**2. Input-Series Output-Series (ISOS) DC-DC Converter**

In this section, the ISOS DC-DC converter circuit diagram, as well as the ISOS DC-DC converter SSM, are discussed in detail. The analysis carried out in this section, as well as the following sections, is not restricted to unidirectional power flow and can be applied for bidirectional power flow. In addition, a three-module based DAB topology is considered. Such configurations are employed when galvanic isolation is required.

To reduce the SSM in terms of complexity, it is assumed that all the modules of the ISOS, ISOP, IPOP, and IPOS DC-DC converter have an equal turns ratio and effective duty cycle as well as the same inductor and capacitor values. In other words, the SSM for the four architectures is derived, assuming ideal conditions. The SSM, carried out in this section and the following sections, is used in Section 7 to support the controller design for each configuration.
