A Decentralized Control Strategy for Single-Phase Cascaded Photovoltaic Inverters with MPPT Ability

Cascaded inverters can improve efficiency and reduce cost, so it is widely used in photovoltaic (PV) grid connected power generation system. However, aging or partial shielding of PV panels will lead to their different maximum power points (MPP). This paper proposes a decentralized control strategy for grid-connected cascaded PV inverters without any communication, which is capable of integrating PV inverters of different capacities connected in series into the grid, and enable them to achieve maximum power point tracking (MPPT) independently. Compared with the traditional centralized control method relying on real-time communication, the proposed scheme has advantages of improved reliability and decreased costs. The overall system stability is analysed, and the stability condition is derived as well. The Hardware-In-the-Loop test results show that all the inverters in the cascaded system have their output frequency and voltage phase synchronized autonomously, and achieve MPPT independently even in the presence of variation of light condition. Thus, the feasibility of the proposed method is verified.