An Efficiency Analysis of a Salient Pole and a Flux Barrier Synchronous Reluctance Machine including Flux Weakening

In this work two different rotor topologies for synchronous reluctance machines are discussed regarding the efficiency including flux weakening operation of a variable speed drive. For a low power industrial drives, currently utilized with an induction machine, a salient pole and a flux barrier reluctance rotor are designed to replace the squirrel cage rotor at lower machine costs. Both rotors are built up and implemented in the common three phase stator. The rotor change for this drive is proposed, because generally a higher attention of electric machine's efficiency is set to the part load region according to the latest IEC standards. The machine parameters as well as the torque and power characteristic are discussed and finally the machine efficiency is analyzed by measurements. As expected from the finite element analysis the salient pole rotor provides a higher power than the flux barrier type, especially at higher speeds. The salient pole machine prototype is able to fulfill the required power characteristic of the application, but the flux barrier machine does not. Additionally, the salient pole rotor shows a higher part load efficiency. From the loss analysis a high loss portion is identified as the mechanical friction loss, which dramatically limits the machine efficiency for both rotors. Thus, a friction loss reduction by improved ball bearings is proposed, which would improve the drive efficiency significantly.