Optimal design of cylindrical air-gap synchronous permanent magnet couplings

Different types of structures for ironless synchronous cylindrical air-gap permanent magnet couplings are studied. In these structures, radially and tangentially oriented magnets are placed in ironless cores. The structures present a very small inertia and offer important benefits in many cases. An efficient method to calculate the torque of these types of couplings is presented. It is based on analytical formulas for the forces between parallelepipedical magnets. Optimal designs for each type of coupling and each number of pole pairs are determined by using a nonlinear optimization method. The design results are analyzed. The different types of structure are compared. The influence of the number of pairs of poles and of the main characteristic dimensions of each coupling is discussed. The results show that an ironless coupling structure where both radially and tangentially oriented magnets are used is a very advantageous solution.