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Development and Operational Control of Two-String Maximum Power Point Trackers in DC Distribution Systems

This paper develops the operational control of two maximum power point trackers (MPPTs) for two-string photovoltaic (PV) panels in dc distribution systems. This dc distribution system is connected to ac grid via a bidirectional inverter. Two PV strings and two MPPTs are implemented in this system. The proposed MPPT topology consists of buck and boost converters to deal with wide output voltage range of PV panels. To accurately determine the input current of MPPTs, the PV-string configuration check is accomplished online. The perturbation and observation method are applied for maximum power point tracking. Moreover, the current balancing of two MPPT modules in parallel is achieved. In this paper, the system configuration and the operational principle of the proposed MPPT are first introduced. Afterward, the perturbation and observation method and the mode transition are demonstrated. Flowcharts of the online PV-string configuration check and current balancing are explained. The validity of configuration check and current balancing is verified via the experimental results. Maximum power tracking performance and power conversion efficiency are also obtained.