Active Management of Voltage Control Devices in PV-Rich Distribution Systems
Creators: name: Noori Rahim Abadi, Seyyed Mahdi
Publisher: name: The Australian National University
Year: 2023

description: In the last decade, environmental concerns and technological advancement have led to a transition from centralised fossil fuel-based generation towards distributed energy resources (DER), such as rooftop photovoltaic (PV) systems. This transition, however, has resulted in new technical challenges, such as the over-voltage problem. Traditionally, the distribution system operators (DSOs) periodically manage slow-acting regulating devices such as on-load tap changers or suggest a grid reinforcement plan to keep the networks secure. However, such approaches may no longer be reliable, as they are either too costly or were designed to control fluctuations caused by slow changes in demand. Fortunately, the utilisation of PV smart inverters presents an alternative solution to the voltage rise problem. An important question arises: how to coordinate voltage control devices in PV-rich distribution systems to guarantee a safe and economical operation for both the networks and consumers? This thesis explores innovative technical solutions to answer this question. The first step towards finding a solution is to establish whether the DSOs can rely on existing communication-less control devices, or there is an urgent need to invest in building a communication infrastructure in the PV-rich distribution systems. Our analysis of various available standards and innovative control schemes confirms the inadequacy of existing communication-less schemes to deal with the voltage rise problem. Hence, with the uptake of PV systems in the distribution systems, it is highly suggested that the DSOs invest in a communication infrastructure to coordinate the inverters with other existing voltage control devices. Assuming that a communication infrastructure exists in distribution systems, we study how to realise a control algorithm that coordinates thousands of residential inverters. We propose two approaches based on the application of affinely adjustable robust counterpart (AARC) methodology that respond to changes in local real power (AARBP) and voltage magnitude (AARBV), respectively. Through numerical simulations, we show that our proposed approaches can keep the voltages inside the accepted limits for a wider range of scenarios compared to alternative approaches in the literature while significantly decreasing the reactive power usage, real power loss, and line congestion. Next, we build upon our approach by extending its modelling in three main ways. Firstly, it extends the modelling to three-phase unbalanced distribution systems. Secondly, it allows to fully control both real and reactive power output of the PV inverters. Finally, it incorporates the probability distribution function of uncertain parameters to improve the performance of our approach in scenarios away from the worst-case realisation of the uncertainty. Our simulations confirm that our approach is robust against parameter uncertainty while decreasing the real power curtailment up to 60\% compared to the conventional AARC approach. Finally, we further extend our approach to incorporate soft constraints. We propose an adjustable scenario optimisation-based solution approach that maximises the usage of DER generation within the operation horizon while providing the required level of network security. Our modelling i) guarantees hard constraints satisfaction, ii) allows fast-acting devices, e.g., inverters, to adjust in response to live realisations, and iii) enables the operators to maintain the soft constraints with a pre-determined probability using a joint chance-constrained (JCC) program. We show that our approach outperforms the conventional scenario optimisation and adjustable robust approaches, respectively, by 88% and 86% in our experiments.