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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 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).

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.

A new concept of high-voltage dc-dc power conversion is presented in this paper. Its distinctive feature lies in distributing the high input voltage asymmetrically between two primary-side series-connected switch pairs. This allows using switches of optimal ratings in their respective class: the low-voltage switch pair implemented with MOSFETs only, and the high-voltage switch pair implemented with insulated gate bipolar transistors (IGBTs) only. As the switches in a switch pair are of the same type and voltage rating, they are maximally utilized. With an active snubber on the secondary side of the isolation transformer, a hybrid zero-voltage-switching-zero-current-switching (ZCS) scheme, which is different from the zero-voltage and zero-current-switching technique, is realized and makes all IGBTs be zero-current-switched and all MOSFETs be zero-voltage-switched from very light load to full load condition with minimal circulating energy. The ZCS snubber energy is completely released to the load, leading also to a duty-cycle gain. The operating principles, dc analysis, and design guidelines will be given. A 2-kW, 1500/48-V experimental prototype has been built and evaluated. The measured efficiency of the converter is found to be 92.4% at the rated condition. [ABSTRACT FROM AUTHOR]

A new current-driven soft-switched full-bridge converter is presented in this paper. By connecting a switchedcapacitor snubber in parallel with the primary winding of the coupling transformer, all main switches are zero-current-switched (ZCS) and the switches in the snubber are zero-voltage-switched (ZVS). The proposed converter has the following key features. First, the transformer leakage inductance is utilized as a part of the resonant circuit for the soft-switching actions. Second, the snubber capacitor voltage is adaptively controlled: the capacitor is charged to the minimum necessary energy for switching the main switches at zero current, depending on the actual value of the input/load current. Thus, less resonant energy is circulated. Third, there is no extra voltage stress on the switches and the current through the switches is limited to the value of the input current. Consequently, the conduction losses are kept minimum. The cyclical switching operation and control of the converter are described. A tradeoff design of the snubber circuit is given: the requirement of reducing the duration of the resonant intervals for minimizing the dutycycle loss is superimposed on the requirement of getting ZCS for a very large range of the line voltage and load. A 530-V/15-kV, 5-kW prototype has been built and evaluated. The experimental results confirmed the theoretical predictions. A comparative study on the converter efficiency with and without the proposed snubber circuit is given, showing the superiority of the proposed solution. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]