Impact assessment of harmonics emissions on active distribution network planning and operation

Abstract

Modern distribution networks (DNs) now have increased penetration of switching electronic loads and grid-integrated renewable distributed generators (RDGs) like photovoltaics (PVs). The trend of RDG integration has being promoted by the quests for the reduction of greenhouse gas emissions whilst growth in the use of electronically controlled devices is facilitated by the increasing demand for automation in many facets of life. While the integration of these switching electronic devices into the power grid might be advantageous to the customers, distribution network operators (DNOs) worry that high penetration of these devices might challenge their network operations. This is because the power conditioners of the above network components emit harmonic currents and voltages which affect the utility equipment by way of overheating, mal-operation and damage. Moreover, past DNs had the planning and operational philosophy that the harmonics emission levels were negligible. With the increased presence of these RDG converters and nonlinear loads, the assumption of infinitesimally small harmonics level need to be re-evaluated. Consequently, this PhD research investigated the impacts of harmonics pollution from power converters of PVRDGs and switching electronic devices on active DN performance indices such as network losses. Firstly, advanced harmonic domain models of single and three-phase PVRDGs adequate for representing the actual interaction between DNO network and the switching devices were developed. Next, detailed advanced harmonic model of typical DNs has evolved from this research. These improved models have been used to study harmonic pollution challenges such as harmonics induced electrical losses and resonance phenomenon in distribution systems with high penetration of PVRDGs and switching loads. The constraints imposed by network unbalance and harmonics emission on exploiting PVRDGs for maximizing loss reduction benefits have also been analyzed. The technical insights gained from this research work are beneficial to utilities in the design and planning of their system operation.