Showing papers on "Converters published in 1995"

Multilevel converters-a new breed of power converters

Abstract: Multilevel voltage source converters are emerging as a new breed of power converter options for high-power applications. The multilevel voltage source converters typically synthesize the staircase voltage wave from several levels of DC capacitor voltages. One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between different levels normally involve voltage clamping or capacitor charge control. There are several ways of implementing voltage balance in multilevel converters. Without considering the traditional magnetic coupled converters, this paper presents three recently developed multilevel voltage source converters: (1) diode-clamp, (2) flying-capacitors, and (3) cascaded-inverters with separate DC sources. The operating principle, features, constraints, and potential applications of these converters are discussed.

Performance limits of switched-capacitor DC-DC converters

Abstract: The theoretical performance limits of two-phase switched-capacitor (SC) DC-DC power converters are discussed in this paper. For a given number of capacitors k, the complete set of attainable DC conversion ratios is found. The maximum step-up or step-down ratio is given by the k/sup th/ Fibonacci number, while the bound on the number of switches required in any SC circuit is 3k-2. Practical implications, illustrated by several SC power converter examples, include savings in the number of components required for a given application, and the ability to construct SC power converters that can maintain the output voltage regulation and high conversion efficiency over a wide range of input voltage variations. Limits found for the output resistance and efficiency can be used for selection and comparison of SC power converters. >

Comparative study of proportional-integral, sliding mode and fuzzy logic controllers for power converters

Abstract: This paper presents a comparative evaluation of the proportional-integral, sliding mode and fuzzy logic controllers for applications to power converters. The mismatch between the characteristics which lead to varying performance is outlined. This paper also demonstrates certain similarities of both the fuzzy logic controller and sliding mode controller. Sensitivity of these controllers to supply voltage disturbances and load disturbances is studied and results are presented.

Soft-switching techniques in PWM converters

Abstract: A number of soft-switching pulse-width-modulated (PWM) converter techniques have been proposed, aimed at combining the desirable features of both the conventional PWM and resonant converters while avoiding their respective limitations. In this paper, three classes of zero-voltage soft-switching (PWM) converters (namely the zero-voltage-switched (ZVS) quasi-square-wave converters, ZVS-PWM converters, and zero-voltage-transition PWM converters) and two classes of zero-current soft-switching PWM converters (namely, the zero-current-switched PWM converters and zero-current-transition PWM converters) are reviewed, and their merits and limitations are assessed. Experimental results of several prototype of converters are presented to illustrate each class of converter.

Dynamics of one-cycle controlled Cuk converters

Abstract: One-cycle control is a nonlinear control method. The flow-graph modeling technique is employed to study the large-signal and small-signal dynamic behavior of one-cycle controlled switching converters. Systematic design method for one-cycle control systems is provided with the Cuk converter as an example. Physical insight is given which explains how one-cycle control achieves instant control without infinite loop gain. Experimental results demonstrate that a Cuk converter with one-cycle control reflects the power source perturbation in one-cycle and the average of the diode voltage follows the control reference in one cycle. >

PWM-switch modeling of DC-DC converters

Abstract: The introduced PWM-switch modeling method is a simple method for modeling pulse-width-modulated (PWM) DC-DC converters operating in the continuous conduction mode. The main advantage of this method is its versatility and simple implementation compared to other methods. The basic idea is the replacement of the switches in the converter by their time-averaged models. These switch models have been developed in such a way that the converter model provides the same results as the state-space-averaging technique but not including nonlinear effects. Simple rules for determination of the switch models are obtained. The resulting model is a time-averaged equivalent circuit model where all branch currents and node voltages correspond to their averaged values of the corresponding original currents and voltages. The model also includes parasitics, second-order effects and nonlinearities, and can be implemented in any circuit-oriented simulation tool. The same model is used for the simulation of the steady-state and the transient behavior. >

AC/DC/AC PWM converter with reduced energy storage in the DC link

Abstract: The paper introduces the family of quasi-direct converters, i.e., forced-commutated ac/dc/ac converters including small energy storage devices in the dc link. In particular, the case of three-phase to three-phase quasi-direct converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported

DC-DC converter design for battery-operated systems

Abstract: This paper describes performance, design and optimization of DC-DC converters for energy limited, battery operated systems. Variable-frequency operation is used to achieve voltage regulation and high efficiency for an extremely wide range of load currents. An experimental 15 W, 3.3 V buck converter has been constructed to demonstrate design and optimization techniques. The converter employs synchronous rectification to reduce conduction losses, and discontinuous, variable-frequency, current-mode control with optimum peak current to maximize efficiency for a wide range of loads. Applications include portable computers, hand-held instruments, and telecommunications. >

Interleaving technique in distributed power conversion systems

Abstract: In distributed power supply systems, the parallelism of DC-DC converters is a basic architecture. In this paper, we use the time domain method to show that the amplitude of the input/output current ripple of N(/spl ges/1) parallelly interleaved modules is always less than or equal to that of the individual modules for buck, boost, flyback, Cuk, and SEPIC converters if the phase shift among the modules is 2/spl pi//N. Furthermore, the insight gained from the time domain method allows us to develop efficient numerical algorithms for predicting the net ripple amplitude in interleaved power modules,. >

Nonlinear-carrier control for high power factor boost rectifiers

Abstract: Novel nonlinear-carrier (NLC) controllers are proposed for high-power-factor boost rectifiers. In the NLC controllers, the switch duty ratio is determined by comparing a signal derived from the main switch current with a periodic, nonlinear carrier waveform. As a result, the average input current follows the input line voltage. The technique is suitable for boost power converters operating in the continuous conduction mode. Input voltage sensing, the error amplifier in the current-shaping loop, and the multiplier/divider circuitry in the voltage feedback loop are eliminated. The current-shaping is based on switch (as opposed to inductor) current sensing. The NLC controllers offer comparable or improved performance over existing schemes, and are well-suited for simple integrated-circuit implementation. Experimental verification on a 240 W rectifier is described. >

Switching frequency dependent averaged models for PWM DC-DC converters

Abstract: This paper introduces a new averaging method for PWM DC-DC power converters which yields averaged models that are switching frequency dependent. The new models are obtained by using periodic ripple functions to improve the averaging approximation. Two important benefits are the correction of DC offset error in steady-state and the modeling of switching frequency effects on closed-loop performance and stability.

Acoustic noise cancellation techniques for switched reluctance drives

Abstract: The levels of acoustic noise emitted by the switched reluctance drive are noted as being above those of competing variable speed drives. In other respects the switched reluctance drive offers distinct advantages. In a previous paper, the authors described a new technique for the cancellation of radial vibrations of the stator. This new technique was limited to power converters offering a zero voltage freewheel path. This paper describes further development of the technique which allows noise cancellation to be achieved with all types of power converter. The techniques disclosed in this paper include a smoothing method, a three stage commutation method for converters with one switch per phase and a noise cancellation technique suitable for switched reluctance drives incorporating an extended zero voltage freewheel period for improved efficiency. The techniques are all compared, with experimental and simulated results.

Digital control for switching converters

Abstract: In this paper, several different techniques for designing discrete controllers for switching power converter applications are presented. Simulation results are also provided for illustration purposes.

A comparative study of a class of full bridge zero-voltage-switched PWM converters

Abstract: Four implementations of a full-bridge zero-voltage-switched PWM power converter are discussed. The merits and limitations of each implementation are reviewed and their key features and characteristics are compared. In addition, experimental performance comparisons of the four power converters were performed on 1 kW/400 V laboratory prototypes. >

A multilevel voltage-source converter system with balanced DC voltages

Abstract: In this paper, a multilevel voltage-source converter system is proposed for high-voltage, high-power applications such as back-to-back interconnection of power systems, large induction motor drives, and electrical traction drives. Multilevel voltage-source converters have a voltage unbalance problem in the DC capacitors. The problem may be solved by use of additional voltage regulators or separate DC sources. However, these solutions are found not to be practicable for most applications. The proposed converter system can solve the voltage unbalance problem of the conventional multilevel voltage-source converters, without using any additional voltage balance circuits or separate voltage sources. The mechanism of the voltage unbalance problem is analyzed theoretically in this paper. The voltage unbalance problem of multilevel converters in the DC capacitors has been solved by the proposed internal connections of the AC/DC and DC/AC converters. The validity of the new converter system is demonstrated by simulation and experiment. >

Feed-forward pulse-width modulators for switching power converters

Abstract: This paper describes pulse width modulators (PWMs) that employ feedforward compensation to improve the steady-state and dynamic responses of power converters. It is shown how ideal feedforward PWMs (FF-PWMs) can be constructed for all duty-ratio controlled switch-mode power converters operating in the continuous conduction mode. A power converter with FF-PWM behaves at low frequencies as a linear power amplifier with constant gain independent of operating conditions. The proposed FF-PWM can be easily implemented using the same building blocks found in conventional PWM controllers. Experimental and simulation examples are included to illustrate applications of the FF-PWM.

Performance optimization of Cuk converters by sliding-mode control

Abstract: A novel approach to the design of sliding-mode controllers for Cuk converters is presented, which is valid for both complete state feedback (fourth-order controller) and reduced state feedback (second-order controller). According to the proposed design criteria, both control techniques ensure excellent static and dynamic performances, also resulting in simple control implementation and minimum size of energy transfer capacitor. Experimental results are reported, and compared with those obtained with other popular control techniques. >

Passivity-based controllers for the stabilization of DC-to-DC power converters

Abstract: Average models of PWM regulated DC-to-DC power supplies are shown to be Euler-Lagrange systems. As such, passivity-based dynamical feedback controllers can be derived for the indirect stabilization of the average output voltage. The derived controllers are based on a suitable stabilizing "damping injection" scheme. The approach is applied to regulate DC-to-DC power converters of the "boost" and "buck-boost" types. The effectivity and robustness of the proposed duty ratio synthesis policies are tested, via computer simulations, on a stochastically perturbed model of a switched "boost" converter.

Efficiency and noise performance of wavelength converters based on FWM in semiconductor optical amplifiers

Abstract: All optical frequency converters are key devices for new-conception optical networks A theoretical model is presented to evaluate performances of frequencies converters based on highly nondegenerate four-wave mixing (FWM) in semiconductor amplifiers Conversion efficiency and noise performances are evaluated in generic saturation conditions and compared with experimental results >

Comparative evaluation of PWM AC-AC converters

Abstract: Recently a new family of AC-AC power converters has been proposed for AC power conditioning. They are solid state functional equivalents of transformers with a continuously variable transformation ratio. Operating on the principle of pulse width modulated control using gate turn off devices like IGBTs, they have been shown to have significant performance advantages compared to older generation thyristor based phase controlled power converters. The family of proposed converters include buck, boost, buck-boost and Cuk power converters. This paper is aimed at presenting the design guidelines and the results of a comparative study of these power converters. Detailed design equations are provided along with a typical examples of design of various power converters for a power conditioning application. >

A comparative study on paralleling schemes of converter modules for distributed power applications

Abstract: Three different paralleling schemes for multi-module converters are investigated. For each paralleling scheme, benefits and limitations are addressed for distributed power applications, and guidelines for designing the feedback controller are presented. Results of the analysis are verified by both frequency- and time-domain simulations.

Self-adjusting input current ripple cancellation of coupled parallel connected hysteresis-controlled boost power factor correctors

Abstract: As this paper shows, the magnetic coupling of the inductances of two hysteresis-controlled single-phase AC-to-DC boost power converters connected in parallel leads in connection with a delayed switching of the power transistors to a self-adjusting staggered switching of the partial systems. Thereby, a significant reduction of the ripple of the resulting mains current as compared to the uncoupled case is obtained. Based on the analytical description of the current shapes within a pulse period the dependency on the circuit parameters of the occurring phase displacement of the switching functions of the partial systems is calculated. Furthermore, the effect of an unsymmetry of the power converters on the system behavior is analyzed and the automatic adjustment of the phase shift within a mains period is investigated by digital simulation. The theoretical considerations are verified by measurements on a laboratory model. Finally, the possibility of a substitution of the magnetic coupling of the input inductances of the partial systems by a coupling of the current controls of the power converters is discussed. >

Small-signal analysis of DC-DC converters with sliding mode control

Abstract: The paper deals with small-signal analysis of DC-DC power converters with sliding mode control. A suitable small-signal model is developed, which allows selection of control coefficients, analysis of parameter variation effects and characterization of the closed-loop behavior in terms of audiosusceptibility, output and input impedances and reference-to-output transfer function. Unlike previous analyses, the model includes effects of the filters used to evaluate state variable errors. Simulated and experimental results demonstrate model potentialities. >

Lossless snubber circuit for use in power converters

Abstract: A switching power converter employing a novel lossless zero-voltage-switching passive snubber network having a power range of up to 5 KW is presented. The passive snubber network improves efficiency, power density, and transient performance, reduces switching losses and EMI, and permits fixed frequency operation of the switching power converter. The passive snubber network also reduces and/or eliminates large peak currents and reverse recovery current spikes normally seen in conventional switching power converters. The proposed passive snubber network may be used in various switching power converter topologies such as boost, buck, balanced, and flyback power converters.

Multilevel converters and derived topologies for high power conversion

Abstract: This paper deals with techniques for series connection of semiconductors, of converters, or of commutation cells (including imbricated cells converters). The pros and cons of each technique are studied, as well as the specific know-how related to these techniques. A special point of interest concerns the possible improvement of input and output waveforms by increasing the apparent switching frequency and interleaving of the control signals. A few actual examples are given in the field of choppers and voltage-source inverters. Finally, current balancers for parallel associations are derived from the study of the voltage-balancing property observed in multilevel converters.

A 6-b, 4 GSa/s GaAs HBT ADC

Abstract: A GaAs-AlGaAs heterojunction bipolar transistor (HBT) process was developed to meet the speed, gain, and yield requirements for analog-to-digital converters (ADC's). The HBT has current gain of over 100 and f/sub T/ and f/sub MAX/ of over 50 GHz. A 6-b, 4 GSa/s (4 giga-samples/s) ADC was designed and fabricated in this process. The ADC uses an analog folding architecture, includes an on-chip master-slave track-and-hold (T/H) circuit, and provides Gray-encoded digital outputs. The ADC achieves 5.6 effective bits at 4 GSa/s, a faster clock rate than any noninterleaved semiconductor ADC reported to date. It has a resolution bandwidth (the frequency at which effective bits has dropped by 0.5 b) of 1.8 GHz at 4 GSa/s, higher than any published ADC. The chip operates at up to 6.5 GSa/s. GaAs HBT IC's are especially prone to high operating temperatures. This led to reliability problems that were overcome by the use of a fast DC thermal simulator written for this project. A SPICE model for self-heating effects is also described. >

Design considerations on low-voltage low-power data converters

Abstract: In this paper, we discuss theoretical and practical issues concerning low-voltage and low-power data converters. By looking at a series of constraints affecting the design of basic elements and building blocks, the paper analyzes different architectures for Nyquist rate data converters and discusses important aspects of low-voltage and low-power operation. Following this, the minimization of power consumption in the very popular sigma-delta technique is considered. A number of hints and indications are provided throughout the paper.

Digital I/Q demodulator

Abstract: I/Q demodulation is a common and useful RF signal processing technique used in charged-particle accelerators. When implemented with conventional analog RF components, a number of inherent errors can degrade the I/Q Demodulator performance, including gain balance, quadrature-phase balance, DC offsets, impedance match, and carrier leakage. Recent advances in high-speed analog-to-digital converters allow the I/Q demodulator to be implemented digitally, greatly reducing these systematic errors. This paper describes the design of a digital I/Q demodulator that will be applied to the PEP-II B factory.

Simulation model for ultrasonic motors powered by resonant converters

Abstract: A rotary traveling wave type ultrasonic motor powered by a resonant converter is modeled to optimize the overall drive performance by simulation and to develop suitable control strategies for the drive. Based on mechanical approaches in modeling the stator under consideration of unsymmetries and reflecting the nonlinear stator/rotor-contact by an elastic contact model, an extended contact model of the stator/rotor interaction with closed form solutions for nonideal traveling waves is derived referring to a two-mode approximation of the stator and piezoceramic. By incorporation of a converter model into the mechanical subsystem, a proper simulation model for ultrasonic drives is presented, whereby some interesting phenomena are verified by simulations and explained by strong graphical means.