A Three-Phase Grid-Connected Microinverter for AC Photovoltaic Module Applications

A photovoltaic (PV) microinverter converts the dc from a PV panel to ac directly, which has the advantages of improved energy harvesting, friendly “plug-and-play” operation, enhanced flexibility/expandability, excellent system redundancy, and no dc cabling/safety issue; therefore, it is an attractive solution for the grid-connected PV system. In ac PV module applications, the features such as power density, reliability, efficiency, and reactive power capability are essential for the microinverters. In order to overcome the drawbacks of the conventional microinverters, including the power density/reliability issues caused by the bulky input capacitors and the limited output reactive power capability, a three-phase microinverter without energy storage capacitors is proposed in this paper. The proposed microinverter consists of a flyback stage, a third-harmonic injection circuit, and a line-commutated current-source-type inverter. The flyback stage realizes maximum power point tracking, while the third-harmonic injection circuit is responsible for output power factor correction. In addition to having the potential of achieving compact structure, long lifetime, and high efficiency, the developed microinverter provides extended output reactive power control range and three-phase balanced output. Finally, the proposed topology and the method are verified by simulations and experimental results.