Controller circuit for motor

A controller circuit for a motor, comprising:

• a minor controller structured to control a minor loop with a current flowing through the motor as a controlled variable;
• a major controller structured to control a major loop with a rotational speed of the motor as a controlled variable;
• wherein at least one of the major controller and the minor controller comprises:
• a proportional-integral (PI) compensator structured to generate a manipulated variable based on an error between a detected value of a controlled variable of the motor and a reference value of the controlled variable;
• and
• an automatic tuning circuit structured to optimize a parameter of the PI compensator;
• wherein the PI compensator comprises:
• an integrator structured to integrate the error;
• a first coefficient circuit structured to multiply an output of the integrator by a first coefficient;
• an adder structured to add the output of the first coefficient circuit and the error;
• and
• a second coefficient circuit structured to multiply an output of the adder by a second coefficient,
• wherein the automatic tuning circuit is structured to vary the first coefficient and to adjust it to a value at which a phase difference between the error and the controlled variable becomes 90 degrees.