Motor control unit and electric power steering apparatus equipped with the same

A motor control unit that calculates respective phase duties for a pulse width modulation (PWM)-control based on a current command value and controls a motor via an inverter configured with upper-stage and lower-stage field-effect transistor (FET) bridges, comprising:

• a current detector to detect respective phase currents of said motor;
• an upper-stage maximum heat generation-phase specifying means to calculate respective heat generation amounts of upper-stage FETs and specify an upper-stage maximum heat generation-phase;
• a lower-stage maximum heat generation-phase specifying means to calculate respective heat generation amounts of lower-stage FETs and specify a lower-stage maximum heat generation-phase;
• an upper-stage selecting means to select an upper-stage selecting duty and an upper-stage selecting phase current based on said upper-stage maximum heat generation-phase;
• a lower-stage selecting means to select a lower-stage selecting duty and a lower-stage selecting phase current based on said lower-stage maximum heat generation-phase;
• a duty operating amount calculating section to calculate a duty operating amount in order to distribute a heat generation which is concentrated in a specific FET to plural FETs based on said upper-stage selecting duty and said upper-stage selecting phase current, and said lower-stage selecting duty and said lower-stage selecting phase current;
• and
• a duty operating section to operate said respective phase duties so as to operate duties of all FETs with maintaining voltages between terminals of said respective phases based on said duty operating amount.