Aggie E Bike

Team

• Rees Hatch
• Mahmoud Monsour
• Garret Witmer
• Oscar Silva
• Layan Nimri

Introduction

Aggi-E-Bike reinvents the electric drive for an bicycle to achieve higher power density while still being cost-effective. The challenge to push converters to be smaller comes with the trying to remove heat generated by the non-ideal circuit components. The interdisciplinary Aggi-E-Bike team has worked side by side to tackle this challenge. The team will also be representing USU at IEEE's 2019 Inter-national Future Energy Challenge (IFEC) final competition in late July in Madison, Wisconsin. The competition requirements and judging criteria have heavily influenced the design decisions made for the project; requirements such as no forced air cooling and a fixed motor speed limit.

The chosen topology for the converter is the standard 3-phase bridge (inverter). Given the specifications, a front-end convert-er was deemed unnecessary and been omitted from the design. The selection of the power switches in the inverter is a trade-off for performance and cost. State-of-the-art eGaN FETs were se-lected due to their incredible low on-resistance and switching times. The eGaN packages are also miniaturized to aid in the heat transfer from package to heat sink.

Control Strategy

The control of the converter is done through modulation of in-verter switches. The primary system input is the user throttle lo-cated on the handlebars, and the output is the torque applied to the wheel of the bicycle. To simplify the control of the 3-phase system, field-oriented control (FOC) is used to regulate direct and quadrature current components. Current measuring IC's provide current feedback and the motor's hall sensors are used to calculate the motor speed and position, which is required for FOC.

The goal of the enclosure design was to find the optimized shape to balance surface area with volume while still maintain-ing the entire case below 62 °C with the surface being no more than 48 °C. We achieved this by taking advantage of a honeycomb struc-tured design giving the case dimensions of 3.75" x 2.5" x 1.5". The diagrams shown to the right shows the temperature gradi-ent at two different cut planes on the case. From the diagram one can tell that the highest temperature achieved is 46.5 °C. It is also apparent the effective-ness of the honeycomb structure as in slice (1), the maximum temperature isn't reached until the very top.