Three effective vectors-based current control scheme for four-switch three-phase trapezoidal brushless DC motor

This study presents a novel three effective vectors (TEV) current control scheme for four-switch three-phase inverter in cost-effective brushless DC motor drive with improved performance. This scheme overcomes the possible distortion of three-phase currents caused by phase C back-EMF, and quasi-square current waveforms are attained by inserting two adjusting vectors in each control period based on the conventional switching modulation scheme. The duty cycles of the two adjusting vectors are further calculated using a simple P controller. Integral variable structure control principle with advantages of high bandwidth and strong robustness against external disturbance is used to control the tracing of reference current by actual currents. The stability of the proposed TEV current control scheme is demonstrated by selecting a candidate Lyapunov function, based on which the range of duty cycles of adjusting vectors are also determined. Experimental results verify that the proposed scheme is simple and can provide small current ripple, with good performance in speed.