The present invention relates to a method and
control system to control the speed of centrifugal compressors operating within a
vacuum pressure swing adsorption process to avoid an operation at which surge can occur and directly driven by an
electric motor that is in turn controlled by a
variable frequency drive, while subsequently operating the
vacuum pressure swing process between set limits of highest adsorption and lowest
desorption pressure. In accordance with present invention an optimal speed for operation of the compressor is determined at which the compressor will operate along a peak efficiency operating line of a
compressor map thereof. This speed is adjusted by a feed back speed multiplier when the flow or other parameter referable to flow through the compressor is below a minimum and a
feed forward multiplier during evacuation and evacuation with purge steps that multiplies the feed back multiplier to increase speed of the compressor and thereby avoid surge. The speed is then adjusted by a global
speed factor which serves to adjust the average speed of the motors over all steps of the repeating cycle such that the process operates within high and low pressure limits.