Dual-buck residential photovoltaic inverter with a high-accuracy repetitive current controller

This paper describes a dual-buck inverter (DBI) for residential photovoltaic power conversion systems. The DBI consists of unidirectional and bidirectional switching legs, which are operated at different frequencies to attain high efficiency. The operation modes of the DBI are analyzed and a third- order control model is derived based on the analysis. Since the third-order model cannot be easily handled by the current controller design, a simple first order-model is obtained with proper assumptions and manipulations. After this, a repetitive current controller using the first-order model is designed to improve the accuracy of the current regulation in both continuous and discontinuous conduction modes. Due to the universal operation of the designed repetitive controller, the tracking accuracy for a low power reference is drastically enhanced, and this significantly improves the maximum power point tracking (MPPT) ability of the PV system. In order to verify the performance of the proposed scheme, a 3-kW DBI prototype was built and tested. The experimental results demonstrate that the proposed scheme not only reduces the total harmonic distortion of the output current, but also achieves highly accurate power tracking performance with high efficiency.