## 2 Overview of EV and PV Systems
### PV Systems  
When studying how to integrate PV systems into the grid, first, it is very important to understand how a PV panel work. Figure 2 shows the current-voltage (I-V) and power-voltage (P-V) characteristic curves of a PV module. There are two important parameters of a PV module--short-circuit current (ISC), which is the current that flows through the solar cells when its voltage is zero; and open-circuit voltage (VOC), which is the maximum voltage a solar cell can provide when the current is zero. The power drawn from a solar module is a product of the PV module voltage and current setpoints. As can be seen in Figure 2, the power-voltage (P-V) characteristic curve of a PV module has a single maximum power point (MPP) corresponding to a specific current (IMPP) and voltage (VMPP) under a level of constant irradiance [28]. Then, one of the main purposes of a DC-DC converter used on a PV system is to achieve the MPP of the PV array. It is also important to understand the different categories of structures generally used to connect the PV source to the load. These types of structures are known as centralized, string structure, and module architectures. The centralized structure aims at connecting all the PV modules of a PV array to a single converter, which, depending on the system needs, can be a DC-DC converter or a DC-AC inverter, as shown in Figure 3a. The main advantages of using this structure are the low-cost installations and the simplicity of control as discussed in the literature [30]. However, the main drawback of this structure is the high variation of the output power due to the mismatch conditions of the series-connected PV modules. Mismatch conditions are generally caused by partial shading or dust accumulation in the PV modules or, in other cases, due to silicon impurities or aging of the solar panels. Therefore, when these mismatch conditions arise, a decrease in system efficiency is expected since the system cannot extract the maximum power from the PV array [28]. Some of the most used inverter topologies when using  
Figure 2: Current-voltage (I-V) and power-voltage (P-V) characteristic curves of a photovoltaic (PV) module [29]. this type of structure are low-frequency transformers and three-phase full bridges using insulated-gate bipolar transistors (IGBTs) [19]. On the other hand, string and module structures for PV systems were designed and developed to extract the maximum energy from the system [28; 31]. Figure 3b shows the string system architecture. As can be seen from the figure, PV modules are series-connected and grouped in different strings. Unlike the centralized structure, each PV string has its own DC-DC converter or AC-DC inverter that uses a maximum power point tracking (MPPT) controller to extract the MPP of each string. This type of structure aims to increase the efficiency of the system when mismatch conditions appear compared to the centralized structure, although the power losses remain significant within the same strings [28]. To further improve the MPP tracking efficiency of the solar PV system under mismatched conditions, the use of integrated module inverter structures has been proposed in the literature. In this structure, each PV module has its own power converter with an MPPT controller, as shown in Figure 3c. The main benefit of using this structure is the improvement on the MPP tracking efficiency for each PV module, thus decreasing the power losses produced by mismatch conditions. However, the use of this type of structure increases costs since a power converter is required for each photovoltaic module used [31; 32]. As described in the literature, in order to achieve high DC bus voltages in PV-grid tied systems, a PV module series connection is usually used, allowing it to supply power to both the AC grid and battery storage devices at a high efficiency (in this case, to the EV battery charger) [28; 33]. However, as discussed above, one of the main challenges to solve on the PV stage is the mismatch conditions that affect the power provided by the PV array.