Evaluation and enhancement of solar PV hosting capacity for management of voltage rise in LV networks

Abstract

Proliferation of solar photovoltaics (PV) in low-voltage (LV) distribution networks is inciting technical challenges in network design and operation with regard to the quality of power. Violations of operational performance limits are increasingly evident at higher solar PV penetration levels, in particular, local voltage rise has become the major issue of concern in LV distribution networks. As the solar PV industry continues to grow, emerging challenges need to be addressed by adopting best policies and practices at a utility level. Thus, to comply with stipulated network operational limits, distribution network operators (DNOs) are compelled to develop comprehensive techniques to determine acceptable levels of solar PV hosting capacity (HC) and explore HC enhancement options. Complexity of modelling distribution networks is a barrier for DNOs to decide levels of maximum solar PV penetration using stochastic approaches. Thus, there is a necessity to develop a systematic approach to assess solar PV HC, considering factors such as geographic layout of networks and their electrical characteristics. This thesis extends the knowledge of managing of solar PV integration in LV networks by developing systematic approaches to evaluate solar PV HC subjected to over voltage curtailment. In this regard, a novel feeder based solar PV HC evaluation approach was developed to address the diverse network characteristics of multi feeder systems in LV distribution networks. To assess the voltage violations and critical factors a ecting the solar PV HC, a comprehensive analysis of potential power quality issues was conducted on a practical LV distribution network in Sri Lanka. The approach proposed in this thesis establishes a safe limit for solar PV HC for a given distribution feeder based on the locational and operational aspects of the solar PV units deployed on a LV network. The safe limit for HC was developed employing a number of sensitivity analyses considering factors in uencing solar PV HC. Further, the proposed feeder based solar PV HC approach was extended to develop a generic method to quantify solar PV HC under di erent operating con- ditions of PV inverters. Thus, it can be used as an approximate guide or a rule of thumb to evaluate solar PV HC at a given point on an LV feeder without using complex stochastic techniques. With the increasing demand for solar PV systems, development of both solar PV HC assessment and enhancement techniques is essential in managing network voltage. DNOs have recognised the need for smart PV inverter technologies to maintain acceptable voltage levels in distribution networks. Smart PV inverters possess fast and exible active and reactive power control functions such as; Volt-VAr and Volt-Watt control modes which can be used to manage over-voltage conditions that often limit the solar PV HC. At present, most of solar PV connection standards provide a set of rules and guidelines to mitigate voltage violations by enabling VoltVAr and Volt-Watt control modes of the inverters. In particular, it is imperative to analyse the impact of such solar PV connection standards on HC assessment and its potential to enhance solar PV HC. Thus, a detailed analysis of smart solar PV inverter capabilities and a comparative evaluation of solar PV HC enhancement facilitated by di erent connection standards are presented in this thesis. Electricity utilities around the world seek to develop strategies to increase solar PV integration while maintaining acceptable network performance. Hence, more generalised and straightforward tools are required to rapidly assess solar PV HC without complex and extensive network modelling and simulations. Extending the deterministic outcomes, a nomogram based solar PV HC assessment approach is proposed in this thesis to determine HC values speci c to any location of a given conductor. Further, solar PV connection criteria is proposed which permits the electric utilities to approve new solar PV connections which facilitates reasonable modelling insights to assess HC. The proposed nomogram based solar PV HC assessment approach and solar PV connection criteria cover technical and regulatory aspects to manage PV integration in LV distribution networks. For the continued development of solar PV as a distributed generation, accuracy of PV connection approval process is crucial to correctly and easily allow PV connections that will not cause issues. Therefore, grid codes, distribution codes or guidelines on interconnection of solar PV require to be re ned or re-written in relation to solar PV HC assessment/enhancement and approval criteria for new PV connections in LV distribution networks. The solar PV HC assessment/enhancement and solar PV connection criteria proposed in this thesis shall be a contribution to further improvement of the available guidelines/standards on solar PV installation in LV networks. All network modeling and simulations presented in this thesis were carried out in DIgSILENT PowerFactory platform.