Patent ID: 7352151

Claim:
A method of estimating a magnetic pole position in a synchronous motor having salient poles, comprising the steps of: providing a motor model expression for estimating the magnetic pole position from an instructed voltage applied to the motor, a current generated from the instructed voltage and a parameter; and calculating an estimated magnetic pole position in the motor from the instructed voltage, the generated current and the parameter according to the motor model expression, wherein the step of calculating the estimated magnetic pole position comprises: applying, to the motor, a phase matching voltage which has a frequency higher than that of the instructed voltage and has a phase matching with the estimated magnetic pole position previously obtained; detecting a phase matching current generated from the phase matching voltage from the motor; correcting a value of the parameter such that a difference in phase between the phase matching voltage and the phase matching current substantially becomes zero, and calculating an estimated magnetic pole position from the instructed voltage, the generated current and the parameter having the corrected value.