Optimal Power Flow for Active Distribution Networks: Advanced Formulations, Practical Considerations and Laboratory Demonstration

Abstract

The rapid growth of renewable distributed generation (DG) has introduced unconventional challenges for distribution companies (e.g., dealing with voltage rise). To enable future DG growth, a promising alternative (to the otherwise capital-intensive and time-consuming network reinforcements) is the real-time orchestration of DG and existing network assets using advanced schemes. In this context, the operational usage of Optimal Power Flow (OPF)—an optimisation-based technique traditionally found in transmission network applications, albeit using simplified formulations—as a decision-making engine has gained tremendous interest in recent literature. Nonetheless, before such schemes can be readily integrated in the control room of distribution networks, there are several practical challenges that must be addressed.

Firstly, the operational usage of OPF requires a fast and scalable formulation that can handle the size (thousands of nodes) and complexity (phase unbalances, discrete devices) of typical distribution networks. Furthermore, since the differences in device-specific characteristics in the sub-minute scale (delays, ramp rates and deadbands) may lead to coordination issues when multiple devices are being controlled simultaneously, additional adaptations are necessary to ensure OPF-based setpoints can be implemented in real-world applications. Finally, while active power curtailment is inevitable at times, since such actions has a direct impact on the return on investment for DG owners, the implications from different fairness objectives (e.g., removing disparity in renewable energy harvesting or financial benefits) as well as the trade-offs between fairness (reducing disparity) and efficiency (aggregated performance) need to be first understood.

In this PhD project, the following research is carried out to address the aforementioned challenges:

- A linearised, three-phase AC OPF is developed to cater for multi-voltage level distribution feeders and integer variables. Its performance is demonstrated using a realistic MV-LV residential feeder (from the primary substation down to individual connection points of 4,626 single-phase consumers) with over 4,900 nodes.

- The necessary adaptations in existing device controllers and the OPF formulation are proposed, allowing network participants and assets to be successfully controlled using OPF-based schemes in an operational setting with minute-scale control actions. Particularly, the importance of the proposed adaptations in preventing short-term voltage spikes are demonstrated using a rural distribution feeder with multiple actively managed on-load tap changers and wind farms.

- The implications and trade-offs from different fairness considerations are investigated using several OPF-based schemes, each considering a unique and contrasting fairness objective. The findings highlight the multi-facet nature of curtailment fairness and the importance of identifying the most appropriate objective for a given application. Furthermore, it can help operators/policymakers to make informed decisions when a portfolio of DG is to be managed.

- A hardware-in-the-loop demonstration platform is built using commercially available software and hardware at the Smart Grid Lab of The University of Melbourne. This implementation extends beyond static plots and tables by introducing a rich and interactive user interface, and thus enabling a more realistic and engaging way of showcasing advanced schemes to industry.