Showing papers on "Converters published in 2007"

Decoupled Double Synchronous Reference Frame PLL for Power Converters Control

Abstract: This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL

Data converters

Abstract: This book is the first graduate-level textbook presenting a comprehensive treatment of Data Converters. It provides comprehensive definition of the parameters used to specify data converters, and covers all the architectures used in Nyquist-rate data converters. The book uses Simulink and Matlab extensively in examples and problem sets. This is a textbook that is also essential for engineering professionals as it was written in response to a shortage of organically organized material on the topic. The book assumes a solid background in analog and digital circuits as well as a working knowledge of simulation tools for circuit and behavioral analysis.

Modeling of Quantization Effects in Digitally Controlled DC–DC Converters

Abstract: In digitally controlled dc-dc converters with a single voltage feedback loop, the two quantizers, namely the analog-to-digital (A/D) converter and the digital pulse-width modulator (DPWM), can cause undesirable limit-cycle oscillations. In this paper, static and dynamic models that include the quantization effects are derived and used to explain the origins of limit-cycle oscillations. In the static model, existence of dc solution, which is a necessary no-limit-cycle condition, is examined using a graphical method. Based on the generalized describing function method, the amplitude and offset-dependent gain model of a quantizer is applied to derive the dynamic system model. From the static and dynamic models, no-limit-cycle conditions associated with A/D, DPWM and compensator design criteria are derived. The conclusions are illustrated by simulation and experimental examples

Predictive Control Strategy for DC/AC Converters Based on Direct Power Control

Abstract: This paper proposes predictive direct power control (P-DPC), a new control approach where the well-known direct power control is combined with predictive selection of a voltage-vectors' sequence, obtaining both high transient dynamics and a constant-switching frequency. The developed P-DPC version is based on an optimal application of three voltage vectors in a symmetrical way, which is the so-called symmetrical 3 + 3 vectors' sequence. The simulation and experimental results of the P-DPC are compared to standard voltage-oriented control (VOC) strategies in a grid-connected three-phase voltage-source inverter under 400-V 15-kVA operation conditions. The P-DPC improves the transient response and keeps the steady-state harmonic spectrum at the same level as the VOC strategies. Due to its high transient capability and its constant-switching behavior, the P-DPC could become an interesting alternative to standard VOC techniques for grid-connected converters

Small-Signal Discrete-Time Modeling of Digitally Controlled PWM Converters

Abstract: The letter presents an exact small-signal discrete-time model for digitally controlled pulsewidth modulated (PWM) dc-dc converters operating in constant frequency continuous conduction mode (CCM) with a single effective A/D sampling instant per switching period. The model, which is based on well-known approaches to discrete-time modeling and the standard Z-transform, takes into account sampling, modulator effects and delays in the control loop, and is well suited for direct digital design of digital compensators. The letter presents general results valid for any CCM converter with leading or trailing edge PWM. Specific examples, including approximate closed-form expressions for control-to-output transfer functions are given for buck and boost converters. The model is verified in simulation using an independent system identification approach.

Comparison of 2.3-kV Medium-Voltage Multilevel Converters for Industrial Medium-Voltage Drives

Abstract: This paper compares the expense of power semiconductors and passive components of a (2.3 kV, 2.4 MVA) two-level, three-level neutral-point-clamped, three-level flying-capacitor, four-level flying-capacitor, and five-level series-connected H-bridge voltage source converter on the basis of the state-of-the-art 6.5-, 3.3-, 2.5-, and 1.7-kV insulated gate bipolar transistors for industrial medium-voltage drives. The power semiconductor losses, the loss distribution, the installed switch power, the design of flying capacitors, and the components of an sine filter for retrofit applications are considered.

Energy Management Power Converters in Hybrid Electric and Fuel Cell Vehicles

Abstract: Using a bidirectional dc-dc converter along with low-voltage energy storage for the high-voltage dc bus and traction motor drives has been a prominent option for hybrid electric and fuel cell vehicles. This paper will describe the significance of energy management power converters and their circuit topology options for efficiency, size, and cost considerations. Whether isolated or nonisolated, soft switching techniques have been widely used in high-power bidirectional dc-dc converters. Through some design examples, the component selection and circuit design optimization are discussed, and their efficiency evaluation results are also given. Major difficulties of developing a high-power bidirectional dc-dc converter are found in lack of high-power passive components and lack of multiphase dc-dc controllers. More development work needs to be done in these areas

Energy Management Power Converters in Hybrid Electric and Fuel Cell Vehicles Suitable switching devices and passive electrical components, for increasing the efficient handling of high-power conversion required by these vehicles, are not yet available.

Abstract: Using a bidirectional dc-dc converter along with low-voltage energy storage for the high-voltage dc bus and traction motor drives has been a prominent option for hybrid electric and fuel cell vehicles. This paper will describe the significance of energy management power converters and their circuit topology options for efficiency, size, and cost considera- tions. Whether isolated or nonisolated, soft switching techni- ques have been widely used in high-power bidirectional dc-dc converters. Through some design examples, the component selection and circuit design optimization are discussed, and their efficiency evaluation results are also given. Major difficulties of developing a high-power bidirectional dc-dc converter are found in lack of high-power passive components and lack of multiphase dc-dc controllers. More development work needs to be done in these areas.

Optimal Modulation of Flying Capacitor and Stacked Multicell Converters Using a State Machine Decoder

Abstract: Modulation of flying capacitor and stacked multicell converters is complicated by the fact that these converters have redundant states that achieve the same phase leg voltage output. Hence, a modulator must use some secondary criteria such as cell voltage balancing to fully define the converter switched state. Alternatively, the modulator can be adapted to directly specify the cell states, such as has been proposed for the harmonically optimal phase disposition (PD) strategy. However the techniques reported to date can lead to uneven distribution of switching transitions between cells, and the synthesis of narrow switched phase leg pulses. This paper presents an improved strategy that decouples the tasks of voltage level selection and switching event distribution. Conventional PD and centered space vector pulsewidth modulation (CSVPWM) strategies are used to define the target voltage level for the converter, and a finite state machine is then used to distribute the transitions to the converter cells in a cyclical fashion. Experimental results for a four-level flying capacitor inverter are presented, verifying that the natural balancing properties of this converter has been preserved, the cell switching utilization is equal and the expected harmonic gains of PD and CSVPWM compared to phase shifted carrier PWM have been achieved

A Cooperative Imbalance Compensation Method for Distributed-Generation Interface Converters

Abstract: Distributed generation has attracted great attention in recent years, thanks to the progress in new generation technologies and advanced power electronics. The Micro-grid has been a successful example by integrating various generation sources with the existing power distribution network through power electronics converters. The Micro-grid converters are required to operate in a de-centralized fashion, and the power- frequency droop control and reactive power-voltage droop control have been adopted for this purpose. In this paper, a droop control technique for imbalance compensation within the three- phase AC distributed generation system is proposed for Micro- grid converters. The proposed technique allows even sharing of imbalance current among various converters, can be seamlessly integrated with existing active power-frequency droop control and reactive power-voltage droop control to improve the power quality within the distributed power system. Its control functionalities are discussed, simulation and laboratory test results are also presented to validate the proposed method.

Analysis and Implementation of a High Efficiency, Interleaved Current-Fed Full Bridge Converter for Fuel Cell System

Abstract: An interleaved current-fed full bridge (ICFFB) dc-dc converter is proposed in this paper that has low input current ripple to meet the fuel cell demands. By interleaving two isolated CFFB converters with parallel input and series output connection, both input current ripple and output voltage ripple can be reduced. In addition, the size of the magnetic components and current stress of the semiconductor devices on the input side are also reduced. Similarly, smaller voltage rating components can be used on the output side. Only one digital signal processor microcontroller is used to generate phase-shifted gate signals and to implement a cascaded digital control system. The main features of the proposed converter are high efficiency, small passive component size, and small input current ripple. Experimental results for a 1.2-kW interleaved CFFB converter are provided in the paper

A Fast-Response Sliding-Mode Controller for Boost-Type Converters With a Wide Range of Operating Conditions

Abstract: This paper proposes a fast-response sliding-mode controller for controlling boost-type converters requiring a fast dynamical response over a wide range of operating conditions. The various aspects of the controller, which include the method of generating the reference-current profile, the choice of sliding surface, the existence and stability properties, and the selection of the control parameters, are discussed. Experimental results are presented to validate the theoretical design and to illustrate the strength of the proposed controller. It is demonstrated that, with the proposed controller, the boost converter has a faster response and a lower voltage overshoot over a wide range of operating conditions as compared to that under the widely used peak current-mode controller. Moreover, it is easily realized with simple analog circuitries.

1MHz High Efficiency LLC Resonant Converters with Synchronous Rectifier

Abstract: This paper proposes a novel synchronous rectifier driving scheme for resonant converters. An LLC resonant converter with proposed synchronous rectification is designed and analyzed. It is a high efficiency, high power density solution for future frond end converters. Hold up time extension capability is achieved for designed LLC resonant converter without sacrificing the efficiency for nominal condition. 1kW, 1MHz LLC resonant converter with proposed SR is built to demonstrate its advantages (size and efficiency) over the diode rectification and PWM converter. Overall 95.1% efficiency and 96W/in3 power density are achieved.

Autotuning of Digitally Controlled DC–DC Converters Based on Relay Feedback

Abstract: This paper proposes a simple autotuning technique for digitally controlled dc-dc converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of proportional-integral-derivative parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the relay feedback control on the output voltage. The proposed algorithm is simple, requires small tuning times, and it is compliant with the cost/complexity constraints of integrated digital integrated circuits. Simulation and experimental results of a synchronous buck converter and of a dc-dc boost converter confirm the effectiveness of the proposed solution

A D-Q Frame Controller for a Full-Bridge Single Phase Inverter Used in Small Distributed Power Generation Systems

Abstract: This paper presents a Direct-Quadrature (DQ) rotating frame control method for single phase full-bridge inverters used in small hybrid power systems. A secondary orthogonal imaginary circuit is created to provide the second phase required for the transformation; thus a DQ model of the inverter is obtained and its controller designed emulating the controls of three-phase power converters. The proposed controller attains infinite loop gain in the rotating coordinate, thus providing zero steady-state error at the fundamental frequency of the converter. The proposed controller is designed and validated through simulations using a DQ-frame average model in Matlab and a detailed switching model in Saber, as well as experimental results obtained with a 2.5 kW single phase full-bridge inverter prototype using a DSP/FPGA based digital control system where the proposed DQ-frame controller is fully implemented.

Conducted EMI Reduction in Power Converters by Means of Periodic Switching Frequency Modulation

Abstract: Spread spectrum clock generation techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of megahertz. Nowadays, the switching frequency of power converters has been increasing up to values that make worthy the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. First, theoretical principles of frequency modulation using three periodic patterns for the modulating function are presented. The influence of some important modulation parameters on the EMI reduction is analyzed and some considerations about the EMI filters design are also presented. The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and confirmed with experimental results obtained from tests carried out on two converters. The first one is a 2.5 W buck converter that can be switched up to 1 MHz and the second one is a 600 W boost converter switching at 40 kHz. In both cases, attenuations obtained in conducted EMI are evaluated. Finally, special attention has been paid to input current and output voltage ripple in order to evaluate possible undesired side-effects produced by this technique.

ZVT interleaved boost converters for high-efficiency, high step-up DC-DC conversion

Abstract: The narrow turn-off period of the conventional boost converters limits their applications in high step-up DC-DC conversion. The voltage gain is extended without an extreme duty-cycle by the winding-coupled inductor structure. However, the leakage inductance induces large voltage spikes when the switch turns off. An active-clamp circuit is introduced here to clamp the switch turn-off voltage spikes effectively and to recycle the leakage energy. Both the main switches and the auxiliary switches are ZVT during the whole switching transition. Meanwhile, the output diode reverse-recovery problem is alleviated because the leakage inductance of the coupled inductors is in series with the output diode. Furthermore, a family of ZVT interleaved boost converters for high efficiency and high step-up DC-DC conversion is deduced. The experimental results based on 40-380 V front-end applications verify the significant improvements in efficiency

Z-Source AC–AC Converters Solving Commutation Problem

Abstract: A new family of Z-source ac-ac converters with buck-boost ability are proposed, including four switches single-phase structure and six switches three-phase structure. New commutation strategies for these converters are proposed and safe commutation can be achieved without snubber circuit. The commutation strategies are easily to realize by sampling only voltage signals, and two switches are always turned on, so switching loss can be reduced. Analysis based on state-space averaging reveals the relationship between Z-source inductor current and filter inductor current as well as voltage ratio. The design considerations of voltage-fed single-phase topology are given as an example. Simulation results on the voltage-fed topologies and experimental results on voltage-fed single-phase topology verified the unique features of Z-source ac-ac converters and the proposed commutation strategies. These converters have merits such as less conduction and switching loss, less devices, therefore high efficiency and reliability can be achieved.

Interleaved Zero-Current-Transition Buck Converter

Abstract: This paper introduces interleaved zero-current-transition (ZCT) converters where two sets of switches are operating out-of-phase and share the load power equally. Turn-on transitions at zero current and a significant reduction of the losses associated with diode reverse recovery are accomplished through addition of two small inductors. This paper describes a 30-kW (300 V/100 A) interleaved ZCT buck converter operating at 32-kHz effective switching frequency. Losses and efficiency of the experimental prototype compare favorably against the standard and interleaved hard-switched buck converters. Constant frequency operation with low switching losses and low output current ripple is very well suited for the realization of dc power supplies in plasma processes.

Circuit Theoretic Classification of Parallel Connected DC–DC Converters

Abstract: This paper describes a classification of paralleling schemes for dc-dc converters from a circuit theoretic viewpoint. The purpose is to provide a systematic classification of the types of parallel converters that can clearly identify all possible structures and control configurations, allowing simple and direct comparison of the characteristics and limitations of different paralleling schemes. In the proposed classification, converters are modeled as current sources or voltage sources, and their connection possibilities, as constrained by Kirchhoff's laws, are categorized systematically into three basic types. Moreover, control arrangements are classified according to the presence of current sharing and voltage-regulation loops. Computer simulations are presented to illustrate the characteristics of the various paralleling schemes

Analysis of Inductor Current Sharing in Nonisolated and Isolated Multiphase dc–dc Converters

Abstract: Current sharing among inductors is an important issue in both isolated and nonisolated dc-dc converters. In this paper, average current sharing is in-depth modeled and analyzed for both interleaved multiphase buck converters and isolated current-doubler dc-dc converters. The features and comparison of various current-sharing techniques used in isolated and nonisolated dc-dc converters are presented, and the corresponding design guidelines are provided based on the theoretical analysis. The analysis reveals that the state-of-the-art current-sharing technique for multiphase buck converters cannot be directly applied to isolated current-doubler rectifier (CDR) dc-dc converters to achieve balanced inductor currents. Passive and active current-sharing methods are proposed for isolated current-doubler dc-dc converters to balance two inductor currents. Experimental results are presented to verify the modeling analysis and the proposed current-sharing techniques for CDRs in isolated dc-dc converters.

A High-Frequency Resonant Inverter Topology with Low Voltage Stress

Abstract: This document presents a new switched-mode resonant inverter, which we term the Phi2 inverter, that is well suited to operation at very high frequencies and to rapid on/off control. Features of this inverter topology include low semiconductor voltage stress, small passive energy storage requirements, fast dynamic response, and good design flexibility. The structure and operation of the proposed topology are described, and a design procedure is introduced. Experimental results demonstrating the new topology are also presented. A prototype Phi2 inverter is described that switches at 30 MHz and provides over 500 W of rf power at a drain efficiency above 92%. It is expected that the Phi2 inverter will find use as a building block in high performance dc-dc converters among other applications [1], [2].

DC–DC Converter-Aware Power Management for Low-Power Embedded Systems

Abstract: Most digital systems are equipped with dc-dc converters to supply various levels of voltages from batteries to logic devices. DC-DC converters maintain legal voltage ranges regardless of the load current variation as well as battery voltage drop. Although the efficiency of dc-dc converters is changed by the output voltage level and the load current, most existing power management techniques simply ignore the efficiency variation of dc-dc converters. However, without a careful consideration of the efficiency variation of dc-dc converters, finding a true optimal power management will be impossible. In this paper, we solve the problem of energy minimization with the consideration of the characteristics of power consumption of dc-dc converters. Specifically, the contributions of our work are as follows: 1) We analyze the effects of the efficiency variation of dc-dc converters on a single-task execution in dynamic voltage scaling (DVS) scheme and propose the technique for dc-dc converter-aware energy-minimal DVS. 2) is then extended to embed an awareness of the characteristics of dc-dc converters in general DVS techniques for multiple tasks. 3) We go on to propose a technique called for generating a dc-dc converter that is most energy efficient for a particular application. 4) We also present an integrated framework, i.e., , based on and , which addresses dc-dc converter configuration and DVS simultaneously. Experimental results show that is able to save up to 24.8% of energy compared with previous power management schemes, which do not consider the efficiency variation of dc-dc converters.

DC-DC converters for electric vehicle applications

Abstract: An integral part of any modern day electric vehicle is power electronic circuits (PECs) comprising of DC-AC inverters and DC-DC converters. A DC-AC inverter supplies the high power electric motor and utility loads such as air-conditioning system, whereas a DC-DC converter supplies conventional low-power, low-voltage loads. However, the need for high power bidirectional DC- DC converters in future electric vehicles has led to the development of many new topologies of DC-DC converters. This paper presents an overview of state-of-the-art DC-DC converters used in battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and fuel cell vehicles (FCVs). Several DC-DC converters such as isolated, nonisolated, half-bridge, full-bridge, unidirectional and bidirectional topologies, and their applications in electric vehicles are presented.

A Nonlinear Control for DC–DC Power Converters

Abstract: A nonlinear control is proposed and its application to the regulation of the dc-dc converters of the boost and buck types is investigated. The proposed controller, which assumes the exponential form of the linear multiloop controller, provides an additional tuning parameter which can used to modify the output response. The system stability in the presence of uncertain load and line voltage as well as the relationship between the nonlinear and linear control strategies are studied. Numerical and experimental results to illustrate the features of the proposed strategy are also presented

A Comprehensive Study of Harmonic Cancellation Effects in Interleaved Three-Phase VSCs

Abstract: This paper presents a systematic study of the effects of interleaving on three-phase voltage-sourced converters (VSC). Analytical results are developed for the spectra of converter phase currents, common-mode voltages, and dc-link currents for the general case of interleaving N parallel modules with a common dc link. It will be shown, both analytically and numerically, that ripple cancellation effects similar to what have been widely observed in buck dc-dc converters, that is, the elimination of harmonic sidebands other than those centered at TV multiples of the carrier frequency, can also be achieved by proper interleaved operation of N three-phase VSC modules. This will be shown to be true not only for the ac phase currents, as previously known, but also for the common-mode voltage as well as the dc-link current. Analytical results are also presented for the circulating current among parallel modules. Additionally, a relationship between interleaved VSCs and capacitor-clamped multilevel converters is established and used to extend the analytical results developed for interleaved VSCs to multilevel converters.

A New Switching Strategy for Pulse Width Modulation (PWM) Power Converters

Abstract: This paper presents a new switching strategy for pulse width modulation (PWM) power converters. Since the proposed strategy uses independent on/off switching action of the upper or lower arm according to the polarity of the current, the dead time is not needed except instant of current polarity change. Therefore, it is not necessary to compensate the dead time effect and the possibility of arm short is strongly eliminated. The current control of PWM power converters can easily adopt the proposed switching strategy by using the polarity information of the reference current instead of the real current, thus eliminating the problems that commonly arise from real current detection. In order to confirm the usefulness of the proposed switching strategy, experimental tests were done using a single-phase inverter with passive loads, a three-phase inverter for induction motor drives, a three-phase ac/dc PWM converter, a three-phase active power filter, and a class-D amplifier, the results of which are presented in this paper

A novel low-loss modulation strategy for high-power bi-directional buck+boost converters

Abstract: A novel low-loss, constant-frequency, zero-voltage-switching (ZVS) modulation strategy for bi-directional, cascaded, buck-boost DC/DC converters, used in a hybrid electrical vehicle (HEV), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the purposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the anti-parallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a multi-phase converter equipped with the low-loss modulation. Experimental measurements performed with a converter prototype verify the mode of operation and the ZVS principle.

Very High Frequency Resonant Boost Converters

Abstract: This document presents a resonant boost topology suitable for very high frequency (VHF, 30-300 MHz) dc-dc power conversion. The proposed design features low device stress, high efficiency over a wide load range, and excellent transient performance. Two experimental prototypes have been built and evaluated. One is a 110 MHz, 23 W converter which uses a high performance rf LDMOSFET. The converter achieves higher than 87% efficiency at nominal input and output voltages, and maintains good efficiency down to 5% of full load. The second implementation, aimed towards integration, is a 50 MHz 17 W converter which uses a transistor from a 50 V integrated power process. In addition, two resonant gate drive schemes suitable for VHF operation are presented, both of which provide rapid startup and low-loss operation. Both converters regulate the output using high-bandwidth on-off hysteretic control, which enables fast transient response and efficient light-load operation. The low energy storage requirements of the converters allow the use of coreless inductors in both designs, thereby eliminating magnetic core loss and introducing the possibility of easy integration.