## 1 Introduction  
Technological progress has led to a rapid growth of the use of distributed photovoltaic electricity production. However, this trend did not prevail for a long time because it failed to match the required voltage quality in low-voltage grids (LVG). Cases of violation of upper voltage limit have been identified [1; 2; 3; 4; 5]. Very soon, it becomes clear that in distribution grids, the reactive power support is needed when distributed generation (DG) is in operation [1; 2; 6; 7; 8].  
The literature extensively discusses the possibility of using the smart inverter of photovoltaic (PV) facilities to eliminate the upper voltage limit violations in low-voltage (LV) smart grids. Each inverter is upgraded with \(cos\varphi(P)\) or \(Q(U)\) local controls [9; 10; 11]. The grid operator determines the reactive power contribution of the PV inverters by fixed or variable target values [12]. The latter can be set by remote control, i.e., online presetting of target values, or by schedules [13]. The set value may be a constant power factor [12; 13; 14; 15; 16; 17], constant reactive power [12; 13; 14; 16; 17], constant voltage at a given bus [13; 18], \(Q(U)\) characteristic [11; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23], or \(cos\varphi(P)\) characteristic [12; 14; 16; 17; 21; 22; 23]. \(P\) and \(Q\) are the active and reactive power provided by inverter; \(cos\varphi\) is the power factor set at inverter level; \(U\) is the voltage of the feeder bus where the inverter is connected. These methods are further refined by including more local variables [14; 15; 16; 18; 19; 21]. Although all of these methods act on local variables, many studies require a communication infrastructure to coordinate them by sending set points [18] or certain parameters [20]. This complicates the practical implementation of the local Volt/var control strategies, and therefore, their use is still very limited. Furthermore, PV inverters in \(cos\varphi(P)\) or \(Q(U)\) operation mode causes an excessive reactive power flow, thus increasing considerably the grid loss and loading of the distribution transformers (DTRs) [24; 25]. The constant power factor operation mode even exacerbates the problem of unnecessary \(Q\)-flows and grid losses [21].  
All of the local Volt/var control strategies mentioned above provoke distributed var-sinks throughout the length of the feeder. As an alternative, in this work, we introduce concentrated var-sinks at the end of each violated feeder. The concentrated var-sink is modeled as a variable inductance \(L\), i.e., concentrated local control strategy \(L(U)\). We discuss the effectiveness of distributed versus concentrated Volt/var local control strategies in LVG in three cases. Firstly, their theoretical behavior is analyzed and compared in a very simplified model. Secondly, the behavior of distributed \(Q(U)\) and concentrated \(L(U)\) local control is investigated and compared in a test overhead feeder. Thirdly, the impact of both control strategies on the reactive power exchange of an urban and rural real grid is explored and compared. Additionally, their effect on the medium-voltage grid (MVG) is analyzed. Finally, conclusions are presented.