Showing papers on "Forward converter published in 2007"

A Bidirectional DC–DC Converter for an Energy Storage System With Galvanic Isolation

Abstract: This paper addresses a bidirectional dc-dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to a dc side of the dc-dc converter without any chopper circuit. Nevertheless, the dc-dc converter can continue operating when the voltage across the energy storage device drops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc-dc converter. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.

A Bidirectional Isolated DC–DC Converter as a Core Circuit of the Next-Generation Medium-Voltage Power Conversion System

Abstract: This paper describes a bidirectional isolated dc-dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc-dc converter is intended to use power switching devices based on silicon carbide (SiC) and/or gallium nitride, which will be available on the market in the near future. A 350-V, 10-kW and 20 kHz dc-dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate insulated gate bipolar transistors and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. Loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc-dc converter. As a result, the overall efficiency may reach 99% or higher

Buck-Boost Converter for Sensorless Power Optimization of Piezoelectric Energy Harvester

Abstract: This paper presents a comprehensive model for miniature vibration-powered piezoelectric generators and analyses modes of operation and control of a buck-boost converter for the purpose of tracking the generators optimal working points. The model describes the generator's power dependence with the mechanical acceleration and frequency, and helps in the definition of the load behaviour for power optimization. Electrical behaviour of the input of buck-boost converter in discontinuous current mode turns out to be in perfect agreement with the considered optimization criteria with a very simple, sensorless control. Experimental results show that the converter controlled by a very low consumption circuit effectively maximizes the power flow into a 4.8 V rechargeable battery connected to the converter output. The converter's efficiency is above 84% for input voltages between 1.6 and 5.5 V, and for output powers between 200 muW and 1.5 mW. The presented circuit and control can be used as well for power optimization of electromagnetic energy harvesting devices.

High-efficiency dc/dc voltage converter including capacitive switching pre-converter and up inductive switching post-regulator

Abstract: A DC/DC converter includes a pre-converter stage, which may include a charge pump, and a post-regulator stage, which may include a Buck converter. The duty factor of the post-regulator stage is controlled by a feedback path that extends from the output terminal of the DC/DC converter to an input terminal in the post-regulator stage. The pre-converter steps the input DC voltage up or down by a positive or negative integral or fractional value, and the post-regulator steps the voltage down by a variable amount depending on the duty factor at which the post-regulator is driven. The converter overcomes the problems of noise glitches, poor regulation, and instability, even near unity input-to-output voltage conversion ratios.

A High Efficiency Dual-Mode Buck Converter IC For Portable Applications

Abstract: This paper presents the design of a novel wide output current range dual-mode dc to dc step-down (Buck) switching regulator/converter. The converter can adaptively switch between pulsewidth modulation (PWM) and pulse-frequency modulation (PFM) both with very high conversion efficiency. Under light load condition the converter enters PFM mode. The function of closing internal idle circuits is implemented to save unnecessary switching losses. The converter can be switched to PWM mode when the load current is greater than 100 mA. Soft start operation is designed to eliminate the excess large current at the start up of the regulator. The chip has been fabricated with a TSMC 2P4M 0.35 mum polycide CMOS process. The range of the operation voltage is from 2.7 to 5 V, which is suitable for single-cell lithium-ion battery supply applications. The maximum conversion efficiency is 95% at 50 mA load current. Above 85 % conversion efficiency can be reached for load current from 3 to 460 mA.

A Single-Inductor Switching DC–DC Converter With Five Outputs and Ordered Power-Distributive Control

Abstract: An integrated five-output single-inductor multiple-output dc-dc converter with ordered power-distributive control (OPDC) in a 0.5 mum Bi-CMOS process is presented. The converter has four main positive boost outputs programmable from +5 V to +12 V and one dependent negative output ranged from -12 V to -5 V. A maximum efficiency of 80.8% is achieved at a total output power of 450 mW, with a switching frequency of 700 kHz. The performance of the converter as a commercial product is successfully verified with a new control method and proposed circuits, including a full-waveform inductor-current sensing circuit, a variation-free frequency generator, and an in-rush-current-free soft-start method. With simplicity, flexibility, and reliability, the design enables shorter time-to-market in future extensions with more outputs and different operation requirements.

High-efficiency DC/DC voltage converter including up inductive switching pre-regulator and capacitive switching post-converter

Abstract: A DC/DC converter includes a pre-regulator stage, which may include a boost converter, and a post-converter stage, which may include a charge pump. The duty factor of the pre-regulator stage is controlled by a feedback path that extends from the output terminal of the pre-regulator stage or the post-converter stage. The pre-regulator steps the input DC voltage up by a variable amount depending on the duty factor, and the post-converter steps the voltage at the output of the pre-regulator up or down by an positive or negative integral or fractional value. The converter overcomes the problems of noise glitches, poor regulation, and instability, even near unity input-to-output voltage conversion ratios.

Voltage Scalable Switched Capacitor DC-DC Converter for Ultra-Low-Power On-Chip Applications

Abstract: This paper presents a voltage scalable switched capacitor (SC) DC-DC converter which employs on-chip charge- transfer capacitors. The DC-DC converter makes use of multiple topologies to achieve scalable voltage generation while minimizing conduction loss and a technique called divide-by-3 switching to minimize the loss due to bottom-plate parasitics. It also uses automatic frequency scaling to reduce switching losses. The converter employs an all digital control which consumes no static power. The voltage scalable SC DC-DC converter with integrated on-chip charge-transfer capacitors was implemented in a 0.18 mum CMOS process and achieves above 70% efficiency over a wide range of load powers from 5 muW to 1 mW, while delivering load voltages from 300 mV to 1.1 V. The active area consumed by the converter is 0.57 mm2.

Power-Factor-Corrected Single-Stage Inductive Charger for Electric Vehicle Batteries

Abstract: A novel power-factor-corrected single-stage alternating current/direct current converter for inductive charging of electric vehicle batteries is introduced. The resonant converter uses the current-source characteristic of the series-parallel topology to provide power-factor correction over a wide output power range from zero to full load. Some design guidelines for this converter are outlined. An approximate small-signal model of the converter is also presented. Experimental results verify the operation of the new converter

Current bypass for distributed power harvesting systems using dc power sources

Abstract: A converter circuit providing multiple current bypass routes between the output leads to provide reliability in a series connection of several converters. If the converter malfunctions due to component failure, the current bypass routes provide a path for the current that views the malfunctioning converter as substantially a short. Diodes prevent backflow into the power source connected to the converter. Redundancy is provided in the bypass portions of the converter circuit that provides alternate parallel paths in case a defective component in one of the paths opens the circuit along that path. In one example, the converter is implemented as a buck plus boost converter where either the buck or the boost portion or both are operative responsive to a controller controlling the switches of both portions. Most of the converter circuit may be implemented in an integrated circuit.

A New PWM ZVS Full-Bridge Converter

Abstract: A soft-switched full-bridge (FB) converter that features zero-voltage-switching (ZVS) of the bridge switches over a wide output-load range is introduced. The proposed converter achieves ZVS with substantially reduced duty-cycle loss and circulating current. The control of the proposed converter can be implemented either with the phase-shift or pulsewidth modulated (PWM) technique. The performance of the proposed topology was verified on a 2-kW (48-V/40-A) experimental PWM FB converter prototype operating at 120 kHz from a 380-V dc input

Tri-Modal Half-Bridge Converter Topology for Three-Port Interface

Abstract: This letter proposes a novel converter topology that interfaces three power ports: a source, a bidirectional storage port, and an isolated load port. The proposed converter is based on a modified version of the isolated half-bridge converter topology that utilizes three basic modes of operation within a constant-frequency switching cycle to provide two independent control variables. This allows tight control over two of the converter ports, while the third port provides the power balance in the system. The switching sequence ensures a clamping path for the energy of the leakage inductance of the transformer at all times. This energy is further utilized to achieve zero-voltage switching for all primary switches for a wide range of source and load conditions. Basic steady-state analysis of the proposed converter is included, together with a suggested structure for feedback control. Key experimental results are presented that validate the converter operation and confirm its ability to achieve tight independent control over two power processing paths. This topology promises significant savings in component count and losses for power-harvesting systems. The proposed topology and control is particularly relevant to battery-backed power systems sourced by solar or fuel cells

Impact of power density maximization on efficiency of dc-dc converter systems

Abstract: The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density further different aspects, like thermal management and electromagnetic effects must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of DC-DC converter systems has been developed at the Power Electronic Systems Laboratory of the ETH Zurich. Based on this procedure three converter topologies - a phase shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter - are optimized with respect to power density for a telecom supply (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is presented. Further more, the sensitivity of the optimum with respect to junction temperature, cooling and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5 kW supply a density of approximately 12 kW/ltr. and a switching frequency of ca. 130 kHz results.

Design of a 1-MHz LLC Resonant Converter Based on a DSP-Driven SOI Half-Bridge Power MOS Module

Abstract: In this paper, the design of a 1-MHz LLC resonant converter prototype is presented. Aiming to provide an integrated solution of the resonant converter, a half-bridge (HB) power metal oxide semiconductor (MOS) module employing silicon-on-insulator technology has been designed. Such a technology, which is suitable for high-voltage and high-frequency applications, allows enabling HB power MOSFET modules operating up to 3MHz with a rated voltage of 400V. The power device integrates the driving stages of the high-side and low-side switch along with a latch circuit used to implement over-voltage/over-current protection. The module has been designed to be driven by a digital signal processor device, which has been adopted to perform frequency modulation of the resonant converter. By this way, output voltage regulation against variations from light- to full-loaded conditions has been achieved. The issues related to the transformer design of the LLC resonant converter are discussed, too. Owing to the high switching frequency experienced by the converter, 3F4 ferrite cores have been selected for their low magnetic power losses between 0.5 and 3 MHz and core temperatures up to 120degC. The resonant converter has been designed to operate in an input voltage range of 300-400V with an output voltage of 12V and a maximum output power of 120W. Within these design specifications, a performance analysis of the LLC converter has been conducted, comparing the results obtained at the switching frequencies of 500kHz and 1MHz. A suitable model of the LLC resonant converter has been developed to aid the prototype design.

DC–DC Power Converters

Abstract: DC–DC power converters employ switched-mode circuitry to change dc voltages and currents with efficiencies approaching 100% Basic converter circuits can reduce the voltage (buck converter), increase the voltage (boost converter) or both (buck-boost, Cuk, and SEPIC converters) Transformer-isolated circuits include the bridge, forward, and flyback converters Loss mechanisms include conduction loss arising from resistances or forward voltage drops of the power components, and switching loss generated during the transistor and diode switching transitions Synchronous rectifiers can be employed to reduce the significant conduction loss caused by diode forward voltage drops in low-voltage applications The discontinuous conduction mode may arise when the inductor current is sufficiently small, which causes the output voltage to be strongly load-dependent Voltage-mode control employs pulse-width modulation to regulate the converter output voltage or other quantities through variation of the transistor duty cycle Another popular technique is current-mode control, in which a circuit eauses the peak transistor current to follow a control reference signal Averaging methods are commonly employed to model the dynamics and efficiency of dc–dc power converters The state-space averaging method leads to an equivalent circuit model that predicts the converter small-signal transfer functions The circuit averaging technique is easily applied to simulate the converter transfer functions, in both continuous and discontinuous conduction modes, using computer programs such as SPICE 1 Introduction 2 Converter Circuit Topologies 3 Analysis of Converter Waveforms 4 Transformer Isolation 5 Switch Implementation 6 Discontinuous Conduction Mode 7 Current-Mode Control 8 DC-DC Converter Modeling Keywords: pulse-width modulation; voltage-mode control; buck converter; boost converter; buck-boost converter; state-space averaging method

A Current Fed Two-Inductor Boost Converter With an Integrated Magnetic Structure and Passive Lossless Snubbers for Photovoltaic Module Integrated Converter Applications

Abstract: In this paper, a photovoltaic (PV) module integrated converter is implemented with a current fed two-inductor boost converter cascaded with a line frequency unfolder. The current source is a sinusoidally modulated two-phase buck converter with an interphase transformer. The boost cell operates at a fixed duty ratio and has an integrated magnetic structure. The two inductors and the transformer are integrated into one magnetic core. Passive lossless snubbers are employed to recover the energy trapped in the transformer leakage inductance and to minimize the switching losses. The two-inductor boost converter output interfaces with the mains via an unfolding stage, where the MOSFETs are driven by the PV gate drivers. Experimental results are provided for a 100-W converter developing a single phase 240-V 50-Hz output

Integrated bi-directional converter for plug-in hybrid electric vehicles

Abstract: This invention relates to a power module for a plug-in hybrid electric vehicle including an integrated converter having a rectifier changing AC to DC, a DC/DC converter changing from a first voltage to a second voltage, and a battery storing electrical energy. The integrated converter operates in three modes 1) AC plug-in charging mode, 2) boost mode supplying power from the battery to the electrical bus and 3) buck mode supplying power from the electrical bus to the battery. The integrated converter utilizes the same single inductor during each of the three operating modes to reduce cost and weight of the system.

Soft-Switching Zeta–Flyback Converter With a Buck–Boost Type of Active Clamp

Abstract: This paper presents the system analysis, design consideration, and implementation of a soft-switching zeta-flyback converter to achieve zero-voltage switching (ZVS). In the proposed converter, the zeta and flyback topologies are adopted in the output side to achieve the following features: to share the power components in the transformer primary side, to achieve the partial magnetizing flux reset, and to share the output power. The buck-boost type of active clamp is connected in parallel with the primary side of the isolation transformer to recycle the energy stored in the leakage inductor of isolated transformer and to limit the peak voltage stress of switching devices due to the transformer leakage inductor when the main switch is turned off. The active clamp circuit can make the switching devices to turn on at ZVS. Experimental results taken from a laboratory prototype rated at 240 W, input voltage of 150 V, output voltage of 12 V, and switching frequency of 150 kHz are presented to demonstrate the converter performance. Based on the experimental results, the circuit efficiency is about 90.5% at rated output power, and the output voltage variation is about 1%.

The Tapped-Inductor Boost Converter

Abstract: In many emerging applications it is required a high boosting gain; in the literature has been proposed many topologies to make this possible, since the traditional dc-dc boost converter can not make the very high boosting function by itself. In this paper a different approach to obtain the high boosting gain is proposed: the tapped-inductor boost converter. This converter has few components and high efficiency, and also operates in a simple way. Analysis and experimental results are presented.

Capacitor Voltage Balance for the Neutral-Point- Clamped Converter using the Virtual Space Vector Concept With Optimized Spectral Performance

Abstract: This paper presents a new pulsewidth modulation (PWM) for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped (NPC) direct current-alternating current (dc-ac) converter. The balancing of the neutral-point voltage is achieved over the full range of converter output voltages and for all load power factors with the minimum output voltage distortion at around the switching frequency. The simple phase duty-ratio expressions in d-q-0 coordinates that define this modulation are presented. The performance of this modulation approach and its benefits over other previously proposed solutions are verified through simulation and experiments.

LCL-T Resonant Converter With Clamp Diodes: A Novel Constant-Current Power Supply With Inherent Constant-Voltage Limit

Abstract: The LCL-T resonant converter behaves as a constant-current (CC) source when operated at the resonant frequency. The output voltage of a CC power supply increases linearly with the load resistance. Therefore, a constant-voltage (CV) limit must be incorporated in the converter for its use in practical applications wherein the open-load condition is commonly experienced by a CC power supply, such as in an arc welding power supply. A novel LCL-T resonant converter with clamp diodes is proposed in this paper, which has built-in CC-CV characteristics. Since the CC-CV characteristics are inherent to the converter, and complex feedback control is not required, the proposed converter is rugged and reliable. The principle of operation of the converter is explained. Experimental results on a 500-W prototype are presented to demonstrate the inherent CC-CV behavior of the converter. Simple extensions of the topology featuring variable CV limits are described

Active-Clamping ZVS Flyback Converter Employing Two Transformers

Abstract: This paper presents a two-transformer active-clamping zero-voltage-switching (ZVS) flyback converter, which is mainly composed of two active-clamping flyback converters. By utilizing two separate transformers, the proposed converter allows a low-profile design to be readily implemented while retaining the merits of a conventional single-transformer topology. The presented two-transformer active-clamping ZVS flyback converter can approximately share the total load current between two secondaries. Therefore, the transformer copper loss and the rectifier diode conduction loss can be decreased. Detailed analysis and design of this new two-transformer active-clamping ZVS flyback converter are described. Experimental results are recorded for a prototype converter with an ac input voltage ranging from 85 to 135 V, an output voltage of 24 V and an output current of 8 A, operating at a switching frequency of 180 kHz.

Analysis and Design of LLC Resonant Converter with Integrated Transformer

Abstract: LLC resonant converter has a lot of advantages over the conventional series resonant converter and parallel resonant converter; narrow frequency variation over wide load and input variation, Zero Voltage Switching (ZVS) for entire load range and integration of magnetic components. This paper presents analysis and design consideration for half-bridge LLC resonant converter with integrated transformer. Using the fundamental approximation, the gain equation is obtained, where the leakage inductance in the transformer secondary side is also considered. Based on the gain equation, the practical design procedure is investigated to optimize the resonant network for a given input/ output specifications. The analysis and design procedure are verified through an experimental prototype converter.

High-Efficiency Active-Clamp Forward Converter With Transient Current Build-Up (TCB) ZVS Technique

Abstract: In this paper, an active-clamp forward converter with transient current build-up zero-voltage switching (ZVS) technique is proposed. The proposed converter is suitable for the low-voltage and high-current applications. The structure of the proposed converter is the same as that of the conventional active-clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during the very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve the high efficiency and low electromagnetic-interference noise resulting from the soft switching without any additional conduction losses and shows the high power density resulting from the high efficiency and no additional components added. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and a significant improvement in the efficiency for the 100-W (5 V, 20 A) prototype converter

A Bi-Directional DC/DC Converter for an Energy Storage System

Abstract: This paper addresses a bi-directional dc/dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to one of the dc buses of the dc/dc converter without any chopper circuit. Nevertheless, the dc/dc converter can continue operating when the voltage across the energy storage device droops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc/dc converter. A laboratory model of the energy storage system rated at 200 V and 2.6 kJ designed and constructed in this paper verifies that the dc/dc converter can charge and discharge the capacitor bank properly. Moreover, the dc/dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.

DC Voltage Control of the DC Micro-grid for Super High Quality Distribution

Abstract: DC micro-grid is a novel super high quality electric power system. The power is transmitted through dc distribution line and converted to required ac or dc voltages by converters placed near loads. Those load side converters do not need transformers by choosing proper dc distribution voltage (plusmn170 V). The dc power line is composed of 3 wires: +170 V line, neutral line and -170 V line. The distribution voltages have to be balanced to keep high quality power supplying. In this paper, a voltage balancer for dc distribution are proposed and studied. Computer simulation results demonstrated that dc micro-grid was able to supply both ac and dc power to loads simultaneously and stably by 3-wire dc distribution line and load side converters. In addition, another voltage balancer (dc/dc converter type) is also proposed and studied in the last section.

Analysis of Decoupled d-q Vector Control in DFIG Back-to-Back PWM Converter

Abstract: The doubly-fed induction generator (DFIG) is a 'special' variable speed induction machine and is widely used as modern large wind turbine generators. It is a standard, wound rotor induction machine with its stator windings directly connected to the grid and its rotor windings connected to the grid through an AC/DC/AC PWM converter. The AC/DC/AC converter normally consists of a machine-side converter and a grid-side converter, both of which are controlled by decoupled d- q control approaches. In order to gain proper control of a DFIG and appropriate DFIG integration with the grid, it is important to understand the power control characteristics of the two AC/DC converters. This paper focuses on the analysis of traditional decoupled d-q vector control approaches for control of DFIG wind turbines. A typical d-q control concept that has been used widely in DFIG converter control is reviewed in the paper. Then, detailed study is performed to investigate the power control characteristics of DFIG converter using decoupled d-q control approaches. Deficiencies of conventional d-q control mechanisms are discovered and analyzed both analytically and through computer simulation. An extensive simulation study is performed to examine the power control characteristics of DFIG PWM converter under different d-q control conditions.

An Analysis of the ZVS Two-Inductor Boost Converter under Variable Frequency Operation

Abstract: The two-inductor boost converter has been previously presented in a zero-voltage switching (ZVS) form where the transformer leakage inductance and the MOSFET output capacitance can be utilized as part of the resonant elements. In many applications, such as maximum power point tracking (MPPT) in grid interactive photovoltaic systems, the resonant two-inductor boost converter is required to operate with variable input output voltage ratios. This paper studies the variable frequency operation of the ZVS two-inductor boost converter to secure an adjustable output voltage range while maintaining the resonant switching transitions. The design method of the resonant converter is thoroughly investigated and explicit control functions relating the circuit timing factors and the voltage gain for a 200-W converter are established. The converter has an input voltage of 20V and is able to produce a variable output voltage from 169V to 340V while retaining ZVS with a frequency variation of 1MHz to 407kHz. Five sets of theoretical, simulation and experimental waveforms are provided for the selected operating points over the variable load range at the end of the paper and they agree reasonably well. The converter has achieved part load efficiencies above 92% and an efficiency of 89.6% at the maximum power of 200W