## 6 Grid Impact
### Stability of Power Systems/Grids  
Power electronics systems are increasingly present in electrical networks to regulate the greater penetration of RES, which can cause the global system to lose inertia and lead to problems with reactive power generation, frequency control, and imbalance between load and power generation [132; 134; 120].  
Due to their power electronics, chargers can be a source of network instabilities, making it necessary to control the location of the charger, monitor the SoC of the battery, and plan EV charge/discharge strategies to avoid destabilizing the network [121; 147].  
The combination of charging EVs, smart grid management, and renewable production can result in configuration that, rather than destabilizing the grid, has the opposite effect. EV charging and renewable production are random and distorting grid elements in separation; however, with proper smart control and V2G use it is feasible to transport energy where it is needed, stabilize grids through ancillary services such as frequency regulation, and avoid demand peaks even when performing a fast charge [130; 138].  
In order for these systems to favor the stability of the network, it is necessary to accurately model the network to obtain valid results [135].  
EVs can act as auxiliary services for management, network flexibility, and demand-side management [127; 137].  
To maintain a correct balance between demand and supply while ensuring that the electrical network works reliably, ancillary services supporting the network can be used to maintain sustainability and reliability. DSOs traditionally control local voltage and congestion prevention while TSOs control frequency (spinning and non-spinning reserve and regulation). With increased penetration of EVs and RES, DSOs will have to take on more responsibility in the spinning reserve and regulation areas [104; 148].  
The main ancillary service stabilizing an EV infrastructure network is the spinning reserve service (using V2G, where the energy stored in the EV is transferred to the network to collaborate or resolve situations of insufficient generation or supply failure, along with active power support/load leveling and peak load shaving), which mitigates consumption peaks or valleys at very specific times of the day caused by usage habits. In this way, \"load leveling\" will activate the EV charging mode, absorbing energy from the network when global electrical demand is low, while \"peak load shaving\" provides (injects) energy from EVs to the network when the demand is high. Reactive power support/voltage regulation/power factor correction is another service for grid reliability. It requires proper voltage and power factor regulation, which is corrected by a static reactive compensator. With the implementation of V2G, the capacitive power source can be obtained from the EV connected to the grid through its DC-link capacitor connected in a bidirectional EV charger. Thus, monitoring the EV voltage through a meter in the charger means that reactive power can be compensated for by regulating the phase angle. If grid voltage is high enough, the EV starts charging; otherwise, it stops charging [125; 131; 142].  
Installation of EV charging stations on weak buses causes grid instability problems such as power/economic losses and voltage instability. Fast charging stations cause even more instabilities. Several simulation studies have been carried out to determine these effects, which are highly dependent on the location of the network, finding that the system takes more time to recover previous conditions. Installing RES or local storage on charging stations has been found to improve network stability [141; 122; 143].