# Voltage Optimization in PV-Rich Distribution Networks--A Review
###### Abstract  
There is a rising trend to integrate different types of distributed generation (DG), especially photovoltaic (PV) systems, on the roofs of existing consumers, who then become prosumers. One of the prosumer impacts is voltage violations, which conventional strategies find hard to solve. However, some prosumers, such as those with PV with inverters in their configurations, can actively participate in voltage optimization. To help find the optimal PV inverter setting with the objective of voltage optimization, an optimal power flow (OPF) can be a promising and reliable tool. This paper tries to shed light on the complex problem of voltage optimization in distribution networks (DNs) with PV prosumers. Relevant scientific papers are analyzed and optimization characteristics such as objective functions, variables, and constraints are summarized. Special attention is given to the systematization and classification of papers according to the mathematical formulation of the optimization problem (linear, nonlinear, integer, etc.) and the applied solving methods. Both analytical and computational intelligence optimization methods as well as their advantages and limitations are considered. Papers are also categorized according to the distribution network model used for testing the developed solutions. active distribution networks; optimal power flow; prosumers; PV inverter volt/VAR optimization; review +
Footnote †: journal: Applied Sciences  
optimal power flow (OPF) has proven to be an efficient tool for the operation of active DNs. In order to illustrate the problem/solution principle of PV inverters, a case study is developed in this paper presenting the low voltage DN with the connected PVs. Different power flow simulations are presented and they include:  
* the situation when PVs production is maximal and voltage rise along the feeder is present;
* the situation when PV inverters inject reactive power. Nowadays, optimal management of active DNs represents an attractive topic, and a large and growing body of literature focuses on this topic. Some related reviews on the optimization DNs are listed in Table 1. Refs. [10,11] show the impact of PV on DNs, the related problems, and possible solutions. Refs. [12, 13, 14] study voltage violation mitigation and voltage control strategies. Ref. [12] deals with voltage control methods in DNs with PVs and their advantages and disadvantages. In addition to [12], a comprehensive review of voltage control methods is given in [13]. In [14], voltage control models and methods are divided according to the communication strategy. The application of OPF in DNs is discussed in [15,16]. The researchers in [15] address a probabilistic approach to solving OPF in active DN. The authors in [16] study OPF in smart DNs and microgrids according to objectives, methods, and future challenges. While refs. [15,16] present interesting and useful reviews of OPF application to modern DNs, they are mainly focused on active power objectives [16] and probabilistic OPF [15]. So far, the research gap is present in the area of voltage optimization objectives in the case of using PV inverters for reactive power management. The problem/solution principle of using PV inverter reactive power for voltage mitigation motivated the authors of this paper to focus their review on scientific papers that applies OPF for voltage optimization in the DN using PV inverter reactive powers. The contributions of this review paper are:  
1. Summary and classification of OPF objectives and variables in the case of voltage optimization in the DNs using PVs reactive power.