Control method of PV hybrid systems with grid-connected MMC to overcome uneven irradiances.

This paper proposes a modified structure and its control method for a hybrid modular multilevel converter (MMC)-based photovoltaic (PV)–battery energy storage system (BESS). The modified structure consists of PV arrays that are directly connected with sub-modules SMs, and batteries that are interfaced with the DC port of the SMs using a DC/DC converter. The control strategy implements an independent maximum power point tracking (MPPT) control for each of the PV arrays by individual SM voltage control for variable conditions. Embedded BESSs work as power and voltage compensators for the arms, and they are able to eliminate the weakness of the PV plant such as power mismatching and unsmooth power under variable illumination and partial shading. This is accomplished by average arm power control and moving average filter for the BESSs in each arm. Moreover, due to the contribution of the BESSs, it offers a lower total harmonic distortion (THD) under variable working conditions. The effectiveness and robustness of the method are verified by simulation results, which were obtained by conducting time-domain simulations in PSCAD/EMTDC under variable conditions. [ABSTRACT FROM AUTHOR]