Cogging torque reduction by optimal design of PM synchronous generator for wind turbines

In this study, design and optimization of a surface-mounted permanent magnet synchronous generator (PMSG) have been carried out for use in low power wind turbines. In the successive optimization steps based upon the parametric solution method, design parameters of skew, pole embrace, and pole arc offset are chosen to be optimized so that the cogging torque is reduced. Cogging torque is a type of torque ripple coming from the machine design and causes undesired vibration and acoustic noise during the operation of machine. Moreover, although the effect of cogging torque in high power surface-mounted PMSGs is not sensible, it becomes important in low power applications to maintain good dynamical behavior. Analytical and finite element analysis (FEA) are conducted after obtaining the magnet structure that provides minimum cogging torque. Electrical and electromagnetic distributions are presented according to the changes in the corresponding design parameters. While the cogging torque in the initial design is 522.7 mNm, it has been reduced to 49.1 mNm in the optimized generator, which in turn means an improvement of about 90%. The generator under consideration has the specifications of 2.5 kW, 120 V, 14-pole with an inner type-rotor.