DC-AC-AC converter for PV plant in medium voltage grid-connected systems

Large-scale PV plants (hundreds of MW) are a reality and are being used to generate high-power levels in medium-voltage (MV) utilities. To achieve this goal, some new power electronics systems based on medium-frequency AC-links (MFAC) and multilevel output configurations have been proposed to interfacing with the MV utility. Most of these systems rectify the MFAC voltage, generating a DC bus and then invert the DC voltage to generate a line frequency AC voltage. This paper presents a three-phase cascaded multilevel converter topology with reduced-energy conversion stage and multiples AC medium-frequency (MF) links. The proposed converter is composed by modules connected in cascaded. Each module has three conversion stages: Input converter (DC-AC), isolation stage (medium-frequency transformer) and output converter (AC-AC). In order to validate the proposed topology simulations of a 100 kW system are performed, taking into account balanced and unbalanced DC source cases. The proposed system is validated through a 1.5 kW single-phase five-level laboratory prototype.