Investigation on Efficient Coordinated Control of String‐Type PV Optimizers Under Irradiation Imbalance

ABSTRACT In grid‐connected photovoltaic (PV) systems, string‐type PV optimizers can realize maximum power point tracking (MPPT) based on the characteristics of single PV panels under irradiation imbalance, so as to improve the energy utilization rate of PV panels. However, the power loss of the PV optimizers cannot be ignored. Meanwhile, the coordinated start/stop control of PV optimizers with PV inverters deserves further investigation. In this paper, a high‐efficiency coordinated control method for grid‐connected PV system is proposed. Based on the operating modes and loss of both PV optimizers and inverters, the optimal operating mode of PV optimizers under different irradiation conditions is obtained, especially in case of irradiation imbalance of PV panels. The proposed method also realizes higher reliability and lower power loss in the coordination of the first and second stages of the PV system with the control logic design during the starting, stopping, and fault cases. Experiments are carried out with three 700 W string‐type PV optimizers, and the results verify that the proposed method realizes higher conversion efficiency and reliability under different operating cases.