A Current Control Scheme of Brushless DC Motors Driven by Four-Switch Three-Phase Invertersvv

Abstract-Based on brushless DC motors (BLDCM) driven by four-switch three-phase inverter (FSTPI), a current control scheme is proposed to reduce the current ripple of both normal conduction region and commutation region. Assuming c-phase winding is connected to the middle point of DC-link capacitance, in the normal conduction region when a-phase and b-phase windings conduct, the current of c-phase may not be zero because of c-phase back electromotive force (back-EMF). The proposed strategy adds two regulating vectors into each control cycle based
on traditional PWM scheme, and controls the c-phase current to be zero by controlling the working time of regulating vectors in each control cycle. In the commutation region, the non-commutated phase or the outgoing phase switch is modulated by comparing the change rate of incoming phase and outgoing phase currents to maintain the non-commutated phase current constant. Compared with traditional current control strategy, good control effect is kept both in the normal conduction region and the commutation region by accurately controlling the working time of voltage vectors. The proposed strategy do not need to adjust the parameters of the controller and it is simple and easy to implement. The experimental results prove the correctness and effectiveness of the control strategy.