Control device for bearingless motor, motor system, and control method for bearingless motor

A control device for a bearingless motor, the bearingless motor including a rotor and a stator including an electric motor winding that generates torque, the rotor and the stator being disposed with a predetermined gap, the control device being configured to control the bearingless motor, the control device comprising:

• observing circuitry to compute an estimated current based on a voltage command value of the electric motor winding or a voltage detection value that is a detection value of a voltage applied to the electric motor winding, the estimated current being an estimated value of a current flowing through the bearingless motor;
• and
• axial position control circuitry to output a d-axis current command value for controlling an axial position of the rotor in response to input of a current error, the current error being a difference between the estimated current and a current detection value that is a value of a current of the electric motor winding.

A control method for a bearingless motor, the bearingless motor including a rotor and a stator including an electric motor winding that generates torque, the rotor and the stator being disposed with a predetermined gap, the control method being for controlling the bearingless motor, the control method comprising:

• computing an estimated current based on a voltage command value of the electric motor winding or a voltage detection value that is a detection value of a voltage applied to the electric motor winding, the estimated current being an estimated value of a current flowing through the bearingless motor;
• and
• estimating and outputting an estimated axial speed that is an estimated value of an axial speed of the rotor in response to input of a current error, the current error being a difference between the estimated current and a current detection value that is a value of a current of the electric motor winding.