BS in Electrical Engineering
Electrical Engineering Department
The ongoing Energy Harvesting from Exercise Machines (EHFEM) project at Cal Poly San Luis Obispo seeks to provide renewable energy without the high cost of implementation by harvesting DC power generated on machines used for physical exercise. The EHFEM project consists of numerous subprojects that involve converting different types of exercise machines for power generation. This project specifically works by scaling the output voltage from an elliptical machine using a DC-DC converter and sending it through an Enphase Micro-inverter to feed AC power back to the power grid and minimize energy spending. As a subset of the much larger project, the design presented in this paper seeks to improve on a previously designed SEPIC topology for the project’s DC-DC converter by providing an input protection scheme.
DC-DC converter circuits operate within set parameters regarding current and voltage at their input. Any input above the designed limits may adversely affect the circuit. Implementing an input protection circuit helps to prevent damage to the DC-DC converter in the off chance that inputs stray outside the designed operating range. This paper proposes a two stage input protection circuit to limit the input of the DC-DC converter to within its operational range of 5 V to 65 V. The first stage uses capacitive filtering and decoupling techniques to protect against overvoltage transients and smooth the DC signal. The second phase of protection deals with sustained overvoltages associated with the Enphase Micro-inverter’s start-up period where an open load appears across the DC-DC converter. The design operates without significant loss of energy when within the operating range, and, during overvoltage events, allows the DC-DC converter to remain in operation with a 65V input. The device also minimizes fabrication costs to allow recovery of its initial production costs within 10 years of normal use and uses a minimal number of components without use of any excessively large components to facilitate an easy assembly and device installation.