Showing papers on "Forward converter published in 1989"

Analysis and design of optimum-amplitude nine-switch direct AC-AC converters

Abstract: The maximum input-output transformer ratio, or output voltage ability, of direct AC-AC pulse-width-modulated converters is explored. An intrinsic limit, independent of the control algorithm, is found. A suitable novel converter control algorithm is discussed which achieves such maximum output amplitude ability and displays some interesting features. Finally, the opportunity to implement AC-AC converter control with the use of feedback techniques is considered, and a feedback-based control algorithm for the converter is proposed. >

A 1 kW, 500 kHz front-end converter for a distributed power supply system

Abstract: The analysis, design, and performance are discussed of a prototype high power-density converter suitable for use in the front-end of a distributed power supply system. The system delivers 1 kW to a regulated 40 V distribution bus from the rectified utility line. Its switching frequency is 500 kHz, and it uses a phase-shifted pulse-width modulation technique to avoid primary-side switching losses. The converter's topology is a standard power MOSFET H-bridge that drives a transformer. The output of this transformer is rectified by a full bridge of Schottky diodes. The switches of this forward converter are operated in a fixed-frequency PWM mode. The dominant parasitic elements are the transformer's leakage inductor, the MOSFETs' output capacitors, and the rectifiers' junction capacitors. Of these three groups of parasitic elements, only the leakage inductors do not result in a direct switching loss. To avoid MOSFET switching losses, the converter is controlled with a special gate-drive pattern that permits full recovery of the MOSFETs' capacitive energy. At the same time this drive scheme gives zero-voltage switching for the MOSFETs. The converter's efficiency at full load approaches 90%. >

Power conversion apparatus for DC/DC conversion using dual active bridges

Abstract: A DC/DC power converter suitable for high power applications has an input converter which converts the DC input voltage to an AC voltage and supplies this voltage to a transformer. The output of the transformer is provided to an output converter which converts the AC to a DC output voltage at a controlled level to a load. Both the input and output converters are composed of active gate controlled switching devices and are switched in a soft-switched manner to minimize switching losses and increase switching frequency. The converters can be implemented in single phase or polyphase configurations and can be controlled to closely maintain the output voltage provided to the load at a desired level.

Design of feedback loop in unity power factor AC to DC converter

Abstract: In certain applications it is desirable to convert the utility AC voltage to a DC voltage in such a way as to present a unity power factor load A common means of doing this is a circuit consisting of a bridge rectifier followed by a boost converter Various control schemes for this boost converter are discussed, including their tradeoffs as to power factor, output voltage transient regulation, and cost of implementation A nonlinear regulation-band circuit that has a favorable combination of properties is presented >

Resonant DC/DC converter with class-E inverter and class-E rectifier

Abstract: A new type of high-frequency high-efficiency resonant DC/DC converter is proposed, analyzed, and verified experimentally. It is called a class-E converter because it consists of a class-E inverter and a class-E rectifier. The class-E rectifier acts as an impedance inverter and is compatible with the class-E inverter. Consequently, the converter can operate with load resistances from a full load to infinity while maintaining zero-voltage switching of the transistor in the inverter and the diode in the rectifier. It operates safely with a short circuit at the output. Because of a high value of the load quality factor Q/sub 1/, a narrow frequency range suffices to regulate the DC output voltage over the whole load range. The measured relative bandwidth was delta f/f/sub min/=42.2% as the load resistance was varied from 70 Omega to open circuit. The measured efficiency at the full load was 89% with a 9 W output power at 1 MHz. A family of class-E/sup 2/ resonant DC/DC power converters is given. The possibility of reduction of class-E/sup 2/ converters to lower-order resonant and pulse-width-modulation converters is shown. >

New control strategy for matrix converter

Abstract: The authors propose a control strategy for the matrix converter which allows output voltage of 0.866 times the supply voltage to be generated. They discuss how to eliminate voltage and current spikes in the commutation. The system operation is examined and confirmed by experiments using a matrix converter with anti-parallel-connected SITs (static induction thyristors). >

Dc/dc converter switching at zero voltage

Abstract: A two switch, DC/DC converter provides sufficient inductive energy storage at the termination of the "on" period of each switch to alter the charge on the intrinsic and stray capacitance of the combination of switches producing zero voltage across the alternate switch prior to its turn on. A short dead-band between the turn on pulses provided by the control circuit allows time for this transition. Thus the energy stored in the capacitance of the switches is returned to the source and load rather than being dissipated in the switching devices. This greatly improves the efficiency of the converter particularly when operating at high frequency. The unique topology of the converter provides other new and useful characteristics in addition to zero voltage switching capability such as operation as constant frequency with pulse-width-modulation for regulation, quasi-square wave output current, and the ability to integrate the magnetic elements with or without coupling.

Fluorescent lamp controllers

Abstract: An electronic controller for fluorescent lamps includes a DC to AC converter which supplies high frequency current to the lamps and a preconditioner stage which includes a switched mode power supply connected to accept line power and produce a DC input for the DC to AC converter. The switched mode power supply and the DC to AC converter are synchronized to operate in a fixed phase relationship and/or at the same frequency.

Parallel resonant converter with zero voltage switching

Abstract: A parallel resonant converter as disclosed having in one embodiment a variable inductance and having a control circuit which operates the switches of the converter under zero voltage switching conditions and under continuous conduction mode by maintaining the quality factor of the resonant circuit generally equal to the DC conversion ratio.

Dual sepic PWM switching-mode DC/DC power converter

Abstract: A steady-state analysis and experimental results for a dual sepic pulse-width-modulated (PWM) DC/DC power converter for both continuous and discontinuous modes of operation are presented. The converter is dual to a sepic converter, but it can also be derived from a forward converter by replacing one of its rectifier diodes with a coupling capacitor. The circuit acts as a step-down or step-up converter, depending on the value of the ON switch duty cycle. The transformerless version of the converter has a positive DC/DC voltage transfer function. Therefore, the circuit is suitable for distributed power systems. Design equations for all circuit components are derived. Experimental results measured at 100 kHz were in good agreement with theoretical predictions. >

Strobed DC-DC converter with current regulation

Abstract: A DC-DC converter regulates the maximum current through an inductor. The DC-DC converter operates within a paging receiver and boosts a voltage from a single cell battery to substantially 3.1 VDC in order to operate circuits which require more voltage than that produced by the single cell battery. Such circuits include CMOS microcomputers and code plug. The DC-DC converter is current regulated thus providing for improved power conversion efficiency. The DC-DC converter is active when the voltage is below a minimum voltage and inactive when above a maximum voltage. The DC-DC converter provides for a wide range of load currents from the converted voltage without being controlled by a microcomputer and while delivering the power to the loads with an improved efficiency.

Zero voltage switching half bridge resonant converter

Abstract: A DC to DC converter combines a half-bridge inverter with a resonant rectifier through a series LC circuit which conducts power at substantially a single frequency. Energy stored in the parasitic capacitors of the two power switches are transferred from one parasitic capacitor to the other in order to enhance efficiency of operation. The transfer is controlled by controlling the relative phase between the voltage and current in the inverter section.

Class E DC/DC converters with an inductive impedance inverter

Abstract: The analysis, design equations, and experimental verification are presented for a class E DC/DC switching-mode high-efficiency resonant DC/DC converter with a transformer center-tapped rectifier. The analysis is performed at a constant current through the DC-feed choke and using the high Q/sub 1/ assumption (Q/sub 1/>or=5). The converter can operate under safe conditions for load resistances ranging from a full load to an open circuit. This feature has been obtained by using an inductive impedance inverter. The results of the analysis are then generalized for the entire family of class E DC/DC converters. Experimental results show good agreement with the theoretical predictions. The measured total efficiency was 89% at 1 MHz with 15 W output power. A narrowband FM regulation ( delta f/f=12%) of the DC output voltage was achieved as the load was varied from a minimum resistance (full load) to an open circuit. >

Cascaded buck converter circuit with reduced power loss

Abstract: Two or more buck converter circuits are cascaded in such a manner that the output of one serves as the input to the next, with the input voltage to each succeeding buck converter stage being reduced in magnitude. The total circuit losses are substantially reduced as compared to the losses generated in a single buck converter having the same input voltage range and the same output voltage and output current. Both positive and negative output terminals may be provided for an output stage.

Fluorescent dimming ballast utilizing a resonant sine wave power converter

Abstract: In a method or combination, a DC voltage supply, a converter including a series or a parallel resonant circuit (LR, CR, TR) for converting the DC voltage to a sinusoidal current, and a load (T1, T2) including at least one fluorescent lamp responsive to the sinusoidal current to effect excitation of the lamp.

Pulse width modulation power transmission system

Abstract: A converter for interconnecting two electric networks to transmit electric power from one network to the other, each network being coupled to a respective power generator station. The converter, having an AC side and a DC side, includes a bridge of semiconductor switches with gate turn-off capability coupled to a control system to produce a bridge voltage waveform having a fundamental Fourier component at the frequency of the electric network coupled to the AC side of the converter. The control system includes three inputs for receiving reference signals allowing to control the frequency, the amplitude and the phase angle of the fundamental Fourier component with respect to the alternating voltage of the network coupled to the AC side of the converter. Through appropriate feedback loops, the converter may be used to maintain at a predetermined level the power flowing therethrough or to keep at a preset value the voltage across the DC terminals of the converter and, in both cases, to maintain the frequency synchronism between the fundamental Fourier component and the alternating voltage of the network coupled to the DC side of the converter.

Steady state analysis of the parallel resonant converter with LLCC-type commutation network

Abstract: A novel converter topology known as LLCC-type parallel resonant converter (PRC-LLCC), in which the tank circuit consists of two inductors and two capacitors, is introduced. Using the state-plane approach, the steady-state analysis of the PRC-LLCC operating in the continuous conduction model is carried out. It is shown that by using the state variable transformation technique the steady-state response of the converter can be represented by two state-plane diagrams. Using these diagrams and the circuit equations, a set of control characteristic curves which are useful for converter design is derived. Based on these curves, a design procedure along with a specific design example is given. The correctness of the analysis results is verified via computer simulations. >

Parallel AC/DC transmission lines steady-state induction issues

Abstract: Steady-state induction at fundamental-frequency into an HVDC transmission circuit from parallel AC lines can lead to several adverse impacts on system performance. Based on a generic analysis of the impact on converter performance, a threshold of 0.1% fundamental-frequency ripple on DC current is established as a point beyond which detailed studies of the effect on converter performance should be required. Guidelines are provided for the calculation of steady-state induction to the DC converters, which should be carried out if significant exposures exist. Should steady-state induction exceed a threshold beyond which the converter can operate satisfactorily, several mitigation options exist. >

Unbalanced PWM converter analysis and corrective measures

Abstract: The analysis of an unbalanced PWM AC-to-DC converter by the transfer function approach is presented. The proposed analysis procedure provides for closed-form assessment of all harmonics generated under unbalanced operating conditions by suitably decomposing the converter transfer function into positive and negative sequence components. A three-phase converter operating with programmed PWM patterns is fully analyzed. The distortion at the output of the PWM converter is evaluated under unbalance. The increase in distortion under unbalance is attributed primarily to the appearance of a second-harmonic component. An algorithm for selectively cancelling the generated second-harmonic component at the converter output under unbalance is presented. Suitable implementation techniques for the proposed algorithm are also discussed. >

A PWM GTO current source converter-inverter system with sinusoidal inputs and outputs

Abstract: A current-source-type GTO converter-inverter system with pulsewidth modulation (PWM) techniques is presented. The inverter circuit consists of six main GTOs, two auxiliary GTOs, and three shunt-filter capacitors, and the converter circuit has the same arrangement as the inverter. The system realizes sinusoidal input and output voltage/current by a simple PWM strategy. Two auxiliary GTOs contribute to shaping the inverter output current into the sinusoidal wave, controlling the DC link voltage, and shaping the converter input current into the sinusoidal wave. The PWM pattern in the inverter, the PWM methods, and the DC link voltage control for the converter are explained in detail. The experimental waveforms of the input and output voltage/current are shown when a 2.2 kW induction motor is driven. The input and output characteristics in the DC link voltage control of the converter are given. >

Performance of low loss synchronous rectifiers in a series-parallel resonant DC-DC converter

Abstract: The functionality of efficient synchronous rectifier components, specially developed for resonant DC-DC converter topologies designed to operate at high frequency, has been demonstrated in a series-parallel converter circuit operating at 420 kHz and 85 W Conduction losses for these components are three times lower than for Schottky diodes Switching conditions for efficient operation have been identified both experimentally and using accurate multilevel modeling >

Dual switched mode power converter

Abstract: A dual power converter is introduced which addresses the problem of output ripple and switching losses in a switched power converter. One stage of the power converter is a conventional PWM (pulse-width modulated) converter, and the other stage is a linear source. The linear source controls the voltage directly, and the output current of the linear stage is used to generate the control signal for the switching stage. This scheme is modeled as a two-stage control system, and the overall response is obtained in terms of the individual transfer functions. The PWM converter supplies most of the current, while the linear source supplies the reverse of the ripple current. Two DC-to-DC buck converters have been designed and implemented, giving excellent ripple suppression and high efficiency at very low switching frequencies. >

AC/DC converter using resonant network for high input power factor

Abstract: An AC/DC converter is provided, suitable for use in an advanced single phase, sine wave voltage, high frequency power distribution system, such as that used on a 20 kHz Space Station Primary Electrical Power Distribution System. The converter comprises a transformer, a resonant network, a current controler, a diode rectifier and an output filter. The voltage source is converted into a sinusoidal current source. The output of this current source is rectified by the diode rectifier and is controlled by the current controller. The controlled rectified current is then filtered by the output filter to obtain a constant voltage across the load.

Three-phase AC-to-AC series resonant power converter with reduced number of switches

Abstract: An apparatus and method is disclosed for an improved AC--AC series-resonant converters incorporating power pulse modulation with internal frequencies of tens of kHz is applied to a series-resonant converter system for generating synthesized multiphase bipolar waveforms with reversible power flow and low distortion. The high pulse frequency allows the application of the principle of modulation and demodulation for fast system response. Switches are required which have bidirectional current conduction and voltage blocking ability. The conventional series-resonant AC--AC converter applies a total of 24 anti-parallel thyristors. The circuit configuration of the present invention is a series-resonant AC--AC converter with only 12 thyristors. Use of the converter results in a higher efficiency and lower costs. The alternative power circuit has three neutrals, related to the polyphase source, the load and the converter, which may be interconnected and the high-frequency component of the source and load currents will flow through the connection between the neutrals.

Regulated flyback converter with spike suppressing coupled inductors

Abstract: Flyback converters can generate multiple voltage levels by rectifying and filtering multiple windings on a single power transformer. Different voltages should be related by the turns ratio of the respective windings. Transformer leakage inductance causes leading edge voltage spikes on some windings causing the filters to peak charge to a higher value than expected. The addition of a small coupled inductor between two or more windings will block the leading edge spike allowing the filter to charge to the correct voltage. The turns ratio of the coupled inductor is selected to cancel the leading edge voltage spike on the desired winding. The coupled inductor can be used to correct the voltage of a winding used for feedback purposes as well as improving the cross regulation between multiple converter outputs.

Evaluation and design of megahertz-frequency off-line zero-current-switched quasi-resonant converters

Abstract: A performance comparison of flyback, forward, and half-bridge zero-current-switched quasi-resonant converter topologies for high-frequency offline applications is presented. It is shown that the half-bridge topology with secondary side resonance operating in half-wave mode is most suitable. A complete design procedure for the half-bridge power stage and the voltage-feedback control is presented together with experimental results for a 300 V DC hybridized converter which operates with conversion frequencies from 400 kHz to 2 MHz and delivers 1.5-16 A at 5 V DC. >

Class-E DC/DC converters with a capacitive impedance inverter

Abstract: Analysis and design rules are presented for three class-E switching-mode DC/DC power converters, each with a capacitive impedance inverter. Experimental results are given for one of the converters. A zero-voltage switching technique is achieved for both class-E inverters and rectifiers. Therefore, the efficiency of the converters is very high at switching frequencies in the megahertz range. By applying a capacitive impedance inverter, lossless operation of the class-E inverter can be obtained for a wide range of converter load resistance, from full load to infinity. Experimental results are in excellent agreement with the theoretical calculations. Only a 12% relative bandwidth of the switching frequency is required to maintain a constant DC output voltage for the load resistance from full load to infinity at about 1 MHz with 15-W output. >

Power source for emergency lighting systems

Abstract: A buck/boost converter is driven by a high frequency dc-to-dc flyback converter to provide substantially constant output power, independent of the output voltage, to an inductor to provide current to a load having a v-i characteristic that is suitable for use with a current power source, such as a plurality of parallely-connected LEDs. The flyback converter repetitively generates a battery-simulated output voltage that is current-limited and which may be used to charge a battery as well as to provide power to the buck/boost converter. The buck/boost converter includes a switching circuit for repetitively transferring current to the load and a current sensor circuit operating in conjunction with the switching circuit to change the state of the buck/boost converter to repetitively open the switching means and initiate release of the current to the load.

Power converter and method of controlling the same

Abstract: A power converter converts AC input power into AC output power to which a load is connected. This power converter comprises a controller for controlling power converting operation of the power converter, a DC voltage detector for detecting a DC voltage of the DC power to provide a DC voltage signal, a first reference generator for generating a first reference, an output detector for detecting a condition of the AC output power to provide an output condition signal, a second reference generator for generating a second reference in response to the output condition signal, a condition detector for detecting a condition of the AC input power to provide an output condition signal, and a selector for supplying the second reference to the controller when the input condition signal is provided.

DC/DC converter with class E zero-voltage-switching inverter and class E zero-current-switching rectifier

Abstract: A class-E resonant DC/DC power converter is introduced and verified experimentally. It is composed of a class-E zero-voltage-switching inverter and a class-E zero-current-switching rectifier. Therefore, it offers high efficiency at high frequencies. The measured DC/DC efficiency was 82.64% at full load with 7.3-W output power. A relative frequency range of only 6.12% was sufficient to regulate the DC output voltage at 20 V for load resistances ranging from 55 Omega to infinity. >