show the d- and q- axis current waveforms
before and after compensation. Before compensation, motor daxis
current has a prominent current ripple. This is because
that the flux linkage that couples to motor stator winding is
changing referring to different rotor permanent magnet
position. Since the field of rotor permanent magnet is not an
ideal sinusoidal distribution, the back-EMF induced stator daxis
current inevitably contains some ripple. Once the
harmonic back-EMF is compensated, the d- axis current ripple
is controlled and its transient peak value has been reduced
from 0.2 A to 0.05 A. The same result can be observed with
the q- axis current. After compensation the current ripple of
the q- axis current is reduced from 0.08 A to 0.06 A. This has
verified improvement of the proposed compensation strategy.