On the Control of a Solid State Transformer for Multi-MW Utility-Scale PV-Battery Systems

Abstract

The utility-scale photovoltaic (PV)-battery systems typically include multiple power converters connected to the grid via traditional line frequency transformers (LFT), which may be considered bulky, and inefficient when compared with the emerging solid state transformers (SST). This paper proposes a SST with power and voltage controls for utility-scale PV-battery systems. The PV system was modeled based on available data from a universal solar facility located in Kentucky, USA. Furthermore, this paper provides detailed controller designs for the proposed utility-scale PV-battery system based on a SST which includes: the PV-side dual-active bridge (DAB) converter tracks the maximum power point, the PV inverter for steady power transformation to the grid, battery-side DAB converter for maintaining stiff dc bus voltage, and the battery inverter for voltage support and balanceing the power mismatch between the grid demand and the PV generation. Moreover, medium frequency transformer (MFT) and Silicon Carbide (SiC) MOSFETs are utilized in the DAB converters and inverters, to improve the efficiency of the PV-battery system. The simulation results based on the data retrieved from an operational PV facility, on one hand, are presented to confirm the benefits of the proposed SiC SST based PV-battery system; on the other hand, provide an alternative analysis on power losses and efficiency for the utilityscale PV farms.