primary side, and preferably has a near-unity turns ratio with the primary which is the inverse of the coupling coefficient. However, the additional winding is not connected between the two DC inputs, but instead has one end coupled through an intermediate capacitor to the corresponding end of the primary, and the other end coupled through a capacitor to the negative DC input. By use of appropriate reactances a balancing current is maintained in the additional winding, which keeps the total current through the primary absolutely flat. The intermediate capacitor which links the primary and additional windings also provides efficient snubbing: it catches the energy stored in the primary leakage inductance, and also limits the maximum voltage on the switch. This results in a converter with no ripple at the input, high efficiency, and very efficient snubbing. Moreover, by using a second active element for regeneration, energy loss during switching of the primary switch is minimized.

Extended range DC-DC power converter circuit

Abstract: A single-stage power converter has an input-to-output transfer characteristic with two portions, each having a different operational characteristic, with each portion being selected by changing ONLY the duty-cycle of the power switching devices. At low input voltage the converter operates as a Boost converter, while operating as a Buck converter for greater input voltages. This transfer characteristic is provided by a circuit wherein the primary winding center tap of a split-primary power transformer is coupled through an inductive element, with one of the pair of push-pull power switching devices connected to each primary winding end. Secondary winding rectification and filtering provides the power supply output in the Boost mode, and a portion of the power supply output in the Buck mode. The remainder of the Buck-mode output is supplied by the energy stored in the inductive element, preferably by use of a secondary winding on a transinductor (multiple-winding inductive) element having a primary winding providing the energy-storing inductance L.

Optimum dynamic performance of a buck converter

Abstract: The application of optimal control theory concepts justifies the use of a bang-bang control to reach in minimum time a specified reference in steady-state in the case of the buck converter. The derived control function is unique and insensitive to the converter initial conditions. The converter trajectories in the phase-plane are used as control functions and sliding-mode control is introduced to regulate the output voltage.

A single stage power factor corrected AC/DC converter

Abstract: This paper presents a single-stage isolated power converter topology 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 power converter, but incorporates an additional transformer winding, an 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 power converter's output is operated in the discontinuous mode to minimize the bulk capacitor voltage variations when the output load is varied. Analysis of the power converter is presented and performance characteristics are given. Further, design guidelines to select critical components of the circuit are presented. Finally, experimental results on a 160 W, universal input, 54 VDC output power converter are given which confirm the high efficiency and high power factor features of the proposed topology.

A new control method preventing transformer DC magnetization for voltage source self-commutated converters

Abstract: A DC component contained in an output of a voltage source self-commutated converter causes a converter transformer to be DC-magnetized, in the worst case causing an overcurrent due to saturation. We experienced the DC-magnetization of the converter transformer of a 50 MVA self-commutated SVC installed in the Shinshinano Substation of Tokyo Electric Power Company when system disturbances occurred by energizing of an adjacent large capacity transformer. After analysing the problem, a novel DC magnetization prevention control was developed that makes a fast flux correction according to the voltage DC component detected in the converter output. This method was applied to the 50 MVA self-commutated SVC and produced satisfactory operation results.

Auxiliary series resonant converter: a new converter for high-voltage, high-power applications

Abstract: The power converter presented in this paper has been designed to meet high-quality power requirements in high-voltage, high-power applications such as X-ray imaging, traveling wave tube RF generation, etc. The new power converter is based on a series resonant power converter (SRC) which is modified by adding low power auxiliary circuitry. The so obtained auxiliary SRC (ASRC) maintains zero-voltage switching (ZVS) for both main and auxiliary devices over the entire operating range. The ASRC can operate and regulate voltage even at no load conditions. The additional reactive energy used to maintain soft switching and voltage regulation at light loads is controllable independently of power converter load. This contributes to higher efficiency, especially at heavy loads. The ASRC control is identical to that of a standard SRC, so fast and robust transient response can be obtained with relatively simple controller structure. The paper also presents power converter analysis and design, and experimental results from a 100 kW, 150 kV prototype.

A buck quadratic PWM soft-switching converter using a single active switch

Abstract: High-switching frequency associated with soft commutation techniques is a trend in switching converters. Following this trend, a buck pulsewidth modulation (PWM) converter is presented. The DC voltage conversion ratio of this converter has a quadratic dependence on duty cycle, providing a large stepdown. This new buck quadratic PWM soft-single-switched converter, having only a single active switch, provides a high efficient operating condition for a wide load range at high-switching frequency. In order to illustrate the operating principle of this new converter, a detailed study including theoretical analysis, relevant equations and simulation, and experimental results is carried out.

Simulation of a slack-moored heaving-buoy wave-energy converter with phase control

Abstract: A mathematical model is presented for a slack-moored wave-energy converter (WEC), consisting of a semi-submerged heaving buoy moving relative to a submerged plate. For the WEC investigated the diameter of the cylindrical buoy is 3.3 m and the cylinder ends are, at equilibrium, 3.1 m below mean water level and 2.0 m above. The plate has diameter 8.0 m, is 0.2 m thick and is submerged 10 m. The geometry is chosen so that the heave excitation forces on the two bodies are approximately equal in magnitude, but in opposite direction, for wave periods we want to absorb energy from. A high-pressure hydraulic machinery is proposed for energy production and motion control. A valve in the machinery can be actively controlled, and it is used to obtain largest possible power production, and to limit the excursion of the buoy, in order to protect the hydraulic machinery. In addition, an end-stop device is provided as a safety measure, in case the control fails to limit the excursion. A procedure is developed for control of the device in both sinusoidal and irregular waves. This procedure determines the opening instant of the controllable valve so that, in small waves the extrema of the relative velocity between the bodies coincide with the extrema of the excitation force, while in larger waves the opening instant is delayed to constrain the excursion. The control procedure is also used to keep the plate in the desired mean position, since the submerged body has no hydrostatic stiffness. Results are presented for calculations with sinusoidal waves, and irregular waves based on a Pierson-Moskowitz spectrum. In sinusoidal waves the energy production is largest for waves with period 4 s and 5 s. The control procedure is not totally successful, since the mean position of the piston is usually negative for long wave periods, and the full length of the available piston stroke is not utilised. In irregular waves the power production has an approximately linear increase with the significant wave height. The control procedure is not able to constrain the excursion sufficiently, so the end-stop device is engaged too often. The excursion of the piston does also here usually have a negative mean value, which means that the available piston stoke is not fully utilised. By further development of the control procedure it should be possible to solve these problems, and at the same time increase the power production. On the basis of a scatter table, for a wave climate where the average incident wave power per unit width is approximately 37 kW/m, the year-average power production is estimated to be approximately 4.9 kW. However, the size of the device is relatively small for the wave climate investigated. Further, a duration curve is presented, which shows the percentage of the year the mean power production is above a certain level.

Zeta converter operating in continuous conduction mode using the unity power factor technique

Abstract: Several topologies have been researched in search of a structure which not only is able to fulfil the requirements of the power factor and the amount of harmonics injected in a line foreseen in the norms, but which would also show the best ensemble of characteristics. Although being the most frequently employed and studied structure, the boost converter presents some limitations in its application, for it is not a naturally isolated structure and because it only operates as step up voltage. As an alternative to these limitations the Zeta converter operating in discontinuous mode applied to the power factor correction was proposed (D.C. Martins, 1994). The Zeta converter showed itself as very attractive because it operates as step up as well as step down voltage, beside the fact of being a naturally isolated structure and processing power at one single stage. But in applications which imply high power, the operation of a converter in discontinuous mode is not attractive because it results in high RMS values of the currents causing high levels of stress in the semiconductors. Aiming to extend the alternative by use of the Zeta converter in power factor correction to applications in higher powers, and having in mind the main characteristics and advantage of this converter in face of the limitations of the boost converter, this paper presents the study of the Zeta converter operating in continuous conduction mode for power factor correction by using the average current mode control.