A fiber processing system including a refiner configured to process fibrous matter. The system further includes a plurality of measurement units coupled to the refiner to measure different operating conditions of the refiner, and a first control system coupled to the plurality of measurement units and configured to receive a plurality of operation conditions of the refiner from the plurality of measurement units. A processing unit is coupled to the control system and configured to estimate a production disturbance and a feed consistency disturbance of the refiner based on the plurality of operation conditions. The system also includes a second control system coupled to the processing unit and configured to generate a target operating condition based on the production disturbance and the feed consistency disturbance. The first control system is further configured to control an operation of the refiner based on the target operating condition.