Performance of a three-phase permanent magnet motor operating as a synchronous motor and a brushless DC motor

Abstract

The performance of a three-phase permanent magnet (PM) motor operating as a synchronous motor and brushless DC (BLDC) motor is discussed. The PM motor, when operating as a synchronous machine, is supplied with constant frequency, meaning constant rotor speed operation. When operating as a BLDC motor, the supply frequency changes according to the actual rotor speed. It means the speed signal is fed back to the controller, which generates the appropriate frequency to supply the stator winding. This means the BLDC motor cannot operate without a position sensor. The objective of the project was to analyze and compare the performance of the motor operating as a BLDC and synchronous motor. To do this, mathematical models for both operation modes (that allowed us to analyze the performance in dynamic conditions) were proposed. The analysis was carried using the results obtained from simulation done with the MATLAB/SIMULINK software package. To analyze the motors’ performance in steady-state conditions, simpler motor models were proposed and calculations carried out using MATLAB m-files. The results obtained from the two types of models were compared and a good match was observed. To verify the simulation mathematical model, an experiment was performed on the real object where the synchronous motor was tested. The motor was supplied from a 3-phase inverter board (controlled by dSPACE controller) which operated in conjunction with MATLAB/SIMULINK. This allowed us to supply the motor with variable frequency at a constant voltage to frequency ratio. Despite the small discrepancies between the experimental and simulation results, the mathematical model used to analyze the synchronous motor was verified.