US Patent 7960930 Control apparatus and method for motor drive system

In the rectangular-wave voltage control mode, torque feedback control, in which the voltage phase of the rectangular-wave voltage is adjusted based on the deviation of the torque estimated value from the torque command value, is performed. A torque estimation portion calculates the torque estimated value using the motor currents calculated based on the values detected by a current sensor and a rotational position sensor, as in the case of the PWM control mode. Namely, the same state quantity (quantity detected by the sensors) of the alternating-current motor is used in the motor control in both the rectangular-wave voltage control mode and the PWM control mode.