Control and Commissioning of Active Magnetic Bearing (AMB) System for High-speed 1 MW Turbo Blower

This paper describes the design process, control and commissioning of active magnetic bearings (AMB) for a 1 MW, 11 500 rpm turbo blower used in the pulp and paper industry. Turbo blowers in pulp and paper applications work in a harsh environment. During the operation, the rotor is prone to high unbalance due to dirt buildup on the impeller. Implementing magnetic bearings helped to improve overall system efficiency and allowed stable operation with unbalance forces. AMB topology selection is described and justified from the overall turbo blower unit design perspective. Due to limited observability and controllability, only the robust model-based controller was selected to provide stable levitation throughout the operational range. The model based ℋ∞ approach scheduled over the speed with mixed-sensitivity formulation has been selected as a solution. The commissioning was performed by adjusting the plant model to the measured peak values and then by accelerating step by step and capturing identification data at each speed point. It allowed reaching the nominal speed despite working close to the first forward and on top of the first backward mode. Further system tests confirmed stable operation under all load conditions. Stable turbo blower operation has also been validated in situations of high unbalance force tested by installing a dummy impeller with added weights.