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The interleaved converter topology has attractive features that include high output current, small output-current ripple, and fast transient response. In this paper, an interleaved four-phase forward converter using an integrated transformer is proposed for telecommunication and computer applications. The proposed converter requires only one integrated transformer instead of four step-down transformers. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated transformer are derived. The circuit operation and design criteria are described. Theoretical analyses are verified by simulated and experimental results. Index Terms--Converter with small output-current ripple, integrated magnetics, integrated transformer, interleaved four-phase forward converter, regenerative LC snubber circuit.

This paper presents an implementation of integrated inductor for typical dimmable electronic ballasts having two power processing stages. The inductor used in the front-stage power factor corrector is integrated with the resonant inductor in the output-stage of the ballast inverter, so that the usage of the magnetic core material, and thus the cost, can be reduced. Existing circuit schematic can be retained without requiring any modification. Most importantly, the ballast performance is similar to the original design with two separate inductors. Based on using a z-parameter gyrator-capacitor model, modeling, design, and analysis of the ballast operation will be presented. A comparative study of using two separate inductors and integrated-inductor designs on the core volume, conduction and hysteresis losses, inductor current waveforms, input current harmonics, output lamp crest factor, overall efficiency, and costing will be carried out. Simplified design procedures will be given. The structure has been successfully applied to a 36-W prototype. Index Terms--Electronic ballast, integrated magnetics (IM), series resonant inverters.

A hot swap of power modules is required by high-availability parallel power module systems. With the hot-swappable paralleled power modules, the system up-time can be maximized, the system maintenance and repair can be simplified, and the system upgrade can be allowed for. In this paper, a simple hot-swap solution is proposed for the paralleled power modules which use current-sharing (CS) interface circuits to do the CS work. By redesigning the basic function circuits of the CS interface circuits [4] (such as the under voltage protection circuit, the current-sharing circuit, and the light load protection circuit etc.), an additional hot-swap function can be implemented 'parasitically.' There is no extra hot-swap controller and no compatibility problem between the hot-swap and CS solutions used. A prototype CS interface circuit with a 'parasitic' hot-swap function was designed, implemented, and tested. The results show that the proposed hot-swap solution is feasible and suitable. Index Terms--Current-sharing (CS) interface circuit, hot swap, paralleled power module.

Optimal control methodology is applied to the design of the feedback loops of a multi-inverter uninterruptible power supplies system. The control signals thus obtained will minimize a performance index, which is a function of the output voltage error, the inductor currents of all inverters and the reference signals. This enables the controller to achieve the desired objectives like minimization of the circulating current and reduction of error of the output voltage. The robustness of the controller has also been investigated. Through frequency-domain analysis, it is shown that variations in the number of paralleled inverters in the system have only small influence on the performance of the system. Therefore, the optimal controller designed for a fixed number of inverters can also work well in systems with variable number of paralleled inverters. Three experimental 110 Vac/l.1 KVA inverters are built and paralleled to verify the analysis and theoretical predictions. Index Terms--Inverters, optimization, power electronics, statespace methods.

An interleaved three-phase forward converter using an integrated transformer is proposed in this paper. This type of converter has the attractive features of flexible voltage conversion ratio, high output current (due to the parallel connection of outputs), near-zero output-current ripple (due to the output-current-ripple cancellation), fast transient response (due to the small effective output-filtering inductance), and is particularly suitable for high-output-current and low-output-voltage applications such as telecommunication and computer systems. The integrated transformer of the proposed converter consists of three step-down transformers on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated transformer are derived. Based on the equivalent-circuit model, the principle of operation of the proposed converter is explained. The analysis and design criteria of the basic circuit, the operation of the regenerative LC snubber circuit, the simulation, and experimental verification are also described. Index Terms--Integrated magnetics, integrated transformer, interleaved three-phase forward converter.

This paper proposes a current-sharing (CS) circuit for parallel power modules. The interface circuit enables the outputs of independent and nonidentical power modules to equally share the load current in a fault-tolerant oring-connection power supply system. No CS interconnections among the power modules are required. In the proposed interface circuit, the output currents of the parallel power modules are sensed by measuring the inductor voltage drops and controlled in a hysteresis manner. A practical CS interface circuit is implemented. The experimental results are in good agreement with the theoretical analyses. Index Terms--Current-sharing (CS) interface circuit, parallel power modules (PPMs).

A three-phase interleaved continuous-inductor-current-mode (CICM) boost converter with zero diode reverse-recovery loss is proposed. In the converter, the di/dt of the output rectifiers is controlled by an integrated magnetic component. All the output rectifiers can be turned off softly and a very high efficiency is obtained. The equivalent-circuit model of the integrated inductors, the operation principle of the converter, and the design issues are discussed. Simulation and experimental results are presented.

An interleaved two-phase forward converter using an integrated magnetic component is proposed for telecommunication and computer applications. The integrated magnetic component consists of two step-down transformers and two output-filtering inductors on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated magnetic component are presented. The circuit operation and design criteria of the proposed converter are described. All theoretical analyses are verified by simulated and experimental results.

The characteristics of a novel single-switch high-power-factor regulator with low output current ripple are studied. By employing a modified-boost converter cell as the input stage and a double-ended forward converter cell as the output stage, a high power factor and near-zero output current ripple are achieved. This regulator also eliminates the need for an extra clamping switch to recycle the transformer leakage energy and to reduce the switch voltage stress. The analysis, design, simulation, and experimental results are reported to verify the operation and performance of the proposed regulator. Index Terms--Double-ended forward converter, integrated magnetics, integrated transformer, single-stage isolated power-factor-corrected power supply (SSIPP).

A single-switch continuous-conduction-mode boost converter with reduced reverse-recovery and switching losses is proposed. By utilizing the leakage inductances of a pair of coupled inductors and two additional rectifiers, the turn-off rates (di/dt) of the boost output rectifier and the additional rectifiers are slowed down to reduce the reverse-recovery loss. The boost power transistor is also operated under a low-voltage turn-on condition to reduce the switching loss. Experimental results are presented to confirm the theoretical analysis and the performance of the proposed converter. Index Terms--Boost converter, continuous conduction mode (CCM), low-voltage turn-on, reverse-recovery loss.

This paper presents a neural network with a novel neuron model. In this model, the neuron has two activation functions and exhibits a node-to-node relationship in the hidden layer. This neural network provides better performance than a traditional feedforward neural network, and fewer hidden nodes are needed. The parameters of the proposed neural network are tuned by a genetic algorithm with arithmetic crossover and nonuniform mutation. Some applications are given to show the merits of the proposed neural network. Index Terms--Genetic algorithm (GA), neural network, short-term load forecasting.

Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N + X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. A multi-inverter system with instantaneous average-current-sharing scheme is presented in this paper. By introducing a disturbance source to represent all the sources that may cause current unbalances, a model of the system can be built. Some key issues are discussed based on the model, including stability of the current-sharing controller, impedance characteristics and voltage regulation. Three experimental 110 Vac/1.1 KVA inverters are built and paralleled to verify the theoretical predictions. Index Terms--Load sharing, multi-inverter system, parallel operation.

We introduce a method to use z parameters to model the interface between an electric circuit and a magnetic component. With this model, the electrical equivalent circuit of any complex integrated magnetic component can be developed easily. We describe the simulation and design of integrated magnetics using a z-parameter two-port network model. We use a single-switch regulator with power-factor-correction and a single integrated magnetic component as an example to demonstrate the practical applications of integrated magnetics in modern power converters. For the same example, we analyze the problem of uneven magnetic flux density in an integrated magnetic component and propose a possible solution to the problem. Index Terms--Integrated magnetics, modeling of magnetic components, simulation of integrated magnetics.

An analogue neural-network controller for UPS inverter applications is presented. The proposed neural-network controller is trained off-line using patterns obtained from a simulated controller, which had an idealized load-current-reference. Simulation results show that the proposed neural-network controller can achieve low total harmonic distortion under nonlinear loading condition and good dynamic responses under transient loading condition. To verify the performance of the proposed NN controller, a hardware inverter with an analogue neural network (NN) controller (using mainly operational amplifiers and resistors) is built. Additionally, for comparison purposes, a PI controller with optimized parameters is built. Experimental results confirm the simulation results and show the superior performance of the NN controller especially under rectifier-type loading condition. Implementing the analogue neural-network controller using programmable integrated circuits is also discussed. Index Terms--Neural network control, UPS inverter.

The design and analysis of a single-switch electronic ballast with near-unity power factor and soft-switching characteristic are presented. The ballast circuit is simple and has a small component count. The experimental results for an 80-W ballast show that it has a power factor higher than 0.99 and a total harmonic distortion of 12 %. The operating frequency is between 20-40 kHz. The output power is adjustable and the circuit is reliable. Index Terms--Electronic ballast, fluorescent lamps, soft switching, unity power factor.

A new design and fabrication method for planar windings with multilayers is presented. This method can virtually eliminate external soldering or conductive vias, thus reducing dc resistance and increasing reliability. Compared to the previously reported folding methods for winding fabrication, this method maximizes the use of the window height and minimizes the waste of copper area in manufacturing. The winding pattern is cut using a computer numerically controlled machine, or the punching/pressing process, which is cleaner than the commonly used etching process. The whole winding assembly is completed by a folding process. The primary and secondary windings in a transformer can be interleaved, resulting in low leakage inductance. Practical examples of low-profile transformers and inductors were constructed and tested in an active-clamped forward dc-dc converter with self-driven synchronous rectifiers. Experimental results are presented to show that such transformers/inductors are particularly useful for the design of low-profile and high-power density converter modules. Index Terms - Geometry, planar windings, transformer windings, z-folding.

Conventional zero-current-switching quasi-resonant converters (ZCS-QRC's) suffer from the disadvantages of high switch current stress and variable switching frequency. This paper proposes the use of a 'current-clamping circuit' to overcome these disadvantages. By incorporating such a circuit into the family of ZCS-QRC's, a new family of actively clamped ZCS-QRC's using insulated gate bipolar transistors (IGBT's) is derived. These converters feature high (and constant) switching frequency and zero-current turn-off (without increased current stress), which are particularly useful for high-power applications where minority-carrier semiconductor devices (such as IGBT's and bipolar junction transistors) are used as power switches. The design criteria, simulation, and experimental results are reported. Index Terms - Insulated gate bipolar transistor, power converters, quasi-resonant, zero-current switching.

This paper studies a particular single-stage power-factor-correction (PFC) switching regulator employing a discontinuous-conduction-mode (DCM) boost-input cell and a continuous-current-mode (CCM) forward output cell. Although this single-stage PFC regulator can provide a reasonably high power factor when its PFC stage is operating in discontinuous mode, substantial reduction in line-current harmonics is possible by applying a suitable frequency-modulation scheme. This paper derives a frequency-modulation scheme and proposes a practical implementation using a simple translinear analog circuit. A quantitative analysis on the total harmonics distortion (THD) of the line current when the circuit is subject to a limited range of frequency variation is presented along with some considerations for practical design. Experimental data obtained from a prototype confirms the effectiveness of the proposed frequency-modulation scheme. The proposed analog translinear circuit allows custom integrated circuit (IC) implementation, making it a viable low-cost solution to the elimination of line-current harmonics in switching regulators. Index Terms - Control, power factor correction, switch-mode power supplies.

This paper presents a general method of modeling, synthesizing, and analyzing quasi-resonant converters (QRC's), including actively clamped QRC's. First, the concept of the pulse-width modulation (PWM) switch model is generalized to encompass all PWM (nonisolated) converters. Then, by adding inductor-capacitor (LC) elements and auxiliary switches into the PWM switch, QRC families are synthesized. DC and small-signal analyses can be carried out based on these switch models. Furthermore, the duality relationship between zero-voltage-switching (ZVS) and zero-current-switching (ZCS) QRC's is established systematically and rigorously. Index Terms - Converter topologies, modeling of quasi-resonant converters, PWM switch, quasi-resonant converters, quasi-resonant PWM switch, synthesis of quad-resonant converters.

The characteristics of Cuk converters in discontinuous-capacitor-voltage mode operation are studied. A Cuk converter in this mode of operation is an inherent power-factor corrector and features soft turn-off switching. Simulation and experimental results are reported to verify the theoretical analysis. In addition, the advantages and disadvantages of power-factor correction circuits using Cuk converters in discontinuous-inductor-current mode operation and Cuk converters in discontinuous-capacitor-voltage mode operation are discussed. Index Terms - AC-DC power conversion, converters, power electronics, power quality.

The design of a fuzzy logic controller for dc/dc converters is described in this paper. A brief review of fuzzy logic and its application to control is first given. Then, the derivation of a fuzzy control algorithm for regulating dc/dc converters is described in detail. The propo11pel01-sosed fuzzy control is evaluated by computer simulations as well as experimental measurements of the closed-loop performance of simple dc/dc converters in respect of load regulation and line regulation.

The design, analysis and trade-offs of a novel method to sense the inductor and dc output currents of PWM converters are presented. By sensing and adding appropriately the currents in the transistor, rectifier and capacitors of a converter using current transformers, the waveforms of inductor and dc output currents can be reconstructed accurately while maintaining isolation. This method offers high bandwidth, clean waveform, practically zero power dissipation and simple circuit. The technique is applicable to all PWM converters in both continuous and discontinuous modes, and is most suitable for the implementation of current mode control schemes like hysteretic, PWM conductance control, and output current feedforward. This approach has been experimentally verified at a wide range of current levels, duty cycles, and switching frequencies up to 1.4 MHz.

Based on some new techniques which we have proposed for the modeling of PWM-controlled converters, the low-frequency behavior models of hysteretic current-mode controlled C uk converters, including the ones with coupled inductors, are developed. These models are simple, accurate and easy to use. Computer simulations based on such models are carried out for the analysis of the partial derivative of V(sub o)/partial derivative of V(sub i) and partial derivative of V(sub o)/partial derivative of I(sub C) transfer characteristics and transient responses. The simulations are also verified by experimental measurements.

Boost converters are widely used as power-factor-corrected preregulators. In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple. A major design criterion then is to ensure equal current sharing among the parallel converters. In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated. The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch. In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss. The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented. Simulation and experimental results are also given. Index Terms--Coupled inductors, current sharing, interleaved boost converters.

An actively damped bidirectional flyback converter is proposed. The converter's operation is examined in detail. All switches in the converter have zero-voltage-switching characteristics. A low-frequency behavior model and small-signal transfer functions are derived. It is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter. It is expected that such bidirectional converters will find wide applications in the interconnection of multiple sources of dc power to a common bus (e.g., in a dc uninterruptible power supply). Simulation and experiment results are also presented. Index Terms--Active clamping, bidirectional converter, flyback converter.

Although most power factor correction (PFC) circuits use the boost topology, the flyback topology does have the advantages of input-output isolation, inrush current limiting and voltage step-down capability. In this paper, the problems associated with flyback PFC circuits are identified. These problems are solved by using a novel regenerative clamping circuit. The circuit topology, analysis, design considerations and experimental results of the new flyback PFC circuit are presented. Index Terms--Flyback converter, power factor correction, regenerative clamping, soft switching.

The characteristics of actively clamped double-ended (ACDE) converters are studied. It is found that they possess interesting features such as near-zero output current ripple and requiring no magnetic reset winding. A low-frequency behavior model of the ACDE converter is derived, from which important relationships among output voltage [V.sub.o], input voltage [V.sub.i], and duty cycle D are obtained. When compared with other forward-derived converters, an ACDE converter has extra poles and zeros in the small-signal control-to-output and input-to-output transfer functions. The design criteria and experimental results are also reported. Index Terms--Active-clamping, double-ended converter, forward converter, forward-derived converters.

This paper describes a new technique to model the behavior of the magnetizing current in a transformer-coupled switch-mode dc-dc converter. The new technique uses a virtual magnetizing winding, together with a virtual magnetizing current source, to account for the effect of the magnetizing inductance on the switching operation of the transformer. By including the effect of the magnetizing current, the behavior model of a switch-mode converter can be made more complete. The model developed is particularly useful for the analysis and low-frequency behavior simulation of complex converters such as actively-clamped converters, where the magnetizing current significantly affects the characteristics of the converter. Index Terms--Low-frequency behavior model, virtual magnetizing winding.

In this paper, a simple control method is presented for a single-stage single-switch isolated power-factor-correction (PFC) regulator that can simultaneously achieve unity power factor and fast output voltage regulation while keeping the voltage stress of the storage capacitor low. The converter topology comprises essentially a cascade combination of a discontinuous-mode boost converter and a continuous-mode forward converter. The proposed control utilizes variation of both duty cycle and frequency. The role of varying the duty cycle is mainly to regulate the output voltage. Changing the frequency, moreover, can achieve unity power factor as well as low-voltage stress. Basically, the switching frequency is controlled such that it has a time periodic component superposed on top of a static value. While the time periodic component removes the harmonic contents of the input current, the static value is adjusted according to the load condition so as to maintain a sufficiently low-voltage stress across the storage capacitor. The theory is first presented which shows the possibility of meeting all three requirements using a combined duty cycle and frequency control. An experimental prototype circuit is presented to verify the controller's functions. Index Terms--Analog integrated circuits, power conversion harmonics, switched mode power supplies.

The complete dc characteristics of the three-phase modular power-factor-correction (PFC) converters using single-phase pulsewidth modulation (PWM) dc-to-dc converter modules for high-power application are studied. Using circuit averaging, the converter input and output quantities are determined numerically. Both the continuous and discontinuous output current modes of operation (CCM and DCM) are studied in detail. Near-unity power factor can be achieved with the converter modules operating in the DCM. An averaged model was used to study and determine the boundaries between DCM and CCM over the full period of the three-phase input voltage. It is found that high power factor is inherent in the converter system provided that the converters are operated in the DCM and the voltage conversion ratio is selected properly. The criteria for obtaining high power factor are analyzed and the optimal circuit parameters are determined to obtain the best achievable power factor. Both simulations and experimental results from a 1.5-kW prototype using full-bridge converter modules have confirmed the analysis. Index Terms--Ac/dc, modular converters, PFC, PWM.