Analysis and Modeling of Cascaded DC-DC Converters in Grid-Connected PV-HYDRO Power Systems at Medium Voltage AC

The cascaded DC-DC converter remains a preferred topology in medium-voltage photovoltaic (PV) and hydro power systems, offering high voltage conversion efficiency, flexibility, and independent control capabilities. However, conventional centralized control methods face challenges in achieving optimal string maximum power point tracking (MPPT) due to power mismatches. Additionally, the high costs and delays caused by the spatial separation of PV arrays and hydro power stations make centralized control less practical. To address this, we propose a distributed multimode control strategy for cascaded DC-DC converters that incorporates voltage, power, and gain constraints alongside distributed MPPT control. Within this frame-work, each sub module (SM) can dynamically switch between multiple operational modes to optimize energy extraction from both solar and hydro sources. This distributed approach enables independent string MPPT and self-regulated voltage distribution without requiring real-time communication, thereby improving system versatility and resilience. The proposed strategy extends the optimal operating range, simplifies mode transitions, and enhances overall applicability for medium voltage AC grid-connected PVhydro power systems.