PRACTICAL ASPECTS REGARDING COMSOL CAD MODELS USED FOR DESIGNING A BRUSHLESS DC MOTOR

Abstract

The paper presents the main steps for designing a brushless dc motor (BLDC) with the aid of numerical modelling. In the first stage, an analytical pre-design is done, which is then followed by a design optimization based on resolving successive 2D Finite Element Method (FEM) models made in COMSOL Multiphysics v.5.3. The torque versus rotor position dependencies at different current supply are determined from numerical solutions of the magnetic field problems. Magnetic saturation, cogging and ripple torque, as well as the coil inductance required for proper design of the controller, are computed and values optimized by numerical analysis. Further, by coupling the magnetic model with electric circuit equations, the back phase and line to line EMF are computed. In addition, the paper presents practical aspects regarding numerical modeling, such as the best way to compute the electromagnetic torque and the inductance from the field solution. Firstly, a steady-state magnetic field step-by-step solution method was applied to compute torque for different rotor angles. In the second instance, the COMSOL dynamic “rotating machine” model was used, considering no induced currents but using the program ability to rotate the mesh and use previous magnetic field solutions for computing consecutive step-angle solutions, in order to save computational time.