Voltage Regulation at Grid Edge: Tuning of PV Smart Inverter Control Harsha V. Padullaparti, Naveen Ganta, and Surya Santoso Department of Electrical and Computer Engineering The University of Texas at Austin, TX, USA Email: harshap@utexas.edu Abstract—Smart inverters with appropriate settings can im- prove voltage regulation in a distribution grid. However, tuning their settings for each PV for best possible benefits is not feasible. In this paper, a procedure to tune the PV smart inverter settings by grouping the PVs in the feeder neighborhoods experiencing undervoltages is proposed. Analysis supporting the implemen- tation of common smart inverter setting within a given feeder neighborhood is presented. The voltage regulation performance of the tuned PV smart inverter settings is then compared to that of the settings recommended in literature using voltage range and variability indices. The results show that, with the use of tuned settings, voltage range is reduced by 64% and variability index is by 82.5% compared to unity power factor inverter setting in the studied circuit. Index Terms—Distribution System, Inverter, Photovoltaics, Voltage regulation. I. I NTRODUCTION Distribution utilities are required to deliver power to the customers connected on the low-voltage secondary circuit while maintaining acceptable service voltages at the load connection points. The low-voltage secondary circuit can also be referred to as grid edge [1]. The commonly used service voltage magnitudes on the secondary circuit in the U.S. are 120 V and 240 V. ANSI C84.1 voltage standards [2] specify the acceptable levels of service voltages as ±5% of nominal voltage level, which translates to 0.95 to 1.05 per unit (pu) voltage. When a service voltage goes below 0.95 pu, it is considered as an undervoltage violation. On the other hand, when the service voltage exceeds 1.05 pu, then it is an overvoltage violation. Utilities employ traditional voltage regulation devices, connected on the primary, such as load tap changer (LTC), mid-line voltage regulators, and capacitor banks to maintain acceptable service voltages, i.e., to perform voltage regulation. Despite the application of these devices, some distribution circuits still experience undervoltages in some feeder neighborhoods (circuit sections). Typically, the loads connected in the feeder neighborhoods farther from the substation experience undervoltage violations during the peak load period due to excessive voltage drops across the circuit elements and lack of sufficient reactive power support [3], [4]. In such situations, advanced voltage regulation devices reported in [1], [5], [6] can be employed to augment the traditional voltage controls to improve the voltage regulation [3]–[5]. These devices, connected at the grid edge, help regulate the load voltages by injecting the series voltage or providing capacitive reactive power. Alternatively, the smart inverters of the PV systems installed in the feeder neighbor- hoods experiencing undervoltages can be tuned to provide appropriate reactive power support to mitigate undervoltage violations and to enhance the voltage regulation. The active voltage regulation by the PV installed in distri- bution grids was not permissible in the past [7]. Nonetheless, recent standards permit utilizing the PV smart inverter func- tionality for voltage regulation [8]. However, the determination of appropriate PV smart inverter settings is a complex process as numerous settings are possible to implement on a smart inverter and the feeder response to a given setting depends upon a wide variety of parameters such as the feeder charac- teristics, loading condition, PV size, and PV location [9]. As such, detailed studies with numerous scenarios [10] are needed to customize the smart inverter settings for each individual PV based on its associated impact on the distributed grid to achieve the ‘best’ possible benefits. However, such analysis may not be feasible for time-constrained utilities due to limited engineering and data resources [9]. While attempts have been made for this reason to develop simplified methods to derive smart inverter settings [9], [11], they primarily focused on improving PV hosting capacity and developing off-the-shelf inverter settings. In this work, a procedure to tune the PV smart inverter settings by grouping the PVs in the feeder neighborhoods experiencing undervoltages is proposed for voltage regulation. The analysis supporting the implementation of a common smart inverter settings for all the PVs within a given feeder neighborhood is presented. The performance of the tuned PV smart inverter settings is compared to that of the settings recommended in [9], [12] using voltage range and voltage variability indices. The results show that, implemen- tation of the tuned settings is very effective leading to the reduction of voltage range by 64% and variability index by 82.5% compared to the unity power factor inverter setting in the studied circuit. II. DISTRIBUTION CIRCUIT DETAILS One of the standard distribution test circuit models devel- oped by EPRI namely ‘Circuit 5’ is used in this study. The one- line diagram of the circuit, generated using Sandia GridPV tool [13], is shown in Fig. 1. This circuit has a 115/12.47 kV, 10 This accepted version article has been published in Proceedings of the IEEE PES T&D Conference & Exposition, Denver, CO, April 2018.