Stationary plane based investigation of the behavior of PM BLDC drives

The paper investigates the behavior of permanent magnet (PM) brushless DC (BLDC) drives in the stationary plane. The vectors of the phase currents and back-emfs are first drawn under ideal square-wave current supply. Development of a constant torque from the motor is explicated with the help of the vector representation. Trajectories of the tips of the motor current and voltage vectors are then traced for various motor speeds taking into account the phase commutations. Torque developed by the motor and its ripple are determined from the vector tip trajectories. Theoretical findings are supported by simulation results obtained by using the data of a PM BLDC drive designed for the propulsion of electric vehicles