A variable speed power converter controls the speed of a load in a material handling system as a function of the torque required to move the load. While the power converter is running, the torque being produced in the motor is determined. The power converter then determines the maximum rotational speed of the motor as a function of the torque currently being produced and of the torque-speed curve of the motor. The power converter then commands the motor to rotate at this maximum rotational speed. The power converter periodically monitors the torque being produced and adjusts the maximum rotational speed of the motor throughout the run.