Patent ID: 7193387

Claim:
An AC motor drive system for operating an AC induction motor, the motor drive system comprising: a switching system including a plurality of switching devices coupled between an AC power source and an induction motor, the individual switching devices operative to selectively couple a corresponding motor lead to the AC power source according to a corresponding switch control signal; and a motor startup control system for controlling the motor speed during startup, the motor startup control system comprising: a hybrid model reference adaptive system (MRAS) component including: a torque-based MRAS component providing a first error term representing a difference between a calculated torque value and an estimated torque value; and a rotor flux-based MRAS component providing a second error term representing a difference between a calculated rotor flux and an estimated rotor flux; a speed estimate controller providing a rotor speed estimate according to a controller error input; a motor controller providing a motor controller output for controlling the motor speed during startup according to a desired startup speed profile and according to the rotor speed estimate; a switch control circuit providing a plurality of switch control signals to control operation of the switching devices of the switching system during startup of the motor according to the controller output; and an error selector operatively coupled with the hybrid MRAS component and with the speed estimate controller to provide the error input to the speed estimate controller, the error selector providing the first error term as the controller error input when the rotor speed estimate is less than or equal to a first threshold and providing the second error term as the controller error input when the rotor speed estimate is greater than the first threshold.