## 2 Power System Impacts of EVs
### Voltage/Current Distortions
In systems without harmonic components, the _THD_ value will not take any value. The _THD_ value calculation in current waveform with harmonic components is expressed in Equation (1):  
\[THD=\frac{\sqrt{\sum_{n=2}^{\infty}I_{n}^{2}}}{I_{1}}=\frac{\sqrt{I_{2}^{2}+I_{ 3}^{2}+..+I_{n}^{2}}}{I_{1}} \tag{1}\]  
where \(I_{n}\) defines the nth harmonic component of the current, and \(I_{1}\) defines the fundamental component value of the current signal. Supraharmonics are known as distortions in the current waveform with a frequency range of 2 kHz to 150 kHz. The increasing amount of EVs and EVSEs with power electronic converters triggered above 2 kHz also significantly increases the amount of supraharmonic distortions in the current and voltage waveforms. These high-frequency harmonic distortions affect the operation of sensitive devices connected to smart grids. In addition, this increases the thermal stress in the devices and reduces their lifetime [52]. Since EVs are generally charged with high power and are more susceptible to supraharmonic distortions than other consumer electronics, the impact on low-voltage installations is more significant. Supraharmonics induce various effects on low-voltage networks and the electronic devices tied to them. For a weak network in a high-impedance situation, the system current has supraharmonic components with large amplitudes, this may also the increase voltage distortion. The voltage disturbances reproduce extra supraharmonic currents into the plant, influencing more equipment. Basically, the electronic equipment is generally not immune to distortions in the aforementioned frequency values, as the supraharmonic emissions have been partially standardized until now. These problems can cause them to overheat and shorten their useful lifetime [53]. The faulty operation of power line communications, audible noise, and electromagnetic incompatibility are other negative adverse effects of supraharmonics [54]. In smart grids, EV load alterations can cause overcurrent, which is defined as an increase in the current. When the typical load current is exceeded in the smart grid, this results in an overcurrent [55]. Overcurrents can cause the destruction of the switching elements. In addition, the overloading of EVs is the main source of these problems. Circuit breakers and fuses are used to safeguard electronic equipment from hazardous overcurrents [56]. The start-up of EV loads is one of the reasons for the voltage sag in the main voltage. When a voltage sag problem occurs, the nominal voltage value decreases to between 0.1 and 0.9 pu. The duration of the voltage sag varies between half a period and 1 min. In addition, faults in the power system are also known as the most important factor causing voltage sags. After this problem occurs, very high currents can be seen in the system. Voltage sag can create harmful effects such as data loss and damage to equipment. On the other hand, the disconnection of EV loads may cause a rise in the network voltage [57]. An increase in voltage value is called a swell. In this situation, the value of the increase in voltage is more than 0.1 pu. The time interval of the swell problem is half a period to one minute. Voltage swell can cause hardware damage in smart grid systems [58]. \[V_{grid}<0.9\ \text{pu}\to Sag \tag{2}\]  
\[V_{grid}>1.1\ \text{pu}\to Swell \tag{3}\]  
The single-phase connection of EVs with smart grids causes unbalanced loading. This is because smart grids comply with system stability limitations and have considerable loading requirements in most cases. As a result, voltage imbalances occur. In this case, the amplitude values in the three phases differ from each other [57]. In addition, the dissimilar characteristics and loading planning of EVs create unbalancing issues. Loading characteristics have a large impact on the smart grid's voltage reliability [59]. As shown in Table 2, voltage fluctuations are defined as random voltage variations occurring in the range of 0.9-1.1 pu.