# Modern MultiPort Converter Technologies: A Systematic Review
## 2 General Classification and Operation Principles
### Bidirectional and Unidirectional Multiport Converters  
Applications for energy storage systems are driving the demand for multiport bidirectional converters. The power flow in these converters can pass either direction. These converters are mostly used in EV or HEV, including trains, nano and microgrids, and other types of electric drivetrain systems. The well-known isolated bidirectional converter is a dual active bridge (DAB). In [65] an innovative multiport bidirectional converter is suggested for electric car energy storage. Both bidirectional boost and buck modes can be operated with the help of the proposed converter. The multiport converter has three ports via which energy can pass. The suggested converter's primary characteristics are its low component number, low peak voltage of the major switches, and minimal losses. Furthermore, the suggested converter uses only two power switches, which facilitates the transfer of power between the sources.  
In order to operate with a higher switching frequency, achieve a better power density, and improve the efficiency of the bidirectional converter authors in [66] suggests a zero-voltage-transition (ZVT) three-level DC-DC converter. To test the converter operation mode, a 650 W prototype has been created. At a switching frequency of 200 kHz, it achieved the maximal efficiency of 95.5%.  
In [67] authors introduce a three-port integrated bidirectional DC-DC converter for a DC distribution system. One port on the low voltage side of the proposed converter is picked as the current source port because it works with PV panels that have a wide range of voltage. Additionally, the current source port's interleaved design can deliver the needed low current ripple to help PV panels achieve optimal power point tracking. Additionally, it is demonstrated that the two control variables duty cycle \(D\) and phase-shift angle \(\varphi\) can be separately adjusted in a three-phase system to achieve better MPPT characteristics.  
The power flow in unidirectional types of multiport converters is only in one direction. The energy source can be used only to supply power to the load. These converters are widely used in renewable energy applications in the absence of energy storage systems. A bidirectional multiport converter can be developed by substituting unidirectional semiconductors with bidirectional ones.  
In [68], a multiport converter based module-level technique is provided for capturing the maximum of power from a solar system under partial shadowing. Each module in the multiport converter topology has a dedicated switch connected in series with it so that it can run at its peak power. Each module operates independently of the others and reaches its own MMPT depending on the operational environment. Additionally, the MPC is resistant to short-circuit and module mismatch circumstances.  
The authors in [69] present an advanced multiport DC-DC converter. The proposed converter is made up of numerous switched capacitor cells, with each cell having two diodes, an active switch, and a switched capacitor. Due to its simplicity and ease of expansion, this structure may accommodate applications requiring a large number of inputs, ranging from two to an infinite number. High frequency is used to run the converter. Because non-resonant versions do not need resonant inductors, they are compact and have a simple topology.