English In today’s world, global warming that is due to use of fossil fuels is becoming an important issue and motivates us to use renewable energy sources such as solar and wind energy. Because of safety requirements and the issue of partial shading, the parallel configuration of the solar panels is preferable compared to the series scheme in residential PV systems. However, since the voltage of each panel is considerably lower than the electrical grid voltage, implementation of the parallel configuration necessitates the use of a high step-up DC/DC converter to adapt the PV voltage level to the load voltage level. If the energy generation unit is equipped with battery for energy storage, another high-step up converter might be used to increase the output voltage of the battery to the high voltage level required by the PV inverter. The utilization of separate DC/DC converters for the PV generation and battery storage units is inefficient and bulky and it also increases the overall cost of the system. Separate DC/DC converters can be substituted with a multi-port DC/DC converter. Recently researches have been focusing on combining all DC/DC stages into a single, compact and low cost converter which includes inputs for PV modules and a bidirectional path for the battery port. This kind of converters are known as TPCs. In this thesis, after reviewing some of the recently developed TPCs, the first TPC is proposed which is based in the SEPIC converter and includes only two switches. One of the switches is turned-on under ZVS condition intrinsically and the other one is turned-on under very low voltage-low current. Therefore, the switching losses of the converter is reduced considerably. The conduction losses of the converter are also very low because of using minimum semiconductor elements in the high current paths such as PV and battery port current paths. One of the other key features of the proposed converter is the low current ripple for the PV input which is necessary for better utilization of MPPT without using extra filters. Both of the switches operate under low voltage stress in comparison to the output terminal voltage and this feature leads to utilization of lower drain to source resistance and therefore, lower conduction losses. The second proposed converter is similar to the first one, but with lower switching losses and better voltage gain. Actually, the turn-off switching losses of the converter is reduced to zero because of suing two passive lossless snubbers. All modes of operation, design considerations and experimental results for both of the proposed converters are presented and at last, they are compared to other TPCs. Key words: DC-DC power converter, Hybrid power system, High step-up, Three-port converter