Design of an Electric Motor for Marine Applications : A Compact Motor Design Study

Sammanfattning

This thesis investigates how an electric motor can be designed for a retrofit hybrid propulsion concept intended for leisure boats. In the proposed concept, the electric motor is mounted around the propeller shaft for use at low speeds to reduce emissions and noise from the combustion engine. This creates the need for a small and compact motor that can provide the required torque and speed while operating submerged. The motor must also be designed with an open area through the rotor to allow exhaust gases from the combustion engine to escape through the propeller hub. The main design requirements were a maximum outer stator diameter of 110 mm, a maximum stack height of 120 mm, a minimum torque of 10 Nm at 300 rpm, a top speed above 500 rpm, and a minimum open cross-sectional rotor area of 30 cm2. The design process was performed in several steps. A baseline design was provided, but it showed significant limitations in both electromagnetic and thermal performance. Initial estimates were therefore made, and the motor geometry was calculated. Based on these values, simulations were performed in Motor-CAD to further improve the design. The final motor design fulfilled the main requirements and produced an average torque of 23.75 Nm at 500 rpm. The final open rotor area was 33.3 cm2, which satisfies the requirement for exhaust gas flow. The motor was simulated as submerged in water at a temperature of 25°C, resulting in a maximum winding temperature of 48.7°C and a magnet temperature of 36.8°C. This indicates that the motor design is promising in a simulation environment, however, several limitations still need to be addressed. Further work is needed on mechanical stress and design, manufacturing tolerances, more advanced thermal simulations that represent a motor in moving water, and motor control strategies for maximizing performance.