Control method of compressor motor and inverter equipped with the same method

An inverter, comprising:

• a plurality of switching elements for driving a three-phase DC motor in accordance with a rotational frequency command signal from an external device;
• a calculator for calculating a rotational velocity and a rotational acceleration of said motor from a back-emf signal of said motor;
• a detector for detecting an amplitude of a phase current of said motor;
• and
• a control program comprising an overload suppression routine,
• wherein, when said amplitude of said phase current exceeds a first set point I1, said overload suppression routine stops activation of said motor, and when said amplitude of said phase current is less than said first set point I1, but greater than a second set point αI2, which is smaller than said first set point I1, said overload suppression routine decelerates said rotational velocity of said motor at a predetermined deceleration, and when said amplitude of said phase current is less that a third set point αI3, which is smaller than the second set point αI2, said overload suppression routine accelerates the rotational velocity of said motor at a predetermined acceleration, and further wherein α is a constant.

A method of controlling a compressor motor that is driven by an inverter, comprising:

• calculating a rotational velocity and a rotational acceleration of said motor, in response to back-emf signals of said motor;
• detecting an amplitude of a phase current of said motor;
• when said amplitude of said phase current exceeds a first set point I1, stopping activation of said motor;
• when said amplitude of said phase current is less than said first set point I1, but greater than a second set point αI2, which is less than said first set point I1, decelerating said rotational velocity of said motor at a predetermined rate;
• and
• when said amplitude of said phase current is less than a third set point αI3, which is less than said second set point αI2, accelerating said rotational velocity of said motor at a predetermined rate,
• wherein, α is a constant.