Modeling of Coupled Harmonic Current Source for Grid-connected Inverters

Power systems are entering the era of high proportions of new energy and power electronic equipment. The interaction between grid background harmonics and grid connected inverters (GCIs) leads to frequency coupling effect which results in additional frequency components injecting into the power networks. However, there is limited research on the modeling of harmonic sources based on the frequency coupling effects. Hence, this paper firstly analyzes the harmonic response and emission mechanisms of frequency coupling effect caused by dq axis asymmetric control of GCIs. Then the transmission process of harmonic components in sampling delay progress, outer loop, inner loop, phase-locked loop, signal modulation module, and filter of the inverter is deduced. Voltage-controlled coupled harmonic current source models are established considering the frequency coupling effect, suitable for harmonic/interharmonic power flow studies of public supply networks. The proposed models are verified by time-domain simulations under different single harmonic and by hardware-in-the-loop simulations under multiple harmonics. Finally, the impacts of the outer loop, inner loop, phaselocked loop and output power, and the characteristics of harmonic admittance are analyzed.