A novel sensorless control method for four-switch, brushless DC motor drive without using any 30° phase shifter

This paper introduces a novel and low cost brushless DC (BLDC) motor drive. Proposed drive is a four-switch inverter for a three-phase BLDC motor, without any mechanical hall sensors. The proposed concept is based on the fact that in a four-switch topology, the zero crossing points of the stator terminal voltages Vao and Vbo-Vao and -Vbo coincide to six commutation instants and can be used to commutate the current in phases A, B and C respectively. These stator voltages are actually line-to-line voltages and are measured respect to point o (middle point of DC-Bus) easily. Hence, it is not necessary to delay 30deg after zero crossing points of the measured voltages which are prevalent in the other conventional six-switch and four-switch BLDC motor drives. This approach made it possible to detect rotor position in relatively wide range of speed variation. Also direct phase current control (DCC) method is used to control the phase current in four-switch inverter. The performance of the developed concept is demonstrated by simulation.