Field oriented control of pm synchronous machine with modulated inverter. The first component of i_dq controls 'field', the second controls 'torque' at constant 'field'.
For pm machine (psi_pm > 0, x_d = x_q) i_d can be set to zero. For reluctance machines (psi_pm = 0, x_d > x_q) i_d must have a positive value.
See for example:
sm_ctrl.motor.tau_el loadInertia.flange_p.tau sm_ctrl.motor.w_el loadInertia.w