Combined Unipolar and Bipolar PWM for Braking Control of Brushless DC Motor

This paper proposes a novel hybrid PWM mode for braking control of the brushless dc motor in the electric vehicle drive applications. To simplify the hardware circuit topology and reconstruct the real-time motor currents, a single dc-link current sensor sampling method is employed. However, in small duty ratio applications, the current signals cannot be sampled accurately under the conventional unipolar PWM mode due to the limitation of amplifier bandwidth and analog to digital converter sampling time. Therefore, a hybrid PWM mode based on unipolar-bipolar switching is used to obtain the current signals in a wide duty ratio range. The method proposed in this paper combines the advantages of unipolar and bipolar PWM, and realizes the real-time current control of brushless dc motor in the braking process. Simulation and experimental results verify the feasibility of the proposed control mode.