Patent ID: 7759897

Claim:
A method for sensorless estimation of rotor speed and position of a permanent magnet synchronous machine, when the permanent magnet synchronous machine is fed with a frequency converter, the method comprising the steps of forming a stator voltage reference for the permanent magnet synchronous machine, injecting a high frequency signal (u c ) into the stator voltage reference, measuring a DC-link current (i dc ) of the frequency converter when the permanent magnet synchronous machine ( 4 ) is fed with a voltage (u s,ref ) corresponding to a sum of the stator voltage reference and the injected signal, calculating a stator current estimate (î s ), calculating a current error (ĩ s ) as a difference between the stator current estimate and the measured DC-link current, and estimating a rotor speed ({circumflex over (ω)} m )and position ({circumflex over (θ)} m ) of the permanent magnet synchronous machine based on the current error, wherein the injected high frequency signal (u c ) comprises a direct axis component and a quadrature axis component, the direct axis component having a first frequency and the quadrature axis component having a second frequency, the first and second frequencies being different.