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

Small electric drives with power from a few hundred watts up to one kilo watt, developed for car actuators, drivetrains, electric bikes or scooters, are nowadays often realized as permanent magnet synchronous machine. For mass production, these machines are designed with delta-connected stator windings. But the influence of the delta-connection is often not investigated. Hence, this paper presents a comparison of copper- and iron-losses for star- and delta-connected windings. Testbench measurements are performed over the whole operating range on a built-up prototype machine, which allows switching between a star- and a delta-connected stator winding system. Precise copper-loss detection, especially including the zero-sequence current in delta-connection, is enabled by additional phase-current sensing. A new approach for determining fundamental iron-losses is introduced.The results show that the overall losses are smaller for delta-connection. The consideration of the individual loss components show that, for this prototype, the zero-sequence current at delta-connection leads to lower iron losses. In this case, the smaller amount of iron-loss outweighs the additional copper-losses. Therefore, the delta-connected machine shows a better efficiency than the star-connected machine.