Performance improvement of brushless DC machine by zero-sequence current injection

A novel current control strategy for Brushless DC machines (BLDCs) is presented in this paper. It aims to increase BLDC exploitation compared to conventional current commutation (two-phase-on) and three-phase-on control approaches. The proposed current control strategy consists in injecting a suitable zero-sequence current in order to exploit the BLDC zero-sequence back-emfs. Thus, increased torque capability and/or reduced Joule losses can be achieved compared to conventional control approaches. As a result, BLDC competitiveness can be increased, even in comparison with Brushless AC machines (BLACs). The effectiveness of the proposed approach is validated through both theoretical and finite element analyses, the latter being carried out by means of JMAG. The analyses regard the comparison between BLAC and BLDC driven by different control strategies.