Radial excitation force generated by permanent magnet motor using d-axis current injection

This paper proposes a dynamic characteristics measurement method for condition monitoring in a rotor system with a permanent magnet (PM) motor. The PM motor is used not only as a torque generator but also as an exciter for measuring the dynamic characteristics of the rotor system. The radial excitation force is generated by current injection into the d-axis motor windings under eccentricity. The principle of the radial excitation force generation is theoretically discussed in this paper. Furthermore, the force is numerically calculated and experimentally measured to verify the proposed excitation method. It becomes clear that the radial force from the motor windings is proportional to the d-axis current and eccentricity. Thus, the force can be used to measure the frequency response functions of rotor systems as a stability index under eccentricities such as unbalanced vibration.