Active management of distribution systems with distributed energy resources

Abstract

Over the last decade, the world has witnessed a widespread adoption of distributed energy resources (DERs) in the distribution networks (DNs) due to the rapid advances in renewable DER technologies. This trend may bring about lot of economic and environmental benefits. However, it also introduces adverse impacts on the DN operations because of the uncertainty and intermittency of renewable DERs. These impacts include but are not limited to the severe voltage variations and significant load ramps. In order to mitigate these effects, the potential of DERs has been explored to provide ancillary services, e.g. voltage regulation and frequency control. On the other hand, since DERs are geographically dispersed over the entire DN, it is considerably challenging in coordinating them. Therefore, this thesis focuses on addressing these concerns by developing advanced management approaches. To overcome the complexity in coordinating various devices and promote a competitive energy trading environment, a novel transactive energy trading framework is proposed with detailed designs for the end-use customers. Particularly, the author innovatively integrates a novel Nash bargaining based bilateral energy trading mechanism with an efficient distributed optimal power flow (OPF) technique to maximize the benefit of customers and to enhance the system reliability and security. With some rigorous analysis, the proposed model is converted into a two-stage problem, where the first stage determines the optimal energy trading and dispatch decisions, and the second stage settles the optimal payments. To implement this framework in a decentralized manner, an advanced distributed algorithm is developed. Numerical results demonstrate the economic and technical advantages of this framework. To address the severe voltage variations caused by the intermittent photovoltaic (PV) output, a distributed online voltage control algorithm is developed based on dual ascent method. Conventional distributed algorithms implement voltage control only when the algorithms converge, while the proposed algorithm is able to carry out voltage control immediately. In particular, a closed-form solution is derived for the PV controllers to locally update the active and reactive power set-points based on local voltage measurements and information exchange with their neighboring PV systems. The objective is to minimize the total loss, while maintaining the bus voltages within the acceptable ranges. The effectiveness and robustness of the proposed algorithm are verified in case studies. To mitigate the significant load ramps caused by the diurnal pattern of PV power, the author proposes a novel look-ahead dispatch model for the DNs with multiple distributed ESSs. The dispatch problem is formulated as a finite horizon optimization problem and is carried out utilizing model predictive control method (MPC) that takes both current and future information into account. Thus, the short-sightedness can be avoided. The numerical results show that the proposed model can bring about a significant reduction of maximum ramp and power losses. To alleviate the PV ramp event (PRE) induced voltage violations, a robust dispatch model is proposed that enables systematic coordination between on-load tap changer (OLTC) and PV inverters. Particularly, this model is formulated as a two-stage robust optimization problem, where the first stage determines the OLTC step and maximum admissible PV output (MAPO), and the second stage evaluates the feasibility of the first stage result under all possible realizations of PRE. MAPO is proposed to quantify the operational PV hosting capacity. Column-and-constraint generation algorithm is employed to solve the problem. Case study on IEEE 33-bus distribution system validates the effectiveness of the proposed model in eliminating PRE induced voltage violations.