Showing papers on "Flyback transformer published in 2008"

Optimum Design of the Current-Source Flyback Inverter for Decentralized Grid-Connected Photovoltaic Systems

Abstract: Two alternative modes of operation for the current-source flyback inverter are investigated in this paper. The discontinuous conduction mode (DCM), where a constant switching frequency (CSF) control method is applied, and the boundary between continuous and DCM (BCM) that is introduced for photovoltaic (PV) applications in this paper (where a variable switching frequency control method is applied). These two control methods are analytically studied and compared in order to establish their advantages as well as their suitability for the development of an inverter for decentralized grid-connected PV applications. An optimum design methodology is developed, aiming for an inverter with the smallest possible volume for the maximum power transfer to the public grid and wide PV energy exploitation. The main advantages of the current-source flyback inverter are very high-power density and high efficiency due to its simple structure, as well as high-power factor regulation. The design and control methodology are validated by personal computer simulation program with integrated circuit emphasis (PSPICE) simulation and experimental results, accomplished on a laboratory prototype.

Integrated Buck-Flyback Converter as a High-Power-Factor Off-Line Power Supply

Abstract: This paper investigates the integrated buck-flyback converter (IBFC) as a good solution for implementing low-cost high-power-factor ac-dc converters with fast output regulation. It will be shown that, when both buck and flyback semistages are operated in discontinuous conduction mode, the voltage across the bulk capacitor, which is used to store energy at low frequency, is independent of the output power. This makes it possible to maintain the bulk capacitor voltage at a low value within the whole line voltage range. The off-line operating modes of the IBFC are also investigated to demonstrate that the control switch of the proposed converter handles lower root-mean-square currents than those in similar integrated converters. The off-line operation of the IBFC is analyzed to obtain the design characteristics of the bulk capacitor voltage. Finally, the design and experimental results of a universal input 48 V-output 100 W ac-dc converter operating at 100 kHz is presented. Experiments show that the IEC-61000-3-2 input current harmonic limits are well satisfied and efficiency can be as high as 82%.

A Novel ZCS-PWM Flyback Converter With a Simple ZCS-PWM Commutation Cell

Abstract: This paper proposes a novel zero-current-switching pulsewidth-modulation (ZCS-PWM) flyback dc/dc converter using a simple ZCS-PWM commutation cell. The main switch and auxiliary switch operate at ZCS turn-on and turn-off conditions, and all uncontrolled devices in the proposed converter operate at zero-voltage-switching (ZVS) turn-on and turn-off. In addition, given constant frequency and decreasing commutation losses, the proposed converter has no additional current stress and conduction loss in the main switch compared to the conventional hard switching flyback converter. The averaging approach is used to estimate and examine the steady-state of the proposed converter. The principle of operation, theoretical analysis, and experimental results of the new ZCS-PWM flyback converter, rated 150 W and operating at 80 kHz, are provided in this paper to verify the performance of the proposed converter.

An On-Line UPS System With Power Factor Correction and Electric Isolation Using BIFRED Converter

Abstract: This paper presents the design consideration and performance analysis of an on-line, low-cost, high performance, and single-phase uninterruptible power supply (UPS) system based on a boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter. The system consists of an isolated ac/dc BIFRED converter, a bidirectional dc/dc converter, and a dc/ac inverter. It provides input power factor correction, electric isolation of the input from the output, low battery voltage, and control simplicity. Unlike conventional UPS topologies, the electrical isolation is provided using a high frequency transformer that results in a smaller size and lower cost. Detailed circuit operation, analysis, as well as simulation and experiment results are presented. A novel digital control technique is also presented for UPS inverter control. This controller follows the reference current and voltage of the inverter with a delay of two and four sampling periods, respectively.

Family of Zero-Current Transition PWM Converters

Abstract: In this paper, a new auxiliary circuit is introduced for applying to buck, buck-boost, zeta, forward, and flyback converters. This auxiliary circuit provides a zero-current switching condition for all switching elements. The proposed zero-current transition (ZCT) pulsewidth-modulated buck converter is briefly described. Also, a ZCT flyback converter is analyzed, and its different operating modes are presented. Design considerations are explained, and a design example along with the experimental results of the ZCT flyback converter is presented.

A Single-Stage High-Power-Factor Electronic Ballast Based on Integrated Buck Flyback Converter to Supply Metal Halide Lamps

Abstract: In this paper, a novel single-stage electronic ballast with a high power factor is presented. The ballast circuit is based on the integration of a buck converter to provide the power factor correction, and a flyback converter to control the lamp power and to supply the lamp with a low-frequency square-waveform current. Both converters work in discontinuous conduction mode, which simplifies the control. In spite of being an integrated topology, the circuit does not present additional stress of voltage or current in the main switch, which handles only the flyback or buck current, depending on the operation mode. To supply the lamp with a low-frequency square-wave current to avoid acoustic resonances, the flyback has two secondary windings that operate complementarily at a low frequency. The design procedure of the converters is also detailed. Experimental results from a 35-W metal halide lamp are presented, where the proposed ballast reached a power factor of 0.95, a total harmonic distortion of 30% (complying with IEC 61000-3-2), and an efficiency of 90%.

System and method for synchronous rectifier drive that enables converters to operate in transition and discontinuous mode

Abstract: A synchronous rectifier is switched in accordance with a primary switch transition and a reference signal representing current in a current storage device to which the synchronous rectifier is coupled. A current emulator provides a signal representing current in the current storage device as a volt-second product so that current stored in the current storage device while the primary switch is on is discharged by the synchronous rectifier. The use of a current emulator provides an inexpensive solution for controlling synchronous rectifier transitions without resorting to more expensive current sensing solutions that are commercially impracticable. Blanking intervals are provided for avoiding false transitions of the synchronous rectifier when the primary switch turns on and after the synchronous rectifier turns off. The disclosed system and method can be applied to flyback converters for a synchronous rectifier on the secondary side of a transformer, or the inductor of buck converters.

Design of high efficiency Flyback converter with energy regenerative snubber

Abstract: The flyback converter is frequently used for multiple outputs and low power application due to its simplicity and both step-up and step-down characteristics. However, the high leakage inductance of the flyback transformer can causes high voltage spike and could damage the main transistor when the switch is turned off. Therefore, a turn-off snubber is needed to limit the peak voltage stress. In this paper, some common snubbers are discussed in comparison with the energy regenerative snubber. The operation of the energy regenerative snubber is analyzed and the design procedures are optimized for energy efficiency followed by experimental verification.

An improved single-stage Flyback PFC converter for high-luminance lighting LED lamps

Abstract: This paper presents a high-performance LED lamp driver with an improved single-stage Flyback configuration. A constant current control method is used to regulate the lamp current and brightness. A laboratory prototype has been built and tested. With the prototype, high efficiency, high power factor, and constant lamp current can be achieved under different pieces of LED series connection. Copyright © 2007 John Wiley & Sons, Ltd.

Family of zero current zero voltage transition PWM converters

Abstract: A new auxiliary circuit is introduced for buck, buck-boost, forward and flyback converters. This auxiliary circuit provides zero current, zero voltage switching condition for the main switch while providing zero current switching condition for the auxiliary switch and diodes. In this converter family, there is no additional voltage and current stress on the main switch. The proposed auxiliary circuit is applied to a buck converter and the resulting ZCZVT PWM buck converter is analysed and its operating modes are presented. A simple design method for auxiliary circuit is discussed. The experimental results of a 175 W ZCZVT buck converter operating at 100 KHz are presented. Other converter topologies with the proposed auxiliary circuit are also introduced.

Three-pin integrated synchronous rectifier and a flyback synchronous rectifying circuit

Abstract: A three-pin integrated synchronous rectifier is the synchronous rectifier chip where the quantity of connection pins is the smallest possible quantity. The three-pin integrated synchronous rectifier uses a control pin to receive a control signal used as a power bias voltage and a synchronous pulse to make the synchronous rectifier chip operate normally. The control signal is obtained from the output pin of an auxiliary winding via a diode. The other pins are respectively the drain pin and the source pin of an internal power transistor and are connected with the output winding and the voltage output terminal for transmitting the power of the transformer to supply current for the loading.

Comparative analysis of buck-boost converters used to obtain I–V characteristic curves of photovoltaic modules

Abstract: In this paper, the usefulness of several topologies of DC-DC converters for measuring the characteristic curves of photovoltaic (PV) modules is theoretically analyzed. Eight topologies of DC-DC converters with step-down/step-up conversion relation (buck-boost single inductor, CSC (canonical switching cell), Cuk, SEPIC (single-ended primary inductance converter), zeta, flyback, boost-buck-cascaded, and buck-boost-cascaded converters) are compared and evaluated. This application is based on the property of these converters for emulating a resistor when operating in continuous conduction mode. Therefore, they are suitable to implement a system capable of measuring the I-V curve of PV modules. Other properties have been taken into account: input ripple, devices stress, size of magnetic components and input-output isolation. The study determines that SEPIC and Cuk converters are the most suitable for this application mainly due to the low input current ripple, allow input-output insulation and can be connected in parallel in order to measure PV modules o arrays with greater power. CSC topology is also suitable because it uses fewer components but of a larger size. Experimental results validate the comparative analysis.

A Practical Transformer Core Loss Measurement Scheme for High-Frequency Power Converter

Abstract: A practical method to measure transformer core loss in a high-frequency switching mode power converter is proposed. The method is also applicable when the transformer has dc bias in the magnetizing current. Practical issues to minimize the measurement error are discussed. The measurement results are very close to simulation results obtained from a time-domain finite element analysis solver. Detailed error analysis for the proposed method provides useful guidelines on transformer core loss measurement for switching mode power supplies.

3boost: A High-Power Three-Phase Step-Up Full-Bridge Converter for Automotive Applications

Abstract: This paper describes a simple dc-dc step-up converter topology for switch-mode dc power supplies. The proposed configuration is well suited for high-power applications with battery supply. In the automotive framework, the push-pull architecture is the most widespread. However, as power increases, the use of a full-bridge architecture is mandatory. This paper presents a full-bridge architecture where the traditional single-phase transformer is replaced by a three-phase transformer. A prototype was realized and tested for the power supply of automotive devices. In this environment, one of the most important requirements is the ability to provide a burst of power during short-duration events, together with high-efficiency and high-quality output voltage. The latter constraints can be achieved by only using closed-loop switch-mode dc-dc converters at high switching frequency, thus reducing converter efficiency and creating electromagnetic-compatibility (EMC) problems. In this paper, the aforementioned issues were tackled relying on an open-loop topology. Open-loop converters are feasible if the output resistance of the converter is as low as possible, and a possible solution is the minimization of power losses. The solution is the use of a three-phase transformer with a delta-wye connection within a full-bridge converter topology. The configuration will be referred to as 3boost power supply. The three-phase transformer replaces the common single-phase transformer, and it is driven by a three-phase full-bridge inverter operating in six-step modulation. At secondary, a three-phase full wave diode rectifier is used to obtain the output dc voltage level. Therefore, a unitary transformer utilization factor is achieved. A simple theoretical comparison between the three types of converters-push-pull, conventional full bridge, and 3boost is shown. A low-power version of the converter was realized. Experiments confirm that this topology allows to achieve a high efficiency, a lower ripple factor, and a good EMC behavior.

Method and apparatus for providing power conversion using an interleaved flyback converter with automatic balancing

Abstract: A method and apparatus for converting DC input power to DC output power. The apparatus comprises a plurality of parallel connected flyback circuits. A controller is coupled to the switches within the flyback circuits to provide accurate timing and automatic current balancing amongst the plurality of flyback circuits.

Dimmer control leakage pull down using main power device in flyback converter

Abstract: A flyback controller-may include a dimmer input configured to receive a chopped and rectified AC voltage. Each cycle of the signal may have an off period which is substantially attenuated but not always zero due to leakage of a dimmer control from which the chopped AC voltage originates, and an on period which substantially tracks the AC voltage. The ratio of the off period to the on period may be dependent upon a setting of the dimmer control. The flyback controller may include a control circuit configured to generate a switching signal based on the signal from the dimmer input. The switching signal may controllably oscillate between its on and off states during the on periods of the chopped and rectified AC voltage so as to controllably regulate current that is delivered by a secondary winding of a transformer in a flyback converter. The switching signal may be in the on state during the off periods of the chopped and rectified AC voltage, thereby preventing a voltage build up from the dimmer control leakage.

Basic DC-to-DC Converters

Abstract: This paper generically classifies and unifies basic single-switch, single-inductor, DC-TO-DC converters. The boost and buck/boost flyback converters are shown to be supplementary, each being part of the same three-port terminal transfer function. Realizing one of these converters inherently results in the other as a fully functional composite output port. Three-port examination of the forward converter reveals it too combines two different converter voltage/current transfer functions. Generalized three-port analysis is used to specify the requirements of a realizable universal DC-TO-DC converter theoretically capable of producing isolated output DC and AC voltage and current in the range plusmninfin.

Flyback power supply with forced primary regulation

Abstract: A flyback converter with forced primary regulation is disclosed. An example flyback converter includes a coupled inductor including a first winding, a second winding, and a third winding. The first winding is coupled to an input voltage and the second winding is coupled to an output of the power converter. A switched element is coupled to the second winding. A secondary control circuit is coupled to the switched element and the second winding. The secondary control circuit is coupled to switch the switched element in response to a difference between a desired output value and an actual output value to force a current in the third winding that is representative of the difference between the desired output value and the actual output value. A primary switch is coupled to the first winding. A primary control circuit is coupled to the primary switch and the third winding. The primary control circuit is coupled to switch the primary switch to regulate the output of the power converter in response to the forced current.

Advanced Control of a Resistance Spot Welding System

Abstract: This paper deals with a middle-frequency resistance spot welding system. It consists of an input converter, welding transformer, and a full-wave rectifier mounted at the transformer secondary. The welding current at the full-wave rectifier output is normally controlled by the pulse width modulated primary voltage of the transformer supplied by the input converter. The unequal ohmic resistances of the two transformer's secondary circuits and the different characteristics of the diodes of output rectifier certainly lead to the magnetic saturation which, consequently, causes the unwanted spikes in the transformer's primary current and over-current protection switch-off. This disadvantage of classical spot welding systems is completely eliminated by the proposed advanced hysteresis controller (AHC), which keeps transformer iron core saturation within prescribed bounds regardless of how unequal the ohmic resistances and diodes' characteristics in the transformer's secondary circuits are. This is achieved by a combined closed-loop control of the welding current and closed-loop control of the iron core saturation level. The proposed AHC assures a very short rise time of the welding current and the best possible utilization of the transformer iron core.

Linearity in led dimmer control

Abstract: A flyback controller may generate a switching signal for controlling the delivery of input current into a primary winding of a transformer in a flyback converter that has a secondary winding in the transformer and that is driven by AC output from a dimmer control that is chopped at a phase angle based on a setting of the dimmer control. The flyback controller may include a tracking input configured to receive a dimmer output tracking signal that is representative of the instantaneous magnitude of the output from the dimmer control. The flyback controller may include an averaging circuit configured to average the dimmer output tracking signal so as to generate an average dimmer output signal that is representative of a time-averaged value of the dimmer output tracking signal. The flyback controller may be configured to cause the average output current in the secondary winding of the transformer to vary as a function of the average dimmer output signal when the phase angle exceeds a threshold. The flyback controller may be configured to generate the switching signal with a duty cycle that causes the luminance level of light produced by one or more LEDs to vary when the phase angle exceeds a threshold by what appears to the human eye to be a more linear function of the phase angle than if the luminance level actually varied as a linear function of the phase angle.

Method and apparatus of providing synchronous regulation circuit for offline power converter

Abstract: A synchronous regulation circuit is provided. A secondary-side switching circuit is coupled to the output of the power converter to generate a synchronous signal and a pulse signal in response to an oscillation signal and a feedback signal. An isolation device transfers the synchronous signal from the secondary side to the primary side of the power converter. A primary-side switching circuit receives the synchronous signal to generate a switching signal for soft switching a transformer. The pulse signal is utilized to control a synchronous switch for rectifying and regulating the power converter. The synchronous switch includes a power switch and a control circuit. The control circuit receives the pulse signal for turning on or off the power switch. The power switch is connected between the transformer and the output of the power converter. A flyback switch is operated as a synchronous rectifier to freewheel the inductor current of the power converter. The flyback switch is turned on in response to the off state of the power switch. The turn-on period of flyback switch is correlated to the turn-on period of the power switch.

Rating and design issues of DVR injection transformer

Abstract: The load side voltage disturbances can be effectively mitigated by connecting a series compensating device called dynamic voltage restorer (DVR). Generally, DVR is realized by a voltage source inverter with dc storage device and a series injection transformer. Rating and design issues of an injection transformer are of much concern for the proper operation of the DVR. Voltage underrating of the transformer may lead to its saturation whereas overrating increases the cost and size of the DVR. The voltage applied to the primary winding of the transformer is a combination of several components of different frequencies. In view of above, rating and design issues are presented in this paper. A novel method is proposed to find the voltage rating of the transformer as a function of the fundamental frequency. Furthermore, to reduce the effects of current harmonics in the transformer, A-factor is used. A PSCAD model is used to validate the efficacy of the proposed design method to find the voltage rating, and overall performance of the DVR. The experimental studies confirm the proposed method.

Apparatus and method for regulating constant output voltage and current on primary side in a flyback converter

Abstract: A voltage detector circuitry extracts a signal on primary side of a transformer in a flyback converter, which is proportional to the output voltage of the converter without voltage drop on the rectifier diode and leakage inductance effect on the transformer, and good output regulation is achieved without opto-coupler. To accurately detect the output voltage on the primary side, the knee point of the voltage on an auxiliary winding of the transformer is detected. A current limit proportional to the input voltage of the converter is produced from the voltage on an auxiliary winding for stabilizing the output current in constant current mode.

Matrix converter fed open-ended power electronic transformer for power system application

Abstract: A matrix converter controlled 3-phase power electronics transformer is proposed for power system application. The proposed system uses three matrix converters and a three phase high frequency transformer in order to achieve isolation and, voltage and current transformation from primary to secondary. The primary side of the transformer is open-ended and two matrix converters connected to both sides of the opened primary side control the voltage by use of high frequency switching. By use of high frequency switching the size of the transformer is reduced. Another matrix converter connected to the star connected secondary side of the transformer converts back the high frequency chopped voltage at the output of the transformer to normal line frequency voltage by synchronized switching with primary side converters. By applying phase shift control to the forward rotating and backward rotating vectors the input power factor and output power factor are decoupled and unity power factor operation is achievable at the input.

The parametric current transformer, a beam current monitor developed for LEP

Abstract: Toroidal transformers are used to measure the beam current in beam lines and accelerators. Placing such a transformer in the feedback loop of an operational amplifier will increase the useful frequency range (active current transformer). A magnetic modulator can be added to extend the response to DC current, maintaining with a control loop the transformer core at a zero flux state. The magnetic modulator in the parametric current transformer gives not only the DC response but provides parametric signal amplification up to a transition frequency of about 500 Hz. The low frequency channel (magnetic modulator) and the high frequency channel (active current transformer) are linked together in a common feedback loop. A large dynamic range together with good linearity and low distortion is obtained. This arrangement protects the magnetic modulator from dynamic errors in case of a sudden beam loss, which could impair its zero stability. Dynamic overload protection is an important condition to obtain high resolution and good zero stability, even in applications which require in principle only a very limited frequency response.

Flyback constant voltage converter having both a PWFM mode and a PWM mode

Abstract: A flyback AC/DC switching converter has a constant voltage (CV) mode. The CV mode has sub-modes. In one sub-mode (“mid output power sub-mode”), the output voltage (VOUT) of the converter is regulated using both pulse width modulation and pulse frequency modulation. Both types of modulation are used simultaneously. In a second sub-mode (“low output power sub-mode”), VOUT is regulated using pulse width modulation, but the converter switching frequency is fixed at a first frequency. By setting the first frequency at a frequency above the frequency limit of human hearing, an undesirable audible transformer humming that might otherwise occur is avoided. In some embodiments, the converter has a third sub-mode (“high output power sub-mode”), in which pulse width modulation is used but the switching frequency is fixed at a second frequency. By proper setting of the second frequency, undesirable EMI radiation and other problems that might otherwise occur are avoided.

Derating of transformers under non-sinusoidal loads

Abstract: Transformers are normally designed and built for utilizing at rated frequency and prefect sinusoidal loads. Supplying non-linear loads by transformer leads to higher losses, early fatigue of insulation, and reduction of the useful life of transformer. To prevent these problems rated capacity of transformer supplying non-linear loads must be reduced. In this paper, at first, a useful model of transformer under harmonic condition is presented. The model in addition to ordinary parameters includes a potential difference defined as the second derivative of the load current that represents eddy current losses in windings and the other stray losses represented as a resistor in series with the leakage inductance and dc resistance. Finally, losses and capacity of 50 KVA transformer under harmonic load current is calculated. This model simulated in MATLAB/Simulink and then its results are compared with losses and capacity calculated by standard.

Sensor for high voltage environment

Abstract: Sensor for measuring electrical parameters in a high voltage environment comprising a high voltage side (4) for connection to high voltage conductors, a low voltage side (6) for connection to low voltage power supply and measurement signal control circuitry, a measurement signal circuit (16), and a power supply circuit (14), and at least one isolating transformer (18, 20) for transmission of electrical power supply and/or measurement signals between the low voltage side and the high voltage side. The isolating transformer comprises at least a first and a second transformer core (28), a transformer coil (33) on a circuit board around a branch (27) of the transformer core on the high voltage side and a transformer coil (32) on a circuit board around a branch (29) of the transformer core on the low voltage side, the isolating transformer further comprising an intermediate coil (36) encircling at least one branch of each said at least two transformer cores.

LLC resonant converter for wireless energy transmission system with PLL control

Abstract: This paper presents a wireless transcutaneous energy transmission system utilizing the magnetic coupling of coils. No physical wire connection is required between the circuits inside and outside the body. Because the transformer is the contactless transformer, the coupling efficient of the transformer is not good as normal transformer. The parameter of the leakage inductance of transformer will be larger than the magnetizing inductance of transformer. An LLC resonant converter is used outside the body. The LLC resonant converter could have higher power conversion efficiency to improve wireless transcutaneous energy transmission system efficiency. In addition, the soft-switching structure of a LLC resonant converter is utilized. A phase locked loop is adopted to control the LCC resonance to facilitate the steady electrical energy transfer. According to the experimental results, the system can deliver an output power around 1W to the load circuits inside the body and the output voltage can be regulated at 4V.