A Fixed Frequency Full-Bridge Three-Level DC-DC LCL-Type Series Resonant Converter for Large Scale Solar PV Plants Applications

Large scale solar PV plants are typically connected into medium voltage AC grids using line frequency transformers, which are bulky. In application where size and/or weight are important an attractive alternative is the use of multilevel inverter configurations such as cascaded H-bridge multilevel inverters, where power converters play a vital role in the system architecture. This paper presents the operation, design, optimization and some simulation results for a fixed frequency full-bridge three-level LCL-type high frequency (HF) transformer isolated DC-DC resonant converter for large scale solar PV plants applications. Operation of the converter is illustrated for different operating intervals, including key waveforms and equivalent circuits. A design procedure using approximate analysis for 10 kW, 750 V input voltage, 750 V output voltage and 100 kHz switching frequency is presented. A novel optimization problem to determine the optimal converter design is introduced. The converter is controlled using phase shift technique. Results show that all MOSFETs achieved ZVS for a range of operating points from full-load to light-load.