An improved Phase Variable Model Based on Electro-magnetic Field Coupled with its External Circuits for Performance Evaluation of Permanent Magnet Brushless DC Motors

This paper presents the comprehensive performance evaluation of a brushless permanent magnet (PM) DC (BLDC) motor in dynamic conditions by an improved phase variable model based on electro-magnetic field coupled with its external circuits. In the proposed model, the inductances, back electromotive force (emf) and cogging torque are obtained by nonlinear finite element analysis (FEA). The phase variable model is built and implemented in the MATLAB/Simulink through a method of look-up table to decide the emf which depends on rotor position. Furthermore, based on a mathematical function for the decision to the voltage of the three phase winding central point, the model could not only solve the problem to decide the input voltage of the phase which is in a non-energized condition, and also make the transient current process during the commutation clear. The theoretical verification is also given in detail. By using the developed model, the comprehensive performance of BLDC motors could be investigated.