# Modern MultiPort Converter Technologies: A Systematic Review
## 2 General Classification and Operation Principles
### Isolated Multiport Converters  
Galvanic isolation between the input and output stages is a typical feature of the isolated multiport converters, as shown in Figure 4.  
Thanks to the pulse transformer's turns ratio, it can also be used for buck and boost applications in addition to galvanic isolation. The isolated multiport converters' primary feature is the use of separate windings for each power input. The fluxes of each main winding contribute to the voltages induced in the secondary winding. Isolated multiport converters are typically employed in RES and hybrid electric vehicle (HEV) applications. Isolated multiport converters have a number of benefits, such as less risk of electric shock, a wide range of voltage gain, noise filtering, and integration of various voltage ratings. In [38], a new topology for a galvanically separated DC-DC converter is described; it includes fuel cells and batteries as input sources and simultaneously powers both a high-voltage (HV) and a low-voltage (LV) load. The converter allows electrical power to flow between sources and back towards the battery during recuperation so that the battery can be recharged while in flight. It also allows power to flow from sources to the load. A real-time (RT) hardware-in-the-loop (HIL) test bench is used to confirm the converter design's functionality. The suggested idea is easily adaptable to any fuel cell and battery motor train for all-electric flights of various sizes. There are two conversion stages in the \begin{table}
\begin{tabular}{l c c} \hline \hline
**Components** & **Proposed n-Port Cuk-Cuk Converter** & **(n-1) Individual Cuk Converters** \\ \hline Inductors & n & 2(n \(-\) 1) \\ Capacitors & n & 2(n \(-\) 1) \\ Switches & n \(-\) 1 & n \\ Diodes & 1 & 2(n \(-\) 1) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of components in [35]. Figure 4: Structure of isolated double-input-double-output (DIDO) port converter system. converter. A hybrid converter is made up of capacitor-inductor-inductor-capacitor (CLLC) and inductor-inductor-capacitor (LLC) converters. Lastly a 1 kW prototype is emulated with the help of OP4510 real-time HIL. The results of these tests are described, and they closely resemble the waveforms predicted analytically. A novel isolated current-fed DC-DC boost type converter is suggested and developed in [39]. The converter is using two input power sources based on a multi-transformer structure. This converter is suitable for the application of fuel cells and super-capacitors in a hybrid energy system. The proposed multiport converter can draw power from two different DC sources with lower voltage and send it separately or simultaneously to the higher voltage DC bus or load using a specific transformer windings connection technique. In both dual-input mode and single-input mode, the suggested converter's detailed operating principle has been examined by the authors. Additionally, ground loop decoupling, the magnetic integration structure, and other means to expand the number of input ports are presented. The main power flow path, which consists of four transformers and eight diodes acting as a secondary side rectifier, is shared by both input ports of the proposed converter and may be independently controlled, resulting in a higher power density. This is one of the converter's most notable features. At the same time, there are some drawbacks of the proposed MPC, such as complicated transformer winding connections and separate ground connections. Aiming at low inertia DC micro-grid bus voltage quality and the energy storage system's state of charge balance issue, taking into account the pressing need for distributed micro-sources with high up/down ratios, electrical isolation, and high-efficiency converters, a multiport isolated DC-DC converter is suggested in [40]. A parallel and coordinated control technique appropriate for four port-isolated converter is proposed to achieve the balance of the energy storage state of charge and the proportional relationship of output power.