Electrical Engineering Department
BS in Electrical Engineering
David B. Braun
The EHFEM project aims to convert the energy generated by exercise in a gym to electrical power and transport said energy to the grid. At the top level, this project includes several components including: a voltage and current protection system, a DC-DC converter, and an inverter. This project improves upon past voltage protection systems  . The DC-DC converter takes the user-generated energy from the elliptical trainer and passes it to the grid. The user can generate voltage spikes upwards of 100V, far above the current DC-DC converter’s maximum limit. The voltage protection circuit sits between the energy harvesting machine and the DC-DC converter and limits the voltage allowed across the converter. This ensures voltage spikes cannot overload and damage the energy harvesting mechanism. An inverter designed for solar cells expects current to increase as voltage decreases and places a dangerous demand on the DC-DC converter.  The voltage protection circuit works in conjunction with a current protection circuit to stabilize voltage and current outputs to the DC-DC converter and prevent any damage.
In 2014, Byung Yoo and Sheldon Chu designed a DC-DC converter with an operating range of 6 - 51V. At the same time, Cameron Kiddoo and Eric Funsten designed a voltage protection system (VPS) to work within this range. Their design monitored the input voltage and diverted the power to ground when it exceeded 51V using an IGBT. This project proposes a VPS that operates both within the converter’s range and improves upon previous VPSs. The VPS regulates the incoming elliptical trainer voltage and passes it through five capacitors to filter out high frequency transients and power supply noises as well as to smooth out sharp spikes to produce a DC signal. When the elliptical voltage exceeds 51V, the output voltage at the source terminal of the transistor also reaches 51V, at which point the transistor stops the voltage from rising further. A high power PMOS and a power resistor ease the power dissipation requirement of the NMOS. Minimizing power loss as well as component count and size allows for an easily assembled system with a payback period of ten years at normal use.