Electric Generator for Ocean Wave Energy Converter

Abstract

This paper presents design of a Radial Flux Permanent Magnet (RFPM) ring generator for an ocean Wave Energy Converter (WEC). It has a large diameter 61.4 cm and low speed 37.5 rpm. Three phase one layer concentrated winding design is investigated. The design was carried out with the help of SmartCAD machine design and Comsol software. Contribution is done to add an optimization loop to the machine design software. Monte-Carlo method is used to optimize the design with the objective of high efficiency and low cost. Cost optimization includes cost of material, cost of production and cost of losses or efficiency. Production cost is added to the SmartCAD design tool as a separate subroutine. Three groups of slot and pole combinations are considered. The slot and pole combinations with Np = Ns ± 2k where k=1, 2 are further narrowed down to Np = Ns + 2, with higher fundamental winding factor and lower cogging torque amplitude. The optimal design has 72 slots and 74 poles with 86.7% efficiency. Cost of material and production is estimated of 3085 NOK. With assumption of 4000 hours operational time per year and life time of ten years, the cost per kWh for the WEC is estimated. Based on the SmartMotor experience, cost of the mechanical and electrical parts will be roughly as 1 NOK/kWh per year. This is comparable to the cost of Salter duck and higher than IPS OWEC. The further investment and improvement is worthy. The Finite Element Analysis (FEA) is then used to confirm optimality of the design. The parameters are measured in Comsol and then compared with the Matlab result. The entire machine is simulated as rotor moving across one pole pair.