Current-fed Converter Research Articles

Gyrator Realization Based on a Capacitive Switched Cell

Efficient power gyrator realization by means of a controlled switch cell is presented. It is shown that a switching cell may be controlled so as to acquire low-frequency gyrative characteristics (on average). A realization suitable for operation with current sources is presented, that employs a switched capacitor. Due to the capacitive input, a gyrator of this nature is suitable for operation with current sources. The main applications of such gyrators are expected in superconductive magnetic energy storage systems and current-fed converters, due to the stiff-current characteristic imposed by a magnetic storage element. Other possible applications include sources with softer i-v characteristics, such as photovoltaic generators and sources of significant output inductance

A High-Performance, Integrated Magnetics Scheme for Buck-Cascaded Push–Pull Converter

This letter proposes a new integrated magnetics scheme for the buck cascaded current-fed push-pull converter. While integrating the transformer and inductor into a common structure, the proposed scheme also alters the operating characteristics of the basic converter. This leads to several advantages such as, continuous output current, zero voltage switching (ZVS), and zero current switching (ZCS) for the switches of the push-pull stage, and reduced conduction losses. The principle of operation of the proposed scheme is analyzed using the gyrator-capacitor model. Experimental results from a 12 V/5 A proof-of-concept prototype are presented demonstrating the advantages of the proposed scheme.

A new power converter for fuel cells with high system efficiency

This paper presents a new high-efficiency grid-connected single-phase converter for fuel cells. It consists of a two-stage power conversion topology. Since the fuel cell operates with a low voltage in a wide voltage range (25 V–45 V) this voltage must be transformed to around 350–400 V in order to be able to invert this dc power into ac power to the grid. The proposed converter consists of an isolated dc–dc converter cascaded with a single-phase H-bridge inverter. The dc–dc converter is a current-fed push-pull converter. The inverter is controlled as a standard single-phase power factor controller with resistor emulation at the output. Experimental results of converter efficiency, grid performance and fuel cell dynamic response are shown for a 1 kW prototype. The proposed converter exhibits a high efficiency in a wide power range (higher than 92%) and the inverter operates with a near-unity power factor and a low current THD.

Performance evaluations of three-phase current-fed soft switching PWM converter with switched capacitor-type quasi-resonant snubber

A novel prototype topology of a three-phase current-fed PWM converter with a switched capacitor type quasi-resonant snubber is proposed in the paper, which can operate under the principle of zero current switching (ZCS) commutation. However, soft switching performance is affected by output DC current in the proposed quasi-resonant snubber. In particular, PWM current is decreased in the small current region with DC current on the output side, because the charging and discharging period of a switched capacitor increases as the output DC current decreases. The operating performance in the small current region with DC current on the output side, for which performance is problematic in this converter, is investigated in the paper. Further, converter performances from the relationship between soft switching performance and the charging and discharging periods of the switched capacitor are estimated on the basis of the experimental results by a laboratory prototype of this converter.

A novel three-phase, current-fed ZCS-PWM converter incorporating a single resonant DC link soft commutation snubber

This paper presents a novel prototype three-phase current-fed PWM converter with a switched-capacitor-type resonant DC link commutation circuit operating with a new optimum PWM pattern strategy, designed with consideration for a low-pass filter. This converter can operate based on the principle of zero current soft-switching commutation. First, the steady-state operating principle of this converter with a new resonant DC link snubber circuit is described in relation to an equivalent operating circuit, together with the practical design procedure of the switched-capacitor-type resonant DC link circuit. Second, the three-phase current-fed PWM converter with the switched-capacitor-type resonant DC link circuit is discussed from a theoretical viewpoint based on a design example. An actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open-loop control scheme so as to obtain a new optimum PWM pattern. Finally, an experimental setup of this converter is demonstrated in a laboratory to confirm the zero current soft-switching commutation of this converter. Comparative evaluations between current-fed hard-switching PWM and soft-switching PWM converters are implemented from the viewpoint of PWM converter characteristics. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 57–67, 2000

New conceptual three-phase current-fed soft switching pulse width modulation converter with switched capacitor type resonant dc link

This paper presents a novel prototype of three-phase current-fed PWM converter with a switched capacitor type resonant dc link snubber circuit, which can basically operate under a principle of zero current soft switching commutation. The optimum PWM pattern-based control scheme proposed by the authors is effectively applied for this active converter. In this paper, the steady-state operating principle of a new converter circuit treated here is described. The practical design procedure of this converter is discussed from a theoretical point of view. The feasible experiment to confirm zero current soft switching commutation of this converter is concretely implemented and evaluated herein.

Current-fed three-phase and voltage-fed three-phase active converters with optimum PWM pattern scheme and their performance evaluations

This paper describes a new approach to select the optimum sinewave pulsewidth modulation (PWM) patterns suitable for a large-capacity current-fed active PWM power converter and a practical design procedure to determine circuit constants of a low-pass filter connected to suppress higher line current harmonics flowing into the utility-grid AC power source. A feasible test is implemented by building a prototype 500 kW three-phase current-fed PWM power converter which is designed and controlled on the basis of the proposed considerations. It is verified from a practical point of view that these new conceptual considerations are more effective and acceptable to minimize higher harmonic current components flowing into the utility-grid AC power source. This experimental setup provides highly efficient steady-state characteristics of the current-fed three-phase PWM power converter under the operating condition of a unity power factor correction and sinewave line current shaping schemes. Furthermore, this unique optimum PWM pattern derived from the theoretical method proposed here is conveniently applicable to a voltage-fed three-phase PWM converter. It is verified that this optimum PWM pattern provides excellent switching performance with a lower switching frequency mode than the conventional carrier-based PWM scheme.

Current-fed multiresonant isolated DC-DC converter

A novel topology, current-fed multiresonant dc-dc converter (CF-MRC) was studied theoretically and experimentally. The new topology differs from previously described current-fed push-pull parallel-resonant topologies in the fact that the output is coupled to the current of the resonant inductor and in the addition of a second capacitor across the transformer. The main features of the proposed converter are an inherent protection against a short and open circuit at the output, a high voltage gain and zero voltage switching (ZVS) over a large range of output voltage. These characteristics make it a viable choice for applications, such as a high voltage capacitor charger, that require controllable current sourcing over a wide output voltage swing.

Stability in high-output-voltage push-pull current-fed converters

The relationship between the magnetizing inductances of a transformer and of a choke coil in high-voltage power supplies is studied. The analysis defines the conditions for high switching frequency and stable operation of high-voltage power supplies without power loss increases. This approach is confirmed by the implementation of a high-voltage power supply operating at 200 kHz with an efficiency of 86%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Considerations on the relationship between distributed capacitance and iron loss in high-voltage transformers

This paper describes the results of an analysis on the relationship between distributed capacitance and iron loss in a high-voltage transformer applied to a push-pull current-fed converter in a high-voltage power supply. There are two operating modes in a push-pull current-fed converter; a boost mode and buck mode. In both modes, the maximum amplitude of magnetic flux density in the transformer decreases with increasing distributed capacitance. The reason for this is that the product of the transformer voltage and time decreases as the capacitance increases. Consequently, when distributed capacitance exists in a transformer, the transformer temperature rise due to iron loss is smaller than that in transformers without distributed capacitance. This indicates that the transformer temperature rise due to iron loss, which varies along with the distributed capacitance, needs not be taken into consideration in transformer thermal design even if the distributed capacitance increases in a high-voltage transformer.

A Simplified Analytical Model for a Current-Fed Force-Commutated Converter

The current-fed force-commutated converter (CFFCC) has recently received considerable attention in the electric drives area. It may also have future power conversion applications in electric utility systems. In order to facilitate the study of CFFCC systems a simplified converter model is developed and investigated in this paper. The simplified model is a quasi-steady-state representation based on an average value and fundamental frequency formulation of the circuit equations. Comparisons with exact circuit solutions and a detailed analog computer simulation demonstrate the validity of the simplified model under steady-state and transient conditions.