A Medium Voltage DC Collection Grid for Large Scale PV Power Plant with SCR Converter and Integrated Solid-State Transformer (SST)

This paper proposes a medium voltage (MV) DC collection grid concept for large-scale PV power plant with a line commutated 12-pulse SCR converter and an integrated solid-state transformer (SST) for utility interface. DC power from the PV power plant sections is first processed via a line commutated 12-pulse converter employing an inverter grade SCR's is interfaced to a SST powered by a higher frequency AC-AC converter. The objective of this paper is having the SST operate at medium frequency (360Hz or 720Hz), to reduce the transformer size/weight to 1/3rd to 1/5th. It is shown due to 12-pulse operation a high-quality utility line current can be achieved with the cancellation of 5th and 7th harmonic currents. The proposed approach is a robust current fed system, that improves power density, is simple to control with an integrated solid-state transformer. Simulation results presented on an example 150 kW PV power plant to validate the concept. Experimental results from a scale down laboratory type 1kW system are also discussed.