Showing papers on "Converters published in 1987"

A comparison of half-bridge resonant converter topologies

Abstract: The half-bridge series resonant, parallel resonant and combination series-parallel resonant converters are compared for use in low output voltage power supply applications. It is shown that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, removes the main disadvantages of those two converters. Analyses and breadboard results show that the combination series-parallel converter can run over a large input voltage range and a large load range (no-load to full-load) while while maintaining excellent efficiency. A useful analysis technique based on classical ac complex analysis is also introduced.

Quasi-Resonant Converters-Topologies and Characteristics

Abstract: In designing switching dc-dc converters, the effort to increase operating frequency to reduce weight, size, and cost of magnetic and filter elements is constantly hampered by higher switching stresses and switching losses. To overcome these obstacles, the concept of the "resonant switch" is proposed. By incorporating additional inductor and capacitor elements to shape the semiconductor switch's current waveform, a "zero-current switching" property can be realized. Based on the resonant switch technique, a new host of quasi-resonant converter circuits have been derived, which can be operated in the megahertz range.

Pseudo-resonant full bridge DC/DC converter

Abstract: This paper proposes a new dc/dc converter topology which combines the ease of control and wide range of conventional dc/dc converters, with low switching losses, low dv/dt and low EMI that is typical of zero voltage switched resonant converters. Consequently, the ratings of these components are substantially lower than for similarly rated resonant topologies. Operation at very high frequencies is possible and is shown with the fabrication of a 200 watt, 1 MHz dc/dc converter.

Dc-to-Dc converters using multi-resonant switches

Abstract: A generalized multi-resonant switch that combines current-mode and voltage-mode resonant switches. Application of the multi-resonant switch in zero-voltage switched multi-resonant converters results in reduction of the voltage stress to the switching transistor, increase of the load range and reduction of the switching frequency bandwidth. Each embodiment of the multi-resonant converter includes a multi-resonant switch having an active switch, a passive switch and reactive components for causing the active and passive switches to operate in a multi-resonant manner.

A unified analysis of converters with resonant switches

Abstract: Quasi-resonant converters are a recently introduced family of single-switch resonant converters featuring zero-current or zero-voltage switching. Recognition of the topological structure uniting these converters — and the PWM converters on which they are based — leads to general models of their dc and low-frequency ac behavior. An expression is derived that yields the dc conversion ratio of a quasi-resonant converter in terms of the well-known conversion ratio of the underlying PWM topology. A small-signal, low-frequency dynamic model is developed whose parameters also incorporate the PWM conversion ratio. The dc and ac models reveal that any quasi-resonant converter with a full-wave resonant switch has dc and low-frequency behavior identical to that of its PWM parent, with switching frequency control replacing duty ratio control. Converters with half-wave resonant switches act more like PWM converters under current programming or discontinuous conduction mode, exhibiting lossless damping in the small-signal model and output resistance at dc.

Static and dynamic modeling of tapped-inductor dc-to-dc converters

Abstract: Six different topologies of tapped-inductor dc-to-dc converters derived from buck, boost and buck-boost topologies are analyzed. Both dc and ac analysis in continuous and discontinuous operating modes are considered. The influence of the tapped inductor turn ratio (λ) is very important in the circuit behaviour. Particulary in the poles and zeros distribution of the transfer function. Some important conclusions about the dynamical characteristics of converters are derived from this study. Theoretical results are compared with those obtained from experiment carried out on some prototypes. Generalized conclusions are presented considering classical buck, boost and buck-boost (non tapped-inductor) as a particular case of these converters.

Generalized Functional Model for Three-Phase PWM Inverter/Rectifier Converters

Abstract: The traditional circuit-based analysis of static power converters has proven to be unsuitable for handling the design requirements of the ever-growing number of circuit topologies. This situation has prompted the introduction and use of analysis methods based on converter function rather than circuit configuration. Such a method is presented, the novel feature of which is that it is simultaneously applicable to a group of converter families instead of individual converters. The resulting advantages are obvious, and they are conclusively demonstrated here.

An Efficient Algorithm for the Time-Domain Simulation of Regulated Energy-Storage DC-to-DC Converters

Abstract: An algorithm is presented for the efficient and accurate simulation of switched-mode piecewise-linear systems, a subclass of which includes regulated energy-storage dc-to-dc converters. Three key features of the new algorithm that lead to significant improvements in computational efficiency and accuracy are 1) a state-transition-matrix table-lookup scheme to solve differential equations describing the system, 2) a modified binary-search strategy to obtain an initial estimate of the instant at which the system topology switches, and 3) a quadratic extrapolation for the accurate final determination of the switching instant. The computational efficiency of a program using the new algorithm is demonstrated by comparing its execution time with that of a program employing a standard fixed-step-size integration algorithm. The accuracy of the new algorithm is verified by comparing results obtained from the simulations with results obtained analytically, and by comparing data from the simulation of two different regulated converters with data measured experimentally.

Circuit-oriented discrete-time modeling and simulation for switching converters 1

Abstract: A generalized discrete-time modeling and simulation program, applicable to any PWM, resonant or quasi-resonant converter, has been developed. From a circuit description, this program automatically generates state-space equations corresponding to each switching interval and performs time-domain simulation by using state-transition equations with a fast-convergence algorithm for topological changes.

Generalization of resonant switches and quasi-resonant DC-DC converters

Abstract: The concept of resonant switch topology is defined and is used to develop a procedure to classify known quasi-resonant converters or to synthesize new ones. Two new resonant switch topologies and the corresponding classes of converters are identified by the synthesis procedure. The steady-state performance of one converter is analyzed and verified.

Stabilizing the Frequency of Hysteretic Current-Mode DC/DC Converters

Abstract: A systematic investigation of methods to stabilize the operating frequency of hysteretic current-mode dc/dc converters through control of the current hysteresis is presented. The control laws for every power stage are derived, and two open-loop and two closed-loop circuits are shown and analized in detail. The interaction of the major voltage control loop and the frequency control circuitry is also investigated for buck converters. It is shown that, if the average inductor current is programmed, the two mechanisms are independent, while if the peak inductor current is programmed, they are not. The frequency control circuitry in the latter case decreases the phase margin of the voltage control loop and can lead to instability. Simple circuits are developed to implement the superior average inductor-current programming. As a consequence of being controlled via the current hysteresis, the operating frequency cannot be stabilized in the light mode, where VO/RL < IH/2. In the special case, where the frequency of the converter is stabilized by a phase-locked loop, a method and circuit are shown to solve this problem and achieve constant frequency operation at any load.

Design Considerations for Very High Frequency Resonant Mode DC/DC Converters

Abstract: The demand for higher switching frequencies in power converters has rekindled interest in resonant mode topologies. Conventional resonant converter circuits, however, are not optimized for high-frequency operation. A new resonant mode dc/dc converter topology exhibits desirable characteristics including zero switching losses, elimination of snubbers, simple control strategy, and circuit operation that is insensitive to parasitics such as diode reverse recovery. Analysis and design techniques are discussed in detail and are experimentally verified with a 150-W prototype converter operating in the frequency range 500 kHz-1 MHz.

Two-inductor boost and buck converters

Abstract: The derivation, analysis and design of a coupled inductor boost converter is presented. Aspects of the qualitative ac behavior of coupled inductor converters are discussed. Considerations for the design of the magnetics for such converters is addressed.

Constant-frequency, clamped-mode resonant converters

Abstract: Two novel Clamped-Mode Resonant Converters are proposed which operate at a constant frequency while retaining many desired features of conventional series- and parallel-resonant converters. State-plane analysis techniques are employed to identify all possible operating modes of clamped-mode series-resonant converter and define their mode boundaries. The control-to-output characteristics are derived that specifies the regions for natura; and forced commutation The predicted operating modes are verified using a prototype circuit.

Zero-voltage-switched quasi-resonant buck and flyback converters — Experimental results at 10 MHz 1

Abstract: Experimental results of buck and flyback zero-voltage-switched quasi-resonant converters (ZVS-QRCs) operating above 5 MHz are presented. A design procedure is presented that minimizes voltage stress to the transistor while maintaining zero-voltage-switching for all loads. A novel, quasi-resonant gate drive scheme is proposed and implemented in a buck converter. The drive is simple and provides high switching speed. Power dissipation in the gate drive is substantially reduced due to the quasi-resonant operation. Due to a much reduced switching losses, dv/dt, and di/dt, the ZVS-QRCs are particularly suitable for very-high-frequency distributed power supply applications.

Integrated-magnetics power converter

Abstract: Novel switched mode boost-buck integrated magnetic power converters are disclosed featuring two winding bobbins, a new boost section with enhanced gain, means for operating the converter in a continuous mode of energy storage under minimum output loading conditions while providing adequate time for removing the magnetization energy of the transformer part of the integrated magnetics, and other new and different converter topologies.

Unified Topological Modeling Method of Switching DC-DC Converters in Duty-Ratio Programmed Mode

Abstract: A unified continuous small-signal modeling method of switching dc-dc converters operating in duty-ratio programmed mode is presented. The method can be considered a new implementation of the widely known state-space averaging approach. Its principal advantage is a reduction of the order of the matrices to be inverted resulting in a significant simplification of the modeling procedure, especially for more complex converter configurations. The method leads to the unifled expressions for the elements of two useful forms of circuit model, namely, Y-parameter model and ladder LC filter-form model. To demonstrate the usefulness of the proposed modeling technique the dynamic model of the ?uk converter with damping network is derived.

C-2C ladder-based D/A converters for PCM codecs

Abstract: A family of C-2C ladder-based D/A (digital-to-analog) converters is presented. The best of these uses only 43 unit capacitors to implement a 13-b converter for use in PCM (pulse-code modulation) codecs. The practical feasibility of these networks is confirmed by actual on-chip implementation.

Design considerations for very high frequency resonant mode dc/dc converters

Abstract: The demand for higher switching frequencies in power converters has rekindled interest in resonant mode topologies. Conventional resonant converter circuits, however, are not optimized for high-frequency operation. A new resonant mode dc/dc converter topology exhibits desirable characteristics including zero switching losses, elimination of snubbers, simple control strategy, and circuit operation that is insensitive to parasitics such as diode reverse recovery. Analysis and design techniques are discussed in detail and are experimentally verified with a 150-W prototype converter operating in the frequency range 500 kHz-1 MHz.

Overload-protection methods for switching-mode DC/DC converters: Classification/ analysis/ and improvements

Abstract: Switching-mode DC/DC converters must be protected against overload, to prevent failure of the converter or the external current-carrying hardware. This paper collects, classifies, analyzes, and evaluates the known protection methods, and describes a new negative-feedback frequency modulator which prevents short-circuit-current runaway. Test data prove the effectiveness of the new scheme.

A study of a system of current fed converters as an active three phase filter

Abstract: Three single phase current fed converters operating in pwm mode, are combined as an active power filter of 15 kVA. The undesired limit cycle shown by the system is eliminated by feedback loop compensation. Analog, computer and analytical models which predict remarkably similar system responses are used to investigate the technique. The analytical model involves describing function methods. The losses in the converters are modelled, and used as a feedback reference to allow losses in the system to be accurately covered from the supply. The system behaves as an accurate, fast active filter for distortion in power networks. Results illustrating this include a comparison between the system response without control loop compensation and that with control loop compensation. This is shown for the computer simulation as well as the practical system. Some more results include the response of the system to both a balanced and an unbalanced set of references in the three phases. The last results shown, illustrate the ability of the system to compensate a non-linear load.

Design-oriented analysis of common switching DC to DC converters

Abstract: A general, computer-aided analysis of power electronic circuit dynamics is proposed. An automatic generation of dynamic models from a circuit specification is the starting point for a symbolic, automatable, exact, ‘top-down’ procedure, that contrasts with circuit-specific analyses. The algorithm is suitable for analysing any converter containing two reactive elements, covering the common switching power stages: buck, boost, buck-boost converters. The method is illustrated by application to the computation of the transient response of a boost converter; the computer results are compared with those obtained by applying the ‘state space averaging’ method and with laboratory results.

Modeling the frequency-domain behavior of magnetic-amplifiercontrolled high-frequency switched-mode power supplies

Abstract: A small-signal equivalent circuit which models the frequency-domain behavior of magneticamplifier- controlled switched-mode converters operating in the continuous-mmf mode is presented. The equivalent circuit, which is based upon stateaveraging techniques, can be used with a circuitanalysis program such as SPICE to evaluate the frequency-domain behavior of a magneticamplifier- controlled converter prior to circuit implementation. Two high-frequency switched-mode converters which employ magnetic amplifiers as output-voltage regulators are discussed. To show the validity of the derived equivalent circuit, measurement results of the small-signal frequencydomain behavior of the two switched-mode converters are compared with results produced by simulations employing the equivalent circuit.

A Systematic Method for the Stability Analysis of Multiple-Output Converters

Abstract: The dynamics of multiple-output dc-dc converters are discussed. A multi-input-multi-output (MIMO) feedback system model incorporating effects of the output fluctuation is derived for the converter. Based on system theoretic tools, a set of stability conditions is obtained for the MIMO model; the result is used to formulate a stable margin. A practical five-output converter was selected for illustration of the proposed analytic tool. The effects of the input filter and coupled inductor on system stability margin are investigated.

A High-Frequency Inverter Cycloconverter Cascade

Abstract: A conversion technique using high-frequency inverters and cycloconverters is presented. The technique has application to battery charger and inverter applications. The high operating frequencies and reversible nature of the converters can result in significant cost, weight, and size reductions. The technique is applied to produce high-efficiency converters for photovoltaic systems. Results for a 6-kVA 110-Vdc/240-Vac single-phase converter are presented. The converter consists of two phase square wave inverters supplying a four-pulse cycloconverter stage. A peak conversion efficiency of 95 percent is achieved with a total output distortion below 3 percent. Standing losses are extremely low, being approximately 1 percent of the converter rating. The converters are reversible by nature and operation as an ac-dc intertie is possible.

An implementation of current-mode control for a series-resonant DC-DC converter

Abstract: A new implementation of the (average) current mode control for a series resonant converter operated in the frequency range higher than the circuit resonant frequency will be introduced. The controller design is based on the ASDTIC (Analog-Signal-to-Discrete-Time- Interval Converter) concept but has some improvements over the original design which often suffered from static and dynamic instabilities. Some experimental results of a breadboarded converter with this new controller will be presented and the near-optimum fast response characteristics of the combination of this controller and the load current feedforward will be included to show the similarity between the current-mode controller for switching-mode converters and series-resonant converters.

A computer-aided design and simulation tool for switching converters

Abstract: A fully automated computer-aided design approach is presented which results in an optimal power stage and control circuit design. The design meets all dc, small signal and large signal closed-loop performance specifications. The proposed approach is very efficient; it can help in reducing component and manufacturing costs as well as design time and is successfully demonstrated on a multiple-output flyback converter breadboard.