OPF-Based CVR Operation in PV-Rich MV–LV Distribution Networks

Abstract

Conservation Voltage Reduction (CVR) has been traditionally applied adopting moderate settings at primary substations and when distributed generation was uncommon. However, as new infrastructure is deployed across Europeanstyle MV and LV networks, driven by increasing photovoltaic (PV) penetration levels, the opportunity arises to develop more advanced CVR schemes. This work proposes a centralized, threephase AC OPF-based CVR scheme that, using monitoring, onload tap changers (OLTCs) and capacitors across MV and LV, actively manages voltages to minimize energy consumption, even with high PV penetration, whilst considering MV-LV constraints. To tackle scalability issues brought by discrete variables, a twostage approach is proposed to solve the OPF as a non-linear programming problem (relaxing integer variables). A process that continuously checks customer voltages is adopted to trigger the optimization only when needed. Moreover, CVR benefits are not only quantified at a network level but also for customers, providing useful insights to policy makers. The proposed control is assessed using a realistic, unbalanced UK residential MV-LV network (2,400+ customers) with high PV penetration, and 1-min resolution time-varying profiles and load models. Results demonstrate that the proposed control effectively coordinates voltage regulation in MV and LV levels throughout the day, minimizing energy imports for all customers.

A Comprehensive Multi-Period Optimal Power Flow Framework for Smart LV Networks

“…In terms of MP-OPF features, the authors of [9] eliminate the neutral phase through Kron reduction and calculate an optimal control strategy through an iterative approach (constant P/Q load). The technique is also used in [10], where the current-based formulation is employed instead (simultaneous study of MV and LV network). The work [11] proposes a current-mismatch MP-OPF to optimize a feeder's operation, ignoring the grounding and assuming full controlability of residential ES systems by the DSO (constant P/Q load).…”

“…This work draws inspiration from and significantly extends several past works. The current-based formulation is a combi-nation of [9], [10], [31], extended to include the interactions with the neutral and ground wires and the rotation of each phase to a common reference plane. The load modelling is adapted from [5], also accounting for partial load flexibility.…”

On the Implementation of OPF-Based Setpoints for Active Distribution Networks

“…At the same time, this also entails the need for more granular data (e.g., time resolution of seconds) to realistically capture this phenomenon as the averaging effect of lower resolutions data (e.g., minutes) will mask such spikes or fluctuations. Lastly, apart from using control cycles, alternative approaches to trigger the decision-making process can be adopted, such as the problem persistency mechanism used in [32].…”

“…Since these sources of flexibility can exhibit different operating characteristics to the devices investigated in this work, the proposed methodology can help to ensure the OPF-based setpoints are adequately implemented in practice. It is also worth mentioning that, while an OPF formulated using the branch flow model has limitations when dealing with a meshed network (e.g., required when catering for network reconfiguration), an alternative formulation (e.g., as in [32]) can be used without affecting the validity of the proposed adaptations. This is because these adaptations focus on the behavior of devices, not the power flow equations.…”

CVR and Loss Optimization Through Active Voltage Management: A Trade-off Analysis

“…For example, quadratic programming was used to minimize total energy loss through the installation and scheduled switching of static capacitors in a step by step iterative procedure in [14]. A centralized, three phases AC OPF-based CVR scheme was implemented as a mixed integer nonlinear program in [20] to minimize the overall energy consumption of a PV-rich unbalanced MV-low voltage (LV) distribution network in the UK. A Pareto-based multi-objective optimization using discrete particle swarm optimization (PSO) was used to simultaneously optimize power loss and the number of switching operations and deviations of bus voltages from their rated values subject to system constraints in [21].…”