A simple approach to current THD prediction for small-scale grid-connected inverters

The total harmonic distortion (THD) of the grid current is the key parameter to gauge the performance of power quality for grid-connected inverter output as well as required by the grid interconnection standards, such as AS4777 and IEEE1547. However, the prediction of current THD is complicated and normally accompanied by massive amounts of numerical calculations, which depends on many factors such as control algorithms, modulation techniques, switching frequencies of power electronics devices and etc. In this paper, a simple method that the output current is decomposed into a fundamental component and ripple currents is proposed to estimate the current THD for small-scale grid-connected inverters. In addition, as current harmonics in high frequency ranges can be attenuated or even eliminated by filter technologies, a particular model of current THD performance based on the requirement of the grid interconnection standards is built afterwards. The THD prediction model of the grid current is verified by experiments conducted on a 10kW single-phase inverter.