Abstract: The current freewheeling phenomenon and its causation of torque ripple were analysed. With the relationship between rotor and coil position, the traditional selection rules of voltage space vector were modified. To effectively control the freewheeling current, two different voltage space vector under the three-phase conduction model was proposed, making current keep close to the ideal curve and inhibit torque ripple. For speed adjustment, the Pang-Pang control was carried out after flow stage. The simulation model was carried out under the Simulink environment. The simulation results show that the proposed voltage space vector can effectively adjust the freewheeling current at the whole speed range and control the torque directly so that the percentage of torque ripple can be controlled below 8%.

Key words: brushless dc motor, the freewheeling current, voltage space vector, simulation modeling