Patent ID: 7023169

Claim:
A method for changing the speed of a motor group, in particular for starting or stopping it, the motor group comprising a plurality of squirrel-cage induction motors or synchronous motors and network converters arranged for their control, when the nominal supply power, the acceleration power at the final speed of the motors and the losses of the used power are known, on starting, the method comprising: determining a first time instant, when the motor input power corresponds to the nominal supply power, acceleration taking place at predetermined acceleration rate; accelerating the motors up to the first time instant substantially at the predetermined acceleration rate; calculating a base value for the acceleration rate as a function of the speed of the motors, at which acceleration rate the motor input power corresponds to the nominal supply power; accelerating the motors with varying acceleration rate after the first time instant so as to achieve the final speed, and wherein the redetermined acceleration rate to reach a final V max is determined by calculating V max /T acct is the time that elapses to accelerate the group with constant torque to the final speed at the acceleration power.