A Single-Stage High-Frequency-Link Medium Voltage Ac to Dc Converter for Utility-Scale Grid Integration of Solar and Storage

This article presents an innovative galvanically isolated medium-voltage ac (MVAC) to low-voltage dc (LVDC) converter for MV grid integration of utility-scale renewables and storage. The converter supports bidirectional power flow at any power factor with high power quality. In the proposed solution, transformers are operated at high frequency, significantly reducing size and weight compared with conventional low-frequency step-down transformers followed by a hard-switched two or three-level ac–dc converter solution. The single-stage approach results in line frequency switching of MVAC side converter, leading to negligible switching loss and the elimination of large electrolytic capacitors needed for filtering second harmonic power, improving reliability, power density, and efficiency. A three-level architecture is adopted on each module's ac side high-frequency switched bridge, increasing the module voltage rating. This results in a 50% reduction in the number of series-connected modules and hence the complexity. Integration of LVDC side bridges into a single H-bridge dramatically reduces switch count, improves soft-switching capability, and reduces high-frequency rms current in the LVDC side bridge of the converter. This article provides a step-by-step design methodology. Experimental validation is demonstrated through an SiC-based 1.5 kV, 5 kW three-phase ac to LVDC module, achieving 95.8% efficiency and 3% ac side line current THD. The results affirm the efficacy of the proposed topology, modulation, and control strategy.