Analytical Calculation of Line Current for Brushless DC Motor

In order to easily and accurately predict mechanical characteristics of brushless DC motors,the analytical calculation of the line current was done.Firstly,the commutation process including the case of induction and resistance was analyzed based on the motor circuit model and voltage balance equation.It was analyzed that the ratio of electromagnetic time constant and a commutation cycle period at a state angle was the main reason of the three-phase transient current variations,which makes line current calculation model divided into two parts.Then,the analytical expressions of the phase transient current variations were derived.At last,line current analytical solutions were given by the means of Matlab.The calculating results of two typical prototypes were compared and verified with experimental data.The error was less than 5%,and the method was easy and fast and had a high precision.As a result,the method in this paper can provide a reference for the motor design and application.