## 2 Power System Impacts of EVs
### Impact on Power System Stability  
Power system stability is defined as the return to a normal or stable operating state after a malfunction in the power system. Power outages in the power system have a significant impact on the stability of the smart grid. In addition, EVs have non-linear load characteristics in the power system and create various stability problems in the network. The fact that EVs have equipment such as a DC-DC converter and inverter power electronics causes some power quality deterioration, and this affects the grid. In addition,  
Figure 1: An illustration of the roles of EVs and other suppliers/consumers in the smart grid. uncertainties such as the charging times, power ratings, and connection locations of EVs in the smart grid cause some difficulties in estimating the load behavior [37]. Therefore, connecting a large number of EVs to the smart grid causes significant concerns. EVs are not only distributed energy storage devices but also power electronic converters and dynamic loads that affect the stability of the power system as an electrical load [38]. The power system stability effects caused by EVs in smart grids are summarized in Table 1. Among these effects, voltage instability occurs when the reactive power demand is not met and in overload situations [39]. System planning and the operation of EVs in smart grids are important in order to ensure the voltage stability of loads. It is known that EV load group characteristics connected to the network cause voltage instabilities [40]. Although EV loads tend to consume more energy in low-operating voltage situations, they also negatively affect the voltage stability of the system. In order to minimize voltage stability problems, the optimal placements, quantity, and power ratings of EV charging stations should be determined according to the network structure [41]. Frequency stability and its control are significant problems for system design and operation in smart grids. Various control loops serve to keep the system frequency at a constant set value. The general purpose of these control structures is based on a certain amount of power reserve that is kept ready against power deviations [42]. Variations in power supply and demand may have a significant impact on grid frequencies. For example, if more power is needed than that available, the frequency will be less than the nominal value. In the opposite case, injecting the excess power value to the system will cause the frequency value to increase. Electrical systems require real-time equality between generation and consumption to provide a stable grid frequency. Otherwise, the grid frequency deviates from the desired value. More power has to be generated and supplied to keep the grid frequency within the allowed range if a high-rated load from the EVs is placed on the grid. Additionally, there are uncertainties related to the EVs' departure and arrival times. As a result, the consumer side becomes more unpredictable for power systems [43]. Small-scale distortions that occur while trying to synchronize the power system are defined as oscillatory effects. The interactions between EV energy generation/consumption changes and system component controllers while connected to the smart grid cause oscillations. In the system, the capacity of synchronous machines to ensure the balance between electromagnetic and mechanical torques specifies the oscillatory stability of a smart grid integrated with EVs [44]. Oscillatory effects are classified under several modes like local mode, inter-area mode, and torsional mode. In local mode, the oscillating effects are limited according to a singular energy generation unit or a restricted local region of power generation systems. This mode is characterized by the oscillation of the local power generation unit against the rest of the entire power generation system. The frequency oscillation values occurring in this mode typically vary in the 0.7-2.0 Hz band. The oscillation of generators in one area relative to generators in another area is called inter-area mode.