Comparison of Brushless DC Motor Drives with 180/120-Degree Inverter Systems

This paper compares the brushless dc motors with 180/120-degree inverters and the average-value modelling of these systems. In 180-degree inverters, each phase is always connected to the dc source and the average voltages are readily known. In 120-degree inverters, each phase is open-circuited for a fraction of revolution resulting in discontinuous phase current and different commutation-conduction patterns, which makes it challenging to obtain an accurate average-value model. This paper investigates the averaging approach that neglects the commutation time, and shows that this approach may degrade model accuracy when the stator resistance is relatively small. The paper also suggests a new approach to overcome the limitations of existing models.