DTC of B4-Inverter-Fed BLDC Motor Drives With Reduced Torque Ripple During Sector-to-Sector Commutations

The paper deals with the direct torque control (DTC) of brushless DC (BLDC) motor drives fed by four-switch inverters (also known as B4-inverters) rather than six-switch inverters (also known as B6-inverters) in conventional drives. The B4-inverter could be regarded as a reconfigured topology of the B6-inverter in case of a switch/leg failure which represents a crucial reliability benefit for many applications especially in electric and hybrid propulsion systems. The principle of operation of the BLDC motor is firstly recalled considering both cases of B6- and B4-inverters in the armature, with emphasis on the two- and three-phase conduction modes. Then, the DTC of B4-inverter-fed BLDC motor drives is treated considering three strategies, such as: 1) DTC-1: a strategy inspired from the one intended to B6-inverter-fed BLDC motor drives; 2) DTC-2: a strategy that considers a dedicated vector selection subtable in order to independently control the torques developed by the phases connected to the B4-inverter legs during their simultaneous conduction; and 3) DTC-3: a proposed strategy that eliminates the torque dips penalizing DTC-2 during sector-to-sector commutations. Following the design of the corresponding vector selection tables and subtables (if any), an experimentally based comparative study of the three DTC strategies is carried out considering, in the first step, the BLDC motor steady-state operation under DTC-1 and DTC-3. Then, the comparison is extended to the BLDC motor features during sector-to-sector commutations, under DTC-2 and DTC-3. The experimental results clearly validate the predicted performance of the proposed DTC strategy.