Eliminating DC-Link Oscillations in Dynamic Power Reserve Control Through Interleaved Photovoltaic Strings

Advanced reserve power point tracking (RPPT) algorithms are becoming popular and are expected to replace the conventional maximum power point tracking (MPPT) and flexible power point tracking (FPPT) algorithms. RPPT enables power reserve availability while injecting flexible power into the grid. Hence, it combines the MPPT and FPPT functionalities simultaneously. However, due to inherent continuous sweeping across the PV curve, RPPT suffers from high dc-link voltage fluctuations. For this reason, this paper extends the RPPT concept from the single-string photovoltaic (PV) system to the multi-string PV system. Specifically, a two-string PV system is proposed, where two PV strings that are interleaved at the dc-link. This approach offers advantages over using a single PV string of the same capacity, notably by reducing the ripple in the dc-link voltage caused by RPPT. The effectiveness of this proposed algorithm in the interleaved PV system is demonstrated through simulation results under varying grid frequency and irradiance conditions.