# Modern MultiPort Converter Technologies: A Systematic Review
## 2 General Classification and Operation Principles
### High-Gain and Low-Gain Multiport Converters  
An important aspect of classifying multiport converters is the gain factor. Based on an application-oriented strategy and the demands of high gain or low gain, multiport converters can be chosen. This is important for the transfer of electrical power from the hybrid system based on various energy sources to the load. Various techniques, including the use of standard interleaved and cascaded boost converters, can be employed to attain a high gain [57; 58; 59]. The circuit's cost and control complexity are raised as a result of the application of these topologies, though. A number of isolated topologies are used, and in order to obtain high voltage gain, they employ transformers with the necessary turn ratio. Utilizing intermediate storage sources such as inductors and capacitors, high-gain topologies achieve high gain. In comparison to multiport converters that are coupled in series, the switching devices are under substantially more stress because of the high gain.  
The high gain is essential in fields such as motor drives and renewable energy. To meet load requirements, these converters raise the low voltage from energy storage systems and renewable energy sources to high voltage. By raising the turns ratio in the high-frequency transformer, it is possible to achieve high gain in isolated multiport converters. In [60] a multiport high-gain converter is proposed. The power source has one port, the battery has two ports, and the high voltage DC bus has three ports. In both boost/battery discharge and buck/battery charging modes, the operation of the converter is examined. The converter's operation and in-depth theoretical analysis are presented. The proposed converter is capable of bidirectional and inter-source power transfer. A gain comparison with other converters is performed. For the purpose of validating the theoretical and practical analysis of the converter, a 744 W converter is simulated in Matlab/Simulink environment.  
This research work [61] proposes a new architecture that combines the benefits of multi-input converters and high-gain converters. Two input ports are included in the suggested topology: one bidirectional port for an energy storage device and one unidirectional port for a solar energy source. To get high voltage gain, coupled inductor technology is applied. The topology and theoretical analysis are offered to clarify the operating principles. In [62], a DC-DC converter topology with a high step-up output is shown. Two input ports and four switches are part of the converter topology that is being suggested.  
Low-gain multiport converters are ideal solutions for use in electric car propulsion systems and some renewable energy applications. In [63] a multiport buck DC-DC converter is the subject of the investigation. Then, for each item, the relationship between the critical inductance in continuous conduction mode and discontinuous conduction mode is estimated after studying various operational modes of the converter for two, three, and four input sources. When the minimum inductor current is zero for a portion of the switching period (\(I_{LV}=0\)), the converter functions in DCM mode. Otherwise, it operates in CCM mode when the minimum inductor current is positive (\(I_{LV}>0\)).  
In [64] the authors propose a low-gain multiport converter which is carefully synthesized based on a topology that is a part of the switched-resonator converter family (SwRC). No transformer is used, and all ports share a common ground. The Route-Matrix concept is developed to identify the power multiplexing paths. A 250 W laboratory prototype's experimental examinations verify the validity of the suggested converter and the offered theoretical analysis of its working principles.