Direct-drive Vernier machine with innovative stator design for enhanced demagnetization withstand capability

This paper proposes a Vernier machine with an improved stator design that adopts open stator slots and permanent magnets installed on both the rotor and stator. Compared to an existing Vernier machine in the literature, referred to as Design 1, the exclusive stator slots for permanent magnets in the proposed machine help mitigate demagnetisation issues by physically isolating the windings and the magnets. Additionally, the open stator slot design facilitates the installation of form-wound coils which is desirable for large generators used in direct-drive wind power applications. Using 2-dimensional finite element analysis, the proposed design is compared with a conventional surface-mounted permanent magnet machine, a conventional Vernier machine and Design 1. The findings indicate that the proposed Vernier machine uses both odd and even harmonics to generate torque, and it can exhibit superior electromagnetic performance, including torque and efficiency, compared to the conventional surface-mounted permanent magnet machine and conventional Vernier machines and demonstrate comparable electromagnetic performance to Design 1. Furthermore, to enhance the torque-to-mass ratio of the proposed Vernier machine, through-slots below the stator magnets are introduced and found to be effective without significantly compromising torque and efficiency. The simulations have been validated by experiments based on a prototype.