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The control of rotatory field machines (induction machine with squirrel cage rotor, permanent magnet synchronous machine, synchonous reluctance machine) may follow the same principles, if we use space phasors. The components of the current space phasor in a coordinate system aligned with the rotating magnetic field are d- and q-component:

• direct axis aligned with the magentic field: The d-axis current controls the magnetic field.
• quadrature axis perpendicular to the magnetic field: The q-axis current controls the torque; this is the same as the armature current.

Additional necessary prerequisites:

• Determining the amplitude and the position of the magnetic field, i.e. a position encoder for synchronous machines and a field model for induction machines.
• A strategy for determing the reference magnetizing current, especially in the field weakening region, and a d-axis current contoller following the same principles as the q-axis currrent controller.