Showing papers on "Forward converter published in 2001"

Development of a microcontroller-based, photovoltaic maximum power point tracking control system

Abstract: Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.

A natural ZVS medium-power bidirectional DC-DC converter with minimum number of devices

Abstract: This paper introduces a new bidirectional, isolated DC-DC converter. A typical application for this converter can be found in the auxiliary power supply of hybrid electric vehicles. A dual half-bridge topology has been developed to implement the required power rating using the minimum number of devices. Unified zero-voltage switching was achieved in either direction of power flow with neither a voltage-clamping circuit nor extra switching devices and resonant components. All these new features allow high power density, efficient power conversion, and compact packaging. Complete descriptions of operating principle and design guidelines are provided in this paper. An extended state-space averaged model is developed to predict large- and small-signal characteristics of the converter in either direction of power flow. A 1.6-kW prototype has been built and successfully tested under full power. The experimental results of the converter's steady-state operation confirm the soft-switching operation, simulation analysis, and the developed averaged model. The proposed converter is a good alternative to full-bridge isolated bidirectional DC-DC converter in medium-power applications.

Steady-state analysis of the LLC series resonant converter

Abstract: The operating modes of the LLC series resonant converter are analyzed to determine the steady-state operating point and mode boundaries. The three-element LLC series resonant converter is realized by adding an inductor to the basic two-element series resonant converter topology. Unlike the two element series resonant converter, which is limited strictly to step down operation, the LLC converter is capable of both step up and step-down. A wide range of output power is controlled with only a narrow variation in operating frequency. In addition, zero-voltage switching can be achieved over the entire operating range. All of these desirable properties are obtained essentially for free, as the additional resonant inductor can be realized simply by introducing an air gap in the main power transformer.

Buck-boost PWM converters having two independently controlled switches

Abstract: Single-switch step-up/step-down converters, such as the buck-boost, SEPIC and Cuk, have relatively high voltage and current stresses on components compared to the buck or the boost converter. A buck-boost converter with two independently controlled switches can work as a boost or as a buck converter depending on input-output conditions, and thus achieves lower stresses on components. Using the converter synthesis method from D. Zhou (1995), families of two-switch buck-boost converters are generated, including several new converter topologies. The two-switch buck-boost converters are evaluated and compared in terms of component stresses in universal-input power-factor-corrector applications. Among them, one new two-switch converter is identified that has low inductor conduction losses (50% of the boost converter), low inductor volt-seconds (72% of the boost converter), and about the same switch conduction losses and voltage stresses as the boost converter.

A fast dynamic DC-link power-balancing scheme for a PWM converter-inverter system

Abstract: The authors propose a new power converter control scheme for a converter-inverter system. The strategy is to fully utilize the inverter dynamics in controlling the converter dynamics. The authors obtain the power dynamics for both converter and inverter systems, and control the converter power so that it matches the required inverter power exactly. Then, in the ideal case, no power flows through the DC-link capacitors and, thus, the DC-link voltage does not fluctuate even though a very small amount of the DC-link capacitance is used. In forcing the converter power to match the inverter power, the authors utilize the master-slave control concept. They control the DC-link voltage level indirectly through the stored capacitor energy in order to exploit the advantage of the linear dynamic behavior of the capacitor energy. This helps them to circumvent a complex control method in regulating the DC-link voltage. Through simulation and experimental results, the superiority of the proposed converter control scheme is demonstrated.

Stacked multicell converter (SMC): properties and design

Abstract: We present in this paper a new topology of multilevel converter allowing an increase of input voltage level compared with the imbricated cells converter, while decreasing the stored energy in the converter. This new topology called SMC (stacked multicell converter) consists of a hybrid association of commutation cell making it possible to share the voltage constraint on several switches, and also to improve the output waveforms of the converter in terms of number of levels and switching frequency. After the introduction, the second part is devoted to the presentation of the topology. We give some explanation about the control of the SMC converter, and give some basics design properties for the SMC topology. Some simulation and experimental results obtained on a 50 kVA experimental set-up are presented.

Apparatus and method for efficiently amplifying wideband envelope signals

Abstract: Systems and methods for amplifying an RF input signal include employing a moderately power efficient wide bandwidth device, such as an AB-type amplifier, to amplify the power residing in the high frequency components of the input signal, and a highly power efficient narrow bandwidth device, such as a synchronous buck DC/DC converter, to amplify the power residing in the low frequency components of the input signal. The amplified low frequency components and high frequency components are then combined to produce an amplified replica of the RF input signal. A positive feedback loop is provided between the output of the AB-type amplifier and the input of the DC/DC converter to provide stability to the amplified RF signal. A negative feedback loop is provided between the output of the DC/DC converter and the input of the AB-type amplifier to minimize interference introduced by the DC/DC converter.

Design and performance evaluation of low-voltage/high-current DC/DC on-board modules

Abstract: The topology selection, design, and performance evaluation of an on-board DC/DC converter, which delivers power from a 48 V input to a 1.2-1.65 V/70 A microprocessor load, are presented. It was shown that the symmetrical half-bridge topology with the current doubler and synchronous rectifiers is a suitable approach for this application. The measured full-load efficiency of a 200 kHz experimental half-bridge converter was higher than 82% in the entire output and input voltage range.

A zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation

Abstract: A new primary-side-assisted zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation is proposed. The proposed DC-DC converter uses only one auxiliary transformer and two diodes to obtain ZCS for the leading leg. It has a simple and robust structure, and load current control capability even in short circuit conditions, The possibility of magnetic saturation due to asymmetricity of circuits or transient phenomena is greatly reduced, which is a very attractive feature in DC-DC converters with transformer isolation. The power rating of the auxiliary transformer is about 10% of that of the main transformer. Operation of a 12 kW prototype designed for welding application was verified by experiments.

Sample and hold method to achieve square-wave PWM current source for light emitting diode arrays

Abstract: An apparatus for controlling overshoots in the switching of LED arrays in a system having a switching voltage converter providing the biasing voltage for the LED array. By synchronizing a switching converter to an LED turn-on signal, loading on the voltage converter can be controlled such that output conduction of the converter only occurs when LEDs that are to be displayed are switched on to provide loading to the output of the converter. A Sample and hold method is employed to effectively store the current information in a previous “on” interval and use it for the current control in a following interval with inhibited current overshoot.

A novel modeling and control method for three-phase PWM converters

Abstract: The pulse-width modulated (PWM) voltage-source converter (VSC) and current-source converter (CSC) are the building blocks of most of the switch-mode power electronic systems. Irrespective of the converter type, the controller is supposed to fulfill two objectives: (1) real power flow control which leads to the regulation of the DC quantity (DC voltage in VSC and DC current in CSC), and (2) reactive power flow control on the AC-side. The major difficulty in control is caused by the nonlinearities in the converter model. The existing control techniques are based on the design of the PI-controllers without the knowledge of the converter model, linearizing the nonlinear model, or splitting the original system into linear and nonlinear parts and dealing with them separately. In this paper, a power balance equation and nonlinear input transformation are used to derive a linear model from the original nonlinear model. Then, a decoupled state-feedback control method is applied to the new model. The accuracy of the new model and the performance of the applied control method are evaluated using the simulation results obtained from the PSCAD/EMTDC simulation package. It is shown that as a result of using the new model and applying the state-feedback control technique, the dynamics of the system are considerably improved resulting in short response times. It is also shown that the approach taken in modeling and control results in excellent results even at low switching frequencies making the scheme very suitable for high-power applications.

Symmetrical DC/DC converter

Abstract: A symmetrical DC/DC converter selects an energy transferring direction and a step-up or a step-down operation as well as a desired step-up or a step-down ratio. The converter includes a single inductor with a pair of switching devices connected to its terminals in a symmetrical arrangement with respect to the inductor. The converter is operable as a step-up converter and a step-down converter in a manner such that one and the other of the switching devices are used as an input switch and an output switch, respectively, and that one and the other of the switching devices are conversely used as an output switch and an input switch, respectively.

A double ZVS-PWM active-clamping forward converter: analysis, design, and experimentation

Abstract: This paper presents an isolated DC-DC converter based on two ZVS-PWM active-clamping forward converters connected in series and coupled by a single high-frequency transformer. The proposed converter features no switching losses from no-load to full-load operation and low conduction losses. This converter is suitable for high input voltage (>400 VDC) and high power applications. Operation principles, theoretical analysis and design example, are presented, as well as experimental results taken from a 3 kW laboratory prototype.

A new low-stress buck-boost converter for universal-input PPC applications

Abstract: In converters for power-factor-correction (PFC), universal-input capability (ability to operate from any AC line voltage, world-wide) comes with a heavy price in terms of component stresses and losses, size of components, and restrictions on the output DC voltage. A new two-switch topology is proposed to offer very significant performance improvements over the single-switch buck-boost converters (including flyback, SEPIC, and Cuk topologies) and conventional two-switch buck-boost cascaded converters. The proposed converter has buck-boost conversion characteristic, switch conduction losses comparable to the boost converter, no inrush current problem, and potential for smaller inductor size compared to the boost converter.

Active-clamp DC/DC converters using magnetic switches

Abstract: Although DC/DC power converters with coupled inductors can provide high voltage gain to meet the requirements of many emerging applications, their efficiency is degraded by losses associated with the leakage inductors. The active-clamp technique recycles the leakage energy, but at the price of increasing topology complexity. A family of high-efficiency, high step-up DC/DC power converters is proposed in this paper. The proposed converters, which use diodes and coupled windings instead of active switches to realize clamp functions, present better performance than their active-clamp counterparts. The efficiency of a 35 W front-end converter for a high intensity discharge lamp ballast is higher than 90% with 12 V input and 100 V output. The high efficiency is achieved because the leakage energy is recycled and the switch voltage stress is minimized.

Range winding for wide input range front end DC/DC converter

Abstract: Hold up time requirement is a special requirement for a front end (FE) converter. The converter needs to provide output voltage within regulation for 20 ms after the AC input is lost. When designing the FE DC/DC converter, we want it to operate over a wide input range so that we can use less high voltage bus capacitor to meet the requirement. The converter efficiency is reduced at normal operating conditions, in order to cover wide input range. This paper demonstrates a new method to cover wide input range while also optimizing the normal condition operation with range winding.

A new driving scheme for synchronous rectifiers: single winding self-driven synchronous rectification

Abstract: Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results.

High power DC-to-DC converter for supercapacitors

Abstract: The purpose of this paper is to present Solectria's approach to the design and realization of a high power, nonisolated DC-to-DC power converter for supercapacitors. The study focuses on supercapacitor specific design rules and on how to integrate the unit into a system with other energy storage devices and converters. Two applications are presented to illustrate the validity of the suggested approach: an electric vehicle with supercapacitor load leveling, and a 50 kW pulsed power source.

Maximum power tracking technique for solar panels

Abstract: The present invention provides an apparatus and method for tracking the maximum power point of a solar panel. A pulsewidth-modulated converter, for example a SEPIC or Cuk converter, is provided between the output of the panel and the load, and a perturbation is introduced into a switching parameter of the converter.

A front-end DC/DC converter for network server applications

Abstract: Network server power supplies call for a dual universal AC line input and 48V DC input front-end converters to generate the 380 V DC bus. To realize the DC input front-ends, nonisolation DC/DC power converters, such as continuous current mode (CCM) boost converters, are not good candidates because of their power limitations under extreme duty cycles. Cascade DC/DC power converters can meet this specific application requirement with the deficiency of extra complexity and higher cost. Although coupled inductor DC/DC converters can provide high step-up voltage gain without the penalty of extreme duty ratio, their efficiency is poor due to the losses associated with the leakage inductors. In this paper, a clamp mode coupled inductor boost converter with no extreme duty ratio is presented. The proposed topology utilizes coupled inductor to achieve high step-up gain as well as to alleviate the output rectifier reverse recovery problem. The efficiency of a 1 kW prototype is higher than 90% under nominal operation condition.

System and method for regulating multiple outputs in a dc-dc converter

Abstract: A multiple output flyback converter provides independently controlled high-bandwidth secondary side voltage regulation for rapid response to small signal changes at the multiple outputs on the secondary side. Each of the multiple output circuits includes a fast local feedback loop to perform rapid and precise secondary side voltage regulation. The fast local secondary side feedback loops compensate for small changes in the load on the order of 1 to 5 percent. By providing each output circuit with independent secondary-side control, the last or final voltage output is controlled from the primary side. A further feature of the inventive circuit is that the input circuit of the converter includes an active clamp circuit for recovering both energy in the leakage inductance and additionally recovers residual energy in the magnetic field of the secondary winding of the transformer at the end of each energy cycle.

An improved boost PWM soft-single-switched converter with low voltage and current stresses

Abstract: This paper presents an improved regenerative soft turn-on and turn-off snubber applied to a boost pulsewidth-modulated (PWM) converter. The boost soft-single-switched converter proposed, which has only a single active switch, is able to operate with soft switching in a PWM way without high voltage and current stresses. This is achieved by using an auxiliary inductor, which is magnetically coupled with the main inductor of the converter. In order to illustrate the operating principle of this new converter, a detailed study, including simulations as well as experimental results, is carried out. The validity of this new converter is guaranteed by the obtained results.

Novel inverter topologies for single-phase stand-alone or grid-connected photovoltaic systems

Abstract: Photovoltaic and battery systems often operate in small stand-alone or grid-connected applications, where the generator voltage is lower than the grid voltage. To boost the voltage up to the grid level a further element, either a DC/DC converter or 50 Hz transformer, is connected in series with a PWM inverter. To reduce the high cost of such low power systems, the costs of the power electronics should be minimized. In this paper, several new low-cost inverters with and without HF-transformers are presented. Simulation and experimental results of their operation and control for stand-alone as well for grid-connected applications are discussed.

Multi-phase switching converters and methods

Abstract: Multi-phase switching converters and methods that provide fast response and low ripple on the converter inputs and outputs. The converters include multiple converter stages that are normally operated in sequence into a common load. However upon sensing that operation of one of the converter stages does not bring the converter back into regulation, multiple converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again. In the embodiment disclosed, upon sensing that operation of one of the converter stages does not bring the converter back into regulation, all converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again starting with the stage with the lowest inductor current.

Power factor correction (PFC) circuit that eliminates an inrush current limit circuit

Abstract: Aspects for a power converter with power factor correction (PFC) circuit are described. The aspects include a buck/boost circuit for achieving a DC voltage from an AC input voltage signal line without developing an inrush current from the AC input voltage line, and a DC/DC converter circuit coupled to the buck/boost circuit for converting the DC voltage to a desired voltage level. The aspects are achieved in a straightforward, cost effective, and adaptable manner.

Primary side control circuit of a flyback converter

Abstract: Voltage feedback in flyback converters is typically done with the assistance of opto-couplers, to preserve electrical isolation. However the output voltage also exists (in part) across the primary side switch when in its off state. This paper investigates the extraction of the output voltage within one switching cycle. Good results are obtained from a flyback converter with a novel control circuit using cycle by cycle control. The converter works in both continuous and discontinuous mode of operation.

Flyback power converter with secondary-side control and primary-side soft switching

Abstract: A flyback power converter is described which provides multiple independently regulated outputs. Zero-volt primary side switching is achieved at a resonance minimum which occurs at the end of each energy cycle between a primary side capacitor and an isolation transformer primary winding.

Multiple output power supply including one regulated converter and at least one semi-regulated converter

Abstract: A power supply, including a regulated switchmode converter, a PWM controller, a semi-regulated converter, and a linear regulator. The regulated switchmode converter is for converting an input voltage to a first output voltage. The PWM controller is responsive to the first output voltage, and includes an output terminal coupled to a control terminal of a switch of the regulated switchmode converter. The semi-regulated switchmode converter is for converting the input voltage to an intermediate output voltage, and includes a switch having a control terminal coupled to the output terminal of the PWM controller. The linear regulator is coupled to the semi-regulated switchmode converter and is for converting the intermediate output voltage to a second output voltage.

Multiple port bi-directional power converter

Abstract: In one embodiment of the present invention, a bi-directional power converter is described. The converter comprises a first bi-directional DC-DC conversion device having a first plurality of bi-directional DC-DC converters, a plurality of power supply ports, each connected to at least one of the first plurality of bi-directional DC-DC converters, and a voltage medium capacitor, which is connected to each of the first plurality of bi-directional DC-DC converters and has a first voltage greater than a second voltage measured at each of the power supply ports. The converter further may comprise a third bi-directional DC-DC converter device, which is connected to the voltage medium capacitor and is connected to a voltage high capacitor. The converter also may comprise a bi-directional AC-DC conversion device, which bi-directional AC-DC conversion device is connected to the voltage high capacitor and at least one inductor, which is connected to a plurality of AC ports. In another embodiment of the present invention, at least one of the DC ports may be a hydrogen fuel cell.

Inductor current synthesizer for switching power supplies

Abstract: A circuit and method for sensing the inductor current flowing to a load from a switching power supply without using a sense resistor in the path of the inductor current. In a synchronous buck converter topology, the inductor current is derived by sensing the voltage drop across the synchronous MOSFET of the half-bridge and reconstructing the current using a sample and hold technique. A ripple current synthesizer is employed to reconstruct inductor current outside the sample and hold window. The sampled product I Load ×R DSon is used to update the ripple current estimator with dc information every switching cycle. The resulting voltage waveform is directly proportional to the inductor current. The inductor current synthesizer of the present invention can also be used in boost converter, flyback converter and forward converter topologies.