Patent ID: 8421397

Claim:
A system to control operation of an AC motor, the system comprising: an AC motor drive having an input connectable to an AC source and an output connectable to an input terminal of an AC motor, the AC motor drive comprising: a rectifier connected to the input; a pulse width modulation (PWM) inverter connected to the rectifier by way of a DC bus and having a plurality of switches therein to control current flow and terminal voltages in the AC motor; and a control system connected to the PWM inverter and being configured to generate a command signal to cause the PWM inverter to control an output of the AC motor drive corresponding to the input to the AC motor, the command signal including a frequency reference and a voltage reference; wherein the control system includes a start-up modulator that is selectively operable during a start-up acceleration of the AC motor to a desired reference speed, the start-up modulator being programmed to: determine each of a motor current applied to the AC motor and a voltage of the DC bus; generate a first frequency offset that causes the frequency reference of the command signal to be decreased when the motor current is greater than a reference current threshold; and generate a second frequency offset that causes the frequency reference of the command signal to be increased when the DC bus voltage is greater than a reference voltage threshold.