Effect of Grid Current QSG on Harmonic Current Content in Single-phase Grid-connected Inverter

In a Low Voltage Distribution System (LVDS) the Single-phase Grid-connected Inverters (SGIs) are designed to maintain good power quality. Grid voltage distortion predominantly present in LVDS affects the injected power quality of SGIs. In this paper the effect of grid voltage harmonics on the injected grid current is analyzed through harmonic impedance modeling. The role of the sensed grid current Quadrature Signal Generator (QSG) block used in Synchronous Reference Frame (SRF)-based current controllers is identified to be important in deciding the power quality of SGI. Two of the most widely used QSGs: the SOGI-QSG and TD-QSG, are analyzed and compared in terms of Total Harmonic Distortion (THD) of grid current in this work. Further the theoretical analysis is supported by simulation study and experimental validation on a 250 W prototype of Switched Boost Inverter (SBI). The current THD under distorted grid condition is found to be about 9 times higher when SOGI-QSG is used for sensed grid current as compared to when TD-QSG is used for the same.