New Metric Recommended for IEEE Standard 1547 to Limit Harmonics Injected Into Distorted Grids

IEEE Standard 1547 defines grid connection standards for distributed resources (DRs). This standard sets requirements for harmonic performance, which are particularly relevant when converter-interfaced DRs are considered. Specifically, the standard limits the allowable harmonic current injected by a DR, assuming grid voltage at the point of common coupling (PCC) is harmonic free. In this paper, it is demonstrated, both mathematically and experimentally, that the harmonic current injection of a converter-interfaced DR depends highly on the level of PCC background voltage. This paper presents a mathematical formulation that enables the impact of PCC voltage harmonics on the harmonic current injection of a converter-interfaced DR to be determined via experimental identification of the converters frequency coupling matrix. Experimental tests show that an IEEE 1547-compliant solar inverter with measured total demand distortion (TDD) of 0.66% for an undistorted PCC can produce TDD levels in excess of 20% in the presence of 3% voltage distortion. It is concluded that TDD metrics, as employed in IEEE Standard 1547, provide little insight into the field performance of converter-interfaced DRs when background voltage harmonics are present. Improved FCM-based metrics for assessing the harmonic performance of converter-interfaced DRs in the presence of voltage harmonics are provided.