Showing papers on "Converters published in 2000"

Steady-state analysis of an interleaved boost converter with coupled inductors

Abstract: Boost converters are widely used as power-factor corrected preregulators In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple A major design criterion then is to ensure equal current sharing among the parallel converters In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented Simulation and experimental results are also given

STATCOM control for power system voltage control applications

Abstract: A static compensator (STATCOM) is a device that can provide reactive support to a bus. It consists of voltage sourced converters connected to an energy storage device on one side and to the power system on the other. In this paper the conventional method of PI control is compared and contrasted with various feedback control strategies. A linear optimal control based on LQR control is shown to be superior in terms of response profile and control effort required. These methodologies are applied to an example power system.

Recent developments of high power converters for industry and traction applications

Abstract: The introduction of new high power devices like integrated gate commutated thyristors (IGCTs) and high voltage insulated gate bipolar transistors (IGBTs) accelerates the broad use of pulse width modulation (PWM) voltage source converters in industrial and traction applications. This paper summarizes the state-of-the-art of power semiconductors. The characteristics of IGCTs and high voltage IGBTs are described in detail. Both the design and loss simulations of a two level 1.14 MVA voltage source inverter and a 6 MVA three-level neutral point clamped voltage source converter with active front end enable a detailed comparison of both power semiconductors for high power PWM converters. The design and the characteristics of a commercially available IGCT neutral point clamped PWM voltage source converter for medium voltage drives are discussed. Recent developments and trends of traction converters at DC mains and AC mains are summarized.

Sharing of nonlinear load in parallel connected three-phase converters

Abstract: In this paper, a new control method is presented which enables equal sharing of linear and nonlinear loads in three-phase power converters connected in parallel, without communication between the converters. The paper focuses on solving the problem that arises when two converters with harmonic compensation are connected in parallel. Without the new solution, they are normally not able to distinguish the harmonic currents that flow to the load and harmonic currents that circulate between the converters. Analysis and experimental results on two 90-kVA 400-Hz converters in parallel are presented. The results show that both linear and nonlinear loads can be shared equally by the proposed concept.

Out of control because of harmonics-an analysis of the harmonic response of an inverter locomotive

Abstract: Presents a method to use linear analysis to capture the frequency coupling of nonlinear and time-varying components. System stability is analyzed by connecting the harmonic transfer functions of the different component models. This facilitates an object-oriented approach to modeling, which supports reuse of models. An analysis of the complete railway system is, of course, difficult. Several locomotives can be moving along the power distribution line at the same time, and depending on the distance between them, the interaction changes. The power consumption also changes, depending on operating modes. During normal operation, energy is consumed from the network, but as modern locomotives use electrical braking, the power flow changes direction during deceleration, and energy is delivered back to the grid. The inverter trains are not passive systems. The converters are controlled with only limited system knowledge (local measurements of currents and voltages), making analysis and control design an even bigger challenge.

Generation of a family of non-isolated DC-DC PWM converters using new three-state switching cells

Abstract: This paper introduces a new family of PWM DC-DC nonisolated converters. The new converters are generated using three-state commutation cells, comprising two active switches, two diodes and coupled inductors. The main advantages over the classical converters are low conduction and commutation losses, and low input and output current ripple. Due to these features, the new converters are suitable for low voltage and high current applications. Theoretical analysis and experimentation results are presented.

Principle of a multi-load/single converter system for low power induction heating

Abstract: The induction heating appliances used for cooking generally include two or four inductors and in the most common solution, a converter is connected to each inductor. The main aim of this paper is to suggest a way of building a multi-load/single converter system, based on the use of a series-resonant ZVS inverter supplying several resonant loads. The principle can be probably extended to different applications (DC-to-DC converters, high power induction heating applications) but their study has been restricted to a low power induction heating context. In order to make this study, suitable models for the loaded inductors had to be found. Therefore, in the first part of this document, a number of different electrical inductor models, from the basic L-R equivalent circuit to a representation taking into account eddy currents effects, are presented. The second part describes the multi-load operating principle with respecting ZVS conditions, by the analysis of an R-L inductor model. Finally, the third part completes this work with simulations, including a more realistic model of the inductors and the associated experimental validation. These emphasize the interest of this original system that is currently being evaluated for an industrial application.

Symmetrical multilevel converters with two quadrant DC-DC feeding

Abstract: In the technology sector of power electronics and control, the multilevel converter technology is still a rather new research area, but the application possibilities in the field of power drives and energy will demand more solutions with this promising technology. In the future, more converter systems will be realized with the multilevel topology. Up to now, multilevel converters have only been used in very particular applications, mainly due to the high costs and complexity of the multilevel converter system. The high costs are due to the fact that the latest technology on semiconductors, magnetic material for inductor and transformer cores and control system technology had to be used. But nowadays new developments in the fields of power semiconductors such as the IGBT, IGCT and perhaps in the future SiC switches as well as improvements of the performance of magnetic cores used in medium frequency transformers will favor the multilevel converters for many other application fields. It can be noted that the industrial trend is moving away from heavy and bulky passive components towards power converter systems using more and more semiconductor elements controlled by powerful processor systems integrating intelligent multi-task control algorithms. The presented work is a contribution to the large field of multilevel converters. It shows a certain kind of multilevel converter in a single phase and a three-phase configuration, called the series-connected four-quadrant converters (SCFQ). The two specialties of the presented converter type are a) that all the multilevel converter steps are fed by an identical DC voltage and b) that every multilevel converter step is realized with an individual AC-DC converter or four-quadrant converter. This type of multilevel converter is called multilevel converter with symmetrical feeding. In this work, a general theoretical development has been done for the use of this multilevel converter type. A special type of DC-DC converter is presented, in order to feed the individual four-quadrant converters of the multilevel converter with a constant DC voltage. All the developments and methods used are based on mathematical expressions. Various simulations using the latest software simulation tools are accomplished and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results with all types of the used converters, which have been realized in the framework of this thesis. The main application for the multilevel converter presented in this work is the frontend power converter in locomotives. Instead of using a heavy low-frequency transformer to reduce the high-voltage from the catenary to a supportable voltage for the semiconductors, a multilevel converter concept is used. The multilevel converter is directly coupled to the catenary. There are many advantages compared to the existing solutions. In the same context, a novel solution of a multilevel converter has been developed for a locomotive usable on different power lines. The converter allows not only the operation on the high AC voltage power line (15kV), but also can be coupled to a medium-voltage DC power line (3kV). Three different configuration types of the locomotive converter have been developed and tested in a complex simulation environment. Besides the locomotive application, there are many more interesting applications for the symmetrical multilevel converter, e.g. in the fields of energy transmission (FACTS, static VAR compensators, electronic high-voltage transformers, etc.) and industrial drives. But certainly in the future with the availability of cheap semiconductors adapted to the needs of the multilevel converter, even more applications in lower power fields will be realized.

Packet loss in a bufferless optical WDM switch employing shared tunable wavelength converters

Abstract: We propose an architecture for a bufferless packet optical switch employing the wavelength dimension for contention resolution. The optical packet switch is equipped with tunable wavelength converters shared among the input lines. An analytical model Is proposed in order to determine the number of converters needed to satisfy prefixed packet loss probability constraints. This analytical model very accurately fits with simulations results. A sensitivity analysis of the required number of converters as a function of the main system parameters (number of input and output lines, number of wavelengths, ...) and traffic parameters has been carried out. Making use of the introduced dimensioning procedure we have observed that the proposed architecture allows a saving in terms of employed number of converters with respect to the other architectures proposed in literature. Such a saving can reach about 95% of the number of converters.

Sliding-mode control of interleaved boost converters

Abstract: Boost topologies in interleaved operation under sliding-mode control are analyzed in this paper. First, the interleaving connection of two identical boost converters results in a new step-up structure whose closed-loop dynamics are asymptotically stable with good start-up and excellent load regulation when a self-oscillating sliding-mode control is applied to the converter. For a duty cycle of 50%, the new regulator acts as a small-ripple voltage doubler. Later, an extension of the voltage doubler yields a voltage quadrupler with similar dynamic characteristics. Simulated and experimental results verify the theoretical predictions.

Multi-converter multi-machine systems: application for electromechanical drives

Abstract: A formalism is defined to describe systems composed of several electrical machines with several electrical and/or mechanical converters. So, a first classification of multi-converter multi-machine systems is proposed in order to point out their influences on the global power conversion: cost reduction, conversion quality... Three examples are presented with this specific formalism.

A comparative investigation on the use of random modulation schemes for DC/DC converters

Abstract: A comparative investigation on the use of random modulation schemes for DC/DC power converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM) and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in DC/DC power converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a DC/DC buck converter operating in the continuous conduction mode. The PSD of the output under each scheme is presented and compared.

An accurate statistical yield model for CMOS current-steering D/A converters

Abstract: To obtain a high resolution CMOS current-steering digital-to-analog converter, the matching behavior of the current source transistors is one of the key issues in the design. At this moment, these matching properties are taken into account by the use of time consuming and CPU intensive Monte Carlo simulations. In this paper a formula is derived that allows us to accurately describe the impact of the mismatch on the INL (integral non-linearity) yield of current-steering D/A converters without any loss of design time.

Negative impedance stabilizing controls for PWM DC-DC converters using feedback linearization techniques

Abstract: Power electronic converters, when tightly regulated, have constant power sink characteristics at their inputs. This is a destabilizing effect, which is known as negative impedance instability, for the DC/DC converters feeding these loads in a multi-converter power electronic system. In this paper, necessary and sufficient conditions of stability for PWM DC/DC converters with constant power and conventional constant voltage loads are expressed. A nonlinear robust stabilizing controller based on feedback linearization techniques is proposed. Furthermore, the stability of the proposed controller for the Buck converter using the second theorem of Lyapunov is verified.

Transfer function of current modulator in PWM converters with current-mode control

Abstract: Several different expressions have been derived in previous publications for the transfer function of the current modulator used in pulsewidth modulated (PWM) dc-dc power converters with current-mode control. These expressions give results higher than the measured ones and exhibit many other problems, e.g., one expression gives an infinite value when no slope compensation is used. This paper presents a derivation for the transfer function of the current modulator used in PWM converters with fixed-frequency, trailing-edge modulation, peak-current-mode control for two cases: without and with slope compensation. In addition, feedforward terms are also derived.

A Four-Level Inverter Based Drive with a Passive

Abstract: Multilevel inverters are suited for high power drive applications due to their increased voltage capability. Specifically, as compared to three level inverters, for a given dc bus voltage, a four-level inverter is able to synthesize better waveforms with re- duced device ratings. In a medium voltage drive, a conventional diode bridge rectifier is a low cost multilevel solution if the dc bus voltages can be balanced from the inverter side alone. In this paper, operation of four-level drive with a passive rectifier is investigated, and modulation constraints of the inverter, arising from the capac- itor voltage balancing requirements are examined. Simulation and experimental results are presented to demonstrate the link voltage balancing strategy and the performance of the four-level drive. Index Terms—Diode clamped inverters, four level inverters, high power drives, multilevel converters.

A mismatch insensitive CMOS dynamic comparator for pipeline A/D converters

Abstract: A new fully differential CMOS dynamic comparator topology suitable for pipeline A/D converters with a low stage resolution is proposed. A thorough analysis of its function and a comparison to a widely used dynamic comparator are given in this paper. The proposed topology, based on two cross coupled differential pairs and switchable current sources, has a small power and area dissipation and it is shown to be very robust against transistor mismatch.

Theoretical study of switching power converters with power factor correction and output regulation

Abstract: This paper discusses a systematic method for deriving basic converter configurations that achieve power factor correction (PFC) and voltage regulation. The discussion begins with a general three-port representation of power supplies that provide PFC and voltage regulation. Based on this representation and a power flow consideration, a systematic procedure is derived to generate all possible minimal configurations. It is found that two basic converters are, in general, required for implementing any of the possible configurations. Among these configurations only a few have been known previously and been used in practice. The various possible configurations are compared in terms of their theoretical efficiency and control requirements of the basic constituent converters.

Multi-converter FACTS devices: the generalized unified power flow controller (GUPFC)

Abstract: This paper introduces the new concept of multi-converter (three or more) voltage-sourced-converter (VSC) based FACTS devices as well as DC "control sub-networks". A control subnetwork is defined as a multi-terminal DC transmission system utilizing a number of series and shunt converters connected together and embedded in the AC power system for ultimate control capability. A special case consisting of three converters, namely, the generalized unified power flow controller (GUPFC) is discussed in detail. A fundamental frequency model of the GUPFC and its controls is developed in EMTP and used to demonstrate its performance and capability in a test power system. It is shown that this GUPFC consisting of one shunt converter and two series converters is capable of simultaneously controlling five power system quantities, i.e., the bus voltage at a substation and the real and reactive power flows on two lines exiting the substation. Test results are presented indicating the controller performance for reference tracking and in response to a three-phase fault on the system.

Space Vector Modulation and Control of Multilevel Converters

Abstract: This dissertation is the result of the research and development of a power conditioning system for superconductive magnetic energy storage systems (SMES). The dominant challenge of this research was to develop a power conditioning system that can match slowly varying dc voltages and dc currents on the superconductive magnet side with the ac voltages and ac currents on the utility side. At the same time, the power conditioning system was required to provide a bi-directional power flow to the superconductive magnet. The focus of this dissertation is a three-level diode-clamped dc/ac converter, which is a principle part of the power conditioning system. Accordingly, this dissertation deals with the space vector modulation (SVM) of three-level converters and introduces a computationally very efficient three-level SVM algorithm that is experimentally verified. Furthermore, the proposed SVM algorithm is successfully generalized to allow equally efficient, real-time implementation of SVM to dc/ac converters with virtually any number of levels. The most important advantage of the proposed concept is that the number of instructions required to implement the algorithm is almost independent from the number of levels in a multilevel converter. More on the side of the control of multilevel converters, particular attention in this dissertation is paid to the problem of charge balance in the split dc-link capacitors of three-level neutral-point-clamped converters. It is a known fact that although the charge balance in the neutral point (NP) can be maintained on a line cycle level, a significant third harmonic current iii flows into the NP for certain loading conditions, causing the neutral-point voltage ripple. The logical consequence of that ripple is the deteriorated quality of the output voltage waveforms as well as the increased voltage stress on the switching devices. This was the motivation to more carefully explore the loading conditions that cause the imbalance, as well as to study the fundamental limitations of dc-link capacitor charge balancing algorithms. As part of this work, a new model of the neutral-point current in the rotating coordinate frame is developed as a tool for the investigation of theoretical limitations and in order to provide some insight into the problem. Additionally, the low-frequency ripple is quantified and guidelines are offered that can help determine the correct size for the dc-link capacitors. Because the study of the neutral-point balance identified the loading conditions that (under some possible system constraints) cause an unavoidable neutral-point voltage ripple, a feed-forward type of control …

Analysis, simulation and design of series resonant converter for high voltage applications

Abstract: Series resonant converters find application in high voltage power supplies where the large transformer parasitics have to be accounted for. This paper deals with the analysis, simulation and design of the phase modulated series resonant converter. Steady state analysis for the above resonant frequency operation is presented. Two modifications, one for extending the zero voltage switching range and the other providing inherent short circuit protection are also introduced. Experimental results on a laboratory model are shown to verify the design procedure.

Computer-aided small-signal analysis based on impulse response of DC/DC switching power converters

Abstract: The paper describes a method for automated small-signal frequency response analysis based on transient response obtained using a general-purpose simulation tool such as simulation program with integrated circuit emphasis (SPICE). The method is based on using the simulation tool to evaluate the converter impulse response. The main advantage of the proposed method as a design verification tool is that frequency responses can be generated efficiently for any converter configuration and any model complexity supported by the general-purpose simulator. Application examples are included to demonstrate very good correlation between the generated responses and experimental data, and to compare the results with predictions of approximate analytical methods. In particular, the method is applied to investigate high-frequency dynamics of pulse width modulation (PWM) converters operating in discontinuous conduction mode, and the results are used to compare and validate several existing analytical modeling approaches.

New start-up schemes for isolated full-bridge boost converters

Abstract: Two new start-up schemes for isolated full-bridge boost converters are proposed in this paper. The control timing for each scheme, which is compatible with the PWM control timing for the normal boost mode operation, is investigated. Design considerations on the relationships between the turns ratios of the boost choke windings and the main transformer windings, and its effects on the operation of the converter, are studied. The two proposed start-up schemes are experimentally verified on a 1.6 kW, 12 V/288 V prototype.

Possibilities of obtaining small-signal models of DC-to-DC power converters by means of system identification

Abstract: This paper presents some existing system identification methods and the results obtained when applying these methods to a forward DC-to-DC power converter. Some of the advantages and disadvantages of the methods are presented. With system identification, measured data from a system's input and output can be processed to results in a model of the system.

A robust load-sharing control scheme for parallel-connected multisystems

Abstract: Parallel connection of inverters or converters is one useful method for solving the high power requirements. However, a load-sharing problem among parallel-connected systems is not an easy task, since crosstalk may take place among the subsystems. We develop a general methodology for solving the load sharing problem using the master-slave concept. In synthesizing the input to the slave system, we utilize system-dynamics-dependent filters. With the proposed method, we can equally distribute the load, or can give a certain offset (in load) to a specific subsystem. To show the usefulness of the proposed control scheme, we perform a simulation study with two practical systems: a current-balancing control in parallel-connected pulsewidth modulation converters and a speed and tension control for a bridle roll system in a steel mill.

Double-output Luo converters, an advanced voltage-lift technique

Abstract: Mirror-symmetrical double-output voltages are specially required in industrial applications and computer periphery circuits. Double output DC-DC converters can convert the positive input source voltage to positive and negative output voltages by two conversion paths. Because of the effect of parasitic elements, the output voltage and power-transfer efficiency of DC-DC converters are limited. The voltage-lift technique is a popular method that is widely applied in electronic circuit design. This technique gives a good way of improving circuit characteristics, and has been successfully applied for DC-DC converters. As are single output (positive and negative output) Luo converters, double-output Luo converters are a series of new DC-DC step-up converters using only one switch. They are developed from prototypes using the advanced voltage-lift technique. These converters perform from positive to positive and negative DC-DC voltage-increase conversion with high power density, high efficiency and cheap topology in a simple structure. They are different from any other existing DC-DC step-up converters and possess many advantages including high output voltage with small ripples. Therefore these converters will be widely used in computer peripheral equipment and industrial applications, especially for high double-output voltage projects.

Soft-switching techniques for PWM full bridge converters

Abstract: This paper proposes a family of modulation strategies for PWM full bridge converter including nine modulation strategies, which can be classified into two kinds according to the turn-off sequence of the two power switches in the oblique diagonal line of the two bridge legs. The concept of leading leg and lagging leg is introduced to realize soft-switching for PWM full bridge converters. The realization of soft-switching for both leading leg and lagging leg is proposed, based on which, soft-switching techniques for PWM full bridge converters can be classified into two kinds: zero-voltage-switching (ZVS) and zero-voltage and zero-current-switching (ZVZCS). The modulation strategies and topologies for the two kinds of soft-switching PWM full bridge converters are proposed.

A hysteresis current-regulated control for multi-level drives

Abstract: Most multi-level converters are controlled through the use of voltage-source based control techniques such as space-vector modulation or multi-level sine-triangle modulation. However, in many applications such as field oriented drives, a high bandwidth current-source inverter based control is more desirable. In this paper, the concept of a multi-level hysteresis current-source control is set forth. The new control is experimentally verified using a four-level converter/induction motor drive system and the results are compared to a space vector modulation controller. A dynamic study involving a step change in current command demonstrates the controls high bandwidth.

A quadratic buck converter with lossless commutation

Abstract: High switching frequency associated with soft commutation techniques is a new trend in switching converters. Following this trend, the authors present a buck pulsewidth modulation converter, where the DC voltage conversion ratio has a quadratic dependence on duty cycle, providing a large step-down. By introducing two resonant networks, soft switching is attained, providing highly efficient operating conditions for a wide load range at high switching frequency. Contrary to most of the converters that apply soft-switching techniques, the switches presented are not subjected to high switch voltage or current stresses and, consequently, present low conduction losses. The authors present, for this converter, the principle of operation, theoretical analysis, relevant equations and simulation and experimental results.

On the design of sliding mode control schemes for quantum resonant converters

Abstract: The design of sliding mode control schemes for quantum resonant converters is introduced hy means of two different approaches. First, an easy-to-use procedure for devising nonlinear control structures is established, using Lyapunov's well-known stability criteria. Second, an alternative method that provides linear sliding surfaces is also developed, considering reaching, existence, and stability conditions. The application of both control design techniques is illustrated in detail by means of three selected examples. The advantages and drawbacks of the resulting control circuits are examined. Simulation and experimental results corroborate the expected features of the close-loop quantum converters.