Pseudo constant power times speed operation in the field weakening region of IPM synchronous machines

Interior permanent magnet (IPM) synchronous machines have been known to have good field weakening characteristics and extended operating speed range over the surface mounted PM designs. Due to the constraints of some applications and the associated designs, there is a class of IPM synchronous machines which has characteristics current, X_PM/L_d, less than its peak current rating. Previous works have revealed that this type of IPM machine has limited range of constant power operation. However, not much work has been reported regarding the determination of the range and the nature of operations beyond the constant power operations. This paper presents criteria to determine the speed range of constant peak power operations and introduces a term, base power speed, to represent the corner point where constant power operation ceases. A concept of "pseudo constant power times speed operation" is introduced to describe the operations beyond constant power region. Good agreement is obtained between the simulation and experiment results done on a prototype IPM synchronous machine. Results presented in this paper are expected to help the understanding of IPM synchronous machine operations in the field weakening region.