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This paper proposes a high-efficiency bidirectional dual-active-bridge (DAB) inverter using a novel hybrid modulation for a stand-alone power generating system with a low input voltage. The proposed DAB inverter consists of a DAB dc–dc converter and a synchronous rectifier (SR) for unfolding. The DAB dc–dc converter transforms the low dc voltage into a rectified sine wave that pulsates twice the grid frequency. The rectified sine wave unfolds into the grid voltage by SR. The proposed hybrid modulation combines a phase shift control and a variable frequency control. The variable frequency control converts the nonlinear function of the phase shift angle into a linear function and controls the output power. This leads to a simple closed-loop control for the sinusoidal current waveform, a low harmonic distortion, and a high-voltage conversion ratio without an increase of the transformer turn ratio. Since the proposed DAB inverter has only a single power conversion stage, it has a simple structure, high power density, and low cost. It also has a high efficiency of 94.2% by a zero-voltage switching (ZVS) turn on of the switches in two full bridges (FBs). The operation principle of the proposed DAB inverter using this hybrid modulation is analyzed and verified. Experimental results for a 1-kW prototype are obtained to show the performance. [ABSTRACT FROM AUTHOR]

This paper presents a highly efficient asymmetrical pulse-width modulated (APWM) full-bridge converter for renewable energy sources. The proposed converter adopts full-bridge topology and asymmetric control scheme to achieve the zero-voltage switching (ZVS) turn-on of the power switches of the primary side and to reduce the circulating current loss. Moreover, the resonant circuit composed of the leakage inductance of the transformer and the blocking capacitor provides the zero-current switching (ZCS) turn-off for the output diode without the help of any auxiliary circuits. Thus, the reverse recovery problem of the output diode is eliminated. In addition, voltage stresses of the power switches are clamped to the input voltage. Due to these characteristics, the proposed converter has the structure to minimize power losses. It is especially beneficial to the renewable energy conversion systems. To confirm the theoretical analysis and validity of the proposed converter, a 400 W prototype is implemented with the input voltage range from 40 to 80 V. [ABSTRACT FROM PUBLISHER]

This paper presents a novel microinverter for a single-phase grid-connected photovoltaic (PV) system. The proposed microinverter consists of a step-up dc–dc converter using an active-clamp circuit with a series-resonant voltage doubler and a high-efficiency inverter with single-switch-modulation step-down converters. The active-clamp circuit provides zero-voltage switching (ZVS) turn-on, recycles the energy stored in the leakage inductance of the transformer, and limits switch voltage stress. Moreover, to remove the reverse-recovery problem of the rectifier diodes, a series-resonant voltage doubler is used. Thus, this whole process provides high efficiency. To improve efficiency and reliability in the proposed inverter, only a single switch is modulated at the switching frequency without a shoot-through problem. A modified controller is also adopted to achieve fast output control. Thus, the proposed PV microinverter has the structure to minimize power losses. The experimental results show a maximum efficiency of 96.2% for a 400-W microinverter. [ABSTRACT FROM PUBLISHER]