Showing papers on "Converters published in 1994"

Pulsewidth modulation for electronic power conversion

Abstract: The efficient and fast control of electric power forms part of the key technologies of modern automated production It is performed using electronic power converters The converters transfer energy from a source to a controlled process in a quantized fashion, using semiconductor switches which are turned on and off at fast repetition rates The algorithms which generate the switching functions-pulsewidth-modulation techniques-are manifold They range from simple averaging schemes to involved methods of real-time optimization This paper gives an overview >

Integrated Analog-To-Digital and Digital-To-Analog Converters

Abstract: List of Figures List of Tables List of Symbols Preface 1 The converter as a black box 2 Specifications of converters 3 High-speed A/D converters 4 High-speed D/A converters 5 High-resolution A/D converters 6 High-resolution D/A converters 7 Sample-and-hold amplifiers 8 Noise-shaping D/A conversion 9 Sigma-delta A/D conversion 10 Voltage and current references 11 Limitations of comparitors 12 Technology and device matching 13 Testing of D/A and A/D converters Index

Control techniques for power factor correction converters

Abstract: The aspects regarding control strategies for Power Factor Correction (PFC) converters are investigated. The major control techniques to absorb sinusoidal input currents in boost PFC's are reviewed and analyzed. Their extension to other converter topologies is discussed and some experimental results for a PFC based on the Sepic topology are reported, which allow comparison of converter performance with different control techniques. Lastly, some considerations regarding dynamic operation are given, together with information about control IC's specifically developed for PFC applications.

Small-signal modeling and control of three-phase PWM converters

Abstract: The paper presents a systematic approach to small-signal modeling, and control design of three-phase PWM converters. The well established design procedures used in DC-DC converter control design, are adapted for the three-phase converter control based on the similarity in the small-signal dynamics of the three-phase converters and their DC-DC counterparts. The approach is especially beneficial in three-phase rectifier control, which is reduced to a single-input single-output system after closing the current loops. The modeling approach is verified on a 10 kW three-phase boost rectifier switching at 15.6 kHz with DSP control. A wide-bandwidth output voltage control loop is then designed based on the verified small-signal transfer functions. >

Investigation of the output droop characteristics of parallel-connnected DC-DC converters

Abstract: The analytical proof that output voltage droop characteristics of parallel-connected DC-DC power converters are only appropriate for very limited applications is presented. Because the converters are rarely made to be identical, near-uniform current-sharing without additional control can be achieved only when converters connected in parallel have similar characteristics of being very close to the ideal current sources. This can occur at a cost of poor voltage regulation. As an alternative, the current-sharing control technique, which requires no remote-sensing, is proposed. The technique ensures uniform or designated current distribution throughout the specified load range. A control circuit module is independently implemented without any preliminary knowledge or any circuit modification of the source converters. >

An overview of power factor correction in single-phase off-line power supply systems

Abstract: The main objective of this paper is to summarize the state of the art of power factor correction in off-line power supply systems. The study is only focused on equipment fed from a single-phase line and it covers theoretical aspects, control strategies, power topologies and future trends. The authors cover AC-DC converters, DC-DC converters in resistor emulators, multiplier approach control, average current mode control, variable hysteresis control, one- and several-switch power topologies, and soft switching. >

Digital-signal-processor-based control of three-phase space vector modulated converters

Abstract: The paper presents the implementation of a DSP-based controller for three-phase, space-vector modulated converters. The implementation is illustrated for the control of a 2 kW, ZVS matrix power converter-based three-phase PWM rectifier. The controller features very high data processing speed (converter switching frequency of 100 kHz), and provides high-quality, low-distortion power converter input currents and output voltages. The controller can be implemented using only a few standard integrated circuits, providing high reliability and low cost. >

Space vector modulated, zero-voltage transition three-phase to DC bidirectional converter

Abstract: Operation and implementation of the novel, space vector modulated, zero-voltage transition, three phase voltage source inverter/boost rectifier is presented. The converter is intended for high performance, medium power applications requiring bidirectional power flow. The proposed modified space-vector modulation allows all switches to be operated with soft-switching and constant frequency. The modulation algorithm also eliminates any low frequency distortion caused by the zero-voltage transitions and can be applied to any soft switching PWM three-phase converters. A simple, digital signal processor based implementation of the modulator and current regulators, operating with 30 /spl mu/s sampling time, is described. Measured efficiency of the 30 kHz, IGBT prototype is around 95%, and distortion of the three-phase currents is extremely small. >

Design of portable systems

Abstract: The increasing demand for portable operation has elevated power consumption to be one of the most critical design parameters. This paper presents various low-power techniques required for the design of portable systems. Low-power operation is achieved using reduced supply voltages (1-1.5 V) coupled with a system level optimization of the switching activity that involves logic design, re-synchronization, signal correlations and number representation. The support circuitry required for low-voltage operation is presented which includes level-shifters, DC-DC converters and D/A converters. >

A novel family of DC-DC PWM converters using the self-resonance principle

Abstract: Obtaining soft-switching operation for PWM power converters, except for a few cases, has required either high switch voltage stresses or high switch current stresses, or both. This paper presents a new class of commutation self-resonant PWM power convertor that overcomes this great disadvantage as well as being able to operate without switching losses in high switching frequencies for a wide line and load range. The circuit diagram and the phase-plane of each power converter of a family of such converters are also presented. In order to emphasize the principal characteristics of these new converters, a study, including experimental results, is carried out in detail for the buck and zeta converters. >

Power supply system for supplying electric power to a load through plural converters

Abstract: The invention relates to a power supply system having plural converters connected in parallel. The current of each of the plural converters is detected and each of the converters is controlled so as to match each of the converters to a maximum current value from among the detected current values. In the parallel converters, when one or more converter fails, having an output current of zero, the remaining converters are each partially charged equally to maintain the load current. Since a common bus is arranged between plural converters and plural loads, it is possible to carry out a redundant operation having a high reliability. Since a stable output can be obtained without being affected by the failed converter, a power supply system having the redundancy and the high reliability can be attained.

Control of DC-DC converters with linear optimal feedback and nonlinear feedforward

Abstract: This paper describes a new control design procedure for PWM DC-DC converters. The control action has two components: a linear feedback, designed via the LQ approach, and a nonlinear feedforward. The proposed control scheme guarantees excellent regulation of the output voltage, even in the presence of large variations of the input reference signal, as pointed out by numerous simulations carried out on different converter topologies. Good performances are also achievable when a suitably designed estimator is inserted into the control loop to reconstruct internal variables and input voltage disturbances from output voltage measurements. >

PSPICE simulation of three-phase inverters by means of switching functions

Abstract: Static power converters can be analyzed by means of widely available circuit simulation software packages such as PSPICE. However, they are usually modeled as a set of real switches, which results in long execution times and possible convergence problems in the case of complex circuits. This paper proposes macromodels to simulate three-phase power converters on such packages. The proposed macromodels are based on converter switching functions rather than actual circuit configuration, and they are suited for steady state and large signal transient analysis at system level. In this approach, voltage source inverters (VSI), current source inverters (CSI), and controlled rectifiers (CR) are simulated as multiport networks avoiding the physical nonlinear micromodels of the power switches. Computer memory and the run-times required for the simulation are thereby minimized. Complete examples of VSI, CSI and CR, with different PWM techniques, are given with specific reference to the PSPICE software to illustrate the effectiveness of the proposed models. >

Output plane analysis of load-sharing in multiple-module converter systems

Abstract: This paper explores the origin of the DC current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a/spl times/b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters. >

Summation of harmonic currents produced by AC/DC static power converters with randomly fluctuating loads

Abstract: A method for analyzing the asymptotic behavior of the sum of randomly varying harmonic currents produced by static power converters is described. It has been shown by virtue of the central limit theorem that as the number of harmonic sources is large enough, the vectorial sum of random harmonic vectors approaches a bivariate normal distribution. However, methods of determining its parameters for realistic harmonic-generating loads need to be developed. This paper deals with the case of AC/DC static power converters. With the operating condition of each converter being known, the parameters of the bivariate normal distribution can be effectively determined. Monte-Carlo simulation is performed to justify the proposed method. >

Zero-voltage-transition converters using an inductor feedback technique

Abstract: A technique using inductor feedback is presented for achieving zero-voltage switching (ZVS) in PWM controlled topologies. These converters exhibit low voltage and current stresses characteristic of hard-switched PWM converters, yet achieve ZVS with minimal current and voltage rating of the auxiliary soft-switching circuitry. Based on this technique, an experimental 730 W, 300 kHz boost converter is designed for universal off-line power factor correction. A complete analysis and a design procedure are also presented. >

A fuzzy controller for DC-DC converters

Abstract: A controller for DC-DC converters based on fuzzy logic is proposed. Being free of complex equations and heavy computation, the controller is expected to control converters that operate at high frequencies. This paper presents the derivation of fuzzy control rules for the basic converter circuits and simulations of the performance of the closed-loop converters in respect of start-up transient, load regulation and line regulation. >

Design criteria for power factor preregulators based on Sepic and Cuk converters in continuous conduction mode

Abstract: Sepic and Cuk converters used as power factor preregulators in continuous conduction mode are analyzed. The application of the average current mode control technique to obtain sinusoidal input current is investigated. It is shown that, unlike the usual boost topology, the gain of the internal current loop depends strongly on the instantaneous input voltage. Moreover, the presence of undamped complex poles and zeroes makes difficult the design of a stable control. The paper shows that stability can be achieved by using a suitable damping network, which properly shapes the current loop transfer function without introducing significant power losses. With this provision, a standard PI controller can be used to ensure the desired phase margin in any operating condition. Detailed design criteria of both power and control stages are given in the paper. Results of a 300 W prototype based on the Sepic topology are also reported. >

Resonant reset forward topologies for low output voltage on board converters

Abstract: The minimization of size and losses are the main goals in the design of high power density and low output voltage onboard DC/DC power converters. Forward topology with resonant reset combines the simplicity of its power stage with the feasibility to implement self driven synchronous rectification. Several operation modes for this topology are proposed and analyzed in this paper: fixed frequency PWM and constant off-time variable frequency, with and without zero voltage switching (ZVS). Design guidelines and experimental results are also provided for 3.3 V output voltage converters, featuring efficiencies up to 90%. >

Power supply system.

Abstract: PURPOSE:To obtain a stable output without being influenced by a failed converter by a method wherein the largest output current among the output currents of respective converters is detected and the respective converters are so controlled as to have their output currents agree with the largest output current CONSTITUTION:DC-DC converters Con1-Con4 are composed of forward converters A control circuit CC detects an output voltage Vs1 and controls a switching device Mo with an output signal Gs1 to make the output voltage Vs1 a required value stably The detection signal of a current detector Cs which detects the output current is inputted to the control circuit CC and a control line CL by which the largest current among the output currents of the respective converters which are connected in parallel with each other is detected and the respective converter currents are made to follow the largest current is connected to the control circuit CC With this constitution, even if a failed converter whose output current is zero is included in the parallel converters, a load can be shared by the remaining converters while the failed converter is left as it is

Average models as tools for studying the dynamics of switch mode DC-DC converters

Abstract: A novel methodology for teaching the subject of the dynamic response of switch mode DC/DC power conversion (SM) systems was developed and tested in the class environment. The method applies equivalent circuit models of the power stage and the duty-cycle generation circuitry to describe the low frequency behavior of SM systems and to perform numerical and symbolic analyses by general purpose computer packages (SPICE, MATLAB, MATHEMATICA). Continuous and discontinuous conduction modes of classical PWM topologies, for both voltage and current control methods are discussed. >

Zero-voltage-transition converters using a simple magnetic feedback technique

Abstract: This paper presents a simple active energy recovery circuit which can be magnetically coupled to any isolated or nonisolated switching power converter to achieve zero-voltage switching (ZVS) of the power devices. Converters using this soft-switching technique exhibit low voltage and current stresses characteristic of hard-switched PWM converters, yet achieve ZVS thus enabling higher frequency operation. Based on this technique, an experimental 300 W, 250 kHz boost converter is designed for offline power factor correction. Steady-state analysis as well as simulations are also presented. >

Bidirectional DC/DC power conversion using constant frequency multi-resonant topology

Abstract: A family of bidirectional DC/DC converters is proposed using the constant frequency zero-voltage switching (ZVS) multi-resonant topology. This family of converters provides ZVS operation of all semiconductor devices from no-load to full-load while achieving full DC conversion ratio range, and has inherent short-circuit protection capability. Analysis and design considerations of a buck/boost bidirectional converter are discussed along with experimental results supporting the proposed concept. >

Mismatch effects in time-interleaved oversampling converters

Abstract: Recently, a new architecture was proposed which utilizes the concept of time-interleaving in oversampling converters. Using this architecture, one is theoretically able to achieve higher resolutions by using an array of interconnected modulators without increasing the oversampling ratio or order of the modulators. Alternatively, the same resolution can be maintained with wider bandwidth input signals. This paper presents the first experimental results on this new family of modulators. As well, the practical issue of component mismatch for these converters are studied and some suggestions are made to alleviate the effects of this problem. >

Total compensation of line-side switching harmonics in converter-fed AC locomotives

Abstract: PWM-controlled line-side power converters of modern AC traction locomotives inject harmonic currents into the feeding overhead line. This causes problems of electromagnetic interference. Passive or active filters are usually provided for a partial reduction of the line harmonics. A novel and superior approach employs a switched electronic compensator. It generates an exact replica of the harmonic current, feeding it to the high-voltage transformer to produce a harmonic counter MMF. The transformer main flux is then forced to be sinusoidal, and so is the induced voltage in the primary. The line current, being low-pass filtered by the transformer leakage inductance, assumes a pure sinusoidal waveform. The compensator operates in the low switching frequency range of the main power converters. Its installed power is only 1% of the traction power. Operation, control and design considerations are described. Results from laboratory tests at full power level are presented. >

Zero-voltage-transition (ZVT) 3-phase PWM voltage link converters

Abstract: An improved zero voltage transition (ZVT) pulse width modulation (PWM) link converter is provided which introduces a space vector modulation scheme and an auxiliary circuit which includes a commutation power supply or special switch arrangement used to discharge resonant inductor currents to zero and to recover commutation energy. In an alternate embodiment, an improved ZVT PWM link converter provides an auxiliary switch for each main switch in the converter to achieve ZVT. The novel ZVT converters provide zero-voltage switching without increasing switching action of the main switches. In this way, the advantages of PWM control is maintained. Conduction loss, turn-off losses, and voltage stress of the main switches are the same as in conventional PWM converters, but the dominant turn-on losses are eliminated, so total power losses are minimized.

Comparison of high efficiency low output voltage forward topologies

Abstract: The main goal in the design of on board converters for distributed power architectures is size minimization, with power losses being the main constraint to achieve this objective Very high efficiency has been obtained in this work in low output voltage (33 V) forward topologies, thanks to the use of self-driven synchronous rectification Forward PWM topology with active clamp (FAC), forward with resonant reset (FRR) and forward with multiresonant switch ZVS-MRC are compared in this paper from the point of view of efficiency, switching frequency, losses in the synchronous rectifiers, transformer demagnetization, semiconductor stresses and EMI >

Parallel control type dc/dc converter

Abstract: A parallel control type DC--DC converter supplies an output voltage to a load based on voltages supplied from independent power sources. The DC--DC converter is provided with at least first and second converters powered by the independent power sources and commonly grounded and including a switching element, a control circuit driving the switching elements within the first and second converters by ON-pulses having the same width depending the output voltage, and a circuit coupling outputs of the first and second converters in parallel and producing the output voltage.

Robust controller design for a parallel resonant converter using /spl mu/-synthesis

Abstract: DC-to-DC resonant power converters have been the subject of much attention recently. These power converters have the potential to provide high-performance conversion without some of the problems associated with classical pulse-width modulation (PWM)-based converters, thus allowing for smaller, lighter power supplies. However, in order to achieve this, a suitable control circuit, capable of maintaining the desired output voltage under different operating conditions, is required. In the past, small-signal models obtained around the nominal operating points were used to design controllers that attempted to keep the output voltage constant in the presence of input perturbations. However, these controllers did not take into account either load or components variations, and thus could lead to instability in the face of component or load changes. Moreover, the prediction of the frequency range for stability was done a posteriori, either experimentally or by a trial-and-error approach. In this paper, the authors use /spl mu/-synthesis to design a robust controller for a conventional parallel resonant power converter. In addition to guaranteeing stability for a wide range of load conditions, the proposed controller rejects disturbances at the power converter input while keeping the control input and the settling time within values compatible with a practical implementation. These results are validated by means of detailed nonlinear circuit simulations obtained using PSpice.