# Research on Optimal Voltage Control of Distribution Network with the Participation of EVs and PVs
## 3 Case Studies
### Basic Information of the Test Cases  
The single-line diagram of the IEEE 123-node test feeder is shown in Figure 11, with three EV charging parks and six solar systems integrated. The power ratings for a single EV charging park and single solar system are 600 kW and 200 kW, respectively. To take into account the impact of preliminary load demand variation on the grid voltage profiles, selected residential load profiles are randomly distributed to the default loads, as in Figure 12. Figure 12 also denotes that the distribution network has the highest preliminary power consumption during the period of 7 p.m. to 11 p.m., which overlaps with the charging peak period of EVs. The EVs gathering to charge at peak hours can result in under-voltages issues and the overloading of power transformers and distribution cables. The typical PV generation profiles applied to the six solar systems are illustrated in Figure 13, assuming all the solar systems are operating on a sunny day. It is observed from Figure 13 that the solar systems have the highest power generation during the period of 10 a.m. to 2 p.m., which may mitigate the grid congestion due to EV charging. All applied daily load profiles and PV generation profiles are taken from a database disclosed by a UK DNO [41]. To provide the grid voltage support, all six solar systems are characterized by a voltage droop control, as described in Figure 6. The minimum allowed power factor for all solar systems is 0.9 (leading or lagging).  
Based on the Monte Carlo simulations conducted in Section 2.3.1, it is expected that each EV charging park with a power rating of 600 kW can accommodate up to 250 EVs per day. To emulate the uncontrolled EV charging behaviors, it is assumed that 700 EVs are connected to three EV charging parks with a combination of different arrival times and charging durations. All EVs are charged at unity power factor without considering the power losses during the charging process. As EVs of different transport types are featured by diversified charging patterns, it is assumed that all the 700 EVs are made up of private cars, buses, taxis, and exclusively-used cars, with their percentage share equaling 85%, 2%, 5%, and 8% respectively. Each EV's arrival time, initial battery SoC, battery capacity, type of charging, and charging period are randomly generated from its typical  
Figure 11: The single-line diagram of the IEEE 123-node test feeder with EVs and PVs connected.  
charging pattern, as defined in Table 1. All the EVs have the V2G capability and can provide bidirectional active power flow between the power grid and the EV battery. It should be noted that the lithium-ion EV battery enters into constant voltage charge mode with a significantly slow charging speed when the EV battery SoC is above a threshold value of around 95%. Therefore, the expected EV battery SoC after charging is assumed to be 95%. For unregulated EV charging, all EVs are charged at their rated charging power once they arrive at the EV charging parks, with their aggregate daily EV charging demand profiles illustrated in Figure 14. It is noticed that the diversity of EV types results in several spikes in aggregate EV charging demands during the day. When those spikes are superimposed on the peak power consumption of preliminary loads, the bus voltages may drop below the safe margin. To address this issue, six OLTC transformers and four capacitor banks are deployed, and their basic information can be found in [42]. The minimum and maximum bus voltages are 0.95 pu and 1.05 pu, respectively. The optimization problems associated with the two-stage voltage control are solved with a modified JAYA evolutionary algorithm, with its details provided in [43].  
Figure 14: The charging demand profiles allocated to three EV charging parks.  
Figure 12: The normalized daily load profiles applied for the IEEE 123-node test feeder.  
Figure 13: The normalized PV generation profiles of the six solar parks.