Showing papers on "Flyback transformer published in 2012"

Review of solid state transformer in the distribution system: From components to field application

Abstract: The emergence of high power converters makes the modern power grid more active than it was before. One of the research directions in this area is the solid state transformer, which aims at replacing the traditional 50/60 Hz power transformer by means of high frequency isolated AC/AC solid state conversion techniques. This paper presents a systematical technology review essential for the development of solid state transformer in the distribution system, especially focusing on the following four areas: high voltage and high frequency power devices, high power and high frequency transformers, AC/AC converter topologies, and applications of solid state transformer in the distribution system. For each category, the state-of-art technologies are reviewed and possible research directions are presented. It is concluded that the solid state transformer is an emerging technology for the modernization of the future smart grid.

A Low Cost Flyback CCM Inverter for AC Module Application

Abstract: The unfolding-type flyback inverter operating in discontinuous conduction mode (DCM) is popular as a low-cost solution for a photovoltaic (PV) ac module application. This paper aims to improve the efficiency by using a scheme based on continuous conduction mode (CCM) for this application. Design issues, both for the power scheme and the control scheme, are identified and trade-offs investigated. An open-loop control of the secondary current, based on feedback control of the primary current, is proposed in order to bypass the difficulties posed by the moving right half plane zero in the duty cycle to secondary current transfer function. The results presented show an improvement of 8% in California efficiency compared to the benchmark DCM scheme for a 200-W PV module application. The output power quality at rated power level is capable of meeting IEC61727 requirements. The stability of the flyback inverter in CCM has been verified at selected working conditions.

Single-Stage, Universal-Input AC/DC LED Driver With Current-Controlled Variable PFC Boost Inductor

Abstract: This paper presents a single-stage flyback power-factor-correction (PFC) circuit with a variable boost inductance for high-brightness LED applications for the universal input voltage (90-270 Vrms). The proposed circuit overcomes the limitations of the conventional single-stage PFC flyback with a constant boost inductance that cannot be designed to achieve a practical maximum bulk-capacitor voltage level (i.e., less than 450 V) at high line while meeting required line-current harmonic specifications at low line. According to the proposed method for achieving variable boost inductance, the boost inductance has a constant high value at high line, while at low line it is reduced proportionally to the load current, so that the IEC 61000-3-2 class C and corresponding Japanese JIS C 61000-3-2 class C line-current harmonic limits are satisfied. The proposed single-stage PFC flyback LED driver with the variable boost inductor is experimentally verified on a 24-V/91-W prototype circuit.

Single-Magnetic Cell-to-Cell Charge Equalization Converter With Reduced Number of Transformer Windings

Abstract: In this paper, a new cell-to-cell charge equalization converter using a multiwinding transformer is proposed. The proposed scheme achieves the direct cell-to-cell charge transportation by buck-boost and flyback operation. In this operation, the adjacent two cells share either a current path or a tap of multiwinding transformer. Therefore, the number of windings ia cut in half in comparison to the number of batteries, resulting in a small circuit size. To verify the operation of the proposed charge equalization converter, an experiment with a lithium-ion battery stack is performed.

A Three-port Flyback for PV Microinverter Applications With Power Pulsation Decoupling Capability

Abstract: A novel single-stage photovoltaic (PV) microinverter with power decoupling capability is proposed in this paper The proposed topology is based on three-port flyback with one port dedicated to power decoupling function so as to reduce the decoupling capacitance, thus allowing for long lifetime film capacitor to be used Operation principle is analyzed in details Key design considerations, including key parameter selections, predictive control strategy, and the dc voltage balance control across the power decoupling capacitor, are given in this paper A 100-W microinverter prototype is built to verify the proposed topology Experimental results show the proposed topology can achieve power decoupling, while maintaining good efficiency

Single-Switch High Step-Up Converters With Built-In Transformer Voltage Multiplier Cell

Abstract: In this paper, a built-in voltage gain extension cell is proposed to give a universal topology derivation on next-generation high step-up converters for large voltage gain conversion systems. Several improved single-switch high step-up converters with built-in transformer voltage multiplier cell are derived with some advantageous performance, which includes extremely large voltage conversion ratio, minimized power device voltage stress, effective diode reverse-recovery alleviation, and soft-switching operation. The turns ratio of the built-in transformer can be employed as another design freedom to extend the voltage gain, which shows great design flexibility. Compared with their active clamp counterpart, only one MOSFET is required to simplify the circuit configuration and improve the system reliability. The over resonance frequency and the below resonance frequency operation modes are studied to explore the circuit performance, and the key parameter design criterion is provided to show a valuable guidance for future industrial applications. Finally, the experimental results from a 500 W 36-380 V prototype are provided to validate the effectiveness of the main contributions in this paper.

A Novel Output Current Estimation and Regulation Circuit for Primary Side Controlled High Power Factor Single-Stage Flyback LED Driver

Abstract: A novel output current estimation and regulation circuit for the primary side controlled high power factor (PF) single-stage flyback LED is proposed in this paper. The proposed output current estimation and regulation circuit is composed of a novel output current estimation circuit and a negative feedback networks. The output current estimation circuit can estimate the output current in the primary side and then achieve output current regulation through negative feedback. The proposed output current estimation and regulation circuit is suitable for discontinuous conduction mode (DCM) and boundary conduction mode (BCM). The output of the proposed output current estimation and regulation circuit is a half-sine waveform and followed by the primary current, hence high PF can be achieved. Detailed theoretical analysis and design considerations were presented. Two 340 mA/25 V laboratory LED driver prototypes operating in DCM and BCM were built up. The experimental results verified theoretical analyses.

A Weighted-Efficiency-Oriented Design Methodology of Flyback Inverter for AC Photovoltaic Modules

Abstract: An innovative design methodology that optimizes the weighted efficiency of a single-phase, single-stage flyback inverter for ac-photovoltaic (PV) module applications is proposed. This novel approach combines the essential advantages of the flyback topology with high-efficiency design in the direction of a reliable, cost-effective, and high-performance PV system. The proposed methodology focuses exclusively on choosing the inverter design parameters, taking into consideration the PV module characteristics and the topology operation constraints. In order to meet this goal, an analytical losses calculation should be performed. Since the problem is complicated, special effort is given to manipulate the equations and variables in such a way to minimize the number of parameters. The proposed methodology is also verified experimentally.

Efficiency Optimization in Digitally Controlled Flyback DC–DC Converters Over Wide Ranges of Operating Conditions

Abstract: This paper presents an approach to efficiency optimization in digitally controlled flyback dc-dc converters over wide ranges of operating conditions. Efficiency is characterized and optimized based on power loss modeling and multivariable nonlinear constrained optimization over power-stage and controller parameters. A valley switching technique is adopted to reduce MOSFET turn-on switching loss in discontinuous conduction mode. An optimization procedure is formulated to minimize power loss weighted over a range of operating points, under a cost constraint. A lookup table-based digital controller is applied to achieve on-line efficiency optimization by programming switching frequencies and operating modes based on the efficiency optimization processes. The proposed on-line efficiency optimization approach is verified by experimental results on a low cost 65 W flyback dc-dc prototype.

A Primary-Side Control Scheme for High-Power-Factor LED Driver With TRIAC Dimming Capability

Abstract: This paper proposes a primary-side control scheme for low-power light-emitting diode (LED) driver with Flyback topology. With average primary-side current signal and transformer auxiliary winding voltage signal, the output current can be derived and regulated precisely by the proposed control scheme without any isolated feedback circuit. Furthermore, the proposed primary-side control scheme can be implemented with power factor correction control to achieve high input power factor, which is usually required for LED drivers. Since the triode for alternating current (TRIAC) dimming is very popular in practical application, it is preferred that the LED driver can also be compatible with TRIAC dimming. With the proposed control scheme, the input characteristic of the LED driver is resistive like an incandescent bulb. No extra dummy load is needed to provide the TRIAC holding current. Both the output current signal and TRIAC dimming signal can be obtained at the primary side, the TRIAC dimming function can be easily implemented and linear dimming characteristic can be achieved. Detailed operation principles and design considerations of the proposed control scheme are presented in the paper. The experimental results from a 15-W prototype verify the theoretical analysis.

Cascaded H-bridge multilevel converter for large-scale PV grid-integration with isolated DC-DC stage

Abstract: The integration of large-scale PV systems to the grid is a growing trend in modern power systems The cascaded H-bridge (CHB) converter is a suitable candidate for the grid interconnection due to its modular characteristics, high-quality output waveforms and capability of connecting to mediumvoltage grids However, the CHB converter requires isolated DC sources In order to avoid the leakage currents caused by the high potential differences across the parasitic capacitance of the PV panels to ground, an isolated DC-DC conversion stage is required when the CHB topology is used The objective of this paper is to compare two PV system configurations based on the CHB multilevel converter using two isolated DC-DC converter topologies, namely the boost-half-bridge (BHB) and the flyback, for their performance on providing isolation and achieving individual MPPT at the DC-DC power conversion stage of large-scale PV power systems Simulation results from a 263 kW PV system based on a seven-level CHB converter with the two aforementioned isolated DC-DC converters are provided for comparison and evaluation with different input PV voltages

High frequency bus converter with low loss integrated matrix transformer

Abstract: The trend in isolated DC/DC converters is increasing output power demands and higher operating frequencies. Improved topologies and semiconductors can allow for lower loss at higher frequencies. A major barrier to further improvement is the transformer design. With high current levels and high frequency effects the transformers can become the major loss component in the circuit. High values of transformer leakage inductance can also greatly degrade the performance of the converter. Matrix transformers offer the ability to reduce winding loss and leakage inductance. This paper will study the impact of increased switching frequencies on transformer size and explore the use of matrix transformers in high current high frequency isolated applications. This paper will also propose an improved integrated matrix transformer design that can decrease core loss and further improve the performance of matrix transformers.

Hybrid distribution transformer: Concept development and field demonstration

Abstract: Today's distribution system is expected to supply power to loads for which it was not designed. Moreover, high penetration of distributed generation units is redefining the requirements for the design, control and operation of the electric distribution system. A Hybrid Distribution Transformer is a potential cost-effective alternative solution to various distribution grid control devices. The Hybrid Distribution Transformer is realized by augmenting a regular transformer with a fractionally rated power electronic converter, which provides the transformer with additional control capabilities. The Hybrid Distribution Transformer concept can provide dynamic ac voltage regulation, reactive power compensation and, in future designs, form an interface with energy storage devices. Other potential functionalities that can be realized from the Hybrid Distribution Transformer include voltage phase angle control, harmonic compensation and voltage sag compensation. This paper presents the concept of a Hybrid Distribution Transformer and the status of our efforts towards a 500 kVA, 12.47 kV/480 V field demonstrator.

Output current estimation for an isolated flyback converter with variable switching frequency control and duty cycle adjustment for both PWM and PFM modes

Abstract: A fly-back power converter has a current-estimating control loop that senses the primary output current in a transformer to control the secondary output. A primary-side control circuit switches primary current through the transformer on and off. A discharge time when a secondary current through an auxiliary winding of the transformer is flowing is generated by sampling a voltage divider on an auxiliary loop for a knee-point. A normalized duty cycle is calculated by multiplying the discharge time by a current that is proportional to the switching frequency and comparing to a sawtooth signal having the switching frequency. The peak of a primary-side voltage is sensed from the primary current loop and converted to a current and multiplied by the normalized duty cycle to generate an estimated current. An error amp compares the estimated current to a reference to adjust the oscillator frequency and peak current to control primary switching.

Tapped-Inductor Buck HB-LED AC–DC Driver Operating in Boundary Conduction Mode for Replacing Incandescent Bulb Lamps

Abstract: High-brightness light-emitting diodes (HB-LEDs) are recognized as being potential successors of incandescent bulb lamps due to their high luminous efficiency and long lifespan. To achieve these advantages, HB-LED ballast must be durable and efficient. Furthermore, for this specific application, ac-dc HB-LED ballast requires a high-step-down ratio, high power factor and low cost. This paper presents a tapped-inductor buck power factor corrector (PFC) operating in boundary conduction mode design for replacing incandescent bulb lamps. This low-cost solution presents a suitable high-step-down ratio without galvanic isolation in order to produce an output voltage of about 20 V from line voltage. In addition, the tapped-inductor buck PFC maintains high efficiency in comparison to other one stage solutions widely used to design low-cost ac-dc HB-LED drivers (e.g., flyback PFCs). Static analysis, input current distortion analysis, and an average small signal model of the tapped-inductor buck PFC have been implemented in this paper both to check the validity of the proposed solution and to provide a suitable design procedure of the ac-dc HB-LED driver. Finally, a 12-W experimental prototype was developed to validate the theoretical results presented.

Single-Phase Transformer Inrush Current Reduction Using Prefluxing

Abstract: Power transformers can experience large inrush currents upon energization, the severity of which depends on the source strength, the leakage impedance and residual flux of the transformer, and the angle of the applied voltage at energization. A novel inrush current reduction strategy has been implemented which involves setting a single-phase transformer's residual flux to a known polarity after the transformer has been de-energized, a process called “prefluxing,” and controlling the instant of transformer energization based on the flux polarity, seeking not to eliminate inrush current but to substantially reduce it. Unlike a popular suggested solution, this strategy does not require prior knowledge of the transformer's flux. The device used for prefluxing is simple in construction and operates at substantially lower voltage levels when compared to the transformer's rated voltage. The presented strategy has been successfully implemented on an 18-kVA laboratory transformer with inrush current levels reduced below the rated current of the transformer even when accounting for typical breaker deviations. This paper describes the operation of the reduction strategy, including theory, device sizing, and implementation, and presents the successful laboratory results, all of which provide the basis for implementing inrush current reduction in three-phase transformers using a three-pole circuit breaker.

Power electronic transformer (PET) converter: Design of a 1.2MW demonstrator for traction applications

Abstract: A power electronic transformer converter made of cascaded multiple cells with a medium frequency link can replace the bulky traditional transformer in various applications with several advantages, including reduced size and weight, and energy savings. This paper describes the design of a 1.2MW power electronic transformer (PET) demonstrator for traction applications. Several design challenges, i.e. the selection of the IGBT modules, the design of the multiple-functional medium frequency transformer, and the mechanical arrangement to achieve the high voltage insulation between the grid voltage and ground potential, have been discussed. The experimental results, obtained from the developed PET demonstrator, are presented.

Low cost transformer isolated boost half-bridge micro-inverter for single-phase grid-connected photovoltaic system

Abstract: This paper presents a low cost high efficiency transformer isolated micro-inverter for single-phase grid-connected photovoltaic (PV) system. The proposed micro-inverter is composed of two stages, an isolated dc-dc converter stage and an inverter stage with a dc link. A high frequency transformer isolated high voltage gain boost half-bridge dc-dc converter is used at the first stage to achieve maximum power point tracking (MPPT) and to step up the PV voltage to the high voltage dc-link. A pulse width modulated (PWM) full-bridge inverter with LCL filter is used at the second stage to output the synchronized sinusoid current with unity power factor to the grid. By utilizing the transformer leakage inductance, two primary side switches can achieve zero voltage switching (ZVS). A 210 W prototype of the proposed micro-inverter has been built and tested. The efficiency of the proposed boost half-bridge dc-dc converter has been measured according to the PV curve, which is up to 98.2%. Experimental results are provided to demonstrate the validity and features of the proposed circuit.

Off-the-line primary-side regulation LED lamp driver with single-stage PFC and TRIAC dimming using LED forward-voltage and duty-variation tracking control

Abstract: Non-isolation LED drivers [1] are more attractive than isolated drivers in terms of efficiency and lower fabrication cost. However, some areas such as bar-typed fluorescent lamp retrofit applications still require a solution with isolation. Even for replacement of the incandescent and compact fluorescent lamps, some LED lamp makers prefer isolated driver solutions due to safety issues. One of the popular solutions is the flyback converter which is widely used in low-to-moderate power applications [2]. However, generally, it requires secondary voltage or current-sense circuit, and opto-coupler isolator to form a feedback loop. Thus, primary-side regulation (PSR) flyback converters have been steadily used in LED applications since they do not need secondary circuits and isolator [3]. This paper introduces a PSR method for LED lamp which satisfies low price, good efficiency, high power factor (PF) and triode AC switch (TRIAC) dimming control.

A Start-Up Scheme for a Three-Stage Solid-State Transformer With Minimized Transformer Current Response

Abstract: This letter is focused on developing a start-up scheme for a three-stage solid-state transformer that includes a high-frequency transformer. The proposed scheme is aiming at minimizing the high-frequency transformer current during the start-up transient. As a result, the input-inrush current is also eliminated. The scheme is implemented with no extra cost by synchronizing the start-up of rectifier stage and dc-dc converter stage. The scheme is compared with other start-up methods. The theoretical analysis and experimental results are provided to verify the proposed start-up scheme.

Soft-Switching Boost Converter With a Flyback Snubber for High Power Applications

Abstract: This paper presents a soft-switching boost converter with a flyback snubber for high power applications. The proposed converter configuration can achieve both near zero-voltage and zero-current soft-switching features, while it can reduce the current and voltage stresses of the main switch. In this paper, several passive and active snubbers associated with boost converters are first reviewed, and their limitations are then addressed. One of the boost converters with a flyback snubber is proposed and analyzed in detail to explain the discussed features. Experimental results obtained from a 5-kW boost converter have confirmed that the proposed converter configuration is attractive and feasible for high power applications.

Three-Level Forward–Flyback Phase-Shift ZVS Converter With Integrated Series-Connected Coupled Inductors

Abstract: In this paper, a novel three-level Forward-Flyback phase-shift converter is proposed for high-input voltage and high-efficiency applications. The primary-side structure of this converter is similar to that of the conventional three-level phase-shift converters, which makes the switch voltage stress only half of the input voltage and the voltage on the capacitor divider autobalanced. There are only two coupled inductors in this converter and each coupled inductors has two windings. The primary windings of the two coupled inductors are in series to achieve buck-type conversion. And their secondary windings operate in the interleaved mode to sustain the large current. The coupled inductors operate in Flyback and Forward modes to enhance the magnetic core utility rate. Furthermore, the two coupled inductors can be integrated into a magnetic core to further improve the power density. In addition, zero-voltage-switching performance of the inner switches at light load condition can be provided because the magnetizing current can be employed to charge and discharge the parallel capacitors. As a result, the switching losses are minimized at a wide load range. A 500 V prototype is tested to verify the advantages of the proposed converter.

A Novel Integrated DC/AC Converter With High Voltage Gain Capability for Distributed Energy Resource Systems

Abstract: In this paper, a novel high voltage gain single-stage dc/ac converter is proposed for distributed energy resources. A flyback-type auxiliary circuit is integrated with an isolated Cuk-derived voltage source inverter to achieve a much higher voltage gain. It is seen that through this integration, the capacitors of the flyback and the Cuk circuits are paralleled for charging and in series for discharging automatically. Due to the capacitive voltage dividing, the dc-side switch voltage stress can be reduced and the losses can be reduced as well. Besides, the low influence of coupling coefficient of flyback-type auxiliary circuit on the inverter characteristic renders the proposed inverter design rather flexible and easy. Steady-state characteristics, performance analysis, simulation and experimental results are given to show the merits of the proposed integrated inverter. Finally, based on the same integration concept, a family of different topologies is also presented for reference.

Digitally controlled active clamp interleaved flyback converters for improving efficiency in photovoltaic grid-connected micro-inverter

Abstract: Flyback converters show the characteristics of current source when operating in discontinuous conduction mode (DCM) and boundary conduction mode (BCM), which makes it widely used in photovoltaic grid-connected micro-inverter. In this paper, an active clamp interleaved flyback converter operating with combination of DCM and BCM is proposed in micro-inverter to achieve zero voltage switching (ZVS) for both of primary switches and fully recycle the energy in the leakage inductance. The proposed control method makes active-clamping part include only one clamp capacitor. In DCM area, only one flyback converter operates and turn-off of its auxiliary switch is suggested here to reduce resonant conduction losses, which improve the efficiency at light loads. Performance of the proposed circuit is validated by the simulation results and experimental results.

Effects of current and voltage harmonics on distribution transformer losses

Abstract: The drive to improve energy efficiency and reduce electrical loading has resulted in energy efficient lighting such as compact fluorescent lamps (CFLs) replacing conventional incandescent lamps However, the presence of such non-linear loads has brought about the injection of voltage and current harmonics into electrical networks As transformers are the interface between the supply and the non-linear loads, the investigation of their effects on transformer losses is of great importance These harmonics can cause excessive loss and abnormal temperature rise in the transformers, thus reducing their operational life span This paper investigates the impact of current and voltage harmonics of the loads on a single-phase 25kVA distribution transformer Harmonic spectra of a range of non-linear loads including CFL, LED tube, PC and fluorescent lamp are obtained A single-phase inverter is used for harmonic generation to simulate power supply harmonics injected into the transformer Open circuit and short circuit tests are conducted on the transformer under the effect of harmonics, and the impacts on core loss are analyzed

Saturation Compensation Strategy for Grid Connected Converters Based on Line Frequency Transformers

Abstract: This paper deals with the compensation of magnetic saturation in line frequency transformer coupled, grid-connected power converters. The developed strategy originates from the choice of controlling the actual current injected in the grid (output of the line frequency transformer) instead of the input current of the transformer, as usually proposed. As a matter of fact, better power quality cannot neglect the direct control of the injected grid current. An effective solution providing zero steady-state error at grid frequency and superior disturbance rejection involves the use of a d- q current controller synchronous with the grid voltage. For this reason, the proposed saturation compensation strategy has been implemented inside the d -q reference frame. The downside is that closing the current feedback at the transformer output renders impossible to control the dc current at transformer input, leading to core saturation. A core saturation compensation strategy, based only on the monitoring of the output current distortion around voltage zero crossings, is here presented. Moreover, since the proposed solution does not rely on dc measures, offset problems are avoided. Experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation.

High-voltage modular power supply using parallel and series configurations of flyback converter for pulsed power applications

Abstract: To cover wide range of pulsed power applications, this paper proposes a modularity concept to improve the performance and flexibility of the pulsed power supply. The proposed scheme utilizes the advantage of parallel and series configurations of flyback modules in obtaining high-voltage levels with fast rise time (dv/dt). Prototypes were implemented using 600-V insulated-gate bipolar transistor (IGBT) switches to generate up to 4-kV output pulses with 1-kHz repetition rate for experimentation. To assess the proposed modular approach for higher number of the modules, prototypes were implemented using 1700-V IGBTs switches, based on ten-series modules, and tested up to 20 kV. Conducted experimental results verified the effectiveness of the proposed method

High-Voltage Modular Power Supply Using Parallel and Series Configurations of Flyback Converter for Pulsed Power Applications

Abstract: To cover wide range of pulsed power applications, this paper proposes a modularity concept to improve the performance and flexibility of the pulsed power supply. The proposed scheme utilizes the advantage of parallel and series configurations of flyback modules in obtaining high-voltage levels with fast rise time (dv/dt). Prototypes were implemented using 600-V insulated-gate bipolar transistor (IGBT) switches to generate up to 4-kV output pulses with 1-kHz repetition rate for experimentation. To assess the proposed modular approach for higher number of the modules, prototypes were implemented using 1700-V IGBTs switches, based on ten-series modules, and tested up to 20 kV. Conducted experimental results verified the effectiveness of the proposed method.

Triac dimming systems for solid-state loads

Abstract: A triac dimming system for solid-state loads, LEDs, is based on a flyback DC/DC converter and includes a transformer. The transformer includes a first coil and a second coil. The first coil is configured to receive a first voltage based on an output of a PWM switching circuit. The second coil is configured to generate a first current based on the first voltage to power the solid-state load. The system also includes a third coil. The third coil is configured to generate a second supply voltage based on the first voltage. A bleeder module includes a PWM controlled switch and is connected to the secondary load side of the transformer.

Inductorless forward-flyback soft-switching converter with dual constant on-time modulation for photovoltaic applications

Abstract: A family of inductorless forward-flyback converters utilizing dual constant on-time modulation is proposed, in order to maintain high efficiency over a wide load and input range. The main switch is turned on for the constant half resonant period to achieve zero-current-switching for the forward diode and to minimize the deadtime between the two output diodes. The auxiliary active switch is in the on-state with a very short constant interval to realize zero-voltage-switching for the main active switch, even if the magnetizing inductor operates in the continuous current mode. Experimental results for a 250 W hardware prototype verifies soft-switching operation from zero to full load over 25 to 45 V input range and the CEC weighted efficiency reaches 97%. The proposed converter is attractive for the tree-type PV system applications.