## 5 PV Systems with Distributed Architecture
### Distributed PV Systems  
For the latter approach, each solar panel is connected to its associated individual DC-DC converter to supply energy to the output [92]. Each individual converter can achieve MPPT on the associated PV panel. Thus, each PV panel can output its maximum power. Figure 16 shows a traditional distributed PV system with individual converters. As can be seen in this figure, the output voltage, \(v_{o}\), and power, \(p_{o}\), are limited if each solar panel is operated at the MPP, because the generated PV power highly depends on the weather conditions, and the output currents (\(i_{o1}\), \(i_{o2}\ldots i_{om}\)) of each converter are identical. When the required output power is lower than the overall PV power, an additional power  
Figure 14: Centralized PV system with a string PV panel. Figure 15: Centralized PV system with bypass diodes. curtailment algorithm is required, which increases the complexity of the control and reduces the reliability of the PV system. In addition, the use of full-power DC-DC converters in this PV system architecture results in low power conversion efficiency. To improve the efficiency, some architectures with PPR have been proposed [93,94], as shown in Figures 17-19. As can be seen in these figures, the PV panels are connected in series with the output so that they can supply a part of the PV power to the output directly, resulting in high efficiency. Figure 16: Traditional distributed PV system with individual converters. Figure 17: Distributed PV system architectures. (**a**) Individual DC-DC converters connected between each PV panel and the output. (**b**) A DC-DC converter connected between PV panels and the output. Figure 18: Distributed PV system architecture with DC-DC converters connected between each PV panel. Figure 17a and 17b show distributed PV system architectures with each DC-DC converter connected between a PV panel and the output and with a DC-DC converter connected between the PV panels and the output, respectively. As can be seen in these figures, each PV panel can output its maximum power at multiple string current levels. However, in Figure 17a, due to the direct connection of the negative of input and output, isolated DC-DC converters are required [95]. In Figure 17b, the DC-DC converter is a multi-port converter, which could be different types of converters, such as a multi-winding converter [96] or a switched-capacitor converter [97]. A switched-capacitor converter was proposed in [97] for PV systems with differential power processing. Instead of inductors, ceramic capacitors are employed, resulting in lower costs and smaller volume. However, the main disadvantage of this architecture is the flexibility of the conversion ratio in most cases, reducing the reliability of the PV system when the weather conditions frequently change. An architecture based on battery equalizer was proposed in [98], with the advantage of just using one inductive storage element. However, only one inductor to process the PV power to the output results in high current pressure on the inductor. Additionally, since the output voltage, \(v_{o}\), is the sum of the PV voltages on n solar panels (\(v_{pv1}\), \(v_{pv2}\)\(\ldots\)\(v_{pvn}\)), the voltage difference between the output and each PV panel is high if a long-string PV module is used. Therefore, a high voltage step-up ratio of each DC-DC converter is needed, increasing the pressures on the converters. Figure 18 shows a distributed PV system architecture with a DC-DC converter connected between each PV panel. The main advantage of this architecture is that the voltage ratios of DC-DC converters are not affected by the load voltage, reducing the voltage rating [99]. However, when the PV string length increases, the maximum power processed by any DC-DC converter increases [100]. This causes an increase in the required current rating with the PV string length. Moreover, the distributed MPPT algorithm is required for easy scalability.