Optimal Inverter VAR Control in Distribution Systems with High PV Penetration (1112.5594v1)

Abstract: The intent of the study detailed in this paper is to demonstrate the benefits of inverter var control on a fast timescale to mitigate rapid and large voltage fluctuations due to the high penetration of photovoltaic generation and the resulting reverse power flow. Our approach is to formulate the volt/var control as a radial optimal power flow (OPF) problem to minimize line losses and energy consumption, subject to constraints on voltage magnitudes. An efficient solution to the radial OPF problem is presented and used to study the structure of optimal inverter var injection and the net benefits, taking into account the additional cost of inverter losses when operating at non-unity power factor. This paper will illustrate how, depending on the circuit topology and its loading condition, the inverter's optimal reactive power injection is not necessarily monotone with respect to their real power output. The results are demonstrated on a distribution feeder on the Southern California Edison system that has a very light load and a 5 MW photovoltaic (PV) system installed away from the substation.

• The paper presents a methodological approach to optimize volt/VAR control (VVC) in distribution systems with high photovoltaic (PV) penetration by leveraging modern inverter capabilities.
• The optimization is formulated as a radial optimal power flow problem solved using a conic relaxation of DistFlow, demonstrating a convex and exact solution for optimal VAR injections.
• Simulations show that optimal inverter VAR control can reduce energy consumption by over 1%, enhance voltage regulation within ANSI limits, and effectively manage voltage fluctuations under high PV penetration.

Optimal Inverter VAR Control in Distribution Systems with High PV Penetration

The paper presents a methodological approach to optimize volt/VAR control (VVC) in electrical distribution systems experiencing high penetration levels of photovoltaic (PV) generation. By leveraging the advanced capabilities of modern inverter technology, the paper aims to mitigate rapid and large voltage fluctuations haLLMark in renewable energy systems.

The inverter VAR control is cast as a radial optimal power flow (OPF) problem that seeks to minimize line losses and reduce overall energy consumption, incorporating Conservation Voltage Reduction (CVR). The authors employ a conic relaxation of the DistFlow representation for solving radial power flow equations, which is demonstrated to be a convex and exact solution. This approach is particularly applicable in contexts where the traditional VVC methodologies, relying on devices such as OLTCs and shunt capacitor banks, are insufficient due to the variable and fast frequency nature of PV generation.

A central focus of the paper is on the evaluation of the effectiveness of inverter VAR control within Southern California Edison (SCE)'s distribution networks, which include lightly loaded circuits with significant PV installations. The simulations are conducted on feeder data exhibiting heavy solar generator capacity installed away from the substation, showcasing substantial voltage fluctuations across varied solar conditions. By examining different scenarios of solar outputs and load conditions, the paper explicates the optimal reactive power modulation enabled by inverter interfaces.

Several factors are considered crucial in determining optimal VAR injections, particularly the trade-off between minimizing line losses and the CVR effect. With inverter control, the simulation reveals reductions in energy consumption of over 1% and enhanced voltage regulation, all while maintaining operation within ANSI C84.1 specified voltage limits under varying load constraints.

The paper's primary contributions lie not only in demonstrating the feasibility of inverter VAR control as a reliable high-penetration PV solution but also insist on its practical applications. By exploiting inverter capabilities, utilities can manage voltage more effectively without incurring significant infrastructure costs, thus contributing to the transition toward a more sustainable and renewable-focused grid.

The findings have implications for the expanding adoption of distributed energy resources, emphasizing the need for revising standards like IEEE 1547, which currently discourage active inverter voltage regulation participation. The proposed optimization method opens avenues for advanced monitoring and control systems, which are pivotal as grid compositions evolve toward more distributed and renewable forms.

Looking forward, the paper suggests several paths for future inquiry, including further refinement of convex relaxation techniques and exploring scalability across wider grid networks. There is potential for improvement in adaptive algorithms that anticipate and adjust to real-time solar fluctuation patterns, thus enhancing the reliability and efficiency of distribution system operations.