Control of a SiC-based Cascaded Multilevel Converter cell for solar applications

Central inverters based on conventional topologies are the current preferred solution in solar farms because of their low cost and simplicity. However, such topologies have some disadvantages: poor Maximum Power Point Tracking (MPPT), and the use of bulky filters and Low Frequency (LF) transformers. An attractive alternative in this case is the Cascaded Multilevel Converter (CMC), which can provide a distributed MPPT control, allied with overall reduced footprint and high flexibility. A CMC cell using silicon carbide devices has been proposed and designed in previous works to incorporate three main functions: MPPT control of a Photovoltaic (PV) array, galvanic isolation through a Solid-State Transformer (SST) and control of grid power flow. This work proposes a closed-loop control strategy for each stage of the CMC cell and shows its validation thorough simulations. Experimental results are performed and presented in a single-phase 6.2 kW prototype cell. These results lead to the conclusion that the applied control techniques are suitable to the PV application.