This thesis presents the topic of using the Four-Switch Buck-Boost topology as a DC-DC converter for the Energy Harvesting from Elliptical Machines Project. The project works toward providing a modular synchronous power generation system. Due to the dynamic and sporadic output voltage and power characteristics of the Precor elliptical machine, the system requires a DC-DC converter as a voltage preregulator. The inherent wide input range, high efficiency, and low parts cost of this converter well suit the application. This paper further discusses other topologies and their shortcomings, as well as characterizes the Precor elliptical machine and Enphase Microinverter for interfacing. This report contains a detailed discussion on component selection and PCB layout. The converter averages 94% efficiency during a normal workout power range. This paper also derives a system level control scheme for a modular grid-tie energy harvesting power electronics unit. The Four-Switch Buck-Boost topology efficiently and effectively harvests energy from the Precor elliptical machine as a constant input impedance and wide input voltage regulator for a constant voltage grid-tie inverter.