Distribution network capacity assessment: Incorporating harmonic distortion limits

The capacity of distributed generation (DG) connected in distribution networks is increasing as part of the drive to connect renewable energy sources. Due to widespread application of power electronic inverter interfaces, DG can inject harmonic current through the point of common connection into the upstream network. Harmonic current emission may cause voltage distortion problems when harmonic resonance exists in the network. Harmonic distortion is one area of concern for electric utilities in determining whether DG could be connected, although there are differences in utility practices in applying limits. To explore the impact of harmonic regulations on the ability of distribution networks to host DG, this work incorporates harmonic voltage constraints into an established optimal power flow (OPF) planning method. The case study shows that harmonic distortion limits have substantial impacts on the allowable penetration of DG. Furthermore, the complex interconnectivity between DG locations means that voltage, thermal and harmonic constraints have a large influence on the location preference for DG capacity.