Control methods for a brushless DC motor drive with a new converter topology

This paper presents a control strategy for a brushless DC motor (BLDCM) drive with a new converter topology. The new topology is based on the conventional voltage-fed inverter, but includes an additional source such as a capacitor or a battery, and requires connection to the BLDCM neutral. The objective of the proposed control strategy is to control the otherwise unregulated voltage across the additional source, while maintaining commanded speed or torque. Three variations of the control strategy are presented. A detailed simulation model is used to evaluate the performance of the considered converter with proposed control strategy, and compare it to a conventional voltage-fed inverter BLDCM drive. Performance measures include torque per unit current, copper losses per unit current, inverter losses, and efficiency. It is also shown that exact torque and speed control can be exercised at up to twice the rated speed. Simulation results for operation at twice the rated speed with the torque controlled to half the rated value are provided to demonstrate that. This is a major advantage over the conventional BLDCM drive, where speed and torque are usually uncontrolled above rated speed. In addition, the drive is shown to deliver rated power (at rated speed) with only half the dc link voltage.