## 2 Power System Impacts of EVs
### Voltage/Current Distortions  
In a smart grid, the generated electrical energy should be supplied to receiving-end users as a smooth waveform. Electrical quality also means that power companies have to supply power without nonstationary disturbances that may affect the operation of connected loads. In recent decades, electrical quality has become a major concern for both users and plants and grid operators. With more critical loads and sensitive devices in smart grids, users need a better quality of electrical power at all times. Differences in electrical current/voltage waveforms that are far from the ideal can be defined as the most important electrical power quality problems. The current/voltage problems that occur due to the EVs connected in a smart grid are characteristically different from each other. The effects of these problems cause different destructions and malfunctions in the other connected power loads [46]. However, the duration of the effect on the user's side also varies. Table 2 shows potential power quality influences and the electrical characteristics of EVs connected to a smart grid. The electrical characteristic properties of voltage/current distortions are explained in [47]. As shown in the power quality influences of EVs in a smart grid, the most common problems owing to EV-smart grid integration are presented as harmonics, supraharmonics, and overcurrents. Sags, swells, unbalances, and fluctuations are voltage distortions that affect the users in the smart grid. EVs and charging stations contain a significant number of power electronic converters. These transducers provide them with a non-linear characteristic [48]. The non-linear \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Distortion** & **Causes** & **Effects** & **Duration** & **Magnitude** & **Waveform** \\ \hline \multirow{5}{*}{Current} & Current & Non-linear characteristics of EVs and EVSEs & Overheating of components & Steady state & 0–100 th \\ \cline{2-6}  & & Power electronic converters triggered above 2 kHz & Cause to overheat and shorten the useful life of the equipment & Steady state & 2–150 kHz \\ \cline{2-6}  & & EV load alterations & Malfunction of switching components & \textgreater{}1 min & \textgreater{}1.1 pu \\ \hline \multirow{5}{*}{Vollage} & Sags & Start-up of EV loads & Data loss and damage & 0.5 cycle–1 min & 0.1–0.9 pu \\ \cline{2-6}  & & Switching off EV loads & Hardware damage & 0.5 cycle–1 min & 1.1–1.4 pu \\ \cline{2-6}  & & Unbalanced loading & Unequal overheating and sequence currents & Steady state & 0.5–2\% \\ \cline{2-6}  & & Integration level and charging rate of EVs & Intermittent & 0.1–7\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Potential voltage/current distortions due to EVs integrated with the smart grid. behavior of these systems in a smart grid causes harmonic distortions on current waveforms. Due to the fact that household loads vary throughout the day and EVs charge only during specific times, current harmonics occur dynamically [49]. Serious issues might arise from the impact of current harmonics on electrically linked equipment. Moreover, the overall efficiency of the system would decrease, and malfunctions may occur if these harmonics are present in the grid. In an electric power plant, current harmonics can be a multiple of the fundamental frequency of the system [50]. The form or properties of a current waveform in relation to its fundamental frequency is a way to define the harmonics caused by EVs and charging stations. Harmonics are present in waveforms that depart from a sine wave appearance. The amount of harmonic distortion in the current waveform is estimated according to the concept of total harmonic distortion (_THD_) [51]. The _THD_ value is defined as the ratio of the sum of the powers of the harmonic components to the power of the fundamental frequency [47]. For an ideal current shape, it is a complete sine wave consisting of only the fundamental frequency, and the _THD_ value is zero.