Patent ID: 7626350

Claim:
A motor drive apparatus for driving an N phase (where N is an integer of 2 or more) motor by an N phase PWM drive signal, comprising: a speed detection unit operable to detect the rotor speed of said N phase motor and outputting a speed signal containing a frequency component related to said rotor speed; a drive control signal generator operable to generate a first voltage drive control signal and a second voltage drive control signal; a drive signal generator operable to generate said PWM drive signal based on said first voltage drive control signal; a drive output unit operable to supply power to said N phase motor based on said PWM drive signal; a current phase detection unit operable to detect a zero cross phase of a motor current flowing to said N phase motor; and a phase difference generator operable to detect a phase difference between the zero cross phase of said motor current and the phase of said second voltage drive control signal to generate a phase difference signal; wherein said drive control signal generator comprises: a control voltage generator operable to output said second voltage drive control signal at a frequency determined by said speed signal, the phase of said second voltage drive control signal being controlled based on said phase difference signal; a torque control signal generator operable to generate a torque control signal specifying the torque of said N phase motor; and a multiplier operable to control the amplitude of said first voltage drive control signal based on said second voltage drive control signal and said torque control signal.