Unified Coordination Control of MPPT and Frequency Support for Single-Stage Multiport Inverter-Connected PV-ESS Hybrid Systems

Integrating the energy storage system (ESS) into photovoltaic (PV) generation systems is an effective solution to realize frequency support. The single-stage multiport inverter (SSMI) offers a high-efficiency solution for PV-ESS hybrid systems compared to conventional two-stage configurations due to the removal of dc/dc converter. However, it is challenging to realize maximum power point tracking (MPPT) and frequency support simultaneously due to the coupled power flows in SSMI. To address this issue, two independent power buffers are developed to smooth PV generation fluctuations and deal with frequency change. On top of that, a unified control is proposed to coordinate the power buffers by regulating the charge/discharge of ESS. Besides, the operation capacity and stability analysis of the proposed unified coordination strategy are derived in detail. Finally, experimental tests are carried out to verify the effectiveness of the proposed solution. With the proposed unified coordination strategy, the MPPT of the PV unit and desirable frequency support are realized simultaneously. Moreover, the proposed SSMI-based solution shows around 2% higher system efficiency than the conventional two-stage strategies.