Effect of the Interaction of Different Manufacturing Imperfections on the Unbalanced Radial Forces in a Sub-Fractional HP Single-Phase BLDC Motor

Unbalanced magnetic forces have been identified as one of the main causes of noise and vibration in small permanent magnet machines. Dynamic and static eccentricity as well as non-uniform magnetization are known as the dominant sources of the aforementioned forces. This paper analyzes the effect of the inter-action of these different types of manufacturing imperfections on the unbalanced radial forces, focusing particularly on their phase difference. It shows the wide range of resulting distributions of the magnetic force that significantly exceeds those of the single-effect analyses. This explains the widespread structure-borne noise observed with sub-fractional HP machines, also reflected in extensive experimental investigations. The analyses also explore how dynamic eccentricity can counteract non-uniform magnetization and vice versa.