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A Reliable Three-Phase Single-Stage Multiport Inverter for Grid-Connected Photovoltaic Applications

This paper presents a new three-phase single-stage multiport inverter (SSMPI). The proposed topology contains no electrolytic capacitors. Therefore, its reliability and lifetime are improved in comparison with the well-known two-stage multiport voltage source inverters. In addition, the SSMPI has a modular structure and the number of input ports can be easily increased. The input ports of the SSMPI can be fed by different photovoltaic (PV) strings. Therefore, the SSMPI can be used in PV power plants with multiple PV strings to enhance the reliability and the lifetime of the power plant. The SSMPI can extract the maximum power from multiple PV strings with different irradiations, orientations, and characteristics. In this paper, the SSMPI structure and its challenges in switching command generation and control are explained. Then, a new switching algorithm based on space vector modulation and a novel control strategy are developed to fulfil the requirements of the SSMPI. The simulation and experimental test results of a 2.4 kW prototype show that the proposed converter can inject three-phase currents to the grid with a unity power factor and without using any ac current sensors. Moreover, the maximum power is extracted from the input ports in different test conditions.