Dynamic model of brushless DC drive using FE method based characteristics

In general, a brushless dc (BLDC) motor is modeled by using a trapezoidal waveform as a back electromotive force (E.M.F.). It is a simple model with moderate accuracy. However, when BLDC motor operates in a high speed range where the back E.M.F. plays an important role to the characteristic of the machine, the trapezoidal back E.M.F. could lead to erroneous results. Although the finite element (FE) analysis can be applied for modeling with high accuracy, it takes so much time to simulate one operating point. Moreover, it is complicated and time-consuming to run in the dynamic operations. Therefore, it needs to be optimized between accuracy and time consumption. This paper presents a dynamic simulation model of BLDC motor with more accuracy comparing to the conventional simulation model. It uses the back E.M.F. and inductance which are obtained from the finite element method (FE method). The model was implemented in MATLAB/Simulink and PLECS program. In this work, the outer rotor BLDC motor for electric bicycles was used. The results of simulation model were verified by experiment.