Independent Voltage Oriented DC-Side Sensorless Control of Three-Phase Cascaded H-bridge Multilevel Inverter With Decentralized MPPTs

This project aims at designing an efficient and economical photovoltaic system architecture. The PV arrays are broken into groups. Each group is connected to one of the H-Bridges in a three-phase based multilevel inverter. Each H-bridge is controlled by an independent MPPT block in conjunction with the grid controller. The cost is then reduced by eliminating the PV-side current and voltage sensors in each H-bridge. This is done by properly tracking the PV string power using the ac-side sensors. Estimating both PV current and voltage is important to have a plug and play capability for PV strings in the conventional PV grid-connected systems. The control of the reference dc voltages is based on separate Voltage-Oriented Control (VOC). The phase-unbalanced issue caused by partial shading might occur on the PV modules. Therefore, the zero-sequence injection is done by circulating energy among the H-bridges from each phase in the same hierarchal order.