coordinate system, whose direct axis d- is aligned with the rotor flux space vector φ and the q- axis is perpendicular to
the rotor flux, means that the q-axis component of the rotor flux space vector is always zero. The stator voltage
components u sd and u sq r cannot be considered as decoupled control variables for the rotor flux and electromagnetic
torque. The direct axis component u sd also depends on and
the quadrature axis component sq also depends on .
Considering the rotor-voltage equation of the squirrel cage machine in a reference frame which is fixed to the rotor flux
[16], the Eq. (13) is exported. sd