Method and apparatus for controlling an AC motor and detecting malfunctions

摘要

Disclosed are methods and apparatus for quickly measuring a primary resistance value of an AC motor without using high precision detectors and detecting malfunctions such as breaking of wire in the AC motor or in a power converting mechanism, open phase, and three-phase unbalance. A voltage drop attributable to the primary resistance of the AC motor can be estimated by using an estimated resistance value R1#, which is estimated in turn by an integral or proportional-plus-integral operation on the deviation between a detected magnetizing current value IM and a reference magnetizing current value IM*, in place of an actual primary resistance value R1. The time for the estimated resistance value R1# to reach the true primary resistance value is reduced with a varying reference magnetizing current value IM**. Variations of the estimated primary resistance values R1#s between the phases are corrected with a mean estimated primary resistance value R1M# according to a reference phase value phi *. Malfunctions such as open phase and breaking of wire are detected by comparing estimated primary resistance values obtained according to the reference phase value phi *.