Generally, the torque control of the PM motor is achieved
by controlling the stator current based on the fact that motor
electromagnetic torque is proportional to the armature current
and the permanent magnet. Space vector control is applied for
high performance PMSM control and the control is normally
executed in the rotor d/q reference frame which has a
synchronous rotating speed with the PM rotor. Ideal motor
mathematic model are used in PMSM space vector control by
neglecting the saturation of armature and the wastages of eddy
and magnetic hysterics. Motor three phase windings are
considered electrical symmetry and rotor permanent magnet(PM) is sinusoidally distributed. Yet this is not always the case
because rotor permanent magnet state varies greatly with
different motor [4][5][6], and motor operation condition will
also influence the rotor PM state [7][8]. That means rotor
permanent magnet intrinsically contains harmonic component.
Rotor flux linkage estimation and compensation is a
reasonable solution for better motor operation [9][10]. Since
the modeling of the PM state is complicated, and there is not a
universal mathematical equation considering all PM state, it
will bring great difficulty to the proper control of PM motor.
This paper proposed a harmonic back-EMF compensation
strategy aiming at reducing the influence of the non-ideal rotor
permanent magnet. In the proposed method an ideal model is
used which provides referenced motor terminal voltage.
Comparing this reference with the inverter output,
compensation voltage is calculated and fed back to the motor
to counteract influence of the harmonic back-EMF. Detailed
analysis together with simulation and experimental results are
described in below sections.