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A new soft-switched, current-driven full-bridge converter is presented. The structure utilizes a simple snubber formed by two unidirectional switches and a capacitor to realize soft-switching operation over a wide line and load range. All primary-side switches are operated with zero-current switching (ZCS) and the snubber switches are operated with zero-voltage switching. The energy used for soft-switching is self-adaptable. For a given input current, the snubber capacitor is charged to the minimum required energy for ZCS of the switches. Thus, less resonant energy is used and the conduction loss can be kept minimal. The cyclical switching operation and control of the converter will be discussed. By compromising the voltage stress on the switches and loss of duty cycle (i.e., the regulation range), an optimized design procedure of the circuit elements is derived. The input voltage range and load variation that ensure both output voltage regulation and soft switching are determined. By studying the small-signal characteristics of the entire system, a current-controlled feedback control circuit has been implemented with a DSP. The experimental results measured on a 5-kW, 530-V/15-kV prototype confirms the advantages of the proposed converter. Index Terms--Adaptable soft switching, dc--dc conversion, high-voltage converter, zero-current switching (ZCS).

A high-voltage zero-voltage-zero-current-switched dc-dc converter with low voltage stress is presented in this paper. Its circuit structure is extended from a previously developed zero-voltage-switched dc-dc converter consisting of six series-connected switching devices, one three-phase transformer, and an output current tripler. The voltage stress on each switching device is only one-third of the input voltage. Compared with the previous converter, apart from retaining the advantage of having low voltage stresses on the switches, the main advancements of the proposed converter have also included 1) wider soft-switching range; 2) elimination of circulating energy on the primary side during the freewheeling stage; and 3) use of phase-shift pulsewidth modulation in output voltage control. Detailed topological operations and steady-state characteristics of the converter will be given. A 2.2-kW, 990-V/110-V dc-dc converter prototype has been built and tested. Experimental results are favorably compared with the theoretical predictions. Index Terms--DC-DC conversion, high-voltage converter, soft-switching converters.

A few simple switching structures, formed by either two capacitors and two-three diodes (C-switching), or two inductors and two-three diodes (L-switching) are proposed. These structures can be of two types: 'step-down' and 'step-up.' These blocks are inserted in classical converters: buck, boost, buck-boost, Cuk, Zeta, Sepic. The 'step-down' C- or L-switching structures can be combined with the buck, buck-boost, Cuk, Zeta, Sepic converters in order to get a step-down function. When the active switch of the converter is on, the inductors in the L-switching blocks are charged in series or the capacitors in the C-switching blocks are discharged in parallel. When the active switch is off, the inductors in the L-switching blocks are discharged in parallel or the capacitors in the C-switching blocks are charged in series. The 'step-up' C- or L-switching structures are combined with the boost, buck-boost, Cuk, Zeta, Sepic converters, to get a step-up function. The steady-state analysis of the new hybrid converters allows for determing their dc line-to-output voltage ratio. The gain formula shows that the hybrid converters are able to reduce/increase the line voltage more times than the original, classical converters. The proposed hybrid converters contain the same number of elements as the quadratic converters. Their performances (dc gain, voltage and current stresses on the active switch and diodes, currents through the inductors) are compared to those of the available quadratic converters. The superiority of the new, hybrid converters is mainly based on less energy in the magnetic field, leading to saving in the size and cost of the inductors, and less current stresses in the switching elements, leading to smaller conduction losses. Experimental results confirm the theoretical analysis. Index Terms--DC-DC hybrid converter, switched capacitor, switched inductor, steady-state analysis.

A high-voltage dc-dc converter with low voltage stress on the power switches and high output current capacity is presented. This converter exhibits three distinct features. First, the voltage stress on the primary switches is only one-third of the input voltage, so that switches of low voltage rating and thus of low on-resistance can be used. This leads to reduced conduction loss. Second, all the switches are soft-switched, so that the switching loss can be reduced. Third, the rectifier is a current tripler, so that the output current capacity, and thus the power handling capacity of the converter are increased. A 5.1-kW, 1000-V/48-V dc-dc converter prototype has been built and tested. Experimental results are favorably compared with theoretical predictions. Index Terms--DC-DC conversion, high-voltage converter, high load current converter.

A novel zero-voltage zero-current switching (ZVZCS) three-level converter with pulsewidth modulation (PWM) phase-shift control is proposed. The ZCS of the lagging switch is obtained by using a regenerative passive snubber in the secondary. In order to reduce the voltage stress on the rectifier's diodes, a few passive elements are inserted into the primary: a small inductance, two diodes, and a small additional winding of the main transformer. In each half-cycle, one of these diodes will conduct for a short time in order to clamp the voltage of the snubber's capacitor, and thus, the rectifier stress, at ([n.sub.2]/[n.sub.1])([V.sub.in]/2), [n.sub.1], and [n.sub.2] being the transformer's primary and, respectively, secondary turns number. The three-level configuration allows for the reduction of the voltage stress across the power switches to half of the input voltage [V.sub.in]. The conditions for assuring ZVS of the leading switch and ZCS of the lagging switch are found. Design constraints on the parallel capacitances of the switches of the leading switch, on the snubber's holding capacitor, and on the additional inductance and winding are hence established, allowing for an optimized design of the converter parameters. A dc analysis allows for the calculation of the effective duty cycle, which enjoys a boost effect due to the proposed snubber. Thus, a further reduction of the primary current stress and rectifier voltage stress is obtained. All the improvements conclude in a high efficiency. The influence of the choice of the parameters' values on the regulation capability is pointed out. Experiments on a prototype of 4.5 kW confirm the results. Index Terms--Pulsewidth modulation (PWM), three-level converter, zero-voltage zero-current switching (ZVZCS).

The cyclically switching operation of a novel zero-voltage-zero-current-switching three-level converter is briefly presented. Based on a steady-state time-domain analysis of each equivalent switching topology, an average model is obtained. Small-signal open-loop ac line-to-output, control-to- output, and output-current-to-output-voltage transfer functions are deducted. The stability, gain margin, and phase margin of the open-loop transfer functions are studied. After designing the closed loop, the study of the audiosusceptibility and closed-loop output impedance allows for a dynamic analysis: the transient responses to changes in the input voltage and load current are obtained. The results got from the small-signal modeling are compared and confirmed by those obtained by PSPICE simulation and those measured in the laboratory, on an experimental converter of 4.5 kW. Index Terms--Converters, modeling, simulation, transfer-functions, transient-response.

Two structures, a switched-capacitor (SC)-based boost converter and a two-level inverter, are connected in cascade. The dc multilevel voltage of the first stage becomes the input voltage of the classical inverter, resulting in a staircase waveform for the inverter output voltage. Such a multilevel waveform is close to a sinusoid; its harmonics content can be reduced by multiplying the stage number of the SC converter. The output low-pass filter, customary after a two-level inverter, becomes obsolete, resulting in a small size of the system, as the SC circuit can be miniaturized. Both stages are operated at a high switching frequency, resulting in a high-frequency inverter output, as required by some industrial applications. A Fourier analysis of the output waveform is performed. The design is optimized with reference to the nominal duty-cycle for obtaining the minimum total harmonic distortion. Simulations and experiments on two prototypes, one with a five-level output and one with a seven-level output, confirm the theoretical analysis. Index Terms--Boost converter, multilevel output waveform inverter, small-signal analysis, switched capacitor (SC).

A detailed analysis and optimized-oriented design of a family of three-level soft-switching converters is presented. The zero-voltage-switching (ZVS) of the outer switches and zero-current-switching (ZCS) of the inner switches is realized by employing a pulse-width-modulation (PWM) phase-shift control and a secondary-assisted passive snubber. The switching operation is discussed by comparing the results produced by the use of different passive snubbers (the author's original one and literature-available ones). The voltage on the rectifier diodes is clamped at a reasonable value, specific to each one of the six snubbers taken into consideration. The voltage stress on each transistor is reduced to half of the input voltage. Lower rated transistors and rectifier diodes can be used, thus reducing the conduction losses. Before turning on/off the inner switches, the snubber's capacitor voltage determines the fall of the primary current to zero, thus avoiding wasteful energy circulation and assuring ZCS. The snubber's energy is recuperated to the load. The outcome of these improvements is a high efficiency in energy processing. Soft-switching-oriented constraints on the converter parameters are expressed as implicit equations, whose graphical solution permits the optimized design of the parameters in order to ensure ZVZCS. A comparative analysis of the effective duty cycle and the boost effect of it, due to the use of the secondary snubber, is performed. The influence of the choices of the parameters values on the regulation capability is pointed out. Experimental results prove the expected high performances of the optimized converters. Index Terms--Regenerative passive snubber, three-level (TL) converters, zero-voltage zero-current-switching (ZVZCS) converters.

A new circuit is proposed for a steep step-up of the line voltage. It integrates a switched-capacitor (SC) circuit within a boost converter. An SC circuit can achieve any voltage ratio, allowing for a boost of the input voltage to high values. It is unregulated to allow for a very high efficiency. The boost stage has a regulation purpose. It can operate at a relatively low duty cycle, thus avoiding diode-reverse recovery problems. The new circuit is not a cascade interconnection of the two power stages; their operation is integrated. The simplicity and robustness of the solution, the possibility of getting higher voltage ratios than cascading boost converters, without using transformers with all their problems, and the good overall efficiency are the benefits of the proposed converter. Index Terms--Pulsewidth-modulated (PWM) dc-dc converter, step-up switching converter, switch capacitor.

This paper presents a generalized circuit structure of bi-directional switched-capacitor dc/dc converters that feature voltage step-down, voltage step-up, and bi-directional power flow. The starting point is the derivation of two structures of single-capacitor bi-directional converter cells. Current control scheme is applied in the capacitor-charging phase, resulting in a near-constant capacitor charging current and low electromagnetic interference. A converter string is then formulated by cascading a number of converter cells, in order to meet the input and output voltage requirements and conversion efficiency. By paralleling two similar strings and operating them in the anti phase, the overall converter input current becomes continuous. A reduced-order modeling and state-space averaging technique are used to study the static and dynamic behavior of the converter. The theoretical conversion efficiency in the step-down and step-up mode, respectively, is investigated for different voltage-conversion ratios and numbers of stages. The performance of the proposed structure is experimentally verified on a 5-V/12-V prototype. Index Terms--DC-DC conversion, power electronics, switched-capacitor (SC) circuits.

Exact nonlinear differential equations of boost pulsewidth modulation converters (either with hard-switching or soft-switching, in continuous and discontinuous conduction mode) are obtained, without using average approximations. An extended system of equations also contains the differential equation of the integrated error between the reference and the output voltage. A positive-definite Lyapunov function is defined, including in its expression a nonlinear integral of type Lurie. Sufficient conditions for the Lyapunov stability of the system are determined. Consequently, constraints on the feedback circuit parameters that assure the large-signal stability of the system are formulated. These constraints relate the parameters of the feedback circuit with the values of the power stage elements, load, switching frequency, steady-state duty-cycle. For different values of the steady-state duty-cycle, graphical boundaries which assure the large-signal stability for all the variation of the load are designed. Simulations and experiments confirm the stability of the design. Index Terms--Boost regulator, large-signal stability, Lyapunov stability.

A new type of zero-voltage-transition pulsewidth modulation (PWM) dc-dc converter is developed by adding two active switches and three diodes to the structure of a quasi-resonant converter. The resonant capacitors are not discrete elements, their role is played by the parasitic capacitances of the MOSFET's. By adjusting the interval between the operation of the active switches, a duty-cycle control is obtained. Soft-switching is ensured for all switches for a wide line range and load range. One of the additional diodes is connected in the input circuit and the energy flow in the resonant stage is transferred from a path defined by the two additional transistors to a path given by the two additional diodes in the resonant tank; as a result, the resonant capacitor voltage is prevented from surpassing the input voltage; it drops to zero before the main switch is turned on. All switches are subjected to voltage and current stresses as those in their PWM classical counterparts, implying small conduction losses. The new converter exhibits a high efficiency and good regulation capability.

A dc-ac inverter containing no inductors or transformers is presented. The role of the magnetic devices is played by a switched-capacitor (SC) circuit, formed by two subcircuits. Each SC-subcircuit contains 15 basic cells, each one formed by one capacitor, two MOSFET's and two diodes. The sinusoidal output waveform is realized in a staircase, formed by 64 steps. To achieve each step, the inverter operates like a step-up dc-dc converter: by using a certain number of SC-cells, the input voltage is boosted to the voltage required by the step in consideration. Each step is implemented in a large number of switching cycles. In each cycle, the inverter goes through four phases; according to a designed switching sequence, some of the capacitors of the SC-cells involved in the respective step are in a charging process from line, while the others are in a discharging process to the load. The phases 2 and 4 have a regulation role only. A duty-cycle control is used. A Fourier analysis evidences the clean ac output waveform. The inverter exhibits low weight, high power density, and enhanced regulation for large changes in line and load. Index Terms - DC-AC switching-mode inverter, duty-cycle regulation, switched-capacitor circuit.

A method for determining boundaries on the feedback gains in a switching regulator with multiple feedback, in order to ensure stability for large changes in the load values, is developed. Using an original approach for time-domain analysis, a large-signal, nonlinear, discrete-time model of the closed-loop converter is obtained; the model's equations are expressed in disturbances of the state variables due to disturbance in the load. The first step toward a global stability design is to find the constraint that ensures local stability around the operating point: the nonlinear terms (products of disturbances) are neglected in the model, the z-transform is applied to the linearized equations, and the condition that the eigenvalues are situated inside the unit circle is imposed. The nonlinear model, including the nonlinearity of the pulsewidth modulation (PWM), due to possible saturation, is then considered. A new constraint in terms of feedback gains is found in order to ensure that one and only one real equilibrium point (i.e., the quiescent operating point) exists. Putting together the constraints, boundaries on the feedback gains are found. The method is developed for converters containing two reactive elements, operating in continuous conduction mode. An example of a boost converter with inductor current and output voltage feedback is presented in detail. The large-signal stability of the design is checked by using the state-plane portrait and time-domain simulation. Index Terms - Large signal stability design, modeling technique, power electronics.

A buck converter operating at constant switching frequency, whose active switches and recovery diode commutate at zero-voltage-switching (ZVS), with zero capacitive turn-on losses, is proposed. By using the parasitic capacitances of the switches as resonant capacitors, multiresonance is created. The resonant stage takes place only after the resonant inductor has been discharged, thus avoiding a resonant current peak; the devices are subjected to the same stresses as their counterparts in conventional hard-switching converters. A high efficiency is obtained.

A switched-capacitor-based (SC) step-up dc converter is proposed. It contains no inductors and transformers, thus it can be realized in small size, exhibiting low weight and high power density. Two switched-capacitor circuits, operating in antiphase in each half-cycle, are used to control the energy flow from an unregulated voltage source to a regulated output. The capacitors are charged and discharged according to a designed sequence. To enhance the line and load regulation capability, in each half-cycle, each charging interval is split into two subintervals, which are followed by noncharging subintervals whose duration is dictated by the pulsewidth modulation (PWM) feedback circuit. The new converter is advantageous for applications in which significant line drops are likely to occur.

A soft-switching dc-dc converter, in which the resonant capacitor is replaced by a switched-capacitor circuit, is presented. The new system incorporates a switching technique at zero-current or zero-voltage for each switch and an operation at constant switching frequency. The first feature is due to the presence of a resonant circuit, which shapes the switches' current and voltage waveforms in a sinusoidal form. It assures minimal switching losses. The switched-capacitor circuit determines a simple, discrete control, extends the region in which the soft-switching condition is fulfilled to large values of the load or small values of the input voltage, and prevents the current stress on the electronic devices from increasing with the input voltage. An original design approach allows for choosing the element values so as to get both soft-switching and regulation over a large range of input voltage and load values. Analysis, computer simulation and experiments indicate the operation principles of the new structure and render evident its performances, such as high efficiency and good regulation capability.

A new step-up dc-to-dc converter with high power density is presented. It contains no inductors or transformers. The controlled energy transfer from an unregulated voltage source to a regulated output voltage is realized through a switched-capacitor (SC) circuit. The operation of the switches in the power stage is dictated by a PWM-type feedback circuit. The new regulator is simulated by using an averaged state-space approach. The transient and steady-state waveforms, as well as the ac small-signal input-to-output and control-to-output transfer functions are obtained by both simulation and experiments. The power supply, implemented for a nominal power of 15 W, and input-to-output voltage ratio of 5/12, features high efficiency for this class of powers, small output voltage ripple, continuous input current, low weight and small size.

A new method for time-domain analysis of power electronics circuits is developed based on the following principles: a) at each instant, the switching topology is a linear time-invariant circuit; b) at each instant, the voltage across a capacitor and the current through an inductor have a certain value, like an independent voltage- or current source, respectively; c) generally, no switching relationship between the externally and internally controlled switches may be assumed; d) prior knowledge of the internally controlled switches' operation is not available; and e) the switching action may change the response of the circuit immediately after the switching moment, implying that some constraints may be in violation of the presumed switches' states. The algorithm is based on solving a system of algebraical modified nodal equations at each integration step. The number of systems to be solved equals the number of topologies the converter goes through in a cycle. This feature, and the fact that no solutions of time-differential equations or Laplace transform inverses are required, cause the algorithm to be a fast one. At each step, the presumed state of all the switches is checked, and if some constraints are violated, the program looks for another valid topology. An example, with parasitic effects taken into account, is presented; the experimental results, as well as the simulation results obtained by using other available algorithms, confirmed the accuracy of the results achieved with the presented approach.

Nowadays the groundbreaking tools of contactless energy transfer reveals new opportunities to supply portable devices with electrical energy by eliminating cables and connectors. One of the important applications of such technology is the energy providing to electric and hybrid vehicles, (EV) and (HEV). These contribute to the use of cleaner energy to protect our environment. In the present paper, after exposing the contactless energy transfer (CET) available systems, we examine the appropriateness of these systems for EV. After such exploration, it is shown that the most suitable solution is the inductive power transfer (IPT) issue. We analyze such procedure in general and indicate its main usages. Next, we consider the practice of IPT in EV and the different option in the energy managing in EV and HEV concerning battery charging. Following, we review the modes of using the IPT in immobile case and in on-road running. Following, the modeling issues for the IPT system escorting the vehicle structure are then exposed. Lastly, the electromagnetic compatibility (EMC) and human exposure analyses are assessed involving typical appliance. [ABSTRACT FROM AUTHOR]

The field of switched networks continues to grow rapidly due to advances in semiconductor technology. Switching is employed in designs ranging from microwatts to high switching speeds, and in almost all fields of electronics. Problems in the analysis and design of switching circuits are complex and cannot just be solved by traditional methods based on s-domain closed-form transfer functions. Factors such as nonlinearities and parasitics have to be addressed.

This paper presents a technique for calculating the ac line-to-output and control-to-output transfer characteristics of dc/dc converters, in which the time instants switching from one topology to the next one are a priori unknown and are determined by threshold conditions (i.e., by the time evolution of the converter waveforms). Describing functions are defined for small perturbations in either the input voltage or the control signal. After injecting a sinusoidal perturbation at the frequency of interest into the converter, the fundamental component of the output spectrum is determined. The describing functions are thus evaluated and provide the required ac transfer characteristics. The proposed method is integrated with a previously developed time-domain simulation algorithm, which is based on monitoring the switches positions, allowing the simulator to find automatically the switching instants and topological sequence of operation. Different examples are illustrated, including a classical pulse-width-modulated (PWM) converter, a current-programmed PWM regulator, and a switched-capacitor converter. The simulated results are compared with the experimental measurements and the results in the available literature. Index Terms--Circuit simulation, power electronics, switching circuits.

A dc-dc boost converter operating under zero-voltage-transition conditions is presented. Its excellent performance deserves a detailed analysis. An equivalent circuit is derived in order to characterize the switching sequence. It contains an equivalent current source and an equivalent voltage source whose nonlinear functions take different forms for each switching topology. The small-signal open-loop and closed-loop transfer functions, including the audio susceptibility are derived. Design-oriented stability criteria are formulated. The theoretical time-domain response and Bode characteristics are checked by experiments or PSPICE simulation. Index Terms--PWM boost converter, small-signal analysis, zero-voltage switching.

An introduction is presented in which the guest editors discuss the theme of the issue, Applications of Predictive Control in Micro grids.