To eliminate control error of speed or torque which is caused by temperature change, and ensure stability, by calculating secondary side magnetic flux vector from current vector and calculated primary side magnetic flux vector, calculating rotation speed from the secondary magnetic flux vector and secondary current vector, and estimating secondary side resistance.
By voltage and current vectors from the outputs of voltage and current detecting means 3, 4, primary side magnetic flux vector is calculated by a computing element 7. A secondary side magnetic flux computing element 9 calculates secondary side magnetic flux, from an output current of a phase shift corrector 6 and primary side magnetic flux of a magnetic flux drift limiter 8. A magnetic flux differential computing element 11 calculates a differential value of magnetic flux from the output of the secondary side magnetic flux computing element 9. A secondary side current computing element 12 calculates a secondary side current from an output current of the corrector 6 and the primary side magnetic flux of the output of the limiter 8. A speed calculating means 14 calculates a rotation speed from the secondary side magnetic flux vector and the secondary side differential value, and calculates secondary resistance R2 with an R2 estimation part 16, via an judging part 15.
YASUKAWA SHINOBU
MIYASHITA ICHIRO
