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Several applications need a high power, high output voltage ac/dc converter. The structure includes a dc/dc resonant stage, which is fed from a three-phase line. Due to standards, rectified dc input voltage varies largely from 400 to 750 V affecting the adversely overall design and current levels. In fact, losses in the inverter become unbearable if both switching frequency and transferred power are desired beyond a certain level. In those cases, it is necessary to connect several switches in parallel. As an alternative, the new switches can configure a new modular structure instead, adding more flexibility in the control to compensate input voltage variations. As a result, the required circulating current is reduced to a half, with benefits in total power losses. Moreover, the nature of the topology allows a reconfiguration of the resonant net (LCC) for low power, reducing even further the minimum circulating current under those conditions (fluoroscopy, for instance). In this paper, the new multilevel resonant topology is mathematically modeled and proposed for radiography and fluoroscopy. An example illustrates the design procedure for a given application at 100 kW, 50–150 kV. [ABSTRACT FROM AUTHOR]

Currently, most of the capacitive deionization (CDI) research is oriented to improving the electrode materials. However, if the CDI overall efficiency is to be improved, it is necessary to optimize the CDI cell geometry and the charge/discharge current used during the deionization process. In this paper, an experimental CDI module is electrically characterized, and its performance is derived by solving the differential equations that represent the behavior of a total system. The solving method, which provides a detailed description of energy losses, is applied to a set of theoretical CDI modules whose properties are related to those of actual modules. This allows the extrapolation of the performance obtained to that of other modules with different geometries. From this information, it is possible to derive the optimum geometry that gives rise to the highest efficiency in the whole system for each charging current. The system equations allow an optimal charging current to be derived and an optimal energy-recovery performance to be achieved for any CDI cell. This charging current is a function of parasitic resistances and voltages on the cells along the energy transfer. The theoretical results are compared to experimental measurements conducted on actual CDI cells; good agreement with theoretical predictions was observed. [ABSTRACT FROM PUBLISHER]

The behavior of the series–parallel resonant converter with a capacitor as output filter is analyzed when operating under optimum switching conditions. A polynomial is deduced to quickly compute what switching frequency and duty cycle are necessary at the control to obtain the desired output voltage and power in the converter. This polynomial is so simple that it is suitable for being implemented in low-cost digital processors. It could provide, for instance, a start-up strategy guiding the power supply to a known set point, or it could generate alarms if the currents or voltages measured are larger than expected. In this paper, the steps to obtain such a model are described in detail. As an example, the coefficients of the polynomials are deduced when the series and the parallel capacitor are the same. The grade of accuracy of the model has been demonstrated through experimentation on a prototype. [ABSTRACT FROM AUTHOR]

Several control strategies have been defined for the control of high-voltage power supplies based on resonant topologies. In recent papers, an optimal control based on minimizing the circulating energy in the converter has been proposed. This control is obtained by switching one of the branches of a full-bridge inverter synchronously with the resonant current. In this paper, the problems associated to this issue are analyzed, and a way to implement optimal control is proposed. Moreover, the dynamic behavior of a PRC-LCC converter with a capacitor as output filter is obtained from the mathematical model and verified experimentally. From this study, a second feedback loop is proposed to control the output voltage. Experimental waveforms will demonstrate the dynamic behavior of the closed-loop power supply under extreme variations: full load, short circuit, and no load. [ABSTRACT FROM AUTHOR]

One of the major drawbacks of high-ratio step-up transformers is the high value of their secondary-side capacitor. This value is reflected at the primary side, giving rise to a nondesirable one. There are some converters which include this capacitor in the topology and can cope with it, and even more, they need it. In particular, in high-voltage applications, we will find transformers with a large capacitance value since they use high-ratio step-up transformers. In this kind of applications, it is always interesting not to have inductors at the output filter, with single-capacitor filters being preferred instead. Thus, one of the simplest topologies is the parallel resonant converter (PRC) with a single-capacitor output filter. It can be controlled by the switching frequency and/or duty cycle, which makes zero voltage switching feasible in the power switches. In this paper, the PRC modeling and design and the experimental results are shown in a prototype delivering 3.5 kV and 260 W. [ABSTRACT FROM AUTHOR]

In this paper, the guidelines to design a high-voltage power converter based on the hybrid series parallel resonant topology, PRC-LCC, with a capacitor as output filter are established. As a consequence of the selection of this topology, transformer ratio, and therefore secondary volume, is reduced. The mathematical analysis provides an original equivalent circuit for the steady-state and dynamical behavior of the topology. A new way to construct high-voltage transformers is also proposed, pointing out the advantages and establishing an original method to evaluate the stray components of the transformer before construction. The way to make compatible the characteristics of both, topology and transformer is illustrated in the frame of a practical application. To demonstrate the feasibility of this solution, a high-voltage, high-power prototype is assembled and tested with good performance and similar behavior to the one predicted by the models. Experimental results are shown on this particular. [ABSTRACT FROM AUTHOR]

In high-voltage dc power supplies (hundreds of kilovolts), avoiding the inductance in the output filter is an important asset. Thus, a capacitor as a unique component of that fitter is preferable. On the other hand, a high-voltage step-up transformer shows a high capacitance in its secondary, which can be included in a resonant stage. Both capacitances, i.e., one from the filter and the other from the transformer, are separated by the output rectifier. When this rectifier is on, they are in parallel; when it is off, they are disconnected. A resonant stage where a very large capacitor appears and disappears several times in one period is not linear and has not been dynamically modeled before. This paper shows two simple models for the parallel-series (LCC-type parallel resonant converter) resonant topology with a capacitor as output filter. Its dynamics and steady state are studied and constitute an important help for any designer. [ABSTRACT FROM AUTHOR]

In this paper, a simple method to obtain the small-signal model of discharge lamps, and particularly metal halide (MH) lamps, is proposed. A dc voltage source with a series resistor is used to supply the lamp at the required power level. Then, the lamp response against an input voltage step transient is analyzed. From this analysis, the parameters of the equivalent lamp model can be calculated. The proposed method allows obtaining the lamp model in a straight manner from a single test. With this technique, a 35-W MH lamp is modeled at two different power levels. A validation circuit, which includes a resistive ballast and a capacitance, is analyzed to evaluate the possibilities of the proposed modeling technique. The obtained experimental results are in good agreement with the theoretical analysis. The derivation of a time domain lamp model for SPICE-based computer simulators is also introduced. Finally, an example of application in low-frequency square-waveform electronic ballasts is presented. [ABSTRACT FROM AUTHOR]

Piezoelectric transformers (PTs) are an attractive solution to reduce size and weight in ac/dc converters. In this paper, a PT-based topology is presented together with a control method. As an application, an 8-W ac/dc adapter (110 VAC input, 12 VDC output) is presented operating at frequencies around 500 kHz. [ABSTRACT FROM AUTHOR]

Presents a study which described the characteristics of piezoelectric transformers as a solution to replace magnetic transformers in alternating current to direct current converters. Components of the converter power topology; Operation principle of the quantum-mode control; Comparison of the converter protection in frequency and quantum mode control.

Presents the development of an automatic deceleration system for a winding machine based on a microcontroller in a siderurgy factory. Possible situations in the deceleration process; Detection of the right deceleration point; Purpose of using a microcontroller unit.