# Voltage Optimization in PV-Rich Distribution Networks--A Review
## 3 Voltage Optimization in PV-Rich Distribution Networks--Objectives and Variables
### General Formulation--Objectives and Variables
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Reference**} & **Single/ Multi-Objective** & **Objectives** & **Variables** \\ \hline
[65] & single-objective & min VD & PV inverter reactive power, OLTC \\
[38] & multi-objective & min losses, min VD, min VUF, min PV & PV inverter reactive power \\  & & generation cost, min PV APC cost & PV inverter reactive power and static \\
[66] & multi-objective & min losses, min VD, improvement VSI & PV inverter reactive power and static \\
[53; 54; 67; 68; 69] & multi-objective & min losses, min VD & PV inverter reactive power \\
[70] & multi-objective & min VD, min losses & PV inverter reactive power, CBs, and OLTC \\
[71] & single-objective & min VUF & PV inverter active and reactive power, power \\
[72] & single-objective & min VD & PV inverter reactive power \\  & & min losses, min cost of APC and & \\
[73] & multi-objective & generated/consumed reactive power, min & PV inverter reactive power \\  & & VD & PV inverter reactive power, OLTC, VR, and \\
[74] & multi-objective & min VD, min voltage unbalance & CB \\
[75] & multi-objective & min losses, min VD, min VUF & PV inverter reactive power \\
[32] & single-objective & min VUF & PV inverter reactive power \\
[76] & single-objective & min VD & PV inverter reactive power, OLTC \\
[77] & multi-objective & min losses, min VD, min control action of & PV inverter reactive power, OLTC, SC \\
[78] & single-objective & min VD & PV inverter reactive power, OLTC \\
[79] & multi-objective & min VD, min losses & PV inverter reactive power, OLTC, and SC \\
[57] & multi-objective & min VD, min losses, min reactive power & PV inverter reactive power \\  & & injection, and absorption & PV inverter reactive power \\
[80] & multi-objective & min VD, min losses & PV inverter reactive power, OLTC \\
[81] & single-objective & min VD & PV inverter reactive power, OLTC, and VR \\
[58] & multi-objective & min VD, min losses, min APC & PV inverter reactive power, OLTC and CB \\
[55] & multi-objective & min VD, min losses & PV and EV inverter reactive power, the \\
[56] & multi-objective & min VD, min OLTC tap operation & compensation device \\
[82] & single-objective & min VD & PV inverter reactive power, \\
[83] & multi-objective & min losses, min VUF & PV inverter reactive power \\
[34] & multi-objective & min cost, min losses, min cost associated & PV inverter active and reactive power \\  & & with active power setpoints, min VD & PV inverter active and reactive power \\
[84] & multi-objective & min active and reactive power output, min & PV inverter active and reactive power \\  & & VD, min losses, min peak of reactive & PV inverter reactive power \\
[37] & multi-objective & min VD, min losses & PV inverter reactive power \\  & & min VD, min losses & PV inverter reactive power, OLTC, CB \\
[85] & multi-objective & min VD, min losses & PV inverter reactive power, EV active and reactive power, bus voltages at all time intervals of the day \\
[59] & multi-objective & min VUF, min losses & PV inverter reactive power, OLTC, CB \\
[86] & single-objective & min VD & PV inverter reactive power \\
[88] & multi-objective & min VD, min losses & PV inverter reactive power \\  & & min VD, min losses, min number of & \\
[89] & multi-objective & switching operations of OLTC and CB, min & PV inverter active and reactive power, CB, \\  & & APC & PV inverter active and reactive power, CB, \\
[90] & multi-objective & min VD, min operational cost & PV inverter active and reactive power, CB, \\
[91] & multi-objective & min VD, min losses, min peak of reactive & OLTC, ESS \\
[39] & single-objective & power & PV reactive power \\ \hline \hline \end{tabular} The abbreviations are as follows: CVR: conservation voltage reduction; VSI: voltage stability index; SC: shunt capacitor; AVR/VR: automatic voltage regulator; CB: capacitor bank.  
\end{table} 
Table 3: _Cont._According to the literature review, the multi-objective problem prevails.