Hi all,
I am working on a control problem using a PMSM steady state model. I am not very familiar with hardware so I might need your help on some of the basic information.

The model has three states: angle speed, quadrature-axis current and direct-axis current. I saw some papers assume the the quadrature- and direct-axis stator voltage components as zero, and add only one control law input on the direct-axis current state.

So my question is, in practice, can I add two voltages to the two axis currents receptively? Will there be any difference to use one control input and two control inputs? Thank you.

Hi Shouwei,
I'm not sure I've understood your question. Can you please point out the papers you mention?
Vector current control of a PMSM, but in general, of any polyphase motor, is done imposing stator voltages on the two synchronous axes (for the PMSM rotor axes). In isotropic (i.e. Surface Mount)-PMSMs, the d-axis current is usually controlled to zero, since it doesn't contribute to torque production.

I think you mixed up the control model and the motor model. Normally you command current (id and iq) to control model which will generate corresponding vd and vq. Vd and vq are the inputs of the motor model. Motor model output id and iq which go back to control model as inputs/feedback so that the PI in control model can regulate the current.