Digital repetitive control of a three-phase flat-top-modulated grid tie solar inverter

Grid connected solar inverters are used to feed energy generated by a photovoltaic generator into the mains. High efficiency is a major requirement. Furthermore a low total harmonic distortion (THD) of the output current is needed to comply with regulations. This paper presents the control for a new highly efficient inverter topology. Due to disturbances of the grid voltage and non-linear effects such as dead-time effects in the output stage of the inverter, the output current is distorted, especially when using small output inductors. Furthermore, the investigated inverter is operated with 120deg flat-top modulation to improve efficiency. However, this modulation scheme in combination with an LCL output filter leads to higher THD. As the current distortion is periodic with the grid voltage, a repetitive learning controller can be used to compensate it. In this paper, the design of a vector control including a repetitive controller is outlined. The results of the implementation of the control algorithm on hardware are presented.