In order to reduce this influence, a compensation strategy
is proposed and Fig. 2 shows its principle. In Fig. 2 the “Ideal
model” is the representation of equation (2). In the equation
'a
u , '
bu and '
cu are the analytical terminal voltages based on
this fundamental voltage equation, and they can be regard as a
mathematical expectation. ua, ub and uc are motor real terminal
voltages that applied to the motor. Their physical meaning can
be found in equation (7). The difference of these two voltage
types is the harmonic back-EMF. Since an ideal PM motor
contains no harmonic back-EMF, so subtracting the ideal
voltages '
au , '
bu and '
cu from ua, ub and uc, then the difference
gives the information of the harmonic back-EMF. In order to
counteract its influence, this difference is fed back to motor
winding as voltage compensation