Electric motor control device, electric motor system and electric motor control method

An electric motor system comprising an electric motor control device and an electric motor, the electric motor control device comprising:

• at least one processor or circuit programmed to function as:
• a generating unit configured to generate a drive waveform to an electric motor;
• a position detecting unit configured to detect a rotational phase of the electric motor and to output a detected signal;
• a speed detecting unit configured to detect information of a rotational speed of the electric motor based on the detected signal output by the position detecting unit;
• and
• a control unit configured to control a phase relationship between the rotational phase of the electric motor and a phase of the drive waveform and set an amplitude of the drive waveform corresponding to a difference between a target speed and the information of rotational speed detected by the speed detecting unit to control a speed of the electric motor,
• wherein characteristics of the amplitude of the drive waveform corresponding to an output of the electric motor have a first region in which a relationship between an integrated value obtained by integrating an output voltage of the electric motor and a setting value of the amplitude is linear and a second region in which the relationship between the integrated value and the setting value of the amplitude is non-linear,
• wherein the control unit holds data indicating the characteristics and performs correction on the setting value of the amplitude based on the data in the second region to suppress non-linearity of the setting value of the amplitude of the drive waveform and the output of the electric motor.

An electric motor control method which controls an electric motor, the electric motor control method comprising:

• generating a drive waveform to an electric motor;
• detecting a rotational phase of the electric motor and outputting a detected signal;
• detecting an information of rotational speed of the electric motor based on the detected signal detected in the detecting;
• controlling a phase relationship between the rotational phase of the electric motor and a phase of the drive waveform and setting an amplitude of a drive waveform corresponding to a difference between a target speed and the information of rotational speed detected by the speed detection step to control a speed,
• wherein characteristics of the amplitude of the drive waveform corresponding to an output of the electric motor have a first region in which a relationship between an integrated value obtained by integrating an output voltage of the electric motor and a setting value of the amplitude is linear and a second region in which the relationship between the integrated value and the setting value of the amplitude is non-linear, and
• wherein, in the controlling, the setting value of the amplitude of the drive waveform is corrected based on data indicating the characteristics in the second region to suppress non-linearity of the setting value of the amplitude of the drive waveform and the output of the electric motor.