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A high-efficiency bridgeless three-level power factor correction (PFC) rectifier is proposed. The circuit configuration of the proposed rectifier consists of four metal oxide semiconductor field-effect transistor (MOSFET) switches, and the reverse recovery problems of the switches are eliminated. Also, the proposed rectifier with three voltage levels reduces the power losses, harmonic components, voltage ratings, and electromagnetic interference. To control the grid current and the output voltage effectively, a feed-forward nominal voltage compensator with the mode selector is developed; by presetting the operating point of the grid voltage, this compensator improves the control environment. Thus, the proposed three-level PFC rectifier with developed control algorithm provides high power quality and high efficiency of 99.05%. Experimental results based on a 1-kW prototype are provided to evaluate its performance and verify the analysis. [ABSTRACT FROM AUTHOR]

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 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]