# Impact of the Integration of the Electric Vehicle on Low-Voltage Rural Networks
## 5 Improvements to the Charging Procedures
### Scenario 3: Connection of Specific Power Electronics to Reduce Voltage and Current Unbalance  
The charging control presented in Section 5.1 can prevent overloads and excessive voltage drops, indirectly mitigating unbalances by reducing current intensity. However, it does not address the issue comprehensively, as it lacks individualized control for current flowing through the phase where each charger is connected. Scenario 3 includes using a three-phase, four-leg D-STATCOM (Figure 7a), connected at low voltage to mitigate the unbalance effect [31]. The fourth leg allows the circulation of current through it, thereby enabling the independent control of currents in each phase without the requirement that the sum of phase currents be zero. However, since it lacks an energy source connected to the DC bus, such as batteries or a generation system, it cannot generate the direct component of active power. Nevertheless, it can extract active power from one phase and inject it into another, thereby maintaining the total sum of active power at zero. This configuration allows the control of the homopolar (zero) and the reverse (negative) components of the current, the direct component of the reactive power, and the active power exchange between phases. The goal of this 4 legs D-STATCOM is to have the upstream active power (\(P_{i,\text{up}}\)) equal in all three phases and zero reactive power (\(Q_{i,\text{up}}\)):  
\[P_{i,\text{up}} =\frac{\sum P_{i,\text{down}}}{3} \tag{4}\] \[Q_{i,\text{up}} =0 \tag{5}\]  
Figure 6: Charging profiles of Electric Vehicles in Scenario 2. Figure 7: Description of the D-STATCOM and its operation. (**a**) dlegs D-STATCOM schematics [31], (**b**) D-STATCOM connection and current balance. Then, the D-STATCOM must inject the required active power (\(P_{set_{1}}\)) and reactive power (\(Q_{set_{1}}\)) to compensate for the difference in each phase:  
\[P_{set_{1}} =P_{i,\text{up}}-P_{i,\text{down}} \tag{6}\] \[Q_{set_{1}} =Q_{i,\text{down}} \tag{7}\]  
being \(Q_{i,\text{down}}\) the reactive power downstream. Calculating the current setpoint in each phase (\(\textbf{I}_{set_{1}}\)) is obtained from the apparent power (\(\textbf{S}_{set_{1}}\)) and the voltage in each phase as follows:  
\[\textbf{S}_{set_{1}} =P_{set_{1}}+\text{j}Q_{set_{1}} \tag{8}\] \[\textbf{I}_{set_{1}} =\frac{\textbf{S}_{set_{1}}}{\textbf{V}_{set_{1}}} \tag{9}\]  
Figure 7b shows the connection to the grid and how the D-STATCOM uses the active power exchange between phases to equilibrate the currents upstream of the connection point. The position of the D-STATCOM should be the most suitable to mitigate the effects of the EV charging process. From the results of Scenario 1, Circuit 3 (in pink in Figure 1), which presents the highest voltage drop, was selected. In this circuit, the impact of a 30 kVA D-STATCOM in 5 different positions was analyzed, with Position 1 being the furthest away from the transformer and Position 5 the closest. Table 3 and Figure 8 show the results obtained with the D-STATCOM connected at the five selected circuit positions compared to Scenario 1. In all cases, the voltage drop is improved, although it does not reach a value higher than 0.9 p.u., as shown in Figure 8a. The peak load is reduced by approximately 10% in all cases. The optimal outcome was achieved in Position 2, resulting in a significant reduction in maximum neutral current from 152.1 A to 87.5 A, marking a substantial decrease of 58%. Additionally, this position exhibited the most notable improvement in voltage drop, showing an increase of 4%. Furthermore, in Position 2, there was a notable enhancement in the maximum load of the network, which improved from 85.06% to 72.58%. To analyse these results, the active and reactive power contribution of the D-STATCOM in each phase must be considered, as well as the active and reactive power values per phase upstream of the equipment connection point. Figure 9a,b show the active and reactive power exchanged by each phase of the D-STATCOM.