Optimized control strategy for single-phase multilevel cascaded converter in a distributed PV-BESS system

The paper focuses on the energy management of a single-phase PV-BESS hybrid distributed system sized for residential applications, using a CHB converter topology as grid interface. The CHB is driven with a hierarchical energy management architecture, with a single centralized controller for the upper layer, and with multiple decentralized controllers for the lower layer. The upper layer generates the reference signals to be tracked. In ideal conditions, the CHB should work with all PV modules at their MPP and with unitary power factor. This is not always possible because of some functional constraints (e.g., voltage/current constraints, partial shadowing, SoC mismatches). Therefore, a weighted sum optimization method is proposed to explicitly considers these effects and to compute a set of reference variables to be tracked, in a way to optimize the steady-state system performances while, at the same time, guaranteeing the respect of the aforementioned constraints. In this framework, different functional requirements have been included in the optimization algorithm with higher or lower priority according to different operating conditions. The optimal references are then tracked by a decentralized control layer, using standard feedback control techniques. Numerical analysis and experimental results are carried out in order to validate the optimal algorithm in typical operating conditions and to assess the effectiveness of proposed CHB configuration with the whole control strategy.