Recently, small-scale and highly-distributed photovoltaic power sources have been researched for the high generation efficiency even under severe partial shading conditions. However, power conditioning systems for the sources needs high step-up voltage gain due to the low output of the generating sources. This paper presents a newly-suggested high step-up topology employing a Series-connected Forward-FlyBack (SFFB) converter, which has a series-connected output for high boosting voltage-transfer gain. SFFB is a hybrid type of forward and flyback converter, sharing the transformer for increasing the utilization factor. By stacking the outputs of them, extremely high voltage gain can be obtained with small volume and high efficiency even with a galvanic isolation. The separated secondary windings in low turn-ratio reduce the voltage stress of the secondary rectifiers, contributing to achievement of high efficiency. The single-ended scheme is also beneficial to the cost competitiveness. In this paper, the operation principle and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 100 W SFFB DC/DC converter hardware prototype has been implemented for experimental verification of the proposed converter topology.

Series-Connected Forward–Flyback Converter for High Step-Up Power Conversion

This paper describes a boundary-mode forward-flyback converter (BMFFC) with zero-voltage switching that is able to process power efficiently. The theoretical analysis and operating principle of the BMFFC are presented in detail. A nondissipative LC snubber that recycles energy to the input source is employed in order to suppress the voltage spike caused by the leakage inductance of the transformer. The relatively large snubber capacitor also significantly reduces turn-off loss. Following a detailed design procedure, a 200 W prototype with a 25-50 V dc input and 230 V dc output was constructed and tested in order to evaluate the performance of the BMFFC.

A Boundary-Mode Forward-Flyback Converter With an Efficient Active LC Snubber Circuit

This paper describes a Boundary Mode Forward-Flyback Converter (BMFFC) with zero-voltage switching that is able to process power efficiently. The theoretical analysis and operating principle of the BMFFC are presented in detail. A non-dissipative LC snubber that recycles energy to the input source is employed in order to suppress the voltage spike caused by the leakage inductance of the transformer. The relatively large snubber capacitor also significantly reduces turn-off loss. Following a detailed design procedure, a 200W prototype with a 25-50VDC input and 230VDC output was constructed and tested in order to evaluate the performance of the BMFFC.

Zero voltage switching Forward-Flyback Converter with efficient active LC snubber circuit

This paper presents a zero-voltage switching (ZVS) forward-flyback DC-DC converter, which is able to process and deliver power efficiently over very wide input voltage variation. The proposed ZVS forward flyback DC/DC converter is part of a Micro-inverter to perform input voltage regulation to achieving maximum power point tracking for Photo-voltaic panel. The converter operates at boundary between current continuous and discontinuous mode to achieve ZVS. Variable frequency with fixed off time is used for reducing core losses of the transformer, achieving high efficiency. In addition, non-dissipative LC snubber circuit is used to get both benefits: 1) the voltage spike is restrained effectively while the switch is turned off with high current in primary side; 2) the main switch still keeps ZVS feature. Finally, experiment results provided from a 200W prototype (30Vdc-50Vdc input, 230Vdc output) validate the feasibility and superior performance of the proposed converter.

Forward-flyback mixed ZVS DC-DC converter with non-dissipative LC snubber circuit

In this paper, a new soft switching forward-flyback DC-DC converter is proposed. Due to the leakage inductance of the transformer, conventional forward-flyback converter suffers from low efficiency and high switch stress. For practical implementation of this converter, snubber and clamp circuits are necessary. RCD snubber can limit the voltage spike across the primary switch however the energy of the leakage inductance is dissipated in a resistor. In this study a forward-flyback DC-DC converter is introduced. The auxiliary circuit has only passive elements and thus, the control circuit is simple and is like a regular PWM DC-DC converter. The auxiliary circuit provides ZVS condition for primary switch at turn-off instances. In this paper, operating principles and theoretical analysis are given. Also, simulation results are presented to verify the validity of theoretical analysis.

Soft-single-switched dual forward-flyback PWM DC-DC converter with non-dissipative LC circuit

This paper presents a novel DC-DC converter where both forward and Flyback actions are mixed. Previously, we proposed this converter that has prominent features of reducing the voltage of main switch and the current ripple of output inductor, and as a result, the high efficiency and the size reduction were obtained as reported in the previous paper. And, this paper presents that this converter has four operation modes when the turns ratio of the second and the third windings of the transformer is set to be a certain value. Furthermore, these operation modes are analyzed through the extended state-space averaging method, and are confirmed by simulation. These characteristics are shown by means of a three-dimensional graphics method. This paper presents the detailed analyses of static characteristics for the four operation mode used three-dimensional expression of load characteristics with another winding turns ratio by the extended state-space averaging method.

T. Ninomiya

Papers

Complete analysis of steady-state and efficiency considerations in a Forward-Flyback Mixed Converter