Showing papers on "Flyback transformer published in 2011"

Improved Performance of Serially Connected Li-Ion Batteries With Active Cell Balancing in Electric Vehicles

Abstract: This paper presents an active cell balancing method for lithium-ion battery stacks using a flyback dc/dc converter topology. The method is described in detail, and a simulation is performed to estimate the energy gain for ten serially connected cells during one discharging cycle. The simulation is validated with measurements on a balancing prototype with ten cells. It is then shown how the active balancing method with respect to the cell voltages can be improved using the capacity and the state of charge rather than the voltage as the balancing criterion. For both charging and discharging, an improvement in performance is gained when having the state of charge and the capacity of the cells as information. A battery stack with three single cells is modeled, and a realistic driving cycle is applied to compare the difference between both methods in terms of usable energy. Simulations are also validated with measurements.

High Step-Up Ratio Flyback Converter With Active Clamp and Voltage Multiplier

Abstract: In this paper, an isolated high step-up ratio dc-dc converter aimed to be used in interface systems between low-voltage renewable energy sources, such as photovoltaic panels and fuel cells and the utility grid, is presented. The converter is based on the active clamp flyback topology with a voltage multiplier at the transformer secondary side. Such configuration, while naturally clamping the rectifier diode voltages thus avoiding the use of dissipative snubber circuits, allows the reduction of the circulating current during the active clamp operation due to the resonance involving the transformer leakage inductances and the diode parasitic capacitances. Experimental results taken from a 300-W-rated prototype are reported, showing the absence of parasitic oscillations after diodes and switch transitions and high efficiency, in agreement with the theoretical expectations.

Optimum Injected Current Harmonics to Minimize Peak-to-Average Ratio of LED Current for Electrolytic Capacitor-Less AC–DC Drivers

Abstract: The lifetime of an ac-dc LED driver can be increased by eliminating the electrolytic capacitor. Unfortunately, it results in pulsation with twice the line frequency in the driving current. Injection of the third and fifth harmonics into the input current can reduce the peak-to-average ratio of the driving current, which is beneficial for reliable operation of the LEDs. This letter discusses the relationship between the peak-to-average ratio and the injected harmonics, and the optimum injected third and fifth harmonics to minimize the peak-to-average ratio are obtained, while ensuring that the input power factor is higher than 0.9 to meet the regulatory requirement such as the ENERGY STAR. This optimum injected current harmonics is verified by a flyback-based electrolytic capacitor-less LED driver with 25 V, 0.35 A output.

Establishment of a Switched-Reluctance Generator-Based Common DC Microgrid System

Abstract: This paper presents a dc microgrid including a switched-reluctance generator (SRG) with isolated boost dc-dc converter, a battery energy storage system, and a single-phase three-wire (1P3W) load inverter for generating ac 220/110 V 60-Hz outputs. The 400-V dc grid is established by the SRG with dc 48-V output followed by a current-fed push-pull (CFPP) dc-dc converter. The robust commutation and dynamic control schemes are developed for the SRG to have excellent output performances. For providing the domestic load power sources, a 1P3W transformerless 220/110 V inverter is established. A master and slave robust control schemes are proposed to yield balanced sinusoidal output voltage waveforms in both voltage outputs under varying load conditions. To improve the dc grid power supporting reliability, a battery energy storage system with bidirectional buck-boost interfacing converter is established. It can support the common dc bus voltage immediately when the main power source fault occurs. Conversely, the battery bank can be charged from the common dc bus through the same converter. Particularly, an auxiliary charger formed by a flyback switch-mode rectifier is equipped to allow the battery to be charged from the plug-in utility power as the long duration of microgrid fault occurs. Normal operation and good operating performance of the established microgrid are verified experimentally.

A Three-Phase Unity Power Factor Single-Stage AC-DC Converter Based on an Interleaved

Abstract: This paper presents the design and implementation of a three-phase unity-power-factor single-stage ac-dc converter based on an interleaved flyback topology. The primary market target of the converter is within the telecommunications industry where it supplies high-quality dc power to the telecom loads and performs high-capacity battery charging while providing zero har- monic emission and unity power factor to the utility grid. The main design objective is to produce the lowest cost within a small-size system. The study includes mathematical analysis and simulation steps where the optimum number of cells to be interleaved and the associated phase shifts among the cells are determined while the emphasis being on the design of a perfectly coupled flyback trans- former. Design of a transformer with the lowest leakage inductance and selection of components providing the lowest parasitic effects are critical for obtaining high efficiency and good performance. After the design is verified through simulation studies that uses Simulink and piecewise linear electrical circuit simulation model (PLECS) of the converter, a full-scale prototype is implemented to evaluate the performance of the design. In conclusion, experi- mental results demonstrate that converter works successfully and meets the commercialization expectations.

A Three-Phase Unity Power Factor Single-Stage AC–DC Converter Based on an Interleaved Flyback Topology

Abstract: This paper presents the design and implementation of a three-phase unity-power-factor single-stage ac-dc converter based on an interleaved flyback topology. The primary market target of the converter is within the telecommunications industry where it supplies high-quality dc power to the telecom loads and performs high-capacity battery charging while providing zero harmonic emission and unity power factor to the utility grid. The main design objective is to produce the lowest cost within a small-size system. The study includes mathematical analysis and simulation steps where the optimum number of cells to be interleaved and the associated phase shifts among the cells are determined while the emphasis being on the design of a perfectly coupled flyback transformer. Design of a transformer with the lowest leakage inductance and selection of components providing the lowest parasitic effects are critical for obtaining high efficiency and good performance. After the design is verified through simulation studies that uses Simulink and piecewise linear electrical circuit simulation model (PLECS) of the converter, a full-scale prototype is implemented to evaluate the performance of the design. In conclusion, experimental results demonstrate that converter works successfully and meets the commercialization expectations.

An Interleaved Flyback Converter Featured With Zero-Voltage Transition

Abstract: This paper proposes an interleaved flyback converter, which is remarked with zero-voltage-switched active switches and reduced reverse-recovery loss on the rectifying diodes. The converter is composed of two parallel-operated identical flyback converters and an auxiliary inductor shunted between the diodes. This converter can provide up to 500 W power with highest efficiency as high as 91%. In addition, burst-mode control is equipped to drive the converter at low load. Even at 50-W output, the efficiency is higher than 83%.

A New Standby Structure Using Multi-Output Full-Bridge Converter Integrating Flyback Converter

Abstract: This paper presents a new standby structure where the standby flyback converter is integrated with the zero-voltage-switching multi-output full-bridge dc-dc converter. While the standby power is generated from the conventional flyback converter in standby mode, the auxiliary output of the multi-output full-bridge converter is used for the standby output in normal mode. The validity of this proposed structure is confirmed by the experimental results from 12 V/58 A for the dc-dc output and 5 V/3.2 A for the standby output prototype.

Isolated Single Primary Winding Multiple-Input Converters

Abstract: Multiple-input converters (MICs) have attracted more attentions because of its simpler structure and less devices. In the traditional isolated MICs, each input source always has a primary winding, sharing a secondary winding. When the number of the input sources increases, the number of the primary windings increases, resulting in complicated structure of the transformer, poor coupling, and large leakage inductors. This paper first introduces the concept of pulsating source cells (PSCs), including pulsating voltage source cells and pulsating current source cells, and the connection rules for the PSCs. Then, series- or parallel-connected PSCs are used to replace the input dc voltage source or input dc current source in the isolated single-input converter, and a family of isolated single primary winding (SPW) MICs is proposed. Compared to the traditional isolated MICs, the transformer has only one primary winding, leading to a simplified structure and ease for manufacturing. Furthermore, the voltage stress of the power switches is reduced. The control method of the proposed isolated SPW MICs is proposed. Finally, a flyback SPW double-input converter is analyzed as an example. The operation principle and control method are discussed and a prototype is built to demonstrate the feasibility of this topology.

LED illumination systems

Abstract: An illumination system includes a power supply having a boost converter operating in the discontinuous conduction mode, a flyback converter operating in the critical conduction mode, and a switch coupled to the flyback converter. Several light emitting diodes receive power from the power supply. The boost converter may include a boost inductor (L B ) and a boost diode (D B ), constructed to perform the boost power factor correction (PFC) function. The flyback converter may includes a flyback inductor (L FB ) and a flyback diode (D FB ) and the power supply may be constructed to turn on the switch around the point where the current flowing in the flyback inductor reaches zero value.

Interleaved active clamp flyback inverter using a synchronous rectifier for a photovoltaic AC module system

Abstract: An interleaved active clamp flyback inverter using a synchronous rectifier for a photovoltaic AC module system is proposed. In a conventional single flyback inverter for the photovoltaic AC module system, this inverter has drawbacks of a conduction losses of each switch, transformer copper and high ripple current of capacitor. To overcome these problems, two flyback converter modules with interleaved pulse-width modulation (PWM) are connected in parallel at the input and output sides reducing the ripple current on the input and output capacitors and decrease the current stress on the transformer windings. Thus, the transformer copper losses and the conduction losses on the switches are reduced. Also, reliability and life of capacitor are increased due to reducing the ripple current of input and output capacitors. In order to verify these, theoretical analysis and simulation are performed.

EMI Analysis and Evaluation of an Improved ZCT Flyback Converter

Abstract: Switching power supplies are sources of noise for sensitive circuits. Converters should comply with electromagnetic compatibility (EMC) rules so that the electromagnetic interference (EMI) caused by switching cannot interfere with the normal operation of adjacent circuits and also the converter itself. The produced interference can be in the form of conduction or radiation. In this paper, some techniques are used in switching converters to suppress EMI with emphasis on the conduction form. EMI analysis and evaluation of a conventional flyback converter and a proposed zero-current transition (ZCT) flyback converter is achieved by simulation and experimental results. In addition to evaluating some EMI suppression techniques, the main objective of this paper is to improve EMI in the topology design stage. The operating modes of the improved ZCT flyback are discussed. In addition to the efficiency improvement, the amount of EMI reduction of this ZCT flyback and the effectiveness of some EMI reduction techniques are shown by practical implementation.

Transformer winding loss caused by skin and proximity effects including harmonics in pulse-width modulated DC¿DC flyback converters for the continuous conduction mode

Abstract: High-frequency (HF) transformers used in pulse-width-modulated power converters conduct periodic non-sinusoidal HF currents, which give rise to additional winding losses caused by harmonics. This study presents expressions for winding power losses in a two-winding transformer with periodic non-sinusoidal primary and secondary current waveforms for flyback converters operating in the continuous conduction mode (CCM). Dowell's equation, which takes into account both the skin and proximity effects, is used to determine the primary and secondary winding resistances as functions of frequency. Fourier series of the primary and secondary current waveforms and the winding resistances are used to determine the winding power losses at harmonic frequencies. The harmonic primary and secondary winding loss factors FRph and FRsh are introduced for CCM operation. The theory is illustrated by performance evaluation of the transformer in a flyback converter in CCM over the entire range of converter operation. Power losses in the primary and secondary transformer windings are illustrated as functions of the output power and the DC input voltage.

Zero-voltage transition interleaved high step-up converter with built-in transformer

Abstract: A non-isolated zero-voltage transition interleaved high step-up converter with built-in transformer is proposed for high step-up and large current applications The proposed converter consists of an interleaved structure, a built-in transformer and two sets of active clamp circuits The built-in transformer can provide high voltage conversion ratio and increase the system efficiency without an extreme duty cycle compared with the conventional boost converter The leakage inductance of the built-in transformer removes the output diode reverse-recovery problem, which results in low reverse-recovery losses The active clamp scheme can suppress the surge voltage of the power MOSFETs and recycle the leakage energy, which is helpful to improve the circuit efficiency and reliability Furthermore, zero-voltage switching soft switching performance is achieved for both the main and the clamp switches during the whole switching transition, which reduces the switching losses The operation principle of the converter is analysed and verified At last, some experimental results of a 1 kW prototype with 48 V input and 380 V output are given to demonstrate the effectiveness of the proposed converter

Effect of Repeated Impulses on Transformer Insulation

Abstract: Power transformer plays a vital role in electrical power system. Many of the transformer failures reported are due to insulation failure in windings. The sources of failures are mainly due to impulse overvoltages of different waveshapes and also due to repeated application of impulses. In this paper an attempt has been made to analyze the degradation of transformer insulation for repeated applications of different impulse voltages. As oil impregnated paper (OIP) constitute major insulation of transformer winding, detailed experimental analyses are carried out for OIP insulations using standard test cell for impulse waves of varying front times from 0.064 μs to 1.4 μs and tail times from 6.0 μs to 67 μs. Exponential mathematical models for the voltage-number (V-N) characteristics are derived and used for predicting the number of impulses that OIP can withstand for any wavefront and wavetail. The accuracy of the models are checked with the experimental values.

Zero voltage switching in flyback converters with variable input voltages

Abstract: The disclosed embodiments provide a system that operates a flyback converter. During operation, the system senses an input voltage for the flyback converter. Next, the system uses the input voltage to determine a negative peak current that enables zero voltage switching for a primary switch in the flyback converter. Finally, the system uses the negative peak current to perform the zero voltage switching for the primary switch based on the input voltage, wherein the negative peak current reduces a power loss of the flyback converter.

High step-up continuous input current LCCT-Z-source inverters for fuel cells

Abstract: Z-source inverters (ZSIs) are suited for applications which require a large range of voltage gain, such as in fuel cells. The present paper extends the concept of ZSIs. New type high step-up LCCT-Z-source inverter dedicated for fuel cells is proposed in the paper. Compared to recently proposed modifications of basic Z-source inverter the new topology has the advantages of available continuous input current, improved boost ratio and simple topology. Thanks to application of transformer with turns ratio higher than one the proposed LCCT-Z-source can operate with lower shoot-through ratio and higher modulation index compared to ZSI. The existence of two built-in DC-current-blocking capacitors connected in series with transformer windings prevents the transformer core from saturation. Simulation and experimental results are provided to verify the reliability of the proposed topology.

Continuous uninterruptable AC grounding system for power system protection

Abstract: A continuous grounding system for use in an alternating current system including a transformer is disclosed. The system includes a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting the path through the switch assembly between the electrical connection and the transformer neutral, and the closed position establishing a path connecting the electrical connection to the transformer neutral through the switch assembly, wherein in normal operation of the alternating current electrical device the switch assembly remains in a closed position. The system also includes a DC blocking component positioned in parallel with the switch assembly and connected between the transformer neutral and the ground. The system further includes a control circuit configured to control the switch assembly, the control circuit including a sensor configured to actuate the switch assembly to an open position upon detection of a predetermined harmonic signal threshold at one of the transformer phases or a predetermined threshold of DC current between the transformer neutral and ground.

Two-switch flyback PWM DC–DC converter in discontinuous-conduction mode

Abstract: The two-switch flyback DC–DC converter is an extended version of the conventional single-switch flyback converter An additional switch and two clamping diodes serve as a simple, but an effective way to limit the switch overvoltages, which occur in the conventional single-switch flyback converter due to the ringing of the resonant circuit formed by the transformer leakage inductance and the transistor output capacitance The clamping diodes in the two-switch flyback topology clamp the maximum voltage across each switch equal to the DC input voltage This paper presents a detailed analysis and design procedure of the diode-clamped two-switch flyback converter operated in discontinuous-conduction mode (DCM) A comparison of power losses of the two-switch and the single-switch flyback converters is given The two-switch flyback converter was bread-boarded to validate the theoretical analysis Experimental results from a 20-V/30-W, 100-kHz laboratory prototype verified that the maximum switch voltage is limited to the DC input voltage Copyright © 2010 John Wiley & Sons, Ltd

Research on output current of interleaved-flyback in boundary conduction mode for photovoltaic AC module application

Abstract: Compared to DCM, BCM is a more flexible solution in the interleaved-flyback with grid-tied inverter for PV AC module application, due to its higher power level and larger switching frequency bandwidth. But the variable switching frequency of BCM causes it difficult to get exact relationship between ACM output current i out and reference signal i ref of interleaved-flyback, which has a great influence on THD of output current. This paper analyzes the functional relation between i out and i ref by theoretical derivation, and proposes a design approach of reference signal to decrease THD of output current. The realization of MPPT is also investigated. Finally, simulation and experiment results are presented, validating the proposed functional relation and design approach.

Zero-current-transition two-switch flyback pulse-width modulated DC-DC converter

Abstract: This study presents a zero-current-transition (ZCT) two-switch flyback pulse-width modulated (PWM) DC–DC converter with a simple auxiliary circuit. The auxiliary circuit consists of an active switch and a clamp capacitor. The clamping diodes on the primary side of the two-switch flyback topology clamp the peak voltage across each main switch to the DC input voltage VI. This feature of the two-switch flyback converter is combined with the ZCT feature provided by a simple auxiliary circuit connected on the secondary side of the transformer, which results in a soft-switching two-switch flyback converter. Circuit description, principle of operation, steady-state analysis and design procedure of the ZCT two-switch flyback converter are presented. Simulation and experimental results from a laboratory prototype are given to validate the theoretical analysis.

Automatic battery capacity equalization circuit and implementing method thereof

Abstract: The invention relates to the technical field of management of a battery pack and provides an automatic battery capacity equalization circuit and an implementing method thereof. In the series battery pack, a flyback bidirectional DC-DC (Direct Current to Direct Current) converter is used as a main equalization circuit to carry out transfer of electric energy; the connection between batteries whichneed to be equalized and the flyback bidirectional DC-DC converter is realized by using a relay; and a microprocessor is used to carry out detection of the battery state, equalization control and thelike. When the automatic battery capacity equalization circuit is applied, the capacity of each battery is detected circularly by an MCU (Microprogrammed Control Unit); two batteries which respectively have the highest capacity and the lowest capacity are respectively connected at both ends of the flyback bidirectional DC-DC converter; and the high-capacity battery is used as an input to carry out equalizing charge in a constant current mode or a constant voltage mode on the low-capacity battery until the capacity of the low-capacity battery reaches the capacity average value of the battery pack. Compared with a conventional battery equalization circuit, the automatic battery capacity equalization circuit has the advantages that simple equalizing process, strong controllability, high speed, high efficiency and the like.

A single switch boost-flyback DC-DC converter integrated with switched-capacitor cell

Abstract: Without extreme duty ratio or complexity of circuits, by employing coupled-inductor and switched-capacitor cell achieved high voltage conversion ratio with a single switch is proposed in this paper. Coupled-inductor transfer source energy to secondary side through entire switching period, the leakage energy of coupled inductor is efficiently recycled; the inrush current problem on switched capacitors was restrained by leakage inductor of coupled-inductor; all the above features account to the high efficiency performance. The operating principles and steady-state analyses of continuous-conduction mode and boundary-conduction mode are discussed in detail. To verify the performance of the proposed converter, a 200 W/400 V prototype sample is implemented, the maximum efficiency is up to 96.3%; and full load efficiency is 92.4%.

Driving circuit and driving method applied to flyback-type converter and quasi-resonant soft-switching flyback-type converter applying same

Abstract: The invention provides a driving circuit and a driving method applied to a flyback-type converter and a quasi-resonant soft-switching flyback-type converter applying the same. According to a driving circuit applied to the flyback-type converter, differential coefficient of the drain-source voltage of a main power switch tube in the flyback-type converter is worked out by a differential circuit, thus leading the time when the drain-source voltage achieves valley floor to correspond to the time when the differential voltage passes the zero point in positive direction. A valley floor voltage detecting circuit is connected with the differential circuit and receives a differential voltage signal; when the drain-source voltage of the main power switch tube achieves the valley floor, a valley floor control signal is output, thus controlling the driving circuit to drive the main power switch tube, and further exactly realizing the aim of conducting the valley floor of the main power switch tube. By adopting the driving circuit, the aim of controlling a quasi-resonant soft switch of the main power switch tube is realized precisely, the driving circuit of the flyback-type converter is optimized so that the controlling effect and the reliability are greatly improved, and the realizing cost is reduced.

Hybrid-switching Step-down Converter with a Hybrid Transformer

Abstract: The present invention employs a resonant inductor, a resonant capacitor and a hybrid transformer using a Hybrid-switching method with three switches which results in two distinct switched-networks: one for ON-time interval and another for OFF-time interval. Resonant inductor is placed in series with the hybrid transformer primary to insure the continuity of primary and secondary currents at the switching transitions and thus eliminating completely the potential switching losses at the switching transitions. In the best use of the invention the resonant inductor is replaced by use of the inherent leakage inductance of the transformer and for the first time eliminate the switching losses always associated with the transformer leakage inductance of all other switching converters. The output voltage is controlled by the standard Pulse Width Modulated (PWM) duty ratio control.

Power quality improvement based on novel power electronic transformer

Abstract: This paper presents a novel topology of power electronic transformer. In the design process, the AC/DC, DC/AC, AC/AC converters and high frequency transformer have been used. One matrix converter operates as AC/AC converter in power electronic transformer. The proposed power electronic transformer performs typical functions and has advantages such as power factor correction, voltage sag and swell elimination, voltage flicker reduction and protection capability in fault situations. Power quality improvement with proposed power electronic transformer has been verified by the simulation results.

An Adaptive High-Precision Overpower Protection Scheme for Primary-Side Controlled Flyback Converters

Abstract: A primary-side controlled universal-line flyback converter is widely used for its low-cost and low standby power advantages; however, conventional overpower protection schemes that feature primary-side control often experience inaccurate protection. In this paper, a novel scheme is presented, which achieves a very significant improvement in overpower accuracy while simultaneously meets a critical goal of adding no extra pin compared to conventional schemes when implemented in an IC. Experimental and simulation results verified the proposed strategy, and the scheme was implemented successfully in an IC.

An Adaptive Blanking Time Control Scheme for an Audible Noise-Free Quasi-Resonant Flyback Converter

Abstract: The quasi-resonant (QR) control scheme is widely adopted in a Flyback converter to maximize its efficiency by reducing the switching loss. The switching frequency increases with decreasing load or increasing input voltage. In order to limit electromagnetic interference noise and improve light load efficiency, the maximum switching frequency should be limited. However, the maximum switching frequency limitation adopted in QR control will cause audible noise due to the frequency hopping phenomena at certain load and input condition, which is related to the intrinsic output characteristic of the control scheme. This paper presents a simple solution to eliminate the frequency hopping in the QR Flyback using an adaptive blanking time circuit. The proposed method changes the blanking time automatically to keep the output characteristic smooth that eliminates the audible noise in the transformer. The detailed operation principle and design considerations are presented. The experimental results from a 16 V/4 A prototype are provided to validate the effectiveness of the proposed solution.

Constant current LED driver based on flyback structure with primary side control

Abstract: The design of a 3W constant current LED driver based on flyback structure with primary side control technology is proposed, which eliminates the opto-isolated feedback and secondary regulation circuits which are required in conventional designs. The principle of constant current and constant voltage of the circuit is analyzed, and parameters of the circuit are introduced. The constant current accuracy of the circuit under 60V–260V AC input voltage is 6.4%. The experimental results show that the circuit has the advantages of simple structure, high constant current precision and high stability.

A primary side controlled WLED driver compatible with Triac dimmer

Abstract: This paper proposes a single-stage Flyback PFC Converter with new primary side control scheme for Triac compatible LED drivers. The proposed control scheme can achieve high power factor and efficiency by eliminating the conventional dummy load required for Triac dimmer. Also, almost linear dimming can be achieved by the phase angle feed forward and primary side constant power control. No secondary side current feedback is required, which dramatically simplify the whole circuit and increases the reliability. The detailed operation principles are presented and the experimental results for a WLED driver verified the theoretical analysis.