Loss Comparison of Small Delta- and Star-Connected Permanent Magnet Synchronous Machines

Delta-connected stator windings are often used in mass production of small Permanent Magnet Synchronous Machines (PMSMs). In comparison to star-connected stator windings, a delta-connected winding system offers advantages for manufacturing and lowers production costs. A main disadvantage of motors with such a winding system are additional losses caused by the Zero-Sequence Current Component (ZSCC). In this paper the ZSCC and its impact on the generated losses in a delta-connected PMSM used as a traction motor for a pedal electric cycle (Pedelec) is analysed. The calculated results are compared to those of a star-connected PMSM with the same design. We will show that the amplitude of the ZSCC depends on the operating point of the machine. As a result, the copper losses in the delta-connected machine are up to 5.8 % higher than the ones in the star-connected machine. On the other hand, the iron losses are 1 % smaller in the delta-connected machine. The efficiency of the delta-connected machine is still up to 4 % smaller.