Date

6-2014

Degree Name

BS in Electrical Engineering

Department

Electrical Engineering Department

Advisor

David Braun

Abstract

The goal of the Energy Harvesting from Exercise Machines (EHFEM) project seeks to harness the energy generated by people using exercise machines and deliver this energy to the electric grid [1]. The implementation consists of a protection system, DC-DC converter, and an inverter. This project involves redesigning the existing DC-DC input protection circuit and current limiter for the EHFEM project [2]. The DC-DC converter takes in the power from the exercise machines and converts it to a manageable voltage level for the inverter. Due to a problem where the inverter may overload the converter, a current limiter sets to limit the current between the two circuits [4]. The inverter demanding more current at a lower voltage than the DC-DC converter can provide causes this overload.

The input protection circuit for the DC-DC converter presents another major component of the protection system. The DC-DC converter must operate within set input voltage and current parameters. Concurrent with this project, students Byung Yoo and Sheldon Chu have developed a new DC-DC converter design with an operational range of 6 V to 51 V [7]. This paper proposes a design for an overvoltage protection circuit to limit the input of Yoo’s and Chu’s DC-DC converter to within its operational range. The input protection circuit regulates the incoming voltage from the elliptical machine and filters out any high frequency transient responses with capacitive filtering to generate a smooth DC signal. The circuit also functions to divert excess voltage and current that accumulates during the Enphase Micro-inverter’s startup period where an open load appears across the DC-DC converter leading to an overvoltage level [3]. A current sense circuit ensures the output from the DC-DC converter to the inverter delivers only as much power as the inverter can convert [4]. The device maintains a minimal component count number and lacks any excessively large components permitting easy assembly and installation. The device operates with a minimal loss of energy and minimizes fabrication costs allowing for recuperation of initial production costs over 10 years of normal use.

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