Direct Comparison of Induction Motor and Line-Start IPM Synchronous Motor Characteristics for Semi-Hermetic Compressor Drives

Motors in semi-hermetic compressor drives are mostly fed from line. Because of good cooling conditions, the motors are heavily loaded and employ a specific rotor structure with “C” bore. In the field of semi-hermetic drives, the use of induction motors (IMs) is still dominant, although different motor types with line-starting capabilities, as for example line-start interior permanent magnet synchronous motors (LSIPMSMs), can be used. This work presents the direct performance comparison of a family of commercially available three-phase four-pole IMs for semi-hermetic compressor drives with the equal size prototypes of LSIPMSMs. The motors were rated as 1, 2.5, 3.8, 5.5, 7.5, and 20 hp. The presence of “C” bore in rotor structure can degrade LSIPMSM steady-state performance; therefore, the LSIPMSM designs steady-state performances are evaluated by FEA as well by the experimental method. The motors' dynamic performance is experimentally evaluated as well. The ultimate goal of this study is to reveal the improvement of LSIPMSMs characteristics in comparison to IMs characteristics and to check the possibility for the immediate replacement of existent IMs with LSIPMSMs in the target semi-hermetic compressor application.