High Frequency Integrated Solid State Transformer (SST) for Utility Interface of Solar PV / Battery Energy Storage Systems

In this paper, a high frequency integrated solid state transformer (SST) for utility interface of solar PV / battery energy storage system is proposed. The primary side consists of three 1-phase AC-AC converter blocks with a weak dc-link interfaced to a high frequency transformer. The secondary side of the transformer is connected to the three-phase PWM current source converter (CSC). The input AC-AC converters are modulated using high frequency square wave 20 kHz with 50% duty cycle. CSC is controlled with selective harmonic elimination (SHE) PWM technique with 5th, 7th, 11th, 13th harmonics elimination. It is shown that the utility line currents are of high quality with the elimination of lower order harmonic currents. The proposed approach has the advantages of higher power density, absence of electrolytic capacitors, higher frequency isolation. Simulation results are presented on a 120kW solar PV system employing 1500V DC. Experimental results for a scale down laboratory prototype are discussed to verify the concept.