Simple overlap angle control strategy for commutation torque ripple minimisation in BLDC motor drive

In this paper, a novel overlap angle controlled Direct Torque Control (DTC) scheme is proposed which strikes the balance between commutation torque ripple and losses. The commutation torque ripple in a Brushless DC (BLDC) motor is mainly due to the effect of commutation on non-commutating phase current and it will be more severe in high power applications. DCT techniques are used to reduce the torque ripple. In comparison to the conventional two-phase conduction Six-Step DTC (SSDTC), the commutation torque ripple is considerably reduced by Twelve-Step DTC (TSDTC) but at the cost of increased inverter and winding losses. The proposed method offers commutation torque ripple minimisation and loss optimization simultaneously by controlling the motor operation in hybrid two- and three-phase conduction. The proposed method basically leads to motor operation in three phase conduction during overlap region and in two phase conduction during non-overlap region. The overlap and non-overlap regions are identified by calculating the commutation interval and suitably scaling it by a factor. The proposed method is validated through experimental results and the effect on commutation torque ripple and drive efficiency are compared with SSDTC and TSDTC experimentally.